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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]

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]

The efficient use of solar energy can alleviate the energy shortage, so the photothermal conversion materials have been a hot spot for research. Improved thermal conductivity and higher enthalpy/flexibility can expand the practical application scenarios of photothermal conversion materials. Therefore, a flexible composite material for photothermal conversion is developed in this paper. Among them, carbon nanotube (MWCNT) is the photothermal conversion material, melamine foam (MF) is the supporting skeleton of the composite, and paraffin wax (PW) is the phase change material. According to the results, MWCNT/MF/PW has a high latent enthalpy of 240 J/g. The thermal conductivity of MWCNT/MF/PW (0.129 W/m·K) was improved by 95.5% compared to MF/PW (0.066 W/m·K). MWCNT/MF/PW have a high photo-thermal conversion efficiency (85.16%). Hence, MWCNT/MF/PW exhibit excellent shape recovery due to the response to light and heat. In addition, the outdoor light absorption experiment of the composite PCM water tank indicates that MWCNT/MF/PW as a shell wrapped water tank shows good light absorption and heat preservation effect, which is not available for general photothermal conversion materials. • The MWCNT, MF and PW composite phase change materials were prepared. • The light/heat shape recovery properties of CPCMs with MWCNT was investigated. • The light-absorbing property (85.16%) of composites was studied. • The insulating effect of MWCNT/MF/PW on tank temperature was investigated. [ABSTRACT FROM AUTHOR]

Flexible phase change materials (FPCM) with PA/SEBS/POE were prepared by melt blending method. The microstructure, thermal properties and cycle stability were characterized. The results show that a suitable SEBS and POE ratio can not only provide flexibility, prevent the leakage of paraffin, but also enhance the thermal conductivity. Then expanded graphite (EG) was added to prepare FPCM-EG and to further improve the performance. The experimental results show that the thermal conductivity and cycle stability increase with EG content increasing. When EG content is 15 %, the thermal conductivity is 3.572 W·m−1·K−1, which is 15.5 times of paraffin. And the leakage rate is less than 0.03 % after 20 cycles. After that, the FPCM-EG is used for thermal management of photovoltaic cell-thermoelectric (PV-TE) coupling system under simulated electric heating. The effects of EG content, heating flux and heat dissipation condition on temperature control and thermoelectric conversion performance were explored. The experimental results show that the FPCM-EG can significantly reduce heating surface temperature, improve power output and relieve the impact of heating flux variation. When EG content increases from 10 % to 15 %, the maximum heating surface temperature is reduced from 40.1 °C to 37.8 °C, and the power output is improved by 33.3 %. • Flexible PCMs with high thermal conductivity and latent heat were prepared. • The thermal conductivity is 3.572 W m−1·K−1, latent heat is 134.84 kJ/kg. • After 20 cycles, the leakage rate is less than 0.03 %. • The prepared FPCMs was used for thermal management of PV-TE system. • The surface temperature is reduced and power output is improved significantly. [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 A series of paraffin/expanded graphite (EG) composites with various mass fraction were prepared. The microscopic geometry configuration, thermal conductivity and saturation sorption capacity of EG were obtained. In this paper, a method based on the experiments of EG pores was proposed for constructing geometric models. The geometric model constructed by this method has obvious anisotropy and has been employed in the calculation. Furthermore, the numerical results of thermal conductivity indicate anisotropy of a single-pore. Moreover, it had been observed by experiment that the anisotropy is weakened and transformed to isotropy in the process of combining geometric models with a large number of single pores. The final numerical results agree well with the experiments, which validates the precision and reliability of the proposed model. The increasement of thermal conductivity is also calculated and discussed during the phase change process of paraffin/EG. Highlights • A method of EG pores was proposed for constructing geometric models which has obvious anisotropy. • The SEM micrograph and saturation sorption capacity are employed to build the geometric models of EG pores. • Effective thermal conductivity during non-phase change process and the phase change process was calculated. • The numerical results agree well with the experiments. [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]

In this study, a novel microencapsulated phase change material, paraffin@Cu-Cu 2 O, was prepared by a hydrothermal method. The diameters of the microcapsules were 600–900 nm. The micro morphology, chemical compositions, phase change properties, and thermal stability of the products were characterized. It was calculated that the encapsulation efficiency of the microencapsulated paraffin@Cu-Cu 2 O composite was 62.79%. The melting temperature and freezing temperature of products were close to those of paraffin, but the products had better thermal stability and higher thermal conductivity because of the metal shell materials. Additionally, we compared the paraffin@Cu-Cu 2 O slurry with paraffin emulsion, and we found that the slurry had better light absorbing properties, thermal conductivity, and photo-thermal conversion performance. The developed material is a promising candidate for application in direct absorption solar collector systems. [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]

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]

Phase change materials (PCMs) which possess high thermal conductivity and excellent mechanical property have been prepared in this work according to a dual-level packaging technology. Porous graphite foam with bulk density of 0.25 g/cm 3 which is derived from worm-like expanded graphite is infiltrated by liquid paraffin. The as-infiltrated graphite foam is ball milled into small spheres with diameter of 1–3 mm. Then the spheres are sprayed with a pre-polymer composed of epoxy resin and its curing agent. These spheres are finally hot-pressing at 30 °C for 6 h under 1 MPa to obtain the PCMs. Correspondingly, porous graphite works as the first-level packaging (core) while epoxy resin film acts as the second-level packaging (shell) of paraffin. The thermal conductivity of PCM composites reach to 4.98 W/m K. Meanwhile, the compressive strength of PCM composites keeps a very stable value of 19.50 MPa when temperature increases from 25 to 90 °C. The excellent shape-stability of PCM is attributed to its dual-level packaging structure in which porous graphite prevents the leaking of liquid paraffin from the core and epoxy resin provides a strong polymer network at high temperature. [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]

Radiative cooling promises an effective strategy against global warming by sending waste heat to the deep universe in a passive manner. However, the mismatch between cooling supply and demand can significantly compromise the efficacy of spectrally-static radiative cooling devices in cold weather. Therefore, the present work introduced paraffin wax as the phase change material (PCM) to develop a spectrally self-switchable cover (SSC) for flexible radiative cooling. The transmittance of the paraffin wax at different temperatures, thicknesses and phases was characterized. In the UV-VIS-NIR band, the transmittance of the paraffin wax was over 90% in the liquid phase but below 5% in the solid phase. In the "atmospheric window" band, the transmission of the paraffin wax in the liquid phase was also much higher than that in the solid phase with a maximum difference of 41.1%. The optical constants of various paraffin waxes in solid and liquid phases were calculated according to the two-thickness inversion method. The average error of transmittance between the calculated and measured values was only 1.8% and 4% for the 0.19–1.1 μm and 8–13 μm bands, respectively. Moreover, the microstructure analysis of the solid-state paraffin wax revealed that the size of paraffin grains was around 10 μm with interlocking and irregular grain boundaries. The integrated multilayered-like structure resulted in a significant transmittance reduction of the solid-state paraffin wax. In the end, self-switchable PE-PCM-PE (polyethylene-phase change material-polyethylene) covers were prepared and spectrally characterized. The paraffin-based cover provided a new and low-cost candidate solution for achieving dynamic radiative cooling. [Display omitted] • The paraffin transmittance is significantly different between liquid phase and solid phase. • The multilayer-like structure of paraffin crystal grains reduces the transmittance of solid-state paraffin. • The optical constants of paraffin are considerably different in liquid and solid phases by the two-thickness inversion method. • The polyethylene-phase change material -polyethylene shows potential as a spectrally self-switchable cover. [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]

Highly paraffin/butyl stearate-loaded phase change microcapsules were synthesized by cosolvent-free interfacial polymerization using low-toxicity dicyclohexylmethane-4, 4′-diisocyanate as the shell material. The formation of the microcapsules and their distribution in the epoxy were studied by means of optical microscope and scanning electron microscopy, respectively. The chemical composition of microcapsules was confirmed through Fourier transform infrared spectrometer. And the phase change properties, thermal stability and cyclic thermal stability of microcapsules and their thermal insulation properties and thermal response behavior in the epoxy were investigated through differential scanning calorimetry, thermogravimetric analysis, leakage prevention test, thermal conductivity test and temperature response experiment, respectively. The synthesized spherical microcapsules have distinct core-shell structure with an average diameter of 220.6 μm. The microcapsules achieve an encapsulation rate of 78.5%, with the melting enthalpy and the crystallization enthalpy being 148.5 J/g and 159.2 J/g, respectively. They not only exhibit good thermal stability and cyclic thermal stability, but also can disperse in the epoxy uniformly and combine with the epoxy tightly. In addition, compared with the pure epoxy, the epoxy containing 15 wt% microcapsules experiences a 10.1% decreases in thermal conductivity and a 55.4% increase in delayed time of temperature rise/fall, showing an excellent temperature regulation ability. [Display omitted] • HMDI was employed as the shell material due to low toxicity. • The microcapsules with core-shell structure achieve an encapsulation rate of 78.5%. • High enthalpy microcapsules exhibit 99.2% of heat-storage efficiency. • The microcapsules have high thermal stability, reliability and applicability. • 15 wt% microcapsules increase the time delay by 55.4% for temperature rise/fall. [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 paper, graphite nanoparticles have been dispersed into a paraffin/water emulsion with the purpose of improving the thermal conductivity and photothermal conversion performance of the emulsion. The melting enthalpy and apparent specific heat of 20 wt% paraffin/water emulsion is 39.2 J g − 1 and 9.105 J g −1 K −1 and its melting and freezing temperatures are very close to those of paraffin. Moreover, the 300 heating–cooling cycles test indicates that the paraffin/water emulsions containing 0.1 wt% graphite exhibits good thermal reliability. The viscosities of all samples are lower than 0.0750 Pa s, meeting the transportablilty requirements in pump systems for applications. In addition, the thermal conductivity of the emulsion containing 0.1 wt% graphite increases by 20.0% as compared to the base fluid and its receiver efficiency is higher than 86.0% as the temperature ranges from room temperature to 80 °C. As a result, the paraffin/water emulsion containing graphite with high energy storage capacity, enhanced thermal conductivity and excellent photo-thermal performance, good thermal reliability and good fluidity shows great potential for use as advanced heat transfer fluid (HTF) in the low temperature applications of direct absorption solar collector (DASCs). [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]

Flame retardance of shape stabilized phase change materials (SSPCM) based on paraffin, high density polyethylene (HDPE) and styrene–butadiene–styrene copolymer (SBS) was investigated. The effects of organomontmorillonite (OMMT), expanded graphite (EG) and crosslinking of the polymer matrix were evaluated by means of horizontal burning test, thermogravimetric analysis (TGA) and cone calorimeter. The results showed that the addition of EG and OMMT increased the burning time greatly. The treatment temperature of EG also played an important role owing to the different pore sizes and expansion ratios. When the polymer matrix was crosslinked by tert-butyl hydroperoxide (TBHP), the burning time was further prolonged. TGA results indicated that the vaporization and thermo-oxidation temperature increased and the decomposition of the polymer matrix was hindered in flame retardant SSPCM. The cone calorimeter test demonstrated that the peak heat release rates (PHRR) of flame retardant SSPCM decreased by up to 72.7%, and the formation of CO 2 and CO decreased significantly. The horizontal burning tests implied that the best flame retardant performance was achieved in SSPCM containing OMMT/EG/TBHP which has the longest burning time and large amount of char residue. The flame retardant mechanism was also discussed. [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]

The utilization of aerogel with the 3D network structure is regarded as an important method to construct phase change materials (PCMs). In this work, a series of novel paraffin-based composite PCMs were fabricated with boron nitrid@chitosan aerogel (BNCA) as skeleton materials by a freeze-drying and impregnation method. XRD, SEM, TGA, Hot Disk, DSC and FT-IR were used to character the samples and thermal cycles were employed to measure the shape stability. The results revealed that paraffin wax (PW) had been successful and effectively embedded into the prepared BNCA with a porous structure. Moreover, the morphologies of BNCA/PW composite remained stable after 100 times thermal cycles. In addition, the thermal conductivity of BNCA/PW composite was notably high as 1.14 W/(m·K), which was 4.07 times higher than PW (0.28 W/(m·K)). Simultaneously, the phase temperatures of BNCA/PW composite containing 41 wt% skeleton were 50.5 and 52.9 °C, and its latent heats were 118.4 and 114.9 J/g, respectively. The BNCA/PW composite showed an excellent chemical compatibility between PW and BNCA, and presented broad application prospects in energy storage of electronic systems. [Display omitted] • Synthesis of porous boron nitride@chitosan aerogel by freeze-drying method. • Synthesis of BNCA/PW composite PCMs by vacuum impregnation. • The mass fraction of paraffin can be controlled, without leakage. • Good thermal conductivity and thermal reliability of BNCA/PW composite PCMs. • After 100 thermal cycles, the thermal properties and shape stability of the composite remain good. [ABSTRACT FROM AUTHOR]

In the present work, a thermo-economic performance of the modified hemispherical solar still (MHSS) was studied and compared to traditional hemispherical solar still (THSS). The modulations accounted for two additives, namely: paraffin wax as phase change materials (PCM), and copper oxide (CuO) nanoparticles. Three cases of MHSS were investigated and compared to THSS: (0.3 wt%) CuO nanomaterials were immersed in the basin water, implementing PCM container below the basin, and combining PCM container below the basin plus mixing CuO nanoparticles in the basin water. The basin water depth in all stills was set at 1.0 cm in all cases. Moreover, the thermo-economic performance of the four studied cases was compared and evaluated by determining the freshwater productivity, the daily energy efficiency, and the freshwater cost. Experiments have been carried out on the proposed hemispherical distillers under hot climatic conditions of El-Oued (33°27′N, 7°11′E), Algeria. The results show that the single utilization of CuO/water nanofluid and pure PCM improved productivity by 60.41% and 29.17%, respectively, compared to THSS. While, the dual usage of PCM and CuO/water nanofluid further enhanced the productivity by up to 80.20%, relative to THSS. Moreover, the daily energy efficiencies of the hemispherical distillers under the different studied cases (THSS, MHSS/PCM, MHSS/CuO-water nanofluid, and MHSS/PCM + CuO-water nanofluid) were found to be 35.52%, 45.45%, 56.46%, and 63.61%), respectively. The economic feasibility of these modifications presented that the dual usage of PCM and CuO/water nanofluid is more effective as it reduces the cost of freshwater production by 75% compared to THSS. In the third distiller (Modified hemispherical solar still with 0.3 wt% CuO/water nanofluid (MHSS-CuO/water NF)), the modified was done by adding (0.3 wt%) copper oxide (CuO) nanomaterials to the basin water, to improve the thermal properties of nanofluid and increase the intensity of the absorbed solar energy. In the fourth distiller (Modified hemispherical solar still with paraffin wax as phase change materials and 0.3 wt% CuO/water nanofluid (MHSS-PCM + CuO/water NF)), it was designed and constructed a circular galvanized steel container 1 mm thick, 340 mm diameter, and edge height 40 mm, coated with the black pained. This container was placed inside the wooden basin of the hemispherical solar still. A gap of 20 mm thickness was maintained between the container and the wooden basin on the bottom side and sidewall. 2.0 kg of paraffin wax as phase change materials was placed in the gap between the container and the wooden basin, to store the solar energy in the periods of higher solar rays and recovery it in the periods of low solar rays and after sunset. Moreover, in this modification copper oxide (CuO) nanomaterials were also added to the basin seawater with a concentration of 0.3 wt%, to improve the thermal properties of saline water and increase the intensity of absorbed solar energy, and improve the rates of heat transfer. • Dual usage of PCM and CuO nanofluid has great influence on hemispherical distiller performance. • Thermo-economic performance of the modified hemispherical solar still was studied. • Dual usage of PCM and CuO/water nanofluid enhanced the productivity by 80.20%. • Dual usage of PCM and CuO/water nanofluid reduces the freshwater cost by 90%. • Daily efficiency of MHSS with dual usage of PCM and CuO/water nanofluid reached 63.61%. [ABSTRACT FROM AUTHOR]

Phase change materials (PCMs) are able to melt and solidify at a certain temperature with a high heat of fusion. These promising functional materials for acting as energy as latent heat storage units have one major problem, leakage of the PCMs when molten. Polymer/phase change material (PCM) blends were investigated as a possible solution of PCM leakage. In this research, paraffin was used as the PCM and three types polyethylene (PE) were used as the structural matrix. To investigate the morphology of PE/ paraffin blends and evaluate the influence on blend behavior, paraffin was blended with either high density polyethylene (HDPE), low density polyethylene (LDPE), or linear low density polyethylene (LLDPE) using a parallel co-rotating twin screw extruder. Chloroform extraction was utilized to estimate the maximum amount of paraffin able to be released by the PE network at equilibrium. Scanning electron microscope (SEM) images of chloroform-extracted samples were collected to investigate the blend structure. Thermal transition temperatures and crystallinity of components in the blends were characterized by differential scanning calorimetry (DSC) and polarized optical microscopy (POM) was used to investigate crystal perfection changes of the polyethylenes before and after blending with paraffin. Paraffin leakage of the blends was investigated by accelerated degradation test in an oven at 60 °C. The leakage behavior was analyzed by Korsmeyer–Peppas equation to determine the underlying mechanisms. Chloroform extraction indicated that almost all the paraffin would leak out from the blends in the long run. A co-continuous structure of the blends was evident from the chloroform extraction and subsequent SEM images. While this co-continuous structure controlled leakage behavior, it had little influence on paraffin thermal transition temperatures and crystallinity based on DSC study. In contrast, PE crystal perfection decreased with paraffin level as evident in POM images. This structure resulted in leakage of paraffin in all formulations. [ABSTRACT FROM AUTHOR]

This paper deals with the preparation, characterization, thermal properties and thermal reliability of form-stable composite phase change materials (PCMs), composed of n-octadecane, expanded vermiculite, and perlite for thermal energy storage. The composite PCMs were prepared by incorporation of liquid n-octadecane within the expanded vermiculite (eVMT) and expanded perlite (ePLT), using a vacuum impregnation method. The microstructures of n-octadecane/expanded vermiculite and pearlite were characterized by scanning electron microscopy (SEM). Analysis of Fourier transform infrared spectroscopy (FT-IR) of the prepared composite PCMs showed good compatibility between n-octadecane and the expanded vermiculite and pearlite. The thermal conductivities of composites were reduced, based on the TCi results. Differential scanning calorimetry (DSC) analysis indicated that the n-octadecane/eVMT and n-odtadecane/ePLT composites maintained their large latent heat capacity and original phase change temperatures, due to large surface area and good dispersion of the eVMT and ePLT. TGA analysis revealed that the prepared composite PCMs had good thermal durability in the working temperature ranges. Therefore, n-octadecane based composite PCMs can be considered as suitable candidates for latent heat thermal energy storage, with high thermal performance. [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]

Expanded graphite (EG) powder as a typical porous material has high thermal conductivity and large surface area that are often used to enhance the thermal conductivity of phase change materials (PCMs). Ten composites of paraffin/EG powder with various weight fractions were elaborated by high pressure compression. Their microstructure configuration and thermal properties were characterized with Scanning Electron Microscopy (SEM), Thermal Constant Analyzer. The saturation sorption capacity of EG under compression was experimentally determined. The thermal conductivity of the paraffin/EG composite is greatly enhanced by 41 times in maximum as compared to pure paraffin. Based on the experimental quantification, we propose a novel two-level scale model from micro-scale to macro-scale to compute the thermal conductivity of the composite. The numerical results agree well with the experimental data that validate the precision and reliability of the proposed model. Furthermore, the results reveal that both keeping porous EG structure at original morphology and increasing the saturated sorption capacity of paraffin in EG could eventually improve the heat transfer capacity of the composites. In addition, the proposed model would require more experimental validation based on the composites with different materials in future work. [ABSTRACT FROM AUTHOR]

In this study, expanded graphite (EG)/paraffin (PA)/silica (SiO 2) composite phase change materials (PCM), with good thermal conductivity and impermeability, were fabricated for potential applications in solar energy. The EG-PA was first prepared by vacuum adsorption and then encapsulated by SiO 2 through solid-phase wet grinding in the presence of sodium silicate. Our results show that the EG-PA-SiO 2 composite have optimal properties when the mass ratio of raw material is PA: sodium silicate: H 2 O = 1:9:2:8. The latent heat of melting of the EG-PA-SiO 2 composite prepared at this mass ratio is 106.2 J/g. The core material loss ratio, after washing with petroleum ether, is 4.79%. The thermal conductivity is 2.053 W/m·K, which is 8.5 times higher than that of pure paraffin wax, and the melt permeability is 9.35% after 120 min at 60 °C. Under simulated sunlight, the time required for the composite material to change from 30 °C to 65 °C is reduced by 70.78% compared to PA and the heat absorption and release times are nearly unchanged under multiple cycles. These results indicate that the material has a stable photothermal conversion efficiency. [Display omitted] • Expanded graphite, paraffin and silica composites were made by solid-phase wet grinding method. • Silica encapsulated the composite, reducing leakage. • Composites showed improved thermal conductivity and impermeability. • The composite has stable photothermal conversion, and there is no obvious leaking sign. [ABSTRACT FROM AUTHOR]

Abstract: Paraffin is a common phase-change-material (PCM) exploited in many thermal and solar energy storage applications. Its relatively large latent heat with a stable phase change, nontoxicity and noncorrosivity are the main reasons. Paraffin׳s low thermal conductivity may become a drawback for high power applications. In this study, the effect of adding nanomaterials to enhance paraffin׳s thermal performance is investigated. Nanomagnetite (Fe3O4) particles were prepared by sol–gel method for this investigation. Once characterization of nanomagnetite was done, it was added at 1%, 5%, 10%, and 15% ratios to paraffin (melting range: 46–48°C) to obtain a paraffin nanocomposite. Thermal characterization with Differential Scanning Calorimeter (DSC) shows that the latent heat storage capacity of paraffin has been increased for 10% nanomagnetite composite, while the melting temperature range remained the same. [Copyright &y& Elsevier]

Paraffin/carbon foam composite phase change material (PCM) was prepared with vacuum assistance in the present study, and the structure and thermo-physical properties of the composite PCM were studied. The impregnation ratios were studied comparatively for the cases with and without vacuum assistance, and the results showed that the impregnation process with vacuum assistance was superior to that without vacuum assistance. Micro-Computed Tomography (Micro-CT) technique was used to investigate the inner structural characteristics of the composite PCM. The gray value analysis was conducted, and two dimensional (2D) cross-section images and three dimensional (3D) renderings were constructed accordingly. Both the surface porosity and bulk porosity were obtained from the image analysis. Compared with pure paraffin, the thermal conductivity of the composite PCM was enhanced, e.g., the composite PCM with vacuum assistance was about three times larger than that of pure paraffin. The measured thermal conductivity showed agreement with the theoretical models. The phase change behaviors of the composite PCM were investigated with a differential scanning calorimeter (DSC). The presence of the porous carbon foam affected the phase change behavior of pure paraffin in that the extrapolated onset melting/freezing temperatures shifted from 52.10/60.56°C for pure paraffin to 51.73/61.16°C. The thermal effusivity of the composite PCM was larger than that of pure paraffin, which was apparently advantageous for latent thermal energy storage (LTES). [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]

In this work, a novel sort of form-stable phase change materials (FSPCMs) which possesses simultaneously the shape memory function was designed and prepared. The FSPCMs consist of paraffin with melting point of approximately 53°C as a latent heat storage material and olefin block copolymer (OBC) as a supporting material. With mass percentage of paraffin up to 40wt%, the FSPCMs exhibit good shape stability until temperature approaches 90°C as shown by visual photographs, and this result is confirmed by dynamic mechanical analysis. At the same time, composites with 40wt% paraffin also maintain the excellent mechanical property of OBC and exhibit large elongation at break as well as similar tensile stress, insuring excellent tenacity and deformation ability. The results of shape memory testing demonstrate that the composites possess good shape memory property, with nearly complete shape fixing and recovery. Compared with other reported FSPCMs, this material can be both temperature-controlled and temperature-sensitive, and may show advantages in some advanced applications such as intelligent textile. The diversity of paraffin endows the composites with flexibility of design for applications with wide range of temperatures. Considering the inexpensive sources and easy processing, this work may open up opportunities to produce difunctional FSPCMs in the industrial field. [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]

State-of-the-art multifunctional form-stable phase change materials (FSPCMs) with photo-thermal and electro-thermal dual responses have shown great application potential in sustainable energy utilization. The preparation of photo- and electric-responsive FSPCMs by mixing nano-functional materials such as carbon nanotubes or graphene with phase change materials (PCMs) systems has been extensively studied. Herein, photo and electric dual-responsive nanocapsules (IPW@CLPS@PPy) were designed and constructed by employing industrial paraffin wax (IPW) as the core PCMs, crosslinked polystyrene (CLPS) as the supporting inlayer via miniemulsion polymerization, and polypyrrole (PPy) as the dual functional outlayer via further fast-oxidative chemical polymerization. The resultant IPW@CLPS@PPy exhibits good shape stability, ideal phase change enthalpy (114.2 J/g), excellent thermal stability, and cyclability. Furthermore, the PPy functional outlayer endows IPW@CLPS@PPy nanocapsules with excellent solar light absorption capacity and electrical conductivity, resulting in ideal photo-thermal conversion efficiency (88.4%) and electro-thermal conversion efficiency (80.1%). Consequently, the synthesized IPW@CLPS@PPy has broad application prospects in photo-thermal and electro-thermal conversion/storage fields. This study will not only provide new ideas for the design and synthesis of nanostructured multifunctional FSPCMs but also open up routes towards the development of FSPCMs for energy harvesting, conversion, and storage fields. Herein, IPW was encapsulated by CLPS inlayer via a simple free-emulsifier miniemulsion polymerization, and the nanocapsules were further covered by PPy outlayer via a fast-oxidative chemical polymerization, thus the photo/electric dual-responsive FSPCM (IPW@CLPS@PPy) was prepared. The resultant IPW@CLPS@PPy features excellent shape stability, ideal thermal performance, and photo/electro-thermal conversion ability as well as stability, which promises wide application in the photo and electro-thermal conversion/storage. This research may provide more information for the construction of nanostructured multifunctional FSPCMs and open a new window of energy conversion/storage in different charging modes. • Industrial paraffin wax, cross-linked polystyrene, and polypyrrole formed an integrated composite. • The composite had excellent shape stability, thermal stability, and cyclability. • The composite exhibited high photo/electro-thermal energy conversion efficiency. • The composite possessed ideal functional stability. [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: 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]