Phase Change Material Heat Storage Research Articles

Role of natural convection and battery arrangement for phase change material based battery thermal management unit

Phase change material (PCM) based battery thermal management (BTM) has been of increasing interest due to the passive concept with efficient cooling and temperature uniformity performance. Due to the inherent characteristics of solid-liquid phase change during operation, it is worth in-depth investigation of the influence of buoyancy driven natural convection (NC) on battery thermal behavior. Here, a typical PCM enclosed cylindrical battery unit is considered as the benchmark problem. The effects of battery arrangement and liquid PCM NC on melting process and thermal performance are investigated numerically based on rigorously validated model. It shows that excellent cooling performance could be achieved for battery with the function of latent heat storage of PCM, whether the unit is arranged vertically or horizontally. In addition, the horizontal arrangement (4.1 K) has a better temperature uniformity than the vertical arrangement (5.7 K), which can be ascribed to the varying melting rate of PCM. To further insight into the thermal behavior of BTM unit, the relationship between the melting rate and interface length associated with differential liquid fraction curve is proposed for the first time. When the liquid PCM is full of the upper half of the BTM unit, the length reaches its maximum value and after that the differential liquid fraction is significantly declined, indicating the poor heat transfer and thermal performance. The motivation is to not only explore the fundamental mechanism of passive phase change method, but also to serve as a basis for the design of more practical and efficient PCM based BTM in the future.

Performance assessment of single slope solar still by the incorporation of palm flower powder and micro phase change material for the augmentation of productivity.

Water scarcity necessitates a cost-effective and productive solution. This study focused to enhance the productivity of single slope solar still by incorporating the better weight of palm flower powder (micro-sized) in the basin and micro phase change material heat storage bed under the basin. In this aspect, the different quantity of palm powder weights such as 10, 30, 50, 70, 100, 120 and 150 g in the basin was experimentally examined. The absorber basin containing 50 g of palm powder has better productivity of 37.25%, whereas for 10, 30, 70, 100, 120 and 150 g, they were 11.85, 24.78, 36.8, 33.05, 10.25 and - 20.22% respectively. The influence of palm powder with different weight% impregnated in the paraffin wax was analysed. The maximum thermal conductivity of 0.33 W/m K was obtained in the sample containing palm flower powder of 20 wt%. The experimental investigation was carried out with 50 g of micro-sized palm powder in the basin and thermal storage bed under the basin containing 20 wt% of micro phase change material (PCMPFP-SS) and conventional solar still (CSS). The overall distillate output of PCMPFP-SS was 4670 and 4250 mL/m2 on day 1 and day 2 respectively. On the other hand, the overall distillate output for CSS was 3030 and 2800 mL/m2 on day 1 and day 2. From the economic analysis, it was found that the cost per litre (CPL) of PCMPFP-SS and CSS was $ 0.025 and $ 0.032 respectively. Moreover, the payback period of PCMPFP-SS was lowered from 5.1 to 4.1 months compared to CSS.

Preparation of Organic-Inorganic Coupling Phase Change Materials with Enhanced Thermal Storage Performance via Emulsion Polymerization.

The serious phase separation in inorganic phase change materials, and easy leakage of organic phase change materials are the main obstacles to the practical batch application of phase change heat storage materials. To solve these problems, in this work, emulsion polymerization is introduced as the method for preparing organic-inorganic coupling phase change material (oic-PCM) with high heat storage performance using polyacrylamide (PAM) as the wall material and organic phase change material of cetyl alcohol as the core material, and diatomite is used as a supporting substrate to absorb inorganic sodium sulfate decahydrate (SSD). A differential scanning calorimeter (DSC), X-ray diffractometer (XRD), dust morphology and dispersion analyzer, and thermal conductivity tester were used to characterize the prepared organic-inorganic coupled phase change materials and investigate their performance. The research results show that when the mass fraction of cetyl alcohol is 68.97%, the mass fraction of emulsifier is 3.38%, and the mass fraction of sodium sulfate decahydrate/diatomite is 3.40%. The phase change latent heat of the organic-inorganic coupled phase change material is as high as 164.13 J/g, and the thermal conductivity reaches up to 0.2061 W/(m·k), which proves that the prepared organic-inorganic coupled phase change material has good heat storage performance, showing its good application prospects.

Design and Fabrication of a Phase Change Material Heat Storage Device for the Thermal Control of Electronics Components of Space Applications

In this paper, the design and validation of a heat storage device based on phase change materials are presented, with the focus on improving the thermal control of micro-satellites. The main objective of the development is to provide a system that is able to keep electronics within safe temperature ranges during the operation of manoeuvres, while reducing mass and volume in comparison to other thermal control techniques. Due to the low thermal conductivity of phase change materials, the conductivity of the device as a whole is one of the major challenges of the development. This issue has been solved by means of the use of a lattice of aluminium fins. The thermal behaviour of the proposed solution is assessed with numerical simulation tools, and the results prove that the developed phase change material-based thermal control technique is able to provide the suitable integrated thermal management of micro-satellites. Fabrication challenges found in the project are also explained. Numerical results are validated through a testing stage. The predicted temperature profiles are in good agreement with experimental data and inside the range foreseen for the heat storage device.

Efficacy of angled metallic fins for enhancing phase change material melting

Research on enhancing phase change material (PCM) heat transfer is concentrated in latent heat thermal energy storage (LHTES) field, especially with utilization of metallic fins. One interesting fin parameter that was less explored for a rectangular PCM system, is the metal fin's inclined angle. This research aims to experimentally validate the hypothesis and evaluate the efficacy of angled metallic fins enhancing PCM melting in a sidewall heated cuboid LHTES system. Experiments indicate that three-dimensional PCM melting in the LHTES unit can be characterized as two dimensional. The angled fins considerably influence temperature evolution of local solid PCM around fins. Compared to the horizontal fin, positive inclined fins with angles of +30° and +15° prolong the PCM melting time by 4.0% and 3.8% respectively, while the downward tilted inclined fins at −15° and −30° promote PCM melting by up to 5.2% melting fraction difference. Extending simulations with seven fin angles and three fin lengths explicate the substantial effect on PCM heat storage, melting time, and temperature uniformity. Particularly, the longest fin at the downward angle of −15° reduces the PCM melting time most. The study shows feasibility of utilizing downward angled fins to enhance PCM transient melting in the LHTES unit.

Mechanism and Performance of Composite Phase Change Materials from the Direct Hydrolysis Residue of Municipal Sludge Loaded with Sodium Acetate Trihydrate.

The direct hydrolysis of municipal sludge for the production of oil and gas has become a key research focus, despite the application of hydrolysis residues presenting a challenge. In this study, municipal sludge was directly hydrolyzed in a high-pressure reaction kettle and the hydrolysis residue byproduct was used as a carrier to prepare a composite phase change heat storage material (CPCM), utilizing vacuum impregnation for sodium acetate trihydrate (SAT) loading. The results of Brunauer–Emmett–Teller (BET) and particle size analyses showed that the residue obtained by the hydrolysis of sludge and sawdust with a dry basis ratio of 4:1 had a higher pore volume and a uniform particle size. The adsorption capacity of the hydrolysis residue to SAT reached 600 wt %; the phase change temperature of the CPCM was 56.9 °C, and its latent heat reached 217.9 kJ/kg. The CPCM remained stable during 150 cycles of the melting–solidification process in a water bath and maintained excellent phase change characteristics. The hydrolysis residue can effectively improve the undercooling and phase separation of SAT without other additives.

Thermal management and phase change heat transfer characteristics of LiFePO4 batteries by cooling phase change materials

The cycle life and thermal safety of lithium-iron-phosphate (LiFePO4) batteries are important factors restricting the popularization of new energy vehicles. The study aims to prevent battery overheating, prolong the cycle life of power batteries and improve their thermal safety by discussing the heat production of LiFePO4 batteries to solve the problem of temperature rise in the natural-convection environment and cut the energy consumption in the liquid cooling system. A numerical simulation and experiment are employed to study the heat production characteristics of LiFePO4 batteries and the heat transfer characteristics of the system, with its PCM and coupling PCM of paraffin and expanded graphite), channel liquid, and micro-channel PCM coupling cooled to control the temperature of the batteries. The results show that the temperature goes higher with the discharge rate during discharge. Since it has large internal component values, LiFePO4 produces more heat at the beginning and end of discharge. When the battery pack is discharged at 1C and 2C rates, the mass-flow rates are 1.8 ? 10?3 kg/s and 3.6 ? 10?3 kg/s, the temperature can be controlled at most 40?C, and the temperature difference less than 3?C, respectively. Paraffin is composed of expanded graphite, and the thermal conductivity of the composite heat storage PCM (phase change heat storage materials) is 24 times of that of pure paraffin. Therefore, cooling the active liquid and coupled PCM can improve the cooling efficiency and has a good effect on solving the problem of temperature rise and energy consumption reduction. The research provides a reference for the thermal energy management of LiFePO4 batteries, providing a method of cooling PCM of LiFePO4 batteries.

A New Composite Phase Change Material for Cold and Heat Storage and Its Application

In today's society, energy consumption is growing at an alarming rate. Because of the huge economic benefits brought by traditional industries such as non renewable energy and fossil fuel power generation, people have to study them. The phase-change heat storage materials are widely used in the condensation heat storage due to their high temperature, low density and environmental protection. This paper considers the advantages, disadvantages and application scope of the new energy storage equipment based on the phase-change storage characteristics, and proves through experiments that under certain conditions, the appropriate solid-liquid ratio and the degree of substitution of different components are conducive to improving the performance of the composite storage heat exchanger. In this paper, a new composite phase change material for cold storage and heat storage is tested. The test results show that, because the carbon nanotubes added in the composite phase change material have no latent heat contribution in the whole phase change process, the phase change enthalpy of the composite phase change material will inevitably decrease with the increase of the carbon nanotube mass fraction.

Phase change material heat storage performance in the solar thermal storage structure employing experimental evaluation

One of the most investigated and broadly used mediums in the solar thermal storage systems is using phase change materials. In this research, a comprehensive performance test bench for solar thermal utilization system using a controllable heater to substitute different levels of solar input was established. The test bench is not limited by the weather and equipped with alternative heat storage tanks for different PCMs. The heat storage structure and the performance of paraffin in low temperature system was examined using numerical simulation method. The results showed that the heating power received by PCM was stable at 6–8 kW under the heating condition of 85 °C. At the stage of incompletely melting, the temperature difference between the inside and outside was as high as 31.6, which can reduce the loss of heat to a great extent.

Shape-stable phase change composites based on carbonized waste pomelo peel for low-grade thermal energy storage

Phase change materials (PCMs), like polyethylene glycol (PEG), have been widely applied to the storage and utilization of low-grade thermal energy, which is a momentous part of energy utilization and conversion. Furthermore, one of the important ways to solve the practical problems of easy leakage and slow speed of heat storage of PCMs is to prepare the phase change composites (PCCs) featured with stable shape, high enthalpy retention and improved thermal conductivity. For this purpose, we focused on the waste bio-based pomelo peel, which was converted into biochar as the supporting material of PEG through a simple carbonization process, then vacuum impregnated with four different molecular weights of PEG to obtain the PCCs characterized by no leakage, high loading and enhanced thermal diffusion ability. The DSC results revealed that the melting enthalpy of several PCCs were about 160 J/g, which were slightly lower than that of pure PEG, but the relative enthalpy efficiency still exceeded 90%. Meanwhile, PCCs had excellent thermal stability and cycling stability, and the mass loss in 200 heat-cooling cycles was only 2.69% at most, which is beneficial to the preservation of enthalpy. The tests of solar-thermal conversion and storage manifested that PCCs could make full use of the solar radiation heat energy, with the efficiency of about 75%∼x223C 80%. With the low-cost and waste-recycling, this work provides a new choice for further efficient and comprehensive utilization of low-grade thermal energy including solar radiation heat energy.

Experimental Research of the Heat Storage Performance of a Magnesium Nitrate Hexahydrate-Based Phase Change Material for Building Heating

Phase change heat storage material is a preferred material in solar building heating or off-peak electric-heat storage heating technology and is the research focus. A compact phase change thermal storage device has been designed and experimentally studied for improving heating system load in this work. A new type, magnesium nitrate hexahydrate-based phase change material has been studied to improve the cooling degree and crystallization difficulty. The focus of this study is on the heat charging and discharging characteristics of this new phase change material. The heat storage device has two groups of coils, the inner side which carries water and the outer side which is the phase change material. A testing system was built up to value the thermal cycling performance of the heat storage device. The measurement data include phase change material temperature field, water inlet and water outlet mean temperature, heat charging and heat discharging depth, and flow rates over the operating period. The results show the phase change material has a quick response with the operating temperature range of 20–99 °C. Its latent heat is 151.3 J/g at 91.8 °C. The heat storage density of this phase change material is about 420 MJ/m3. The thermal performance degradation is about 1.8% after 800 operation cycles. The phase change thermal storage device shows flexibility and a great potential to improve the capacity and economy of heating systems.

Theoretical study on melting of phase change material by natural convection

Natural convection plays a crucial role in latent heat storage system. Determining how natural convection affects the melting of phase change material (PCM) will provide a better understanding of the melting process and give helpful advice on strengthening techniques. The research content of this paper is a mathematical model is established to explain the melting process of PCM affected by natural convection. The mathematical model of phase change melting process is given by introducing the natural convection and the temperature gradient. A coordination factor (Co) based on the mathematical model, which is an instantaneous quantity and proportional to the heat exchange rate and the intensity of natural convection, is introduced to explain the melting process. A square-shaped and shell-tube (concentric, eccentric) PCM heat storage unit were numerically analyzed in more detail. It is found that the Co factor is closely related to the melting rate. It will not promote the melting rate when Co less than 0 while it will promote the melting rate when Co higher than 0, and the higher the Co value, the faster the melting rate. This model gives a clear and quantitative explanation for the problem of melting interface movement affected by natural convection, as well as that increasing the heating temperature and changing only the shape of the heat storage unit can greatly enhance the heat storage rate in this study. The model also provides theoretical guidance for the study of the phase change heat storage enhancement.

Effect of EG particle size on the thermal properties of NaNO3–NaCl/EG shaped composite phase change materials

The adsorption capacity of expanded graphite (EG) with three different particle sizes of 32 mesh, 50 mesh, and 80 mesh was studied by the water-soluble adsorption method. The self-made NaNO3–NaCl (95–5 wt%) was selected as the phase change heat storage material, and the three kinds of EG were used as additives. The 80 wt% NaNO3–NaCl/20 wt% EG shaped composite phase change materials (CPCM) were prepared and their properties were tested and analyzed. The research results showed that the smaller the particle size, the stronger the adsorption capacity of EG. However, the choice of EG should consider the particle size of the phase change material (PCM). The 50 mesh EG was more suitable as the adsorption carrier of NaNO3–NaCl. Compared with pure NaNO3–NaCl, NaNO3–NaCl/EG had a lower degree of supercooling, which improved the heat storage capacity of the material. As the particle size of EG decreased, the thermal conductivity increased slightly. The study analyzed the relationship between the EG adsorption capacity and its particle size, and prepared NaNO3–NaCl/EG heat storage material with high heat storage density and high thermal conductivity. It was helpful to promote the application of EG based composite heat storage materials and the development of heat storage technology.

Ternary chloride salt–porous ceramic composite as a high-temperature phase change material

In this study, a ternary salt/porous Si3N4 composite was prepared as a high-temperature shape-stabilized phase change material by pressure impregnation. In this composite, the ternary salt composed of 50 wt% sodium chloride (NaCl), 30 wt% potassium chloride (KCl), and 20 wt% magnesium chloride (MgCl2) was acted as the high-temperature phase change material. A porous Si3N4 ceramic was acted as the skeleton material and heat transfer enhancer. The porosity infiltration ratio of the pores reached 89.19%, demonstrating the good chemical compatibility of Si3N4 with chloride salts. The thermal conductivity of the composite was over six times greater than that of pure ternary salts. The thermal physical properties of the composite were stable even after 300 thermal cycles. The coefficients of thermal conductivity obtained by theoretical analysis and calculation were compared to the experimental values. All the results showed that this composite is a promising candidate as a shape-stabilized high-temperature phase change heat storage material.

Technical research on heat storage and function expansion of thermos cup

The new multi-functional heat preservation cup can not only achieve long-term heat preservation, but also keep the water temperature at a more suitable temperature for drinking in a short time. It uses paraffin phase change heat storage material as the filler of the inner liner sandwich, which can absorb the heat in the water temperature and achieve rapid cooling; solar panels are used above the cup cover to supply power for electronic devices, which can save energy and protect the environment and avoid the trouble of charging back and forth; At the same time, a variety of electronic devices are added to the cup cover to enrich the customer's experience.

Asphaltenes as novel thermal conductivity enhancers for liquid paraffin: Insight from in silico modeling

The practical use of paraffin and other organic phase-change materials for heat storage is largely limited by their low thermal conductivity. In this paper we employed 60 microsecond-long atomic-scale computer simulations to explore for the first time whether the asphaltenes, natural polycyclic aromatic hydrocarbons, can be used as thermal conductivity enhancers for paraffin. We focused on a simple model molecule of asphaltene (a polycyclic aromatic core decorated with the peripheral alkane chains) and showed that the asphaltenes of such molecular architecture are not able to improve the thermal conductivity of paraffin. This is most likely due to the steric constraints imposed by the peripheral alkane groups, which prevent formation of the extended ordered asphaltene aggregates. To overcome this, we proposed a possible chemical modification of the asphaltene molecules through removing the peripheral alkane groups from their aromatic cores; this could be achieved e.g. by thermal cracking (dealkylation) of asphaltenes. It turns out that such a chemical modification drastically changes the situation: the modified asphaltenes form extended columnar aggregates which can serve as thermal conduction paths, considerably enhancing the thermal conductivity of a liquid composite sample. This effect, however, vanishes upon cooling because the columnar extended stacks of chemically modified asphaltenes transform into the helical twisted structures, which reduces the overlap of adjacent asphaltenes in aggregates. Importantly, all the simulations have been carried out with two different all-atom force fields. We have demonstrated that both computational models give qualitatively similar results. Overall, our findings clearly show that chemically modified asphaltene molecules can be considered as promising carbon-based thermal conductivity enhancers for liquid paraffin; this result can be used for optimizing the paraffin-based thermal energy storage systems.

Effect of composite orders of graphene oxide on thermal properties of Na2HPO4•12H2O/expanded vermiculite composite phase change materials

The leakage of Na2HPO4•12H2O phase-change materials (PCMs) in the liquid state can be prevented by encapsulating them into porous expanded vermiculite (EV) to prepare composite PCMs. The main issues of EV-based composite PCMs are the low thermal conductivity and the crystal water loss of inorganic hydrated salt. Graphene oxide (GO) can help enhance the thermal conductivity of composite PCMs and firmly adsorb water molecules through oxygen groups. The composite orders of GO play an important role in adjusting the thermal properties of composite PCMs because the suitable positions of GO in the stratified structure of EVs would positively influence the PCMs. The Na2HPO4•12H2O/EV composite with GO was prepared in three different orders. Compared with the common method that involves compositing GO in Na2HPO4•12H2O, compositing GO on the hole wall of the EV exhibited a higher thermal conductivity of 0.54 W/m•K and compositing GO out of Na2HPO4•12H2O/EV exhibited better thermal stability, which incurred a weight loss of 4.14% at a high temperature. A thermal energy storage behaviour analysis indicated that GO-modified PCMs show a large heat storage capacity (melting process: 98–126 J/g; solidification process: 56–91 J/g). Two new composite orders positively affected the heat storage of the composite PCMs.

Preparation and properties of low-cost phase-change heat storage materials based on semi-coke ash

Preparation and properties of low-cost phase-change heat storage materials based on semi-coke ash

Study on the synthesis and thermal properties of magnesium chloride hexahydrate–magnesium sulfate heptahydrate–activated carbon phase change heat storage materials

Study on the synthesis and thermal properties of magnesium chloride hexahydrate–magnesium sulfate heptahydrate–activated carbon phase change heat storage materials

Preparation and properties of composite phase change material based on solar heat storage system

Solar phase change hot water storage tank is a kind of storage / exothermic system with solar energy as heat source and phase change heat storage material. It can store heat during the day, continue to operate at night with stored heat without consuming other energy. Because of the poor thermal conductivity of solid-liquid phase heat storage materials, carbon fiber is added to enhance the thermal conductivity of phase change materials. Stearic acid is used as phase change material, carbon fiber as heat transfer material and ethyl cellulose as auxiliary material to prepare carbon fiber / stearic acid composite phase change material. Carbon fiber / stearic acid in the mass ratio of 7.5:92.5 is the optimal material and the chemical compatibility, phase change temperature, phase change latent heat, thermal conductivity and thermal stability of carbon fiber / stearic acid are measured by using SEM, XRD and DSC. From the DSC test, the latent heat capacity was determined as 192.6 J/g and the phase change temperature as 67.7°C. Thermal conductivity was measured as 0.4011 W/m⋅K. The storage / exothermic experimental system of carbon fiber / stearic acid composite phase change material is built. The melting process and solidification process of the composite phase change material are tested, and the storage / exothermic characteristics are analyzed. SEM and DSC analysis results revealed that the PCM had high thermal stability. XRD revealed that the binary eutectic mixture had good chemical stability. Thus, the new PCM possessed high latent heat with good thermal and chemical stabilities making it a potential phase change material for solar heat storage applications.