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Thermal energy storage (TES) systems are significant to solve inevitable intermittency and curtailment issues of clean renewable energy sources. Thus, the high-density and high-efficient TES technologies are required to achieve carbon neutrality. This study aims to synthesize an egg-carton-shaped paraffin microsheet for high-density latent heat storage. Poly(methyl methacrylate) (PMMA) microparticles (3 μm in diameter) are homogeneously placed onto a silicon wafer (10 × 10 mm2) via Langmuir–Blodgett technique. The PMMA monolayer on the silicon wafer is then dipped in a colloidal silica sol and dried to form the bottom structure of the egg-carton. Paraffin, a phase change material with a large melting enthalpy, is injected into the void space of the egg-carton produced by the decomposition of the PMMA particles. Finally, the upper silica shell covers the egg-carton structure with spherical paraffin to ultimately obtain an approximately 3.4-μm-thick microsheet for latent heat storage. The thermal performance of the paraffin microsheets is evaluated using differential scanning calorimetry. The encapsulation ratio, defined as the mass ratio of the paraffin to the microsheet, is calculated to be approximately 80.2%. This novel paraffin microsheet enables an increase in the TES capacity and ultimately overcomes poor heat transfer in paraffin owing to its low thermal conductivity. [Display omitted] • Egg-carton-shaped paraffin microsheet with 3.4 μm thickness is synthesized by Langmuir–Blodgett technique, sol-gel reaction, and dip-coating. • Low TEOS concentration improves denseness of the egg-carton-shaped SiO 2 structure. • 35% enhanced heat storage capacity was obtained in the paraffin microsheet, compared to water. [ABSTRACT FROM AUTHOR]

Traditional water-based PV/T systems have low heat storage density, high PV backsheet temperatures, and low energy utilization in practical applications. In this work, nanoparticles were applied to improve thermal conductivity and simultaneously emulsions were added to enhance energy storage density of the conventional heat transfer media. Furthermore, the synergistic effect of nanocomposite Phase Change Material Emulsions (PCME) as the heat transfer medium on the thermoelectric efficiency of PV/T was studied in a real system. Specifically, the water-based 30 % paraffin emulsions with graphene oxide (GO) concentration of 0.01, 0.02 and 0.03 wt% were prepared by ultrasonic stirring and their thermophysical properties were characterized. The results show that the 30 wt% paraffin emulsion with addition of 0.02 wt% GO has the phase change temperature of 35 °C, latent heat of 42.93 J/g, thermal conductivity of 0.505 W/(m·K) and viscosity coefficient of 0.91. It shows the thermal efficiency of the paraffin/GO emulsion increased by 92.28 %, the electrical efficiency increased by 8.87 %, the comprehensive efficiency increased by 45.75 %, and 15.8 % increase in heat collection for the heat exchange tank in comparison with the water. It is concluded application of PCME would improves the thermoelectric performance of the system than traditional water-based PV/T systems. • Applying paraffin emulsions with GO nanoparticles to a practical PV/T system. • Optimal nanocomposite paraffin emulsion is selected by performance testing. • Comparing the performance and pumping consumption with water-based PV/T systems. • Greater improvement in thermoelectric efficiency of PV/T systems compared to water. [ABSTRACT FROM AUTHOR]

Chemically activated biochar with richer pore structure and higher specific surface area is well suited for loading phase change materials (PCMs). However, the effect of structural characteristics and abundant surface functional groups of chemically activated biochar on the thermal properties of PCMs has not been systematically investigated. Here, shape-stable samples were prepared by introducing biochar obtained by activation with different chemical reagents (ZnCl 2 , H 3 PO 4 , KOH, and K 2 CO 3) into three organic PCMs (paraffin, stearic acid, and polyethylene glycol). The results indicated that the biochar activated by KOH possessed the highest specific surface area of 1344.45 m2/g, followed by biochar activated by ZnCl 2 , H 3 PO 4 , and K 2 CO 3 of 1297.35, 1062.74, and 891.38 m2/g, respectively. The loading capacity of KOH-activated biochar was as high as 82.12 %, 83.13 %, and 80.81 % for the three organic PCMs, and the melting enthalpies of corresponding composite PCMs were 163.82, 168.54, and 139.96 kJ/kg. Additionally, the influence degree on the enthalpies of the three PCMs was only 10.84 %, 12.26 %, and 7.74 %, while that of ZnCl 2 and H 3 PO 4 -activated biochar was as high as 53.61 % and 44.22 %, 52.10 %, and 57.74 %, 55.35 % and 45.79 % indicating the two biochar were not suitable as support materials for PCMs. Moreover, ZnCl 2 -activated biochar has the most apparent upgradation on PCMs' thermal conductivity, which could increase the thermal conductivity of the three organic PCMs by 1.318, 1.34, and 1.229 times, respectively, followed by H 3 PO 4 , K 2 CO 3 , and KOH-activated biochar. • Chemically activated biochar had larger specific surface area. • Encapsulation capacity of KOH-activated biochar for organic were significant. • Influence degree of ZnCl 2 and H 3 PO 4 -activated biochar was obvious. • ZnCl 2 -activated biochar had the most apparent upgradation on thermal conductivity. [ABSTRACT FROM AUTHOR]

Abstract Paraffin is mainly preferred as an organic phase change material (PCM) in thermal energy storage (TES) systems especially for cooling and heating of buildings implementations. In order to develop form-stable and thermally stable blends natural minerals (Colemanite, Ulexite and Mg(OH) 2) were used to prepare composites via direct impregnation method. These mineral compounds are abundant locally and known to be thermally stable as they show multi-step thermal decompositions. Thermal, morphological and chemical properties of these composites were characterized by thermogravimetric analysis (TGA), the differential scanning calorimetry (DSC), Fourier Transform Infrared Spectroscopy (FT-IR), Scanning Electron Microscope (SEM). Results of analyses indicate that the introduction of mineral phase to the paraffin is achieved adequately despite of minor mixing problems that show a form-stable behaviour. Comparing energy storage abilities of these composites, Mg(OH) 2 or Colemanite containing blends are found to be the promising composites. Highlights • Boron-based PCM Composites of non-toxic nature were prepared. • A simple direct impregnation method was used. • Colemanite, Ulexite, Mg(OH) 2 composites are developed for TES building applications. • Thermal and physical analyses are carried out to determine mineral influence in PCM. [ABSTRACT FROM AUTHOR]

Abstract Nanocomposites consisting of paraffin/graphene nanoplatelets mix embedded in carbon foams via vacuum infiltration were fabricated with the aim of developing new phase change material (PCM) formulation with excellent shape stabilization, improved thermal conductivity and outstanding thermal reliability and structural stability. Physicochemical and thermal properties of the nanocomposites were evaluated using a suite of techniques such as scanning and transmission electron microscopy, X-ray diffraction, attenuated total reflection - Fourier transform infrared spectroscopy, nitrogen adsorption analyzer, differential scanning calorimetry, mechanical tester, Raman spectroscopy, thermal conductivity analyzer and thermogravimetric analyzer. The carbon foams exhibited good cyclic compressive behavior at a strain of up to 95% and kept part of their elastic properties after cyclic testing. Due to the robust mechanical integrity and layered meso-/macroporous morphology of these carbon foams, the nanocomposites are well equipped to cope with volume changes without leaking during thermal cycling. A 141% thermal conductivity enhancement observed for the carbon foam nanocomposite demonstrates the contributing role of the carbon foam in creating effective heat transfer through its conductive 3D network. The results have shown that proper chemical modification and subsequent carbonization of the low cost porous foams can lead to ultralight multifunctional materials with high mechanical and physical properties suitable for thermal energy storage applications. Highlights • Developed new carbon foam nanocomposites for thermal energy storage. • Carbon foam can embed the PCM mix while enhancing its thermal conductivity. • PCM consists of graphene nanoplatelets dispersed in paraffin wax. • A 141% thermal conductivity enhancement of the nanocomposite has been demonstrated. • Nanocomposites exhibit excellent thermal reliability and stability. [ABSTRACT FROM AUTHOR]

Abstract Encapsulated paraffin-type phase change materials are considered important candidates for thermal energy storage applications. In this paper, we present icosane coated in a layer-by-layer fashion using the weak polyelectrolytes poly(acrylic acid) and poly(allylamine) in order to create ultra-thin cross-linkable and robust polymer encapsulations with storage capacities close to the pristine icosane. After coating, SEM images displayed an average particle size between 20 and 50 µm. Generally, smooth surface structures of the coated particles compared to uncoated icosane-surfactant particles, 1H NMR and FT-IR spectra as well as fluorescence imaging confirmed the successful encapsulation. Calculations of the PCM content revealed that the final product consisted of 88.6% core material. Accordingly, the resulting PCM capsules showed high storage capacities of 199.1 J g−1 close to the original value of pristine icosane (223.6 J g−1). Thermal stability was confirmed by TGA, revealing an increased resistance to thermal degradation of the coated particles (T 10, bulk = 175.7 °C and T 10, capsule = 186.8 °C). Moreover, repeatability and reliability of the phase change behavior were confirmed in thermal cycling experiments including 100 heating-cooling cycles with no observable influence on the performance of our material. Graphical abstract fx1 Highlights • Layer-by-layer coated phase change materials have been fabricated. • Weak polyelectrolytes can provide stable encapsulation of icosane as PCM. • A storage capacity close to the pristine PCM can be maintained. [ABSTRACT FROM AUTHOR]

The use of paraffin, salts and salt hydrates as phase change materials (PCMs) have been researched extensively and used in a number of commercial applications. However, metals and metal alloys, which possess a high storage density on a volume basis as well as a substantially higher thermal conductivity, has received much less attention. This paper discusses the considerations for the use of metal and metal alloys as phase change materials for high temperature thermal storage applications, as well as summarises the literature on the limited research in this area. Although some pure metals and metal alloys present interesting thermal properties to be used as PCMs in thermal storage systems, there is a lack of understanding on the implications of the metallurgical aspects related to the melting and solidification of these materials under thermal cycling at high temperatures. The main issues to be considered include vapour pressure, undercooling, corrosion, segregation, changes in composition and microstructure, changes in thermal properties and undesired reactions. Further research is needed before these materials can be used as PCMs in thermal energy storage systems in industry. [ABSTRACT FROM AUTHOR]

Green, stable, and high-performance phase change materials with photothermal/electrothermal capabilities are crucial for solar thermal utilization. In this paper, biomass cellulose nanocrystals (CNCs), konjac glucomannan (KGM), MXene (a two-dimensional material), and AgNO 3 were first mixed through a simple and fast physical process and then subject to directional freeze-drying and thermal annealing successively. The resulting lightweight porous carbon aerogels further adsorbed paraffin to yield a composite phase change material PMCKA. PMCKA had a high loading rate (95.16%), high enthalpy (231.38 J/g), exceptional conductivity (147.5 S/m), and remarkable cycle stability. Moreover, the photothermal and electrothermal conversion efficiencies of PMCKA might reach up to 97.45% and 98.89%, respectively. This finding demonstrates superior photothermal and electrothermal conversion performance of PMCKA in solar energy storage. Therefore, PMCKA can probably be widely applied to solar thermal conversion, industrial waste heat recovery, and thermal management of electronic equipment. [Display omitted] • The preparation method of bio-based PMCKA is simple and efficient. • PMCKA has ideal heat storage performance, excellent cycle stability, and thermal stability. • PMCKA has excellent photothermal conversion capability and can effectively recycle solar energy. • PMCKA has good electrothermal cycle stability and adjustability at different voltages. [ABSTRACT FROM AUTHOR]

Sugar alcohols (SA) are attractive phase change materials (PCM) for thermal energy storage applications at low-to-medium temperatures (70–180 °C). Five pure sugar alcohols (xylitol, adonitol, L-arabitol, erythritol, D-mannitol) and three eutectic blends (eythritol/xylitol, L-arabitol/erythritol, L-arabitol/xylitol) are investigated in this paper. Experimental characterization of such materials as PCMs is provided. This encompasses the measurement of their melting point and latent heat of fusion, as well as the experimental determination of all key physical properties (specific heat, thermal conductivity, thermal diffusivity, density, viscosity) as a function of the temperature. The performances of the studied materials are compared to those of most currently used PCMs (paraffin waxes, salt hydrates etc.) in the field of thermal energy storage. The most significant applications, including solar seasonal energy storage, are also discussed. [ABSTRACT FROM AUTHOR]

Organic phase change materials (PCMs) have relatively high latent heat capacities, are stable, nontoxic, and not corrosive. Having such advantages, organic PCM s shall find applications in many more thermal energy storage (TES) systems. Currently their main handicap is finding a cost-effective, environmentally benign and compatible encapsulation method. This study uses SiO 2 , which is preferred in several biocompatible applications, as shell material to microencapsulate two different organic PCMs: Paraffin and Stearic acid. Nanocapsules of these PCMs with sizes in the range of 20–700 nm were produced by in situ emulsion interfacial hydrolysis and polycondensation technique. The resulting microencapsulation ratios observed were 11% for paraffin (PA) and 23% for stearic acid (SA). [ABSTRACT FROM AUTHOR]

Dispersion of highly conductive nanoparticles in Phase Change Materials (PCMs) tends to improve the thermophysical properties of nanocomposites. The current research condenses the synthesis, chemical, physical, and thermal characterization of novel nano-enhanced eutectic phase change materials (NeUPCMs) dispersed with TiO 2 nanofillers for thermal management applications. The base matrix primarily comprises of a eutectic of paraffin wax and palmitic acid. Detailed analysis of the uncertainty of each thermophysical property measured was performed. The synthesized nanocomposite logged a maximal thermal conductivity of 0.59 W/mK (2.3-fold as compared with the base-0.25 W/mK) with 0.5% nanofillers. The composites displayed excellent solar transmissivity (82%) as they were doped with nanofillers having a high refractive index. The latent heat of the NeUPCMs got enhanced by 17% whereas the melting point showed a slight decrement in nanocomposites. Further, zero phase segregation, no subcooling, stable phase transition temperature, and good chemical, and thermal stability were noted from digital scanning calorimetry results with NeUPCMs. The composites exhibited good thermal reliability beyond 500 thermal cycles. It could be potentially deployed in the thermal management of medium-temperature systems like PVT and LCPVT systems. [Display omitted] • Novel nanocomposites were synthesized using paraffin wax, palmitic acid, and TiO 2. • Nanocomposite had a maximal enhancement of 131.5% in thermal conductivity. • 38% rise in solar transmittance when compared with the eutectic base. • Thermophysical properties remained stable even after 500 thermal cycles. [ABSTRACT FROM AUTHOR]

The objective of this study is to overcome the leakage and low thermal conductivity problems of paraffin as PCMs (phase change materials) for thermal energy storage by impregnating SEBS/paraffin/HDPE FSPCMs (form-stable phase change materials) into metal foam. The form-stable composites were prepared by absorbing paraffin into the network of powder-like styrene-b-(ethylene-co-butylene)-b-styrene (SEBS) triblock copolymer and covering high-density polyethylene (HDPE) on pre-prepared SEBS/paraffin mixture. The composites were characterized by using differential scanning calorimetry (DSC), Scanning electron microscope (SEM), Fourier Transform Infrared Spectrometer (FT-IR), X-Ray Diffraction (XRD) and Hot disk. Paraffin leakage was investigated by accelerated degradation test at 80 °C. The melting temperature and latent heat of the composites were determined as 50.56 °C and 151.6 J/g, respectively. FT-IR results revealed good chemical compatibility among paraffin, SEBS and HDPE. SEM images and XRD test results demonstrated that the paraffin had uniformly dispersed into SEBS. This composite was testified able to keep paraffin from seepage with only 2.39 wt% of paraffin loss after 50 thermal cycles test (150 h). In addition, the thermal conductivity of SEBS/paraffin/HDPE was 0.272 W/m K, which was increased up to 2.142 W/m K when copper foam was embedded in the composite. [ABSTRACT FROM AUTHOR]

In this study, paraffin was selected as the phase change materials (PCMs) and rude-Palygorskite (Pal), rinsed-Pal, H + -Pal and organic-Pal were selected as porous materials. A series of paraffin/Pals composite PCMs were prepared by direct impregnation method without vacuuming. In the composite PCMs, up to 150 wt% of paraffin could be loaded in H + -Pal. The Differential Scanning Calorimetry (DSC) tests revealed that paraffin/ H + -Pal composite PCM had a melting temperature of 54–56 °C and latent heat of 132.18 J g −1 . In addition, the composite PCMs were characterized by Scanning Electron Microscope (SEM), Brunauer, Emmett, and Teller (BET) and Fourier Transform Infrared Spectroscopy (FTIR). Good thermal stability was observed for composite PCMs by cycling test; we found that paraffin/H + -Pal composite PCM maintained ~95% of the initial latent heat after the cycling test. In conclusion, the impregnation of Pals with paraffin was a promising method for preparation of excellent PCM composites. [ABSTRACT FROM AUTHOR]

Double-shell alginate microcapsules containing paraffin phase change material (PCM) were prepared for latent heat storage by a method of repeated interfacial coacervation/crosslinking. The proposed process consisted of three main steps: (1) preparation of paraffin containing core particles by dripping an O/W emulsion of melted paraffin and aqueous sodium alginate into a calcium chloride ionic cross-linking solution, (2) encapsulation of the core particles into double alginate shell by ionic gelation/crosslinking by repeated interactions between the sodium alginate and calcium chloride solutions, and (3) consolidation of the capsule shells by contact heat treatment. The effects of process parameters such as the sodium alginate concentration, the calcium chloride concentration in certain stages of the process, and the contact time between the formed core particles and the surrounding alginate solution on the paraffin content and the mean diameter of capsules were studied by experimental design and statistical evaluations. The prepared PCM capsules had uniform sizes, core/shell structure, double-walled non-porous alginate coating, tunable void space inside the core, and suitably high paraffin content at properly selected process conditions, corresponding to 95.0 J/g melting and 91.7 J/g freezing latent heat capacity. Thermogravimetric analysis and repeated thermal cycling evidenced good thermal stability, and proper mechanical strength for leakage free microcapsules. [ABSTRACT FROM AUTHOR]

Paraffin is a common organic phase change material (PCM) that finds many applications in thermal energy storage (TES) systems. One common characteristic of organic PCMs is their low thermal conductivities. This – in turn – causes a slow thermal response when paraffin is used in high power applications. In this study, paraffin–nanomagnetite (Fe 3 O 4 ) composites (PNMC) were prepared by a dispersion technique to enhance their thermal properties. Nano magnetite prepared using the cost-effective sol–gel method was mixed into paraffin at two different mass fractions: 10% and 20%. Scanning electron microscope (SEM) was used to observe the morphologies of nanomagnetite and PNMCs during different stages of the composite production process. SEM analysis results showed that nanomagnetite particles of 40–75 nm in size were homogeneously distributed in the paraffin structure. The latent heat storage capacity of PNMC, measured by differential scanning calorimetry (DSC) at 1 °C/min, was found to be 8% higher than paraffin alone. Thermal conductivities and diffusivities of paraffin and PNMCs were determined by the “DICO” method. For 10% and 20% by weight PNMCs, the thermal conductivities were increased by 48% and 60%, respectively. These results clearly indicate that the addition of Fe 3 O 4 nanoparticles is an efficient and cost effective method to enhance the heat transfer properties of paraffin, when they are incorporated into latent heat storage systems. [ABSTRACT FROM AUTHOR]

The binary paraffin blends/opal composites as shape-stabilized phase changed materials were prepared by adsorbing binary paraffin blends into the natural porous opal. In this study, binary forms of three commercial paraffins (n-octadecane, paraffin wax and liquid paraffin) with different melting temperatures were compound together by the fusion method, and the optimum mixed proportions were determined through differential scanning calorimetry (DSC) analysis. Raw opal was thermally treated in order to improve the adsorption capacity of opal before using as the supporting material. The microstructure and chemical structure of the binary paraffin blends/opal composites were characterized by scanning electronic microscope (SEM) and Fourier transformation infrared (FT-IR) spectroscope. From the FT-IR analysis, there was no chemical interaction between binary paraffin blends and opal. The SEM results showed that the pore size of calcined opal among particles was improved after calcination, and the paraffin blends were well adsorbed and dispersed into the porous structure of the opal because of the capillary effect and physical surface tension forces. There was no leakage of the liquid paraffin from the composites even in the melting state. The thermal properties and thermal stability were investigated by DSC and a thermal cycling test, respectively. The DSC results showed that the phase-transition temperature and the latent heat of the PN2/calcined opal composite PCM were 24.91°C and 59.04±0.84J/g, respectively, which was suitable to be used as the indoor thermal energy storage building material. The thermal cycling test results indicated that the prepared sample was thermally reliable and chemically stable. [ABSTRACT FROM AUTHOR]

The COVID-19 pandemic has led to an increase in construction energy consumption and indoor occupancy; this, in turn, has increased the demand for energy efficiency. Thermal energy storage is an effective method for energy saving and improving efficiency. In this study, improved shape-stabilized phase change materials (SSPCMs) for enhancing the energy efficiency of buildings were manufactured and evaluated. These SSPCMs were prepared via the vacuum impregnation of n-octadecane into bentonite nanoclay. Bentonite exhibits a layered tetrahedral and octahedral crystal structure with Na+ cations (which feature high cation exchange capacity) in the interlayer space. The Na+ ion is a hydrophilic ion that affects the properties of the interlayer. However, paraffin-PCMs are hydrophobic and have poor compatibility with water. Therefore, hydrophobicity is induced in the organic nanoclay by using an organic modifier as the PCM container. Cloisite Na+, Cloisite 15, Cloisite 20, and Cloisite 93 were used to fabricate the SSPCMs. This study compares the amount of PCM impregnated depending on the compatibility of different PCMs between hydrophilic/hydrophobic nanoclays and also evaluates the thermal performance. The observed reduction in peak temperature and the time lag effect of the PCMs confirmed that the organically modified nanoclay and the PCM composites significantly improved the amount of PCM impregnated, thermal conductivity, and latent heat characteristics. The latent heat of the hydrophobic organic nanoclay was 209% higher than that of the SSPCM-based hydrophilic nanoclay. • Composites using paraffin PCM and nanoclay were fabricated and analyzed. • Hydrophobic nanoclay showed 124% higher PCM impregnation than hydrophilic nanoclay. • It was observed that PCM impregnation was affected by the microstructure. • SSPCMs showed up to 84% improved thermal conductivity than pure PCM. • The overall thermal performance in the SSPCM based hydrophobic nanoclay were high. [ABSTRACT FROM AUTHOR]

The thermal performance of a solar pond is affected by the amount of heat lost to the ground through the lower convective zone (LCZ) in which the heat is stored. Studies are focused on decreasing the heat losses, to maximize the energy stored and guarantee the stability of the thermohaline system over time. Phase change materials (PCMs) can help to achieve all these goals, since they work as thermal energy storage (TES), exploiting the latent heat absorbed during the solid-liquid phase change. This paper presents an experimental application of PCMs in the LCZ of a small solar pond. The paraffin wax was enclosed in aluminium cylinders which have been arranged on the bottom. The temperature of the solution in deep is monitored both with and without the PCM. The stability of the pond is analyzed through a laser shadowgraph technique, to visualize the effect of the thermal convection on the interfaces. Results show that the LCZ of the solar pond with PCM is around 3 °C colder than the reference case after a 6-h heating period. The shadowgraph analysis proves that the thermal convection in the reference case is stronger and damage the interface until break. The monitoring of the solar pond with PCM shows an improved stability. • A solar pond integrated with PCM has been designed and built. • After the heating period, the system with PCM results colder in the LCZ. • PCM stabilized the LCZ-NCZ interfaces, as proved with the shadowgraph technique. [ABSTRACT FROM AUTHOR]

In this work, a series of novel multi-energy driven composite phase change materials (PCMs) were fabricated with paraffin wax (PW) as PCM, poly(styrene-b-ethylene-co-butylene-b-styrene) (SEBS) as the thickening agent, and reduced graphene oxide aerogel (rGOA) as multi-energy capture agent and support material. When the mass fraction of SEBS is in the range of 5 wt%-15 wt%, the composite PCMs can be formed as form-stable PCMs (FSPCMs) by the physical reaction. The enthalpy value of PW/SEBS 5 /rGOA is measured as high as 226 J/g. The prepared FSPCMs show a good thermal reliability due to little reduction of enthalpy value after 200 accelerate cycles. And the prepared FSPCMs present a good thermal stability according to the thermogravimetric analysis. The thermal conductivity results show that rGOA slightly improves the thermal conductivity of the FSPCMs. Moreover, the prepared FSPCMs show excellent photo-thermal and electro-thermal conversion performance with the help of rGOA which can harvest the photons and electrons. As a result, the PW/SEBS/rGOA PCMs have great promise in areas such as solar/electrical energy collection, thermal energy storage, and thermal management. [Display omitted] • PW/SEBS/rGO aerogel keeps the shape stability at about 95 wt% PW. • The maximum melting enthalpy of Composite PCM is measured as 226.3J/g. • The enthalpy of Composite PCM only reduced by 3% after 200 thermal cycles. • Composite PCM can be driven by multi-energy to complete phase change process. [ABSTRACT FROM AUTHOR]

Abstract: Novel halogen-free flame retardant hybrid phase change composites were prepared by an in-situ sol–gel process, using paraffin as the thermal energy storage material and tri-(triethoxysilylpropyl) phosphamide as the sol–gel precursor. The structure of paraffin composites was characterized by Fourier transform infrared spectrum (FT-IR) and X-ray diffraction (XRD). The behaviors of thermal stability and thermal energy storage properties were investigated through thermogravimetric analysis (TGA) and differential scanning calorimetry (DSC). The char residue of composites was characterized by FT-IR, XRD and scanning electron microscope (SEM). The flame retardancy property of paraffin composites was investigated by pyrolysis combustion flow calorimetry (PCFC). Results showed that the paraffin composites had good thermal energy storage property as well as enhanced thermal stability and flame retardancy properties. [Copyright &y& Elsevier]

Abstract: A series of polyol acetal derivatives were synthesized through condensation reactions of aromatic aldehyde with polyols, including sorbitol, mannitol, xylitol, and pentaerythritol. They were examined as gelators in the formation of paraffin-based shape-stabilized phase change materials (PCMs), in which 1,3:2,4-di-(4-methyl) benzylidene sorbitol (MDBS) exhibited excellent thermal stability. Three-dimensional netted structural phase change materials were obtained by paraffin doped with different gelators, which were thermally stable so that no leakage of paraffin occurs even under higher temperature than the melting point of paraffin. It was found that PCMs doped with 3wt% expanded and exfoliated graphite (EG) exhibited better thermal conductivity, similar phase change temperature and heat storage density. [Copyright &y& Elsevier]

In this paper, the paraffin/sepiolite composites were fabricated as novel shape-stable phase change materials (SSPCMs) by vacuum impregnation for thermal energy storage. The structure-property relationships and comprehensive performance of sepiolite-based composite SSPCMs prepared with/without treatment of sepiolite from three mineral deposits were investigated. Compared with the natural sepiolite (SEP), the sepiolite after the purification and acidification treatment (TSEP) is a more suitable supporting carrier for paraffin wax. The prepared paraffin/TSEP composite SSPCM exhibits a significant promotion in absorption mass of paraffin and phase change latent heat. The maximum increase in latent heat of melt and crystallization is 78.32 % and 77.47 %. Simultaneously, the prepared sepiolite-based SSPCMs can reach up to 35.18 % paraffin loading. Its highest latent heat of melting and freezing is 60.12 J/g and 57.09 J/g, respectively, and the relative enthalpy efficiency is as high as 94.45 %. In addition, the sepiolite-based composite SSPCMs show good thermal stability and chemical stability according to the thermal cycling test. Moreover, it is demonstrated that sepiolite-based SSPCMs can slow down the spread of heat by absorbing heat energy and have reliable energy storage and temperature regulation performance. Therefore, the inexpensive and abundant sepiolite can be applied in phase change materials for waste heat recovery and temperature regulation. • Paraffin/sepiolite phase change material was prepared by vacuum impregnation. • Sepiolite from three mineral deposits was utilized as support material. • The latent enthalpy of the PCM was improved by acid activation of sepiolite. • The PCM exhibits good phase transition performance and thermal stability. [ABSTRACT FROM AUTHOR]

Xylitol with high latent heat of 243.28 kJ/kg and a significant supercooling degree has been considered to be a potential phase change material (PCM) for long-term thermal energy storage (TES). Xylitol can be kept in a supercooled or supersaturated metastable for a long time. In our study, it took 23 days and 30 min respectively that xylitol liquid and xylitol liquid adding 5 wt% ethanol crystallized completely at room temperature of 15 ± 5 °C. Unfortunately, the low thermal conductivity and leakage of xylitol restrict its thermal performance. In this paper, xylitol/expanded graphite (EG) composite PCMs with 5, 8, 10, 12 and 15 wt% EG content were prepared by an "impregnation and compression" two-step method. The results of SEM, XRD and FT-IR show that xylitol is well impregnated into the micropores of EG and has good chemical compatibility. The thermal performance test shows that the thermal conductivity of composite PCMs increases dramatically and the latent heat decreases with the increase of EG. The experimental results show that the latent heat of 10 wt% EG is 209.73 kJ/kg and 192.18 kJ/kg, respectively, during the charging and discharging process. The thermal conductivity of 10 wt% EG is 3.91 W/(m·K), as 9.29 times as xylitol. Besides, the crystallization of xylitol in EG and the mass loss of the composites have also been studied. The results show that 10 wt% EG composites crystallized completely after 16 days. These results prove that xylitol/EG composite PCMs have broad application prospects in long-term TES. ∙ A shape-stable xylitol/expanded graphite composite phase change material was prepared. ∙ The crystallization process of xylitol liquid and xylitol liquid adding 5 wt% ethanol at ambient temperature was studied. ∙ The thermal properties of shape-stable xylitol/expanded graphite composite phase change material were studied. ∙ The composite was characterized and the feasibility of its application in long-term thermal energy storage was preliminarily proved. [ABSTRACT FROM AUTHOR]

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. [Display omitted] • 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. [ABSTRACT FROM AUTHOR]

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/GA/CF composite PCM is prepared for solar energy conversion and storage. • Thermal conductivity of the composite PCM is more 9 times than that of paraffin. • The composite PCM performs excellent light-to-thermal energy conversion efficiency. • Leakage test establishes the form-stability of the composite PCM. [ABSTRACT FROM AUTHOR]

The current challenge for the application of organic phase change materials is to compromise the conflicting influence of high thermal conductivity matrix content on the heat storage performance and thermal conductivity of phase change composites. Herein, we prepared graphene aerogel (GA) and GA-based paraffin phase change composite (GAP) by the widely reported hydrothermal method and studied the application potential of GA in GAP. The underlying mechanism of paraffin latent heat enhancement caused by GA was discussed from the perspective of the crystallization and phase change process of paraffin. X-ray diffraction and differential scanning calorimetry results showed that as the GA content increased, the paraffin in GAP had an increased crystallinity and exhibited increased latent heat. Activation energy of paraffin's phase change process calculated according to Kissinger model was effectively reduced when GA content was greater than 7.3 wt%, implying a considerable increase in the thermal response rate of GAP. In addition, in order to improve the thermal conductivity enhancement efficiency of GA, thermal conductivity of GAP was predicted by finite element numerical simulation. A good agreement was observed between the experimental and numerical results and some practical suggestions were made for the experimental preparation process. Image 1 • Improvement of PCMs' latent heat caused by graphene aerogel (GA) is explained. • A numerical model is built to predict the thermal conductivity of GA based PCC. • Practical suggestions were made for the preparation process of GA based PCC. [ABSTRACT FROM AUTHOR]

Microencapsulated phase change materials (microPCMs) are not only important thermal energy storage medium but can also be applied in harvesting and storage of solar thermal energy by using solar absorbent materials as the shell. In this study, high energy storage polyurea (PUA) microPCMs for photothermal storage were fabricated from a Pickering emulsion consisting of bio-derived and sustainable regenerated chitin (RCh) from shrimp shells as the emulsifier. Graphene oxide (GO) was used as the photon captor and paraffin wax as the phase change material (PCM). The chemical, physical and thermal properties of the resulting microPCMs were studied. Using 0.1% w/w RCh Pickering emulsifier and 0.1% w/w GO to modify the microPCM, a 92.3% encapsulation efficiency was achieved. The microPCM at a core/shell ratio of 9:1 stored up to 234.7 J/g heat energy, was leak proof, and thermally reliable over 100 heating and cooling cycles with efficient photothermal conversion up to 76.03% conversion efficiency. Therefore, this cost-effective green process can be embraced for fabrication of high-energy storage and reliable functional microPCMs. Image 1 • GO-modified microPCMs with 92.3% paraffin wax were successfully fabricated via RCh stabilized Pickering emulsions. • Phase change enthalpy of the GO-modified microPCMs reached 234.7 J/g. • The GO-modified microPCM displayed high photothermal conversion efficiency up to 76.03%. • The GO-modified microPCMs have well-defined core-shell structure and high thermal stability and reliability. [ABSTRACT FROM AUTHOR]

The paraffin incorporation in device of glass envelope allows the thermal regulation, increasing the thermal comfort and energy efficiency of buildings. Addition of nanoparticles has an advanced application prospect in the field of solar energy collection and storage capacity of glass envelope systems filled with paraffin. The present study conducts an experimental and numerical investigation in order to study photothermal properties of the paraffin incorporated ZnO or CuO nanoparticles. An experimental and theoretical model is also established to analyze the effect of nanoparticles on the thermophysical and optical properties of nano-enhanced paraffin. The results show that due to the presence of the nanoparticles, the transmittance of nano-enhanced paraffin decreases. On the other hand, temperature increment results in a small rise in the transmittance of nano-enhanced paraffin. The results also indicate that the utilized nanoparticles exhibit a higher attenuation to light, and the scattering effect cannot be avoided, where the maximum scattering proportion is 6.3%. Improvements of 5.87 and 13.12% in thermal conductivity of nano-enhanced paraffin at the volume fraction of 5 × 10−4 vol% are obtained using ZnO and CuO nanoparticles, respectively. The evaluation of the photothermal performance based on the temperature variations shows that the CuO/paraffin can absorb more solar energy. The optimum photothermal performance can be satisfied by the nanoparticle volume fraction ranging from 5 × 10−4 to 1.5 × 10−3 vol%. • Photothermal properties of the paraffin incorporating ZnO or CuO nanoparticles were investigated. • Effects of temperature and volume fraction on photothermal properties were studied. • Optimum nanofluid concentration for glazed structure was determined. • Optimum range of nanoparticle concentration was 5 × 10−4 ~ 1.5 × 10−3 vol%. [ABSTRACT FROM AUTHOR]

When solar radiation reaches its peak value during the midday, buildings' external walls absorb the highest amount of heats and result in dramatic spikes in cooling load and energy consumption. To flatten the energy peak, promote energy efficiency, and preserve thermal comfort, this study developed a novel foamed thermal insulation cement block with extraordinary heat storage capacity. To prepare the proposed foamed cement block, a paraffin/expanded graphite composite phase change heat storage material with a phase transition temperature of 41.9 °C and an enthalpy value of 207.8 J/g was used to load paraffin into expanded graphite in a water bath at 44 °C. After mixing the paraffin/expanded graphite composite phase change material (PCM) with cement, foams were added, stirred and poured into the mold to make a novel foaming cement thermal insulation block. Due to its porous structure, the foamed cement has lightweight as well as high heat preservation capacity. To investigate the characteristics of the proposed material, this investigated its physical structure, thermal conductivity, and heat energy storage performance when the material mass fractions of PCM are 10%, 15%, 20%, 25% and 30%, and regular (pure) cement blocks. The experimental results show that there is no chemical reaction during material preparation. In addition, composite materials' PCM mass fraction and their thermal storage capacity increase simultaneously. The comprehensive analysis shows that foamed cement blocks with 30% PCM contents have the best thermal energy storage performance and can maintain the lowest average indoor temperature. Therefore, the proposed foamed cement blocks can be applied to building outer surfaces and sandwiched middle enclosures to develop energy efficiency insulation walls. [ABSTRACT FROM AUTHOR]

The latent heat thermal storage using Phase Change Materials (PCMs) is one of the essential aspects to be addressed for rapid expansion of utilisation of Renewable Energy sources and waste heat. The major disadvantage of PCMs, deployed in such thermal storage systems, is their low thermal conductivity and, in some cases, low latent heat. Paraffin wax/expanded graphite (PW/EG) composite PCMs with the EG mass fraction of 2%, 4%, and 6% were prepared by absorption of molten organic material into the EG structure. FireCarb TEG-315 and FireCarb TEG-160 were used as EG of A- and B-type, respectively, and PW 53–57 °C was deployed as the PCM in this study. Polarizing optical microscope, scanning electron microscopes and Fourier transform infrared spectroscopy were used to characterize the structure of composite PCMs. Thermal properties of pure Paraffin and produced composite materials were determined using a differential scanning calorimeter and thermal conductivity analyser. One of originalities of this work is that the statistical method of assessment of heterogeneity in composite PCMs was proposed for the first time with the use of Matlab software. This method was deployed for the quantitative assessment of uniformity of the EG distribution in composite PCMs structure. The novelty of obtained results is in detection of intermolecular interaction between B-type EG and PW. This interaction further enhances thermo-physical properties of the PW/EG composites. In contrast to pure PW and PW/A-type EG composite PCMs, in which the solid-solid transition and solid-liquid phase change are observed, PW/B-type EG compositions exhibit only the solid-liquid phase change. The heat storage capacity in both types of compositions was found to be almost identical. Despite of prolonged sample's ultrasonic treatment, the structure of PCM compositions was found to be far from being homogeneous. However, the thermal conductivity of compositions with 6 wt % of EG was determined to be 0.977 W/m°C for the PCM with A-type EG and 1.263 W/m°C for the PCM with B-type EG in comparison with the value of 0.258 W/m°C for pure PW. These values of the thermal conductivity correspond to the enhancement ratios of 3.79 and 4.9, respectively. If uniformity in the EG distribution in PW can be improved, then the thermal conductivity of composite PCMs would also considerably increase. Findings of this work are being used for designing a cost efficient solar thermal storage system with the reduced charging/discharging times as a part of an international project funded by EC. Image 1 • Paraffin wax/expanded graphite (EG) compositions with EG mass fractions of 2%, 4%, and 6% were analysed. • FTIR analysis indicates that B-type of two (A- and B-) types of tested expanded graphite interacts with paraffin. • The compositions with A-type EG exhibit solid-solid transition and solid-liquid phase change. • The compositions with B-type EG exhibit the solid-liquid only phase change. • Thermal conductivity enhancement ratio is 3.79 and 4.9 for PCM compositions with A- and B-type 6wt% EG, respectively. [ABSTRACT FROM AUTHOR]