Search

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]

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]

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]

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]

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]

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]

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]

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

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

In this work, the latent heat enhanced polyethylene glycol (PEG)/cellulose aerogel (CA)-dopamine form-stable composite phase change materials (PCD fs-CPCMs) were constructed by facile in-situ fabrication method based on the freeze casting. Under the simultaneous synergistic effect of CA and dopamine modification, the PCD fs-CPCMs achieved ultra-high encapsulation capacity of ~95 wt% and latent heat of ~194.3 J/g. Furtherly, compared with before the dopamine modification, the latent heat of PCD fs-CPCMs was increased by ~18.9%, and the difference between theoretical and experimental value was significantly reduced, indicating that the modification effectively promoted phase change behavior and improved heat storage characteristic of PEG. The ultra-high encapsulation capacity was mainly attributed to the lightweight and porous characteristic of CA and the effective entanglement and combination of PEG molecular chain. The increased latent heat was mainly ascribed to the construction of new combination approaches among PEG, CA and dopamine, resulting in the weakening of hydrogen bond effect (before and after modification: O-H⋯O > O-H⋯N or N-H⋯O) so that the confinement effect of surfaces was weakened and modified surface-induced phase change behavior was promoted. Moreover, the PCD fs-CPCMs exhibited excellent chemical compatibility, reasonable heat storage and release rates, and acceptable thermal reliability and stability. [Display omitted] • PCD fs-CPCMs with large encapsulation capacity and latent heat were fabricated in-situ based on freeze casting. • Dopamine modification showed positive effect on increasing latent heat (~18.9%) of PCD fs-CPCMs. • New constructed combination approaches weakened hydrogen bond effect so that phase change behavior was promoted. [ABSTRACT FROM AUTHOR]

Sustainable utilization of solar energy with a more compact solar heating system is a significant research. In this study, a novel form-stable composite phase change material (PCM) was prepared for application in solar energy conversion and storage. Paraffin as PCM was encapsulated in the matrix consist of copper foam (CF) loaded with graphene aerogel (GA) in order to improve thermal conductivity, prevent leakage and convert solar energy to thermal energy. The melting temperature and the latent heat of the composite PCMs were determined to estimate thermal storage performance. The thermal conductivities of composite PCMs measured by transient plane heat source method were more than 9 times higher than that of paraffin. Besides, the composite PCMs showed uniform temperature distribution and perfect shape-stabilization when heated. Furthermore, the composite PCMs exhibited an excellent light-to-thermal energy conversion efficiency (up to 97%) in the experiment of light-to-thermal energy conversion, which demonstrated the potential of the composite PCM for solar energy conversion and storage. • Paraffin/GA/CF composite PCM is prepared for solar energy conversion and storage. • Thermal conductivity of the composite PCM is more 9 times than that of paraffin. • The composite PCM performs excellent light-to-thermal energy conversion efficiency. • Leakage test establishes the form-stability of the composite PCM. [ABSTRACT FROM AUTHOR]