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Advances in Heat Transfer Enhancement

A topical collection in Energies (ISSN 1996-1073). This collection belongs to the section "J1: Heat and Mass Transfer".

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Editors

Dipartimento di Ingegneria, Università degli Studi della Campania “Luigi Vanvitelli”, Via Roma 29, 81031 Aversa (CE), Italy
Interests: heat transfer; thermal systems, energy saving, nanofluids, PCMs, active solar systems, passive solar systems, heat conduction in solids irradiated by moving heat sources, natural and mixed convection in material processing and in thermal control of electronic equipments, forecast of energy consumption
Department of Engineering, "Luigi Vanvitelli" University of Campania, Aversa, province of Caserta, Italy
Interests: computational fluid dynamics; entropy generation; convective heat transfer; heat transfer by nanofluids; thermal storage; heat transfer in porous media; heat transfer in microchannels

Topical Collection Information

Dear Colleagues,

The importance of improving heat transfer performance is well known in the fields of industry and research. Techniques for improving heat exchange can be divided as passive or active methods. The passive methods do not require external power sources, such as special geometries, treated surfaces, extended surface (fins), rough surfaces, additives for fluid, and so on, whereas the active methods require an external power source (electrical/mechanical) to realize the advanced heat transfer mechanism, such as the stirring of the ferrofluid with an electromagnetic field, vibrating surface. New techniques to improve heat transfer have recently appeared in engineering research, as the insert of nanoparticles or porous medium, with high thermal conductivity, in working fluids to increase their effectivity thermal conductivity and convective heat transfer coefficients. In recent years, many research activities on heat transfer have been addressed to microflow due to its new applications of microfluidic systems and components, such as biochemical cell reaction, micro electric chip cooling, channels, nozzles, diffusers, pumps, mixers, heat pipes, sensors, transducers, and actuators.

The scope of this Special Issue is to examine original research papers as well as review articles on the most recent developments and research efforts on this subject.

Prof. Dr. Sergio Nardini
Dr. Bernardo Buonomo
Guest Editors

Manuscript Submission Information

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Keywords

  • heat transfer
  • heat transfer enhancement techniques
  • active technique
  • passive technique
  • heat transfer in porous media
  • nanofluids
  • microchannel
  • convection heat transfer
  • entropy generation minimization

Published Papers (46 papers)

2024

Jump to: 2023, 2022, 2021, 2020, 2019

17 pages, 4530 KiB  
Article
Research on the Temperature Distribution in Electrically Heated Offshore Heavy Oil Wellbores
by Suogui Shang, Kechao Gao, Xinghua Zhang, Qibin Zhao, Guangfeng Chen, Liang Tao, Bin Song, Hongxing Yuan and Yonghai Gao
Energies 2024, 17(5), 995; https://doi.org/10.3390/en17050995 - 20 Feb 2024
Viewed by 315
Abstract
The electric heating process for lifting heavy oil has been widely applied. However, research on its temperature field laws mostly focuses on onshore heavy oil wells, while research offshore is limited. Therefore, based on the energy conservation equation and heat transfer theory, a [...] Read more.
The electric heating process for lifting heavy oil has been widely applied. However, research on its temperature field laws mostly focuses on onshore heavy oil wells, while research offshore is limited. Therefore, based on the energy conservation equation and heat transfer theory, a transient one-dimensional wellbore temperature model coupled with the temperature and viscosity of heavy oil and considering the effect of time was developed. In order to verify the accuracy of the model, the results of the previous model were used for comparison with the present model, and the results showed that the model has good accuracy. The results show that a reasonable selection of the process parameters of electric heating can increase the production of heavy oil while saving development costs and improving the economic benefits of the oilfield. The conclusions and recommendations of this paper can provide a theoretical basis and guiding suggestions for the optimal design of process parameters for lifting heavy oil using an offshore electric heating process. Full article
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2023

Jump to: 2024, 2022, 2021, 2020, 2019

16 pages, 5542 KiB  
Article
Hydrothermal Conversion of Microalgae Slurry in a Continuous Solar Collector with Static Mixer for Heat Transfer Enhancement
by Hao Chen, Fangfang Lou, Xueyi Zhang, Chengjun Shen, Weicheng Pan and Shuang Wang
Energies 2023, 16(24), 7986; https://doi.org/10.3390/en16247986 - 09 Dec 2023
Cited by 1 | Viewed by 569
Abstract
The continuous solar collector is a promising heater and reactor for the hydrothermal liquefaction (HTL) of microalgae biomass. To enhance the heat transfer and hydrothermal conversion of microalgae slurry in solar-driven reactors, a static mixer is inserted in the flow channel of the [...] Read more.
The continuous solar collector is a promising heater and reactor for the hydrothermal liquefaction (HTL) of microalgae biomass. To enhance the heat transfer and hydrothermal conversion of microalgae slurry in solar-driven reactors, a static mixer is inserted in the flow channel of the solar collector. A numerical model combining CFD and HTL reactions of microalgae biomass is proposed. Six composition equations of protein, carbohydrates, lipids, biocrude, aqueous phase and biogas were proposed, while corresponding HTL kinetics were utilized to simulate the conversion rate of the reactants and products. The effects of the twist ratio of the static mixer (3–10), flow rate (30–80 L/h) and solar intensity (650, 750, 850 W/m2) on the flow resistance, heat transfer and organics formation of microalgae slurry were investigated. The swirl flow caused by the static mixer with a twist ratio of three increased the convective heat transfer coefficient (97 W·m−2·K−1) by 2.06 times, while the production rate of biocrude (0.074 g·L−1·s−1) increased by 2.05 times at 50 L/h and 750 W/m2. This investigation gives guidance for utilizing static mixers in solar-driven reactors to optimize the heat transfer and HTL of microalgae biomass with solar heat sources. Full article
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45 pages, 45870 KiB  
Article
A Comparative Study on Numerical Flow Simulations of a Centrifugal Electronic Cooling Fan Using Four Different Turbulence Models
by Martin Kirchhofer, Michael Krieger and Dominik Hofer
Energies 2023, 16(23), 7864; https://doi.org/10.3390/en16237864 - 30 Nov 2023
Viewed by 793
Abstract
In this study the flow field of a centrifugal electronic cooling fan operating at an off-design point of 0 Pa static fan pressure is investigated by means of Computational Fluid Dynamics. The results obtained by four different turbulence models, the realizable k- [...] Read more.
In this study the flow field of a centrifugal electronic cooling fan operating at an off-design point of 0 Pa static fan pressure is investigated by means of Computational Fluid Dynamics. The results obtained by four different turbulence models, the realizable k-ϵ model, the SST k-ω model, a Reynolds Stress Model, and Scale-Adaptive Simulation are analyzed and compared. The focus lies on describing how the flow through impeller and volute influences the fan outlet flow field, and velocity profiles and velocity fluctuations at the outlet are compared to previously published measurements. All models tend to underpredict the measured outlet flow rate, but are capable of producing the characteristic C-shaped profile of high velocities, previously determined in Constant Temperature Anemometry measurements. However, the realizable k-ϵ model is significantly too diffusive, leading to blurred velocity contours. The other models exhibit reasonable agreement with the measured flow field, but show differences in a number of aspects. The SST k-ω model, for instance, even produces local inflow in a confined area. The SAS approach overpredicts the length of the lower lobe of the C-shape. The research is relevant to improve simulation results of impingement cooling and heat sink optimization using centrifugal fans. Full article
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13 pages, 5385 KiB  
Article
Prediction and Measurement of the Heat Transfer Coefficient in Direct, Oil-Cooled Batteries
by Robert Camilleri and Nolan Meignen-Viaud
Energies 2023, 16(23), 7725; https://doi.org/10.3390/en16237725 - 23 Nov 2023
Viewed by 1000
Abstract
This paper presents an experimental measurement of the heat transfer coefficient (HTC) in a direct, oil-cooled lithium-ion battery at low Reynolds numbers. As demands on the electric vehicle battery pack increase, the role of thermal management to safeguard the pack becomes more important. [...] Read more.
This paper presents an experimental measurement of the heat transfer coefficient (HTC) in a direct, oil-cooled lithium-ion battery at low Reynolds numbers. As demands on the electric vehicle battery pack increase, the role of thermal management to safeguard the pack becomes more important. Therefore, it is expected that various means for enhancing the HTC are sought. One way to increase the HTC is by shifting from air cooling to liquid cooling. The application of direct oil cooling in batteries has not yet been implemented. This paper explores this by developing the concept and an experimental steady-state technique to measure the HTC for direct oil cooling on a cylindrical 18650-cell battery at low Reynolds numbers. The experimental measurements are validated against known empirical correlations in the literature, showing that, despite the complex arrangement of cylindrical battery cells in packs, the classical correlations can be a useful tool to develop an oil-cooled battery thermal management system. A simplified correlation was also developed. Full article
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13 pages, 2078 KiB  
Article
Experimental Investigation of Temperature Distribution in a Laminar Boundary Layer over a Heated Flat Plate with Localized Transverse Cold Air Injections
by Muhammad Ehtisham Siddiqui, Ammar A. Melaibari and Fahad Sarfraz Butt
Energies 2023, 16(17), 6171; https://doi.org/10.3390/en16176171 - 25 Aug 2023
Viewed by 793
Abstract
This study presents an experimental investigation focused on the interaction between a transverse injection of cold air (blowing) and the boundary layer over a heated flat plate. The flat plate was equipped with a cylindrical coil heater positioned at its center along the [...] Read more.
This study presents an experimental investigation focused on the interaction between a transverse injection of cold air (blowing) and the boundary layer over a heated flat plate. The flat plate was equipped with a cylindrical coil heater positioned at its center along the flow direction. The constant heat flux was maintained using a variable resistance potentiometer. The flat plate with the heater was mounted inside a subsonic wind tunnel to sustain a constant laminar air flow. The primary objective of this research was to examine the effects of cold air injections through localized holes in the flat plate near the trailing edge on the thermal boundary layer thickness δt(x,Rex,Pr). The thermal boundary layer thickness was measured using K-type thermocouples and PT-100 RTD sensors, which are made to move precise, small distances using a specially constructed traversing mechanism. Cold air was injected using purposefully fabricated metal capillary tubes force-fitted into holes through the hot flat plate. The metal tubes were thermally insulated using class-F insulation, which is used in electric motor windings. The presented work focused on a fixed free-stream velocity and a fixed cold-injection velocity less than the free-stream velocity but for two-variable heat fluxes. The results show that the thermal boundary layer thickness generally increased due to the secondary cold flow. Full article
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9 pages, 1772 KiB  
Technical Note
Negative Impact of Thermal Loads on Pressure and Non-Pressure Boiler Parts
by Piotr Duda and Łukasz Felkowski
Energies 2023, 16(15), 5768; https://doi.org/10.3390/en16155768 - 02 Aug 2023
Cited by 1 | Viewed by 687
Abstract
Issues related to the proper design of power boiler elements taking account of thermal loads are still relevant in this era of increasing variability of the boiler power output over time. The aim of this work is to present a thermal and strength [...] Read more.
Issues related to the proper design of power boiler elements taking account of thermal loads are still relevant in this era of increasing variability of the boiler power output over time. The aim of this work is to present a thermal and strength analysis for a section of the membrane wall of a steam boiler, designed and manufactured in compliance with international standards, and approved for operation by a pressure equipment supervisory authority. Although the procedures were followed as required, the boiler membrane wall became cyclically damaged. The cause of such periodic damage to the boiler can be explained based on the conducted analyses. Full article
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14 pages, 1756 KiB  
Article
Selection of Organic Fluid Based on Exergetic Performance of Subcritical Organic Rankine Cycle (ORC) for Warm Regions
by Muhammad Ehtisham Siddiqui, Eydhah Almatrafi, Usman Saeed and Aqeel Ahmad Taimoor
Energies 2023, 16(13), 5149; https://doi.org/10.3390/en16135149 - 04 Jul 2023
Cited by 1 | Viewed by 797
Abstract
The organic Rankine cycle (ORC) exhibits considerable promise in efficiently utilizing low-to-medium-grade heat. Currently, there is a range of organic fluids available in the market, and selecting the appropriate one for a specific application involves considering factors such as the cycle’s thermodynamic performance, [...] Read more.
The organic Rankine cycle (ORC) exhibits considerable promise in efficiently utilizing low-to-medium-grade heat. Currently, there is a range of organic fluids available in the market, and selecting the appropriate one for a specific application involves considering factors such as the cycle’s thermodynamic performance, plant size, and compatibility with turbomachinery. The objective of our study is to examine the exergetic performance of the ORC with internal heat regeneration. We analyze 12 different organic fluids to evaluate their suitability based on parameters like exergy efficiency and heat exchange area requirements. Additionally, we investigate the need for internal heat regeneration by comparing the overall exergy performance with a simpler ORC configuration. To ensure broad applicability, we consider source temperatures ranging from 150 to 300 °C, which are relevant to industrial waste heat, geothermal sources, and solar energy. For each case, we calculate specific net power output and the UA value (heat exchanger conductance) to gain insights into selecting the appropriate organic fluid for specific source temperatures. Cyclohexane, benzene, isopropyl alcohol, and hexafluorobenzene show poor exergy efficiency due to their high boiling points. Pentane and cyclopentane provides the highest exergy efficiency of 62.2% at source temperature of 300 °C, whereas pentane is found to be the most suitable at source temperatures of 200 and 150 °C with exergy efficiency of 67.7% and 61.7%, respectively. At 200 °C source temperature, RE347mcc achieves 65.9% exergy efficiency. The choice of organic fluid for a given heat source is highly influenced by its critical properties. Moreover, the normal boiling temperature of the organic fluid significantly impacts exergy destruction during the condensation process within the cycle. Full article
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21 pages, 1998 KiB  
Review
Heat Transfer Coefficient Distribution—A Review of Calculation Methods
by Piotr Duda
Energies 2023, 16(9), 3683; https://doi.org/10.3390/en16093683 - 25 Apr 2023
Cited by 4 | Viewed by 2096
Abstract
Determination of the heat transfer coefficient (HTC) distribution is important during the design and operation of many devices in microelectronics, construction, the car industry, drilling, the power industry and research on nuclear fusion. The first part of the manuscript shows works describing how [...] Read more.
Determination of the heat transfer coefficient (HTC) distribution is important during the design and operation of many devices in microelectronics, construction, the car industry, drilling, the power industry and research on nuclear fusion. The first part of the manuscript shows works describing how a change in the coefficient affects the operation of devices. Next, various methods of determining the coefficient are presented. The most common method to determine the HTC is the use of Newton’s law of cooling. If this method cannot be applied directly, there are other methods that can be found in the open literature. They use analytical formulations, the lumped thermal capacity assumption, the 1D unsteady heat conduction equation for a semi-infinite wall, the fin model, energy conservation and the analogy between heat and mass transfer. The HTC distribution can also be calculated by means of computational fluid dynamics (CFD) modelling if all boundary conditions with fluid and solid properties are known. Often, the surface on which the HTC is to be determined is not accessible for any measuring sensors, or their installation might disturb the analysed phenomenon. It also happens that calculations using direct or CFD methods cannot be performed due to the lack of required boundary conditions or sufficiently proven models to analyse the considered physical phenomena. Too long a calculation time needed by CFD tools may also be problematic if the method should be used in the online mode. One way to solve the above problem is to assume an unknown boundary condition and include additional information from the sensors located at a certain distance from the investigated surface. The problem defined in this way can be solved by inverse methods. The aim of the paper is to show the current state of knowledge regarding the importance of the heat transfer coefficient and the variety of methods that can be used for its determination. Full article
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18 pages, 4154 KiB  
Article
Dynamic Simulations on Enhanced Heat Recovery Using Heat Exchange PCM Fluid for Solar Collector
by Yawen Ren and Hironao Ogura
Energies 2023, 16(7), 3075; https://doi.org/10.3390/en16073075 - 28 Mar 2023
Viewed by 1183
Abstract
Facing the goal of carbon neutrality, energy supply chains should be more low-carbon and flexible. A solar chemical heat pump (SCHP) is a potential system for achieving this goal. Our previous studies developed a silicone-oil-based phase-change material (PCM) mixture as a PCM fluid [...] Read more.
Facing the goal of carbon neutrality, energy supply chains should be more low-carbon and flexible. A solar chemical heat pump (SCHP) is a potential system for achieving this goal. Our previous studies developed a silicone-oil-based phase-change material (PCM) mixture as a PCM fluid for enhancing heat recovery above 373 K in the solar collector (SC) of the SCHP. The PCM fluid was previously tested to confirm its dispersity and flow properties. The present study proposed a 3D computational fluid dynamics model to simulate the closed circulation loop between the SC and reactor using the PCM fluid. The recovered heat in the SC was studied using several flow rates, as well as the PCM weight fraction of the PCM fluid. Furthermore, the net transportable energy is considered to evaluate the ratio of recovered heat and relative circulation power. As a result, it was verified that the recovered heat of the SC in the experiment and simulation is consistent. The total recovered heat is improved using the PCM fluid. A lower flow rate can enhance the PCM melting mass and the recovered heat although sensible heat amount increases with the flow rate. The best flow rate was 1 L/min when the SC area is 1 m2. Furthermore, the higher PCM content has higher latent heat. On the other hand, the lower content PCM can increase the temperature difference between the SC inlet and outlet because of the lower PCM heat capacity. For the 1 L/min flow rate, 2 wt% PCM fluid has shorter heat-storing time and larger net transportable energy than 0 wt% PCM fluid (426 kJ←403 kJ) for the SCHP unit. Full article
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32 pages, 33541 KiB  
Review
Experimental/Numerical Investigation and Prediction of Fouling in Multiphase Flow Heat Exchangers: A Review
by Rached Ben-Mansour, Sami El-Ferik, Mustafa Al-Naser, Bilal A. Qureshi, Mohammed Ahmed Mohammed Eltoum, Ahmed Abuelyamen, Fouad Al-Sunni and Ridha Ben Mansour
Energies 2023, 16(6), 2812; https://doi.org/10.3390/en16062812 - 17 Mar 2023
Cited by 2 | Viewed by 1904
Abstract
Fouling build-up is one of the most challenging problems for heat exchangers in industry. The presence of fouling leads to a degradation of system efficiency, an increase in operating cost, and possibly, a harmful environmental impact. For this reason, fouling analysis has become [...] Read more.
Fouling build-up is one of the most challenging problems for heat exchangers in industry. The presence of fouling leads to a degradation of system efficiency, an increase in operating cost, and possibly, a harmful environmental impact. For this reason, fouling analysis has become an extremely important research subject in order to have a safe and efficient operation. The analysis is more difficult where phase change of fluids is involved during the heat transfer process, as in the case of boilers and condensers, which are critical units in industrial facilities. Due to the lack of a comprehensive review of fouling analysis for the case of multiphase heat exchangers, this paper examines available approaches and techniques used for fouling characterization, modeling, monitoring, and prediction in heat exchangers for both single-phase and multiphase heat exchangers with a focus on fouling in thermal desalination systems. It also gives an overview of heat exchanger condition monitoring solutions available in the market. Full article
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22 pages, 6315 KiB  
Article
An Adaptive Matrix Method for the Solution of a Nonlinear Inverse Heat Transfer Problem and Its Experimental Verification
by Piotr Duda and Mariusz Konieczny
Energies 2023, 16(6), 2649; https://doi.org/10.3390/en16062649 - 11 Mar 2023
Viewed by 819
Abstract
An adaptive matrix inverse (AMI) method is presented to identify the temperature and unknown boundary heat flux in a domain of a regular or irregular shape with temperature-dependent properties. The nonlinear problem is broken down into a number of linear submodels, and for [...] Read more.
An adaptive matrix inverse (AMI) method is presented to identify the temperature and unknown boundary heat flux in a domain of a regular or irregular shape with temperature-dependent properties. The nonlinear problem is broken down into a number of linear submodels, and for each submodel, the temperature is obtained in measuring points. Next, based on the matching degree between the temperatures measured and calculated by each prediction submodel, the submodels are weighted and combined to create the full model for the solution of an inverse nonlinear heat transfer problem. Comparisons are also made with the existing multiple model adaptive inverse (MMAI) algorithm and method based on the Levenberg–Marquardt algorithm (LMA). The results of the presented numerical tests for undisturbed and disturbed “measuring” data indicate that the heat fluxes identified by the AMI method are close to the exact values. The application of the presented method for bodies with an irregular shape is also demonstrated. The AMI method has been experimentally verified during the thick-walled cylinder cooling process. The proposed method can be applied in online diagnostic systems for thermal state monitoring. Full article
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2022

Jump to: 2024, 2023, 2021, 2020, 2019

14 pages, 2480 KiB  
Article
Study of the Combustion Process for Two Refuse-Derived Fuel (RDF) Streams Using Statistical Methods and Heat Recovery Simulation
by Piotr Brożek, Ewelina Złoczowska, Marek Staude, Karolina Baszak, Mariusz Sosnowski and Katarzyna Bryll
Energies 2022, 15(24), 9560; https://doi.org/10.3390/en15249560 - 16 Dec 2022
Cited by 4 | Viewed by 1622
Abstract
This study characterises materials that belong to the group of refuse-derived fuels (RDF). This group of materials regarded as an alternative fuel is derived from industrial, municipal solid and commercial wastes. The aim of this study is to evaluate the quality of waste [...] Read more.
This study characterises materials that belong to the group of refuse-derived fuels (RDF). This group of materials regarded as an alternative fuel is derived from industrial, municipal solid and commercial wastes. The aim of this study is to evaluate the quality of waste composition, demonstrate statistically different values and the energy efficiency of the fuel derived from waste. Data on incinerated waste were collected from two different sources. The basic physical and chemical parameters of waste include density and water content. The lower heating value (LHV) of waste, chlorine concentration and ash content of two groups of incinerated waste were also evaluated and compared for a given period of time (one year, with monthly breakdown). Statistical analysis indicated the differences in the combustion of waste groups, visualized by box plots and other diagrams to show the distribution of the results. An analysis of exhaust gas parameters was carried out, both in terms of chemical composition and energy parameters. The RDF combustion process was presented through simulations for the adopted conditions of heat recovery. It was found that for each kilogram of RDF, about 3.85 kWh (13,860 kJ) of heat can be obtained. The combustion process was simulated using Aspen Plus software. Full article
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21 pages, 3647 KiB  
Review
Compact Thermal Storage with Phase Change Material for Low-Temperature Waste Heat Recovery—Advances and Perspectives
by Daniela Dzhonova-Atanasova, Aleksandar Georgiev, Svetoslav Nakov, Stela Panyovska, Tatyana Petrova and Subarna Maiti
Energies 2022, 15(21), 8269; https://doi.org/10.3390/en15218269 - 05 Nov 2022
Cited by 4 | Viewed by 2042
Abstract
The current interest in thermal energy storage is connected with increasing the efficiency of conventional fuel-dependent systems by storing the waste heat in low consumption periods, as well as with harvesting renewable energy sources with intermittent character. Many of the studies are directed [...] Read more.
The current interest in thermal energy storage is connected with increasing the efficiency of conventional fuel-dependent systems by storing the waste heat in low consumption periods, as well as with harvesting renewable energy sources with intermittent character. Many of the studies are directed towards compact solutions requiring less space than the commonly used hot water tanks. This is especially important for small capacity thermal systems in buildings, in family houses or small communities. There are many examples of thermal energy storage (TES) in the literature using the latent heat of phase change, but only a few are commercially available. There are no distinct generally accepted requirements for such TES systems. The present work fills that gap on the basis of the state of the art in the field. It reviews the most prospective designs among the available compact latent heat storage (LHS) systems in residential applications for hot water, heating and cooling and the methods for their investigation and optimization. It indicates the important characteristics of the most cost- and energy-efficient compact design of an LHS for waste heat utilization. The proper design provides the chosen targets at a reasonable cost, with a high heat transfer rate and effective insulation. It allows connection to multiple heat sources, coupling with a heat pump and integration into existing technologies and expected future scenarios for residential heating and cooling. Compact shell-tube type is distinguished for its advantages and commercial application. Full article
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25 pages, 13771 KiB  
Review
Review of the State-of-the-Art Uses of Minimal Surfaces in Heat Transfer
by Krzysztof Dutkowski, Marcin Kruzel and Krzysztof Rokosz
Energies 2022, 15(21), 7994; https://doi.org/10.3390/en15217994 - 27 Oct 2022
Cited by 8 | Viewed by 3917
Abstract
The design of heat exchangers may change dramatically through the use of additive manufacturing (AM). Additive manufacturing, colloquially known as 3D printing, enables the production of monolithic metal bodies, devoid of contact resistance. The small volume of the exchanger, its lightness of weight, [...] Read more.
The design of heat exchangers may change dramatically through the use of additive manufacturing (AM). Additive manufacturing, colloquially known as 3D printing, enables the production of monolithic metal bodies, devoid of contact resistance. The small volume of the exchanger, its lightness of weight, and the reduction of its production costs, compared to conventional methods, make the production of heat exchangers by AM methods conventional technologies. The review study presents a new look at the TPMS as a promising type of developed surface that can be used in the area of heat transfer. (Thus far, the only attractive option. The most important feature of additive manufacturing is the ability to print the geometry of theoretically any topography. Such a topography can be a minimal surface or its extended version—triply periodic minimal surface (TPMS). It was practically impossible to manufacture a TPMS-based heat exchanger with the method of producing a TPMS.) The issues related to the methods of additive manufacturing of metal products and the cycle of object preparation for printing were discussed, and the available publications presenting the results of CFD simulations and experimental tests of heat exchangers containing a TPMS in their construction were widely discussed. It has been noticed that the study of thermal-flow heat transfer with the use of TPMSs is a new area of research, and the number of publications in this field is very limited. The few data (mainly CFD simulations) show that the use of TPMSs causes, on the one hand, a several-fold increase in the number of Nu, and on the other hand, an increase in flow resistance. The use of TPMSs in heat exchangers can reduce their size by 60%. It is concluded that research should be carried out in order to optimize the size of the TPMS structure and its porosity so that the gains from the improved heat transfer compensate for the energy expenditure on the transport of the working fluid. It has been noticed that among the numerous types of TPMSs available for the construction of heat exchangers, practically, four types have been used thus far: primitive, gyroid, I-WP, and diamond. At the moment, the diamond structure seems to be the most promising in terms of its use in the construction of heat exchangers and heat sinks. It is required to conduct experimental research to verify the results of the CFD simulation. Full article
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11 pages, 1738 KiB  
Article
Complex Heat Exchange in Friction Steam of Brakes
by Ivan Kernytskyy, Aleksandr Volchenko, Olga Szlachetka, Orest Horbay, Vasyl Skrypnyk, Dmytro Zhuravlev, Vasyl Bolonnyi, Volodymyr Yankiv, Ruslan Humenuyk, Pavlo Polyansky, Aleksandra Leśniewska, Dariusz Walasek and Eugeniusz Koda
Energies 2022, 15(19), 7412; https://doi.org/10.3390/en15197412 - 09 Oct 2022
Cited by 2 | Viewed by 1260
Abstract
In this article the structural features of friction pairs of brakes are analyzed. Heat transfer processes with new boundary conditions are described analytically with the addition of flow conditions and the appearance of a boundary thermal layer to convective heat transfer. The joint [...] Read more.
In this article the structural features of friction pairs of brakes are analyzed. Heat transfer processes with new boundary conditions are described analytically with the addition of flow conditions and the appearance of a boundary thermal layer to convective heat transfer. The joint action of heat conduction and convection fields is presented. The release of heat during friction is due to the destruction of adhesive bonds in the actual contact zones, and the stress–strain state of micro-roughnesses. It should be said that due to the presence of accompanying transfer processes, complex heat transfer is much more complex compared to purely conductive, convective, and radiative heat transfer, which significantly complicates its analytical and experimental study. In this regard, the processes of complex heat transfer are currently studied little. From the point of view of non-equilibrium thermodynamics, the main task of describing the transfer process is to establish a relationship between the magnitude of the specific flux and the surface-volume temperatures that it causes in the metallic friction elements of the brakes. Additionally, as a result, an assessment of conductive and convective heat transfer in friction pairs of brake devices was made. Full article
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36 pages, 17520 KiB  
Article
Thermodynamic Optimization of Advanced Organic Rankine Cycle Configurations for Geothermal Energy Applications
by Nenad Mustapić, Vladislav Brkić, Željko Duić and Toni Kralj
Energies 2022, 15(19), 6990; https://doi.org/10.3390/en15196990 - 23 Sep 2022
Cited by 3 | Viewed by 1770
Abstract
The Organic Rankine Cycle (ORC) is commonly accepted as a viable technology to convert from low to medium temperature geothermal energy into electrical energy. In practice, the reference technology for converting geothermal energy to electricity is the subcritical simple ORC system. Over time, [...] Read more.
The Organic Rankine Cycle (ORC) is commonly accepted as a viable technology to convert from low to medium temperature geothermal energy into electrical energy. In practice, the reference technology for converting geothermal energy to electricity is the subcritical simple ORC system. Over time, geothermal ORC plants with more complex configurations (architectures) have been developed. In the open literature, a large number of advanced architectures or configurations have been introduced. An analysis of the scientific literature indicates that there is some confusion regarding the terminology of certain advanced ORC system architectures. A new categorization of advanced configurations has been proposed, with a special emphasis on the application of geothermal energy. The basic division of advanced plant configurations is into dual-pressure and dual-stage ORC systems. In this study, the real potential of advanced ORC architectures or configurations to improve performance as compared with the simple ORC configuration was explored. The research was conducted for a wide range of geothermal heat source temperatures (from 120 °C to 180 °C) and working fluids. Net power output improvements as compared with the basic subcritical simple ORC (SORC) configuration were examined. The ability to produce net power with different ORC configurations depends on the magnitude of the geothermal fluid temperature and the type of working fluid. At a lower value of geothermal fluid temperature (120 °C), the most net power of 18.71 (kW/(kg/s)) was realized by the dual-pressure ORC (DP ORC configuration) with working fluid R1234yf, while the double stage serial-parallel ORC configuration with a low-temperature preheater in a high-temperature stage ORC (DS parHTS LTPH ORC) generated 18.51 (kW/(kg/s)) with the working fluid combination R1234yf/R1234yf. At 140 °C, three ORC configurations achieved similar net power values, namely the simple ORC configuration (SORC), the DP ORC configuration, and the DS parHTS LTPH ORC configuration, which generated 31.03 (kW/(kg/s)) with R1234yf, 31.07 (kW/(kg/s)) with R1234ze(E), and 30.96 (kW/(kg/s)) with R1234ze(E)/R1234yf, respectively. At higher values of geothermal fluid temperatures (160 °C and 180 °C) both the SORC and DP ORC configurations produced the highest net power values, namely 48.58 (kW/(kg/s)) with R1234ze(E), 67.23 (kW/(kg/s)) with isobutene for the SORC configuration, and 50.0 (kW/(kg/s)) with isobutane and 69.67 (kW/(kg/s)) with n-butane for the the DP ORC configuration. Full article
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13 pages, 1605 KiB  
Article
The Effect of Heat Source on Cost of Preparation of Household Food Packaging Waste for Recycling
by Andrzej Marcinkowski and Paweł Haręża
Energies 2022, 15(16), 5894; https://doi.org/10.3390/en15165894 - 14 Aug 2022
Viewed by 1171
Abstract
The study concerns the preparation of post-consumer food packaging for selective collection that takes place in households. The previously reported results suggested that the economic cost of washing the packaging exceeded the value of recyclable materials. A shortage of up-to-date papers on the [...] Read more.
The study concerns the preparation of post-consumer food packaging for selective collection that takes place in households. The previously reported results suggested that the economic cost of washing the packaging exceeded the value of recyclable materials. A shortage of up-to-date papers on the economic balance of packaging washing, taking into account current trends in the increase of prices of materials and energy carriers, has been identified. The main objective of this study was to determine the effect of the application of particular heat sources on the total cost of preparing the glass and plastic packaging for selective collection, as well as to compare the cost with the economic value of recyclables. Over the last ten years, a drop in the purchase price of glass cullet and post-consumer plastic, as well as an increase in the cost of cold and hot water, have been reported. Accordingly, the profit of packaging cleaning, defined as the difference between the value of recyclable materials and the cost of washing them, has decreased. The energy consumed for water heating was identified as the most relevant factor affecting the entire economic balance. Even assuming the most efficient water heating solutions, the pre-treatment of the post-consumer food packaging turned out to be unprofitable. The conclusion reached in the previously published study has been confirmed. Full article
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15 pages, 3170 KiB  
Article
Multi-Objective Constructal Design for Square Heat-Generation Body with “Arrow-Shaped” High-Thermal-Conductivity Channel
by Hongwei Zhu, Lingen Chen, Yanlin Ge, Shuangshuang Shi and Huijun Feng
Energies 2022, 15(14), 5235; https://doi.org/10.3390/en15145235 - 19 Jul 2022
Cited by 10 | Viewed by 1113
Abstract
Based on the square heat-generation body (HGB) with “arrow-shaped” high-thermal-conductivity channel (HTCC) model established in the previous literature, we performed multi-objective optimization (MOO) with maximum temperature difference (MTD) minimization and entropy-generation rate (EGR) minimization as optimization objectives for its performance. Pareto frontiers with [...] Read more.
Based on the square heat-generation body (HGB) with “arrow-shaped” high-thermal-conductivity channel (HTCC) model established in the previous literature, we performed multi-objective optimization (MOO) with maximum temperature difference (MTD) minimization and entropy-generation rate (EGR) minimization as optimization objectives for its performance. Pareto frontiers with optimal set were obtained based on NSGA-II. TOPSIS, LINMAP, and Shannon entropy decision methods were used to select the optimal results in Pareto frontiers, and the deviation index was used to compare and analyze advantages and disadvantages of the optimal results for each decision method. At the same time, multi-objective constructal designs of the “arrow-shaped” HTCC were carried out through optimization of single degree of freedom (DOF), two DOF, and three DOF, respectively, and the thermal performance of the square heat-generation body under optimizations of different DOF were compared. The results show that constructal design with the MOO method can achieve the best compromise between the maximum thermal resistance and the irreversible loss of heat transfer of the square heat-generation body, thereby improving the comprehensive thermal performance of the square heat-generation body. The MOO results vary with different DOF, and optimization with increasing DOF can further improve the comprehensive thermal performance of square HGBs. Full article
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24 pages, 6114 KiB  
Article
Modelling, Analysis and Entropy Generation Minimization of Al2O3-Ethylene Glycol Nanofluid Convective Flow inside a Tube
by Sayantan Mukherjee, Nawaf F. Aljuwayhel, Sasmita Bal, Purna Chandra Mishra and Naser Ali
Energies 2022, 15(9), 3073; https://doi.org/10.3390/en15093073 - 22 Apr 2022
Cited by 5 | Viewed by 1404
Abstract
Entropy generation is always a matter of concern in a heat transfer system. It denotes the amount of energy lost as a result of irreversibility. As a result, it must be reduced. The present work considers an investigation on the turbulent forced convective [...] Read more.
Entropy generation is always a matter of concern in a heat transfer system. It denotes the amount of energy lost as a result of irreversibility. As a result, it must be reduced. The present work considers an investigation on the turbulent forced convective heat transfer and entropy generation of Al2O3-Ethylene glycol (EG) nanofluid inside a circular tube subjected to constant wall temperature. The study is focused on the development of an analytical framework by using mathematical models to simulate the characteristics of nanofluids in the as-mentioned thermal system. The simulated result is validated using published data. Further, Genetic algorithm (GA) and DIRECT algorithm are implemented to determine the optimal condition which yields minimum entropy generation. According to the findings, heat transfer increases at a direct proportion to the mass flow, Reynolds number (Re), and volume concentration of nanoparticles. Furthermore, as Re increases, particle concentration should be decreased in order to reduce total entropy generation (TEG) and to improve heat transfer rate of any given particle size. A minimal concentration of nanoparticles is required to reduce TEG when Re is maintained constant. The highest increase in TEG with nanofluids was 2.93 times that of basefluid. The optimum condition for minimum entropy generation is Re = 4000, nanoparticle size = 65 nm, volume concentration = 0.2% and mass flow rate = 0.54 kg/s. Full article
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20 pages, 6456 KiB  
Article
Analysis of Entropy Generation on Magnetohydrodynamic Flow with Mixed Convection through Porous Media
by Munawwar Ali Abbas, Bashir Ahmed, Li Chen, Shamas ur Rehman, Muzher Saleem and Wissam Sadiq Khudair
Energies 2022, 15(3), 1206; https://doi.org/10.3390/en15031206 - 07 Feb 2022
Cited by 8 | Viewed by 1471
Abstract
Various industrial operations involve frequent heating and cooling of electrical systems. In such circumstances, the development of relevant thermal devices is of extreme importance. During the development of thermal devices, the second law of thermodynamics plays an important role by means of entropy [...] Read more.
Various industrial operations involve frequent heating and cooling of electrical systems. In such circumstances, the development of relevant thermal devices is of extreme importance. During the development of thermal devices, the second law of thermodynamics plays an important role by means of entropy generation. Entropy generation should be reduced significantly for the efficient performance of the devices. The current paper reports an analytical study on micropolar fluid with entropy generation over a stretching surface. The influence of various physical parameters on velocity profile, microrotation profile, and temperature profile is investigated graphically. The impact of thermal radiation, porous medium, magnetic field, and viscous dissipation are also analyzed. Moreover, entropy generation and Bejan number are also illustrated graphically. Furthermore, the governing equations are solved by using HAM and code in MATHEMATICA software. It is concluded from this study that velocity and micro-rotation profile are reduced for higher values of magnetic and vortex viscosity parameter, respectively. For larger values of Eckert number and thermal radiation parameters, Bejan number and entropy generation are increased, respectively. These findings are useful in petroleum industries and engineering designs. Full article
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15 pages, 43030 KiB  
Article
Structural Optimization of Self-Supporting Rectangular Converging-Diverging Tube Heat Exchanger
by Feng Jiao, Ming Wang, Meilin Hu and Yongqing He
Energies 2022, 15(3), 1133; https://doi.org/10.3390/en15031133 - 03 Feb 2022
Cited by 1 | Viewed by 1209
Abstract
A three-dimensional numerical investigation of turbulent heat transfer and fluid flow characteristics of the new heat exchanger and self-support of a rectangular converging-diverging (SS-RCD) tube bundle heat exchanger with different inserts was performed. The values of the Reynolds number varied from 27,900 to [...] Read more.
A three-dimensional numerical investigation of turbulent heat transfer and fluid flow characteristics of the new heat exchanger and self-support of a rectangular converging-diverging (SS-RCD) tube bundle heat exchanger with different inserts was performed. The values of the Reynolds number varied from 27,900 to 41,900. The baseline case (without an insert) was compared with two enhanced configurations: one circular hole in the baffle plate (one-circle case) and a rectangular hole in the baffle plate (one-rectangle case). Compared with the baseline case, the airside Nusselt number (Nu) of the enhanced cases improved by 39.6~48.0% and 36.2~40.2% and had an associated friction factor (f) penalty increase of 53.9–66.7% and 60.7–77.8%, respectively. The baseline case was compared with three enhanced configurations: one-circle case, two-circle case, and three-circle case baffle plate. Compared with the baseline case, Nu of the enhanced cases improved by 39.6–48.0%, 36.2–45.4%, and 35.0–44.2%, with f penalty increases of 53.9–66.7%, 44.9–60.0%, and 43.8–60.0%, respectively. The overall performance was conducted by heat transfer enhancement factor (η). It was found that the one circle case obtained the best overall performance. The numerical results were analyzed from the viewpoint of the field synergy principle. It was found that the reduction in the average intersection angle between the velocity vector and the temperature gradient (θ) was one of the essential factors influencing heat transfer performance. Full article
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60 pages, 13226 KiB  
Review
A Review of Recent Passive Heat Transfer Enhancement Methods
by Seyed Soheil Mousavi Ajarostaghi, Mohammad Zaboli, Hossein Javadi, Borja Badenes and Javier F. Urchueguia
Energies 2022, 15(3), 986; https://doi.org/10.3390/en15030986 - 28 Jan 2022
Cited by 62 | Viewed by 5901
Abstract
Improvements in miniaturization and boosting the thermal performance of energy conservation systems call for innovative techniques to enhance heat transfer. Heat transfer enhancement methods have attracted a great deal of attention in the industrial sector due to their ability to provide energy savings, [...] Read more.
Improvements in miniaturization and boosting the thermal performance of energy conservation systems call for innovative techniques to enhance heat transfer. Heat transfer enhancement methods have attracted a great deal of attention in the industrial sector due to their ability to provide energy savings, encourage the proper use of energy sources, and increase the economic efficiency of thermal systems. These methods are categorized into active, passive, and compound techniques. This article reviews recent passive heat transfer enhancement techniques, since they are reliable, cost-effective, and they do not require any extra power to promote the energy conversion systems’ thermal efficiency when compared to the active methods. In the passive approaches, various components are applied to the heat transfer/working fluid flow path to improve the heat transfer rate. The passive heat transfer enhancement methods studied in this article include inserts (twisted tapes, conical strips, baffles, winglets), extended surfaces (fins), porous materials, coil/helical/spiral tubes, rough surfaces (corrugated/ribbed surfaces), and nanofluids (mono and hybrid nanofluids). Full article
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2021

Jump to: 2024, 2023, 2022, 2020, 2019

16 pages, 2789 KiB  
Article
Optimal Experimental Design for Inverse Identification of Conductive and Radiative Properties of Participating Medium
by Hua Liu, Xue Chen, Zhongcan Chen, Caobing Wei, Zuo Chen, Jiang Wang, Yanjun Duan, Nan Ren, Jian Li and Xingzhou Zhang
Energies 2021, 14(20), 6593; https://doi.org/10.3390/en14206593 - 13 Oct 2021
Cited by 1 | Viewed by 1135
Abstract
The conductive and radiative properties of participating medium can be estimated by solving an inverse problem that combines transient temperature measurements and a forward model to predict the coupled conductive and radiative heat transfer. The procedure, as well as the estimates of parameters, [...] Read more.
The conductive and radiative properties of participating medium can be estimated by solving an inverse problem that combines transient temperature measurements and a forward model to predict the coupled conductive and radiative heat transfer. The procedure, as well as the estimates of parameters, are not only affected by the measurement noise that intrinsically exists in the experiment, but are also influenced by the known model parameters that are used as necessary inputs to solve the forward problem. In the present study, a stochastic Cramér–Rao bound (sCRB)-based error analysis method was employed for estimation of the errors of the retrieved conductive and radiative properties in an inverse identification process. The method took into account both the uncertainties of the experimental noise and the uncertain model parameter errors. Moreover, we applied the method to design the optimal location of the temperature probe, and to predict the relative error contribution of different error sources for combined conductive and radiative inverse problems. The results show that the proposed methodology is able to determine, a priori, the errors of the retrieved parameters, and that the accuracy of the retrieved parameters can be improved by setting the temperature probe at an optimal sensor position. Full article
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15 pages, 2254 KiB  
Article
Analysis of the Parameters of the Two-Sections Hot Side Heat Exchanger of the Module with Thermoelectric Generators
by Mirosław Neska, Mirosław Mrozek, Marta Żurek-Mortka and Andrzej Majcher
Energies 2021, 14(16), 5169; https://doi.org/10.3390/en14165169 - 21 Aug 2021
Cited by 8 | Viewed by 1373
Abstract
One of the methods of converting thermal energy into electricity is the use of thermoelectric generators (TEG). The method can be used in low-temperature waste heat conversion systems from industrial installations, but its serious limitation is the low efficiency of thermolectric generators and [...] Read more.
One of the methods of converting thermal energy into electricity is the use of thermoelectric generators (TEG). The method can be used in low-temperature waste heat conversion systems from industrial installations, but its serious limitation is the low efficiency of thermolectric generators and the relatively low power of the electric waveforms obtained. Increasing the obtained power values is done by multiplying the number of TEGs used, grouped into modules (MTEG). In such systems, the design of the module is extremely important, as it should ensure the best possible heat transfer between both sides of the TEG (hot and cold), and thus obtaining maximum electrical power. The article presents an analysis of a two-section flat plate heat hot side exchanger MTEG. The key parameters like effectiveness of exchange and MTEG efficiency and their impact on the efficiency of heat use and generated electric power were indicated. The tests showed an improvement in these main system parameters for the mixed cycle (co-current and countercurrent—inward direction) of the hot side heat exchanger, compared to the countercurrent flow in both sections of this exchanger. Full article
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23 pages, 11043 KiB  
Article
Thermal and Flow Simulation of Concentric Annular Heat Pipe with Symmetric or Asymmetric Condenser
by Eui-Hyeok Song, Kye-Bock Lee and Seok-Ho Rhi
Energies 2021, 14(11), 3333; https://doi.org/10.3390/en14113333 - 06 Jun 2021
Cited by 5 | Viewed by 2453
Abstract
The current research work describes the flow and thermal analysis inside the circular flow region of an annular heat pipe with a working fluid, using computational fluid dynamics (CFD) simulation. A two-phase flow involving simultaneous evaporation and condensation phenomena in a concentric annular [...] Read more.
The current research work describes the flow and thermal analysis inside the circular flow region of an annular heat pipe with a working fluid, using computational fluid dynamics (CFD) simulation. A two-phase flow involving simultaneous evaporation and condensation phenomena in a concentric annular heat pipe (CAHP) is modeled. To simulate the interaction between these phases, the volume of fluid (VOF) technique is used. The temperature profile predicted using computational fluid dynamics (CFD) in the CAHP was compared with previously obtained experimental results. Two-dimensional and three-dimensional simulations were carried out, in order to verify the usefulness of 3D modeling. Our goal was to compute the flow characteristics, temperature distribution, and velocity field inside the CAHP. Depending on the shape of the annular heat pipe, the thermal performance can be improved through the optimal design of components, such as the inner width of the annular heat pipe, the location of the condensation part, and the amount of working fluid. To evaluate the thermal performance of a CAHP, a numerical simulation of a 50 mm long stainless steel CAHP (1.1 and 1.3 in diameter ratio and fixed inner tube diameter (78 mm)) was done, which was identical to the experimental system. In the simulated analysis results, similar results to the experiment were obtained, and it was confirmed that the heat dissipation was higher than that of the existing conventional heat pipe, where the heat transfer performance was improved when the asymmetric area was cooled. Moreover, the simulation results were validated using the experimental results. The 3-D simulation shows good agreement with the experimental results to a reasonable degree. Full article
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14 pages, 2868 KiB  
Article
Numerical Investigation into the Natural Convection of Cryogenic Supercritical Helium in a Spherical Enclosure
by Yinan Qiu, Hua Zhai, Yao Zheng, Gang Lei, Tianxiang Wang, Li Wang and Shuiming Shu
Energies 2021, 14(9), 2584; https://doi.org/10.3390/en14092584 - 30 Apr 2021
Cited by 8 | Viewed by 1692
Abstract
As an ideal pressurized gas, helium, especially supercritical helium, has been widely used in the pressurization system of various launch vehicles and spacecraft. This work mainly focuses on the natural convection of cryogenic supercritical helium in a spherical enclosure. Firstly, a three-dimensional numerical [...] Read more.
As an ideal pressurized gas, helium, especially supercritical helium, has been widely used in the pressurization system of various launch vehicles and spacecraft. This work mainly focuses on the natural convection of cryogenic supercritical helium in a spherical enclosure. Firstly, a three-dimensional numerical model is established and verified with experimental data. Then, the effects of inflation pressure and heating power on the flow and heat transfer characteristics are simulated. At the same time, the relationship between the Rayleigh number and Nusselt number is studied in detail. Finally, an improved natural convection heat transfer correlation modified by introducing the density ratio is obtained. The results show that the increase of the inflation pressure in the cavity is helpful to enhance the natural convection heat transfer of the cryogenic supercritical helium, and the temperature distribution in the cavity tends to be more uniform when the inflation pressure in the cavity increases. As to the improved natural convection heat transfer correlation, the average error between the simulation results and the calculated values is approximately 8%, which can better describe the natural convection heat transfer of cryogenic supercritical helium in the spherical enclosure. Full article
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25 pages, 13777 KiB  
Article
Evaluation on Enhanced Heat Transfer Using Sonochemically Synthesized Stable Zno-Eg@Dw Nanofluids in Horizontal Calibrated Circular Flow Passage
by Waqar Ahmed, Zaira Zaman Chowdhury, Salim Newaz Kazi, Mohd. Rafie Bin Johan, Irfan Anjum Badruddin, Manzoore Elahi M Soudagar, Sarfaraz Kamangar, Muhammad Abbas Mujtaba, Mustabshirha Gul and T.M. Yunus Khan
Energies 2021, 14(9), 2400; https://doi.org/10.3390/en14092400 - 23 Apr 2021
Cited by 6 | Viewed by 1619
Abstract
In this research, Zinc Oxide-Ethylene @ glycol distilled water based nanofluid was synthesized using the sonochemical method. The convective heat transfer properties of as synthesized nanofluid were observed for a closed single circular tube pipe in turbulent flow regimes. The prepared nanofluids were [...] Read more.
In this research, Zinc Oxide-Ethylene @ glycol distilled water based nanofluid was synthesized using the sonochemical method. The convective heat transfer properties of as synthesized nanofluid were observed for a closed single circular tube pipe in turbulent flow regimes. The prepared nanofluids were characterized by ultra violet spectroscopy (UV–VIS), UV–VIS absorbance, X-Ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), Transmission electron microscopy (TEM) and stability analysis. Five calibrated k-type thermocouples were mounted on the surface of the test section. Analytical data related to heat transfer properties of the synthesized nanofluid for the heat exchanger, incorporated with the closed circular tube test section were collected. The addition of ZnO solid nanoparticles in the EG@DW mixture enhanced the value of thermal conductivity and other thermophysical characteristics of the nanofluids. Maximum thermal conductivity was observed at 45 °C for using 0.1 wt.% of ZnO nanoparticles EG@DW nanofluid. Increasing the wt.% of ZnO solid nanoparticles in the EG@DW mixture had increased the thermal conductivity subsequently with change in temperature from 20 to 45 °C. Furthermore, Nusselt numbers of ZnO-EG@DW-based nanofluid was estimated for the various concentration of ZnO present in EG@DW-based fluid. The presence of ZnO solid nanoparticles into the EG@DW base fluid escalate the Nusselt (Nu) number by 49.5%, 40.79%, 37% and 23.06% for 0.1, 0.075, 0.05 and 0.025 wt.% concentrations, respectively, at room temperature. Varying wt.% of ZnO (0.1, 0.075, 0.05 and 0.025) nanoparticles had shown improved heat transfer (h) properties compared to the base fluid alone. The absolute average heat transfer of ZnO-EG@DW nanofluid using the highest concentration of 0.1 wt.% was improved compared to the EG@DW mixture. The magnitude of absolute average heat transfer was increased from 600 W/m2k for the EG@DW mixture to 1200 W/m2k for ZnO-EG@DW nanofluid. Similarly, the heat transfer improvement for the other three wt.% (0.075, 0.05 and 0.025) was noticed as 600–1160, 600–950 and 600–900 W/m2k, respectively, which is greater than base fluid. Full article
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2020

Jump to: 2024, 2023, 2022, 2021, 2019

25 pages, 12945 KiB  
Article
Performance of Supercritical CO2 Power Cycle and Its Turbomachinery with the Printed Circuit Heat Exchanger with Straight and Zigzag Channels
by Muhammed Saeed, Khaled Alawadi and Sung Chul Kim
Energies 2021, 14(1), 62; https://doi.org/10.3390/en14010062 - 24 Dec 2020
Cited by 11 | Viewed by 2265
Abstract
Since printed circuit heat exchangers (PCHE) are the largest modules of a supercritical carbon dioxide Brayton cycle, they can considerably affect the whole system’s performance and layout. Straight-channel and zigzag-channel printed circuit heat exchangers have frequently been analyzed in the standalone mode and [...] Read more.
Since printed circuit heat exchangers (PCHE) are the largest modules of a supercritical carbon dioxide Brayton cycle, they can considerably affect the whole system’s performance and layout. Straight-channel and zigzag-channel printed circuit heat exchangers have frequently been analyzed in the standalone mode and repeatedly proposed for sCO2BC. However, the impact of heat exchanger designs with straight and zigzag-channel configurations on the performance of the cycle and its components, i.e., the turbine and compressor, has not been studied. In this context, this study evaluates the effect of different heat exchanger designs with various values of effectiveness (ϵ), inlet Reynolds number (Re), and channel configuration (zigzag and straight channel) on the overall performance of the sCO2BC and its components. For the design and analysis of PCHEs, an in-house PCHE design and analysis code (PCHE-DAC) was developed in the MATLAB environment. The sCO2BC performance was evaluated utilizing an in-house cycle simulation and analysis code (CSAC) that employs the heat exchanger design code as a subroutine. The results suggest that pressure drop in PCHEs with straight-channel configuration is up to 3.0 times larger than in PCHEs with zigzag-channel configuration. It was found that a higher pressure drop in the PCHEs with straight channels can be attributed to substantially longer channel lengths required for these designs (up to 4.1 times than zigzag-channels) based on the poor heat transfer characteristics associated with these channel geometries. Thus, cycle layouts using PCHEs with a straight-channel configuration impart a much higher load (up to 1.13 times) on the recompression compressor, this in turn, results in a lower pressure ratio across the turbine. Therefore, the overall performance of the sCO2BC using PCHEs with straight-channel configurations is found to be substantially inferior to that of layouts using PCHEs with zigzag-channel configurations. Finally, optimization results suggest that heat exchanger’s design with inlet Reynolds number and heat exchanger effectiveness ranging from 32 k to 42 k and 0.94>ϵ>0.87, respectively, are optimal for sCO2BC and present a good bargain between cycle efficiency and its layout size. Full article
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14 pages, 3886 KiB  
Article
Study on Heat Transfer Performance of Antifreeze-R134a Heat Exchanger (ARHEx)
by Liping Pang, Kun Luo, Shizhao Yu, Desheng Ma, Miao Zhao and Xiaodong Mao
Energies 2020, 13(22), 6129; https://doi.org/10.3390/en13226129 - 23 Nov 2020
Cited by 1 | Viewed by 1581
Abstract
In this paper, the liquid cooling and vapor compression refrigeration system based on an Antifreeze-R134a Heat Exchanger (ARHEx) was applied to the thermal management system for high-power avionics in helicopters. The heat transfer performance of the ARHEx was studied. An experimental prototype of [...] Read more.
In this paper, the liquid cooling and vapor compression refrigeration system based on an Antifreeze-R134a Heat Exchanger (ARHEx) was applied to the thermal management system for high-power avionics in helicopters. The heat transfer performance of the ARHEx was studied. An experimental prototype of ARHEx was designed and established. A series of experiments was carried out with a ground experimental condition. A heat transfer formula for the antifreeze side in the ARHEx was obtained by means of the coefficient of Nusselt number with experimental analysis. The performance of heat transfer and pressure drop for the refrigerant side of the ARHEx was deduced for the given condition. Full article
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49 pages, 8498 KiB  
Review
Recent Advances in the Critical Heat Flux Amelioration of Pool Boiling Surfaces Using Metal Oxide Nanoparticle Deposition
by Hesam Moghadasi, Navid Malekian, Hamid Saffari, Amir Mirza Gheitaghy and Guo Qi Zhang
Energies 2020, 13(15), 4026; https://doi.org/10.3390/en13154026 - 04 Aug 2020
Cited by 21 | Viewed by 4711
Abstract
Pool boiling is an effective heat transfer process in a wide range of applications related to energy conversion, including power generation, solar collectors, cooling systems, refrigeration and air conditioning. By considering the broad range of applications, any improvement in higher heat-removal yield can [...] Read more.
Pool boiling is an effective heat transfer process in a wide range of applications related to energy conversion, including power generation, solar collectors, cooling systems, refrigeration and air conditioning. By considering the broad range of applications, any improvement in higher heat-removal yield can ameliorate the ultimate heat usage and delay or even avoid the occurrence of system failures, thus leading to remarkable economic, environmental and energy efficiency outcomes. A century of research on ameliorating critical heat flux (CHF) has focused on altering the boiling surface characteristics, such as its nucleation site density, wettability, wickability and heat transfer area, by many innovative techniques. Due to the remarkable interest of using nanoparticle deposition on boiling surfaces, this review is targeted towards investigating whether or not metal oxide nanoparticles can modify surface characteristics to enhance the CHF. The influence of nanoparticle material, thermo-physical properties, concentration, shape, and size are categorized, and the inconsistency or contradictions of the existing research results are recognized. In the following, nanoparticle deposition methods are presented to provide a worthwhile alternative to deposition rather than nanofluid boiling. Furthermore, possible mechanisms and models are identified to explain the amelioration results. Finally, the present status of nanoparticle deposition for CHF amelioration, along with their future challenges, amelioration potentials, limitations, and their possible industrial implementation, is discussed. Full article
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21 pages, 9351 KiB  
Article
MHD Heat Transfer in W-Shaped Inclined Cavity Containing a Porous Medium Saturated with Ag/Al2O3 Hybrid Nanofluid in the Presence of Uniform Heat Generation/Absorption
by Mohamed Dhia Massoudi, Mohamed Bechir Ben Hamida, Hussein A. Mohammed and Mohammed A. Almeshaal
Energies 2020, 13(13), 3457; https://doi.org/10.3390/en13133457 - 03 Jul 2020
Cited by 21 | Viewed by 2060
Abstract
In this paper, a 2D numerical study of natural convection heat transfer in a W-shaped inclined enclosure with a variable aspect ratio was performed. The enclosure contained a porous medium saturated with Ag/Al2O3 hybrid nanofluid in the presence of uniform [...] Read more.
In this paper, a 2D numerical study of natural convection heat transfer in a W-shaped inclined enclosure with a variable aspect ratio was performed. The enclosure contained a porous medium saturated with Ag/Al2O3 hybrid nanofluid in the presence of uniform heat generation or absorption under the effect of a uniform magnetic field. The vertical walls of the enclosure were heated differentially; however, the top and bottom walls were kept insulated. The governing equations were solved with numerical simulation software COMSOL Multiphysics which is based on the finite element method. The results showed that the convection heat transfer was improved with the increase of the aspect ratio; the average Nusselt number reached a maximum for an aspect ratio (AR) = 0.7 and the effect of the inclination was practically negligible for an aspect ratio of AR = 0.7. The maximum heat transfer performance was obtained for an inclination of ω = 15 and the minimum is obtained for ω = 30 . The addition of composite nanoparticles ameliorated the convection heat transfer performance. This effect was proportional to the increase of Rayleigh and Darcy numbers, the aspect ratio and the fraction of Ag in the volumetric fraction of nanoparticles. Full article
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17 pages, 3797 KiB  
Article
Boiling Heat Transfer Performance of Parallel Porous Microchannels
by Donghui Zhang, Haiyang Xu, Yi Chen, Leiqing Wang, Jian Qu, Mingfa Wu and Zhiping Zhou
Energies 2020, 13(11), 2970; https://doi.org/10.3390/en13112970 - 10 Jun 2020
Cited by 10 | Viewed by 2574
Abstract
Flow boiling in microporous layers has attracted a great deal of attention in the enhanced heat transfer field due to its high heat dissipation potential. In this study, flow boiling experiments were performed on both porous microchannels and a copper-based microchannel, using water [...] Read more.
Flow boiling in microporous layers has attracted a great deal of attention in the enhanced heat transfer field due to its high heat dissipation potential. In this study, flow boiling experiments were performed on both porous microchannels and a copper-based microchannel, using water as the coolant. As the heat flux was less than 80 W/cm2, the porous microchannels presented significantly higher boiling heat transfer coefficients than the copper-based microchannel. This was closely associated with the promotion of the nucleation site density of the porous coating. With the further increase in heat flux, the heat transfer coefficients of the porous microchannels were close to those of the copper-based sample. The boiling process in the porous microchannel was found to be dominated by the nucleate boiling mechanism from low to moderate heat flux (<80 W/cm2).This switched to the convection boiling mode at high heat flux. The porous samples were able to mitigate flow instability greatly. A visual observation revealed that porous microchannels could suppress the flow fluctuation due to the establishment of a stable nucleate boiling process. Porous microchannels showed no advantage over the copper-based sample in the critical heat flux. The optimal thickness-to-particle-size ratio (δ/d) for the porous microchannel was confirmed to be between 2–5. In this range, the maximum enhanced effect on boiling heat transfer could be achieved. Full article
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19 pages, 3316 KiB  
Article
Analysis of Enhanced Pool Boiling Heat Transfer on Laser—Textured Surfaces
by Łukasz J. Orman, Norbert Radek, Jacek Pietraszek and Marcin Szczepaniak
Energies 2020, 13(11), 2700; https://doi.org/10.3390/en13112700 - 28 May 2020
Cited by 34 | Viewed by 2669
Abstract
Enhancement of pool boiling heat transfer can be attained with a number of passive and active techniques. The paper experimentally analyses the impact of laser treatment of the copper surfaces on pool boiling heat transfer of distilled water and ethyl alcohol. The samples [...] Read more.
Enhancement of pool boiling heat transfer can be attained with a number of passive and active techniques. The paper experimentally analyses the impact of laser treatment of the copper surfaces on pool boiling heat transfer of distilled water and ethyl alcohol. The samples were modified with a laser beam to produce longitudinal grooves of highly developed microstructures in the laser textured area. Specimens of different groove depths, groove widths and micro-fin widths were produced. The results indicate a significant influence of laser processing on heat flux dissipated from the surfaces and heat transfer enhancement for all the samples tested. The experimental results have been generalized in the form of a heat flux correlation based on a modified model of enhanced pool boiling heat transfer. Full article
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16 pages, 6292 KiB  
Article
Heat-Transfer Characteristics of a Cryogenic Loop Heat Pipe for Space Applications
by Jaehwan Lee, Dongmin Kim, Jeongmin Mun and Seokho Kim
Energies 2020, 13(7), 1616; https://doi.org/10.3390/en13071616 - 02 Apr 2020
Cited by 13 | Viewed by 2668
Abstract
Infrared detectors on satellites and spacecraft require cooling to increase their measurement sensitivity. To efficiently cool infrared detectors in a zero gravity environment and in limited spaces, a cryogenic loop heat pipe (CLHP) can be used to transfer heat over a certain distance [...] Read more.
Infrared detectors on satellites and spacecraft require cooling to increase their measurement sensitivity. To efficiently cool infrared detectors in a zero gravity environment and in limited spaces, a cryogenic loop heat pipe (CLHP) can be used to transfer heat over a certain distance by the capillary forces generated from porous wicks without a mechanical power source. The CLHP presented in this study transfers the heat load to a condenser 0.5 m away from an evaporator at temperatures below −150 °C. The CLHP with two evaporators includes a subloop for initial start-up, and uses a pressure reduction reservoir (PRR) for the supercritical start-up from room to cryogenic temperature. Nitrogen is used as the working fluid to verify the thermal behavior of the CLHP, and the heat-transfer capacity according to the nitrogen charging pressure of the PRR is investigated. To simulate a cryogenic environment, the CLHP is installed inside a space environment simulator, including a single-stage GM (Gifford McMahon) cryocooler to cool the condenser. The CLHP is horizontally installed to simulate zero gravity. The heat-transfer characteristics are experimentally evaluated through the loop circulation of the CLHP. Full article
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16 pages, 1902 KiB  
Article
Convective Heat Transfer Enhancement through Laser-Etched Heat Sinks: Elliptic Scale-Roughened and Cones Patterns
by Luigi Ventola, Matteo Fasano, Roberta Cappabianca, Luca Bergamasco, Francesca Clerici, Luciano Scaltrito, Eliodoro Chiavazzo and Pietro Asinari
Energies 2020, 13(6), 1360; https://doi.org/10.3390/en13061360 - 15 Mar 2020
Cited by 4 | Viewed by 2310
Abstract
The efficient dissipation of localized heat flux by convection is a key request in several engineering applications, especially electronic ones. The recent advancements in manufacturing processes are unlocking the design and industrialization of heat exchangers with unprecedented geometric characteristics and, thus, performance. In [...] Read more.
The efficient dissipation of localized heat flux by convection is a key request in several engineering applications, especially electronic ones. The recent advancements in manufacturing processes are unlocking the design and industrialization of heat exchangers with unprecedented geometric characteristics and, thus, performance. In this work, laser etching manufacturing technique is employed to develop metal surfaces with designed microstructured surface patterns. Such precise control of the solid-air interface (artificial roughness) allows to manufacture metal heat sinks with enhanced thermal transmittance with respect to traditional flat surfaces. Here, the thermal performance of these laser-etched devices is experimentally assessed by means of a wind tunnel in a fully turbulent regime. At the highest Reynolds number tested in the experiments ( R e L 16 , 500 ), elliptic scale-roughened surfaces show thermal transmittances improved by up to 81% with respect to heat sinks with flat surface. At similar testing conditions, cones patterns provide an enhancement in Nusselt number and thermal transmittance of up to 102% and 357%, respectively. The latter results are correlated with the main geometric and thermal fluid dynamics descriptors of the convective heat transfer process in order to achieve a predictive model of their performance. The experimental evidence shown in this work may encourage and guide a broader use of micro-patterned surfaces for enhancing convective heat transfer in heat exchangers. Full article
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16 pages, 13774 KiB  
Article
Performance Evaluation of Wire Cloth Micro Heat Exchangers
by Hannes Fugmann, Sebastian Martens, Richard Balzer, Martin Brenner, Lena Schnabel and Carsten Mehring
Energies 2020, 13(3), 715; https://doi.org/10.3390/en13030715 - 06 Feb 2020
Cited by 3 | Viewed by 2636
Abstract
The purpose of this study is to validate a thermal-hydraulic simulation model for a new type of heat exchanger for mass, volume, and coolant/refrigerant charge reduction. The new heat exchanger consists of tubes with diameters in the range of 1 m m and [...] Read more.
The purpose of this study is to validate a thermal-hydraulic simulation model for a new type of heat exchanger for mass, volume, and coolant/refrigerant charge reduction. The new heat exchanger consists of tubes with diameters in the range of 1 m m and wires in the range of 100 m , woven together to form a 200 × 200 × 80 m m 3 wire cloth heat exchanger. Performance of the heat exchanger has been experimentally evaluated using water as inner and air as outer heat transfer medium. A computational thermal and fluid dynamic model has been implemented in OpenFOAM®. The model allows variation of geometry and operating conditions. The validation of the model is based on one single geometry with an opaque fabric and air-side velocities between 1 and 7 m / s . The simulated and measured pressure drops are found to be in good agreement with a relative difference of less than 16%. For the investigated cases, the effective heat transfer coefficients are in very good agreement (less than 5%) when adapting the contact resistance between tubes and wires. The numerical model describes the fluid flow and heat transfer of the tested heat exchanger with adequate precision and can be used for future wire cloth heat exchanger dimensioning for a variety of applications. Full article
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2019

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22 pages, 6043 KiB  
Article
A Study on the Mechanism of Convective Heat Transfer Enhancement Based on Heat Convection Velocity Analysis
by Hui Xiao, Zhimin Dong, Rui Long, Kun Yang and Fang Yuan
Energies 2019, 12(21), 4175; https://doi.org/10.3390/en12214175 - 01 Nov 2019
Cited by 11 | Viewed by 2536
Abstract
This paper explores the mechanism of convective heat transfer enhancement in a new perspective. In this paper, a new parameter called heat convection velocity is proposed based on the field synergy principle. It is defined as the velocity projection on the temperature gradient [...] Read more.
This paper explores the mechanism of convective heat transfer enhancement in a new perspective. In this paper, a new parameter called heat convection velocity is proposed based on the field synergy principle. It is defined as the velocity projection on the temperature gradient vector and reflects the magnitude of the velocity component that contributes to heat convection. Three typical cases are taken into consideration to investigate the influence factors of Nusselt number theoretically. The results indicate that the Nusselt number can be enhanced by increasing the mean heat convection velocity and the dimensionless mean temperature difference. Through theoretical analysis, three suggestions are found for designing heat transfer enhancement components: (a) the overall synergetic effect should be improved; (b) the fluid with lower temperature gradient should be guided to the region where the temperature gradient is higher; (c) temperature distribution should be an interphase distribution of hot and cold fluid. Besides, the heat convection velocity is used to investigate the mechanism of convective heat transfer in the smooth tube. It is found that the increase of Nusselt number is due to the increase of heat convection velocity. In addition, according to design suggestions, a new insert is invented and inserted in the circular tube. With heat convection velocity analysis, it is found that there is much potential of increasing heat convection velocity for enhancing the convective heat transfer in the circular tube. Full article
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20 pages, 10156 KiB  
Article
Experimental Investigation on Heat Transfer Mechanism of Air-Blast-Spray-Cooling System with a Two-Phase Ejector Loop for Aeronautical Application
by Jia-Xin Li, Yun-Ze Li, Ben-Yuan Cai and En-Hui Li
Energies 2019, 12(20), 3963; https://doi.org/10.3390/en12203963 - 18 Oct 2019
Cited by 7 | Viewed by 2635
Abstract
This paper presents an air-oriented spray cooling system (SCS) integrated with a two-phase ejector for the thermal management system. Considering its aeronautical application, the spray nozzle in the SCS is an air-blast one. Heat transfer performance (HTP) of air-water spray cooling was studied [...] Read more.
This paper presents an air-oriented spray cooling system (SCS) integrated with a two-phase ejector for the thermal management system. Considering its aeronautical application, the spray nozzle in the SCS is an air-blast one. Heat transfer performance (HTP) of air-water spray cooling was studied experimentally on the basis of the ground-based test. Factors including pressure difference between water-inlet-pressure (WIP) and spray cavity one (PDWIC) and the spray volumetric flow rate (SVFR) were investigated and discussed. Under a constant operating condition, the cooling capacity can be promoted by the growth factors of the PDWIC and SVFR with the values from 51.90 kPa to 235.35 kPa and 3.91 L h 1 to 14.53 L h 1 , respectively. Under the same heating power, HTP is proportional to the two dimensionless parameters Reynolds number and Weber number due to the growth of droplet-impacting velocity and droplet size as the increasing of PDWIC or SVFR. Additionally, compared with the factor of the droplet size, the HTP is more sensitive to the variation in the droplet-impacting velocity. Based on the experimental data, an empirical experimental correlation for the prediction of the dimensionless parameter Nusselt number in the non-boiling region with the relative error of only ± 10 % was obtained based on the least square method. Full article
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25 pages, 6008 KiB  
Article
Microclimate Thermal Management Using Thermoelectric Air-Cooling Duct System Operated at Five Incremental Powers and its Effect on Sleep Adaptation of the Occupants
by Kashif Irshad, Salem Algarni, Mohammad Tauheed Ahmad, Sayed Ameenuddin Irfan, Khairul Habib, Mostafa A.H. Abdelmohimen, Md. Hasan Zahir and Gulam Mohammed Sayeed Ahmed
Energies 2019, 12(19), 3695; https://doi.org/10.3390/en12193695 - 27 Sep 2019
Cited by 3 | Viewed by 2486
Abstract
In this study, the microclimate of the test room was regulated using thermoelectric air duct cooling system (TE-AD) operated at input powers-240 W, 360 W, 480 W, 600 W, 720 W, and 840 W, on subsequent nights. Fifteen (15) healthy male volunteers were [...] Read more.
In this study, the microclimate of the test room was regulated using thermoelectric air duct cooling system (TE-AD) operated at input powers-240 W, 360 W, 480 W, 600 W, 720 W, and 840 W, on subsequent nights. Fifteen (15) healthy male volunteers were recruited to sleep under these test conditions and their sleep quality was assessed by studying objective measures such as sleep onset latency (SOL), mean skin temperature and heart rate as well as subjective parameters like predicted mean vote (PMV) and predicted percentage of dissatisfied (PPD). There was a consistent improvement on all studied parameters when the power of the system was increased from 240 W to 720 W. The mean sleep onset latency time was reduced from (M = 40.7 +/− 0.98 min) to (M = 18.33 +/− 1.18 min) when the operating power was increased from 240 W to 720 W, denoting an improvement in sleep quality. However, increasing the power further to 840 W resulted in deteriorating cooling performance of the TE-AD system leading to an increase in temperature of the test room and reduction in sleep comfort. Analysis of subjective indices of thermal comfort viz. PMV and PPD revealed that subjects are highly sensitive towards variations in microclimate achieved by changing the operating power of the TE-AD. This device was also found to be environmentally sustainable, with estimated reduction in CO2 emission calculated to be around 38% as compared to the conventional air-conditioning. Full article
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12 pages, 2169 KiB  
Article
Thermal-Hydraulic Studies on the Shell-and-Tube Heat Exchanger with Minijets
by Jan Wajs, Michał Bajor and Dariusz Mikielewicz
Energies 2019, 12(17), 3276; https://doi.org/10.3390/en12173276 - 26 Aug 2019
Cited by 6 | Viewed by 2400
Abstract
In this paper a patented design of a heat exchanger with minijets, with a cylindrical construction is presented. It is followed by the results of its systematic experimental investigations in the single-phase convection heat transfer mode. Based on these results, validation of selected [...] Read more.
In this paper a patented design of a heat exchanger with minijets, with a cylindrical construction is presented. It is followed by the results of its systematic experimental investigations in the single-phase convection heat transfer mode. Based on these results, validation of selected correlations (coming from the literature) describing the Nusselt number was carried out. An assessment of the heat exchange intensification level in the described heat exchanger was done through the comparison with a shell-and-tube exchanger of a classical design. The thermal-hydraulic characteristics of both units were the subjects of comparison. They were constructed for the identical thermal conditions, i.e., volumetric flow rates of the working media and the media temperatures at the inlets to the heat exchanger. The experimental studies of both heat exchangers were conducted on the same test facility. An increase in the heat transfer coefficients values for the minijets heat exchanger was observed in comparison with the reference one, whereas the generated minijets caused greater hydraulic resistance. Experimentally confirmed intensification of heat transfer on the air side, makes the proposed minijets heat exchanger application more attractive, for the waste heat utilization systems from gas sources. Full article
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14 pages, 4124 KiB  
Article
Heating Performance Enhancement of High Capacity PTC Heater with Modified Louver Fin for Electric Vehicles
by Myeong Hyeon Park and Sung Chul Kim
Energies 2019, 12(15), 2900; https://doi.org/10.3390/en12152900 - 27 Jul 2019
Cited by 20 | Viewed by 3575
Abstract
Electric vehicles use positive temperature coefficient (PTC) heaters and heat pumps to warm the vehicle cabin. High-capacity PTC heaters are needed because heat pump performance decreases sharply in the winter months due to low outdoor temperatures. The weight of PTC heaters is an [...] Read more.
Electric vehicles use positive temperature coefficient (PTC) heaters and heat pumps to warm the vehicle cabin. High-capacity PTC heaters are needed because heat pump performance decreases sharply in the winter months due to low outdoor temperatures. The weight of PTC heaters is an important heater design factor for improving the single-charge travel distance of electric vehicles. A fin shape is necessary to improve the heater’s heat transfer performance in comparison to its weight. To develop a 6 kW class high-capacity PTC heater for electric vehicles, this study presents a numerical analysis of heat flow according to a modified louver fin’s geometric shape variables and evaluates heating performance. Based on the geometric shape of an initial plate-shaped fin prototype, a numerical analysis was performed on the width, position, height, and angle to develop a modified louver fin while considering heat transfer performance and ease of manufacturing. An improved prototype was built using the developed modified louver fin, and its heating performance under standard conditions was evaluated. The improved prototype had a heating performance of 6.05 kW, an efficiency of 98.0%, a pressure drop of 18.3 Pa, and a heating density of 3.81 kW/kg. Compared to the initial prototype, its heating performance and heating density were improved by approximately 15.7%. Full article
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17 pages, 2056 KiB  
Article
Free Convection of Hybrid Nanofluids in a C-Shaped Chamber under Variable Heat Flux and Magnetic Field: Simulation, Sensitivity Analysis, and Artificial Neural Networks
by Hamed Bagheri, Mohammadali Behrang, Ehsanolah Assareh, Mohsen Izadi and Mikhail A. Sheremet
Energies 2019, 12(14), 2807; https://doi.org/10.3390/en12142807 - 22 Jul 2019
Cited by 20 | Viewed by 2368
Abstract
In the present investigation, the free convection energy transport was studied in a C-shaped tilted chamber with the inclination angle α that was filled with the MWCNT (MultiWall Carbon Nanotubes)-Fe3O4-H2O hybrid nanofluid and it is affected by [...] Read more.
In the present investigation, the free convection energy transport was studied in a C-shaped tilted chamber with the inclination angle α that was filled with the MWCNT (MultiWall Carbon Nanotubes)-Fe3O4-H2O hybrid nanofluid and it is affected by the magnetic field and thermal flux. The control equations were numerically resolved by the finite element method (FEM). Then, using the artificial neural network (ANN) combined with the particles swarm optimization algorithm (PSO), the Nusselt number was predicted, followed by investigating the effect of parameters including the Rayleigh number (Ra), the Hartmann number (Ha), the nanoparticles concentration (φ), the inclination angle of the chamber (α), and the aspect ratio (AR) on the heat transfer rate. The results showed the high accuracy of the ANN optimized by the PSO algorithm in the prediction of the Nusselt number such that the mean squared error in the ANN model is 0.35, while in the ANN model, it was optimized using the PSO algorithm (ANN-PSO) is 0.22, suggesting the higher accuracy of the latter. It was also found that, among the studied parameters with an effect on the heat transfer rate, the Rayleigh number and aspect ratio have the greatest impact on the thermal transmission intensification. The obtained data also showed that a growth of the Hartmann number illustrates a reduction of the Nusselt number for high Rayleigh numbers and the heat transfer rate is almost constant for low Rayleigh number values. Full article
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21 pages, 3812 KiB  
Article
A Novel Analytical Modeling of a Loop Heat Pipe Employing the Thin-Film Theory: Part I—Modeling and Simulation
by Eui Guk Jung and Joon Hong Boo
Energies 2019, 12(12), 2408; https://doi.org/10.3390/en12122408 - 22 Jun 2019
Cited by 10 | Viewed by 2747
Abstract
In this study, steady-state analytical modeling of a loop heat pipe (LHP) equipped with a flat evaporator is presented to predict the temperatures and pressures at each important part of the LHP—evaporator, liquid reservoir (compensation chamber), vapor-transport tube, liquid-transport tube, and condenser. Additionally, [...] Read more.
In this study, steady-state analytical modeling of a loop heat pipe (LHP) equipped with a flat evaporator is presented to predict the temperatures and pressures at each important part of the LHP—evaporator, liquid reservoir (compensation chamber), vapor-transport tube, liquid-transport tube, and condenser. Additionally, this study primarily focuses on analysis of the evaporator—the only LHP component comprising a capillary structure. The liquid thin-film theory is considered to determine pressure and temperature values concerning the region adjacent to the liquid-vapor interface within the evaporator. The condensation-interface temperature is subsequently evaluated using the modified kinetic theory of gases. The present study introduces a novel method to estimate the liquid temperature at the condensation interface. Existence of relative freedom is assumed with regard to the condenser configuration, which is characterized by a simplified liquid–vapor interface. The results obtained in this study demonstrate the effectiveness of the proposed steady-state analytical model with regard to the effect of design variables on LHP heat-transfer performance. To this end, the condenser length, porosity of its capillary structure, and drop in vapor temperature therein are considered as design variables. Overall, the LHP thermal performance is observed to be reasonably responsive to changes in design parameters. Full article
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15 pages, 4076 KiB  
Article
A Novel Analytical Modeling of a Loop Heat Pipe Employing Thin-Film Theory: Part II—Experimental Validation
by Eui Guk Jung and Joon Hong Boo
Energies 2019, 12(12), 2403; https://doi.org/10.3390/en12122403 - 22 Jun 2019
Cited by 3 | Viewed by 2090
Abstract
Part I of this study introduced a mathematical model capable of predicting the steady-state performance of a loop heat pipe (LHP) with enhanced rationality and accuracy. Additionally, investigation of the effect of design parameters on the LHP thermal performance was also reported in [...] Read more.
Part I of this study introduced a mathematical model capable of predicting the steady-state performance of a loop heat pipe (LHP) with enhanced rationality and accuracy. Additionally, investigation of the effect of design parameters on the LHP thermal performance was also reported in Part I. The objective of Part II is to experimentally verify the utility of the steady-state analytical model proposed in Part I. To this end, an experimental device comprising a flat-evaporator LHP (FLHP) was designed and fabricated. Methanol was used as the working fluid, and stainless steel as the wall and tubing-system material. The capillary structure in the evaporator was made of polypropylene wick of porosity 47%. To provide vapor removal passages, axial grooves with inverted trapezoidal cross-section were machined at the inner wall of the flat evaporator. Both the evaporator and condenser components measure 40 × 50 mm (W × L). The inner diameters of the tubes constituting the liquid- and vapor-transport lines measure 2 mm and 4 mm, respectively, and the lengths of these lines are 0.5 m. The maximum input thermal load was 90 W in the horizontal alignment with a coolant temperature of 10 °C. Validity of the said steady-state analysis model was verified for both the flat and cylindrical evaporator LHP (CLHP) models in the light of experimental results. The observed difference in temperature values between the proposed model and experiment was less than 4% based on the absolute temperature. Correspondingly, a maximum error of 6% was observed with regard to thermal resistance. The proposed model is considered capable of providing more accurate performance prediction of an LHP. Full article
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15 pages, 4702 KiB  
Article
Effect of Different Zigzag Channel Shapes of PCHEs on Heat Transfer Performance of Supercritical LNG
by Zhongchao Zhao, Yimeng Zhou, Xiaolong Ma, Xudong Chen, Shilin Li and Shan Yang
Energies 2019, 12(11), 2085; https://doi.org/10.3390/en12112085 - 31 May 2019
Cited by 16 | Viewed by 3063
Abstract
The channels of a printed circuit heat exchanger (PCHE) can have different shapes, and the zigzag channel shape is one of the most widely used because of the relatively simple manufacturing process and low cost. However, the heat transfer enhancement of a zigzag [...] Read more.
The channels of a printed circuit heat exchanger (PCHE) can have different shapes, and the zigzag channel shape is one of the most widely used because of the relatively simple manufacturing process and low cost. However, the heat transfer enhancement of a zigzag channel is at the expense of increasing the pressure drop. In this paper, new channel shapes of a PCHE, i.e., a zigzag with an inserted straight channel and a zigzag channel with radian, were numerically investigated, with the aim of improving the heat transfer and reducing the pressure drop of supercritical LNG using the SST κ-ω model. The local and total pressure drop and heat transfer performance of supercritical LNG in a zigzag channel, zigzags with 1–5 mm inserted straight channels, and a zigzag channel with radian were analyzed by varying the mass flow rate from 1.83 × 10−4 to 5.49 × 10−4 kg/s. Performance evaluation criteria (PEC) were applied to compare the overall heat transfer performance of the zigzags with 1–5 mm inserted straight channels and a zigzag channel with radian to the zigzag channel of a PCHE. The maximum pressure drop for the zigzag channel was twice the minimum pressure drop for the zigzag channel with radian, while the convective heat transfer coefficient of the zigzag with a 4 mm inserted straight channel was higher, which was 1.2 times that of the zigzag channel with radian with the smallest convective heat transfer coefficient. The maximum value of the PEC with 1.099 occurred at a mass flow rate of 1.83 × 10−4 kg/s for the zigzag with a 4 mm inserted straight channel, while the minimum value of the PEC with 1.021 occurred at a mass flow rate of 5.49 × 10−4 kg/s for the zigzag with a 1 mm inserted straight channel. The zigzag with a 4 mm inserted straight channel had the best performance, as it had a higher PEC value at lower mass flow rates. Full article
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16 pages, 4657 KiB  
Article
Thermal Performance of a Low-Temperature Heat Exchanger Using a Micro Heat Pipe Array
by Jingang Yang, Yaohua Zhao, Aoxue Chen and Zhenhua Quan
Energies 2019, 12(4), 675; https://doi.org/10.3390/en12040675 - 20 Feb 2019
Cited by 8 | Viewed by 3820
Abstract
Domestic heat exchangers, even though widely used in industry, are not adequate for studies on low-temperature flue-gas use technologies. Despite spite their limitations, very few theoretical models have been investigated based on practical applications. Moreover, most of the existing studies on heat exchangers [...] Read more.
Domestic heat exchangers, even though widely used in industry, are not adequate for studies on low-temperature flue-gas use technologies. Despite spite their limitations, very few theoretical models have been investigated based on practical applications. Moreover, most of the existing studies on heat exchangers have focused particularly on one-dimensional and two-dimensional heat transfer models, while limited studies focus on three-dimensional ones. Therefore, this study aims at investigating the thermal performance of a low-temperature flue-gas heat recovery unit in the cold regions. Specifically, this study was conducted in the context of Changchun of Jilin Province, China, a city with the mean ambient temperature of −14 °C and mean diurnal temperature of −10 °C during winter. Experimental results showed that the thermal efficiency of the heat exchanger was higher than 60%. Through assessing the heat exchange coefficient and heat exchange efficiency of the heat exchanger, it is found that the thermal efficiency had been improved up to 0.77–0.83. Furthermore, the ICEPAK software and the standard k-ε RNG turbulence model were used to carry out simulations. The velocity and outlet temperature of fresh airflow and polluted airflow were simulated through setting different inlet temperatures of fresh air and polluted air inlet. Numerical results further indicated that the flow state was laminar flow. The micro heat pipe array side had small eddies and the heat transfer was significantly improved due to the flow of air along the surface of the micro heat pipe. Full article
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