Thermal Energy Transfer and Storage

A case study on the melting performance of a shell-and-tube phase change material (PCM) thermal energy storage unit with a novel rectangular fin configuration is conducted in this paper. Paraffin wax and circulated water are employed as the PCM and heat transfer fluid (HTF), respectively. It can be observed that the melting performance could be significantly improved by using rectangular fins. Melting photographs demonstrate that the melting of the PCM is firstly dominated by heat conduction; then, the melting rate is improved further due to natural convection. Moreover, the results illustrate that the influence of the inlet HTF temperature on the melting performance is significantly greater than that of the inlet HTF flow rate. The liquid fraction of paraffin wax in the PCM unit with a higher inlet HTF temperature is always higher than that with a lower inlet HTF temperature at the same time. The total charging time is reduced by 62.38% and the average charging rate is increased by 165.51% when the inlet HTF temperature is increased from 57 °C to 68 °C. As a result, a higher value of the inlet HTF temperature and a lower value of the HTF flow rate are able to improve the energy efficiency of the PCM unit with a rectangular fin configuration. Full article

Thermal energy storage is an essential technology for improving the utilization rate of solar energy and the energy efficiency of industrial processes. Heat storage and release by the dehydration and rehydration of Ca(OH)₂ are hot topics in thermochemical heat storage. Previous studies have described different methods for improving the thermodynamic, kinetic, and structural stability of Ca(OH)₂ to improve energy storage density, energy storage rate, and cycle stability, respectively. Here, the mechanisms and effects of different techniques on the performance improvement of Ca(OH)₂ and some common problems were reviewed. Specific problems were also clarified based on the characteristics of different technologies. Finally, suggestions for the future development of Ca(OH)₂ heat storage materials were provided. Full article

This study reports an experimental investigation of pool boiling (PB) heat transfer performance of hybrid (two types of particles) and mono (single-particle) nanofluids consisting of Boron nitride (BN) and Silicon dioxide (SiO₂) nanoparticles (NPs). While hybrid nanofluids (HNFs) were prepared in a total particle concentration of 0.05 vol.% with four different percentages of these two types of NPs (are 0.01/0.04, 0.02/ 0.03, 0.03/0.02, and 0.04/0.01 (BN vol.%/SiO₂ vol.%)), two mono nanofluids (MNFs) of BN and SiO₂ nanoparticles were prepared at the same total concentration of 0.05 vol.% for each NP type. Both nanofluids (NFs) were prepared in the base fluid (BF), which is the mixture of 15 vol.% of ethylene glycol (EG) and 85 vol.% of distilled water (DW). Then, the boiling heat transfer performance of these MNFs and HNFs was assessed by experimentation in a pool boiling test rig. The obtained results demonstrated good improvements in critical heat flux (CHF) and burnout heat flux (BHF) of both types of NFs. The CHF increased by up to 80% for BN-based MNF and up to 69% for HNF at 0.04 vol.% BN, which is the maximum percentage of BN into HNF, while the lowest improvement in CHF was 48% for the SiO₂-based MNF compared to the BF. Similarly, the BHF was found to increase with the increasing in the loading of BN nanoparticles and a maximum enhancement of BHF of 103% for BN-based MNF was observed. These HNFs and MNFs exhibited significantly improved pool boiling heat transfer performance compared to this BF, and it became lower by increasing the percentage of SiO₂ NPs in the HNFs. Full article

Thermal energy storage (TES) has a strong ability to store energy and has attracted interest for thermal applications such as hot water storage. TES is the key to overcoming the mismatch between energy supply and demand by using phase change materials (PCMs). However, a common organic PCM characteristic is low thermal conductivity. This causes a slow thermal response for paraffin-AP25, which is not suitable for many applications. Hence, a search is underway for modifications to enhance its thermal properties. Thus, the current investigation introduces a novel PCM system based on the use of waste material as an economic and efficient system. In the current investigation, nanoparticles were added to a PCM; specifically, a technical-grade paraffin-AP25 wax (AP25 wax)/hybrid composite was synthesized via ultrasonic dispersion. The focus of this investigation is to assess the behavior of a PCM for energy storage via charging (melting process) and discharging (solidification process). Nanoparticles of magnetite were prepared via a simple, cost-efficient route, co-precipitation, augmented with aluminum and silicon derived from waste streams from a hydrothermal facility and mixed with paraffin-AP25 wax to form a hybrid composite PCM. Transmission electron microscopy and scanning electron microscopy (augmented with dispersive X-ray analysis, EDX) micrographs, in addition to X-ray diffraction (XRD), show the prepared composite. Different mass fractions of the composite, ranging from 1 to 10 weight %, were embedded in a paraffin-AP25 phase change material. The latent heat storage capacity of the PCM was enhanced by 8% when paraffin-AP25 was applied. Finally, the overall system efficiency was evaluated, and the yield increased by 64% for the 8% hybrid composite. Full article

In view of the main problems of the condensing heat discharge modes of the existing underground air-conditioning system, the technical scheme of using phase change heat storage modules to improve the heat storage capacity of the reservoir is proposed. By establishing a 3D flow and transient heat transfer model of the phase change reservoir, the effects of thermal property parameters, package size and arrangement of the phase change heat storage modules on the heat storage performance of the phase change reservoir were quantitatively analyzed based on three indexes: heat storage capacity per volume Δq, guaranteed efficiency coefficient η and slope of temperature rise per unit load ε. The results show that when the phase change temperature is 29 °C (23 °C increased to 33 °C) and the latent heat value is 250 kJ/kg (100 kJ/kg increased to 250 kJ/kg), Δq (110.92 MJ/m³, 112.83 MJ/m³) and η (1.22, 1.24) under both conditions are at their most, respectively, indicating that the phase change temperature should be less than 4 °C at the outlet temperature of the reservoir, and phase change materials with a high latent heat should be selected in engineering design whenever possible. When the size of the phase change module is 150 mm × 20 mm and the phase change reservoir adopts four intakes, ε (0.259, 0.244) under both conditions is the smallest, indicating that increasing the area of the phase change heat storage module and the fluid and increasing the inlet disturbance of the reservoir can enhance its heat storage capacity. Full article

To save and better deploy waste heat, the use of a mobilized heat storage system (MHSS) with phase change enhancement means is developed. In this paper, three kinds of gradient structures (positive gradient, negative gradient, and non-gradient) are designed in the MHSS system. The uniform porosity is 94% in the non-gradient structure, and the gradient porosities are 86%, 93%, and 98% in the gradient structure, respectively. Numerical models are developed to explore the contribution of the graded metal foam structure to the heat storage and release process. An economic analysis and comparison of MHSS systems with different heat transfer models are carried out. The results show that the positive gradient case can promote the thermal cycle of the melting and solidification process, while the negative gradient case inhibits the thermal cycle. The positive gradient case can reduce the melting time by 9.7% and the solidification time by 4.4%, while the negative gradient can prolong the melting time by 31.4% and the solidification time by 35.9%. Although graded metal foam increases the initial investment by 76.09%, the 1 KW·h heat cost of graded metal foam is reduced by 10.63% compared to pure phase change material (PCM). It is cost-effective in the long run of thermal cycles. Full article

In the first months of 2022, there was a sharp turn in the energy policy of the European Union, initially spurred by increasing energy prices and further escalated by Russia’s invasion of the Ukraine. Further transformation of the energy system will likely be accompanied by the gradual abandonment of natural gas from Russia and an increase of renewable and nuclear energy. Such a transition will not only increase energy security, but also accelerate the pace at which greenhouse gas emissions are reduced in Europe. This could be achieved more effectively if some of the new nuclear energy capacity is optimized to play an increased balancing role in the energy system, thus allowing for deeper market penetration of intermittent renewable energy sources with a reduced need for flexible fossil backup power and storage. A double effect of decarbonization can be achieved by investments in nuclear repowering of coal-fired units, with the replacement of coal boiler islands with nuclear reactor systems. Repowered plants, in turn, operate flexibly via integration with thermal energy storage systems using molten salt. This paper presents the results of a technoeconomic analysis for three cases of nuclear repowering of a 460 MW supercritical coal-fired unit in Poland. The first reference case assumes that three reactors are replacing the existing coal boilers, while the second reference leverages two reactors. The third uses two nuclear reactors equipped with a molten salt thermal energy storage system as a buffer for the heat produced by the reactor system. The analysis of the third case demonstrates how the TES system’s capacity varies from 200 to 1200 MWh, highlighting the possibility of obtaining a high degree of flexibility of the nuclear unit due to TES system without significant drops in the efficiency of electricity production. The economic analysis demonstrates that integration with TES systems may be beneficial if the current levels of daily variation in electricity prices are maintained. For current market conditions, the most attractive investment is a case with two reactors and a TES system capacity of 800 MWh; however, with the increasing price volatility, this grows to a larger capacity of 1000 or 1200 MWh. Full article

Energy storage technology provides a new direction for the utilization of renewable and sustainability energy. The objective of this study is to introduce a novel, wavy, longitudinal fin design, which aims to improve heat transfer in the melting process of a Latent Heat Thermal Energy Storage (LHTES) unit. The main goal is to mitigate the negative effects caused by the refractory zone at the end of the melting phase. A two-dimensional numerical model of LHTES unit is established by using the enthalpy porosity method and verified by experimental data. Through the quantitative comparison between the traditional rectangular fin and the innovative wave fin, the influence of wave fin on the heat transfer mechanism in the heat storage process is revealed. The results show that the average heat storage rate of five and six wave fins is 3.70% and 12.98% higher than that of conventional rectangular fins, respectively, and the average temperature response of six wave fins is 17.78% higher than that of conventional rectangular fins. The addition of the wave fin weakens the negative effect of the refractory zone, but prolongs the heating time of the initial melting point. Full article

Magnetic anisotropy strongly influences the performance of the magnetocaloric effect. We investigated the magnetocaloric properties of the NdAlGe single crystal with I4₁md structure. The temperature-dependent magnetization revealed significant anisotropic properties; stable antiferromagnetic transition at T_N = 6 K for H//a and meta-magnetic spin reorientation at low temperature (T ≤ 5 K) within an intermediate field (H = 2 T) for H//c. During the metamagnetic spin reorientation, the abrupt change of the magnetic entropy leads to a significant magnetocaloric effect with negative magnetic entropy change (∆S_M) by −13.80 J kg⁻¹ K⁻¹ at T_C = 5.5 K for H = 5 T along the H//c axis. In addition, the antiferromagnetic state for H//a shows the inverse magnetocaloric effect(I-MCE) by positive entropy change ∆S_M = 2.64 J kg⁻¹ K⁻¹ at T_N = 6 K for H = 5 T. This giant MCE accompanied by the metamagnetic transition resulted in a significantly large relative cooling power (158 J/kg at H = 5 T) for H//c. The giant MCE and I-MCE can be applied to the rotational magnetocaloric effect (R-MCE) depending on the crystal orientations. NdAlGe exhibits rotational entropy change ∆S_c−a = −12.85 J kg⁻¹ K at T_peak = 7.5 K, H = 5 T. With comparison to conventional MCE materials, NdAlGe is suggested as promising candidate of R-MCE, which is a novel type of magnetic refrigeration system. Full article

Thermal energy storage (TES) systems are dependent on materials capable of operating at elevated temperatures for their performance and for prevailing as an integral part of industries. High-temperature TES assists in increasing the dispatchability of present power plants as well as increasing the efficiency in heat industry applications. Ordinary Portland cement (OPC)-based concretes are widely used as a sensible TES material in different applications. However, their performance is limited to operation temperatures below 400 °C due to the thermal degradation processes in its structure. In the present work, the performance and heat storage capacity of geopolymer-based concrete (GEO) have been studied experimentally and a comparison was carried out with OPC-based materials. Two thermal scenarios were examined, and results indicate that GEO withstand high running temperatures, higher than 500 °C, revealing higher thermal storage capacity than OPC-based materials. The high thermal energy storage, along with the high thermal diffusion coefficient at high temperatures, makes GEO a potential material that has good competitive properties compared with OPC-based TES. Experiments show the ability of geopolymer-based concrete for thermal energy storage applications, especially in industries that require feasible material for operation at high temperatures. Full article

Domestic water heating accounts for 15% to 27% of the total energy consumption in buildings in Australia. Over the past two decades, the latent heat thermal energy storage (LHTES) system has been widely investigated as a way to reduce fossil fuel consumption and increase the share of renewable energy in solar water heating. However, the research has concentrated on the geometric optimisation of the LHTES heat exchanger for the past few years, and this might not be sufficient for commercialisation. Moreover, recent review papers mainly discussed the development of a particular heat-transfer improvement technique. This paper presents perspectives on various solar hot water systems using LHTES to shift focus to on-demand performance studies, as well as structure optimisation studies for faster commercialisation. Future challenges are also discussed. Since the topic is an active area of research, this paper focuses on references that showcase the overall performance of LHTES-assisted solar hot water systems and cannot include all published work in the discussion. This perspective paper provides directional insights to researchers for developing an energy-efficient solar hot water system using LHTES. Full article

The purpose of this study was to develop a process to convert input signals from one facility into another by reflecting geometric and environmental settings. The Dynamic Energy Transport and Integration Laboratory (DETAIL) is one facility in development that aims to emulate the daily interactions among power production industry systems and be capable of receiving real-time data from those systems as inputs. To convert signals and ensure that the temporal sequences and magnitudes reflect the laboratory settings, the ability to scale and project data is essential. To demonstrate this ability, Dynamical System Scaling (a methodology that enables systems to scale and project or extrapolate datasets to desired environments while conserving the observed transient behavior based on first principles) was applied to DETAIL’s thermocline thermal storage system in the Thermal Energy Distribution System. The thermocline system was successfully scaled and a test case was conducted to generate a doubly accelerated energy charge and discharge in reference to past experimental data from the facility. The accelerated data were determined as able to conserve the amount of energy stored and the associated test boundary conditions were charge line maximum temperature, charge line velocity, and thermocline maximum temperature at 354 °C, 0.458 m/s, and 418 °C, respectively. The research results represented a case that required signals to be accelerated without altering the stored energy. Full article

In this work, a commercial paraffin PCM (RT35) characterized by a change range of the solid-liquid phase transition temperature $T_{\mathrm{s}-\mathrm{l}}=29–36$ °C and the low thermal conductivity ${\lambda }_{\mathrm{SL}}=0.2$ W/m K is experimentally tested by submitting it to thermal charging/discharging cycles. The paraffin is contained in a case with a rectangular base and heated from the top due to electrical resistance. The aim of this research is to show the benefits that a 95% porous copper metal foam (pore density $PD=20PPI$) can bring to a PCM-based thermal storage system by simply loading it, due to the consequent increase in the effective thermal conductivity of the medium (${\lambda }_{\mathrm{LOAD}}=7.03$ W/m K). The experimental results highlight the positive effects of the copper foam presence, such as the heat conduction improvement throughout the system, and a significant reduction in time for the complete melting of the PCM. In addition, the experimental data highlight that in the copper-foam-loaded PCM the maximum temperature reached during the heating process is lower than $20K$ with respect to the test with pure PCM, imposing the same heat flux on the top ($P=3.5$ W/m²). Full article

In this work, a new method for constructing the infinite-dimensional Ornstein–Uhlenbeck stochastic process is introduced. The constructed process is used to perturb the harmonic system in order to model anomalously fast heat transport in one-dimensional nanomaterials. The introduced method made it possible to obtain a transition probability function that allows for a different approach to the analysis of equations with such a disturbance. This creates the opportunity to relax assumptions about temporal correlations for such a process, which may lead to a qualitatively different model of energy transport through vibrations of the crystal lattice and, as a result, to obtain the superdiffusion equation on a macroscopic scale with an order of the fractional Laplacian different from the value of 3/4 obtained so far in stochastic models. Simulations confirming these predictions are presented and discussed. Full article

Refrigerant maldistribution severely deteriorates the heat transfer performance of a microchannel evaporator. Compared with the refrigerant distribution among flat tubes along the header, refrigerant distribution among microchannels in the flat tube in the airflow direction has barely been paid attention. In this paper, a heat transfer mathematical model of a microchannel evaporator’s flat tube composed of vertically placed parallel microchannels in the airflow direction was developed. The Refrigerant distribution among the microchannels was evaluated and its influence on heat transfer between air and refrigerant was analyzed. The results showed that the refrigerant distribution and heat transfer performance between air and refrigerant were interrelated and interacted with each other. The temperature of the air leaving the microchannel evaporator changed along the microchannel because of uneven refrigerant distribution among the microchannels, and the air temperature difference between air leaving out of the bottom and the top of the evaporator was approximately 2.13 °C. Ignoring the heat transfer from adjacent microchannels will lead to a small heat transfer deviation for the flat tube; thus, heat transfer among microchannels can be neglected. Full article

In this paper, we propose a concise but general two-dimensional model based on the penetration model in order to simulate the heat and mass transfer and drying kinetics of sludge in the paddle dryer. The sludge control equations were developed to simulate the heat and mass transfer of sludge and the penetration model was introduced to describe the mixing of sludge. Compared to the experimental results in the existing literature, the drying kinetics simulated simulated by the present model were in good agreement with the experimental data under various operation conditions. The effects of four key parameters on drying kinetics in the paddle dryer were studied. The results showed that the water content increased with the increase of sludge flowrate and the decrease of wall temperature and sludge density. Furthermore, the stirring velocity had little effect on the drying kinetics of the sludge. The present study contributes to the better understanding of the sludge drying kinetics and provides guidance for the optimal design of industrial paddle dryers. Full article

Fractional-order proportional integral derivative (FOPID) controllers are becoming increasingly popular for various industrial applications due to the advantages they can offer. Among these applications, heating and temperature control systems are receiving significant attention, applying FOPID controllers to achieve better performance and robustness, more stability and flexibility, and faster response. Moreover, with several advantages of using FOPID controllers, the improvement in heating systems and temperature control systems is exceptional. Heating systems are characterized by external disturbance, model uncertainty, non-linearity, and control inaccuracy, which directly affect performance. Temperature control systems are used in industry, households, and many types of equipment. In this paper, fractional-order proportional integral derivative controllers are discussed in the context of controlling the temperature in ambulances, induction heating systems, control of bioreactors, and the improvement achieved by temperature control systems. Moreover, a comparison of conventional and FOPID controllers is also highlighted to show the improvement in production, quality, and accuracy that can be achieved by using such controllers. A composite analysis of the use of such controllers, especially for temperature control systems, is presented. In addition, some hidden and unhighlighted points concerning FOPID controllers are investigated thoroughly, including the most relevant publications. Full article

Modern aircraft and missiles are gradually integrating thrust vector control systems to enhance their military capabilities. Bypass Dual-Throat Nozzle (BDTN) control is a new fluidic thrust vectoring technique capable of achieving superior performance with large vector angles and low thrust loss. In this study, we analyzed the flow characteristics and performance parameters of BDTN by varying the bypass angle, nozzle convergence angle, and bypass width. The flow governing equations are solved according to a finite volume discretization technique of the compressible RANS equations coupled with the Renormalization Group (RNG) k-ϵ turbulence model for Nozzle Pressure Ratio (NPR = 2~10) to capture the significance of under-expanded and over-expanded jets. Results show that by decreasing the bypass angle from 90° to 35°, there is a 6% increase in vectoring angle while the vectoring efficiency is enhanced by 18%. However, a decrease of 3% in the thrust and discharge coefficients is also observed. When the convergence angle was increased from 22° to 37°, vectoring angle, discharge coefficient, and thrust coefficient increased by 2%, 1%, and 0.26%, respectively. Moreover, vectoring efficiency is also enhanced by 8% by reducing the convergence angle from 37° to 22°. Based on the investigated parameters, it is determined that nozzle convergence angle does not significantly influence thrust vectoring performance, however, bypass width and bypass angle have a significant effect on thrust vectoring performance. Full article

Thermo-mechanical energy storage can be a cost-effective solution to provide flexibility and balance highly renewable energy systems. Here, we present a concise review of emerging thermo-mechanical energy storage solutions focusing on their commercial development. Under a unified framework, we review technologies that have proven to work conceptually through project demonstration at a scale above 1 MW by describing the current state of commercial development, quantifying techno-economic parameters, outlining the challenges, and assessing each technology’s potential for commercial viability. The levelized cost of storage for thermo-mechanical energy storage at storage duration between 8 h and 1 week is cheaper than that of lithium-ion batteries and hydrogen storage; however, energy storage for such duration does not pay for itself at the current renewable penetration levels. For medium-term energy storage to be viable, at the realistic storage cost of 15 USD/kWh to 40 USD/kWh, the investment cost for power components should decrease to one-fifth of the current costs. Thermo-mechanical energy storage can be economically viable at the current investment costs in off-grid systems only when the marginal cost of alternative fuel exceeds 100 USD/MWh. We identified the cost ratio (charge power cost/discharge power cost) and the discharge efficiency as the critical technology-related performance parameters. Other external factors such as wind and solar fractions, demand, interconnections, sector coupling, and market structure play an important role in determining the economic feasibility of thermo-mechanical energy storage. Full article

Solar energy is a sustainable source that can be effectively utilized to address winter heating challenges in buildings. To ensure the efficient application of solar energy for heating purposes and to maintain reliable performance of the heating system, the integration of phase-change materials (PCMs) in thermal energy storage (TES) systems has emerged as a crucial auxiliary approach. This study focuses on the design and simulation of four TES structures: smooth, finned, metallic foam, and metallic foam-finned tubes. It explores their thermal characteristics, such as complete melting time and heat flux, under various flow conditions. Additionally, a residential building in Xi’an is selected as the object, where the proposed solar energy phase-change TES system is employed to meet the heating demand. Economic indicators, including initial investment and investment payback period, are estimated using a static evaluation method. The results highlight that the complete melting time of the TES unit with a metallic foam-finned tube is 4800 s, which is 88.3% less than the smooth tube. Finally, based on the actual project, it is determined that the metallic foam-finned heating system, with an HTF flow rate of 0.25 m/s, requires the fewest TES devices (914) and has a payback period of 13 months. Full article