Form-stable Composite Phase Change Materials Research Articles

Cost-Effective Biochar Produced from Agricultural Residues and Its Application for Preparation of High Performance Form-Stable Phase Change Material via Simple Method.

A new form-stable composite phase change material (PEG/ASB) composed of almond shell biochar (ASB) and polyethylene glycol (PEG) was produced via a simple and easy vacuum impregnation method. The supporting material ASB, which was cost effective, environmentally friendly, renewable and rich in appropriate pore structures, was produced from agricultural residues of almond shells by a simple pyrolysis method, and it was firstly used as the matrix of PEG. Different analysis techniques were applied to investigate the characteristics of PEG/ASB, including structural and thermal properties, and the interaction mechanism between ASB and PEG was studied. The thermogravimetric analysis (TGA) and thermal cycle tests demonstrated that PEG/ASB possessed favorable thermal stability. The differential scanning calorimetry (DSC) curves demonstrated that the capacities for latent heat storage of PEG/ASB were enhanced with increasing PEG weight percentage. Additionally, PEG/ASB had an excellent thermal conductivity of 0.402 W/mK, which was approximately 1.6 times higher than that of the pure PEG due to the addition of ASB. All the study results indicated that PEG/ASB had favorable phase change properties, which could be used for thermal energy storage.

A cost-effective form-stable PCM composite with modified paraffin and expanded perlite for thermal energy storage in concrete

High thermal conductivity in phase change materials (PCM) is preferred in thermal energy storage (TES) systems. Carbon additives are considered as suitable materials for this purpose; however, some important issues such as price and stability for these materials should be considered. In this study, graphite powder and multiwall carbon nanotubes as an inexpensive and a relatively expensive carbon additives were used to improve the thermal conductivity of a long-chain paraffin (P) with a melting peak point of 64 °C. Also an amine functionalization method was applied to enhance the dispersion of CNTs into the non-polar paraffin medium. At first, the thermal conductivity and stability of the materials, as important and critical properties, were evaluated. In the next step, atmospheric impregnation method was conducted to incorporate modified PCM into the expanded perlite (EP) particles and finally, a lightweight concrete was constructed by these form-stable EP/P composites. Thermal behavior of the final concrete sample was studied by a simple handmade apparatus. Also, DSC analysis was conducted to determine the melting/freezing point and latent heat value for modified paraffin and form-stable PCM composites. The maximum allowable volume percent of EP usage for having a structural concrete was also determined by compression strength analysis. Thermal behavior analysis showed promising results for TES of the concrete block containing modified paraffin as phase change materials; also it was found that in form-stable technique, the stability of the additives is not significantly effective due to the narrow pores and channels, which reduce the effect of particles precipitation.

Non-isothermal crystallization behavior of polyethylene glycol/expanded vermiculite form-stable composite phase change material

In this work, non-isothermal crystallization behavior of polyethylene glycol (PEG)/expanded vermiculite (EVM) form-stable composite phase change material (PEG-EVM) was investigated. The activation energy of non-isothermal crystallization of PEG-EVM (−219.7 kJ/mol) was lower than that of PEG (−375.3 kJ/mol), indicating that the energy barrier of heterogeneous nucleation decreased, demonstrating that the EVM significantly accelerated the nucleation of PEG. However, the crystallization kinetic parameters (half-crystallization time, crystallization rate and required cooling rate for a designated relative crystallinity) revealed that the non-isothermal crystalline growth of PEG in PEG-EVM was constrained because the surface interactions of EVM hindered the migration and diffusion of PEG molecular chains to the surface of nucleus.

Polyethylene Glycol-Carbon Nanotubes/Expanded Vermiculite Form-Stable Composite Phase Change Materials: Simultaneously Enhanced Latent Heat and Heat Transfer.

Polyethylene glycol (PEG)-carbon nanotubes (CNTs) with expanded vermiculite (EVM) form-stable composite phase change materials (PCE-CPCMs) were constructed via the efficient synergistic effect between EVM and CNTs. The resultant material demonstrated simultaneously enhanced latent heat and heat transfer. The unique EVM pore structure and CNTs surfaces contributed to the form stability of PCE-CPCMs. The adsorption capacity was 77.75–81.54 wt %. The latent heat of the PCE-CPCMs increased with increasing CNTs content due to the decreasing inhibition effect of EVM and the increasing adsorption capacity of PEG, which was 83.9 J/g during melting and 104.2 J/g during solidification for PCE7.09. The pore confinement and surface EVM interactions inhibited the heat storage capacity of the PCE-CPCMs. Moreover, the inhibition effect on the heat storage capacity of PCE-CPCMs during the melting process was stronger than during solidification due to the crystallization-promoting effect. The heat transfer of PCE-CPCMs was significantly enhanced by the CNTs filler (0.5148 W/(m·K) for PCE7.09) due to the decrease in interfacial thermal resistance and the formation of rapid thermally conductive pathways. Fourier transform infrared spectroscopy, thermogravimetric analysis, and thermal cycles test results confirmed that the PCE-CPCMs exhibited excellent chemical compatibility, thermal stability, and reliability.

Preparation of Stearic Acid/Graphene oxide Based Form-Stable Composite Phase Change Materials

Composite phase change materials (PCM) of stearic acid/graphene oxide were prepared by thiol-alkyne click coupling reaction. Stearic acid was firstly modified with propargyl to introduce thiol-yne clickable sites. Different amounts of graphene oxide were added to thiol-alkyne clickable formulation. To evaluate phase change properties of PCMs differential scanning calorimeter (DSC) was used. Thermal stability and degradation profiles of PCMs were investigated. The structural characterization of stearic propargyl ester and PCMs was performed by ATR-FTIR spectroscopy. The addition of graphene oxide increased the maximum weigh loss temperature from 328 to 351 ˚C with respect to the base formulation. Moreover, the crosslinking of stearic acid prevented the leakage of PCMs.

Low-cost, three-dimension, high thermal conductivity, carbonized wood-based composite phase change materials for thermal energy storage

Thermal energy storage is important for energy saving and social developing. Low-cost, high thermal conductivity, form-stable composite phase change materials are urgent in energy storage and management. In this work, a novel carbonized wood-based composite phase change materials (TDCW) are fabricated by impregnating of 1-tetradecanol (TD) into carbonized wood (CW). CW as supporting material exhibits porous three-dimensional (3D) structure, high specific surface area and high thermal conductivity. In addition, compared with conventional graphene, carbon nanotubes and other one-dimensional (1D) or two-dimensional (2D) carbon materials, CW is inexpensive and has higher loading content of 73.4 wt%. What's more, CW as supporting material is firstly used in composite phase change materials. According to differential scanning calorimetry measurement and thermogravimetric analysis, TDCW possesses high latent heat, good thermal reliability and favorable thermal stability. In addition, thermal conductivities of PW, CW, TDCW measured at axial direction are all higher than that at radial direction and the thermal conductivity of TDCW is 0.669 Wm−1K−1 at axial direction at 50 °C, which is 114% higher than that of pure TD. The results of thermal conductivity and surface temperature variation collected by infrared thermal camera under heating and cooling process demonstrate that TDCW is beneficial for thermal management application. This work not only provides a novel and superior supporting material, but also prepares a suitable phase change temperature, high latent heat and high thermal conductivity composite phase change material for thermal energy storage and management civil applications.

Fabrication and thermal properties of tetradecanol/graphene aerogel form-stable composite phase change materials

In this study, tetradecanol/graphene aerogel form-stable composite phase change materials were prepared by physical absorption. Two kinds of graphene aerogels were prepared using vitamin C and ethylenediamine to enhance the thermal conductivity of tetradecanol and prevent its leakage during phase transition. The form-stable composite phase change material exhibited excellent thermal energy storage capacity. The latent heat of the tetradecanol/graphene aerogel composite phase change materials with 5 wt.% graphene aerogel was similar to the theoretical latent heat of pure tetradecanol. The thermal conductivity of the tetradecanol/graphene aerogel composite phase change material improved gradually as the graphene aerogel content increased. The prepared tetradecanol/graphene aerogel composite phase change materials exhibited good thermal reliability and thermal stability, and no chemical reaction occurred between tetradecanol and the graphene aerogel. In addition, the latent heat and thermal conductivity of the tetradecanol/ethylenediamine-graphene aerogel composites were higher than those of tetradecanol/vitamin C-graphene aerogel composites, and the flexible shape of the ethylenediamine-graphene aerogel is suitable for application of the tetradecanol/ethylenediamine-graphene aerogel composite.

Preparation of Al2O3-coated expanded graphite with enhanced hydrophilicity and oxidation resistance

Expanded graphite (EG), as a new kind of functional carbon-based material, is a vital supporting material and heat transfer enhancer for preparing highly conductive form-stable composite phase change materials (PCMs). However, the hydrophobic nature of EG makes it difficult to incorporate with inorganic PCMs. In this work, we intended to solve this drawback and a modified EG named Al2O3-coated EG which was characterized by enhanced hydrophilicity was developed via a heterogeneous nucleation technique and subsequent heat treatment. Experiments found that the Al2O3 layer on the surface of EG was uniform and essentially amorphous, and was well-bonded to EG via chemical interactions between oxygen atoms from Al2O3 and carbon atoms from EG. The hydrophilicity and oxidation resistance of Al2O3-coated EG could be enhanced by increasing the amount of Al2O3. Most importantly, compared with EG, the water contact angle of Al2O3-coated EG dropped from 90.7° to 33.9° when only 4.4 wt% Al2O3 was used, indicating that the hydrophilicity of EG could be greatly enhanced by low cost. Moreover, molecular dynamics (MD) simulation of the hydrophilicity of EG and Al2O3-coated EG proved that the preparation of Al2O3-coated EG was an efficient and feasible method to improve the hydrophilicity of EG.

Experimental investigation on n–octadecane/polystyrene/expanded graphite composites as form–stable thermal energy storage materials

In this work, polystyrene–based form–stable composite phase change materials (CPCMs) were fabricated by a solution and reflux method. In the composites, the n–octadecane (ODE) was used as thermal energy storage material, the polystyrene (PS) acted as the supporting material, and expanded graphite (EG) was employed as thermal conductive filler to improve the thermal conductivity of the composites. The toluene was adopted as solvent. Both polystyrene and n–octadecane smoothly dissolve in toluene. EG was also easily dispersed into the matrix. CPCMs were obtained after distillation of the toluene. The differential scanning calorimeter (DSC) and a thermogravimetry analyzer (TGA) were adopted to assess the thermal properties and thermal stability of the CPCMs, respectively. Fourier transformation infrared (FT–IR) spectroscope and scanning electronic microscope (SEM) were utilized to determine the chemical structure and microstructure of the ODE/PS/EG composites. The thermal conductivity of the CPCM with 5 wt% content of EG can reach up to 1.01 W/m·K, which is nearly 7 times higher than that of the CPCM without the EG. The latent heat value of CPCM with the highest ODE content (48.5 wt%) is 98.05 J/g, the melting temperature is 27.5 °C, which is close to room temperature. Therefore, the form–stable CPCMs are promising thermal energy storage materials in solar thermal energy storage systems, such as solar heating system in buildings.

Fabrication and characterization of fatty acid/wood-flour composites as novel form-stable phase change materials for thermal energy storage

The fatty acid (FA)/wood-flour (WF) composite form-stable phase change materials (PCMs) were prepared via a direct impregnation method, in which WF was selected as the supporting materials. The surface morphology, chemical structure, crystalline structure, phase change properties, thermal reliability and stability of the prepared FA/WF composite form-stable PCMs were investigated by scanning electron microscopy (SEM), Fourier transform infrared spectrometer (FTIR), X-ray diffraction (XRD), differential scanning calorimeter (DSC), accelerated thermal cycling testing and thermogravimetric analysis (TG), respectively. SEM images showed that the porous spaces of WF can be largely occupied by the impregnated FA without leakage. FTIR and XRD results suggested that there was no chemical reaction but only physical interactions between WF and FA. XRD analysis also demonstrated that the WF had no effect on the crystallization of FA. The prepared FA/WF composite PCMs had high latent heats and a suitable phase change temperature range, especially the maximum latent heats in melting and freezing process for the HW-FSPCM reached 102.6 J/g and 103.5 J/g. The prepared FA/WF composite PCMs exhibited comprehensive thermal reliability and stability from the thermal cycling test and TG analysis.

Microstructure and Characterization of Capric-stearic Acid/Modified Expanded Vermiculite Thermal Storage Composites

In order to improve the thermal storage capacity of expanded vermiculite (EV) based form-stable composite PCM (FS-PCM) via organic modification of EV, first, EV was modified with a sodium stearate (NaSt) as surface modifier, and organic EV (OEV) with hydrophobicity and higher adsorption capacity for fatty acid was obtained. A novel capric-stearic acid eutectic (CA-SA)/OEV FS-PCM with high thermal storage capacity was then developed. OEV and CA-SA/OEV were characterized by scanning electron microscopy (SEM), X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), differential scanning calorimetry (DSC), thermal gravimetry (TG), and thermal cycling test. Results showed that OEV has obvious hydrophobicity and a higher adsorption capacity for fatty acid. Its adsorption ratio has increased by 48.71% compared with that of EV. CA-SA/OEV possesses high thermal storage density (112.52 J/g), suitable melting temperature (20.49 °C), good chemical compatibility, excellent thermal stability and reliability, indicating great application potential for building energy efficiency. Moreover, organic modification of inorganic matrix may offer novel options for improving its adsorption capacity for organic PCMs and increasing heat storage capacity of corresponding FS-PCMs.

Experimental study on a novel form-stable phase change materials based on diatomite for solar energy storage

PCM has been investigated for solar energy storage in recent years. The magnesium nitrate hexahydrate was chosen as PCM due to the suitable melting temperature and high latent heat for solar thermal energy in this paper. In order to prevent the leakage during the phase transition, a novel form-stable composite PCM based on diatomite was prepared by the vacuum impregnation method. The micromorphology, chemical structure, crystalloid phase, thermal properties, supercooling degree, thermal conductivity and thermal reliability were investigated by SEM, XRD, FT-IR, DSC, self-designed device and hot-wire method. FT-IR spectra indicated that there was no chemical reaction during the preparation process. The supercooling tested by the self-designed device was just 0.3 °C which can be neglected. The melting and freezing temperature measured by DSC and step-cooling curve method were 88.89 °C and 83.5 °C, respectively. Furthermore, the latent heat was 69.39 J/g and the adsorptive capacity was 46.78% according the pure PCM used in this study. The thermal reliability test was performed and the results showed that the thermal properties basically unchanged after 2000 thermal cycles.

Supercooling Suppression and Thermal Conductivity Enhancement of Na2HPO4·12H2O/Expanded Vermiculite Form-Stable Composite Phase Change Materials with Alumina for Heat Storage

In the heat storage applications, Na2HPO4·12H2O phase change materials (PCM) show significant defects including form instability, high supercooling degree and low thermal conductivity. Aiming at these drawbacks, the Na2HPO4·12H2O-alumina/expanded vermiculite (EVM) form-stable composite phase change materials (NEA fs-CPCMs) with supercooling suppression and heat transfer enhancement were prepared. The favorable wettability of NEA fs-CPCMs was beneficial to their form-stabilization (encapsulation mass fractions above 59.7 wt %). The supercooling degree of NE5.3 was reduced to 1.4 °C after adding 5.3 wt % alumina as the nucleating agent (decreased by 90%). The surface effects of EVM and alumina and high wettability of PCM-alumina were responsible for the supercooling suppression of PCM. Large specific surface area of EVM could provide nucleation sites for crystallization of PCM. The surface electronegativity of alumina increased the affinity ability and diffusion rate of ions, thus effectively increasing the...

Thermal energy storage properties and thermal reliability of PEG/bone char composite as a form-stable phase change material

Bone char (BC) is a promising porous material that can be used for preparing a form-stable composite phase change material (PCM). In this paper, form-stable polyethylene glycol (PEG 6000)/BC composite PCMs were prepared by impregnation method. The PEG was used as the phase change material, and two different particle sizes of BC (0.8–1 mm: BC-1; 0.25–0.8 mm: BC-2) were acted as the supporting materials. The phase composition and chemical structure of the composite PCMs (PEG/BC-1 and PEG/BC-2) were characterized using X-ray diffraction and Fourier transformation infrared. The results indicated that the PEG can be well impregnated into BC pores with good compatibility. Thermal properties and thermal stability of the composite PCMs were determined by differential scanning calorimeter (DSC) and thermogravimetry analysis (TGA). DSC results showed that the maximum impregnation percentage for PEG into BC-1 and BC-2 was 38.77 and 43.91%, respectively, without melted PCM seepage from the composites. The TGA analysis revealed that the composite PCMs had good thermal stability above their working temperature range. The thermal cycle test of 100 melting–freezing cycles showed that the composite PCMs have good thermal reliability and chemical stability. The form-stable composite PCMs can be used as thermal energy storage material for waste heat storage and solar heating system.

Preparation and thermal properties of fatty acid/diatomite form-stable composite phase change material for thermal energy storage

Phase change materials can be incorporated with building materials to make kinds of composite material, which can be applied in building systems due to their excellent thermal energy storage properties. In this study, a novel form-stable composite PCM CA-LA/Diatomite was prepared using vacuum impregnation method by combining a eutectic mixture of capric-lauric acid (CA-LA) as phase change material (PCM) and diatomite as supporting material. The composite products were characterized by using XRD, FT-IR and SEM analyzing methods. The thermal properties of the composite were measured by Differential Scanning Calorimetry (DSC). The results showed that the composite material melted at 23.61 °C with a latent heat of 87.33 J/g and solidified at 22.50 °C with the latent heat of 86.93 J/g. TGA investigation revealed that the composite had excellent thermal durability above their working temperature ranges. The thermal cycling test showed the composite has a good thermal reliability after 200 thermal cycles. What's more, the expanded graphite was added into the composite in order to increase the heat transfer performance. The results showed that the thermal conductivity of the composite increased gradually by 39.7%, 61.6%, 77.6% and 114.2% for the EG fractions of 3%, 5%, 7%, and 10%, respectively. As a result, the CA-LA/Diatomite/EG composite material of has a potential to be applied in modern buildings and solar energy systems due to its excellent thermal properties, good chemical and thermal reliability and high thermal conductivity.

Preparation and thermal properties of exfoliated graphite/erythritol/mannitol eutectic composite as form-stable phase change material for thermal energy storage

The m-Erythritol (erythritol, ME)/D-mannitol (mannitol, DM) binary system was investigated by differential scanning calorimetry (DSC), and the phase diagram was then obtained. It was found that the eutectic composition was at the mole fraction of erythritol xME = 0.87. The latent heat of fusion (ΔmH) of the eutectic mixture was 322.8J/g with a peak melting temperature (Tp, m) of 114.4°C. A cyclic DSC experiment revealed that the ΔmH of the eutectic mixture slightly decreased, and the Tp, m remained stable over 50 DSC cycles. Exfoliated graphite (EG) was then applied to absorb the eutectic mixture to obtain the EG/eutectic composite form-stable phase change material (PCM) and enhance its thermal conductivity. Good form stability could be obtained when the loading of EG in the EG/eutectic composite reached 2.0wt%. The thermal conductivity of the eutectic mixture was greatly enhanced by EG. When the loading of EG was 10.0wt%, the thermal conductivity increased by 408% compared to that of the eutectic mixture. Additionally, severe supercooling of the eutectic mixture was also greatly alleviated by EG. The best result was obtained when 3.0wt% EG was added, for which the degree of supercooling (ΔT) was 62.6°C and the heat of crystallization (ΔcrH) was 185.7J/g. X-ray diffraction (XRD) experiments revealed that the eutectic mixture was simply a physical mixture of erythritol and mannitol. Thermal gravimetry (TG) investigations showed that the eutectic mixture and the EG/eutectic composite form-stable PCM exhibited good thermal stability for its applications.

Fabrication and characterization of form-stable FA ternary eutectic mixture/GO nanocomposite for thermal energy storage

The thermal conductivity of commonly used phase change materials (PCM) for thermal energy storage (TES), such as, fatty acids, paraffin etc., is relatively poor, which is one of the main drawbacks for limiting their utility. In the recent past, few attempts have been made to enhance the thermal conductivity of PCM by mixing different additives in the appropriate amount. Graphene nanoparticles, having higher thermal conductivity may be a potential candidate for the same, when mixed appropriately with different PCM. In present study, acetic acid , tristearin and stearic acid (CA-PA-SA) ternary eutectic mixture was impregnated into nano-graphene oxide (nano-GO) to prepare a form-stable composite PCM (CAPA-SA/nano-SiO2). The phase change temperature range of the composite PCM is 17.2 ◦C–26 ◦C, which is suitable for indoor thermal environment. The high latent heat value and thermal conductivity of the composite PCM are 169.43 kJ kg-1 and 0.68239 W (m K)-1, which is helpful to stabilize the indoor temperature for a long time and improve human comfort. Furthermore, after 500 heating/cooling cycles, the composite PCM showed good thermal and chemical stability. All the results indicated that the composite PCM is suitable for storing excess solar radiation and reducing the amount and rate of heat loss of buildings in the winter, which will help reduce building energy consumption.

Synthesis and characterization of beeswax-tetradecanol-carbon fiber/expanded perlite form-stable composite phase change material for solar energy storage

In this study, beeswax-tetradecanol/expanded perlite composited with carbon fiber (BW-TD-CF/EP) composite phase change materials (CPCMs) have been prepared via vacuum impregnation method for solar energy utilization. The chemical compatibility, microstructure and thermal properties of CPCMs are characterized and measured, which proves that it is no chemical interaction among the raw materials but physical combination and BW-TD-CF is sufficiently absorbed into the EP porous structure with no leakage even in the molten state. According to differential scanning calorimeter (DSC) results, BW-TD-CF/EP composite melts at 34 °C with high enthalpy value of 178.7 kJ/kg, while thermal cycling measurements show that the form-stable composite PCM has adequate stability after being subjected to 200 melting/freezing cycles. Morever, thermal conductivity of BW-TD/EP composite is enhanced from 0.443 Wm−1 K−1 to 1.245 Wm−1 K−1 by adding CF. In result, the form-stable composite PCMs have more appropriate thermal properties and better thermal stability in building for solar energy utilization.

Preparation and thermal performance of form-stable expanded graphite/stearic acid composite phase change materials with high thermal conductivity

Thermal energy storage plays an important role in improving the working reliability and utilization efficiency of renewable energy systems. Thermal energy storage includes sensible heat storage, latent heat storage using phase change material (PCM) and thermochemical heat storage. In comparison with sensible heat storage, latent heat storage has the distinct advantages of its high energy storage density and stable temperature during the energy storage and release processes. However, low thermal conductivity of PCM is the common drawback for various latent heat energy storage systems. The purpose of the research is to enhance the thermal conductivity of PCM by developing new form-stable composite phase change materials using expanded graphite matrix. Firstly, a preparation method “heating adsorption of liquid SA into expanded graphite (EG) matrix and compressing stable-shape composite” is employed to synthesis form- stable composite phase change material. Twenty samples with different EG contents and packed densities are prepared using stearic acid (SA) as phase change material and two kinds of EG with different dilatation as porous matrix. Secondly, the microstructures, thermal properties and thermal stabilities of different EG/SA samples are tested to analyze the influence of the dilatation of expanded graphite on the thermal performance of form-stable composite phase change materials. Moreover, EG/SA form-stable heat storage units with different EG contents and packed densities are fabricated to analyze the thermal storage/release performance through heating/cooling experiment. The microstructures of EG and EG/SA samples are observed using scanning electron microscopy (SEM) and the results show there exist obvious differences between two kinds of EG and SA distribution in the samples. The EG/SA samples with high dilatation EG are even more uniform because the high dilatation EG has larger pore size and pore volume. The data obtained from differential scanning calorimetry (DSC) show the addition of EG and compressing operation have negligible effect on the latent heat and slightly increase the phase transition temperature of pure SA. The form-stable EG/SA composite PCMs have lower supercooling degree than pure SA. LFA447 flash thermal diffusivity instrument is used to evaluate the effect of EG’s dilatation on the thermal conductivity of EG/SA samples. The results show that the use of high dilatation EG is more effective to improve the thermal conductivity of form-stable EG/SA composite PCMs when packed density is large. The radial thermal conductivity of form-stable 20 wt.%EG/SA phase change composite with packed density of 950 kg m−3 is as high as 19.6 W m−1 K−1 when high dilatation EG is utilized. This figure is more than 110 times higher than that of pure SA. Finally, the thermal stability of EG/SA samples is conducted by repeating the charging and discharging processes of SA. These samples prepared by high dilatation EG have better thermal stability than the samples prepared by low dilatation EG. The EG with high dilatation can assure the uniform distribution of SA inside EG/SA sample and thus prevent the leakage of liquid SA during the phase change transformation process due to its dilated microstructure. The heating/cooling test results show that the heat storage/release time of EG/SA composite units is about 1/8–1/4 of that of pure SA unit, and this means the heat transfer can be significantly enhanced. It suggests that the form-stable EG/SA composite phase change materials prepared by high dilatation EG has good comprehensive performance due to its high thermal conductivity, good thermal stability and no leakage problem.

Properties enhancement of phase-change materials via silica and Al honeycomb panels for the thermal management of LiFeO4 batteries

A novel form-stable composite phase-change material (CPCM) is introduced that features a paraffin wax (PW) and expanded graphite (EG)-based battery thermal management system (BTMS) with additional silica gel and Al-honeycomb (Al-Hc) components. The properties of the CPCM were analyzed in terms of their crystallographic structure, heat transfer capacities, and stress–strain response. The CPCM was applied to a BTMS to determine the temperature response of a battery and the CPCM surface. The results showed that immersing PW/EG CPCM in silica gel could prevent the leakage of liquid PW from a PW/EG CPCM via an encapsulation effect. The degree of super-cooling in a PW/EG/SiO2 CPCM saw reductions of 33% and 21% relative to the super-cooling values of PW PCM and PW/EG CPCM, respectively. This composite also exhibited superior mechanical properties and a lack of surface cracking and deformation after compression testing. It also has a high heat-dissipation efficiency, which was attributed to the presence of the Al-Hc. Lastly, the PW/EG/SiO2/Al-Hc CPCM exhibited excellent thermal management performance when applied to LiFeO4 scenarios, maintaining the operating temperatures well within the 50 °C maximum of the safe and efficient battery operation range.