Heat Storage Material Research Articles

Numerical and experimental analysis of instability in high temperature packed-bed rock thermal energy storage systems

Due to heat losses of preferential areas of packed-bed energy storage systems, transverse temperature variations may occur during the charging, discharging and standby processes. Furthermore, the heat losses of preferential areas of the storage tank cause a lower pressure drop in these areas resulting in an increased mass flow rate and further cooling, and thereby an enhanced transverse temperature variation, in a positive feedback loop – a phenomenon called instability. The transverse temperature variations may deteriorate the performance and thereby the economic feasibility of packed-bed energy storage systems. In this paper, numerical and experimental investigations of an air-based packed-bed rock thermal energy storage system for large-scale high temperature applications are presented. The objective of the study is to predict the instability and to analyze the effect of different standby durations and storage size on the instability of the air-based packed-bed system. Transient axisymmetric computational fluid dynamics models were developed for the standby and discharging processes of the packed-bed thermal energy storage systems. In addition, experimental investigations were carried out at a test facility located at Stiesdal Storage, Denmark, using magnetite rocks as heat storage material and air as heat transfer fluid. The results suggest that the numerical predictions are in good agreement with the test data. The instability phenomenon is found to increase with the standby duration, resulting in a maximum difference of 161 K between the maximum rock temperature and the outlet air temperature for a standby period of 10 h followed by a discharging process. Moreover, the results indicate that the maximum difference between the rock temperature and outlet temperature is 73 K and 56 K for a reduced-scale and a full-scale system (no standby period), respectively.

Impact of wind-driven mixed convection on the performance of passive solar desalination with PCM heat storage in varied Moroccan climates

Mixed convection flows are commonly observed in various technological and industrial applications, including solar stills that are exposed to wind currents and other weather conditions. Combined free and forced convection flows can significantly improve the productivity of solar still devices, making them of practical interest. In fact, a passive solar desalination system with heat storage material is investigated in six climate zones of Morocco and presented by six cities namely: Tangier, Rabat, Ifran, Marrakech, Meknes and Errachidia. This study aims to analyze the effect of mixed convection on the inclined surface of solar desalination systems. Thus, a transient Computational fluid dynamics (CFD) model is developed and investigated under the instantaneous climatic data of the different cities aforementioned. The results indicate that forced convection dominated heat transfer during broad daylight, with the Nusselt number increasing as the Reynolds number increased. Overall, the productivity in Tangier city was found to be significantly higher than that of Rabat, Meknes, Marrakech, Ifran, and Errachidia city, with increases of 45.02%, 50.48%, 23.48%, 83.31%, and 24.89%, respectively.

Numerical analysis of thermal storage and release performance of mechanical thermal storage based on 2-D thermal conductivity differential equation

In order to understand the numerical analysis of the thermal storage and release performance of mechanical heat storage materials, the author proposes a study on the numerical analysis of the thermal storage and release performance of mechanical heat storage materials based on 2-D thermal conductivity differential equations. The author first studied the phenomenon of iron resistance in the sleeve on the overall heat storage performance of the magnesium brick, and made two conclusions about the number of magnets in the sleeve brick. Second, ANSYS is used to model the exothermic process of mechanical heat storage, analyze the temperature distribution, flow field distribution, heat transfer coefficient of heat storage under different conditions, and compare the experimental results. Finally, the experiment shows that the addition of the sleeve does not affect the overall heat storage performance of the magnetic brick, which can extend the service life of the resistance metal and provides some support for the expansion of the use of the heat storage material of the magnetic brick. By using the numerical calculation method to calculate the error, it can be seen that the error between the numerical simulation and experimental results is less than 16, and the experimental results are consistent with the experimental results. The ability to store and release heat of a heat storage facility depends largely on its size structure, and the heat storage and release ability of a small heat storage facility is better than that of a large heat storage facility. For heat storage materials with high thermal conductivity, their heat transfer coefficient will increase with increasing temperature, but the increase is not significant. For thermal accumulators with low thermal conductivity, their heat transfer coefficient will decrease with increasing temperature.

Energy and Exergy Analysis of Forced Convection Solar Drying of Allium Sativum With and With Out Sensible Heat Storage

In this article the energy & exergy analysis of forced convection solar dryer for drying of garlic has been investigated. The exergy parameter, air velocity has been taken to conduct the experiments and its effect on thermal efficiency. Forced draft fans were used in all the two working conditions. During the two conditions, with and without sensible heat storage system, the average air-velocities were 4.5, 9.5 and 11.4 m/s selected as ideal and subsequently its entire effect on thermal efficiency and outlet. The ambient temperatures were between (17-25) °C during the month of October and November. A DC fan is directly connected to the photovoltaic cell in the solar dryer. The thermal energy storage bed was packed with gravels with 1.5 in of thickness up to the surface of flat plate collector, the storage system becomes space-efficient. The average thermal efficiency with sensible heat storage materials was high as compared to system without sensible heat storage. The highest thermal efficiency of 61% was achieved. The maximum collector temperature obtained was 55 °C, with a mean temperature of 42 °C in the drying chamber. The collector’s greatest exergy loss was 30.38 kJ/kg and highest exergy efficiency was 70%.

New materials for the recovery and storage of thermal energy

A significant fraction of the energy generated for industrial and domestic applications is lost in the form of heat. Because of this, thermal-energy storage materials are receiving increasing attention as a means of storing the generated heat for later use. In this paper, a brief description is given of two types of materials used in thermal-energy-storage devices – phase change materials for latent heat storage and photoswitches for chemical energy storage. In addition, we provide a succint account of the experimental and computational tools needed to understand the microscopic mechanisms of energy storage and to facilitate the rational design of new materials.

Analysis of thermal characteristics and thermal storage performance of energy-saving phase change thermal storage materials in buildings

In order to explore the thermal characteristics and thermal storage performance analysis of energy-saving phase change heat storage materials in buildings, taking the common exterior wall insulation composite wall structure in southwestern China as an example, the influence of insulation board structure thickness design on the total cost of residential air conditioning energy consumption and insulation board cost is studied, thus clarifying the concept and calculation origin of economic insulation thickness. The experimental results show that by drawing mathematical functions of energy consumption cost, total cost, and insulation material cost in the same 2-D coordinate, it is intuitively demonstrated that the minimization of total cost can be ensured when the insulation thickness is in an economic state, and the specific economic thickness can be accurately calculated through example data. Therefore, specific measures for improving external wall insulation from refined insulation structure design are proposed. It has been proven that the design of the exterior wall insulation layer structure is an important way to improve the overall energy-saving benefits of building exterior wall insulation.

Scheffler reflector based solar cooking system with dual sensible heat storage material for night cooking application: an experimental investigation

Scheffler reflector based solar cooking system with dual sensible heat storage material for night cooking application: an experimental investigation

Design and manufacturing of forming molds for thermal storage materials and analysis of their thermal storage structures

In response to the shortcomings of concentrated stress, difficult forming, and short service life of commonly used honeycomb ceramic thermal storage materials with square lattice holes, the author has developed a new type of low stress honeycomb ceramic thermal storage material by studying the structure, forming mold, and extrusion forming material of the thermal storage body. The author introduced the changes in specific surface area and porosity of heat storage materials with different geometric structures, and analyzed and compared the structural characteristics of two types of heat storage materials, namely heat storage balls and honeycomb bodies, under the premise of equal heat storage capacity. The trajectory of air-flow in the heat storage chamber was simulated using CFD software, and the pressure loss and centerline velocity changes of different shapes of honeycomb were analyzed. The flow characteristics, pressure distribution, and heat transfer performance of gas inside different shapes of honeycomb were calculated. The experimental results showed that the closer to the circular shape, the smaller the pressure loss of the centerline. The larger the equivalent diameter, the smaller the resistance along the path. From the perspective of cold pressure loss alone, regular quadrilateral holes and regular circular holes are the best choices for the shape of honeycomb openings. The centerline velocity of the equilateral triangle hole is the largest, indicating that the smaller the equivalent diameter is, the greater the average velocity at the outlet is. The resistance along the path of the round hole is the smallest, the regular quadrilateral hole is slightly larger, and the pressure loss of the equilateral triangle hole is the largest, which exceeds the round hole by nearly 1/3. Taking into account factors such as heat storage, specific surface area, flow characteristics, and heat transfer characteristics, quadrilateral honeycomb cells are the best choice.

Visual Simulation of Composite Material Performance Inspection and Interior Decoration Based on Sensor Image Recognition

Abstract Wood-plastic composites, as green eco-materials, are widely used in the field of home and building materials, but with a single function. Phase-change heat storage materials can store or release heat through a physical phase transition to achieve energy savings and emission reduction. In this paper, plant fibers are used as the matrix, which is introduced into wood-plastic composites to construct a function/structure-integrated shaped phase change heat storage wood-plastic composites and endow the wood-plastic composites with the function of storing and releasing heat. The performance of wood-plastic composites is examined using image recognition and X-ray imaging. Simulating and analyzing the thermoregulatory and energy-saving functions of phase change wood-plastic composites in the building heating environment was done by establishing a heat transfer model. Finally, the material was visualized and applied to the interior decoration. The results show that the apparent density of the wood-plastic composite material is 1.15 g/cm3, the tensile property is 42.8 MPa, the flexural modulus is 2455 MPa, and its comprehensive physical and mechanical properties are better than those of the solid wood core when the amount of plant fiber added is 40 phr. At the same time, the thermal conductivity of this material is improved by 7.74% compared with the traditional solid wood core, which shows good energy saving and temperature regulation effects and possesses the potential of energy saving when applied in interior decoration.

Scheffler reflector based solar cooking system with dual sensible heat storage material for night cooking application: An experimental investigation

Scheffler reflector based solar cooking system with dual sensible heat storage material for night cooking application: An experimental investigation

НАПРЯМКИ ПОКРАЩЕННЯ ОСНОВНИХ ХАРАКТЕРИСТИК ТЕПЛОВИХ АКУМУЛЯТОРІВ ТА ТЕПЛОАКУМУЛЯЦІЙНИХ МАТЕРІАЛІВ

The article is devoted to the study of heat storage technologies as the main energy saving measure. The paper conducts a patent search and analyzes scientific papers that cover the issue and present the main material of existing technologies for thermal energy storage. The classification of the main types of heat accumulators (HA) and heat storage materials (HSM) is presented. Heat accumulators are classified: by the nature of accumulation; by the level of operating temperatures; by the duration of the charge-discharge period. The differences and design features of TAMs, advantages and disadvantages are analyzed. The main heat storage materials that are actually used or can be used in the future are identified. The thermophysical properties of heat storage materials, such as specific heat capacity, melting point, density, and density, are described.
 The methodology for calculating the volume of capacitive and phase-transition heat accumulators is determined based on the following initial data: the type of heat storage material, the type and thermal characteristics of the heat carrier, and the temperature drop of the heat storage material. Examples of the practical use of capacitive batteries are given, in particular, a tank battery in a solar heating system, as well as a gravel battery in a solar vegetable garden. The use of crystalline hydrates and organic low-melting compounds (fatty acids and paraffins) as phase-transition heat storage materials is described. The characteristics of thermochemical thermal accumulators, their principle of operation, and their advantages over capacitive and phase-transition accumulation units are presented. The reactions of enrichment of traditional carbon fuels are described, and examples of reactions that can be used as heat storage processes are given. Prospects for further research are identified.

PONDERING THE CHOICE OF PCM AND MATHEMATICAL MODEL IN AUTOMOTIVE LHTS

Phase change materials are latent heat storage materials. As the source temperature rises, the chemical bonds within the PCM break up as the material changes phase. Upon storing heat in the storage material, the material begins to melt when the phase change temperature is reached. The temperature then stays constant until the melting process is finished. The heat stored during the phase change process of the material is called latent heat. Ideally, automotive engine cooling is undesirable from the thermodynamic point of view. If the heat transfer rates from the gas to metal could be reduced, then more power could be produced at a particular fuel flow rate, i.e. the thermal efficiency of the engine would increase. Also the heat removed out via radiator could be reduced and hence smaller radiator size. That is why powertrain thermal management is extremely necessary for good engine reliability and durability with a compromise of the thermal efficiency. One of the most technically and commercially available options for this is the use of latent heat thermal energy storage system. Despite the fact that there are numerous works and reviews covering this topic, the author hopes to draw attention to some aspects of the choice of material and mathematical model for such systems. Keywords: phase-change materials, latent heat, energy storage systems, thermal conductivity, thermo-physical properties, kinetic properties.

From copper concentrate to Cu-based metal oxides for thermochemical heat storage: Impurity impact analysis and redox performance optimization

Copper oxide is a promising material for thermochemical heat storage, but its high cost remains a challenge for large-scale applications. To address this issue, we explore using relatively cheap copper concentrate as a starting material. We heat treat the concentrate and find that it mainly consists of CuO and CuFe2O4. Our thermogravimetric analysis shows that the re-oxidation performance of the concentrate is poor, with only 12.5 % reaction, which is about 32.5 % lower than that of commercial copper oxide (≥99.5 %). Our investigation reveals that impurities in the concentrate inhibit the re-oxidation of copper oxide, and their removal is essential to improve performance. Based on these findings, we optimize the existing purification process that removes impurities to less than 0.1–0.5 wt%. The resulting copper oxide has a content above 99 % and an extraction rate of over 97 %, which can minimize the waste of raw materials and reduce the influence of impurities. The redox properties of the purified copper oxide are comparable to those of commercially available copper oxide. On this basis, the self-made CuO was modified by doping with cheap MgO and Al2O3, whose reduction conversion rate and reoxidation rate could still reach 97.0 % and 96.3 % after 250 redox cycles.

Theoretical and experimental analysis of box-type solar cooker with sensible heat storage

The thermal performance of the current box-type solar cooker is limited, and no provision for evening cooking, which could increase its dependability and attract more consumers. The thermal performance and evening cooking capabilities can be enhanced by employing the waste marble pieces as integrated or portable heat storage material. Also, suggested using a matt black coated aluminium sheet placed additionally below the glass cover to reduce the top heat losses. In this work, two arrangements were proposed: (I) a cooking load with heat storage but no aluminum sheet, and (II) a cooking load with both aluminum sheet and heat storage. The scope of improvement is evaluated using the COMSOL Multiphysics 6.0 software tool and experimental testing conducted in an outdoor environment. The cooking times for arrangements I and II are evaluated experimentally as 154–155 min and 175–176 min respectively, corresponding cooking power are measured as 56.62 W and 48.21 W, respectively and the corresponding thermal efficiencies are 25.79 % and 31.19 %, respectively. The optimal time for heating various weights of marble pieces is investigated using an aluminum sheet cover since the thermal performance and temperature availability till late evening are relatively low. The proposed solar cooker has a payback period of 1.24 years. It is concluded that installing a single solar cooker for two members of a family reduces a total of 148.3 kg of carbon dioxide annually.

Evaluation of shape-stabilized phase-change materials using calcium carbonate-based starfish microporous materials for thermal energy storage

This study investigates the synergistic potential of shape-stabilized phase-change materials (PCMs) integrated with calcium carbonate-based starfish microporous materials for efficient thermal energy storage. By addressing challenges related to traditional PCMs, such as leakage and stability, this research aims to enhance thermal energy storage capabilities. Starfish and bio-based PCMs prepared from starfish were subjected to porosity, thermophysical, and chemical analyses. The porosity analysis revealed that the surface and skeleton of the starfish had sufficient porosities to contain liquid PCMs inside, and the bio-based PCM formed closed cells in the starfish, effectively blocking leakage to the outside. The maximum latent heat, which indicates the thermal energy storage capacity, was 57.66 J/g. This demonstrated thermal stability below 150 °C, making it suitable as a building material. The chemical analysis revealed that bio-based PCM was composed of carbon, oxygen, and calcium commonly found in sea creatures, and it was confirmed that there was no chemical change during phase stabilization, confirming that it was chemically stable. Therefore, the manufactured bio-based PCM has potential as an eco-friendly heat-storage material.

Development of NaCl-MgCl2-CaCl2 Ternary Salt for High-Temperature Thermal Energy Storage Using Machine Learning.

NaCl-MgCl2-CaCl2 eutectic ternary chloride salts are potential heat transfer and storage materials for high-temperature thermal energy storage. In this study, first-principles molecular dynamics simulation results were used as a data set to develop an interatomic potential for ternary chloride salts using a neural network machine learning method. Deep potential molecular dynamics (DPMD) simulations were performed to predict the microstructure and thermophysical properties of the NaCl-MgCl2-CaCl2 ternary salt. This work reveals that DPMD simulations can accurately calculate the microstructure and thermophysical properties of ternary chloride salts. The association strength of chloride ions and cations follows the order of Mg2+ > Ca2+ > Na+, and the coordination number decreases gradually with increasing temperature, indicating a progressively looser and more disordered molten structure. Furthermore, thermophysical properties, such as density, specific heat capacity, thermal conductivity, and viscosity, are in good agreement with the experimental measurements. Machine learning molecular dynamics will provide a feasible multivariate molten salt exploration method for the design of next-generation solar power plants and thermal energy storage systems.

Thermal performance analysis and thermal environment creates effect of a novel solar hot-air phase change bed

Comprehensive heating provides a comfortable indoor but consumes significant energy. Temporal-spatial partitioned heating can meet differentiated thermal demands while reducing energy consumption. A novel solar hot-air phase change bed heating system has been proposed for achieving temporal-spatial partitioned heating. Theoretical analysis models have been established to study the heat transfer process of the hot-air phase change heating bed, and numerical simulations have been conducted to analyze its thermal performance and creation of a comfortable environment. The results demonstrate that at the end of the heat storage, the bed board temperature increased by 1.5 °C for every 5 °C increase in the wind temperature. The maximum temperature difference of the bed board reached 6.1 °C under three different wind speed schemes. During heat release, the bed board heat flux was affected by the phase change material heat storage difference, and the maximum temperature difference of the bed board reached 4.3 °C ∼ 6.7 °C under different schemes. After the first cycle, both indoor and bed board temperature were higher than the initial values. During the daytime, there was excessive heat indoors, and the maximum environmental temperature exceeded the comfortable range by 8.7 °C. At night, the bed was covered with a high-temperature layer, and the bed surface temperature was uniformly distributed, remaining in the thermal comfort zone for 3.8 h to 5.1 h. The research results provide a basis and guidance for utilizing solar hot-air phase change beds to improve differentiated thermal demands.

Agglomeration inhibition mechanism of SiO2 in the Ca(OH)2/CaO thermochemical heat storage process: A reactive molecular dynamics study

As a promising thermochemical heat storage material, the Ca(OH)2/CaO can be agglomerated after repeated heat storage cycles, which will affect its performance severely. Experimental evidence indicated that the dopant of SiO2 particles alleviated the agglomeration phenomenon of Ca(OH)2/CaO. However, the mechanisms have not been clarified in theory, including the agglomeration of Ca(OH)2/CaO and the agglomeration inhibition of SiO2. Investigating these mechanisms is important for the broad application of Ca(OH)2/CaO thermochemical heat storage technology. In this paper, reactive molecular dynamics is employed to simulate and quantify the agglomeration of Ca(OH)2 and the inhibition by SiO2 during the heat storage process. Then, the agglomeration phenomena under the two processes are quantitatively described. The mechanisms are analyzed by using the parameters of kinetics and thermodynamics. From the phenomenological analysis, smaller size changes, larger mass center distances, and smaller atomic displacements indicate that SiO2 doping reduces the tendency of nanoparticles to agglomerate into a larger cluster. From the kinetic perspective, the diffusion of pure Ca(OH)2 clusters conforms to viscous flow, while the diffusion of the SiO2-doped clusters is close to surface diffusion. The dopant of SiO2 increases the activation energy of the diffusion process, which would increase the atomic mobility resistance and thus inhibit the agglomeration. From the thermodynamic perspective, cluster agglomeration is mainly caused by the work done by van der Waals forces, which leads to a decrease in potential energy, especially surface potential energy. By doping SiO2, the interatomic van der Waals forces are increased, which lowers the stable potential energy surface of the clusters, thereby obtaining a more stable structure to inhibit agglomeration.

Dehydration performance of a novel solid solution library of mixed Tutton salts as thermochemical heat storage materials

To improve energy efficiency and reduce greenhouse gas emissions, energy storage technologies are of paramount importance. Thermochemical energy storage (TCES) materials offer high energy storage densities, and systems based on the dehydration of common salt hydrates like MgSO4·7H2O have been extensively investigated, though frequent problems such as agglomeration and unfavorable kinetics highlight the need for further material development. We consulted our VIENNA TCES-database and became aware of the Tutton salts, A2M(XO4)2·6H2O, (X = S or Se) which have also been previously investigated as TCES materials, although the effects of cation substitution on reactivity had remained poorly characterized. Herein, we report the synthesis and characterization of 41 mixed Tutton salts with the composition K2Zn1-xMx (SO4)2·6H2O (M = Mg, Co, Ni, Cu). Two trends were readily apparent: increasing the amount of nickel leads to a predictable increase in the dehydration onset temperature while preserving the simple form of the single dehydration step observed, while the use of copper leads to a predictable decrease in dehydration onset.

Heat Storage as a Way to Increase Energy Efficiency and Flexibility of NPP in Isolated Power System

This paper considers a thermal accumulator using phase transition materials as a way to increase the energy efficiency and maneuverability of nuclear power plants. A low-power nuclear power plant is the object of this study. Such nuclear power plants have a great potential for widespread implementation as sources of thermal and electrical energy for facilities of mineral and raw material as well as fuel and energy complexes located in distant regions. The main principles of development of low-power nuclear power plants are revealed. So, in the development of low-power nuclear power plants, experience in the creation and operation of shipboard nuclear power installations is widely used. The problems of NPP operation in daily maneuvering modes within an isolated power system are revealed. A method for improving the energy efficiency and maneuverability of nuclear power plants is proposed, in particular, through the use of thermal accumulators with a phase change material directly in the NPP circuit. A method of assessment of the dimensions of the heat accumulator and the amount of heat accumulating material is presented. A method of assessment of the efficiency of the accumulator application scheme is presented. The thermal scheme of a promising low-power nuclear power plant with an RITM-200 reactor is compiled. A scheme for switching on a heat accumulator with a phase change material to a scheme for regenerative heating of a turbine is proposed. The heat storage material selection is made, the main elements and characteristics of such an accumulator are determined, and the parameters of the heat transfer fluid’s movement through the accumulator are determined. A mathematical model of the heat exchange in an accumulator based on the finite difference method is compiled, and the simulation results are presented. The results of the experimental verification of the model are presented. As a result of the calculation of NPPs’ thermal schemes in the standard version and the version with a heat accumulator, the power increase in the turbine plant due to the application of accumulated heat in the accumulator discharge mode is determined.