High Temperature Phase Change Materials Research Articles

Controllable preparation and thermal properties of SiC spherical high temperature shape-stable composite phase change materials based on gel-casting

The development of high-temperature composite phase change materials (CPCMs) suitable for mass-production and high-performance is still a very urgent problem in the efficient utilization of renewable energy. In this study, a SiC spherical high-temperature CPCMs based on aqueous gel-casting suitable for batch molding using commercially available silicone molds is proposed. The porosity of the porous SiC framework can be adjusted by changing the content of starch granules in the slurry. The sample containing 20 wt% starch has relatively high open porosity and thermal conductivity, which is considered to be close to the optimal formulation of CPCMs. This formula possesses a high thermal conductivity of 10.2 W·m−1·k−1 benefiting from the continuous thermal transport channels consisting of the uniformly distributed large spherical pores and interconnected small pores. Meanwhile, the thermal storage density of the CPCMs reaches 395.21 J·g−1 in the temperature range of 550 ℃ and 750 ℃ since up to 89.06% of the pores are filled with molten salts. At the same time, the CPCMs exhibit excellent cycle stability in 100 thermal cycles. In particular, these CPCMs can be easily integrated into thermal energy storage (TES) system. Based on the rapid heat storage simulation of the C-D model, the packed-bed latent thermal energy storage system containing spherical CPCMs will have a more uniform temperature distribution and a 26.7% reduction in charging time compared with the traditional packed-bed system. This work provides a new reference for the design of spherical CPCMs in TES systems.

Application and analysis of flip mechanism in the melting process of a triplex-tube latent heat energy storage unit

In order to improve the characteristics of uneven melting in the melting process of the horizontal latent heat energy storage system, the triplex-tube latent heat energy storage unit is taken as the research object, and the flip mechanism is applied to its melting process. Numerical simulation is used for the research, and the numerical model is verified by experimental data. The results show that under different dimensionless times, the melting performance of the unit can be significantly improved by a single flip. When the dimensionless time is 0.4576, it is found that the total melting time of the unit is reduced by 16.17 %, the average heat absorption rate is increased by 14.7 %, but the total heat energy absorption is reduced by 3.85 %. The results show that the addition of a flip can effectively shorten the melting time and increase the heat absorption rate, but it has a negative effect on the total heat absorption in one melting cycle. Moreover, through the comparison of dynamic flow rate, dynamic temperature response, and temperature interval, it is shown that the addition of flip effectively reduces the negative influence of the hard-to-melt zone on the melting performance of the unit during the melting process. The flip mechanism reduces the proportion of high-temperature phase change material in the melting process and makes the melting process more uniform.

Analysis on the thermal behaviour of the latent heat storage system using S-CO2 and H-PCM

Energy storage and utilization of CO2 have attracted increasing attention due to international zero carbon plan. Here, the latent heat storage system using high-temperature phase change material (H-PCM) and supercritical CO2 (S-CO2) is analysed by using CFD simulation, in which the tube containing S-CO2 is submerged in a tank containing the salt with high melting temperature. A new and combined phase transition model is developed to describe the dynamics of PCM in different phase state, and it is validated against experimental data in literature. The dynamics of natural convection is focused, and its effects on the heat storage system are analysed, including maximum natural convection velocity, phase interface, and melting pattern. The results show that natural convection has a great influence on the melting process of the H-PCM in the charging process. The melting pattern of H-PCM could be contrary between the cases with and without considering natural convection. During the discharging process, natural convection has little effect on the heat transfer of energy release due to its short duration. With the increase of ratio between the S-CO2 tube and H-PCM tank, the strength of the natural convection of melting H-PCM is enhanced, especially the duration of natural convection.

Thermal characteristics of melting of a phase change material enhanced by a stainless-steel 304 periodic structure

In this work, melting of a high-temperature inorganic phase change material (PCM) eutectic (with a melting point of 569 °C) within a vertical cylindrical tank has been experimentally investigated. To promote the heat transfer rate, a periodic structure that is constructed by a commercial SS-304 mesh screen has been considered and immersed into the PCM tank. Thermal characteristics of the PCM-periodic structure tank under different initial temperatures (450, 490 and 546 °C) and wall temperatures (620, 640, 660, 680 and 700 °C), are then investigated and reported. The presented experimental data can facilitate practical engineers to find the best operating condition of similar PCM tanks; meanwhile, it can also be employed for the investigation of thermal response of transient heat conduction before melting starts.

Discharge performance of a high temperature phase change material with low-cost wire mesh

Thermal energy storage is increasingly needed in a sustainable world because of its potential of capturing waste heat and being incorporated in solar power plants. For power generation, in particular, as turbine technology advances, a demand for higher temperature thermal energy storage materials also grows. For this purpose, latent thermal energy storage fits in well since it uses phase change materials (PCMs) which generally have a higher energy density compared to their sensible heat counterparts. In the present study, a eutectic Na2CO3(41.69%)-(33.1%)KCl-(25.21%)NaCl phase change material (PCM) with a melting temperature of 569 ° C was chosen as the storage material to experimentally assess the performance benefit of using a readily available stainless steel (ss304) wire mesh (as the periodic structure) to enhance heat transfer within the domain. In addition, for discharging, a numerical model was developed and compared with the experimental results. Furthermore, for discharging, a numerical investigation of the influence of the heat transfer fluid (HTF) flow-rate to the rate of heat transfer was performed. Overall, it was experimentally observed that the charging time for the composite case was shortened by about 35%, compared to the pure PCM case. For discharging, in the axial direction, the composite solidification time when compared to the pure PCM case was on average 10% shorter. Regarding the radial discharging performance of the composite, there was only about 5% improvement compared to the pure PCM case, which was expected due to the thermal contact resistance in the radial direction. Discharging experimental results were used to validate a discharging numerical model. Discharging results from the model showed that increasing the flow rate of the heat transfer fluid (HTF) reduced the time for solidification. It was observed that for the HTF flow rate of 5 L/min, 10 L/min, 20 L/min and 30 L/min, the discharge time was shortened by 23%, 30%, 33% and 35%, respectively.

Development of over 3000 cycles durable macro-encapsulated aluminum with cavity by a sacrificial layer method for high temperature latent heat storage

The high-temperature metallic phase change materials (PCMs) are attracting great attentions as alternatives to sensible heat storage materials in thermal energy storage (TES) systems. However, the high corrosivity, easy leakage and oxidation phenomena of metallic PCMs have limited their applications. This work reports a facile and novel sacrificial layer method with the purpose to create macro-encapsulating aluminum (Al) PCM by alumina (Al2O3) shell characterized by a ‘buffer’ inner cavity. The inner cavity could offer buffer space to accommodate the huge thermal volume expansion of Al core PCM during heating and melting, thereby preventing the breakage of the capsules and ensuring the long-term stability. A series of Al balls with diameters of 4–25 mm were firstly coated with paraffin sacrificial layer then by Al2O3 dough shell, which was finally conducted by the two-step heat treatment, in which a low-temperature stage aimed at removing the paraffin layer while the high-temperature stage aimed at the capsule sintering formation. The final macrocapsules with diameters of 6.5–31.5 mm were obtained, in which the capsules with Al core balls larger than 15 mm showed superior gravimetric and volumetric heat storage density because of their high core–shell ratio. For example, the 25 mm@0.75 mm@2.5 mm macrocapsules could present high heat storage density of 348 kJ/kg and 902 J/cm3 at the temperature range of 600–700 °C. The macrocapsules also showed a long-time thermal cycling stability, since that no damage or leakage was observed over 3000 times of melting and solidification under air atmosphere, indicating that they can be used over 8 years without any degradation of thermophysical properties. This demonstrates the potential application of the Al2O3 encapsulated Al macrocapsules with inner cavity in high-temperature TES systems.

Techno-economic and exergo-economic evaluation of a novel solar integrated waste-to-energy power plant

The content of municipal solid waste generation is increasing due to the industrial and population growth. Energy generation from municipal solid waste is one of the efficient and promising method to dispose waste in a sustainable manner, while reducing the fossil fuel energy limitations. However, conventional waste-to-energy plants have less thermal efficiency due to the higher moisture content that lowers its heating value. The solar thermal integration is one of the proposed solutions to enhance the steam inlet temperature in the power generation system that will further increase the plant performance. In this study, an innovative solar integrated municipal solid waste incineration plant is proposed to advance the waste-to-energy and concentrated solar power thermal energy technologies. The system integration is carried out utilizing the useful solar heat harvested in the heliostat tower receiver system by transferring heat to the working steam of the incineration plant in the heat exchanger and enhance the turbine inlet temperature and the system’s performance considerably. Based on 300 t/d incineration facility, proposed system is investigated exergo-economically by varying certain influential parameters using engineering equation solver and performance has been compared with the conventional reference plant. The system is integrated with high-temperature Phase Change Materials, which able to store thermal energy enough for the light-time system operation. The results attribute that the network output of the proposed integrated facility has substantial improved (almost 12.61 %) but with the penalty of increase in the exergy destruction cost rate. In addition, levelized cost of electricity of the proposed plant is 13.9 % less than the conventional one and it decreases with the rise of steam temperature. Energy efficiency of the proposed plant improves to approximately 36.34 % as direct normal irradiation increases from 650 W/m2 to 900 W/m2. In addition, Incineration boiler is the major source of exergy destruction (almost 50 %) with 175.2 $/hr exergy destruction cost.

Design and Evaluation of a High Temperature Phase Change Material Carnot Battery

In the current study, a high temperature thermal storage system with a hybrid of phase change material and graphite as the storage materials is designed and evaluated as to its applicability for use as a utility-scale Carnot battery. The design includes an externally heated liquid sodium tank, which is used as the heat transfer fluid. This is used to charge and discharge the storage system consisting of a graphite storage medium sandwiched by two phase change materials. Finally, electrical generation is by way of a supercritical carbon dioxide Brayton cycle operated at 700 °C. Detailed modelling of these designs was conducted by way of a previously validated numerical model to predict performance metrics. Using the aforementioned designs, a preliminary cost estimate was undertaken to better determine applicability. From these results, it was found that while the graphite system was the most effective at storing energy, it was also the highest cost due to the high cost of graphite. In total, 18 storage tanks containing nearly 17,400 tons of storage material were required to store the 1200 MWht required to run the sCO2 power block for 10 h. Under the study conditions, the cost of a PCM-based Carnot battery was estimated to be $476/kWhe, comparable to other storage technologies. Furthermore, it was found that if the cost of the graphite and/or steel could be reduced, the cost of the system could be reduced to $321/kWhe.

Preparation and characterization of steel slag-based low, medium, and high-temperature composite phase change energy storage materials

In this study, industrial solid waste steel slag was used as supporting material for the first time, and polyethylene glycol (PEG), sodium nitrate (NaNO3), and sodium sulfate (Na2SO4) were used as low, medium, and high-temperature phase change materials (PCMs). A series of shape-stable composite phase change materials (C-PCMs) were prepared by vacuum impregnation and mixing-sintering methods. The morphology, thermal properties, and thermal reliability of C-PCMs were characterized by scanning electron microscopy (SEM), Fourier transforms infrared spectroscopy (FT-IR), and differential scanning calorimetry (DSC). The results show that the three PCMs are uniformly dispersed in the pores of steel slag, and the maximum loading is 35 %, 40 %, and 50 %, respectively, and they have good chemical compatibility with steel slag. Compared with their pure PCMs, the three prepared C-PCMs showed a reduction in subcooling of 2.64 °C, 4.53 °C and 0.79 °C, respectively, and an increase in thermal conductivity of 172 %, 54.9 % and 82.4 %, respectively, all with good phase change thermal storage properties. Even after 100 thermal cycles, the latent heat retention rate was more than 97 %, which had good thermal reliability. Therefore, it can be concluded that the three kinds of low, medium, and high-temperature C-PCMs have considerable application potential in different temperature areas, such as building latent heat storage, solar energy storage systems, and industrial waste heat recovery system.

Hybrid PCM-steam thermal energy storage for industrial processes – Link between thermal phenomena and techno-economic performance through dynamic modelling

This study aims to assess the performance and economics of novel hybrid thermal energy storage (HyTES) for industrial applications, linking performance to thermal phenomena occurring within the system. The storage hybridisation concept is based on coupling latent heat storage modules containing high-temperature Phase Change Materials (PCMs) with a fast-response steam accumulator. Such hybrid storage, where heat is stored in both forms of steam and latent heat of PCMs, has the potential to capture excess heat produced by the steam generator of any industrial processes, which can then be used at peak times. HyTES performance is dynamically modelled during charging, idle, and discharging stages. The results show that the HyTES provides 14% extra energy storage capacity than the existing steam accumulator within an identical total volume. Furthermore, the study provides technical analysis of HyTES, and thorough comparison between configurations with different PCM volumes, PCM types and charging times. This is essential to ultimately quantify the whole range of benefit of hybrid energy storage. The sensitivity analysis reveals that Incorporating the HyTES significantly improves energy capacity, and the degree of improvement is mainly affected by the charge duration, approximately 15% after 1 h, and 45% after 4 h of charging. Furthermore, it is shown how the PCM properties affect the performance of HyTES. Finally, the CAPEX and O&M cost of the entire system are assessed in different scenarios and found to be 5% less when HyTES replaces the conventional SA.

The study on high temperature exhaust orifice infrared suppression

A type of gas turbine generator unit has lots of advantages, such as small size, light weight, advanced technical performance, strong environment adaptability, rapid start. However, the high temperature exhaust gas generated during the operation of the machine leads to the high temperature and obvious infrared radiation characteristics near the exhaust port. The objective of this paper is to investigate the infrared suppression of the exhaust orifice of the gas turbine generator unit. Meanwhile, some schemes about infrared suppression are proposed, that is, redesigning the exhaust cover or adding grid regenerator of high temperature phase change materials(HTPCMs). The method of computer simulation experiment, relying on Gambit and Fluent for modeling, is used to demonstrate the feasibility of the scheme. Results indicate that the first enrichment of gas turbine exhaust heat can be completed and the exhaust temperature can be reduced by about 200°C when the grid is set as a three-layer pattern crisscrossed up and down.

Analysis of scale and frame interface effects on the solidification properties of solar salt in mesopores

The intermittency and instability of solar irradiation can be effectively overcome by using medium- and high-temperature composite phase change materials (PCMs) for latent heat storage. Studies using metals and organics as phase change materials show that the phase change behavior of mesoporous composite phase change materials is affected by the constraint effect, and its thermophysical parameters (such as phase change point and phase change latent heat) are significantly different from those of macro volume. However, at present, research on molten salt phase change materials, which are widely used in the field of medium- and high-temperature research, is insufficient. Molecular dynamics simulations combined with experimental methods were used to analyze the changes in the freezing point, supercooling degree and enthalpy of solidification of solar salt in mesoporous composite phase change materials, which were based on the self-diffusion coefficient and the potential energy-temperature curve. The results show that a larger mesoporous size leads to a higher freezing point of the solar salt. At the same scale, with the increase in Al2O3 content in the framework, the freezing point of the solar salt first decreases and then increases. The supercooling degree of solar salt decreases with increasing scale. When the mass content of Al2O3 in the framework is in the range of 25 wt%-40 wt%, the supercooling degree of solar salt increases gradually; in contrast, it decreases in the range of 40 wt%-50 wt%, and finally, it increases again in the range of 50 wt%-75 wt%. The latent heat of phase transition increases with increasing scale. With the increase in Al2O3 content in the framework, the latent heat of phase transformation first decreases, then increases, and finally stabilizes. Al2O3 and SiO2 in the interface of the frame can promote heterogeneous nucleation and provide a substrate for the nucleation of molten solar salt. They also reduce the degree of supercooling. It is found that the effect of Al2O3 on nucleation is more significant.

Fluoride microcapsules with high phase change temperature

Microcapsules of high-temperature phase change materials (PCMs) with excellent heat storage capability have numerous applications. Fluoride has a higher phase change temperature and enthalpy value, confirming the significance of using fluoride as a phase change material in high-temperature applications. The authors created a novel fluoride microcapsule with a single carbon shell that can withstand volume expansion during the solid-liquid phase change at high temperatures. Initially, a phenolic resin shell was encapsulated onto the surface of the fluoride particles via a water-induced phase separation process. The phenolic resin shell was then cross-linked and carbonized to obtain the fluoride@carbon microcapsule. The structure and composition of the microcapsules were confirmed by SEM, FT-IR, EDS, TGA, and XRD results. DSC was used to evaluate the enthalpy of the microcapsules and PCMs. The magnesium fluoride@carbon (MgF2 @C) microcapsules had a high phase change temperature of 1262 ℃ and enthalpy of 718.4 kJ/kg, and the lithium fluoride@carbon (LiF@C) microcapsules had a high phase change temperature of 840 ℃ and enthalpy of 458.2 kJ/kg. The MgF2 @C microcapsules have the highest phase change temperature of any PCM microcapsule reported. The structure of the microcapsules was well preserved even after several heat-cool cycles, with no leakage detected, demonstrating excellent thermal stability. This technique can be used to create a variety of PCMs microcapsules, such as fluoride, alloy, metal, and more.

Effect of phase change temperatures and orientation on the thermal performance of a miniaturized PCM heat sink coupled heat pipe

ABSTRACT This study reports the results of experimental and numerical investigations on the thermal performance of a miniaturized phase change material (PCM) heat sink coupled with heat pipe. Initial studies are conducted on two different configurations of PCM heat sink with heat pipe (i) HSHP (i.e., PCM coupled at evaporator of heat pipe) (ii) HPHS (i.e., PCM coupled at condenser of the heat pipe). The results showed a superiority of HSHP over HPHS by up to 98.8% in the charging cycle. Experiments are conducted on HSHP with different melting temperature PCMs. The HSHP with high melting temperature PCM showed high thermal performance.

Orientation impact on structural integrity of a shell and tube latent heat thermal energy storage system

Latent heat thermal energy storage systems can regulate the intermittency of electricity generation in a grid powered by renewable energy sources. Such systems could be used in conjunction with Brayton power generation cycles operating at high temperatures (520 °C–750 °C) delivering higher efficiency. However, a trade-off of higher thermal efficiency can be higher thermal stresses. The isothermal latent heat thermal energy storage and release can reduce the thermal stresses for a specific design. This study investigates the impact of the orientation on the melting process and the consequent thermal stresses in a lab-scale latent heat shell and tube system using a combination of transient computational fluid dynamics and finite element analyses. With a high temperature phase change material melting at 705.8°C, two initial temperatures of 700°C and 650°C were considered in transient analyses, leading to a 50 K and 100 K initial temperature difference across the tubes, respectively. For the structural analysis, an elastic method was employed for the condition of 50 K temperature difference, and an elastic-plastic analysis for the condition of 100 K to account for plastic deformation. The results of the elastic analysis presented the maximum thermal stresses of 63.5 MPa and 106.7 MPa in tubes in the horizontal and vertical orientations, respectively. The stress in the tube sheet was slightly higher (94.5 MPa) for the horizontal system compared with 90.4 MPa in the vertical position. For the condition of 100 K, the results of the elastic-plastic analysis identified the highest stresses of 172.5 MPa and 147.4 MPa in the tube sheets of the horizontal and vertical systems, respectively. For both initial temperature conditions, the stress level in tubes is lower in the horizontal orientation, which is where most cost occurs in a shell and tube system. Particularly important for the 100 K condition, the results show a lower stress of 100 MPa in tubes for a horizontal system compared with 140 MPa in a vertical orientation. In general, the lowest thermal stress occurs where a melt layer forms around tubes during the early stages of a melting process. A higher stress occurred in parts in contact with argon. The highest level of stress occurred in parts in contact with solid PCM, which has direct implications for larger vessel designs. This study provides insights into hydrothermal and mechanical design of a PCM system to prevent and/or manage localised maximum thermal stresses for a cost-effective thermal energy storage system.

Development and performance assessment of a novel solar-assisted multigenerational system using high temperature phase change material

Solar-assisted multi-generation systems are eco-friendly with exceptional thermal performance. In the present study, a novel solar-assisted multi-generational system is proposed and investigated for multiple outputs. The proposed system consists of solar tower with heliostat, combined cycle (topping is Brayton cycle, while bottoming is Rankine cycle with reheat and regeneration processes), single effect Lithium-Bromide/water absorption chiller, heat pump, water-based thermal energy storage system and an electrolyzer. The system is integrated with high temperature phase change material (PCM) based thermal storage system for the continuous system operation. The salt PCM KF-MgF2 is selected from the literature having melting temperature of 1280 K with high density and latent heat of fusion. The storage system ensures the stable and continuous working of the system during off sun hours. The aim of the present study is to thermodynamically and exergo-environmentally investigate the performance of PCM based solar driven multi-generation system.The results of the study depict that energy efficiency of single and multi-generation system is approximately 20.93% and 51.62%, while exergy efficiency is almost 22.51% and 53.45%, respectively. Hydrogen production rate and exergetic sustainability index of the proposed system is approximately 0.00742 kg/s and 0.078, respectively. Energy efficiency of multigeneration system is approximately 15.9% and 61% higher than tri-generation and co-generation systems at concentration ratio of 1000. Exergo-environmental impact index decreases to almost 5% by increasing direct normal irradiation, while exergetic sustainability index and exergy stability factor are increased to 125% and 54.2%, accordingly. Finally, energy efficiency of the single generation and multi generation systems are optimized at 23.56% and 56.83%, respectively.

Microencapsulation of high temperature metallic phase change materials with SiCN shell

Metallic phase change materials (PCMs) have the advantages of large phase change latent heat, high heat storage density and broad application prospects in various high temperature industrial waste heat recovery and utilization. However, due to the strong corrosion of molten metal at high temperature, appropriate packaging technology is the prerequisite for the promotion and application of metallic PCMs. In this research, a high temperature PCM microencapsulating technology with SiCN shell and a new microencapsulation method was proposed. The high temperature microencapsulated phase change materials (MEPCMs) with the core–shell mass ratios of 5:1, 4:1 and 3:1 were prepared by “solvent evaporation-heating curing” method, using SiCN cured by organic polysilazane (OPSZ) as heat resistant shell material and Al-Si particles as core PCMs. The mechanisms of shell formation and coating of OPSZ were studied experimentally, as well as the material properties and thermal performance of MEPCMs. With the increase of temperature, OPSZ gradually formed a dense SiCN shell on the surface of Al-Si particles. The experimental results showed that MEPCMs with the core–shell mass ratio of 4:1 had a high phase change temperature (571.9 °C-573.7 °C) and good heat storage capability (281.2 J/g-282.9 J/g). SiCN shell was conducive to maintain a complete core–shell structure, and exhibited excellent thermal resistance and oxidation resistance to protect inner core materials during thermal cycles. Therefore, the prepared microcapsule was a potential heat storage material, which provided a new idea for developing microencapsulation method of high temperature PCMs.

Experimental and Numerical Analysis for the Discharge Performance of a High Temperature Phase Change Material with Low-Cost Wire Mesh

Experimental and Numerical Analysis for the Discharge Performance of a High Temperature Phase Change Material with Low-Cost Wire Mesh

Effects of natural and Marangoni convections on melting of high-temperature encapsulated phase change material under the earth and the moon gravities

The understanding of melting characteristics and mechanism of high temperature encapsulated phase change material (EPCM) is important for its application in heat storage systems. In this study, a two-dimensional axisymmetric numerical model is established to simulate the melting of spherical EPCMs with air void on the top. Besides buoyancy driven natural convection, Marangoni convection due to the thermocapillary force at the air-molten PCM interface is considered for the first time in this topic. To estimate thermocapillary force more accurately, the air-PCM interface is tracked by the coupled level-set and VOF method. The numerical simulations are conducted for EPCMs with Al2O3 shell and NaNO3 core with the different EPCM diameters and under the different gravity levels. It is found that Marangoni convection mainly affects the early and middle stages of PCM melting process, and its importance relative to buoyancy driven natural convection increases as the diameter of EPCM and gravity level decreases. For the EPCMs with diameter greater than 24 mm under the earth gravity, Marangoni convection has negligible effect, while for 12 mm diameter EPCM under the moon gravity, the complete melting time could be 19% shorter under the additional role of Marangoni convection. The solid PCM profile, fluid flow structure, melting ratio and heat transfer rate during the melting of EPCM under the effects of natural convection and Marangoni convection are also analyzed in detail.

A Review of Phase Change Materials

Phase change materials (PCMs) use latent heat of phase change to store heat, which has the advantages of high energy storage density and low-temperature fluctuation. And it can be applied to many fields such as the building envelope and the Heating Ventilation and Air Conditioning (HVAC) system. The PCM is a kind of energy storage material with great potential, which positively impacts energy conservation and indoor environment improvement. In this paper, the relevant research on PCMs in recent years is reviewed, three common classification methods of PCMs are summarized, and the phase change temperature range is re-divided. The temperature of PCMs is less than 80°C for low-temperature PCMs, between 80°C and 200°C for medium-temperature PCMs, and above 200°C for high-temperature PCMs. Then, the characteristics and thermal properties of some commonly used PCMs are listed, including organic PCMs, inorganic PCMs, and some composite phase change materials (CPCMs). By summarizing the thermal properties of PCMs, it can provide a reference for the selection of PCMs. Finally, the article also introduces several kinds of preparation methods for CPCMs. The solutions to the problems of low thermal conductivity, supercooling, phase separation, and leakage of PCMs are discussed. And the future research topics of PCMs are prospected.