Properties Of Phase Change Materials Research Articles

Synthesis and Studying Physicochemical Properties of Phase-Change Materials Based on Zinc Nitrate Hexahydrate

Synthesis and Studying Physicochemical Properties of Phase-Change Materials Based on Zinc Nitrate Hexahydrate

Structure Design and Heat Transfer Performance Analysis of a Novel Composite Phase Change Active Cooling Channel Wall for Hypersonic Aircraft.

Efficient and stable heat dissipation structure is crucial for improving the convective heat transfer performance of thermal protection systems (TPSs) for hypersonic aircraft. However, the heat dissipation wall of the current TPS is limited by a single material and structure, inefficiently dissipating the large amount of accumulated heat generated during the high-speed maneuvering flight of hypersonic aircraft. Here, a convection cooling channel structure of TPS is proposed, which is an innovative multi-level structure inspired by the natural honeycomb. An active cooling channel (PCM-HC) is designed by using a variable-density topology optimization method and filled with phase change material (PCM). Numerical simulations are used to investigate the thermal performance of the PCM-HC wall, focusing on the influence of PCM properties, structural geometric parameters, and PCM types on heat transfer characteristics. The results demonstrate that the honeycomb-like convection cooling channel wall, combined with PCM latent heat of phase change, exhibits superior heat dissipation capability. With a heat flux input of 50 kW/m2, the maximum temperature on the inner wall of PCM-HC is reduced by 12 K to 20 K. Different PCMs have opposing effects on heat transfer performance due to their distinct thermophysical properties. This work can provide a theoretical basis for the design of high-efficiency cooling channel, improving the heat dissipation performance in the TPS of hypersonic aircraft.

Study on the encapsulation effect and mechanism of hollow ceramsite to phase change materials (PCMs)

In order to promote the development of phase change materials (PCMs) and make them better applied, more in-depth research on the PCMs encapsulation is needed. The hollow ceramsite prepared in this study is a new type of PCMs carrier. Due to its unique structure, the encapsulation of PCMs by hollow ceramsite differs from that of ordinary porous ceramsite. In this paper, the adsorption and sealing effect of hollow ceramsite on PCMs was studied, the key factors affecting the adsorption and sealing effect were determined, and the encapsulation mechanism was revealed. The results show that the driving force of PCMs into the cavity of hollow ceramsite is mainly from the external pressure; the pore size and PCMs properties are the key factors determining the adsorption effect of hollow ceramsite. The pressure on the pore is proportional to the square of the pore diameter; increasing pore size enhances the possibility of the PCMs entering the cavity of ceramsite. The contact angle between PCMs and pores is smaller, and the surface tension of the PCMs in the pores is greater, making it difficult for PCMs to enter the cavity of ceramsite. The sealing mechanism of the coating on infiltrating PCMs is achieved by reducing the pore diameter of the sealing coating and increasing the resistance of PCMs to break through the pore. The sealing mechanism of the coating on non-infiltrating PCMs is achieved by changing the contact property between the PCMs and pore, increasing the energy barrier. After coating, the mass loss rate of infiltrating paraffin was controlled within 5 %, and the leakage rate of non-infiltrating hydrated salt was controlled within 1 %.

Encapsulation effectiveness and thermal energy storage performance of aluminum-graphite composite phase change materials subjected to oxide coating

The utilization of metals as phase change materials (PCMs) in high-temperature latent heat storage technology holds promising prospects, especially when integrated with concentrated solar power (CSP) systems, as it enables higher working temperatures for CSP and enhances power generation cycle efficiency. However, the practical application of metal-based phase change processes faces challenges such as liquid leakage and high-temperature corrosion, which impede their widespread implementation. In this study, aluminum (Al) is employed as the PCM, while expanded graphite (EG) is used as the matrix material. Composite PCMs with embedded structures were synthesized using powder metallurgy techniques. Notably, an oxidation pre-treatment process was employed to create an oxide layer on the surface of Al particles, thereby improving the encapsulation performance and thermal properties of the composite PCM. By increasing the oxidation pre-treatment temperature to 1100°C, the maximum encapsulation ratio was enhanced from 50 wt% to 80 wt%, and the latent heat energy storage density increased from 101.0 J/g to 188.2 J/g. Moreover, the composite PCM subjected to oxidation pre-treatment at temperatures of 670°C and above maintained a stable structure, chemical composition, and energy storage density after 50 thermal cycles. Within the temperature range of 600–700°C, the total energy storage density of the composite PCM reached 284.5 J/g. These results indicate that the oxidation pre-treatment is a promising technology in high-temperature energy storage technology.

Preparation and Performance of Inorganic Hydrated Salt-Based Composite Materials for Temperature and Humidity Regulation

In this work, it was first proposed to combine hydrated salt phase change materials (PCMs) with humidity control materials to prepare the temperature and humidity control material. The composite PCM was prepared by absorbing Na2HPO4·12H2O with colloidal silicon dioxide, and diatomite was selected as the humidity control material. The humidity performance tests found that diatomite had good moisture absorption/desorption capacity and excellent moisture buffering capacity. The supercooling degree tests showed that Na2SiO3·9H2O as nucleating agent effectively reduced the supercooling degree, and the addition of deionized water improved the water loss problem of composite PCMs. The DSC tests showed that the enthalpy and melting temperature of composite PCMs were 153.1 J/g and 28.9°C, respectively. By placing the temperature and humidity control material in different humidity, it was found that the moisture content of diatomite affected the thermal properties of composite PCMs. Diatomite could not only transfer moisture to hydrated salts but also absorb moisture from hydrated salt. The application performance tests of the temperature and humidity control material in the room model showed that it could simultaneously regulate indoor temperature and humidity. Overall, this temperature and humidity control material was more suitable for environments with high relative humidity such as greenhouses.

Effect of varying the thermophysical properties of phase change material on the performance of photovoltaic/thermal-PCM hybrid module numerically

The present investigation uses ANSYS-Fluent to establish a three-dimensional computational model to examine the impact of varying thermophysical properties of phase change material on photovoltaic/thermal system performance. A merit function is employed to determine the impact of varying the PCM thermophysical properties on the system to assess the economic feasibility of a proposed PV/T-PCM setup. The findings indicate that, despite the coolant discharge temperature appearing to be somewhat greater for the PV/T-PCM layout than for the PV/T design, the average PV surface temperature seems to be lower for the PV/T-PCM module. Additionally, the coolant outlet temperature dramatically improves with elevating the PCM melting temperature and thermal conductivity. When the latent heat of PCM elevates from 80 to 240 kJ/kg, the thermal and total energy efficiencies for the PV/T-PCM structure decline from 60.8 to 49.2 % and 72.6 to 61 %, respectively. Moreover, boosting the PCM melting temperature and thermal conductivity, respectively, from 305 to 323 K and 0.1 to 0.5 W/m.K dramatically enhances the total energy efficiency by about 13 and 10 %. It is found that varying the PCM melting temperature has a significantly greater impact on the total energy efficiency of PV/T-PCM module than that for the latent heat of fusion and thermal conductivity, where the total energy efficiency marginally increases from about 47.5 to 77.75 %, when boosting the PCM melting temperature from 305 to 323 K. With increasing the melting temperature and the thermal conductivity of the PCM, the heat to electricity ratio and the merit function value are significantly enhanced for the PV/T-PCM layout.

Phase change materials encapsulated in a novel hybrid carbon skeleton for high-efficiency solar-thermal conversion and energy storage

Phase change materials (PCMs) with high energy density and stationary transition temperature are now considered promising solar energy storage mediums. However, their intrinsic poor light absorption, thermal conductivity and stability severely impede their potential applications. In this study, a novel carbonized hybrid aerogel (CHA) structure was firstly constructed by incorporating MXene and carbon nanofibers (CNFs) into a continuous phase polyamic acid salt (PAAS) aqueous solution, followed by directional freezing, vacuum drying, imidization, and carbonization processes. Finally, the composite PCMs (CPCMs) were fabricated by vacuum impregnation of PCMs into the CHAs. The CPCM, of which CHA consists of 20 wt% MXene and 10 wt% CNF@PDA, demonstrates high solar-thermal conversion efficiency (>91 %), improved thermal conductivity of 0.40 W·m−1·K−1, great thermal stability (enthalpy loss < 0.19 % after 100 cycling tests with no obvious leakage). The introduction of MXene and CNFs endows PCM with broader light absorption spectrum range. The skeleton matrix embedded with bonded MXene sheets and CNFs provides more thermal pathways, light absorption sites and carrying capacity, improves the thermal conductivity, solar-thermal conversion property and stability of PCM. In addition, CPCM also exhibits outstanding EMI SE (95 dB). The multifunctional and high-performance CPCMs shows potential to realize the effective capture and utilization of solar energy. This work provides a new strategy to construct stable and multifunctional hybrid carbon skeleton for high-efficiency solar-thermal conversion and energy storage.

Peridynamic analysis of thermal behaviour of PCM composites for heat storage

One possibility to utilize excess energy from electricity generation or other industrial processes is to use thermal energy storage systems based on phase change materials (PCM). These systems can accumulate and release significant amounts of heat energy during the phase transitions. The volume and properties of PCM undergo rapid changes during the transitions, creating strong physical non-linearities and geometric discontinuities. Describing this complexity with local formulations of the physical processes, i.e., formulations with differential equations, makes the numerical solutions of the corresponding problems challenging. This paper presents a numerical approach for the analysis of such physically complicated systems based on Peridynamics. The approach is illustrated by modelling and analysing the thermal behaviour of a PCM. The computational challenges associated with simulating composite structures with large differences in the heat conductivity of their components are addressed by investigating the influence of different types of peridynamic kernels and their numerical implementation. The results demonstrate that the solution is significantly influenced by the definition of the average thermal conductivity of the peridynamic bonds. The proposed modelling framework provides the base for developing a precise thermo-hydro-mechanical description of PCM composites that can fully represent the complex physical behaviour of thermal energy storage systems.

A Numerical Study to Improve the Efficiency of Solar Collector used for water heating using Phase Change Material

Solar water heaters are an effective technology for harnessing renewable solar energy to provide hot water for households and businesses. However, their efficiency can be impacted by factors like intermittent sunshine, heat losses, and low radiation intensity. The aim of this study is to increase the efficiency of solar water heaters through the use of phase change materials (PCMs). PCMs have the ability to store latent heat during phase change, releasing it later when needed. This study uses numerical simulations to analyze the effect of integrating different PCMs into a flat plate solar collector design. The findings could then be validated experimentally and applied to improve the real-world performance of solar water heating systems. The PCMs are placed inside the collector to absorb heat during the day and release it after sunset to continue heating the water. The research seeks to determine the optimal PCM properties, structure, and placement within the collector to maximize heat storage and transfer. The efficiency and performance of the solar collector system with different PCM configurations have been compared to those of a conventional collector without PCM. The outcomes uncover that the use of suitable PCMs can significantly improve the efficiency and heat output of the solar collector, especially during periods of low radiation and after sunset. The optimal PCM configuration maintains higher water temperatures for longer, allowing solar water heating to continue into the evening. The results may provide valuable insights for using PCMs to boost the efficiency of solar thermal technologies

Optical properties of Sn-substituted GeTe phase-change materials under high pressure

The emerging phase change materials (PCMs) have attracted much attention due to their unique properties and applications. However, the optical properties of PCM at high pressures have not been well explored. In this work, the microstructure and optical properties of GeTe and Sn-substituted GeTe at high pressures up to 30 GPa have been systematically investigated. We find that the substitution of small amounts of Sn for Ge combined with the introduction of high pressure can induce an optical contrast of 117% in crystalline GeTe, which is even higher than the highest optical contrast reported so far (90%) caused by amorphous GeTe to crystalline GeTe. The pressure-induced contrast does not originate from any phase transition as previously, but from the combined effect of Peierls distortion elimination and Ge vacancy formation, which leads to an increase in carrier concentration. The relationship between pressure/atomic composition, Peierls distortion/vacancy formation, and optical contrast can be well explained by a combination of experiments and theoretical calculations. Therefore, this study reveals the effect of high pressure on the optical properties of PCMs and provides new ideas for the design of high-optical-contrast PCMs.

Thermal performance enhancement of multiple tubes latent heat thermal energy storage system using sinusoidal wavy fins and tubes geometry modification

In this paper, performance enhancement of a shell and multiple tube latent heat thermal energy storage system (LHTESS) is numerically investigated by implementing sinusoidal wavy fins and different geometrical designs of heat transfer tubes. The annular space of the shell is filled with the paraffin wax RT35 as phase change material (PCM) and absorbs heat from hot water through the multiple tubes. With the constant total cross-section area of all tubes and fins as the constraint condition, the effect of tube number and tube shape incorporated with the proposed fins on the heat transfer properties of PCM during the melting process is evaluated. The computational results demonstrate that the sinusoidal wavy fins can improve the phase change efficiency compared to the conventional straight fins. The double-pitch sinusoidal wavy fins decrease the total melting time by 9.5% compared to the straight fins for the single-tube case. As the number of HTF tubes increased from one to four, the complete PCM melting time decreased by 38.3%. Geometrical design alterations of heat transfer tubes from circular to petal-shaped are proposed to further improve the thermal performance of multiple tubes LHTESS. The melting rate of PCM is accelerated with an increase in the number of petals. The petal tubes with nine petals can save the charging time up to 24 % in comparison with the circular tubes in a four-tube case with double-pitch sinusoidal wavy fins, and up to 57% compared to the base case with a single circular HTF tube and straight fins.

Enhancing the thermal transfer properties of phase change material for thermal energy storage by impregnating hybrid nanoparticles within copper foams

A phase-change material (PCM) is recommended for thermal energy storage. However, conventional PCMs suffer from poor thermal conductivity. To solve this problem, this study presented different compositions to improve PCM thermal conductivity. The effects of the average specific surface of metal foams and the weight percentage of metal foams and hybrid nanoparticles on the phase-change materials' thermal characteristics were investigated. The findings demonstrate that thermal performance of the PCM composite is noticeably better than that of pure PCM and increasing the weight content of foam metal and hybrid nanoparticles leads to an increase in thermal conductivity of 37.7% for the same type of copper. The results also reveal that thermal conductivity performance increases as the amount of metal foam and hybrid nanoparticles increases. The average specific surface value of 1600 m2/m3 shows better thermal properties compared with other average specific surface values. Moreover, the heat capacity is affected by the increase in the content of metal foam. Many drawbacks have been found in using foam metal in PCM preparation, mainly the fixed shapes of metal foams compared with the formability nature of the PCM, which effects the shapes of the PCM composites and thus limits its use in applications with limited size. This novel approach to improving PCM's thermal behaviour may be applied to the creation of thermal energy storage devices with predetermined characteristics.

RHTC/HO-BNNS structure collaboratively improves thermal conductivity and photothermal conversion properties of phase change materials

The application of phase change materials (PCMs) to improve the efficiency of solar energy has been widely studied. However, most composite PCMs can only maintain high photothermal conversion performance in solid phase environment. To expand the application range of PCM in solar energy field, a flexible composite film which can stably exist in both solid and aqueous environments was prepared. Polyethylene glycol (PEG) as the temperature control core, hydroxyl boron nitride nanosheets (HO-BNNS) and carboxy-rich carbon (RHTC) as the thermally conductive filler and high photothermal converter, respectively, and polyvinylidene fluoride (PVDF) as the flexible supporting material. RHTC/HO-BNNS, as a key bridge, forms a thermal conductivity and photothermal conversion network in the composite film, making its photothermal conversion storage efficiency up to 92.1%, and its thermal conductivity 4 times higher than that of pure PEG. Together with the excellent mechanical strength (2.35 MPa), composite film can be operate at night solar evaporators. It can both improve the effective utilization of solar energy and accelerate the progress of seawater desalination, providing a new idea for expanding the application of PCM.

Bio-Based Polymers for Environmentally Friendly Phase Change Materials.

Phase change materials (PCMs) have received increasing attention in recent years as they enable the storage of thermal energy in the form of sensible and latent heat, and they are used in advanced technical solutions for the conservation of sustainable and waste energy. Importantly, most of the currently applied PCMs are produced from non-renewable sources and their carbon footprint is associated with some environmental impact. However, novel PCMs can also be designed and fabricated using green materials without or with a slight impact on the environment. In this work, the current state of knowledge on the bio-based polymers in PCM applications is described. Bio-based polymers can be applied as phase-change materials, as well as for PCMs encapsulation and shape stabilization, such as cellulose and its derivatives, chitosan, lignin, gelatin, and starch. Vast attention has been paid to evaluation of properties of the final PCMs and their application potential in various sectors. Novel strategies for improving their thermal energy storage characteristics, as well as to impart multifunctional features, have been presented. It is also discussed how bio-based polymers can extend in future the potential of new environmentally-safe PCMs in various industrial fields.

Evaluation of PCM thermophysical properties on a compressed air energy storage system integrated with packed-bed latent thermal energy storage

Compressed air energy storage (CAES) is a promising large-scale energy storage technology to mitigate the fluctuations and intermittence of renewable energies. The application of latent thermal energy storage (LTES) using phase change materials (PCM) to recover compressed waste heat can further improve the energy storage density and round-trip efficiency of CAES. However, there are very few guidelines of PCM selection for a CAES system. In view of the challenge, this study first conducts orthogonal experiments to analyze the effects of the thermophysical properties of PCMs on the performance of the packed-bed LTES and CAES system. Then a PCM selection procedure for CAES is developed based on the orthogonal experiment design and TOPSIS method. The results of range analysis indicate that each thermophysical property of PCM has quite different relative importance to the performance indicators of the CAES system. From the aspect of packed-bed LTES, the density (40.8 %) and latent heat (32.8 %) of PCMs are the top two impact factors for the heat storage rate, while the melting temperature (45.7 %) and thermal conductivity (22.4 %) are the top two impact factors for the residual heat. From the aspect of the CAES system, the density (31.9 %) and melting temperature (24.4 %) are the top two impact factors for the round-trip efficiency, while the density (42.2 %) and latent heat (35.2 %) rank the top two impact factors for the air storage capacity.

A numerical study on the effects of inclination angle and container material on thermal energy storage by phase change material in a thick-walled disc

PurposeThe purpose of this study is to examine the effects of inclination angle on the thermal energy storage capability of a phase change material (PCM) within a disc-shaped container. Different container materials are also tested such as plexiglass and aluminium. This study aims to assess the energy storage capacity, melting behaviour and temperature distributions of PCM with a specific melting range (22°C–26°C) for various governing parameters such as inclination angles, aspect ratios (AR) and temperature differences (ΔT) and compare the melting behaviour and energy storage performance of PCM in aluminium containers to those in plexiglass containers.Design/methodology/approachA finite volume approach was adopted to evaluate the thermal energy storage capability of PCMs. Five inclination angles ranging from 0° to 180° were considered and the energy storage capacity. Also, the melting behaviour of the PCM and temperature distributions of the container with different materials were tested. Two different AR and ΔT values were chosen as parameters to analyse for their effects on the melting performance of the PCM. Conjugate heat transfer problem is solved to see the effects of conduction mode of heat transfer.FindingsThe results of the study indicate that as AR decreases, the effect of the inclination angles on the energy storage capacity of the PCM decreases. For lower ΔT, the difference between the maximum and minimum stored energies was 20.88% for AR = 0.20, whereas it was 6.85% for AR = 0.15. Furthermore, under the same conditions, the PCM stored 8.02% more energy in plexiglass containers than in aluminium containers.Originality/valueThis study contributes to the understanding of the influence of inclination angle, container material, AR and ΔT on the thermal energy storage capabilities of PCM in a novel designed container. The findings highlight the importance of AR in mitigating the effect of the inclination angle on energy storage capacity. Additionally, comparing aluminium and plexiglass containers provides insights into the effect of container material on the melting behaviour and energy storage properties of PCM.

Effects of Superabsorbent Polymer Addition on the Thermal Properties of Eutectic Phase Change Material

In this study, the influence of a super absorbent polymer (SAP) addition on the thermal properties of phase change material (PCM) was investigated. It was found that adding SAP reduced the melting temperature of PCM and improved phase separation properties. While the addition of 1.0 wt% of SAP to PCMs decreased latent heat by 3 J/g to 24.4 J/g, the addition was determined to be necessary to prevent leaks from a functional duct unit (FDU) and assure product stability. The results obtained from a series of brine refrigeration tests indicate that the supercooling temperature decreased by 0.3 °C to 1.7 °C when 1.0 wt% of SAP was added to PCM. The addition of SAP to PCM appears to promote supercooling by encouraging condensation during phase change. As a result of applying SAP-added PCM to the FDU, the isothermal operation performance was improved compared to existing refrigerators.

Preparation and properties of phase-change materials with enhanced radial thermal conductivities based on anisotropic graphene aerogels.

In this study, anisotropic graphene aerogels are prepared using the heat-flow method. Then, graphene aerogels with nanosilver particles are prepared via a silver mirror reaction. The aerogels are soaked in paraffin wax and the effects on the properties of the wax are investigated. The thermal conductivity of pure paraffin wax is 0.2553 W m-1 K-1. For the prepared PCM, the aerogel content was 0.92 vol%; this increases to 1.2234 W m-1 K-1, which corresponds to a thermal conductivity enhancement efficiency of 582%. The axial thermal conductivity is 1.4953 W m-1 K-1, which corresponds to a thermal conductivity enhancement efficiency of 746%. The graphene aerogels with the nanosilver particles show high phase-change efficiency. Owing to the significant improvements in the axial and thermal conductivities, the radial and axial heat transfer properties show good consistency suitable for practical applications.

A numerical and statistical study to determine the effect of thermophysical properties of phase change material for lithium-ion battery thermal management

Lithium-ion batteries’ performance is quite sensitive to temperature, leading to capacity fade, acceleration of aging effect, and possible thermal runaway. The temperature of lithium-ion batteries increases under operating conditions of high discharge rates. The heat released by the battery can be effectively removed using phase change material (PCM). The thermophysical properties of the PCM affect the heat removal performance of the PCM. In this study, the effect of thermophysical parameters such as thermal conductivity, latent heat, specific heat, and density on maximum battery temperature and battery temperature uniformity was numerically investigated. The dominant factors for PCM to prevent temperature increase in a prismatic LiMn2O4 lithium-ion battery were identified by orthogonal design to improve the thermophysical properties of PCM. The thermophysical properties of PCM were changed by incorporating the expanded graphite. Based on what was observed in the current study, the influence of the thermal conductivity of PCM was higher than other thermophysical properties, while the influence of the latent heat on both maximum battery temperature and temperature uniformity was negligible. Density was the second crucial factor that could help reduce the maximum battery temperature and keep the temperature distribution uniform. The results obtained from this study can allow the design of effective battery thermal management systems by improving the thermophysical properties of the PCM.

Energizing the thermophysical properties of phase change material using carbon-based nano additives for sustainable thermal energy storage application in photovoltaic thermal systems

As solar energy are intermittent in nature and not predictable, researchers and scientists are actively developing efficient thermal energy storage (TES) systems intending to maximize the utilization of solar energy. Phase change materials (PCM) are potential materials that are largely accessed towards TES. However, the notable drawback of PCM is their lower thermal conductivity, leading to slower heat transfer rates and reduced thermal energy storage density. Thus, the current study focuses on developing and exploring a PCM composite by embedding paraffin wax and graphene to enhance the heat transfer mechanisms, making it a promising option for TES applications. Various aspects of the composite's performance were examined, including its microstructural behaviour, chemical stability, thermal stability, thermal conductivity, thermal reliability, and heat transfer characteristics. The findings revealed that the inclusion of graphene led to a substantial increase of up to 75.09 % in thermal conductivity while preserving the melting enthalpy of the material. The newly developed nanocomposite also demonstrated chemically and thermally stable up to a temperature of 210 °C, and the thermal stability was slightly enhanced by adding nanoparticles. This nanocomposite also exhibited improved optical absorptance and reduced transmittance, enhancing its potential for solar energy absorption. It further demonstrated durability, maintaining stability even after undergoing 500 thermal cycles. Notably, the overall efficiency of the nano-enhanced PCM integrated photovoltaic-thermal system (PVT) enhanced by 29 % and 49 % greater than the PVT system and conventional PV system. Given these exceptional characteristics and performance enhancements, this nanocomposite material holds promise for significantly advancing future sustainable TES technologies.