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The issue of leakage in phase change materials (PCMs) severely restricts their use as thermal storage materials. In this study, waste coffee grounds-based biochar (WCG) was developed by carbonization and chemical modification as a support material for composite PCMs. The WCG/Paraffin wax (PW) composite PCMs were prepared using the melt impregnation method. The pore structure of alkali-modified biochar (OH-WCG) underwent significant development, and the surface area and total pore volume increased to 21.9 and 12 times that of unmodified biochar, respectively. Leak-free composite PCMs (OH-WCG-40) can be obtained when using OH-WCG as the support material at a biochar addition of 40 wt%. The characterization results indicated the physicochemical compatibility of the biochar in the composite PCMs with the PCMs. Differential scanning calorimetry (DSC) showed the phase transition temperature and the melting enthalpy of OH-WCG-40 were 46.28 °C and 97.69 J/g, respectively. The thermal conductivity of OH-WCG-40 was enhanced by 43% compared to pure PW. After 300 cycles, the composite PCMs exhibited nearly no change in mass and demonstrated good cycling stability. Therefore, alkali-modified biochar is a good support material for composite PCMs which can be used as a good thermoregulation material for temperature regulation of buildings and recycling of solar energy. [Display omitted] • The surface area of the NaOH-biochar is 21.9 times that of the untreated biochar. • The thermal conductivity of the composite PCM is 43% higher than that of paraffin. • The composite PCMs show no mass change after 300 cycles and had good stability. • Only 40 wt% of modified biochar is required to ensure no leakage of the paraffin. [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]

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]

Solar still is an economical device for purify brackish water, however its yield is low. Therefore, present work aims to increase the water output of tubular solar still (TSS) by introducing closed mild steel tubes filled with paraffin wax (as phase change material, PCM) and candle soot derived carbon nanoparticles (CSNP, 0.3 wt%) as dispersant for the first time. Experiments were conducted with three TSS – one with conventional TSS without any PCM, and the other two with only PCM and 0.3 wt % CSNP-PCM to augment the water production. There was an increase in thermal conductivity of 40.59% with 0.3 wt % CSNP over the base PCM. TGA analysis showed excellent thermal durability of 0.3 wt % CSNP-PCM and final degradation temperature was 314.26 °C. In addition, the dispersion of CSNP in PCM also altered the phase change temperatures with meager deviation from base case. The thermal performance analysis of TSS show that full day cumulative fresh water generation by conventional TSS was 3.04 kg/m2, whereas utilizing the PCM and 0.3% CSNP-PCM in tube inside TSS augmented the water generation by 42.4% and 87.82% respectively, than the baseline case. In addition, the modified TSS with PCM and 0.3 wt % CSNP-PCM exhibited higher energy efficiency of 59.26% and 109.94% respectively, than the base line case. The generated fresh water cost was only 0.014 $/kg for TSS with 0.3% CSNP-PCM. It is concluded that conductive CSNP doped PCM with excellent thermal performance significantly enhanced the water output of the SS and could be widely applied in other design of still for better thermal performance. • A new class of nano-enhanced PCM is prepared by functionalized candle soot particle. • TC of base PCM improved by 40.59% using 0.3 wt% CSNP. • TSS with base PCM improved water yield by 42.4% than baseline case. • TSS with CSNP-PCM improved water yield by 87.82% than baseline case. • Freshwater cost/kg using CSNP-PCM based still was 0.014 $. [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: Composite phase change materials (PCM) for latent heat thermal energy storage were made by mixing two different kinds of exfoliated graphite nanoplatelets (xGnP-1 and xGnP-15) into paraffin wax. Direct casting and two roll milling were used to prepare samples. The investigation on the thermal and electrical conductivity of nanocomposites with these two nanoplatelets was performed. Higher thermal conductivity of composite PCM can be achieved with nanofillers of larger aspect ratio, better orientation and lower interface density. The thermal physical properties of the nanocomposites were investigated by differential scanning calorimetry and thermal gravimetric analysis. It was found that the latent heat of the nanocomposites was not adversely affected by the presence of xGnP nanoplatelets and the thermal stability improved. [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]

Abstract: A novel phase change emulsion (PCE) was prepared and its latent heat was measured by DSC. To analyze its feasibility in heat transportation through a piping system, an experimental system was built. The pressure drop of the PCE for turbulent flow was measured and the effects of such facts as the paraffin concentration and flow velocity were discussed. According to the pressure characteristic and latent heat of the PCE, the pumping power consumption rates of PCE to water under the same pipe diameter and a given heat transportation quantity can be obtained. The results show that mass flow rate and pumping power consumption of the PCE decrease greatly compared with water. For example, the decrease can be up to about 73% at V=0.6m/s (20 and 30wt%). Furthermore, the results show that PCE of 20wt% can obtain almost the same pumping power consumption savings as PCE of 30wt% in a certain flow velocity range. Finally, the applications of the PCE in the area of waste heat usage, electrical boiler and solar energy usage were commented. [ABSTRACT FROM AUTHOR]

Abstract: Melting of the binary mixture system of tetradecane and hexadecane in Differential Scanning Calorimetry (DSC) cell has been investigated experimentally and numerically. Different concentrations of tetradecane–hexadecane paraffin mixture were studied. It is found that the phase change process of the binary mixture takes place over a temperature range and the temperature range depends on both the heating rate and the mixture composition. The proposed study shows also that for the same concentration of tetradecane and using various heating rates, we will be able to predict the solidus and liquidus temperature of the binary mixture from DSC curves. [ABSTRACT FROM AUTHOR]

Abstract: Oleochemical carbonates are biobased materials that were readily prepared through a carbonate interchange reaction between renewable C10–C18 fatty alcohols and dimethyl or diethyl carbonate in the presence of a catalyst. These carbonates have various commercial uses in cosmetic, fuel additive, and lubricant applications. Oleochemical carbonates have not been examined for their applicability as phase change materials (PCM). The latent heats of melting and freezing for a series of symmetrical oleochemical carbonates ranging from 21-37 carbon atoms were evaluated to develop a fundamental understanding of the solid–liquid transitions for utilization in thermal energy storage (TES) applications. The phase transitions and associated thermal properties were determined by differential scanning calorimetry (DSC) and thermal gravimetric analysis (TGA). Decyl, dodecyl, tetradecyl, hexadecyl, and octadecyl carbonates had peak melting and freezing points of −2.2, 19.3, 33.7, 44.9, and 51.6 and −6.3, 14.3, 28.7, 40.3, and 46.9°C, respectively. In general, these carbonates exhibited sharp phase transitions and good latent heat properties. The latent heats of melting and freezing for decyl, dodecyl, tetradecyl, hexadecyl, and octadecyl carbonates were 144, 200, 227, 219, and 223 and 146, 199, 229, 215, and 215J/g, respectively. These carbonates represent novel renewable-based PCM chemicals that compliment fatty acids, fatty alcohols, and their fatty acid esters while providing a potentially valuable biobased alternative to paraffin wax and salt hydrate PCM currently dominating the PCM market. [Copyright &y& Elsevier]

Abstract: Mesophase pitch based graphite foams (GFs) with different thermal properties and pore-size were used to increase the thermal diffusivity of phase change material (PCM), paraffin wax, for latent heat thermal energy storage application. To predict the performance of the Paraffin-GFs as a thermal energy storage system, their structure, thermal diffusivity and latent heat were characterized. Results indicated that thermal diffusivity of the Paraffin-GF can be enhanced 190, 270, 500, and 570 times as compared with that of pure paraffin wax. Latent heat of Paraffin-GF systems increased with the increasing of the mass ratio of the paraffin wax in the composite. Moreover, pore-size and thickness of ligaments of the foam played a key role in improving the thermal diffusivity and the storage capacity of the Paraffin-GF system: small pore-size (less paraffin wax were filled) and thicker ligament in GF resulted in a higher thermal diffusivity; large pore-size (less paraffin wax were filled) and thinner ligament in GF resulted in a larger latent heat. [Copyright &y& Elsevier]

Abstract: The shape-stabilized phase change material (PCM) based on paraffin and high-density polyethylene (HDPE) is used as a storage media in thermal energy storage. This storage media can retain the shape even when paraffin is in the liquid state, and no paraffin is observed, but it has a low thermal conductivity and is easily flammable, which limits the utility area in thermal energy storage. The motivation of this study was to improve thermal conductivity and flame retardant property of shape-stabilized PCM. A flame retardant shape-stabilized PCM made of paraffin, HDPE, expanded graphite (EG) and intumescent flame retardant (IFR) was presented. To characterize the resulting product, scanning electron microscopy (SEM), differential scanning calorimetry (DSC), hot disk thermal constants analyzer, attenuated total reflectance fourier transform infrared (ATR-FTIR) and cone calorimeter measurements were employed to investigate their microcosmic shapes, crystalline behaviors and thermal properties. The SEM results indicated that paraffin and EG were well dispersed in the network formed by HDPE. The thermal conductivity and the flame retardant efficiency of IFR could be improved by adding EG. The possible flame retardant mechanism for paraffin/HDPE/IFR/EG as a shape-stabilized PCM was proposed. [Copyright &y& Elsevier]

Abstract: Six novel polymer-based form-stable composite phase change materials (PCMs), which comprise micro-encapsulated paraffin (MEP) as latent heat storage medium and high-density polyethylene (HDPE)/wood flour compound as supporting material, were prepared by blending and compression molding method for potential latent heat thermal energy storage (LHTES) applications. Micro-mist graphite (MMG) was added to improve thermal conductivities. The scanning electron microscope (SEM) images revealed that the form-stable PCMs have homogeneous constitution and most of MEP particles in them were undamaged. Both the shell of MEP and the matrix prevent molten paraffin from leakage. Therefore, the composite PCMs are described as form-stable PCMs. The differential scanning calorimeter (DSC) results showed that the melting and freezing temperatures as well as latent heats of the prepared form-stable PCMs are suitable for potential LHTES applications. Thermal cycling test indicated the form-stable PCMs have good thermal stability although it was subjected to 100 melt–freeze cycles. The thermal conductivity of the form-stable PCM was increased by 17.7% by adding 8.8wt% MMG. The results of mechanical property test indicated that the addition of MMG has no negative influence on the mechanical properties of form-stable composite PCMs. Taking one with another, these novel form-stable PCMs have the potential for LHTES applications in terms of their proper phase change temperatures, improved thermal conductivities, outstanding leak tightness of molten paraffin and good mechanical properties. [Copyright &y& Elsevier]

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]

Pentaerythritol (PE), pentaglycerine (PG), and neopentylglycol (NPG) are non-ionic plastic crystal with high potential for latent heat thermal energy storage (TES) in solar heating applications. These molecules undergo reversible solid phase transitions with unusually large enthalpy of transition (110 J/g - 300 J/g) in the temperature range from 44 °C to 185 °C. To further enhance their heat storage capacity while lowering their price and preserving the advantage of solid phase transitions, a new class of shape-stabilized phase change materials (SSPCMs) in which a polyalcohol with adjustable solid phase transition properties (NPG/PG or PE/PG mixture) supports a cheaper and with higher latent heat solid-liquid PCM (paraffin wax) is proposed in this work. Combined with properly chosen paraffin waxes, NPG/PG mixtures allow tailoring the working temperature of corresponding SSPCMs between 24 °C and 81 °C, whereas PE/PG mixtures allow SSPCMs with phase change adjusted within 81 °C–190 °C temperature range. Produced SSPCMs were thoroughly characterized and their efficiency in terms of heat storage capacity and delivered power upon heat discharge were evaluated. The results achieved show proper anti-leakage effect due to good wettability between paraffins and polyalcohols and inner microstructure of SSPCMs promoting capillarity. In addition, volumetric latent heat storage capacity has been proven to be enhanced up to 45% compared to pure polyalcohols without detrimental effect in discharging power. • TES capacity of plastic crystal based composites was enhanced by adding paraffins. • Transition temperature was tailored by means of binary plastic crystal systems. • SSPCMs microstructure was related to their high paraffin retention capacity. • SSPCMs have potential to enhance TES systems compactness up to 2–3 times. • Capex reduction up to 40% for TES systems could be achieved with the proposed SSPCMs. [ABSTRACT FROM AUTHOR]