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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]

Paraffin wax-graphite foam (P-wax/G-foam) composite was fabricated by using low cost small scale process aiming to produce a stable phase change material with enhanced thermal transport. Its thermophysical properties such as thermal diffusivity, specific heat and thermal conductivity were examined as a function of temperature. The thermal conductivity of the P-wax/G-foam composite in both solid (2.6 W/m K) and liquid (1.8 W/m K) phases is by a factor of ≈ 11 (980%) higher than that of pristine paraffin wax in solid (0.24 W/m K) and by a factor of ≈ 16 (1530%) in liquid (0.11 W/m K) phases, respectively. This is due to both the G-foam morphology and graphitic content, allowing a rapid heat transfer to the P-wax. The thermal conductivity behaviour of the composite is also discussed in term of a theoretical model in which the G-foam is described by a 3D interpenetrating matrix for the P-wax. The model shows the self-consistency of all the measured data. The obtained results demonstrated that the stable P-wax/G-foam composite is a promising material for various thermal energy storage applications such as building and vehicle heating and cooling, solar thermal harvesting, and thermal management of electrochemical energy storage and electronic devices. [ABSTRACT FROM AUTHOR]

This study was to explore the hydrophilic surfactant/Brij L4 mixture scheme for fabrication of highly stable paraffinic nano-emulsions melting at 55 °C by the low-energy phase inversion temperature method that has not been reported previously. Two commercial paraffin waxes were chosen as the PCM agents, Sasolwax 5203 with a higher onset T m of 54 °C in the initial development and OP44E with a lower onset T m of 44 °C for further assessment and fabrication. At accelerated stability testing by thermal approach, the rate of droplet size increase was mainly attributed to Ostwald ripening destabilization mechanism, and decreased by about 5 times for every 5 °C drop. Only a moderate increase in the particle size was observed, from 47.7 nm to 120.6 nm, over a period of 9 months at 45 °C. The exciting results in the accelerated stability evaluation greatly outperformed than those previous results only obtained from the regular stability testing including room temperature storage and heating-cooling cycles in a container, and hence this experimental result can offer a more meaningful reference in terms of service life of nano-emulsions flowing in pipelines. With the optimized surfactant mixtures, a series of highly stable paraffinic nano-emulsions in the working temperature range of 30–50 °C were successfully formulated as promising coolants in the active thermal management system. • High melting point paraffin PCM nano-emulsions/suspensions were fabricated by phase inversion temperature method. • The PCM nano-emulsions remained stable over 9 months at 45 °C up to 120.6 nm particle size. • Ostwald ripening was identified as the major destabilization mechanism at 45 °C or higher. • A novel polymetric nucleating agent has been found effective for supercooling reduction. • The excellent stability and relatively high latent heat were desirable for thermal management. [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]

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]

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]

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]

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]

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]