Form-stable Composite Phase Change Materials Research Articles

Fatty amines/graphene sponge form-stable phase change material composites with exceptionally high loading rates and energy density for thermal energy storage

The development of form-stable phase change materials (FSPCMs) with large latent heat, excellent thermal stability, and recyclability is essential for their practical applications for thermal or solar energy saving. Here, we first report the exploitation of fatty amines (FAs), in this case tetradecylamine (TDA) and octadecylamine (ODA), as novel organic phase change materials (PCMs) for fabrication of FSPCM composites with exceptional high energy density using porous 3D graphene sponge (GS) as porous supporting materials. The resulting fatty amines/graphene sponge composites (FAs/GS) show high latent heat of ranging from 293 kJ kg−1 to 303 kJ kg−1 and low supercooling degree of 7–9 °C. Surprisingly, it is found that the loading rate of these two FAs into GS is as high as 7063–10660 wt%, which is nearly three orders of magnitudes higher than that of most reported FSPCMs. In addition, compared with the FAs, the presence of GS results in an enhancement of thermal conductivity of FAs/GS. After 200 cycles of thermal cycling, the latent heat content of FAs/GS still remains as high as 93.34% (TDA/GS) and 93.83% (ODA/GS), implying an excellent thermal stability. Taking advantages of the merits mentioned above, the findings of this work would not only open a new way for exploiting the FAs as new high-performance organic PCMs, but also provide a possibility for construction of such FAs/GS with great potentials for real energy-saving applications based on their exceptional high energy density, low supercooling degree, unprecedented high loading value, excellent thermal stability and recycling capacity.

A sodium acetate trihydrate-formamide/expanded perlite composite with high latent heat and suitable phase change temperatures for use in building roof

Introducing a phase change material (PCM) with large latent heat, low thermal conductivity, and appropriate phase change temperatures into building roof favors reducing indoor temperature fluctuation and increasing thermal comfort, thus helping to realize building energy conservation. Herein, a sodium acetate trihydrate (SAT)-formamide (FA) mixture was combined with expanded perlite (EP) to prepare a novel composite PCM. It is shown that adding tetrasodium pyrophosphate decahydrate at a loading of 3 wt% can reduce the supercooling degree of the mixture from 34.5 °C to 0.4 °C. The obtained mixture, composed of 77.6 wt% of sodium acetate trihydrate, 19.4 wt% of formamide and 3 wt% of tetrasodium pyrophosphate decahydrate, can be absorbed into EP to prepare a form-stable composite PCM at a mass fraction of 55 wt%, which has a melting point of 40.5 °C and an enthalpy of as large as 148.3 J/g. This composite PCM possesses good thermal reliability and has a thermal conductivity of as low as 0.0978 W/(m·K). The thermal performance of the composite PCM when employed in the roof of a test room was investigated and compared with those of the previously reported CaCl2·6H2O/EP composite PCM and EP. It is found that, the test room with the SAT-FA/EP composite in the roof exhibits slower temperature rise and drop rates, a reduction in the highest temperature, and an increase in thermal comfort, compared with those containing the CaCl2·6H2O/EP composite PCM and EP. The better thermal performance of the SAT-FA/EP composite is attributed to its larger latent heat and more suitable phase change temperatures for use in roof, thereby showing great potential for practical applications.

Preparation and thermal performance of binary fatty acid with diatomite as form-stable composite phase change material for cooling asphalt pavements

The diatomite (DI) was selected as the load matrix, and the stearic acid (SA) and palmitic acid (PA) were chosen as the eutectic binary fatty acids to synthesize the form-stable composite phase change material (CPCM). The microtopography and characteristics of CPCM were described by scanning electronic microscopy (SEM), Fourier transform infrared spectroscopy (FT-IR) and X-ray diffraction (XRD). The thermal performance and stability were confirmed by thermogravimetric analysis (TG) and differential scanning calorimetry (DSC). The maximum eutectics absorption of DI could reach 65.2%. The phase change temperature and enthalpy of CPCM are 52.93 °C and 106.70 J/g, respectively. The crystallization fraction of (SA + PA)/DI could reach 83.10%. Moreover, the DSC results after 100 times heating-cooling process show that CPCM has excellent thermal and chemical stability. For the preparation of temperature-adjusting asphalt mixture, some fine aggregate of 0.075 mm and filler were replaced with (SA + PA)/DI CPCM for the corresponding particle size. The highest temperature reduction of the upper and bottom surface of temperature-adjusting asphalt mixture could reach 8.11 °C and 6.36 °C in laboratory, showing a great promising application for cooling asphalt pavements. Furthermore, pavement performance test of temperature-adjusting asphalt mixture was also conducted. The CPCM with binary fatty acids and DI has the potential to alleviate the rutting diseases of asphalt pavements and the effect of urban heat island.

Paraffin@graphene/silicon rubber form-stable phase change materials for thermal energy storage

A kind of paraffin@graphene/silicone rubber (SR) composite form-stable phase change material (PCM) was prepared in this paper. Paraffin@graphene phase change microcapsules were fabricated by electrostatic self-assembly method, then the microcapsules were added to the SR matrix to prepare paraffin@graphene/SR composites. The microstructure of the composite was characterized by scanning electron microscopy (SEM). Differential scanning calorimetry (DSC) and thermal conductivity test results show that the phase change latent heat is 53.39 J g−1 and the thermal conductivity reaches 0.453 W m−1 K−1 for the composite with 30 phr paraffin@graphene microcapsules. The microcapsules enhance the thermal and mechanical properties of SR, which can be used for thermal energy storage.

Facile preparation of polyethylene glycol/wood-flour composites as form-stable phase change materials for thermal energy storage

The polyethylene glycol/wood-flour (PEG/WF) composites were synthesized as novel form-stable phase change materials (PCMs) using PEG as phase change material and WF as supporting material. The composite products were investigated by Fourier-transform infrared spectrometer, scanning electron microscopy (SEM), the leakage test, X-ray diffraction (XRD), differential scanning calorimeter (DSC), accelerated thermal cycling testing and thermogravimetry analysis (TG), respectively. The results revealed that the maximum latent heats and encapsulation ratio of the synthesized PEG/WF composite form-stable PCMs can reach 90.9 J g−1 and 52.8%, respectively. SEM images demonstrated that the porous tubular-like channel spaces of WF are completely blocked by PEG. The thermal cycling test showed that the synthesized PEG/WF composite form-stable PCMs have superior thermal reliability after 200 melting and freezing cycles without leakage. Additionally, TG results revealed that the prepared PEG/WF composite form-stable PCMs have good thermal stability with the decomposition temperature higher than 200 °C. Thus, the novel PEG/WF composite form-stable PCMs are a promising candidate using in wallboard and building materials due to its excellent thermal properties and thermal reliability.

Capric acid/intercalated diatomite as form-stable composite phase change material for thermal energy storage

Leakage issue and low thermal conductivity largely restrict feasibility of fatty acid in real application of thermal energy storage (TES). In this paper, a novel form-stable phase change material (FSPCM) capric acid/diatomite (CA/DT) for TES was prepared using direct impregnation method by using CA as PCM and diatomite as supporting material. The fabricated composites were investigated in detail via the leakage test to determine the optimization proportion, and the real mechanism of preventing leakage by diatomite was analyzed. The characterization techniques such as thermogravimetric analysis, differential scanning calorimetry, intelligent paperless recorder technology, Fourier transform infrared spectrometer and scanning electron microscopy were applied to systematically investigate the thermal properties, microstructure and thermal compatibility of the prepared composites. The results showed that the maximum mass ratio of CA adsorbed into DT without leakage is as high as 50 mass%, which is mainly ascribed to the porous structure of DT. The selected FSPCM has a melting point of 34.9 °C and latent heat of 89.2 J g−1. What is more, the CA/DT FSPCM exhibits a distinctly enhanced thermal stability by TG analyses. The heat transfer efficiency of the CA/DT FSPCM is higher than that of pristine CA. Due to the high adsorption capacity, high latent heat, good thermal stability as well as low cost, the CA/DT FSPCM can be considered as potential materials for thermal energy storage.

Preparation and characterization of GO/PEG photo-thermal conversion form-stable composite phase change materials

In this paper, graphene oxide (GO) with full band light absorption and photo-thermal conversion property was selected as the photo-thermal conversion material. The GO/PEG composite phase change material (PCM) was prepared by ultrasound-assisted physical blending. The micro-structure, crystallinity and chemical composition of the composite PCMs were characterized by XRD, SEM, and FT-IR analysis techniques, respectively. The thermal storage properties and photo-thermal conversion performance of GO/PEG composite PCMs were tested by DSC and self-assembled photo-thermal conversion test system. The results showed that the inter-layer spacing of GO was enlarged. PEG was distributed between the layers and surfaces of GO through the capillary force of GO and inter-molecular hydrogen bonding. The latent heat of the GO/PEG composite PCMs were more than 80 J/g and the phase transition temperature was 50.5 °C. The composite PCM could absorb visible light (300–800 nm) and store energy through light drive. Photo-thermal conversion efficiency of the GO/PEG reached 0.75, which indicated that the prepared GO/PEG composite PCMs had great application prospect in the field of photo-thermal conversion.

Thermal conductivity enhancement of form-stable tetradecanol/expanded perlite composite phase change materials by adding Cu powder and carbon fiber for thermal energy storage

In this study, form-stable tetradecanol (TD)/expanded perlite (EP) composites by adding Cu powder (CuP) and carbon fiber (CF) to enhance thermal conductivities have been prepared via vacuum impregnation method. The thermal conductivity enhancer (TCE) is introduced by two methods of mixing TCE with phase change materials (PCMs) and implanting TCE into matrix materials. The result demonstrates the former is better than the latter in aspects of thermal property, thermal conductivity and controllability, moreover, adding ratio of TCEs gather in more appropriate interval from 2.5% to 3% suitable for the former. For CPCMs, FT-IR results indicate it is no chemical interaction among raw materials but physical combination via two methods. CPCMs prepared by the method of mixing TCE with PCMs have better phase change latent heat and thermal stability by DSC and TGA, while thermal cycling measurements show that form-stable composite PCMs have adequate stability even after being subjected to 200 melting/freezing cycles. Therefore, the method of mixing TCE with PCMs has better thermal property and controllability than that of implanting TCE into matrix materials and the prepared CPCM has great application prospect in solar energy utilization, building material, indoor cooling instrument and so on for thermal energy storage.

Silicone rubber/paraffin@silicon dioxide form-stable phase change materials with thermal energy storage and enhanced mechanical property

A kind of silicone rubber (SR)/paraffin (Pa)@silicon dioxide (SiO2) composite form-stable phase change material (PCM) was developed in this paper. Pa@SiO2 was obtained by choosing Pa as PCM core microencapsulated in SiO2 shell based on tetraethoxysilane (TEOS) and γ-aminopropyl triethoxysilane (APTES) as precursors, then Pa@SiO2 microencapsules were embedded in SR matrix to fabricate SR/Pa@SiO2 composites. The SiO2 shell can provide a barrier for the melted Pa and meanwhile have reinforcing effect on SR as inorganic filler. The in-situ modification of SiO2 shell using APTES owing to the amino groups can not only prevent agglomeration, but also increase interfacial bonding between Pa@SiO2 with SR. The thermal and mechanical properties of the form-stable PCMs were characterized by differential scanning calorimetry (DSC) and mechanical tests. The results showed that the thermal and mechanical properties of SR/Pa@SiO2 composites were better than those of SR/Pa and SR/Pa/SiO2. Leakage test was conducted by heating the prepared composites over the melting temperature of Pa. The SR/Pa@SiO2 composites were found as form-stable PCM with low leakage rate. The phase change latent heat of the SR/Pa@SiO2 composites was up to 92.39 J g−1 and the composites can be used for thermal energy storage.

Preparation of novel form–stable composite phase change materials with porous silica nanofibrous mats for thermal storage/retrieval

Electrospun SiO2 nanofibrous mats have been widely utilized as substrate of form-stable phase change materials due to large specific surface area and high convection coefficient. In order to overcome the brittleness and enhance the absorption capacity of SiO2 nanofibrous mats as substrate, flexible and hollow SiO2 nanofibrous mats were prepared by single-spinneret electrospinning which eliminated complicated spinneret and unstable structure compared with coaxial electrospinning. Quinary fatty acid eutectics were chosen as representative fatty acid which were adsorbed in SiO2 nanofibrous mats to form form-stable phase change materials. The results showed that hollow structure can be observed as the content of paraffin oil decreased from 1.67 to 0.70 g, and as-prepared hollow nanofibrous mats displayed favorable flexibility. DSC results demonstrated that the largest melting/crystallization enthalpy supported by hollow SiO2 nanofibrous mats was approximately 123.80/120.50 J g−1, which was much higher than solid SiO2 nanofibers. More importantly, after 30 cycles, there was no obvious change for phase change temperature and enthalpy. The thermal conductivity of representative form-stable phase change materials was over three times than that of quinary fatty acid eutectics. Hence, flexible and hollow SiO2 nanofibrous mats were excellent substrate in form-stable phase change materials and would have wide application prospects.

A Form Stable Composite Phase Change Material for Thermal Energy Storage Applications over 700 °C

Thermal energy storage (TES) is a highly effective approach for mitigating the intermittency and fluctuation of renewable energy sources and reducing industrial waste heat. We report here recent research on the use of composite phase change materials (PCM) for applications over 700 °C. For such a category of material, chemical incompatibility and low thermal conductivity are often among the main challenges. Our aims are to address these challenges through the formulation of form-stable composite PCMs and to understand their thermophysical properties. The eutectic K2CO3-Na2CO3 salt was used as a PCM with MgO as a form stabilizer. We found that such a formulation could maintain shape stability with up to 60 wt.% PCM. With a melting point of ~710.1 °C and an energy density as high as 431.2 J/g over a temperature range between 550 °C and 750 °C, the composite PCM was shown to be thermally stable up to 885 °C. An addition of 10 wt.% SiC enhanced the overall thermal conductivity from 1.94 W·m−1 K−1 to 2.28 W·m−1 K−1, giving an enhancement of 17.53%. Analyses of thermal cycling data also showed a high extent of chemical compatibility among the ingredients of the composite PCM.

Emerging mineral-coupled composite phase change materials for thermal energy storage

A mineral-coupled support, flake graphite-carbon nanofiber-modified bentonite, was used to stabilize stearic acid for constructing form-stable phase change material composites. In order to achieve a synergistic improvement of thermal conductivity and loading space, the supporting material was prepared by growing carbon nanofiber on flake graphite surface through chemical vapor deposition technique and then chemically bonding with modified bentonite. The effect of coupling behavior on interfacial thermal resistance was investigated and results show that the thermal conductivity of the coupled supporting material (4.595 W m−1 K−1) is higher than that of non-coupled support (4.291 W m−1 K−1), proving chemical bonding can decrease interface thermal resistance at a certain extent. The performances of composites were further explored, which indicates the obtained composite base on coupled support possesses good chemical compatibility, and great thermal stability under 180 °C. It also shows that this composite with 41.90% loading capability has latent heat value of 79.13 J g−1 for melting and 79.13 J g−1 for freezing, respectively. After 50 heating-cooling cycles, the variation of melting latent heat was within 0.05%, exhibiting a great thermal reliability. Besides, thermal conductivity of this composite is 10.50 times higher than that of pure phase change material, resulting in more rapid heat transfer efficiency, and excellent transient temperature response recorded by thermal infrared images. In all, the composite is a potential candidate for thermal storage applications due to larger latent heat capability and considerable thermal conductivity.

Lauric-stearic acid eutectic mixture/carbonized biomass waste corn cob composite phase change materials: Preparation and thermal characterization

In this study, novel form-stable composite phase change materials (FS-CPCMs) were prepared by the incorporation of a eutectic mixture of lauric-stearic acid (LA-SA) into carbonization corn cob (CNCC). CNCC served as a good supporting material that not only prevented the leakage of LA-SA but also enhanced its thermal conductivity. Scanning electron microscopy results demonstrated that CNCC exhibits a highly porous structure comprising rough micropores. The retention of 77.9 wt% of LA-SA in CNCC without leakage was observed. Differential scanning calorimetry results revealed that LA-SA/CNCC FS-CPCMs melt at 35.1 °C with a latent heat of 148.3 J/g and solidify at 29.7 °C with a latent heat of 144.2 J/g. The thermal conductivity of LA-SA/CNCC FS-CPCMs was approximately 87.5% greater than that of LA-SA. Thermogravimetric analysis and 200-cycle experiments indicated that the LA-SA/CNCC FS-CPCMs exhibit excellent thermal stability and form-stable performance. Therefore, the as-prepared LA-SA/CNCC FS-CPCMs demonstrate promise for building energy-efficiency applications.

Form-stable oxalic acid dihydrate/glycolic acid-based composite PCMs for thermal energy storage

The development of high efficient materials for storage and utilization of sustainable thermal energy is very meaningful. Herein, in this research, an oxalic acid dihydrate/glycolic acid (OG) binary eutectic mixtures with the ratio of 80 wt%/20 wt% was prepared as phase change material (PCM), hydrothermal carbon (HTC) and poly (acrylamide-co-acrylic acid) copolymer (PAAAM) were separately and together used as support materials to solve liquid-state leakage problem and improve thermal conductivity. Three form-stable PCM composites (OG/PAAAM, OG/HTC/PAAAM and OG/HTC) were synthesized. The prepared composites were studied by XRD and FT-IR spectra, their thermophysical properties and PCM storage properties were investigated using differential scanning calorimetry (DSC), thermogravimetric analysis (TGA) and scanning electron microscopy (SEM). The OG/PAAAM, OG/HTC/PAAAM and OG/HTC showed the high loading rate to OG content, which are 1718 wt%, 1329 wt% and 1150 wt%, and the latent heat are 289.6, 313.2 and 318.8 J/g, respectively. In addition, the composites possess excellent recyclability after 101 times melting-freezing cycles. Compared to pure OG, OG/PAAAM and OG/HTC/PAAAM (0.2766, 0.3125 and 0.8538 W/m K), the OG/HTC exhibit a higher thermal conductivity of 1.3867 W/m K.

Thermal management of Li-ion battery pack with the application of flexible form-stable composite phase change materials

A method for thermal management of Li-ion battery pack with the application of various flexible form-stable composite phase change materials (CPCMs) is proposed, and investigated both numerically and experimentally. Flexible CPCMs embedded in battery pack lower the thermal contact resistance, thereby improving the thermal control performance. Experimental results show that with the application of flexible CPCMs, the battery temperature drops by 18 °C at 10 C discharge rate. In addition, flexible CPCM has better thermal control performance than the case of conventional CPCMs. This allows Li-ion battery pack to safely work for an extended period of time without exceeding upper temperature limits. The thermal control performance is observed to vary considerably with three factors: the phase change temperature of flexible CPCMs, working condition, and the ambient temperature. One flexible CPCM with phase change temperature of 33 °C is found to be optimal for small power levels and low ambient temperatures. Another flexible CPCM with 47 °C of phase change temperature is suitable for high power levels, short-term high heat fluxes, and high ambient temperatures. The numerical results are in reasonable accordance with experimental ones.

Characterization and stability study of a form-stable erythritol/expanded graphite composite phase change material for thermal energy storage

A form-stable erythritol/expanded graphite (EG) composite phase change material (PCM) for mid-temperature thermal energy storage (TES) was successfully developed by an “impregnation, compression and sintering” three-step method. Five composite samples were prepared with EG contents of 5, 8, 10, 12 and 15 wt%, respectively. After measuring the thermal properties, it is shown that with the increase of EG content, the thermal conductivity and the freezing temperature are increased, while the melting temperature, the supercooling degree, and the latent heat of the composite PCMs are reduced. Furthermore, the 40 times charging-discharging performance of the form-stable composite PCMs was also tested on a supercooling test platform from room temperature to 130 °C. The charging time and the supercooling degree can be significantly reduced with the increase of the EG content. The present work shows that the 10 wt% EG content of form-stable composite PCM exhibits an optimal overall performance with a high thermal conductivity of 12.51 W/(m·K) (17.38 times higher than the pure erythritol) a low supercooling degree of 19.5 °C (11 °C lower than that of pure erythritol) and a good cyclic stability after 140 cycles. Therefore, it is proposed in this study as a promising PCM for mid-temperature TES.

PEG/3D graphene oxide network form-stable phase change materials with ultrahigh filler content

In situ side-to-side cross-linking of GO maximizes the PEG filler content and enhances the thermal storage density of CPCMs.

Stearic–capric acid/porous nanoceramics as a novel form-stable composite phase change material (FSPCM) for thermal energy storage

This work aims at preparing a novel form-stable composite phase change material (FSPCM), by loading stearic–capric acid (SA–CA) in porous nanoceramics which are employed as the supporting materials. The morphology and microstructure, chemical compatibility, thermal properties and thermal stability are analyzed. The results indicate that the prepared FSPCM freezes at 24.56 °C with latent heat capacity of 73.92 J/g and melts at 22.50 °C with latent heat capacity of 76.40 J/g. The as-prepared composite is demonstrated to reveal good physicochemistry stability and an acceptable absorption ratio. Moreover, the thermal conductivity of FSPCM is nearly 7 times higher than that of pristine PCM.

Synthesis of novel form-stable composite phase change materials with modified graphene aerogel for solar energy conversion and storage

In this study, novel kinds of form-stable composite phase change materials (FS-CPCM) were prepared by the vacuum impregnation method. In the FS-CPCM, lauric acid (LA) was the PCM, and LA was grafted on the surface of graphene aerogel (GA) by an esterification reaction and reduction process to prepare supporting material and increase the thermal conductivity of the FS-CPCMs. The microstructure, thermal storage properties, thermal conductivity and light-to-heat conversion of the FS-CPCMs were investigated. Scanning electron microscopy and Fourier transform infrared spectroscopy were used to demonstrate that the LA was encapsulated effectively in the porous structure of the LA-GA, and the LA/LA-GA FS-CPCMs were prepared successfully. X–ray diffractometer results confirmed that the crystallization of the LA/LA-GA FS-CPCM was better than that of LA/GA FS-CPCM. Thermal conductivity analyses indicated that the thermal conductivities of the LA/LA-GA-1 FS-CPCMs increased 352.1% and 32.6% compared with the conductivities of LA and LA/GA FS-CPCM, respectively. Differential scanning calorimetry results confirmed that the LA/LA-GA-1 FS-CPCM possess good phase change behavior, low undercooling and excellent thermal cycling stability. The melting enthalpy and freezing enthalpy could reach 207.3 J/g and 205.8 J/g, respectively, and the LA/LA-GA FS-CPCM exhibited good thermal reliability and stability. Furthermore, the LA/LA-GA FS-CPCM had excellent photon absorption and the highest efficiency in terms of light-to-heat conversion of 80.6%. Such good performances demonstrate the LA/LA-GA FS-CPCM's potential for use in solar energy storage systems.

Effects of carbon nanotubes additive on thermal conductivity and thermal energy storage properties of a novel composite phase change material

Fatty acids are commonly preferred as phase change materials for passive solar thermoregulation due to their several advantageous latent heat thermal energy storage (LHTES) properties. However, further storage container requirement of fatty acids against leakage problem during heating period and also low thermal conductivity significantly limit their application fields. To overcome these drawbacks of capric acid–stearic acid eutectic mixture as phase change material, it was first impregnated with expanded vermiculite clay by melting/blending method and then doped with carbon nanotubes. The effects of carbon nanotubes additive on the chemical/morphological structures and LHTES properties of the composite phase change material and thermal enhanced change phase change materials were investigated by scanning electron microscope, Fourier transform infrared spectroscopy, X-ray diffraction, differential scanning calorimetry and thermogravimetric analysis analysis techniques. The differential scanning calorimetry results showed that the form-stable composite phase change materials and thermal enhanced composite phase change materials have melting temperatures in the range of 24.35–24.64℃ and latent heat capacities between 76.32 and 73.13 J/g. Thermal conductivity of the composite phase change materials was increased as 83.3, 125.0 and 258.3% by carbon nanotubes doping 1, 3 and 5 wt%. The heat charging and discharging times of the thermal enhanced -composite phase change materials were reduced appreciably due to the enhanced thermal conductivity without notably influencing their LHTES properties. Furthermore, the thermal cycling test and thermogravimetric analysis findings proved that all fabricated composites had admirable thermal durability, cycling LHTES performance and chemical stability.