Thermo doi: 10.3390/thermo4010009
Authors: Shaveshwar Deonarine Navindra Soodoo Laziz Bouzidi R. J. Neil Emery Sanela Martic Suresh S. Narine
The phase behavior of lipids extracted from Astrocaryum vulgare (AV) and Astrocaryum aculeatum (AA) pulp and kernels and their microstructural, thermal and flow properties were studied. The lipid profiles, crystal structures, microstructures, thermal stabilities and flow behaviors of these lipids provided important structure–function information that are useful to assess potential applications in the food, cosmetic and pharmaceutical industries. AV and AA fruits were sourced from the lowlands and rainforests, respectively, of Guyana. AV and AA pulp oils (AVP and AAP) were distinguished from each other in composition and unsaturation, with AVP oils being predominated by a di-unsaturated TAG (2-(palmitoyloxy)propane-1,3-diyl dioleate (POO)) and AAP oils predominated by propane-1,2,3-triyl trioleate (OOO); there were unsaturation levels of 65% and 80%, respectively. The main fatty acids in AVP oils were oleic, palmitic and stearic; for AAP, these were oleic, linoleic, palmitic and stearic. The kernel fats of AV and AA were similar in composition and had saturation levels of 80%, being mainly comprised of tri-saturated TAGs propane-1,2,3-triyl tridodecanoate (LLL) and 3-(tetradecanoyloxy)propane-1,2-diyl didodecanoate (LML). The onset of mass loss (T5%on) of AV and AA pulp oils were similar at 328 ± 6 °C, which were 31 °C ± 9 higher compared to that of the kernel fats, which demonstrated similar T5%on = 293 ± 7 °C. AA and AV pulp oils were liquid at room temperature, with melting points of −5 ± 1 °C and 3 ± 1 °C, respectively; both kernel fats were solid at room temperature, packing in β′ (90% of crystals) and β (10% of crystals) polymorphic forms and melting almost identically at 30 ± 1 °C. Pulp oils demonstrated sporadic nucleation at the onset of crystallization with slow growth into rod-shaped crystallites, leading to an approximately 50% degree of crystallization at undercooling of approximately 40K. Nucleation for kernel fats was instantaneous at undercooling of approximately 23K, demonstrating a spherulitic growth pattern incorporating crystalline lamella and a 90% degree of crystallization. Kernel fats and pulp oils demonstrated Newtonian flow behavior and similar dynamic viscosity in the melt, approximately 28.5 mPa·s at 40 °C. The lipid profiles of AVP and AAP oils were dominated by unsaturated TAGs, suggesting potential nutrition and health benefits, particularly compared to other tropical oils with higher saturation levels, such as palm oil. AAP oil in particular is as unsaturated as olive oil, contains high levels of beta carotene and provides a unique flavor profile. The AAK and AVK lipid profiles and phase transformation indicate potential for applications where a high solid fat content and medium-chain fatty acids are required. Their high lauric and myristic acid content makes them similar to industrially important tropical oils (coconut and palm kernel), suggesting their use in similar formulations. The melting point and plasticity of the kernel fats are similar to that of cocoa and shea butters, suggesting use as replacements in cosmetics, foods and confections. There is, however, the need to better understand their nutritional status and effects on health.
]]>Thermo doi: 10.3390/thermo4010008
Authors: Francesca Villano Gerardo Maria Mauro Alessia Pedace
Given the climate change in recent decades and the ever-increasing energy consumption in the building sector, research is widely focused on the green revolution and ecological transition of buildings. In this regard, artificial intelligence can be a precious tool to simulate and optimize building energy performance, as shown by a plethora of recent studies. Accordingly, this paper provides a review of more than 70 articles from recent years, i.e., mostly from 2018 to 2023, about the applications of machine/deep learning (ML/DL) in forecasting the energy performance of buildings and their simulation/control/optimization. This review was conducted using the SCOPUS database with the keywords “buildings”, “energy”, “machine learning” and “deep learning” and by selecting recent papers addressing the following applications: energy design/retrofit optimization, prediction, control/management of heating/cooling systems and of renewable source systems, and/or fault detection. Notably, this paper discusses the main differences between ML and DL techniques, showing examples of their use in building energy simulation/control/optimization. The main aim is to group the most frequent ML/DL techniques used in the field of building energy performance, highlighting the potentiality and limitations of each one, both fundamental aspects for future studies. The ML approaches considered are decision trees/random forest, naive Bayes, support vector machines, the Kriging method and artificial neural networks. The DL techniques investigated are convolutional and recursive neural networks, long short-term memory and gated recurrent units. Firstly, various ML/DL techniques are explained and divided based on their methodology. Secondly, grouping by the aforementioned applications occurs. It emerges that ML is mostly used in energy efficiency issues while DL in the management of renewable source systems.
]]>Thermo doi: 10.3390/thermo4010007
Authors: Numan Luthfi Takashi Fukushima Xiulun Wang Kenji Takisawa
To ascertain the significance of temperature and residence time of hydrothermal carbonization (HTC) in controlling hydrochar production, multiple regression was employed based on central composite design (CCD) to model the responses of mass yield (MY) and higher heating value (HHV). The hydrothermal reaction was explored at temperatures and times ranging from 150 to 250 °C and 0.5 to 3.5 h. Sorghum bagasse (SB) and microalgae (MA) were used to complex the reaction due to their differences in organic constituents. Simultaneously, the operating parameters were optimized by maximizing the response values under domain constraints in the HHV models. The results show that at least temperature and time in the linear system played a significant role in determining the solids recovery and the energy generation of hydrochars (p-values = 0.00), regardless of the biomass type. Moreover, the optimum conditions of SB and MA hydrochars can be achieved by increasing the temperature to the limit of 250 °C and prolonging the time to 3.5 and 3.25 h, respectively. Both respective conditions resulted in maximum HHVs of 27.54 and 35.83 MJ kg−1.
]]>Thermo doi: 10.3390/thermo4010006
Authors: Stefanos Lempesis Vassilis Gaganis
This paper addresses the often overlooked, yet critical, aspect of designing and optimizing the surface pipeline network for the transportation of geothermal fluids from the wellheads to the delivery point, such as greenhouses, food drying plants, or fish farming units. While research on the geothermal industry predominately focuses on the reservoir and well engineering aspects of exploitation, insufficient attention has been given to the design of the pipeline network, leading to improper design and significant, yet avoidable, energy losses. Thus, this paper presents a comprehensive methodology for modeling and simulating geothermal fluid flow within the pipeline network by fully considering all hydraulic (friction, viscous flow, and gravity effects) and thermal (open air and underground pipeline heat loss) phenomena. These two aspects are handled simultaneously by setting up and solving the coupled set of the governing (differential) equations. We also demonstrate the difficulties that arise when attempting the solution of the mathematical problem, such as potential instability or lack of convergence. Finally, a fully detailed study of the real-world geothermal production system is presented utilizing the developed methodology to optimize the design and operation conditions of the system. By integrating debottlenecking strategies into the analysis, this approach not only maximizes power output, but also identifies and mitigates constraints within the system, ensuring efficient operation and performance increase.
]]>Thermo doi: 10.3390/thermo4010005
Authors: Hasina Tabassum Chowdhury Thaviti Naidu Palleda Naoto Kakuta Koji Kakehi
Preheating is important to improve the mechanical properties of nickel-based superalloys processed by additive manufacturing. The microstructure of IN718 was found to be influenced by the preheating temperature. Different preheating temperatures affect mechanical properties by changing microstructures. This work aims to clarify the thermal behavior for two preheated base plate temperatures (200 °C and 600 °C) on the IN718 superalloy built by the selective laser melting (SLM) process using the finite element method and experiments. The simulation findings indicate that the preheated 600 °C model has a deeper melt pool, a slower transformation of liquid to solid, and a slower cooling rate compared to the 200 °C model. As a result, the interdendritic Niobium (Nb) segregation of IN718 is reduced, thus improving the mechanical properties of additive-manufactured IN718 using the laser. The solidification map derived from the simulation indicates a columnar microstructure for the IN718 superalloy. Preheating increased the size of the dendrite structure and reduced elemental segregation, but it did not affect the morphology or size of crystal grains. We focused on comparing the temperature gradient and cooling rate for the two preheated base plate temperatures using the solidification map of IN718. The simulation confirmed that preheating does not affect the grain structure.
]]>Thermo doi: 10.3390/thermo4010004
Authors: Cornelia Breitkopf
Polymer thermal conductivities play an important role for their potential use in industrial applications. Therefore, great efforts have been made to investigate fundamental structure–property relationships to understand and predict thermal conductivities for polymers and their composites. The review summarizes selected well-proven microscopic theoretical approaches to calculate thermal conductivities such as EMD, NEMD, EMT, and BTE, and cites examples to focus on different qualitative aspects of recent polymer theoretical research. Examples other than polymer materials are given as supplemental information to support the general discussion of heat transport phenomena in solid materials.
]]>Thermo doi: 10.3390/thermo4010003
Authors: Johan Jacquemin
Prior starting this editorial, I do want to wish all of you a Happy New Year and a great 2024 [...]
]]>Thermo doi: 10.3390/thermo4010002
Authors: Ajay D. Pingale Anil S. Katarkar Mahadev Madgule Swapan Bhaumik Sachin U. Belgamwar
Multiwalled carbon nanotubes (MWCNTs) exhibit outstanding physical properties, including high thermal conductivity, excellent mechanical strength, and low electrical resistivity, which make them suitable candidates for a variety of applications. The work presented in this paper focuses on the pool boiling performance of refrigerant R-134a on microporous Cu-MWCNT composite surface layers. A two-stage electrodeposition technique was used to fabricate Cu-MWCNT composite coatings. In order to achieve variation in the surface properties of the Cu-MWCNT composite surface layer, electrodeposition was carried out at various bath temperatures (25 °C, 30 °C, 35 °C, and 40 °C). All surfaces coated with the Cu-MWCNT composite demonstrated superior boiling performance compared to the uncoated surface. Heat transfer coefficient (HTC) values for Cu-MWCNT composite surface layers, prepared at bath temperatures of 25 °C, 30 °C, 35 °C, and 40 °C, exhibited improvements of up to 1.75, 1.88, 2.06, and 2.22, respectively, in comparison to the plain Cu surface.
]]>Thermo doi: 10.3390/thermo4010001
Authors: Hugues Charton Christian Perret Hai Trieu Phan
In this work, different CFD models to compute flows inside a steam ejector were investigated. The results were compared to the analytical models as well as the experimental results from the literature. All the simulations gave realistic results from the hydrodynamic perspective with a relative error of the entrainment ratio between 25% and 40% compared to reference experimental data. However, an analysis of the temperature profiles showed that only realistic results from the thermodynamic perspective were given by multiphase calculations. The first multiphase model tested was the so-called Wet-Steam model from ANSYS Fluent. This model gave inconsistent results for the steam ejector CFD simulation due to the physical boundaries of this model. The second model tested was the Eulerian mixture model, which gave the most realistic results in terms of the physical conditions of the liquid and vapor phases inside the ejector. It also showed that the phase change could have a significant impact on the value of the critical output pressure as a way to improve the performance of the ejector.
]]>Thermo doi: 10.3390/thermo3040040
Authors: Aubrey Jaffer
Since the 1930s, theories of skin-friction drag from plates with rough surfaces have been based by analogy to turbulent flow in pipes with rough interiors. Failure of this analogy at small fluid velocities has frustrated attempts to create a comprehensive theory. Utilizing the concept of a self-similar roughness that disrupts the boundary layer at all scales, this investigation derives formulas for a rough or smooth plate’s skin-friction coefficient and forced convection heat transfer given its characteristic length, root-mean-squared (RMS) height-of-roughness, isotropic spatial period, Reynolds number, and the fluid’s Prandtl number. This novel theory was tested with 456 heat transfer and friction measurements in 32 data-sets from one book, six peer-reviewed studies, and the present apparatus. Compared with the present theory, the RMS relative error (RMSRE) values of the 32 data-sets span 0.75% through 8.2%, with only four data-sets exceeding 6%. Prior work formulas have smaller RMSRE on only four of the data-sets.
]]>Thermo doi: 10.3390/thermo3040039
Authors: Dario Atzori Simone Tiozzo Michela Vellini Marco Gambini Stefano Mazzoni
In recent years, the European Union’s legislation about sustainable development has promoted the gradual decarbonization of all industrial sectors, pushing towards the final goal of a carbon-neutral European glass industry in 2050. Moreover, the COVID-19 pandemic, the war in Ukraine and the consequent natural gas supply crisis have led to significant increases in the costs of traditional energy commodities and CO2 emission allowances. In this scenario, the European glass industry, which is both an energy-intensive sector and a large emitter of CO2, needs to reduce its specific energy consumption, change its energy sources and decarbonize its production process. In order to understand and support this metamorphosis of the glass industry, the follwing questions must be answered: are the technologies reported in scientific publications merely theoretical exercises, or can they be adopted by the industry? In what timeframe can they be adopted? The aim of this study is to review consolidated and emerging technologies applicable to the glass industry and investigate which ones can be implemented in the short or medium term to reduce energy consumption and CO2 emissions related to the glass production process. This study is based on a review of the literature, the materials presented in technical conferences and the opinions of interviewed experts. This study showed that the literature is not very substantial, lacking detailed information on technologies and their effects in terms of energy savings or emissions. More information can be found in the proceedings of selected specialist conferences. This study found that, on one hand, some technologies are mature and only adopted when economically viable, and appropriate boundary conditions are available; the state of the art regarding these technologies was already extensively covered in past publications (e.g., cullet pre-heating). On the other hand, there are many promising technologies in the research or testing phase (i.e., steam methane reforming, process electrification, use of hydrogen); in-depth studies about them are limited due to the novelty of the solutions that they propose or not available due to industrial secrecy issues. In addition to periodicals and specialized conferences, interviews were carried out with managers and technicians from industry, as well as technicians from the Italian glass research institute and industrial machinery producers (especially melting furnaces). The interviews represent added value of this publication, useful in helping us to truly understand the state of the art and degree of readiness of the technologies identified. In addition, the production values of the glass industry were studied: our research confirmed that the most important sub-sectors are flat and container glass, as well as the largest glass-producing nations/continents. Finally, a review of specific energy consumption and CO2 emissions indexes was carried out.
]]>Thermo doi: 10.3390/thermo3040038
Authors: Tryfon C. Roumpedakis Aris-Dimitrios Leontaritis Prokopios Vlachogiannis Efstratios Varvagiannis Antonios Charalampidis Sotirios Karellas
This study regards the evaluation of the performance of a thermally stratified tank as an intermediate combi-storage tank for a solar-driven residential thermal system coupled to a seasonal energy storage system. In such applications, the efficient operation of this intermediate tank is crucial to the enhanced exploitation of the harvested solar energy and the minimization of heat losses. In this perspective, the development of a dedicated model in TRNSYS software and its validation with experimental results are investigated. With respect to the simulation model’s discretization, it was found that beyond 60 nodes, the benefits to the model’s accuracy are almost negligible. Comparing the experimental data with the simulation’s results, the predicted temperature profile converges accurately to the measured values under steady-state conditions (threshold stabilization period of 1000 s after charging/discharging has occurred). However, the response of the model deviates considerably under transient conditions due to the lack of detailed inertia modeling of both the tank and the rest of the system components. Conclusively, the developed 1D simulation model is adequate for on- and off-design models where transient phenomena are of reduced importance, whereas for dynamic and semi-dynamic simulations, more detailed models are needed.
]]>Thermo doi: 10.3390/thermo3040037
Authors: Fabio Peluso
We pursue to illustrate the capabilities of the Dual Model of Liquids (DML) showing that it may explain crossed effects notable in Non-Equilibrium Thermodynamics (NET). The aim of the paper is to demonstrate that the DML may correctly model the thermodiffusion, in particular getting formal expressions for positive and negative Soret coefficient, and another “unexpected” mechano-thermal effect recently discovered in liquids submitted to shear strain, for which the first-ever theoretical interpretation is provided. Both applications of the DML are supported by the comparison with experimental data. The phenomenology of liquids, either pure or mixtures, submitted to external force fields is characterized by coupled effects, for instance mechano-thermal and thermo-mechanical effects, depending on whether the application of a mechanical force field generates a coupled thermal effect in the liquid sample or vice-versa. Although these phenomena have been studied since their discoveries, dating back to the XIX century, no firm theoretical interpretation exists yet. Very recently the mesoscopic model of liquids DML has been proposed and its validity and applicability demonstrated in several cases. According to DML, liquids are arranged on a mesoscopic scale by means of aggregates of molecules, or liquid particles. These structures share the liquid world with a population of lattice particles, i.e., elastic waves that interact with the liquid particles by means of an inertial force, allowing the mutual exchange of energy and momentum between the two populations. The hit particle relaxes the acquired energy and momentum due to the interaction, giving them back to the system a step forward and a time-lapse later, alike in a tunnel effect.
]]>Thermo doi: 10.3390/thermo3040036
Authors: Noemi Schclar Leitão Sérgio Oliveira
In order to conduct thermal analysis of concrete dams, it is necessary to assess and validate the spatiotemporal representations used for modeling the solar radiation and the water temperature boundary conditions. To illustrate this procedure, the thermal analysis of a concrete multiple-arch dam is presented. The article starts by providing an overview of the problem before focusing explicitly on the estimation of solar radiation distribution. Within this section, a comparison between the solar irradiance computed on the downstream face of the dam with or without considering the beam radiation shading at different times of the year is presented. This is followed by an analysis of the seasonal behavior of the water temperature of the dam’s reservoir based on measured data. After calibrating an empirical/statistical law based on temperatures measured at different depths, it is compared with the values estimated by a hydrodynamic model and some temperature profiles measured upstream of the dam. Finally, the article compares the results obtained with the thermal analysis versus the temperature measured by thermometers installed in the concrete.
]]>Thermo doi: 10.3390/thermo3040035
Authors: Stephan Heitmann Tamás Simon Andrea Osburg Michael Fröba
A composite material of alginate and CaCl2 was tested in a laboratory reactor (1 L) for its ability to thermochemically store heat. The material was exposed to air at 25 °C and 25% RH to prevent the salt from dissolving, and the heat evolution was observed over a period of 15 cycles. To evaluate the changes in the material, samples were taken after 5, 10 and 15 cycles and the material properties and calorimetric characteristics were examined. A change of the material in favor of the heat release was determined, so that an increase of the heat storage capacity from 1.28 kJ∙cm−3 to 2.11 kJ∙cm−3 was detected, with a simultaneous steep decrease of the pore volume in the range from 0.01 to 10 μm. The temperature lift of the reactor showed a significant increase, with the first cycle showing the smallest amount.
]]>Thermo doi: 10.3390/thermo3040034
Authors: Stefano Piacquadio Johannes Soika Maximilian Schirp Kai-Uwe Schröder Sauro Filippeschi
The recent literature has introduced the use of architected materials with a metallic lattice structure-based topology to enhance the thermal conductivity of phase change materials (PCM). The potential of such structures lies in the freedom of design with complex geometries. This, however, has introduced novel challenges regarding the analytical description of these materials’ effective thermophysical properties, which are used in order to treat the composite as a homogenized material. Only a few limited works have been presented thus far that have holistically addressed the calculation of such properties. The wide variety of possible geometric parameters in these materials can only be appropriately treated via an adaptable approach that can be extended to upcoming lattice geometries. With this aim in mind, the present work introduces a method to calculate the effective thermal conductivity of the discussed composite PCM. A cell-based approach to calculate the effective thermal conductivity is introduced. The method makes use of Steinmetz’s solids as a basis from which one can derive the porosity of unit cells with variable geometric parameters. Empirical factors are introduced to account for limitations due to the complex geometry and eventual manufacturing imperfections of these structures. Thus, semi-analytical formulae to describe the effective thermal conductivity of the lattice cells are derived for a variety of cuboid and hexagonal prismatic unit cells with generic topological parameters. The formulae are validated against the models and experimental results present in the literature. Finally, an analysis and discussion of the limited validity of homogenization techniques for lattice structures is presented.
]]>Thermo doi: 10.3390/thermo3040033
Authors: Ana L. R. Silva Gastón P. León Maria D. M. C. Ribeiro da Silva Thomas M. Klapötke Jelena Reinhardt
The discrepancy between the calculated (CBS-4M/Jenkins) and experimentally determined enthalpies of formation recently reported for the 2:1 salt TKX-50 raised the important question of whether the enthalpies of formation of other 2:1 C, H, N, O salts calculated using the CBS-4M/Jenkins method are reliable values. The standard (p° = 0.1 MPa) enthalpy of formation of crystalline guanidinium 5,5′-azotetrazolate (GZT) (453.6 ± 3.2 kJ/mol) was determined experimentally using static-bomb combustion calorimetry and was found to be in good agreement with the literature’s values. However, using the CBS-4M/Jenkins method, the calculated enthalpy of formation of GZT was again in poor agreement with the experimentally determined value. The method we used recently to calculate the enthalpy of formation of TKX-50, based on the calculation of the heat of formation of the salt and of the corresponding neutral adduct, was then applied to GZT and provided excellent agreement with the experimentally determined value. Finally, in order to validate the findings, this method was also applied to predict the enthalpy of formation of a range of 1:1 and 2:1 salts (M+X− and (M+)2X2− salts, respectively), and the values obtained were comparable to experimentally determined values. The agreement using this approach was generally very good for both 1:1 and 2:1 salts; therefore, this approach provides a simple and reliable method which can be applied to calculate the enthalpy of formation of energetic C, H, N, O salts with much greater accuracy than the current, commonly used method.
]]>Thermo doi: 10.3390/thermo3040032
Authors: Brandon Wada Oliver Baldwin Gerald Van Hecke
Specific heat capacity at constant pressure cp (J K−1 g−1) is an important thermodynamic property that helps material scientists better understand molecular structure and physical properties. Engineers control temperature (through heat transfer) in physical systems. Differential Scanning Calorimetry (DSC) is an analytical technique that has been used for over fifty years to measure heat capacities with milligram size samples. For existing procedures, such as ASTM E1269−11 (2018), the accuracy of molar heat capacity measurements is typically ±2–5% relative to the literature values, even after calibration for both heat flow and heat capacity. A comparison of different DSC technologies is beyond the scope of this paper, but the causes of these deviations are common to all DSC instruments, although the magnitude of the deviation (observed and accepted) varies with instrument design. This paper presents a new approach (Heat–Cool) for measuring more accurate and reproducible specific heat capacities of materials. In addition to better performance, the proposed method is faster and typically requires no additional calibration beyond the routine calibration of temperature and heat flow, with melting point standards common to all applications of DSC. Accuracy, as used throughout this paper, means deviation from the literature. The estimated standard deviation of repeated measurements of the cp values obtained with the Heat–Cool technique typically falls in the ±1–2% range.
]]>Thermo doi: 10.3390/thermo3040031
Authors: Seamus P. Kane William F. Northrop
Metallic monolith structures are often used in compact reactor applications due to their superior heat transfer properties and lower pressure drop when compared to ceramic monoliths. Endothermic reactions like steam reforming depend heavily on externally supplied heat, making highly conductive supports especially useful. Simulations are invaluable for designing effective reactors with complex catalyst support structures but are conventionally resource-intensive. Additionally, few dedicated heat transfer experiments between monoliths exist in prior literature. To expand general knowledge of heat transfer between metal monolith structures, this work investigated heat exchange in concentric monoliths brazed to a common mantle. A computationally inexpensive quasi-dimensional model was developed and used to predict the heat exchange effectiveness and intrinsic heat transfer rate. The model used a discretized control volume approach and simplified geometries to reduce computational intensity. The model was calibrated against experimental data collected using a steady-state flow bench. After calibration, a parametric study was performed where monolith construction and flow conditions were varied. A parametric analysis showed that for identical catalyst space velocities and volumes, heat exchange effectiveness can be increased by 43.2% and heat transfer rates by 44.8% simply through increasing the surface area to volume ratio of the monolith. The described approach serves as an alternative framework for modeling catalytic heat exchangers without heavy computation and for quickly matching monolith geometries to their intended use and operating range.
]]>Thermo doi: 10.3390/thermo3030030
Authors: Duy Trinh Nguyen Minh Thai Vu Van Vang Le Van Chien Pham
In this study, the operating processes of a four-stroke diesel marine engine from the intake valve closing (IVC) to the exhaust valve opening (EVO) at numerous different charge air conditions were simulated with the AVL FIRE code. The CFD models were validated with engine shop-test technical data. The results showed that increasing the charge air pressure without cooling decreased the actual amount of air supplied to the cylinder. As a result, the combustion process was suboptimal, resulting in a reduction in engine power and an increase in specific fuel oil consumption (SFOC). In addition, less air to cool the combustion chamber coupled with elevated charge air temperatures increased the in-cylinder peak temperature, leading to a significant increase in thermal nitric oxide (NO) emissions. In contrast, by cooling the charge air after turbocharging, the actual amount of air entering the engine cylinders was increased. The abundant charge air helped to cool the combustion chamber better, significantly reducing the in-cylinder peak temperature and then the thermal NO formation. Better combustion also increased engine power, which, in turn, reduced SFOC. In addition, carbon dioxide (CO2) and soot emissions were also reduced.
]]>Thermo doi: 10.3390/thermo3030029
Authors: Cristina Macasoi Viorica Meltzer Elena Pincu
Medazepam, citric acid and their binary mixtures were studied using differential scanning calorimetry (DSC) and Fourier transform infrared spectroscopy (FTIR) for thermal and structural properties. The DSC data show a simple eutectic peak at 370 K. To determine the exact mole fraction at which the eutectic occurs, Tamman’s triangle was used. The obtained results show that the eutectic mixture appears at a molar fraction of medazepam of approximately 0.85. The excess thermodynamic functions GE, SE and μE were calculated, and the results were interpreted to evaluate the interactions that occur between the components of the mixture. The FTIR results were used to confirm the eutectic formation. Solubility tests in deionized water show a 40-times increase in the medazepam solubility from the eutectic mixture, from 0.73 μg/mL to 28.61 μg/mL. However, further tests showed that the acidic character of the sample was the main factor responsible for this increase.
]]>Thermo doi: 10.3390/thermo3030028
Authors: Florian Maranghi Jasmin Raymond
Communities operating urban greenhouses need affordable solutions to reduce their heating consumption. The objective of this study was to compare the ability of different simple ground-based solutions to reduce the heating energy consumption of relatively small urban greenhouses operated all year round in a cold climate. An urban greenhouse located in Montreal (Canada) and its thermal interactions with the ground were modeled with the TRNSYS 18 software. The following greenhouse scenarios were simulated: partially insulating the walls, partially burying the greenhouse below the ground level, reducing the inside setpoint temperature, and using an air–soil heat exchanger (ASHE) or a ground-coupled heat pump (GCHP). The heat exchangers for the last two cases were assumed to be located underneath the greenhouse to minimize footprint. The results showed that reducing the setpoint temperature by 10 °C and burying the greenhouse 2 m below the surface has the most impact on fuel consumption (−33% to −53%), while geothermal systems with a limited footprint (ASHE and GCHP) can reduce the fuel consumption by 21–35% and 18–27%, respectively, depending on the soil thermal conductivity and ground heat injection during summer. The scenarios do not provide the same benefits and have different implications on solar radiation availability, growth temperature, electrical consumption, and operation that must be considered when selecting a proper solution.
]]>Thermo doi: 10.3390/thermo3030027
Authors: Emily Yao William E. Acree
Experiment-based Abraham model solute descriptors are calculated based on recently published solubility data for favipiravir dissolved in 12 chemically diverse organic mono-solvents. The calculated descriptor values indicate that favipiravir engages in intramolecular hydrogen formation that renders the hydroxyl functional group on the pyrazine ring system unable to form intermolecular hydrogen bonds with the surrounding solvent molecules. Our study further shows that the existing group contribution and machine learning methods provide rather poor estimates of the experiment-based solute descriptors of favipiravir. Poor estimation likely occurs, in part, because the methods fail to account for the intramolecular hydrogen-bonds that are believed to be formed. In the current study, it was found that the solute descriptors estimated using three different methods provided rather poor estimates of the observed solubility behavior of favipiravir, with the overall average standard errors between the experimental and predicted molar solubilities exceeding 0.40 log units.
]]>Thermo doi: 10.3390/thermo3030026
Authors: Lahna Acherar Hui-Ying Wang Bruno Coudour Jean Pierre Garo
The objective of this work is to assess the accuracy and limitations of two different semi-empirical soot models: the Laminar Smoke Point (LSP) and soot-yield approach. A global soot formation model based on the LSP concept is embedded within FDS6.7. Quantitative comparisons were made from turbulent buoyant pool fires between several computational results and well-instrumented experimental databases on the soot volume fraction, mass loss rate, heat release rate and gas temperature. The LSP model in combination with soot oxidation and surface growth is validated for most of the methane, ethylene and heptane turbulent buoyant pool fires, covering a wide range of fuel likely to form soot. This paper aims to broaden the scope of the validation of the available semi-empirical soot modelling. For the porous methane and ethylene burner, the LSP model was found to provide a better description of the soot volume fraction. The overall visual soot distribution is also numerically reproduced with the soot-yield approach, but as expected, there are some differences between the prediction and the measurement regarding the magnitude of soot volume fraction. The computed radiant heat flux was compared with experimental data for heptane flame, showing that predictions using both the LSP and soot-yield models were found to be twice the value of experimental data, although the measured HRR (Heat Release Rate) is reliably reproduced in the numerical simulation. For the heptane buoyant pool fires, a sufficient accuracy of the numerical model is confirmed only in some of the locations as compared to the experimental results. It is demonstrated that neither the temperature nor the soot volume fraction can be reliably calculated in the necking flame flapping region when the pyrolysis rate of condensed fuel (heptane) is coupled with radiation/convection heat feedback. This implies that an accuracy of prediction on the turbulent buoyant pool fires depends on the studied fire scenario regardless of the semi-empirical soot models.
]]>Thermo doi: 10.3390/thermo3030025
Authors: Jason E. Thompson Andrew S. Paluch
In general, for an organic compound a plot of the log vapor pressure versus inverse temperature is linear over a wide temperature range. This however can lead to a point of confusion in an undergraduate thermodynamics course. This linear behavior is typically explained using the Clausius/Clapeyron equation. That is, starting with the Clapeyron equation one first assumes (1) that the change in compressibility upon vaporization is approximately 1, or equivalently that the vapor phase may be treated as an ideal gas where the molar volume of the vapor is much greater than that of the liquid, which may be assumed negligible. And second (2), that the enthalpy of vaporization is constant. While the resulting linear behavior is captured, the underlying assumptions are not applicable over the wide range of temperatures of interest. Here we discuss the shortcomings of the conventional explanation of the Clausius/Clapeyron equation. We further demonstrate that a simple solution is to instead assume that the enthalpy of vaporization relative to the change in compressibility upon vaporization is constant. We provide a series of examples and MATLAB code that can be used in an undergraduate thermodynamics course.
]]>Thermo doi: 10.3390/thermo3030024
Authors: Ayah Marwan Rabi Jovana Radulovic James M. Buick
In recent years, there has been an increase in the use of renewable energy resources, which has led to the need for large-scale Energy Storage units in the electric grid. Currently, Compressed Air Energy Storage (CAES) and Pumped Hydro Storage (PHES) are the main commercially available large-scale energy storage technologies. However, these technologies are restricted geographically and can require fossil fuel streams to heat the air. Thus, there is a need to develop novel large-scale energy storage technologies that do not suffer from the abovementioned drawbacks. Among the in-development, large-scale Energy Storage Technologies, Pumped Thermal Electricity Storage (PTES), or Pumped Heat Energy Storage, stands out as the most promising due to its long cycle life, lack of geographical limitations, the absence of fossil fuel streams, and the possibility of integrating it with conventional fossil-fuel power plants. There have been a number of PTES systems proposed using different thermodynamic cycles, including the Brayton cycle, the Rankine cycle, and the transcritical Rankine cycle. The purpose of this paper is to provide a comprehensive overview of PTES concepts, as well as the common thermodynamic cycles they implement, indicating their individual strengths and weaknesses. Furthermore, the paper provides a comprehensive reference for planning and integrating various types of PTES into energy systems.
]]>Thermo doi: 10.3390/thermo3030023
Authors: Dipankar Roy Andriy Kovalenko
3D-RISM-KH molecular solvation theory based on statistical mechanics has been an engine of the multiscale methods framework, which also includes molecular simulation techniques. Its applications range from the solvation energy of small molecules to the phase behavior of polymers and biomolecules. Molecular solvation theory predicts and explains the molecular mechanisms and functioning of a variety of chemical and biomolecular systems. This includes the self-assembly and conformational stability of synthetic organic rosette nanotubes (RNTs), the aggregation of peptides and proteins related to neurodegeneration, the binding of ligands to proteins, and the solvation properties of biomolecules related to their functions. The replica RISM-KH-VM molecular solvation theory predicts and explains the structure, thermodynamics, and electrochemistry of electrolyte solutions sorbed in nanoporous carbon supercapacitor electrodes, and is part of recent research and development efforts. A new quasidynamics protocol couples multiple time step molecular dynamics (MTS-MD) stabilized with an optimized isokinetic Nosé–Hoover (OIN) thermostat driven by 3D-RISM-KH mean solvation forces at gigantic outer time steps of picoseconds, which are extrapolated forward at short inner time steps of femtoseconds with generalized solvation force extrapolation (GSFE). The OIN/3D-RISM-KH/GSFE quasidynamics is implemented in the Amber Molecular Dynamics package. It is validated on miniprotein 1L2Y and protein G in ambient aqueous solution, and shows the rate of sampling 150 times faster than in standard MD simulations on these biomolecules in explicit water. The self-consistent field version of Kohn–Sham DFT in 3D-RISM-KH mean solvation forces is implemented in the Amsterdam Density Functional (ADF) package. Its applications range from solvation thermochemistry, conformational equilibria, and photochemistry to activation barriers of different nanosystems in solutions and ionic liquids.
]]>Thermo doi: 10.3390/thermo3030022
Authors: Edward Kremer
The short and long-range orders in alloys can be assessed based on a new expression for the combinatorial factor, which is more convenient and intuitive than the traditionally used form. This novel expression can be directly applied to reproduce the results of several well-known statistical-thermodynamic models that are typically considered independent or even inconsistent. The short list of models includes Quasichemical Theory, Associated Solution Model, Surrounded Atom Model, and Cluster Site Approximation. As a result, the formalism and interpretation of these models are significantly clarified, allowing us to identify and fix several long-standing errors that might otherwise have gone unnoticed. Multicomponent generalization of these models is also greatly simplified. For systems undergoing a phase transition, an extended version of the theory provides a mechanism that allows the correct critical temperature of phase transition to be reproduced, as well as a significant increase in the accuracy of thermodynamic functions. In the case of order–disorder transformations, the new theory ensures an integrated description of short and long-range orders, which has long been considered an important and difficult problem.
]]>Thermo doi: 10.3390/thermo3020021
Authors: Eileen Trampe Dominik Büschgens Herbert Pfeifer
Tube bundle recuperators are generally designed to operate with smooth tubes. Structured tubes can be used to increase the efficiency of recuperators. Compared to smooth tubes, the surface for heat transfer is increased and thus heat transfer is enhanced. This effect is accompanied by an increased pressure loss, which must be kept as low as possible. Four tube geometries with different honeycomb structures are examined. The results are compared with the performance of a smooth tube. The investigations were carried out both numerically and experimentally at different off-gas and combustion air velocities. The experimental results show that the highest heat transfer is achieved with the concave 6 mm structured tube. The greatest pressure loss also occurs here. The validation of the numerical model has shown issues in resolving the turbulence.
]]>Thermo doi: 10.3390/thermo3020020
Authors: Johan Jacquemin
In this Special Issue of Thermo, a collection of 11 papers is presented based on a preselection of the Editor in Chief of the journal for this particular and specific Special Issue called Feature Papers of Thermo in 2022 [...]
]]>Thermo doi: 10.3390/thermo3020019
Authors: Sabit Rayhan Keishi Kariya Akio Miyara
This study explores the application of zigzag-shaped, finless tubes in enhancing heat transfer performance within heat exchangers. Using three-dimensional numerical simulations, we examined the heat transfer per unit area and the volume of the pressure drop, comparing these findings with a traditional parallel tube heat exchanger. This innovative design strategy involved arranging zigzag-shaped tubes at varying distances, and the thermal transfer and frictional characteristics were tested at different air speeds. This research suggests that the introduction of zigzag heat exchangers, as opposed to traditional fin-and-tube designs, led to a significant improvement in heat transfer. This enhancement is attributed to the swirling flow created around the zigzag tubes, which increased the total heat transfer area. Furthermore, we found that the heat transfer area increased by 14.2%, 32.1%, and 63.9% for tube zigzag angles of 30°, 45°, and 60°, respectively, when compared to a parallel tube heat exchanger. Consequently, the zigzag-shaped tube heat exchanger demonstrated not only superior heat transfer, but also a reduction in frictional pressure loss.
]]>Thermo doi: 10.3390/thermo3020018
Authors: Robert J. Meier Paul R. Rablen
Group contribution (GC) methods to predict thermochemical properties are eminently important to process design. Following earlier work which presented a GC model in which, for the first time, chemical accuracy (1 kcal/mol or 4 kJ/mol) was accomplished, we here discuss classes of molecules for which the traditional GC approach does not hold, i.e., many results are beyond chemical accuracy. We report new ring-strain-related parameters which enable us to evaluate the heat of formation of alkyl-substituted cycloalkanes. In addition, the definition of the appropriate group size is important to obtain reliable and accurate data for systems in which the electron density varies continuously but slowly between related species. For this and in the case of ring strain, G4 quantum calculations are shown to be able to provide reliable heats of formation which provide the quantitative data which we can use, in the case of absence of experimental data, to establish group and nearest-neighbour interaction parameters to extend the range of applicability of the GC method whilst retaining chemical accuracy. We also found that the strong van der Waals that overlap in highly congested branched alkanes can be qualitatively investigated by applying DFT quantum calculations, which can provide an indication of the GC approach being inappropriate.
]]>Thermo doi: 10.3390/thermo3020017
Authors: Maja Ivanovski Darko Goričanec Danijela Urbancl
In this work, the thermochemical properties of municipal solid waste (MSW) are studied using the torrefaction process as the main method for investigation. Torrefaction experiments were carried out using an electric laboratory furnace, at temperatures of 200, 250, and 300 °C. The residence time was set to 90 min. Proximate and ultimate analysis were performed on the torrefied MSW samples and compared with the properties of the raw MSW samples. In addition, the thermal properties of the obtained torrefied MSW samples were evaluated by thermogravimetric analysis (TGA) and derivative thermogravimetric analysis (DTG). The following could be stated: the obtained results showed that mass and energy yields (MY and EY, respectively) decrease with increasing when torrefaction temperature, while the heating values (HHV) increased under the same conditions (from 24.3 to 25.1 MJ/kg). Elemental analysis showed an increase in carbon content (C), from 45.7 ± 0.9 to 52.8 ± 1.05 wt.%, and decrease in oxygen content (O), from 45.6 ± 0.9 to 39.5 ± 0.8 wt.%, when torrefaction temperature is increased, which is consistent with the general definition of the torrefaction process. In addition, enhancement factors (EFs) and fuel ratios (FRs) were calculated, which ranged from 1.00 to 1.02 and 0.16 to 0.23, respectively. Some anomalies were observed during the thermal analysis, which are assumed to be related to the composition of the selected MSW. This study therefore shows that torrefaction pretreatment can improve the physicochemical properties of raw MSW to a level comparable to coal, and could contribute to a better understanding of the conversion of MSW into a valuable, solid biofuel.
]]>Thermo doi: 10.3390/thermo3020016
Authors: Angelo Morro Claudio Giorgi
The paper investigates the techniques associated with the exploitation of the second law of thermodynamics as a restriction on the physically admissible processes. Though the exploitation consists of the use of the arbitrariness occurring in the Clausius–Duhem inequality, the approach emphasizes two uncommon features within the thermodynamic analysis: the representation formula, of vectors and tensors, and the entropy production. The representation is shown to be fruitful whenever more terms of the Clausius–Duhem inequality are not independent. Among the examples developed to show this feature, the paper yields the constitutive equation for hypo-elastic solids and for Maxwell–Cattaneo-like equations of heat conduction. The entropy production is assumed to be given by a constitutive function per se and not merely the expression inherited by the other constitutive functions. This feature results in more general expressions of the representation formulae and is crucial for the compact description of hysteretic phenomena.
]]>Thermo doi: 10.3390/thermo3020015
Authors: Bruno Brunetti Andrea Ciccioli Guido Gigli Andrea Lapi Giulia Simonetti Elisa Toto Stefano Vecchio Ciprioti
The evaporation/decomposition behavior of the ionic liquid 1-butyl-3-methylimidazolium chloride (BMImCl) was studied with various techniques, such as thermogravimetry (TG), Knudsen effusion mass loss (KEML), and Knudsen effusion mass spectrometry (KEMS), in order to investigate the competition between the simple evaporation of the liquid as gaseous ion pairs (NIP: neutral ion pair) and the thermal decomposition releasing volatile species. TG/DSC experiments were carried out from 293 to 823 K under both He and N2 flowing atmospheres on BMImCl as well as on BMImNTf2 (NTf2: bis(trifluoromethylsulfonyl)imide). Both ionic liquids were found undergoing a single step of mass loss in the temperature range investigated. However, while the BMImNTf2 mass loss was found to occur in different temperature ranges, depending on the inert gas used, the TG curves of BMImCl under helium and nitrogen flow were practically superimposable, thus suggesting the occurrence of thermal decomposition. Furthermore, KEML experiments on BMImCl (in the range between 398 and 481 K) indicated a clear dependence of the unit area mass loss rate on the effusion hole diameter, an effect not observed for the ILs with NTf2 anion. Finally, KEMS measurements in the 416–474 K range allowed us to identify the most abundant species in the vapor phase, which resulted in methyl chloride, butylimidazole, butyl chloride, and methylimidazole, which most probably formed from the decomposition of the liquid.
]]>Thermo doi: 10.3390/thermo3020014
Authors: A. Borshchak Kachalov P. Salgado Sánchez U. Martínez J. M. Ezquerro
We explore the preliminary design of a space habitat thermally controlled using phase change materials (PCMs). The PCM is used to maintain a suitable, habitable temperature inside the habitat by isolating it from the external solar radiation. The system is studied numerically considering only diffusive heat transport (conduction), a scenario with practical application to microgravity or reduced gravity environments. The system dynamics are explored for a wide range of governing parameters, including the length of the PCM cell L, the thermo-optical properties—absorptivity α and emissivity ε—at the external boundary of the habitat wall exposed to solar radiation, the eclipse (illumination) fraction τe (τi) of the solar cycle, and the PCM used. We find that the thermo-optical properties at the external radiated boundary, characterized by the absorptivity–emissivity ratio (α/ε), play a key role in the system response and largely define the optimal design of the habitat. This optimum balances the heat absorbed and released by the PCM during repeated illumination and eclipse cycles.
]]>Thermo doi: 10.3390/thermo3020013
Authors: Savvas Savvakis Georgia Dimopoulou Konstantinos Zoumpourlos
The current work investigates the relationship between the shape of an isolator of a concentric rotary piston compressor and the secondary peak pressure developed during each operating cycle. This peak pressure is developed when the piston passes through the isolator cavity, and it is negative for compressor efficiency. The aim of this paper is to identify the isolator cavity shape that minimizes this secondary peak to improve compressor efficiency. This study covers five different cavities that may be used in such compressors. Contrary to our expectations, the conclusion is that the best geometry is the one that can be manufactured with CNC machining. The geometry that can be manufactured with 3D printing also produces a significantly lower secondary peak pressure, but it is not cost-efficient. Another limitation of the 3D printing design is the thin walls that this cavity creates. Very thin walls may cause significant deformation during the compression cycle. The conclusion is that there is a CNC machining design that is cost-efficient and allows for higher compressor performance.
]]>Thermo doi: 10.3390/thermo3010012
Authors: Damian Park Isye Hayatina Mohammed Farid Amar Auckaili
The energy consumption for space cooling is progressively increasing. Integrating renewable energy into space cooling systems is critical for reducing CO2 emissions from the building sector. The salt-based cooling system is an appealing alternative as it can be charged by solar energy. This system is based on the characteristic of endothermic salts, which generate a considerable cooling effect when dissolved in water. A screening test was performed in this work to evaluate the cooling performance of several endothermic salts. Furthermore, a laboratory-scale system was developed to demonstrate the endothermic salt-based thermal storage and cooling generation system. Temperature decreases up to 12.3 °C were observed in the system containing Potassium Chloride salt. The temperature drop was maintained after the system underwent a charging/discharging cycle; however, the cooling period was shortened. The system demonstrated an inherent low efficiency due to the large volume of water required in the discharging phase, demanding a considerable amount of energy to evaporate the water in the charging phase. As a result, the application of this system will be restricted to the usage of low-grade energy during the charging phase.
]]>Thermo doi: 10.3390/thermo3010011
Authors: Barbara Król Krzysztof Kupiec
One of the modern methods of protecting against building heat losses is active thermal insulation (ATI). In winter conditions, ATI works by supplying heat into the envelope, which increases the temperature in the ATI layer. A low-temperature renewable energy medium feeds the active insulation layer directly, e.g., through solar or geothermal energy. A model for heat transfer through the building envelope with an ATI layer was developed. The numerical simulations verified the simplifying assumptions in the model. A relationship was derived to determine the optimal location of the ATI layer in the envelope. The objective function of the summed costs of the thermal energy supplied to the internal space and the envelope was assumed. We took into account the fact that the unit price of energy supplied to the ATI layer is lower than the price of the energy supplied to the internal space. Based on the results of the measurements carried out in a building facility with the ATI layer installed, the actual savings effects due to the ATI layer were compared to the calculated values.
]]>Thermo doi: 10.3390/thermo3010010
Authors: Aubrey Jaffer
Using boundary-layer theory, natural convection heat transfer formulas that are accurate over a wide range of Rayleigh numbers (Ra) were developed in the 1970s and 1980s for vertical and downward-facing plates. A comprehensive formula for upward-facing plates remained unsolved because they do not form conventional boundary-layers. From the thermodynamic constraints on heat-engine efficiency, the novel approach presented here derives formulas for natural convection heat transfer from isothermal plates. The union of four peer-reviewed data-sets spanning 1<Ra<1012 has 5.4% root-mean-squared relative error (RMSRE) from the new upward-facing heat transfer formula. Applied to downward-facing plates, this novel approach outperforms the Schulenberg (1985) formula’s 4.6% RMSRE with 3.8% on four peer-reviewed data-sets spanning 106<Ra<1012. The introduction of the harmonic mean as the characteristic length metric for vertical and downward-facing plates extends those rectangular plate formulas to other convex shapes, achieving 3.8% RMSRE on vertical disk convection from Hassani and Hollands (1987) and 3.2% from Kobus and Wedekind (1995).
]]>Thermo doi: 10.3390/thermo3010009
Authors: Zhao Wang Ali Turan Timothy Craft
Improvements in the efficiency of gas turbine engines over the decades have led to increasing turbine inlet temperatures. This, in turn, has resulted in the need to cool the turbine blades themselves to avoid damage to them. While air-cooling and film-cooling methods have been adopted as the primary methods of gas turbine blade cooling, the heat pipe cooling method shows greater potential in terms of temperature uniformity, maximum allowable gas temperature, reliability, and durability. This paper reviews the state-of-the-art research activities on the radial rotating heat pipes (RRHP) potentially applicable to gas turbine cooling. The emergence of the heat-pipe-cooled turbine blade concept, designs, and variants will be described at the beginning. Then the paper will review the literature addressing the heat transfer performance of RRHPs, and the effects on them of rotational forces, working fluid properties, and geometry, as well as operational limits they may be subject to. Additionally, the effects of secondary flow and numerical simulation of RRHPs will be reviewed and discussed. It can be concluded that fundamental studies are still needed for the understanding of the RRHP, as well as the improvement of numerical models.
]]>Thermo doi: 10.3390/thermo3010008
Authors: Ayah Rabi Jovana Radulovic James Buick
As renewable energy production is intermittent, its application creates uncertainty in the level of supply. As a result, integrating an energy storage system (ESS) into renewable energy systems could be an effective strategy to provide energy systems with economic, technical, and environmental benefits. Compressed Air Energy Storage (CAES) has been realized in a variety of ways over the past decades. As a mechanical energy storage system, CAES has demonstrated its clear potential amongst all energy storage systems in terms of clean storage medium, high lifetime scalability, low self-discharge, long discharge times, relatively low capital costs, and high durability. However, its main drawbacks are its long response time, low depth of discharge, and low roundtrip efficiency (RTE). This paper provides a comprehensive review of CAES concepts and compressed air storage (CAS) options, indicating their individual strengths and weaknesses. In addition, the paper provides a comprehensive reference for planning and integrating different types of CAES into energy systems. Finally, the limitations and future perspectives of CAES are discussed.
]]>Thermo doi: 10.3390/thermo3010007
Authors: Alexander Redkin Iraida Korzun Tatyana Yaroslavtseva Olga Reznitskikh Yuriy Zaikov Sergeiy Kumkov Anna Kodintseva
The isobaric heat capacity of solid eutectic mixtures LiCl-KCl-CsCl, LiBr-CsBr and LiBr-KBr-CsBr was investigated from room temperature up to melting point. The molar heat capacity of all mixtures under study was found to be close to the additive sum of that of pure salts. The heat accumulated up to melting temperature is directly dependent on the melting point.
]]>Thermo doi: 10.3390/thermo3010006
Authors: Thermo Editorial Office Thermo Editorial Office
High-quality academic publishing is built on rigorous peer review [...]
]]>Thermo doi: 10.3390/thermo3010005
Authors: Michelle Wilber Getu Hailu
Accurate soil heat transfer models are needed to predict and adapt to a warming arctic. A numerical model to accurately predict temperatures and thaw depths in soils, both with depth and with horizontal distance from features such as cliffs, was developed in Matlab using the finite element method. The model was validated against analytical solutions to simple versions of the problem and experimental temperature data from borehole thermistor strings on the north shore of Alaska. The current model is most useful for short term (on the order of days) predictions of thaw depth and near surface temperatures in homogeneous soils with existing data to allow the calibration of soil thermal parameters. These are exactly the time scales and capabilities that would integrate well with erosional models to predict the erosion during storm events and summer thaw conditions. Comparisons with analytical solutions show the model to be fairly accurate in predictions of temperatures thaw-depth and temperatures, within about 0.25 °C and 0.02 m respectively, for reasonable arctic soil parameters. Differences between predicted temperatures and thaw-depth against borehole data from Barter Island, Alaska are within about 1 °C and 0.5 m respectively. Comparison to commercial software, which does not directly track and move the phase change boundary, shows that this moving-mesh model has much better agreement. The model developed in this work is flexible and can be modified to model a wide variety of problems, but is efficiently set up to take a surface and thaw-boundary profile (not necessarily horizontal) and use soil parameters and surface boundary conditions appropriate to Arctic regions. It has been verified to appropriately model cliffs, which are particularly vulnerable to erosion.
]]>Thermo doi: 10.3390/thermo3010004
Authors: Elena Pulidori José Gonzalez-Rivera Chiara Pelosi Carlo Ferrari Luca Bernazzani Emilia Bramanti Maria Rosaria Tiné Celia Duce
The biomass waste obtained at the end-of-pipe of the extraction industry can be used as fuel for energy production, aiming at cost reduction/waste disposal issues. However, few systematic investigations into the calorific value of these residues are reported in the literature. In this work, the thermochemical properties of solid residues from different biomasses (residues from citrus peels, leaves, flowers, stems, and poultry feathers used for extraction) as potential biomass fuels have been investigated. The heat of combustion (ΔcH) of the solid residues from citrus (orange, tangerine, lemon, grapefruit, and pomelo), aromatic herbs (rosemary, lavender, thyme, Artemisia vulgaris L. and Ruta chalepensis L.), and poultry feathers biomasses was measured by direct calorimetry. The results were compared with the higher heating values (HHV) calculated using the elemental (CHNOS) and thermogravimetric (TGA) analyses data and with the enthalpy of combustion calculated using the biomass composition predicted by FTIR spectroscopy in tandem with chemometrics. The calculated values match with the corresponding experimental values of ΔcH. The heat of combustion highlights the energetic features of solid residues for their potential uses as alternative biomass for energy production. This information is essential to evaluate the employment of solid residues as fossil fuel substitutes.
]]>Thermo doi: 10.3390/thermo3010003
Authors: Yitong Dong Jiashu Kong Seyedmostafa Mousavi Behzad Rismanchi Pow-Seng Yap
Buildings account for nearly one-third of overall energy consumption in today’s world energy status, in which a considerable part is used for indoor conditioning. Energy efficiency enhancement of buildings components and technologies is a key priority, given the essential need for carbon neutrality and climate change mitigation around the world. Exterior wall insulation is considered as the most effective technology for protecting buildings against continual ambient fluctuations. Proper design and implementation of wall insulation would lead to performance enhancement, energy conservation as well as improved thermal comfort. They can also protect building structures against corrosion and heat fatigue, extending the life of buildings. There are many different types of thermal insulation materials currently on the market, each with its own set of thermal qualities and functionality. This paper aims to examine the qualities, benefits, and drawbacks of several exterior wall insulation technologies, and provide recommendations for how to use various forms of exterior wall insulation in different climates.
]]>Thermo doi: 10.3390/thermo3010002
Authors: Virtue Urunwo Wachikwu-Elechi Sunday Sunday Ikiensikimama Joseph Atubokiki Ajienka
Gas hydrate inhibitors, especially those used in offshore environments, are chemicals. These chemicals are synthetic in nature and pose both technical and environmental risks. This study emphasizes the influence of a Plant Extract (PE) on the phase behavior and equilibrium of structure I (SI) gas hydrate and its inhibition efficiency. The PE was screened using a mini flow loop. From the pressure-temperature phase diagram, the various weight percentages of the PE were able to disrupt the thermodynamic equilibrium conditions of the water and gas molecules to lower temperatures and increase pressures, which caused a shift in the equilibrium curve to an unstable hydrate formation zone. The pressure versus time plot as well as the inhibition efficiency plots for the PE and Mono Ethylene Glycol (MEG) were evaluated. Overall, the inhibition efficiency of the PE was higher than that of MEG for 1 wt% (60.53%) and 2 wt% (55.26%) but had the same efficiency at 3 wt% (73.68%). The PE at 1 wt% had the greatest inhibition effect and adjudged the optimum weight percent with a well-regulated phase equilibrium curve. This shows that PE is a better gas hydrate inhibitor than MEG, which is toxic to both human and aquatic life; therefore, it is recommended for field trials.
]]>Thermo doi: 10.3390/thermo3010001
Authors: Mehdi Bencharif Sergio Croquer Yu Fang Sébastien Poncet Hakim Nesreddine Said Zid
Ejectors have gained renewed interest in the last decades, especially in heat-driven refrigeration systems, to reduce the load of the compressor. Their performance is usually influenced by many factors, including the working fluid, operating conditions and basic geometrical parameters. Determining the relationships between these factors and accurately predicting ejector performance over a wide range of conditions remain challenging. The objective of this study is to develop fast and efficient models for the design and operation of ejectors using artificial neural networks. To this end, two models are built. The first one predicts the entrainment and limiting compression ratio given 12 input parameters, including the operating conditions and geometry. The second model predicts the optimal geometry given the desired performance and operating conditions. An experimental database of ejectors using five working fluids (R134a, R245fa, R141b, and R1234ze(E), R1233zd(E)) has been built for training and validation. The accuracy of the ANN models is assessed in terms of the linear coefficient of correlation (R) and the mean squared error (MSE). The obtained results after training for both cases show a maximum MSE of less than 10% and a regression coefficient (R) of, respectively, 0.99 and 0.96 when tested on new data. The two models have then a good generalization capacity and can be used for design purposes of future refrigeration systems.
]]>Thermo doi: 10.3390/thermo2040030
Authors: Robert Beaufait Willy Villasmil Sebastian Ammann Ludger Fischer
Geothermal energy storage provides opportunities to store renewable energy underground during summer for utilization in winter. Vertically oriented systems have been the standard when employing boreholes as the means to charge and discharge the underground. Horizontally oriented borehole storage systems provide an application range with specific advantages over vertically oriented systems. They are not limited to the surface requirements needed for installation with vertical systems and have the potential to limit storage losses. Horizontal systems can be incorporated into the built environment and utilize underground storage sites below existing infrastructure. An experimental study examines configurations using a mix of renewable energy (photovoltaic panels) and grid energy to charge a storage system during summer for use during winter. A comparison of five different borehole configurations at three different loading temperatures was composed using an experimentally validated numerical model. The horizontal systems studied and analyzed in this work showed improved performance with scale and charging temperature. This paper supports further exploration into specific use cases for horizontal borehole thermal energy storage systems and suggests applications which would take advantage of better performance at scale.
]]>Thermo doi: 10.3390/thermo2040029
Authors: Nikita V. Muravyev Sergey Vyazovkin
This paper is a literature survey that focuses on the present development of thermokinetic publications. It demonstrates that in recent years pyrolysis kinetics has turned into a major application of the thermokinetics. Analysis of the respective publications suggests that too often their quality leaves much to be desired because of the poor choices of the kinetic methods and experimental conditions. It is explained that the proper choices can be made by following the recommendations of the International Confederation for Thermal Analysis and Calorimetry (ICTAC). To help with improving the quality of the kinetic results, the ICTAC recommendations are condensed to a few easy to follow principles. These principles focus on selecting proper computational methods, collecting better experimental data, and efficiently reporting the results. The paramount computational principle is to avoid using the methods that evaluate the activation energy and other kinetic parameters from the data measured at a single heating rate. It is shown that the kinetic parameters evaluated by such methods can give rise to striking examples of failure when estimating the thermal stability at ambient temperature. Because of the vital importance of pyrolysis kinetics studies from an ecological and economical perspective, a substantial improvement of their quality is currently needed.
]]>Thermo doi: 10.3390/thermo2040028
Authors: Ivan Kennedy John Runcie Shuo Zhang Raymond Ritchie
Seasonal oscillations in the partial pressure of carbon dioxide (pCO2) in the Earth’s atmosphere, stronger in northern latitudes, are assumed to show that terrestrial photosynthesis exceeds respiration in summer, reducing the pCO2 in air but increasing its value in winter when respiration exceeds photosynthesis. We disagree, proposing that variation in the temperature of the surface mixing zone of seawater also reversibly regulates the pCO2 in air as a non-equilibrium process between air and seawater. We predict by thermal modelling that carbonate (CO32−) concentration in the surface mixed layer seawater declines in winter by conversion to bicarbonate with CaCO3 (calcite or aragonite) becoming more soluble and, proportional to the fall of temperature, calcite decalcifying more strongly, allowing more CO2 emission to air. Paradoxically, the increasing CO2 concentration in seawater favoring photosynthesis peaking in mid-summer declines simultaneously in autumn and early winter, forced by boundary layer fugacity into phase transfer to the atmosphere, supporting peak atmospheric pCO2 by late winter. These physico-chemical processes reverse in late winter and spring as seawater warms favoring calcification, fugacity forcing CO2 from the atmosphere as bicarbonate declines and carbonate increases, augmenting suspended calcite particles by several percent. Our numerical computation predicts that the larger range of thermal fluctuations in the northern hemisphere could reversibly favor absorption from air of more than one mole of CO2 per square meter in summer with calcite formation potentially augmenting shallow limestone reefs, despite falling pH, if there is a trend for increasing seawater temperature. Another assumption we challenge is that upwelling and advection from deeper water is the sole cause of increases in dissolved inorganic carbon (DIC) and alkalinity in surface waters, even in the southern hemisphere. Instead, some calcite dissolution is favored as water temperature falls near the surface. Standard enthalpy analysis of key DIC reactions indicates why this oscillation is more obvious in the northern hemisphere with seasonal variations in water temperature (ca. 7.1 °C) being almost twice those in the southern hemisphere (ca. 4.7 °C) with a greater depth of the surface mixing zone of seawater in the southern oceans. Questions remain regarding the relative rates of biotic and abiotic inorganic precipitation and dissolution of CaCO3 in the mixing zone. In summary, rapid biogenic calcification is favored by summer photosynthesis, but slower abiotic calcification is also more likely in warmer water. We conclude that the relative significance of terrestrial biotic and seawater abiotic processes in seawater on the seasonal oscillation in the atmosphere can only be assessed by direct seasonal measurements in seawater.
]]>Thermo doi: 10.3390/thermo2040027
Authors: Jaén A. Ocádiz Flores Bas A. S. Rooijakkers Rudy J. M. Konings Anna Louise Smith
Corrected excess Gibbs energies of the liquid solutions in the ACl-ThCl4 (A = Li, Na, K), as well as revised standard enthalpies of formation and standard entropies of the intermediate phases occurring in the binary systems, are presented [...]
]]>Thermo doi: 10.3390/thermo2040026
Authors: Javad Mohammadpour Fatemeh Salehi Ann Lee
Attention to photovoltaic (PV) cells to convert solar irradiation into electricity is significantly growing for domestic usage and large-scale projects such as solar farms. However, PV efficiency decreases on hot days. This paper proposes an effective cooling technique consisting of a 2% nano encapsulated phase change material (NEPCM) slurry and impinging jets (IJs) in a PV system. The impact of five influencing parameters on PV efficiency is studied using a multi-phase volume of fluid (VOF) model encompassing the effects of solar irradiation, latent heat, mass flow rate, number of nozzles, and jet-to-surface distance. The maximum efficiency of 15.82% is achieved under irradiation of 600 W/m2. The latent heat shows a slight improvement at the low particle concentration. Increasing the mass flow rate to 0.12 kg/s enhances the PV output power by 17.32%. While the PV performance is shown to be improved over the increment of the number of nozzles, the jet-to-surface spacing of 5.1 mm records a remarkable PV surface temperature reduction to 33.8 °C, which is the ideal operating temperature for the PV panel.
]]>Thermo doi: 10.3390/thermo2040025
Authors: Pradeep Samui Renu Agarwal
Lead–Bismuth Eutectic (LBE) is a heavy metal liquid alloy used as a coolant for compact high temperature reactors (CHTRs), fast breeder reactor (FBRs) and as a spallation target for ADS. In spite of many advantages due to its thermophysical properties, corrosion towards structural materials remains one of the major issues of LBE. In absence of any oxygen impurity, corrosion in LBE is driven by dissolution processes and the solubility of the main elements of the structural material alloys. Using the CALPHAD method, Thermo-Calc software, a thermodynamic database was developed to assess the interaction between Ni and LBE coolant. The solubilities of Ni in LBE, Bi and Pb liquids have been calculated at different temperatures.
]]>Thermo doi: 10.3390/thermo2040024
Authors: Clemens Biet Sören Krebs
The potential regarding the indicated efficiency of an alternative piston trajectory for a spark ignited methane combustion engine has been investigated in this study. A physics-based cylinder model including a predictive combustion model was used to account for the interaction of the thermodynamics with altered kinematics. Using a genetic optimization algorithm on an adjustable spline, piston trajectories for different piston acceleration limits have been found for both full and part load operating points. All optimization processes led to increased indicated efficiencies up to a maximum of 52%. The increase in efficiency of the optimized piston trajectory is analyzed based on the results of the numeric simulation and can be explained by the following effects: deeper expansion of the working gas, reduced pumping losses, reduced wall heat losses, shorter heat release, and increased trapped air mass.
]]>Thermo doi: 10.3390/thermo2040023
Authors: Khaled Salhein C. J. Kobus Mohamed Zohdy
Foresight of geothermal energy installation is valuable for energy decision-makers, allowing them to readily identify new capacity units, improve existing energy policies and plans, expand future infrastructure, and fulfill consumer load needs. Therefore, in this paper, an improved grey prediction model (IGM (1,1)) was applied to perform the annual geothermal energy installation capacity prediction for the top 10 countries based on installed power generation capacity evaluated at the end of 2021, namely the United States, Indonesia, Philippines, Turkey, New Zealand, Mexico, Italy, Kenya, Iceland, and Japan, for the next nine years for the period from 2022 through 2030. These data can be used by future researchers in the field. Separately, datasets from 2000 to 2021 were collected for each country’s geothermal energy installation capacity to build a model which can accurately predict the annually geothermal energy installation capacity by 2030. The IGM (1,1) model used a small dataset of 22 data points, with one point denoting one year (i.e., 22 years), to predict the capacity of geothermal energy installations for the next nine years. Following that, the model was implemented for each dataset in MATLAB, where appropriate, and the model accuracy was evaluated. Ten separate geothermal energy installation capacity datasets were used to validate the improved model, and these datasets further demonstrated the overall improved model’s accuracy. The results prove that the prediction accuracy of the IGM (1,1) model outperforms the benchmark conventional GM (1,1) model, thereby enhancing the overall accuracy of the GM (1,1) model. The IGM (1,1) model ensures error reduction, suggesting that it is an effective and promising tool for accurate short-term prediction. The results reveal the 2030 geothermal energy installation capacity rankings.
]]>Thermo doi: 10.3390/thermo2030022
Authors: Saeedeh Taheri Dylan John McFarlane Scott William Mattner Graham Ian Brodie
This review explores the use of microwave heating and microwave-generated plasma for biosecurity applications. Microwave heating has been shown to rapidly heat and kill a wide range of pests and pathogens. Examples of microwave thermal disinfestation of soils, grains, hay, and timber are presented and discussed. Microwave energy can also ionize various gasses, including air, to create plasma. Plasmas are described by many characteristics, such as temperature, degree of ionization, and density. In the “after glow” (cold plasma) of a plasma discharge, there are sufficient charged particles and excited atoms to generate elevated UV levels and ionize the surfaces of objects. Examples of cold plasma and plasma-activated water disinfestation of grains and other commodities are also presented and discussed. Brief comments on the scale-up of this technology have also been presented.
]]>Thermo doi: 10.3390/thermo2030021
Authors: Charles Earnest Josh Jones Ashley Dunn
The results obtained from a study of the thermal transformations of polymorphic long-chain normal paraffins (n-C32H66 and n-C36H74) are presented here. The research was performed using a power-compensated Differential Scanning Calorimeter (DSC). Both heating and cooling experiments were performed in dynamic nitrogen atmosphere. Thermodynamic data for both polymorphic transitions, as well as the fusion endotherms, were determined from the DSC thermal curves. Using the heats of transition (∆H), in Joules/gram, obtained from the data in the DSC thermal curves, molar heats of transition (∆H), in kJ/mol, were calculated and compared to previously published values. The molar entropy of transition (∆S) was then calculated for each of the observed thermal events. Additional information is given by the author on obtaining the best results from the use of DSC for the thermal behavior of n-paraffins. This manuscript opens with a review of most of the early work and the results it provided dealing with polymorphism of n-paraffin solids. Some of this referenced work was performed prior to the advent of computerized analytical instrumentation.
]]>Thermo doi: 10.3390/thermo2030020
Authors: Mikhail Batanov-Gaukhman
It is shown that the inert properties of a stationary random process can be expressed in terms of the ratio of its correlation interval τx to the doubled variance Dx. When using a fixed value of Planck’s constant h as a proportionality factor, the ratio hτx/2Dx has the dimension of a kilogram and can be used as an equivalent of a mass standard. It is proposed to use thermal (i.e., Johnson–Nyquist) noise as a reference Gaussian stationary random process. The theoretical substantiation of the project for the creation of “thermoelectric semiconductor ampere-balances” for balancing the inert mass of a quasi-ideal silicon-28 ball is also given. Combining these two projects can provide the basis for a stable and reproducible mass standard.
]]>Thermo doi: 10.3390/thermo2030019
Authors: Luis Fernández Juan Ortega Adriel Sosa
Thermodynamics, as a scientific tool, advises on the control of variables involved in processes of different nature and is particularly useful in the design of equipment, or to obtain previous simulations. However, to generate more accurate models, an exact science is required. Thus, the thermodynamic–mathematical binomial is able to relate the fundamental variables of a system using the potential functions directing the process, although these relationships are not always completely satisfactory, as it is necessary to complete the modelling with a set of parameters, which depend on the experimentation. To ensure a better description of the behavior of a system, in this work a multi-objective optimization procedure (MOP) is applied to the NRTL model, comparing the results with other conventional procedures used to characterize the real properties of the binary methyl methanoate + pentane. The results obtained with the MOP confirmed a better representation of the experimental information with NRTL, analyzing its impact on the simulation/design processes. The set of optimal parametrizations obtained allow several options to be process engineered to select the most appropriate one depending on the specific problem to be designed.
]]>Thermo doi: 10.3390/thermo2030018
Authors: Sergey P. Verevkin Ruslan N. Nagrimanov
Qualitatively, the non-covalent interactions are well-known and help to explain many phenomena in chemistry and biochemistry. Quantitatively, determination of strength this force is a challenging task. The vaporization enthalpy is a reliable measure not only for the intermolecular interactions in the liquid phase, but also as the measure of intermolecular non-covalent interactions in the gas phase for the specific group of compounds, e.g., for the triglycerides. The vaporisation thermodynamics of four triglycerides were studied by using transpiration method, quartz crystal microbalance, and thermogravimetric analysis. Vapour pressure–temperature dependences were used to derive the enthalpies of vaporisation of these very low volatile liquids. Vaporisation enthalpies of the triglycerides available in the literature were collected and uniformly adjusted to the reference temperature 298.15 K and validated using structure–property relationships (chain-length dependence, correlation with retention indices, and correlation with normal boiling points). The consistent sets of evaluated vaporisation enthalpies for the linear and branched triglycerides were used to develop the “centerpiece” based group-additivity method for predicting enthalpies of vaporisation of triglycerides. It has turned out that the family of triglycerides do not obey the group-additivity rules. The reason for that is that the evaporated in the gas phase triglycerides exhibit intensive non-covalent attractive dispersion interactions strongly dependent on the alkyl-chain length. For the first time the intensity of the dispersion interactions was quantified for the family of aliphatic linear triglycerides with the chain length from 3 to 18 carbon atoms. The influence of the branching and unsaturation of the alkyl chains to the strength of the non-covalent interactions was also discussed.
]]>Thermo doi: 10.3390/thermo2030017
Authors: Kaspar M. B. Jansen Lennart Teunissen
Cooling vests containing phase change materials (PCMs) are used to reduce heat stress in hot environments and maintain the body core temperature within a safe range. The performance of such cooling vests depends in a complicated way on the PCM material and mass, the insulation value of the clothing layers and heat loss to the environment. Conventionally, these performance parameters are evaluated experimentally or using a numerical model, both of which do need a certain amount of evaluation time. The objective of this paper is to develop a transient heat transfer model which includes metabolic heat production in the human body, as well as clothing and PCM layers and radiation to the environment but which is presented as a series of closed-form equations that can be evaluated without the need of a numerical solver. We present solutions for the body and PCM temperature as well as for the heat flux, cooling power and cooling duration. The model equations are validated by comparing them with experiments of ice PCM packs on a hotplate, as well as with published experimental and numerical data for the core temperature, heat flux and percentage of environmental heat loss using a Glauber salt type of PCM. Both the hotplate experiments and the model predictions show that the cooling power during PCM melting drops from about 70 to 32 W for increasing insulation layer thicknesses. In addition, the model is seen to compare well with experimental and simulation data in the literature. In a parametric study, we show how the equations can be used to evaluate the effects of PCM melting temperature and PCM thickness on cooling performance. The paper, therefore, can be considered as a practical means to help select the best cooling vest configuration for workers in a hot and humid environment.
]]>Thermo doi: 10.3390/thermo2030016
Authors: Mustafa Mutiur Rahman Ahmed Saieed Muhammad Fasahat Khan Jean-Pierre Hickey
The group combustion characteristics of core–shell nanothermite particles differ from other dispersed solid or liquid fuels. In a core–shell structure, each discrete nanothermite particle can undergo an exothermic reaction as the oxygen atoms in the metal oxide shell undergo a solid state diffusion to oxidize the metal core. This feature allows the spherical core–shell nanothermites to react in the absence of gaseous oxygen, thus modifying their group combustion characteristics compared to char or liquid fuels. Using a number of simplifying assumptions, a theoretical framework was established—based on existing group combustion theory—to examine the characteristics of mass and heat diffusion in nanothermite combustion. First, a model for the quasi-steady state single-particle combustion, in quiescent air, was established. The isolated particle combustion theory serves as the basis for the combustion interaction and mass transfer in a spherical cloud of dispersed nanothermite particles. The type of group combustion is strongly dependent on the diffusion of vapour products, i.e., the interaction is more pronounced when the diffusion of vapour products is higher. The group combustion regimes in dispersed nanothermites were identified and delineated.
]]>Thermo doi: 10.3390/thermo2030015
Authors: Guillaume Ah-Lung Claire Besnard Flavien Ivol Carine Maaliki Terri-Louise Hughes Peter Goodrich Johan Jacquemin
Extraction of alcohols from n-tetradecane using various extraction solvents has been investigated at a range of temperatures from 295 to 393 K under ambient pressure. On the basis of the experimental liquid–liquid equilibrium data, the distribution ratio and selectivity were calculated for the extraction of 1-octanol, 1-decanol, and 1-dodecanol (C8–C12) in 1-ethyl-3-methylimidazolium hydrogensulfate [C2mim][HSO4] and sulfolane. Results showed that moderate selectivities were obtained in sulfolane with very low distribution coefficients. In contrast, [C2mim][HSO4] showed similar selectivity values with higher distribution coefficients. A study of a number of different 1-alcohols (C4–C12) showed that the decrease in hydrogen bonding compared to the increased van der Waals interactions between n-tetradecane and the higher-chain alcohols decreased the extraction selectivity in [C2mim][HSO4]. Increasing the temperature of the ionic liquid extraction medium resulted in increased chemical extraction for 1-butanol and 1-hexanol due to the formation of the corresponding alkylsulfate ionic liquid. In contrast, the selectivity decreased for 1-octanol, 1-decanol and 1-dodecanol due to the partial dissolution of the corresponding alkylsulfate ionic liquid into the n-tetradecane phase.
]]>Thermo doi: 10.3390/thermo2030014
Authors: Carlos Prieto Massimo Cimmino
The study of heat transfer in ground heat exchangers (GHEs) considering the fluid advection inside the pipes; the heat transfer between the fluid and the ground through the grout material; and the thermal interaction between GHEs is a challenging task. The present paper presents a new semi-analytical method that takes into account the aforementioned effects to consider both the short- to long-term effects of GHEs. The heat transfer between the fluid and grout was studied by a transient multipole expansion considering time-dependent fluid temperatures and an advection model for the pipes obtained from an energy balance on the heat carrier fluid. Thermal interactions were analyzed using an equivalent borehole method while penalizing the transient multipole expansion to include thermal interaction effects. Validation of the short-term predictions was performed by comparing the proposed model to experimental data found in the literature and to an FEA model. The proposed model was then compared with a FEA model in long-term simulations of a geothermal field comprised of 24 GHEs for multi-annual simulation. The method resulted in substantial reduction in computational time while preserving good accuracy when compared with the FEA model.
]]>Thermo doi: 10.3390/thermo2030013
Authors: Saeed Mehri Lorenzo Costigliola Jeppe C. Dyre
Physical aging deals with slow property changes over time caused by molecular rearrangements. This is relevant for non-crystalline materials such as polymers and inorganic glasses, both in production and during subsequent use. The Narayanaswamy theory from 1971 describes physical aging—an inherently nonlinear phenomenon—in terms of a linear convolution integral over the so-called material time ξ. The resulting “Tool–Narayanaswamy (TN) formalism” is generally recognized to provide an excellent description of physical aging for small, but still highly nonlinear, temperature variations. The simplest version of the TN formalism is single-parameter aging according to which the clock rate dξ/dt is an exponential function of the property monitored. For temperature jumps starting from thermal equilibrium, this leads to a first-order differential equation for property monitored, involving a system-specific function. The present paper shows analytically that the solution to this equation to first order in the temperature variation has a universal expression in terms of the zeroth-order solution, R0(t). Numerical data for a binary Lennard–Jones glass former probing the potential energy confirm that, in the weakly nonlinear limit, the theory predicts aging correctly from R0(t) (which by the fluctuation–dissipation theorem is the normalized equilibrium potential-energy time-autocorrelation function).
]]>Thermo doi: 10.3390/thermo2030012
Authors: Nima Samkhaniani Alexander Stroh
Pure numerical simulation of phase-change phenomena such as boiling and condensation is challenging, as there is no universal model to calculate the transferred mass in all configurations. Among the existing models, the sharp interface model (Fourier model) seems to be a promising solution. In this study, we investigate the limitation of this model via a comparison of the numerical results with the analytical solution and experimental data. Our study confirms the great importance of the initial thermal boundary layer prescription for a simulation of single bubble condensation. Additionally, we derive a semi-analytical correlation based on energy conservation to estimate the condensing bubble lifetime. This correlation declares that the initial diameter, subcooled temperature, and vapor thermophysical properties determine how long a bubble lasts. The simulations are carried out within the OpenFOAM framework using the VoF method to capture the interface between phases. Our investigation demonstrates that calculation of the curvature of interface with the Contour-Based Reconstruction (CBR) method can suppress the parasitic current up to one order.
]]>Thermo doi: 10.3390/thermo2030011
Authors: Dmitry G. Luchinsky Vasyl Hafiychuck Kevin R. Wheeler Sudipta Biswas Christopher E. Roberts Ian M. Hanson Tracie J. Prater Peter V. E. McClintock
Nonlinear shrinkage of the metal part during manufacturing by bound metal deposition, both on the ground and under microgravity, is considered. A multi-scale physics-based approach is developed to address the problem. It spans timescales from atomistic dynamics on the order of nanoseconds to full-part shrinkage on the order of hours. This approach enables estimation of the key parameters of the problem, including the widths of grain boundaries, the coefficient of surface diffusion, the initial redistribution of particles during the debinding stage, the evolution of the microstructure from round particles to densely-packed grains, the corresponding changes in the total and chemical free energies, and the sintering stress. The method has been used to predict shrinkage at the levels of two particles, of the filament cross-section, of the sub-model, and of the whole green, brown, and metal parts.
]]>Thermo doi: 10.3390/thermo2030010
Authors: Alexander Redkin Evgeniya Il’ina Svetalana Pershina Peter Mushnikov Sergey Stankus Alibek Agazhanov Yuriy Zaikov Anna Kholkina Artyem Artamonov
The LiF–BeF2 system is used as a heat transfer medium in molten salt reactors (MSRs). The thermal diffusivity of Li2BeF4 was studied using the laser flash analysis (LFA) method in solid and transition states. While the thermal diffusivity is shown to decrease slightly in solid-state Li2BeF4, it drops significantly at temperatures close to phase transition. The heat capacity of Li2BeF4 was measured by differential scanning calorimetry (DSC). Some differences were observed between the results obtained in cooling and heating modes. Thermal conductivity was calculated using thermal diffusivity-, density-, and heat-capacity data. The good thermal conductivity of the Li2BeF4 compound in solid and liquid states justifies its use as a heat transfer medium for molten salt reactors.
]]>Thermo doi: 10.3390/thermo2020009
Authors: Francesco Calise Francesco Liberato Cappiello Luca Cimmino Marialuisa Napolitano Maria Vicidomini
The production of biogas by means of the anaerobic digestion process is becoming increasingly attractive in the green economy context. When municipal organic waste is used to produce biogas, a further positive effect on urban waste disposal is obtained. Starting from the anaerobic digestion model n.1, an accurate analysis of the temperature effects on the anaerobic digestion process in a plug flow reactor is performed. This paper aims at presenting a comprehensive and integrated one-dimensional biological and thermal model for a plug flow reactor. Partial differential equations with respect to time and space are considered to model the heat transfer between the reactor and the internal heat exchanger and between the reactor and the environment. In this scope, a suitable simulation code was developed in MATLAB and validated using the data available in literature. The results of the calculations show that temperature plays a crucial role in the anaerobic digestion process, since it strongly affects the kinetic rates of the microbial species and the methane production. The results obtained in terms of temperature fields and biogas production are compared with the ones available in literature, dealing with a continuously stirred tank reactor. The comparison is conducted considering that both reactors process a volumetric waste flow rate of 20 m3/d and have the same structural characteristics. The plug flow reactor resulted better performance with a produced biogas flow rate equal to 2300 Nm3/year.
]]>Thermo doi: 10.3390/thermo2020008
Authors: Ignazio Blanco
The wide category of organic materials containing polymers had a great impact on the last middle century, and continues to nowadays, thus affecting our daily behaviors. The need to investigate their durability has grown, which may be necessary in the successful completion of the application for which these materials were designed, and to mitigate their impact on the environment. The aim of this Special Issue was to allow researchers, in both Industry and Academia, to show their current research in material properties finalized to the lifetime prediction.
]]>Thermo doi: 10.3390/thermo2010007
Authors: Rubin Battino Trevor M. Letcher
Chemical thermodynamics is frequently thought of as being a hard subject and quite abstract. In fact, it is one of the most practical of subjects when you consider that the field of chemical engineering (responsible for endless useful applications) is effectively applied chemical thermodynamics. In this essay, examples of these applications are given, especially with respect to sustainability. The essay first considers the limits of thermodynamics and the constraints put on it in terms of the rigorous definitions of the principal function’s energy, entropy, and Gibbs energy.
]]>Thermo doi: 10.3390/thermo2010006
Authors: Ignazio Blanco
The last few years have been characterized by the development of 3D printing technology; in parallel, many analytical techniques have been proposed for this new technology to favor its development and commercialization. In this short review, I verify how thermal analysis, which I have always dealt with, can help this technology. Fused deposition modeling (FDM) is not a novel technology; however, considering the variety of possibility it offers to printing, as well as the fact that, in the first decade of this century, companies designed their printer machines to print with a limited selection of materials, the potential of this technology is still very large. At this stage, both industry and academy need more information to better develop 3D printing technology, and thermal analysis can absolutely help them to reach this goal.
]]>Thermo doi: 10.3390/thermo2010005
Authors: Bandar J. Bashmmakh Xiaoyu Wang Cynthia J. Jameson Sohail Murad
Noble gas fission byproducts, such as Kr and Xe, are generated within nuclear power reactors are currently being discharged into the atmosphere. This practice has a major economic drawback because of the high value associated with some of these gases. The separations of these gases are economically prohibitive because of the high energy requirement associated with cryogenic distillation. Zeolites, nanoporous materials suitable for gas separation processes, have exhibited high selectivity for such separations. We have used nonequilibrium molecular dynamics (MD) to investigate the separation performance of DD3R framework zeolitic membrane. The effects of pressure, temperature, and pure vs. mixture gas feed conditions are studied in this work to understand and explain, at the molecular level, the mechanisms of these (Kr/Xe) separations. Our studies have shown that the DD3R membrane shows promise for high selectivity ratios of Kr over Xe. MD runs show agreement with experimental trends of the permeation of Kr/Xe pure and mixed gases using DD3R zeolite with high separation factor. Despite the absence of Xe complete permeation through the membrane because of MD timescale limitations, our results are sufficient to describe the mechanisms of these separations.
]]>Thermo doi: 10.3390/thermo2010004
Authors: Reza Hassanian Morris Riedel Asdis Helgadottir Nashmin Yeganeh Runar Unnthorsson
This paper evaluates the photovoltaic (PV) module operating temperature’s relation to efficiency via a numerical heat transfer model. The literature reports that higher PV module operating temperatures impact PV module efficiency. There are dozens of explicit and implicit equations used to determine the PV module operating temperature. However, they are not universal, and for each application, it is necessary to insert a correction coefficient based on the environment and boundary conditions. Using a numerical method covering a more comprehensive range of PV module operation conditions to estimate a global equation, this study considers the solar radiation flux, Gt, solar ray direction with respect to the ground level, γ, convective heat transfer coefficient, h, tilt angle, β, ambient temperature, Ta, PV power output, Ppv, PV panel efficiency, η, and environmental properties. The results match the extant empirical work and related literature. PV module efficiency is found to have a linear relationship to the PV module operating temperature via a numerical heat transfer model corresponding to the well-known PV module. It specifies that heat transfer convection changes with PV module tilt angle, causing PV module operating temperature effects. It also represents the PV module operating temperature variations with ambient temperature and solar flux, like those reported in the literature.
]]>Thermo doi: 10.3390/thermo2010003
Authors: Christine Guéneau Eva Lawrence Thierry Klein Fabrice Gamboa
Under irradiation, the formation of fission products in the (U,Pu)O2 fuel with time has a substantial effect on its chemistry. In particular, migration of the most volatile fission products (Cs, Te, I, Mo) from the center to the periphery of the fuel pellet is induced by the large radial thermal gradient. To predict the thermodynamic properties of the irradiated fuel, thermodynamic modeling of the complex multi-component (Cs-I-Te-Mo)–(U-Pu)–O system is performed using the CALPHAD method. In this work, the thermodynamic assessment of the U–Te sub-system is performed. The literature review reveals a lack of experimental data as well as scattering and inconsistency of some of the data. In particular, no thermodynamic data exist on the liquid. From this review, input thermodynamic and phase diagram data are carefully selected. The Gibbs energy functions are then adjusted by fitting these data. An overall good agreement is obtained with all the selected data except for the enthalpy of formation for UTe which is underestimated by 13% by our model. This could be due to an inconsistency between the enthalpy of formation and vapor pressure data. In a second step, the uncertainties on the thermodynamic parameters and their propagation on the calculated thermodynamic and phase diagram data are estimated using a Bayesian approach. The analysis shows that there are too many parameters (22) for too few data points (120 points). The uncertainties are thus large on some of the calculated data. Moreover the inconsistency of some of the data and the lack of thermodynamic data for the liquid makes the model uncertain. New experimental data such as heat capacity, enthalpy of formation for the compounds, and chemical potentials or activities for the liquid phase would improve the reliability of our model. Measurements of phase diagram data in the U–UTe2 region are also required. However this work provides the first detailed uncertainty analysis of the U–Te CALPHAD model. Moreover our approach, contrary to other Bayesian methods, provides an analytical posterior probability distribution and analytical credible intervals for the calculated thermodynamic quantities. It also speeds up the simulation of the uncertainty estimations on the phase diagram.
]]>Thermo doi: 10.3390/thermo2010002
Authors: Thermo Editorial Office Thermo Editorial Office
Rigorous peer-reviews are the basis of high-quality academic publishing [...]
]]>Thermo doi: 10.3390/thermo2010001
Authors: Parker Maivald Soumya Sridar Wei Xiong
Thermal interface material (TIM) that exists in a liquid state at the service temperature enables efficient heat transfer across two adjacent surfaces in electronic applications. In this work, the thermal conductivities of different phase regions in the Ga-In system at various compositions and temperatures are measured for the first time. A modified comparative cut bar technique is used for the measurement of the thermal conductivities of GaxIn1−x (x = 0, 0.1, 0.214, 0.3, and 0.9) alloys at 40, 60, 80, and 100 °C, the temperatures commonly encountered in consumer electronics. The thermal conductivity of liquid and semi-liquid (liquid + β) Ga-In alloys are higher than most of the TIM’s currently used in consumer electronics. These measured quantities, along with the available experimental data from literature, served as input for the thermal conductivity parameter optimization using the CALPHAD (calculation of phase diagrams) method for pure elements, solution phase, and two-phase region. A set of self-consistent parameters for the description of the thermal conductivity of the Ga-In system is obtained. There is good agreement between the measured and calculated thermal conductivities for all of the phases. Due to their ease of manufacturing and high thermal conductivity, liquid/semi-liquid Ga-In alloys have significant potential for TIM in consumer electronics.
]]>Thermo doi: 10.3390/thermo1030022
Authors: Emilia Fisicaro Carlotta Compari Antonio Braibanti
For many years, we have devoted our research to the study of the thermodynamic properties of hydrophobic hydration processes in water, and we have proposed the Ergodic Algorithmic Model (EAM) for maintaining the thermodynamic properties of any hydrophobic hydration reaction at a constant pressure from the experimental determination of an equilibrium constant (or other potential functions) as a function of temperature. The model has been successfully validated by the statistical analysis of the information elements provided by the EAM model for about fifty compounds. The binding functions are convoluted functions, RlnKeq = {f(1/T)* g(T)} and RTlnKeq = {f(T)* g(lnT)}, where the primary linear functions f(1/T) and f(T) are modified and transformed into parabolic curves by the secondary functions g(T) and g(lnT), respectively. Convoluted functions are consistent with biphasic dual-structure partition function, {DS-PF} = {M-PF} ∙ {T-PF} ∙ {ζw}, composed by ({M-PF} (Density Entropy), {T-PF}) (Intensity Entropy), and {ζw} (implicit solvent). In the present paper, after recalling the essential aspects of the model, we outline the importance of considering the solvent as “implicit” in chemical and biochemical reactions. Moreover, we compare the information obtained by computer simulations using the models till now proposed with “explicit” solvent, showing the mess of information lost without considering the experimental approach of the EAM model.
]]>Thermo doi: 10.3390/thermo1030021
Authors: Hamid Reza Vanaei Mohammadali Shirinbayan Michael Deligant Sofiane Khelladi Abbas Tcharkhtchi
Fused filament fabrication (FFF), an additive manufacturing technique, unlocks alternative possibilities for the production of complex geometries. In this process, the layer-by-layer deposition mechanism and several heat sources make it a thermally driven process. As heat transfer plays a particular role and determines the temperature history of the merging filaments, the in-process monitoring of the temperature profile guarantees the optimization purposes and thus the improvement of interlayer adhesion. In this review, we document the role of heat transfer in bond formation. In addition, efforts have been carried out to evaluate the correlation of FFF parameters and heat transfer and their effect on part quality. The main objective of this review paper is to provide a comprehensive study on the in-process monitoring of the filament’s temperature profile by presenting and contributing a comparison through the literature.
]]>Thermo doi: 10.3390/thermo1030020
Authors: Emily Jane Watkinson Ramy Mesalam Jean-François Vigier Ondřej Beneš Jean-Christophe Griveau Eric Colineau Mark Sierig Daniel Freis Richard M. Ambrosi Dragos Staicu Rudy J. M. Konings
The European Space Agency is funding the research and development of 241Am-bearing oxide-fuelled radioisotope power systems (RPSs) including radioisotope thermoelectric generators (RTGs) and European Large Heat Sources (ELHSs). The RPSs’ requirements include that the fuel’s maximum temperature, Tmax, must remain below its melting temperature. The current prospected fuel is (Am0.80U0.12Np0.06Pu0.02)O1.8. The fuel’s experimental heat capacity, Cp, is determined between 20 K and 1786 K based on direct low temperature heat capacity measurements and high temperature drop calorimetry measurements. The recommended high temperature equation is Cp(T/K) = 55.1189 + 3.46216 × 102 T − 4.58312 × 105 T−2 (valid up to 1786 K). The RTG/ELHS Tmax is estimated as a function of the fuel thermal conductivity, k, and the clad’s inner surface temperature, Ti cl, using a new analytical thermal model. Estimated bounds, based on conduction-only and radiation-only conditions between the fuel and clad, are established. Estimates for k (80–100% T.D.) are made using Cp, and estimates of thermal diffusivity and thermal expansion estimates of americium/uranium oxides. The lowest melting temperature of americium/uranium oxides is assumed. The lowest k estimates are assumed (80% T.D.). The highest estimated Tmax for a ‘standard operating’ RTG is 1120 K. A hypothetical scenario is investigated: an ELHS Ti cl = 1973K-the RPSs’ requirements’ maximum permitted temperature. Fuel melting will not occur.
]]>Thermo doi: 10.3390/thermo1030019
Authors: Leonardo Steyman Reyes Fernández Eliseo Amado-Gonzaléz Erik Germán Yanza Hurtado
Tetrahydrofuran (THF) is an aprotic solvent with multiple applications in diverse areas of chemical, petrochemical, and pharmaceutical industries with an important impact in chemical waste liquid with other solvents. In this work, 51 available VLE data, for isothermal binary mixtures of THF(1) + Benzene(2) and THF(1) + Cyclohexane(2) at 303.15 and 333.15 K, respectively, and isobaric THF(1) + Methanol(2) at 103 kPa and THF(1) + Ethanol(2) at 100 kPa were used in the development of the activity coefficient models. The quality of experimental data was checked using the Herington test. VLE binary data was correlated with models Wilson, NRTL UNIQUAC, and UNIFAC to obtain binary parameters and activity coefficients. The best thermodynamic consistency when conducting the Herington test for the VLE data was found for the THF(1) +Cyclohexane(2) isothermal system and THF(1) + Ethanol(2) isobaric system. The UNIQUAC model for isothermal systems THF(1) + Benzene(2) and THF(1) + Cyclohexane(2), the NRTL model for the isobaric system THF(1) + Methanol(2), and the UNIQUAC model for THF(1) + Ethanol(2) perform better than the other models.
]]>Thermo doi: 10.3390/thermo1020018
Authors: Markus H. A. Piro
A number of codes are used to predict various aspects of nuclear fuel performance and safety, ranging from conventional fuel performance codes to simulate normal operating conditions to integral engineering codes to simulate severe accident behaviour. There has been a number of reportings in the open literature of nuclear fuel codes being informed by thermodynamic calculations, ranging from the use of simple thermodynamic correlations to direct coupling of equilibrium thermodynamic software. Progress in expanding predictive capabilities have been reported, which also includes advances in thermodynamic database development to better capture irradiated fuel. However, this progress has been accompanied by several challenges, including effective coupling of different types of physical phenomena in a practical manner and doing so with a reasonable increase in computational expense. This review paper will summarize previous experiences reported in the open literature in coupling thermodynamic calculations with nuclear fuel codes and applications, identify current challenges and limitations, and offer some perspectives for the community to consider moving forward.
]]>Thermo doi: 10.3390/thermo1020017
Authors: Alexander Aerts
Polonium is formed in relatively large quantities in lead-bismuth eutectic (LBE) cooled nuclear systems. Because of its radiotoxicity and volatility, a good understanding of the chemical equilibria governing polonium release from LBE is required. In this work, a set of thermochemical data is derived for the chemical species involved in the equilibrium between a solution of polonium in LBE and its vapor in inert conditions. The data were obtained by matching thermochemical models with experimental vapor pressure measurements and ab initio results. The dilute-limit activity coefficient of dissolved polonium in LBE is estimated, as well as the solubility of solid lead polonide in LBE. The results indicate that polonium evaporates from LBE according to the experimentally determined Henry’s law, up to dissolved polonium concentrations well above that expected in LBE cooled nuclear systems.
]]>Thermo doi: 10.3390/thermo1020016
Authors: Bianca Schacherl Rachel Eloirdi Rudy J. M. Konings Ondrej Beneš
In the Molten Salt Reactor (MSR) concept, metal fluorides are key components of possible fuel and coolant salts. The fast reactor option opens the possibility for alternatives to the Li based matrix salts, avoiding the costly 7Li enrichment and the tritium production from residual 6Li. Such alternatives can be based on NaF and KF as matrix components. In this study, two pseudo-binary phase diagrams of NaF-UF4 and KF-UF4, and the NaF-KF-UF4 pseudo-ternary system were experimentally investigated using Differential Scanning Calorimetry (DSC). The obtained data were used to perform a full thermodynamic assessment of the NaF-KF-UF4 system. The calculated pseudo-ternary eutectic was found at 807 K and a 68.9-7.6-23.5 mol% NaF-KF-UF4 composition. The comprehensive experimental and modelling data obtained in this work provide further extension of the JRCMSD thermodynamic database describing thermodynamic properties of key fuel and coolant salts for the MSR technology.
]]>Thermo doi: 10.3390/thermo1020015
Authors: Jaroslav Šesták
The development of instrumentation has allowed thermal analysis to become a widely used method not only in calorimetry but also in the field of non-isothermal kinetics that, however, provides a simplified philosophy of measurements. From the beginning, a methodology is used describing the course of reaction in a simplified temperature regime measured in an inert sample. In a most common case of DTA, the degree of reaction is subtracted from the partial areas of the as-cast peak in the unified mode of the peak linear background. Usually, the effect of thermal inertia, resulting from the reality of heat transfer and changing the peak background to a non-linear s-shaped form, is not incorporated. Therefore, the question of whether or not to include this effect of thermal inertia has become a current underlying problem of thermo-analytical kinetics. The analysis of the rectangular input heat pulses and their DTA responding fundamentally point to the need to include it thus becoming essential and not negligible. In the case of parallel evaluations, the effect of inertia can be partially compensated for each other such as in the Kissinger evaluation method. The study presents a broad overview of the thermo-analytical methodology used and points to the often-neglected literature. However, standard mainstream kinetics procedures need be fixed, and an improved solution found to account for the effect of heat transfer and dissipation, which is becoming the focus of thermal analysis methods of future and also the intention of this review.
]]>Thermo doi: 10.3390/thermo1020014
Authors: Thomas Dumaire Rudy J. M. Konings Anna Louise Smith
Understanding the corrosion mechanisms and the effect of corrosion products on the basic properties of the salt (e.g., melting point, heat capacity) is fundamental for the safety assessment and durability of molten salt reactor technology. This work focused on the thermodynamic assessment of the CrF2−CrF3 system and the binary systems of chromium trifluoride CrF3 with alkali fluorides (LiF, NaF, KF) using the CALPHAD (computer coupling of phase diagrams and thermochemistry) method. In this work, the modified quasi-chemical model in the quadruplet approximation was used to develop new thermodynamic modelling assessments of the binary solutions, which are highly relevant in assessing the corrosion process in molten salt reactors. The agreement between these assessments and the phase equilibrium data available in the literature is generally good. The excess properties (mixing enthalpies, entropies and Gibbs energies) calculated in this work are consistent with the expected behaviour of decreasing enthalpy and Gibbs energy of mixing with the increasing ionic radius of the alkali cations.
]]>Thermo doi: 10.3390/thermo1020013
Authors: Marc Barrachin
More than 30 years ago a specialist meeting was held at Joint Research Center Ispra (Italy) from 15 to 17 January 1990 to review the current understanding of chemistry during severe accidents in light water reactors (LWR). Let us consider that, at the end of the 1980s, thermodynamics introduced in the severe accident codes was really poor. Only some equilibrium constants for a few simple reactions between stoichiometric compounds were used as well as some simple correlations giving estimates of solidus and liquidus temperatures. In the same time, the CALPHAD method was developed and was full of promise to approximate the thermodynamic properties of a complex thermochemical system by the way of a critical assessment of experimental data, a definition of a simple physical model and an optimisation procedure to define the values of the model parameters. It was evident that a nuclear thermodynamic database had to be developed with that new technique to obtain quite rapidly prominent progress in the knowledge of thermochemistry in the severe accident research area. Discussions focused on the important chemical phenomena that could occur across the wide range of conditions of a damaged nuclear plant. The most pressing need for improved chemical models is identified with condensed phase mixtures to model the corium progression. This paper reviews more than 30 years of experimental data production in the field of corium thermodynamics. This work has been conducted through multiple international programs (EURATOM, ISTC, OECD) as well as through more specific studies conducted at the national scale. This research has been capitalised in specific databases such as NUCLEA and TAF-ID, databases developed at IRSN and at CEA, respectively, and are now used in degradation models of the severe accident simulation codes. This research is presented in this paper. In the conclusion, we outline the research perspectives that need to be considered in order to address today’s and tomorrow’s issues.
]]>Thermo doi: 10.3390/thermo1020012
Authors: Theodore M. Besmann Juliano Schorne-Pinto
Molten salt reactors (MSRs) utilize salts as coolant or as the fuel and coolant together with fissile isotopes dissolved in the salt. It is necessary to therefore understand the behavior of the salts to effectively design, operate, and regulate such reactors, and thus there is a need for thermodynamic models for the salt systems. Molten salts, however, are difficult to represent as they exhibit short-range order that is dependent on both composition and temperature. A widely useful approach is the modified quasichemical model in the quadruplet approximation that provides for consideration of first- and second-nearest-neighbor coordination and interactions. Its use in the CALPHAD approach to system modeling requires fitting parameters using standard thermodynamic data such as phase equilibria, heat capacity, and others. A shortcoming of the model is its inability to directly vary coordination numbers with composition or temperature. Another issue is the difficulty in fitting model parameters using regression methods without already having very good initial values. The proposed paper will discuss these issues and note some practical methods for the effective generation of useful models.
]]>Thermo doi: 10.3390/thermo1020011
Authors: Hai V. Pham Masaki Kurata Martin Steinbrueck
Since the nuclear accident at Fukushima Daiichi Nuclear Power Station in 2011, a considerable number of studies have been conducted to develop accident tolerant fuel (ATF) claddings for safety enhancement of light water reactors. Among many potential ATF claddings, silicon carbide is one of the most promising candidates with many superior features suitable for nuclear applications. In spite of many potential benefits of SiC cladding, there are some concerns over the oxidation/corrosion resistance of the cladding, especially at extreme temperatures (up to 2000 °C) in severe accidents. However, the study of SiC steam oxidation in conventional test facilities in water vapor atmospheres at temperatures above 1600 °C is very challenging. In recent years, several efforts have been made to modify existing or to develop new advanced test facilities to perform material oxidation tests in steam environments typical of severe accident conditions. In this article, the authors outline the features of SiC oxidation/corrosion at high temperatures, as well as the developments of advanced test facilities in their laboratories, and, finally, give some of the current advances in understanding based on recent data obtained from those advanced test facilities.
]]>Thermo doi: 10.3390/thermo1020010
Authors: Rogelio León Christian Montaleza José Luis Maldonado Marcos Tostado-Véliz Francisco Jurado
The mobility industry has experienced a fast evolution towards electric-based transport in recent years. Recently, hybrid electric vehicles, which combine electric and conventional combustion systems, have become the most popular alternative by far. This is due to longer autonomy and more extended refueling networks in comparison with the recharging points system, which is still quite limited in some countries. This paper aims to conduct a literature review on thermodynamic models of heat engines used in hybrid electric vehicles and their respective configurations for series, parallel and mixed powertrain. It will discuss the most important models of thermal energy in combustion engines such as the Otto, Atkinson and Miller cycles which are widely used in commercial hybrid electric vehicle models. In short, this work aims at serving as an illustrative but descriptive document, which may be valuable for multiple research and academic purposes.
]]>Thermo doi: 10.3390/thermo1020009
Authors: Jaén Ocádiz Flores Bas Rooijakkers Rudy Konings Anna Smith
The ACl-ThCl4 (A = Li, Na, K) systems could be of relevance to the nuclear industry in the near future. A thermodynamic investigation of the three binary systems is presented herein. The excess Gibbs energy of the liquid solutions is described using the quasi-chemical formalism in the quadruplet approximation. The phase diagram optimisations are based on the experimental data available in the literature. The thermodynamic stability of the liquid solutions increases in the order Li < Na < K, in agreement with idealised interactions and structural models.
]]>Thermo doi: 10.3390/thermo1010008
Authors: Miguel Ángel Reyes-Belmonte Alejandra Ambrona-Bermúdez Daniel Calvo-Blázquez
In this work, the flexible operation of an Integrated Solar Combined Cycle (ISCC) power plant has been optimized considering two different energy storage approaches. The objective of this proposal is to meet variable users’ grid demand for an extended period at the lowest cost of electricity. Medium temperature thermal energy storage (TES) and hydrogen generation configurations have been analyzed from a techno-economic point of view. Results found from annual solar plant performance indicate that molten salts storage solution is preferable based on the lower levelized cost of electricity (0.122 USD/kWh compared to 0.158 USD/kWh from the hydrogen generation case) due to the lower conversion efficiencies of hydrogen plant components. However, the hydrogen plant configuration exceeded, in terms of plant availability and grid demand coverage, as fewer design constraints resulted in a total demand coverage of 2155 h per year. It was also found that grid demand curves from industrial countries limit the deployment of medium-temperature TES systems coupled to ISCC power plants, since their typical demand curves are characterized by lower power demand around solar noon when solar radiation is higher. In such scenarios, the Brayton turbine design is constrained by noon grid demand, which limits the solar field and receiver thermal power design.
]]>Thermo doi: 10.3390/thermo1010007
Authors: Tryfon C. Roumpedakis Nikolaos Fostieris Konstantinos Braimakis Evropi Monokrousou Antonios Charalampidis Sotirios Karellas
The present work focuses on the techno-economic assessment and multi-objective genetic algorithm optimization of small-scale (40 kWth input), solar Organic Rankine Cycle (ORC) systems driven by medium-to-high temperature (up to 210 °C) parabolic dish (PDC) and trough (PTC) collectors. The ORCs are designed to maximize their nominal thermal efficiency for several natural hydrocarbon working fluids. The optimization variables are the solar field area and storage tank capacity, with the goal of minimizing the levelized cost of produced electricity (LCoE) and maximizing the annual solar conversion efficiency. The lowest LCOE (0.34 €/kWh) was obtained in Athens for a high solar field area and low storage tank capacity. Meanwhile, the maximum annual solar conversion efficiencies (10.5–11%) were obtained in northern cities (e.g., Brussels) at lower solar field locations. While PTCs and PDCs result in similar efficiencies, the use of PTCs is more cost-effective. Among the working fluids, Cyclopentane and Cyclohexane exhibited the best performance, owing to their high critical temperatures. Notably, the systems could be more profitable at higher system sizes, as indicated by the 6% LCoE decrease of the solar ORC in Athens when the nominal heat input was increased to 80 kWth.
]]>Thermo doi: 10.3390/thermo1010006
Authors: Mengxuan Yan Dongxiao Wang Chun Sing Lai Loi Lei Lai
Microgrids have become increasingly popular in recent years due to technological improvements, growing recognition of their benefits, and diminishing costs. By clustering distributed energy resources, microgrids can effectively integrate renewable energy resources in distribution networks and satisfy end-user demands, thus playing a critical role in transforming the existing power grid to a future smart grid. There are many existing research and review works on microgrids. However, the thermal energy modelling in optimal microgrid management is seldom discussed in the current literature. To address this research gap, this paper presents a detailed review on the thermal energy modelling application on the optimal energy management for microgrids. This review firstly presents microgrid characteristics. Afterwards, the existing thermal energy modeling utilized in microgrids will be discussed, including the application of a combined cooling, heating and power (CCHP) and thermal comfort model to form virtual energy storage systems. Current trial programs of thermal energy modelling for microgrid energy management are analyzed and some challenges and future research directions are discussed at the end. This paper serves as a comprehensive review to the most up-to-date thermal energy modelling applications on microgrid energy management.
]]>Thermo doi: 10.3390/thermo1010005
Authors: Johan Jacquemin
I am honored to take on the role of Editor-in-Chief of Thermo (ISSN 2673-7264) effective from February 2021 [...]
]]>Thermo doi: 10.3390/thermo1010004
Authors: Valentin N. Sapunov Eugene A. Saveljev Mikhail S. Voronov Markus Valtiner Wolfgang Linert
The basic theorem of isokinetic relationships is formulated as “if there exists a linear correlation “structure∼properties” at two temperatures, the point of their intersection will be a common point for the same correlation at other temperatures, until the Arrhenius law is violated”. The theorem is valid in various regions of thermally activated processes, in which only one parameter changes. A detailed examination of the consequences of this theorem showed that it is easy to formulate a number of empirical regularities known as the “kinetic compensation effect”, the well-known formula of the Meyer–Neldel rule, or the so-called concept of “multi-excitation entropy”. In a series of similar processes, we examined the effect of different variable parameters of the process on the free energy of activation, and we discuss possible applications.
]]>Thermo doi: 10.3390/thermo1010003
Authors: Juan A. Conesa
Research abounds in the literature on kinetic analyses using thermogravimetric (TG) runs. Many of these studies use approximations of integral or derivative forms of the kinetic law and all of them use programmed temperatures. In the present work, a numerical integration procedure was discussed and applied to different examples. We focused on materials presenting a single decomposition curve as well as other materials with more complex processes. Different examples were explored, and the methodology was applied to a number of wastes such as coffee husks, polystyrene and polyethylene. In all cases, the actual temperature measured by thermocouples close to the sample is used, and several runs are fitted using the same kinetic parameters, giving robustness to the results.
]]>Thermo doi: 10.3390/thermo1010002
Authors: Sumit Charaya Joseph W. Bozzelli
Structures, thermochemical properties, bond energies, and internal rotation potentials of acetic acid hydrazide (CH3CONHNH2), acetamide (CH3CONH2), and N-methyl acetamide (CH3CONHCH3), and their radicals corresponding to the loss of hydrogen atom, have been studied. Gas-phase standard enthalpies of formation and bond energies were calculated using the DFT methods B3LYP/6-31G(d,p), B3LYP/6-31G(2d,2p) and the composite CBS-QB3 methods employing a series of work reactions further to improve the accuracy of the ΔHf°(298 K). Molecular structures, vibration frequencies, and internal rotor potentials were calculated at the DFT level. The parent molecules’ standard formation enthalpies of CH3–C=ONHNH2, CH3–C=ONH2, and CH3–C=ONHCH3 were evaluated as −27.08, −57.40, and −56.48 kcal mol−1, respectively, from the CBS–QB3 calculations. Structures, internal rotor potentials, and C–H and N–H bond dissociation energies are reported. The DFT and the CBS-QB3 enthalpy values show close agreement, and this accord is attributed to the use of isodesmic work reactions for the analysis. The agreement also suggests this combination of the B3LYP/work reaction approach is acceptable for larger molecules. Internal rotor potentials for the amides are high, ranging from 16 to 22 kcal mol−1.
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