Form-stable Composite Phase Change Materials Research Articles

Fabrication and characteristics of eutectic hydrated salts/fumed silica composite as form-stable phase change materials for thermal energy storage

In this research, a novel form-stable composite phase change material (PCM) for building envelopes was prepared and evaluated. Calcium chloride hexahydrate (CCH) and magnesium nitrate hexahydrate (MNH) were dissolved and mixed uniformly to obtain the binary eutectic hydrated salt (BEHS) with adjustable phase change temperature. With the increase of MNH content, the phase change temperature and latent heat of BEHS gradually decreased. The BEHS with the onset temperature and peak temperature of 21.26 °C and 27.51 °C and corresponding latent heat of 142.4 J/g was selected as the PCM and combined with the support material SiO 2 to obtain BEHS/SiO 2 composite PCMs，where the minimum SiO 2 content to prevent BEHS from leaking was 25 wt%. The characterization results of SEM, XRD and FT-IR indicated that BEHS was successfully filled into the pore structure of SiO 2 , and there was good compatibility between them. By adding 2.5 wt% strontium chloride hexahydrate as a nucleating agent, the supercooling degree of BEHS/SiO 2 composite PCMs was eliminated. The onset temperature and peak temperature of BEHS/SiO 2 composite PCMs were measured to be 17.85 °C and 27.28 °C, respectively, and the corresponding latent heat was 97.3 J/g. A 300 melting and solidification cycles test proved that it possessed good thermal reliability. Moreover, the numerical simulation was performed to evaluate the effect of BEHS/SiO 2 composite PCMs on the thermal performance and energy performance of the building. The obtained results showed that composite PCMs could effectively reduce room temperature fluctuations and energy consumption. • A new type of eutectic hydrated salts/fumed silica composite PCM is prepared. • The thermal properties of eutectic salts are affected by the content of MNH. • The composite PCM has a small supercooling degree and good thermal reliability. • The composite PCM improves the thermal and energy performance of the building.

Form-Stable phase change composites based on porous carbon derived from polyacrylonitrile hydrogel

Three-dimensional hierarchical porous carbon (3D-HPC) carriers were fabricated by pyrolyzing porous polyacrylonitrile hydrogels at high temperature, which were further applied to achieve simultaneous guarantee of the high energy storage density, thermal conductivity, shape stability and optical/electric-thermal energy conversion performance of PCMs. • Synthesis of PAN gels is green and facile; AMPS helps polymerization and pyrolysis. • Carbonization of PAN aerogel produces high-performance 3D-HPC carriers. • 3D-HPC can load PEG > 85 wt% with shape stability and thermal cycling stability. • 3D-HPC/PEG CPCMs present 10 times increase in thermal conductivity than PEG. • CPCMs possess optical/electric-thermal energy conversion capability. How to improve thermal conductivity as well as energy conversion efficiencies and to prevent melting leakage of solid–liquid phase change materials (PCMs) has been the essential challenges for the development of energy storage technology for storing a tremendous amount of waste heat and renewable and sustainable solar energy. Here, we reported the fabrication of high-performance form-stable composite PCMs (CPCMs) using the thermal conductive 3D-HPC carriers produced from the pyrolysis of porous polyacrylonitrile (PAN) copolymer hydrogels to confine the polyethylene glycol (PEG) PCMs. The porous 3D network PAN gel templates generate hierarchical cavities with micro/mesopores on the skeleton after pyrolysis which provides more space as well as the capillary adsorption and chemical interaction for the storage of PEG PCMs. The 3D-HPC/PEG CPCMs show high energy storage density (as high as 173.5 J g −1 ), high phase transformation efficiency and excellent thermal cycle stability. The carbon scaffold highly enhanced the thermal conductivity of CPCMs ∼ 10 times of the pure PEG and ensured its optical/electric-thermal energy conversion performance. This study demonstrates a facile, efficient and green way to fabricate hierarchical porous carbon with controllable porosity and degree of graphitization for improving the energy storage density, thermal conductivity, shape stability and energy conversion performance of PCMs.

In situ preparation of light-driven cellulose-Mxene aerogels based composite phase change materials with simultaneously enhanced light-to-heat conversion, heat transfer and heat storage

The latent heats of form-stable composite phase change materials (fs-CPCMs) were usually reduced while synergistically improving their heat transfer and light-to-heat conversion properties. In this work, the polyethylene glycol/MXene-cellulose aerogels (PMC) fs-CPCMs with simultaneously enhanced light-to-heat conversion, heat transfer and heat storage were prepared by one-step in situ encapsulation method based on freezing casting. The light-to-heat conversion efficiency of PMC fs-CPCMs achieved ∼ 91.6% due to the fact that the MXene acted as an effective photon captor and molecular heater under solar irradiation. The heat transfer of PMC fs-CPCMs was effectively improved by dispersed MXene due to the formation of heat conduction network or path. Importantly, the latent heats of PMC fs-CPCMs (about 183 J/g) were not reduced, because 90 wt% PEG was encapsulated in situ during the formation of pore structures of cellulose-Mxene aerogels under freezing casting. Moreover, the PMC fs-CPCMs showed excellent chemical compatibility and acceptable thermal stability.

Effect of NiCo2O4-modified expanded graphite on heat transfer and storage improvement of CaCl2⋅6H2O

The efficient heat energy storage and conversion can be achieved by form-stable composite phase change material (CPCM) to cope with energy supply and demand imbalances in time and space. The modification of expanded graphite (EG) is important in promoting the phase change behavior of inorganic CPCM. The NiCo2O4 with spinel structure has an excellent thermal conduction channel and great hydrophilia. In this study, the in-situ NiCo2O4 was adopted to optimize the thermal conductivity and improve the thermal reliability of CaCl2⋅6H2O (CCH)-based CPCM. It was found that the obtained CPCM exhibited the enhanced thermal conductivity (4.652 W⋅m − 1⋅K − 1), which was nearly 8.25 times that of CCH (0.564 W⋅m − 1⋅K − 1). The thermal reliability increased, which was ascribable to the improvement of hydrophilicity. Moreover, the CCH-based CPCM showed great chemical compatibility, good energy storage density (149.32 J⋅g − 1), and optimized apparent activation energy (363.62 kJ⋅mol−1). This work will provide new insights into enhanced thermal conductivity and reliability for form-stabilized CPCM by establishing three-dimensional bimetallic oxide channels.

A novel form-stable phase change material based on halloysite nanotube for thermal energy storage

Halloysite nanotube (HNT), a natural and environmentally friendly low-cost material with significant reserves, has become one of promising candidates for preparation of form-stable composite PCM with satisfactory thermal properties owing to their hollow tubule structure and high surface area. The present work prepared the form-stable composite with HNTs and acid etching HNTs (A-HNTs) and compares the properties closely related to thermal energy storage application. Specifically, the micromorphology, thermal properties, shape-stabilized properties, as well as thermal conductivities of the composite materials were characterized by utilizing SEM, TEM, FTIR, DSC, BET, and Hot-disk wire methods, respectively. The results showed that the n-octadecane can both adhere on the inner lumen and the outer wall of HNTs and A-HNTs, while the A-HNTs possess significantly improved absorption thanks to the fact that the pore volume of A-HNTs was enlarged by 19.2% in comparison with HNT, which empowers the extra 5.8% phase transition enthalpy of n-octadecane@A-HNT. In addition, the composite PCMs have a good long-term thermal stability based on multi-cycle heat absorption and release further highlights the potentials in thermal storage application.

Development of composite phase change materials based on n-tetradecane and β-myrcene based foams for cold thermal energy storage applications

β-myrcene based foam / n-tetradecane composite phase change materials (PCMs) were prepared for cold thermal energy storage systems. β-myrcene based foams were synthesized as PCM support material, while n-tetradecane was selected as organic phase change cold storage material due to its appropriate phase change temperature and high heat storage capacity for supplying temperature requirements of the food refrigeration, storage and transportation systems. The polymer foams were prepared in presence of different nanoclay particles by using β-myrcene as bio-based monomer and ethylene glycol dimethacrylate as crosslinker. The form-stable composite PCMs were obtained via impregnation of n-tetradecane into the porous frameworks in one-step. Based on the results, the highest latent heat was measured as 82.14 J/g for form-stable composite PCM, which has framework with higher cavity diameters besides to higher surface area, while the melting and crystallization temperatures determined as 4.37 °C and 1.73 °C.

Heat transfer and storage characteristics of composite phase change materials with high oriented thermal conductivity based on polymer/graphite nanosheets networks

Energy storage materials are being increasingly utilized. However, traditional solid–liquid phase change materials (PCM) have two disadvantages: low thermal conductivity and an inability to maintain stable properties. In this work, a novel anti-leakage, form-stable composite PCM with enhanced thermal conductivity was successfully proposed. This composite PCM uses a cross-linked mixture of paraffin wax and an olefin block copolymer as the base material and expanded graphite as the thermally conductive filler. The vacuum adsorption method and directional molding method were used to achieve shape stability and high thermal conductivity of the material. When the mass ratio of expanded graphite was increased from 5% to 30%, the corresponding thermal conductivity increased from 2.79 to 25.56 W∙m−1∙K−1, which was an improvement of 111 times compared to paraffin wax. When the mass ratio of expanded graphite reached 10%, the heat storage reached its maximum value of 520 J/ cm2, while the peak heat storage power reached 11.5 Wcm−2 with a 30% graphite mass fraction. Battery thermal management experiments showed that, the battery temperature rise could be effectively controlled within 17 °C. In the case of natural convection, the temperature rise reached 39 °C. The proposed composite PCM demonstrates promising potential for application in thermal management, building energy and heat storage.

Three-dimensional montmorillonite/Ag nanowire aerogel supported stearic acid as composite phase change materials for superior solar-thermal energy harvesting and storage

Phase change materials (PCMs) which can harvest regenerative solar energy and convert into storable thermal energy are supposed to be advanced energy storage mediums. Stearic acid (SA) with suitable phase change temperature, large latent heat and negligible supercooling is considered to be promising organic PCMs in solar thermal energy harvesting and storage. However, the low thermal conductivity and poor shape stability of SA inevitably inhibited the energy storage and practical applications. Herein, Montmorillonite nanosheets and silver nanowires (AgNW) have been self-assembled to three-dimensional network structural aerogel and used as supporting matrix for PCMs. Then, novel form-stable composite PCMs have been prepared by impregnating SA into the porous aerogel matrix. The porous matrix can support SA and prevent leakage effectively by the strong surface tension and capillary forces during solid-liquid phase transition. The composite PCMs with more than 94 wt% SA loadings has a specific phase change enthalpy large than 196.48 J/g. Besides, the matrix provided cross-linked thermal conductive fillers and heat transfer path to greatly enhance heat transfer ability, which contributes to the outstanding solar energy harvesting performances. Moreover, the structural, thermal and cycling stability of the composite PCMs are very well under the protection of three-dimensional aerogel structure. Phase separation and sedimentation of thermal conductive fillers during solid-liquid phase transition has also been solved because the AgNW fillers were fixed by the matrix. With excellent thermal energy storage capacity, good shape-stability and superior heat transfer ability, the prepared composite PCMs show considerable potential in solar-thermal applications and sustainable development.

A novel honeycomb-like porous carbon from loofah sponge for form-stable phase change materials with high encapsulation capacity and reliability

Form-stable composite phase change materials (PCM) with high encapsulation capacity and reliability composed of paraffin and honeycomb-like porous carbons are developed. Porous carbons from natural loofah sponge were carbonized under different temperatures with rich honeycomb-like pores about 10 μm in diameter and used as supporting framework to load paraffin whose maximum loading rate is up to 545.58 w.t.% and the enthalpy is up to 146.10 J/g. The samples can keep pristine macron morphology without obvious leakage after heating. The composite PCMs have many advantages such as inexpensive porous fiber keeping a certain degree of mechanical prosperity used as supporting materials and good thermal storage capacity.

A novel energy-effective and carbon-emission reducing mortars with bottom ash and phase change material: Physico-mechanical and thermal energy storage characteristics

Novel cement based mortars containing bottom ash (BA) and phase change material (PCM) as thermal energy storing material were developed for thermal controlling of buildings. Form-stable BA/Capric-Stearic (C-S) acid eutectic mixture composite was produced at an impregnation rate of 30 wt% C-S. Melting temperature and latent heat capacity of form-stable composite PCM were observed as 23.65 °C and 52 J/g, respectively while the mortar containing 30 wt.% composite PCM had a melting temperature of 21.42 °C and latent heat value of 13.62 J/g. Water demand, porosity and absorption was increased depending on the variation of BA/C-S composite PCM. The compressive strength and dry unit weight of the mortar decreased up to 35 MPa at 28th day and 1826 kg/m3. The highest indoor heat difference between reference mortar and BA/C-S composite included-mortar was found to be 2.80 °C for heating and 1.95 °C for cooling period. Analytical approaches revealed that composite PCM adapted buildings have promising annual energy saving and carbon-emission reducing potential for various fuels. It was concluded that usage of the developed composite PCM has high potential for creation novel kinds of energy saving panels, concretes, mortars, bricks etc. used for inside temperature regulation of buildings.

Facile in-situ fabrication of latent heat enhanced cellulose aerogel-based form-stable composite phase change materials based on dopamine modification strategy

In this work, the latent heat enhanced polyethylene glycol (PEG)/cellulose aerogel (CA)-dopamine form-stable composite phase change materials (PCD fs-CPCMs) were constructed by facile in-situ fabrication method based on the freeze casting. Under the simultaneous synergistic effect of CA and dopamine modification, the PCD fs-CPCMs achieved ultra-high encapsulation capacity of ~95 wt% and latent heat of ~194.3 J/g. Furtherly, compared with before the dopamine modification, the latent heat of PCD fs-CPCMs was increased by ~18.9%, and the difference between theoretical and experimental value was significantly reduced, indicating that the modification effectively promoted phase change behavior and improved heat storage characteristic of PEG. The ultra-high encapsulation capacity was mainly attributed to the lightweight and porous characteristic of CA and the effective entanglement and combination of PEG molecular chain. The increased latent heat was mainly ascribed to the construction of new combination approaches among PEG, CA and dopamine, resulting in the weakening of hydrogen bond effect (before and after modification: O-H⋯O > O-H⋯N or N-H⋯O) so that the confinement effect of surfaces was weakened and modified surface-induced phase change behavior was promoted. Moreover, the PCD fs-CPCMs exhibited excellent chemical compatibility, reasonable heat storage and release rates, and acceptable thermal reliability and stability. • PCD fs-CPCMs with large encapsulation capacity and latent heat were fabricated in-situ based on freeze casting. • Dopamine modification showed positive effect on increasing latent heat (~18.9%) of PCD fs-CPCMs. • New constructed combination approaches weakened hydrogen bond effect so that phase change behavior was promoted.

Preparation and thermal performances of Na2HPO4·12H2O/ SiO2 hydrophilic modified expanded graphite form-stable composite phase change material for radiant floor heating system

Based on Na2HPO4·12H2O as phase change material (PCM) and SiO2 hydrophilic modified expanded graphite (MEG) as supporting carrier and thermal conductivity enhancer, a novel Na2HPO4·12H2O/MEG form-stable composite PCM (CPCM) for radiant floor heating system was fabricated by physical mixing method. The SiO2 mass fraction in MEG and MEG content in CPCM were optimized. The adsorption performance of MEG on Na2HPO4·12H2O and morphology of MEG were systematically discussed. The shape stability, pore structure as well as thermal properties of the obtained CPCM were emphatically investigated. Experimental results showed that MEG containing 15% SiO2 possessed optimal hydrophilicity and adsorption capacity for Na2HPO4·12H2O. With MEG mass fraction of 20%, the CPCM exhibited suitable phase change temperature (33.52 °C), high phase change enthalpy (158.5 J/g), low supercooling degree (2.29 °C) as well as favorable thermal conductivity (1.077 W/m·K), along with the outstanding shape stability and thermal reliability. All these suggest that Na2HPO4·12H2O/MEG CPCM has great application potential in radiant floor heating system.

Silica-confined composite form-stable phase change materials: a review

Silica-confined composite form-stable phase change materials: a review

Analysis of Thermoelectric Energy Harvesting with Graphene Aerogel-Supported Form-Stable Phase Change Materials.

Graphene aerogel-supported phase change material (PCM) composites sustain the initial solid state without any leakage problem when they are melted. The high portion of pure PCM in the composite can absorb or release a relatively large amount of heat during heating and cooling. In this study, these form-stable PCM composites were used to construct a thermoelectric power generator for collecting electrical energy under the external temperature change. The Seebeck effect and the temperature difference between the two sides of the thermal device were applied for thermoelectric energy harvesting. Two different PCM composites were used to collect the thermoelectric energy harvesting due to the different phase transition field in the heating and cooling processes. The graphene nano-platelet (GNP) filler was embedded to increase the thermal conductivities of PCM composites. Maximum output current was investigated by utilizing these two PCM composites with different GNP filler ratios. The thermoelectric energy harvesting efficiencies during heating and cooling were 62.26% and 39.96%, respectively. In addition, a finite element method (FEM) numerical analysis was conducted to model the output profiles.

Enhanced light-to-thermal conversion performance of all-carbon aerogels based form-stable phase change material composites

The exploitation of excellent performance form-stable phase change material composites (FS-PCMCs) with enhanced photothermal conversion efficiency and high phase change latent heat is of great significance for thermal energy storage. In this work, a new type of FS-PCMCs with superior light-to-thermal conversion performance were created by impregnation of organic phase change material (1-hexadecylamine (HDA) and 1-tetradecylamine (TDA)) into the graphene aerogel (GA) and all-carbon aerogel (GCA) through a simple direct infusion. The multiwalled carbon nanotubes (MWCNTs) are wound around the inner wall of the GA layer to form a three-dimensional (3D) porous network structure to support fatty amine (FAs), thus achieving shape stability before and after phase transition. Moreover, the FS-PCMCs has extremely high phase transition enthalpy (203.1–248 kJ·kg−1) and good recyclability. More importantly, due to the high absorbance of GCA, it can enhance its light absorption capacity and reduce thermal radiation. The light-to-thermal conversion efficiency of the FS-PCMCs is 72.36%-88.25%. Taking the improvement of the comprehensive properties of the FS-PCMCs, the results of this work may open up a way for rational design and preparation of high-performance FS-PCMCs with enhanced storage capacity and light-to-thermal conversion efficiency for the efficient utilization of solar energy.

A complete numerical model for low temperature composite form-stable phase change material slab based on dynamically simplified temperature transforming method

ABSTRACT Phase change material (PCM) that is used in the roof top slab can minimize the heat infiltration into the living space from the building envelope and increase the indoor thermal comfort level. The major disadvantage of PCM is leakage at liquid state. Expanded graphite (EG) is used here as supporting material for PCM to prevent the leakage and maintains the form stability. The composite PCMs are prepared by adding the EG with various mass ratios, i.e. 3%, 6%, and 9%. The thermal properties of all composite PCMs are determined by DSC and thermal conductivity analyzer. The optimum PCM composition was found at 9% of EG. In this study, the shape-stabilized PCM-integrated roof top was analyzed by simplified temperature transforming (TT) numerical model. The main advantage of this model is that it is used to combine the equivalent enthalpy and heat capacity. The numerical results are validated with experimental values and show the lower mean absolute percentage error (MAPE), i.e. 6.91%. This indicates that present model is well suitable to predict the thermal performance of composite PCM incorporated roof top. The effect of various parameters like thickness of the PCM slab, wind velocity, percentage of EG mass ratio, and location of PCM are investigated by simplified TT model. The results showed that the maximum inner surface temperature reach up to 53°C for BG model (concrete and gypsum) by distributing constant heat flux, i.e. 1,000 W/m2 for 180 min. At this same condition, the inner surface temperature of other PCM models PBG (PCM, concrete, gypsum) and BPG (concreate, PCM, Gypsum) reaches to 50°C and 41°C, respectively. PBG model exhibits excellent thermal performance compared to BPG model. The thermal performance of PCM slab is also investigated by varying the thickness of the PCM layer and found that time lag is raised with the thickness of the PCM slab.

Fabrication of form stable composite phase change materials for thermal energy storage by direct powder incorporation with a preheating process

This work concerns with form stable composite phase change materials (FSCPCMs) for thermal energy storage applications. A vast knowledge base has been established in formulation design, material selection and characterisation. However, research efforts on manufacturing technologies are insufficient, leading to limited information on the relationship between manufacture processes and product properties - the main motivation for this work. A commonly used fabrication method is the so-called direct powder incorporation method. We have modified the direct incorporation method by the integration of a preheating process and used the modified method to fabricate a KNO3-diatomite based FSCPCM. The characterisation of the fabricated FSCPCMs showed that the preheating method not only densified the microstructure, but also gave a significant increase in the thermal conductivity (by 54.91%). The improvements were found to be associated with wettability of the PCM on the matrix surface, whereas porous structure of the matrix material has a small effect.

Design of n-octadecane-based form-stable composite phase change materials embedded in porous nano alumina for thermal energy storage applications

Design of n-octadecane-based form-stable composite phase change materials embedded in porous nano alumina for thermal energy storage applications

Form-stable paraffin/graphene aerogel/copper foam composite phase change material for solar energy conversion and storage

Sustainable utilization of solar energy with a more compact solar heating system is a significant research. In this study, a novel form-stable composite phase change material (PCM) was prepared for application in solar energy conversion and storage. Paraffin as PCM was encapsulated in the matrix consist of copper foam (CF) loaded with graphene aerogel (GA) in order to improve thermal conductivity, prevent leakage and convert solar energy to thermal energy. The melting temperature and the latent heat of the composite PCMs were determined to estimate thermal storage performance. The thermal conductivities of composite PCMs measured by transient plane heat source method were more than 9 times higher than that of paraffin. Besides, the composite PCMs showed uniform temperature distribution and perfect shape-stabilization when heated. Furthermore, the composite PCMs exhibited an excellent light-to-thermal energy conversion efficiency (up to 97%) in the experiment of light-to-thermal energy conversion, which demonstrated the potential of the composite PCM for solar energy conversion and storage.

Paraffin/methyl stearate/multi‐walled carbon nanotubes composite phase change materials with wide service temperature and high latent heat

The paraffin/methyl stearate/multi-walled carbon nanotubes composite form-stable phase change materials (FSPCMs) with a wide phase change temperature (Tpc) range and high latent heat (ΔH) and the subsequent phase change slurry (PCS) based on FSPCMs have been prepared via a direct impregnation method and via a simple dispersion method, respectively. The chemical structures, crystalline properties, surface microstructures, phase change properties, thermal reliability and stability of FSPCMs and the thermal storage and release performance were investigated. The FSPCMs had reversible melting/freezing phase change properties with a wider Tpc range from 21.6°C to 55.3°C than that of pure methyl stearate (from 16.2°C to 32.5°C) and high ΔH of 127 J/g. The FSPCMs had good thermal reliability and stability. The PCS presented evident thermal storage and release performance compared to pure water. The FSPCMs and PCS enable huge potential applications in thermal fields depending on wide Tpc range.