Latent Heat Of Composite Phase Change Materials Research Articles

Research on the high thermal conductivity composite phase change materials with graphite nanosheets for battery thermal safety

Composite phase change material (CPCM) as an efficient battery thermal management strategy has been widely utilized owing to its promising performance, but its thermal conductivity and stability still need to be improved in battery module. Herein, three different kinds of CPCM have been successfully prepared and utilized in battery module, which are composite with PEG, epoxy resin (ER), silver nanoparticles (AgNP) modified with dopamine hydrochloride (PDA) self-assembled on the surface of graphite nanosheets (GNS), denoted as PEE (PEG/ER), PEG(PEG/ER/GNS), and PEGA (PEG/ER/GNS/Ag), respectively. Among them, the AgNP with super-high thermal conductivity has been distributed on the surface of GNS to form laminated nanostructures, promoting the construction of thermal conduction network. The thermal conductivity and latent heat of CPCM are 3.1 W∙m−1∙K−1 and 105.8 J∙g−1, respectively. Furthermore, even under 35 °C ambient temperature, the application of PEGA for battery module can effectively control the maximum temperature below 52 °C and maintained a temperature difference within 6 °C at a 3C discharge rate, which is better than those of battery modules with PEE and PEG. It reveals that the battery module with designed high thermal conductivity CPCM can provide insights into the passive thermal management and other energy storage fields.

Form-stable flexible composite multi-phase change material with high latent heat and enhanced thermal conductivity for thermal management

Form-stable flexible composite phase change materials (PCMs) are widely studied on the application of thermal management of batteries. Usually, the latent heat of composite PCMs is lower than that of pure PCMs due to the existence of additive materials. More composite PCMs are needed when their latent heat is too low to meet the requirements, which limits the development of the compact structure of the thermal management system. In this work, a novel paraffin (PA) -based composite multi-phase change material (m-PCM) with high latent heat was fabricated for thermal management. PA thickened by adding styrene ethylene butene styrene block copolymer (SEBS) and expanded graphite (EG) as enhanced thermal conductivity material were loaded in phase change polymer skeleton (PPS) synthesized from polyethylene glycol (PEG). One side, PPS not only played a role on preventing the leakage of paraffin as supporting material, but also provided the extra latent heat of phase change for the composite m-PCM. On the other side, SEBS was added by increasing the viscosity of PA to solve the problem of poor compatibility between the polymer skeleton and PA. Benefiting from the additional latent heat provided by PPS and the addition of EG, the composite m-PCM exhibited the phase change enthalpies as high as about 221.3 J·g−1 while ensuring the thermal conductivity as high as 1.46 W·m−1·K−1. When heated, the composite m-PCM exhibited the excellent shape-stability and flexibility. After 200 thermal cycles, the composite m-PCM performed the almost constant phase transition properties. The results demonstrate the composite m-PCM has extensive application prospects for efficient thermal management.

Thermal performance revival of composite PCM for hybrid BTMSs by architecture and formula integrated optimization

Composite phase change material (CPCM) cooling is an essential method to ensure better performance of battery thermal management system (BTMS) due to high latent heat. However, long recovery time of CPCM makes it unaffordable especially during continuous high rate discharge–charge cycles. In order to reduce the energy consumption while enhancing the latent heat recovery efficiency, a novel hybrid BTMS architecture coupling with CPCM and liquid cooling is proposed. Liquid cooling is employed to recover the latent heat of PCM. To enhance the heat transfer in BTMS, the structural layout of liquid cooling arrangement is investigated. Meanwhile, mass fraction of expanded graphite (EG) and bulk density of CPCM are considered. Specially, the experiments are conducted to verify the effectiveness of present hybrid BTMS. In solidification, temperature performance especially temperature uniformity is not ideal. Therefore, a novel successive multiple attribute decision making (MADM) algorithm is employed to achieve optimized temperature difference, maximum temperature, solidification rate and mass of CPCM. In MADM algorithm, the order preference by similarity to ideal solution (TOPSIS) is coupled with the analytic hierarchy process (AHP) to solve the multi-objective discrete optimization problem. Results indicate that the optimal solution can make the maximum temperature and temperature difference at the lowest level of 317.51 K and 3.45 K at discharge rate of 4C. Meanwhile, the latent heat of CPCM is improved by about 27.5% at charge rate of 2C. The solution can improve the long-term reliability for the BTMS and the safety and service life for battery module.

Construction of high thermal conductivity MOFs composite phase change materials with reinforced light-to-thermal conversion

Improving the light-to-thermal conversion properties of phase change materials (PCMs) is conducive to the development of their applications in solar thermal energy storage systems. In this work, a porous structure of expanded graphite (EG) modified Ni-MOF was synthesized by hydrothermal synthesis, and scattered in CH 3 COONa‧3H 2 O (SAT) by a physical blending and impregnation method to obtain a novel composite phase change material with reinforce light-to-thermal conversion. The resulting composite PCM showed that the latent heat of composite PCM was 166.6J/g, the supercooling temperature was reduced to 2.5 °C. The porous network structure formed by the close combination of EG and MOF effectively enhanced the heat transfer rate of composite PCM. The thermal conductivity of composite PCM was about 3.21 times that of pure SAT. Furthermore, the composite PCM showed good thermal cycling performance and excellent light-to-thermal conversion properties, which could be suggested as a promising candidate for solar thermal storage systems. • Porous structure of EG@Ni-MOF is synthesized via hydrothermal synthesis method. • The existence of EG@Ni-MOF reinforces the light-to-thermal conversion. • The composite PCM exhibits improved thermal conductivity. • This work provides a new approach for the utilization of solar energy.

Experimental investigation on thermal properties of paraffin/expanded graphite composite material for low temperature thermal energy storage

The technology of latent heat storage with phase change materials (PCMs) is one of the promising means to improve the utilization of renewable energy. Nevertheless, its broad application will be limited due to the low thermal conductivity of PCMs. In this work, paraffin/expanded graphite (EG) composite PCMs by paraffin having a melting point of 62 °C and expanded graphite with three kinds of particle sizes were prepared and characterized. Environmental scanning electron microscope (ESEM) micrographs showed that EG was dispersed homogeneously in composite PCMs. Meanwhile, the distribution uniformity of expanded graphite in composite PCMs was evaluated quantitatively. The thermal conductivities of composite PCMs increase as the mass fraction of EG increases, and the thermal conductivity of paraffin/EG80 (5 wt.%) was 1.492 W/(m·K) in comparison with the value of pure paraffin was 0.355 W/(m·K). X-ray diffraction (XRD) analysis indicated that the fabrication process of composite PCMs was a purely physical process without a new substance produced. Differential scanning calorimeter (DSC) demonstrated that the latent heat of composite PCM was slightly less than the theoretical value. The addition of EG could lead to the improvement of the melting temperature of composite PCMs, while the decrease of the freezing temperature.

Thermal properties of eutectic salts/ceramics/expanded graphite composite phase change materials for high-temperature thermal energy storage

Eutectic chloride salts are a new and novel type of thermal energy storage (TES) material for high-temperature solar TES systems. Their thermal properties and stability are key factors in determining their application in TES systems. In this study, we prepared and characterized eutectic NaCl–KCl–MgCl2/α-alumina/expanded graphite (EG) composite phase change materials (PCMs). The results show that eutectic salts, α-alumina and EG have good crystalline properties and chemical compatibility. The elements are relatively uniform in distribution within the pores and channels. Moreover, the Na, K, and Mg distributions occupy the same locations, indicating the excellent eutectic properties of the salts. The latent heat of composite PCMs decreases with the increase in α-alumina and EG percentage, while the addition of EG to the eutectic salts/α-alumina composite PCM improves the thermal conductivity of the composite PCMs by more than 6 times, from 0.85 to 5.10 W/(m·K). Moreover, after 50, 100, and 300 heating–cooling cycles at 550 °C, the composite PCMs demonstrate enhanced thermal and physical properties at high temperatures. The improved thermal characteristics of composite PCMs with α-alumina and EG allow for promising applications of high-temperature solar TES systems.

In situ one-step construction of monolithic silica aerogel-based composite phase change materials for thermal protection

Currently, numerous studies are devoted to the pursuit of thermal conductivity enhancement of phase change materials (PCMs). On the contrary, few researches are reported to reduce the thermal conductivity of PCMs. Generally, the PCMs with reduced thermal conductivity have great potential in thermal protection application. Herein, we propose a novel in situ one-step strategy to facilely prepare monolithic silica aerogel-based composite PCMs. The silica aerogels possess low thermal conductivity and are used to encapsulate PCMs to prepare composite PCMs, such as polyethylene glycol (PEG) or octadecanol. Compare with PEG2000@silica aerogel, the resulting monolithic octadecanol@silica aerogel have low thermal conductivity (0.12 W m−1 K−1), high latent heat (127.73 J/g), large compressive strength (11 MPa), good hydrophobicity (contact angle 124°) and superior thermal cycling stability. This monolithic silica aerogel-based composite PCMs could prolong heat preservation duration due to the synergistic effect between low thermal conductivity and high latent heat of composite PCMs, showing potential promise for direct application to the thermal insulation and thermal protection device. More importantly, this in situ one-step synthesis strategy is universal for different types of PCMs.

Preparation and characterization of poly (N-methylol acrylamide)/polyethylene glycol composite phase change materials for thermal energy storage

The cross-linked poly (N-methylol acrylamide)/polyethylene glycol (PN-MA/PEG) with an interpenetrating polymer network (IPN) was prepared by emulsion polymerization as composite phase change material (CPCM). N, N′-methylene bisacrylamide (MBA) was used for crosslinking agent. The prepared CPCM was characterized by Fourier Transform Infrared (FT-IR) spectroscopy, X-ray Diffraction (XRD), Differential Scanning Calorimetry (DSC), Thermogravimetric Analysis (TGA), thermal cycle test, Scanning Electron Microscope (SEM) and Transmission Electron Microscope (TEM). FT-IR results stated that there is no chemical interaction between PEG and PN-MA. XRD results indicated that the introduction of PN-MA did not change the crystal type of PEG. PEG still exhibits crystallization behavior under the constraints of cross-linked PN-MA. The DSC results indicated that CPCM melts at 26.24 °C with a latent heat of 106.5 J/g and solidifies at 32.56 °C with a latent heat of 104.9 J/g. The TGA results indicated that the CPCM has good thermal stability and is suitable for thermal energy storage application. The results of thermal cycle test indicated that the macroscopic morphology and latent heat of CPCM were almost unchanged after 40 thermal cycles. SEM and TEM results indicated that the microscopic morphology of CPCM was spherical and the particle size distribution was around 145 nm.

Experimental study of thermo-physical properties and application of paraffin-carbon nanotubes composite phase change materials

In order to improve the thermal conductivity of pure paraffin (RT4) which is regarded as cool storage of phase change material (PCM), four kinds of paraffin-carbon nanotubes cool storage of composite PCMs are prepared by adding different amount of carbon nanotube (CNT) into paraffin, and their thermo-physical properties are tested by using differential scanning calorimeter (DSC) and laser thermal conductivity meter. The results show that, with the increasing of carbon nanotubes, the phase transition temperature of the cool storage of composite PCMs diminishes, phase change latent heat dwindles while thermal conductivity gradually increases. Compared with the pure paraffin, increase in mass fraction of carbon nanotube 3% can provide an increase in thermal conductivity of the solid and liquid 30.3% and 28.5%, and a reduce in the melting and solidification phase change latent heat of composite PCM 8.9% and 9.3%, respectively. Further investigation applies the composite PCMs into the shelf of vertical open -type refrigerated display cabinet to improve the performance. The results show that the shelf filled with the composite PCMs can decrease the internal temperature of the VORDC and temperature fluctuation during the defrosting period. Compared with the ordinary shelf, the lengthways and depthwise temperature different of composite shelf filled into only RT4 reduce by 80.0% and 7.6%, respectively; the lengthways and depthwise temperature different of composite shelf filled into 3%-CNT composite PCMs reduce by 92.0% and 12.2%, respectively. It indicates that the composite PCMs further increases the thermal conductivity of composite shelf and improve the performance of VORDC.

Preparation and thermal properties of mineral-supported polyethylene glycol as form-stable composite phase change materials (CPCMs) used in asphalt pavements

Three kinds of mineral-supported polyethylene glycol (PEG) as form-stable composite phase change materials (CPCMs) were prepared to choose the most suitable CPCMs in asphalt pavements for the problems of asphalt pavements rutting diseases and urban heat islands. The microstructure and chemical structure of CPCMs were characterized by SEM, FT-IR and XRD. Thermal properties of the CPCMs were determined by TG and DSC. The maximum PEG absorption of diatomite (DI), expanded perlite (EP) and expanded vermiculite (EVM) could reach 72%, 67% and 73.6%, respectively. The melting temperatures and latent heat of CPCMs are in the range of 52–55 °C and 100–115 J/g, respectively. The results show that PEG/EP has the best thermal and chemical stability after 100 times of heating-cooling process. Moreover, crystallization fraction results show that PEG/EP has slightly higher latent heats than that of PEG/DI and PEG/EVM. Temperature-adjusting asphalt mixture was prepared by substituting the fine aggregates with PEG/EP CPCMs. The upper surface maximum temperature difference of temperature-adjusting asphalt mixture reaches about 7.0 °C in laboratory, and the surface peak temperature reduces up to 4.3 °C in the field experiment during a typical summer day, indicating a great potential application for regulating pavement temperature field and alleviating the urban heat islands.

Synthesis of the polyethylene glycol solid-solid phase change materials with a functionalized graphene oxide for thermal energy storage

Polyethylene glycol (PEG) as a phase change material possesses three obstacles, such as leakage, low thermal conductivity and low thermal stability. A novel solid-solid phase change material (PCM) based on functionalized graphene oxide (GO), Polyethylene glycol (PEG) was prepared, and the three obstacles of PEG as a PCM was solved in one and the same material. Fourier transform infrared spectroscopy (FTIR), X-ray photoelectron spectroscopy (XPS), Raman and Transmission electron microscope (TEM), X-ray diffraction (XRD), differential scanning calorimetry (DSC), thermogravimetric analysis (TG) and thermogravimetric analysis/infrared spectrometry (TG-IR) were used to study the properties of supporting material and composite PCM (CPCM). The results indicated that the PEG was grafted on the surface of the supporting material; Compared with pure PEG, the latent heat of CPCM with 9.6 wt% supporting material decreased only 5.3%, however, the thermal conductivity of CPCM increased 111% and the heat peak release rate of CPCM decreased 33.4%.

Preparation of binary eutectic chloride/expanded graphite as high-temperature thermal energy storage materials

Binary eutectic chloride (NaCl–CaCl2)/expanded graphite (EG) composite phase change materials (PCMs), used as high-temperature thermal energy storage materials, were prepared by an impregnating method, and the effects of EG additives on thermal properties of compound salts were investigated by TEM, DSC and Hotdisk techniques. The results revealed that both the specific heat capacity and phase change latent heat of composite PCMs decreased with the increase of EG content, the variation of phase change temperature was negligible, and the thermal conductivities of composite PCMs increased linearly with the addition of EG content and density. In particular, the thermal conductivity of the composite PCM with 20wt% of EG and 2g/cm3 of density was 4.937W/(mK), which showed 701.1% higher than binary eutectic chloride. The heating and cooling rate of composite PCMs were higher than binary eutectic chloride, and the melting and freezing platform time also reduced with the addition of EG content.

Preparation and properties of lauric acid/diatomite composites as novel form-stable phase change materials for thermal energy storage

The lauric acid (LA)/diatomite composite phase change materials (PCMs) were prepared using a direct impregnation method, in which LA was chosen as PCM. The chemical structure, chemical compatibility, element composition, crystalline structure, thermal properties and thermal stability of LA/diatomite composite were extensively investigated by Fourier transform infrared (FTIR) spectroscopy, energy dispersive spectroscopy, X-ray diffraction (XRD), differential scanning calorimetry and thermal gravimetric analysis. FTIR and XRD results indicate that there are only physical interactions between LA and diatomite in LA/diatomite composite. The decrease of XRD intensity of composite PCM confirms the reduction of the crystalline size of LA in LA/diatomite composite. The melting and freezing temperatures of composite PCM are 40.9°C and 38.7°C respectively. The latent heat of composite PCM is 57.2J/g. LA/diatomite composite does not decompose when the surrounding temperature is lower than 157°C, indicating that the composite PCM has a good thermal stability.

High thermal performance composite PCMs loading xGnP for application to building using radiant floor heating system

The building sector is known to make a large contribution to total energy consumption and CO2 emissions. Phase change materials (PCMs) have been considered for thermal energy storage in buildings. The aim of this study was to improve the thermal conductivity of PCMs applicable as building materials using a radiant floor heating system. Using exfoliated graphite nanoplatelets (xGnP), composite PCMs were prepared by mixing and melting techniques for high dispersibility, thermal conductivity and latent heat storage. xGnP of 3 and 5wt% was added to three types of liquid pure PCMs (octadecane, hexadecane and paraffin) with different melting points. The composite PCMs loaded with xGnP were characterized by using the SEM technique. The thermal properties of the composite PCM loaded with xGnP were determined by thermal conductivity analysis and DSC analysis. SEM morphology showed homogenous and ordered dispersion of xGnP in the three types of PCMs. The thermal conductivity of composite PCMs was increased with the xGnP loaded contents. The DSC results showed that the melting temperature and latent heat of the composite PCMs loaded with xGnP was maintained. The latent heat of composite PCMs slightly decreases when loading with xGnP. As a result, composite PCMs loaded with xGnP can be considered as energy saving building materials for a residential building using a radiant floor heating system.