Graphite Composite Phase Change Material Research Articles

Experimental study on the temperature control characteristics of graphite foam-based composite phase change materials

Thermal management systems are crucial for ensuring the reliable operation of electronic devices. Heat dissipation using phase change materials (PCMs) is an effective, lightweight method for devices experiencing transient high heat flow. Graphite foam (GF), known for its high thermal conductivity and low density, significantly increases thermal conductivity when combined with PCMs. However, research on the heat transfer characteristics of composite PCMs is limited. This study experimentally investigates the heat dissipation characteristics of a graphite foam-PCM (GF-PCM) composite cooling structure. It explores the impact of factors like the shell's tilt angle, acceleration, and the position of cavities (voids) between the PCM and the shell structure on the transient melting heat transfer of the cooling device under varying thermal source heat flux densities. Results show that using a pure paraffin phase change module, the temperature rise of the heat source increases with the tilt angle, and horizontal placement offers the best heat dissipation and temperature control. The position of the cavity influences heat dissipation; at 30W heating power, a cavity between the heat source and paraffin increases the temperature rise of the heat source by 19.2 %. Furthermore, cavity position is affected by acceleration; at 50W heating power and 3.6g acceleration, the cavity shifts from the top of the module to near the heat source side, increasing its final temperature by 3.7 °C. Acceleration also enhances liquid paraffin convection, significantly affecting paraffin's later melting stage. Adding graphite foam speeds up paraffin melting, reducing the temperature rise of the heat source by 42.8 %, 42.9 %, and 28.3 % at 30W, 40W, and 50W heating powers, respectively. This improvement mitigates the adverse effects of tilt angle, cavities, and uncertainties introduced by acceleration.

Thermal performance of phase change material based heat exchanger filled with inorganic salt/expanded graphite

Solid-liquid latent heat storage, featured by the high-density energy storage capacity, is promising in facilitating the high-penetration renewable energy. However, the design of the heat exchanger is challenging due to the conflicting objectives between the heat transfer efficiency and energy storage capacity. To this end, this paper introduces a comprehensive evaluation index, based on which an orthogonal based design optimization method is proposed for heat exchangers filled with inorganic salt/expanded graphite composite phase change material (CPCM). A thermophysical properties based numerical model is built to describe and analyze the solidification and melting of CPCM. The comprehensive evaluation index is utilized to quantify the overall change in heat storage/release performance relative to the mass change of the baseline phase change heat exchanger. The orthogonal experimental method is employed to investigate the impact of various heat exchanger structural factors on the comprehensive performance, followed by optimization design. Simulation results indicated that the longitudinally finned heat exchanger outperforms the other two heat exchangers in terms of the comprehensive evaluation index. Moreover, the inlet fluid temperature exerts a more significant impact on the comprehensive evaluation index compared to the inlet fluid velocity. Additionally, the effects of pipe spacing, fin number, fin height, and tube material on the thermal performance of the longitudinally finned heat exchanger were examined and analyzed. Among these factors, the fin height was identified as the most substantial contribution to the heat transfer performance, while the tube material has a minor effect.

Investigating the Phase Transition Kinetics of 1-Octadecanol/Sorbitol Derivative/Expanded Graphite Composite Phase Change Material with Isoconversional and Multivariate Non-Linear Regression Methods.

Organic composite phase change materials (PCMs) have been extensively studied, and it is important to investigate the effect of added components on the phase change process of the organic matrix. Herein, the phase transition process of the composite PCM with 1-octadecanol (OD) as the matrix adsorbed by a network framework composed of 1,3:2,4-di-(3,4-dimethyl) benzylidene sorbitol (DMDBS) and expanded graphite (EG) was measured using differential scanning calorimetry (DSC) at several linear heating rates. Using isoconversional and multivariate non-linear regression methods, a two-step consecutive reaction model for the composite PCM was established, while the apparent activation energies and pre-exponential factors were determined. The reaction mechanism of the first step was altered compared to pure OD, while the activation energies significantly decreased at the initial stage of the phase transition process and increased at the later stage. Combined with microscopic morphology analysis, the main reasons were the size and nanoconfinement effect. The predictions of the composite PCM under various conditions suggested that the composite PCM had a wider available temperature range compared to pure OD. This research provided a new idea for the in-depth study of the phase transition process of organic composite PCMs, which was helpful for the evaluation of organic composite PCMs.

Bilayer lattice structure integrated with phase change material for innovative thermal protection system design

In recent years, ceramic matrix composite (CMC) lattice structure has become a promising candidate for a new generation of integrated thermal protection systems (ITPSs) used in the ultrahigh-temperature environment. However, the thermal short circuit effect caused by lattice cores limits their application. In this work, we propose a bilayer CMC lattice structure filled with phase change material (PCM) and thermal insulation material for integrated thermal protection systems (ITPSs) to mitigate the thermal short circuit effect. The numerical simulation method is used to verify the effectiveness of the bilayer lattice structure in mitigating the thermal short circuit effect compared with one-layer ITPS. By inserting the middle face sheet, the thermal insulation effect enhances about 16%. Furthermore, the effects of thermal insulation materials, thermal conductivity and thickness of paraffin/expanded graphite composite PCM, and the diameter of the lattice core strut on the thermal insulation performance are discussed. The results show that the thickness of PCM has an optimal solution. Optimizing results show that when the aerogel insulation fiber is used as the thermal insulation material, the thermal conductivity k=0.82 W/(m⋅K) and the thickness t3=10 mm of PCM, the diameter of the core strut d=1.5 mm, the bilayer PCM-ITPS has the best thermal insulation performance. When the ultrahigh-temperature load is continuously loaded, the highest temperature of Top Face Sheet is more than 2300°C, but the highest temperature of Bottom Face Sheet is only 30.12°C, which thermal insulation effect is far better than the traditional ITPS. This work gives a novel scheme to solve the thermal short circuit effect, improving the thermal protection performance and accelerate the application of lattice structure in ITPS.

Preparation and thermal properties of LiNO3-NaNO3-NaCl/EG composite heat storage material

Nitrate phase change materials (PCM) have important applications in the field of thermal energy storage, but their latent heat value is relatively low. A novel LiNO3-NaNO3-NaCl ternary molten salt with high latent heat was prepared and studied. LiNO3-NaNO3-NaCl/expanded graphite (EG) composite phase change material (CPCM) was prepared by using high thermal conductivity EG as the carrier adsorption material. The performance of PCM and CPCM were tested and analyzed. Compared with LiNO3-NaNO3, the newly prepared ternary nitrate-chloride mixed molten salt has a lower phase change temperature, a higher latent heat value, and a higher thermal decomposition temperature. At the same time, the supercooling degree of LiNO3-NaNO3-NaCl is about half lower than that of LiNO3-NaNO3. There is no chemical reaction between different molten salts or between mixed molten salts and EG. The mixed molten salt is uniformly dispersed into the pore structure of EG, and no agglomeration occurs. Both LiNO3-NaNO3-NaCl and LiNO3-NaNO3-NaCl/EG have good cyclic thermal stability. The addition of EG greatly improves the thermal conductivity of LiNO3-NaNO3-NaCl. When the addition ratio of EG is 20%, the thermal conductivity of ternary molten salt increases from 1.378 to 5.453 W/m·K. The phase change materials added with EG still have high latent heat of phase change. The results show that LiNO3-NaNO3-NaCl/EG has broad application prospects in medium temperature heat storage.

Research on Thermal Management Coupling by CPCM and Liquid Cooling for Vehicle Lithium-Ion Batteries

This study addresses the issue of heat dissipation in 18,650 cylindrical lithium-ion battery packs and proposes a novel heat dissipation model that combines paraffin wax-expanded graphite composite phase change material (CPCM) with liquid cooling. Initially, a comparison is conducted between the heat dissipation effects of the battery pack under natural convection and the heat dissipation achieved through the utilization of CPCM. Subsequently, the CPCM model is employed to identify the optimal battery arrangement. Subsequently, a heat dissipation model is developed by coupling CPCM with liquid cooling. The simulation outcomes obtained using COMSOL software demonstrate that employing the paraffin-expanded graphite CPCM liquid cooling coupled heat dissipation model can achieve a reduction in battery spacing to 0 mm while maintaining the maximum surface temperature of the battery between 20–45 °C and improving the temperature uniformity of the battery during 1–3 C cyclic charging and discharging. This approach ensures the battery pack’s normal operation, enhances safety, and prolongs the battery pack’s service life.

Application of 1-Decanol Loaded in Silica Aerogel and Expanded Graphite Composite Phase Change Materials in Cold Chain Transport Portable Boxes

Application of 1-Decanol Loaded in Silica Aerogel and Expanded Graphite Composite Phase Change Materials in Cold Chain Transport Portable Boxes

Improvement of thermal cycle stability of paraffin/expanded graphite composite phase change materials and its application in thermal management

Paraffin/expanded graphite (PA/EG) composite phase change materials (PCMs) were prepared by melt blending. The effects of EG particle size and pressing direction on heat transfer performance and thermal cycle deformation were studied. The results show that by reducing the particle size of EG, the thermal conductivity is enhanced and the deformation degree of PA/EG during the thermal cycle is alleviated. When the non-pressurized surface is used as the heating surface, PA/EG thermal conductivity is enhanced and the effect of deformation is avoidable. After that, the thermal management performance of PA/EG before and after packaging was experimentally studied. The results show that the reduction of EG particle size is beneficial to thermal management, and the average temperature of the hot surface of PA/EG100(a) is 46.1 °C, which is 1.1 °C lower than that of PA/EG50(a). PA/EG100(b) with the non-pressurized surface as heating surface has better thermal cycle stability, and the change of ambient temperature and heat flux will not affect heat transfer performance. Even for the packaged PA/EG samples, PA/EG100(b) still exhibits better thermal management performance due to the little deformation on heating surface. The present work proves that the non-pressurized surface of PA/EG as heating surface is a better choice for practical applications.

Preparation and Thermal Performance of Fatty Acid Binary Eutectic Mixture/Expanded Graphite Composites as Form-Stable Phase Change Materials for Thermal Energy Storage.

A series of fatty acid binary eutectic mixture/expanded graphite (FABEM/EG) composite phase change materials (CPCMs) were prepared by absorbing a liquid FABEM into the EG. The thermal properties, thermostability, and thermoreliability were determined by differential scanning calorimetry (DSC), thermogravimetric analysis (TGA), and thermal cycling tests, respectively. Fourier transform infrared spectrometry (FT-IR) and scanning electron microscopy (SEM) were used to analyze the chemical structure and microstructure, respectively. Thermal conductivity measurements and heat storage/release experiments were carried out to study the heat transfer performance. The DSC test results show that the phase transition temperatures and latent heat of these CPCMs are in the range of 17.8-55.2 °C and 134.9-176.2 J/g, respectively. FT-IR analysis indicates there is only a simple physical adsorption between EG and the PCM and no chemical reaction occurs. SEM results show that the fatty acid binary eutectic mixtures are well adsorbed in the pores of EG, and EG can provide a certain mechanical strength and prevent phase change materials from leaking. The thermal conductivity measurement and heat storage/release experiment show that the addition of EG greatly improves the thermal conductivities of the CPCMs. TGA test results and thermal cycle tests show that the CPCMs have excellent thermal stability and long-term cycling thermal reliability.

Preparation and Application of Paraffin/Expanded Graphite-Based Phase Change Material Floor for Solar-Heat Pump Combined Radiant Heating Systems

Application of phase change material (PCM) floor as the thermal storage unit in a radiant heating system possesses the advantages of improving indoor comfort with high energy efficiency and favorable economic applicability. This work proposed a novel PCM floor by directly mixing the paraffin/expanded graphite composite PCM (CPCM) with building cements and then explored its practical application performance in a solar-heat pump combined radiant heating system. First, the mass fraction of CPCM was optimized, taking into account the thermal (thermal storage capacity, thermal conductivity, leakage analysis, thermal stability, and reliability) and mechanical properties (combined strength and flexural strength) that the PCM floor should have, and 35% was determined as the optimum mass fraction of CPCM for the PCM floor. Second, the application potential of the studied PCM floor was further evaluated by experimental measurements and TRNSYS simulations. The results showed that the thermal comfort satisfaction rate of the room based on the PCM floor reached 96.8%; by comparing the PCM floor room with the control one without a PCM layer installed in the floor, the enhancement of the PCM floor, that is, the indoor comfort improvement as well as the energy and economic impacts, was well interpreted.

Preparation, thermal storage properties and application of sodium acetate trihydrate/expanded graphite composite phase change materials.

The development of energy storage technology is beneficial for the efficient use of energy and sustainable development. As an effectual approach for storing and transporting thermal energy, latent heat storage using phase change materials (PCMs) has attracted tremendous attention. However, low thermal conductivity, poor stability, and leakages are considerable challenges to the widespread application of solid-liquid PCMs. Composite phase change materials (CPCMs) were prepared by combining expanded graphite (EG) and sodium acetate trihydrate (CH3COONa·3H2O, SAT). EG as a supporting material plays a crucial part in both enhancing the thermal conductivity and preventing the melted PCMs from leakage. The chemical structure, micromorphology, thermal stability, thermal conductivity, phase change behavior and heat storage performance of SAT/EG CPCMs have been extensively investigated by scanning electron microscopy (SEM), Fourier transform infrared spectroscopy (FTIR), X-ray diffraction (XRD), thermal conductivity analysis, differential scanning calorimetry (DSC), and cycling stability measurement. The results of SEM indicate that EG with a loose and porous layered structure has a good molding effect and can adsorb SAT well. XRD and FTIR results show that only a simple physical combination between EG and SAT exists, and no new substances have been produced. Compared with pure SAT, thermal conductivity and supercooling tests show that the supercooling degree of the CPCMs was decreased and the thermal conductivity was increased by 205.1%. In addition, the addition of 2 wt% of disodium hydrogen phosphate dodecahydrate (Na2HPO4·12H2O, DHPD) as a nucleating agent and 0.5 wt% of gelatin as a thickening agent to SAT could reduce the supercooling degree and inhibit the phase separation well. Based on SAT/EG-8% CPCMs, an oven with phase change energy storage was designed and the heat storage/release performance of the oven was investigated under different operating conditions.

Preparation and Thermal Model of Tetradecane/Expanded Graphite and A Spiral Wavy Plate Cold Storage Tank

A cold storage unit can store the cold energy off-peak and release it for building cooling on-peak, which can reduce the electricity load of air conditioning systems. n-tetradecane is a suitable cold storage material for air conditioning, with a phase change temperature of is 4–8 °C and a phase change enthalpy of 200 kJ/kg. However, its low thermal conductivity limits the application of n-tetradecane for high-power cold storage/release. This paper prepares a tetradecane/expanded graphite (EG) composite phase change material (CPCM), whose thermal conductivity can be increased up to 21.0 W/m·K, nearly 100 times over the raw n-tetradecane. A novel model to predict the maximum loading fraction of paraffin in the EG matrix is presented, with an error within 1.7%. We also develop a thermal conductivity model to predict the thermal conductivity of the CPCM precisely, with an error of less than 10%. In addition, an innovative spiral wave plate cold storage tank has been designed for the tetradecane/EG composite. The power and energy density of the cold storage tank are significantly improved compared to that of raw tetradecane. The energy density reaches 40 kWh/m3, which is high among the organic PCM thermal storage tank. This paper shows the significance of thermal conductivity enhancement in designing a cold storage tank.

Highly thermally conductive composite phase-change materials doped with two-dimensional heterogeneous nanohybrids for photo/electro-thermal energy storage

Phase-change thermal storage technology can solve the problem of mismatch between supply and demand of thermal energy. In this study, a meso-erythritol/two-dimensional heterogeneous nanohybrids/expanded graphite (mE/2DHN/EG) composite phase-change material (PCM) was prepared using hydrothermal and molding methods. The experimental results show that the mE/2DHN/EG composite PCM has excellent thermal, photo-thermal conversion, and electro-thermal conversion properties. The thermal conductivity of mE/2DHN/EG is as high as 12.36 W m−1 K−1, which is 17.31 times that of pure mE. In addition, the photo-thermal conversion efficiency of mE/2DHN/EG can reach 75.72 % under the action of 2DHN and can convert a low driving voltage (2.08 V) into medium-high temperature heat (>130 °C) with an efficiency of 70.07 %. This study provides a cost-effective way to manage the photo/electro-thermal response of PCMs.

Paraffin/modified exfoliated graphite composite phase change materials with high performance and stability for thermal energy storage

Paraffin/modified exfoliated graphite composite phase change materials with high performance and stability for thermal energy storage

Preparation and characterization of paraffin/expanded graphite composite phase change materials with high thermal conductivity

Paraffin/expanded graphite (PCM/EG) composite phase change material was prepared. The microstructure, thermal properties and cycle stability of PCM/EG were characterized. The results show that the thermal conductivity of PCM/EG increases with EG content and block density increasing. When EG content is 20%, paraffin can be adsorbed completely and there is no obvious leakage during 60 melting and solidification cycles. EG lamella structure is formed during compression process of PCM/EG, which is perpendicular to pressure direction and beneficial to enhance the directional thermal conductivity. The thermal conductivity of PCM/EG20%-800(b) along EG lamellar structure direction is 7.82 W m−1 k−1, which is 47.8% higher than that perpendicular to EG lamellar direction. In addition, experimental studies were carried out on PCM/EG melting process to reveal the effects of EG content, block density and EG lamellar direction on temperature control performance. The results show that the average temperature of heating surface in melting process of PCM/EG20%-800 is 46.2 °C, which is 4.0% lower than PCM/EG16%-800. In addition, when heat flow direction is parallel to EG lamellar structure direction, the average surface temperature is 44.8 °C, which means a better temperature control effect. The present work provides an efficient method to enhance PCM/EG heat storage and temperature control performance under fixed latent heat.

Thermal properties and application of a novel CaCl2·6H2O/expanded graphite shape-stabilized composite phase change material for electric radiant heating

In recent years, electric heating has been popularized and applied as a heating form of clean energy. In order to realize the peak shifting and valley filling of heating electricity to reduce heating cost and improve energy efficiency, phase-change heat storage electric heating system has become a hot topic of research and application. In this paper, using CaCl2·6H2O as phase change material (PCM), SrCl2·6H2O as nucleating agent and expanded graphite (EG) as porous supporting carrier, a novel shape-stabilized composite PCM was prepared by melt blending method. The thermal physical properties of shape-stabilized composite PCM with different prepared proportions were studied through experiments. The experimental results showed that 88%CaCl2·6H2O + 2%SrCl2·6H2O + 10%EG (50 mesh to 100 mesh) is the optimal prepared proportion of the shape-stabilized composite PCM. The composite PCM with a latent heat of 172.92 kJ/kg, a thermal conductivity of 3.85 W/m·K and a super-cooling degree less than 2 °C, has good shape stability and thermal reliability. A kind of novel electric heating module was fabricated with prepared composite PCM and carbon fiber heating wire. The heat storage and release characteristics of the module were studied through experiments, and the effects of different electric heating power, EG particle size and module size on its thermal performance were also studied. The experimental results showed that the internal temperature of the module was uniform and the module can maintain stable heat dissipation for a long time. The temperature fluctuation of the module surface is relatively small. In summary, the module can meet the heating requirements of buildings when applied to electric radiant heating in the building, and the CaCl2·6H2O/EG shape-stabilized composite PCM shows great promise in building energy saving.

Thermal characteristics enhancement of Na2HPO4⋅12H2O/expanded graphite form-stable composite phase change material by the cationic surfactant modification

Phase change materials (PCMs) are widely used for their effectively thermal energy storage and conversion. Na2HPO4⋅12H2O (DHPD) is a promising inorganic PCM, as it possesses large heat enthalpy and suitable phase change temperature. Hexadecyl trimethyl ammonium chloride (CTAC) hydrophilic structure of composite PCM (CPCM) was formed, because of the poor sealing stability of expanded graphite (EG). Indeed, there is the solid intermolecular attraction between cations of CTAC and the water of DHPD, thereby improving the thermal characteristics. The heat enthalpy of EG/CTAC 0.1-DHPD (ECCD-0.1) CPCM was 299 J/g, and the thermal conductivity of ECCD-0.1 CPCM was 1.411 W/m⋅K. The ECCD-CPCMs showed a great cyclic stability which remained stable after 500 melting-solidification cycles.

Effects of Pore Structure and Pore Size of Expanded Graphite on the Properties of Paraffin Wax/Expanded Graphite Composite Phase Change Materials

In order to study the effects of the pore structure and pore size of porous carrier material on the phase transformation behavior of composite phase change materials (CPCMs), the pore structure and pore sizes of three different sizes of expanded graphites (EGs) (50, 80, 100 mesh) were studied using N2 adsorption-desorption isotherms and scanning electron microscopy. Then, the thermal characterization of CPCMs prepared with paraffin wax and EGs were tested using differential scanning calorimetry and a thermal conductivity tester. The results showed that EG-50 had a more web-like pore structure, and thus, higher adsorption capacity for paraffin wax. The addition of EG could reduce the supercooling degree of CPCMs and improve the thermal conductivity of CPCMs. CPCM with EG-50 had better performance due to its large specific surface area and low interfacial resistance. Compared with paraffin wax, the phase transition temperature (ΔT) of CPCMs increased slightly and the latent heat of CPCMS decreased to varying degrees. As the pore size of EG decreased, its constraint on PCM increased, but ΔT of CPCMs decreased, which was due to the combination of phase transformation behavior of different components in paraffin wax, which violates the conventional change law. It could be seen that the phase change behavior of CPCMs was related not only to the pore size of EG but also to the composition of PCM.

Performance optimization of sodium acetate trihydrate-based phase change material

• Performance optimization of sodium acetate trihydrate-based PCM is conducted. • Additions of deionized water as well as expanded graphite are optimized. • Performances of PCM are observed at both atmospheric and negative pressures. • Optimum PCM shows promising performances in condensing heat recovery system. The application of phase change heat storage technology in condensing heat recovery system of air conditioning can effectively solve the non-synchronization of condensate heat discharge and hot water demand, and thus improve the energy utilization efficiency. For this purpose, a novel sodium acetate trihydrate-based phase change material was prepared and tested in our very recent work, which presented high potential to recover condensation heat. In this work, the sodium acetate trihydrate-based phase change material was further optimized for more promising heat storage and release performance. To begin with, in order to improve the heat storage density of sodium acetate trihydrate-based phase change material, deionized water was added into the mixture and their heat storage and release tests were carried out at atmospheric pressure and vacuum degree of 0.09 and 0.10 MPa. The heat storage density of such phase change material reached 8.2581 kW·h/kg with 7 wt% deionized water added, however, the cycle measurements showed that the heat storage and release performance were unstable under negative pressures. To solve this problem, expanded graphite was used to further stabilize and optimize sodium acetate trihydrate-based phase change material with extra water to improve the cycle stability. The results showed that the addition of 15 wt% expanded graphite in 50 mesh can effectively stabilize heat storage and release performance of these phase change material samples at both atmospheric and negative pressures. In addition, the optimum sodium acetate trihydrate-expanded graphite composite phase change material presents excellent form stability, thermal conductivity (4.566 W/(m·K)) and very comparable heat energy density at both atmospheric pressure (7.6301 kW·h/kg) and vacuum degree of 0.09 MPa (6.3295 kW·h/kg).

Experimental study on lauryl alcohol/expanded graphite composite phase change materials for thermal regulation in building

The application of phase change materials (PCMs) in buildings has received extensive attention in recent years because they can improve indoor thermal capacity and solve the problem of high energy consumption through their greater latent heat. This study proposes to place the PCM in the ceramic tiles to solve the problem of high energy consumption in buildings based on the comfortable temperature of the human body. We introduced a two-level human thermal comfort temperature evaluation index, and consider that the phase change temperature of 24 °C has the best effect on thermal comfort and the whole year energy saving and emission reduction. Then, we built a building model with ceramic tiles filled with lauryl alcohol/expanded graphite and tested its thermal performance. In this study, lauryl alcohol can increase the heat capacity of the room, and lauryl alcohol/expanded graphite can improve the thermal response speed. We also inlay insulation boards between the wall and the ceramic tiles to prevent indoor and outdoor heat exchange and reduce indoor temperature fluctuations, which helps to keep the indoor temperature within a comfortable range for the human body. Compared with the insulation building, this method can extend the time of the indoor temperature in the comfortable temperature zone by 561% during the heating process, and the time of the cooling process can be extended by 471%. This work can reduce the opening time of air-conditioning equipment, so as to achieve the purpose of energy saving and emission reduction.