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A promising solution for challenges in thermal energy storage (TES) and its management is the use of phase change materials (PCMs). The ionic liquids (ILs) offer a unique properties that make them proper candidates for a number of energy related applications. The IL based PCMs are an important category of novel materials that significantly contribute to the efficient use and conservation of solar energy and wasted heat. This work presents a new family of ionic liquids (ILs) 2-hydroxyethylammonium, bis (2-hydroxyethyl) ammonium, and tris (2-hydroxyethyl) ammonium laurate as PCMs for the first time operating in the temperature range of 50–150 °C, and offer a safe and inexpensive capacity. The latent heat of fusion values were 147.13, 131.95 and 113.54 kJ·kg−1 for the [HEA]Lau, [DHEA]Lau and [THEA]Lau, respectively. Also, the thermal stability was obtained to be 99% for the [HEA]Lau. Finally, the thermal-to-electric energy conversion is performed using a homemade electronic data gathering and processing instrument with a PCMs (synthesized ILs) container cell and a commercial thermoelectric generator (TEG) device to record the real-time generated electric energy. The recorded output voltage (open circuit case) of TEG device versus time was measured that demonstrated that after turning off the thermal energy source, the proposed system provides the electric energy for a while (more than 2 h). [ABSTRACT FROM AUTHOR]

The thermal stability of a shape stable composite phase change material (SSCPCM) has been investigated using a thermogravimetric analyser. X-ray diffraction, Scanning Electron Microscope, Fourier transform infrared, Brunauer–Emmett–Teller, and Differential Scanning Calorimeter analysis are used to characterize the PCM and SSCPCM. The activation energy of PCM and SSCPCM is estimated using multiple value model-free methods, namely, Friedman, Kissinger–Akahira–Sunose, Starink, Ozawa–Flynn–Wall, and Vyazovkin. The SSCPCM exhibits 4.96, 6.95, 6.76, 8.02, and 4% higher activation energy than the pure PCM as determined by the Friedman, KAS, OFW, Vyazovkin, and Starink methods, respectively. The degradation temperature of SSCPCM improved by 12.86, 7.85, and 10.41%, compared to PCM, at a heating rate of 5,10, and 15 °C min−1, respectively. ANFIS modeling is used in this study to predict the degradation of PCM and SSCPCM. The mass loss (%) of PCM and SSCPCM samples is predicted by considering the input parameters as PCM type, temperature, and heating rate of the sample. It is found that the combination of a generalized bell-shaped input and a linear output membership function is best suitable for predicting the mass loss. The developed hybrid ANFIS model very well predicts the experimental mass loss of the SSCPCM with a coefficient of determination (R2) of 0.99. [ABSTRACT FROM AUTHOR]

Increasing frequency of extreme weather conditions due to global climate change is threatening citrus orchards. Young seedlings and some citrus varieties like lemons are especially susceptible to frost damage. Many orchards have installed expensive wind machines that use electricity to ward off cold air. When the temperature falls below −4 °C, even for several hours in a year, frost damage can kill citrus trees, thus causing serious economic loses. In this experimental study, we developed new phase change material (PCM) packages for passive solar protection of citrus trees from frost damage. Aqueous solutions of ethanol, ethylene glycol, and propylene glycol were evaluated as three PCMs due to their suitable chemical properties and abundance. Flexible packaging for the PCMs that can be easily applied to citrus trees were developed, and thermal protection performance of developed packages were tested on citrus seedlings. Supercooling of PCMs was seen as a problem during the tests, which was solved by adding a nucleating agent based on silver iodide developed in our laboratory. Results show that the ethanol containing PCM provided the longest thermal protection and succeeded in keeping seedling temperatures within the target interval for 10.5 h, while ethylene glycol and propylene glycol containing PCM packages provided 6.9 and 6.0 h of protection, respectively. [ABSTRACT FROM AUTHOR]

In this study, cetyl alcohol (CA) (CH3(CH2)15OH), which is a fatty alcohol, was microencapsulated by the coacervation method with the titanium-n-butoxide (TNBO). Firstly, at the beginning of the experimental process by thermal and structural analyses, the CA was determined as having a phase change material (PCM) property, then it was microencapsulated with TNBO. In the second step of the study, barite, boron nitride, marble powder, and fly ash were separately added to prepare a series of microencapsulated with TNBO. Lastly, structural and thermal properties of both microencapsulated PCM and composite supported microencapsulated PCMs (CSM-PCMs) have been analyzed by FTIR, DSC, TGA, and SEM devices. Surprisingly, the SEM image of CA turned from torn fiber structure into a particulate structure in the form of groundnut in the SEM images of the microencapsulated CA-Ti taken at different magnifications. After the thermal cycling test, the same analyses have been made before and after thermal cycling to compare the structural and thermal properties. It has been investigated whether to use as insulation material. It is concluded that the most suitable samples, compared with structural and thermal properties, are barite (B) and boron nitride (BN) with microencapsulated samples. The obtained results are shown that CATi-B and CATi-BN are CSM-PCMs and could be suggested in terms of thermal energy storage in buildings as promising PCMs. [ABSTRACT FROM AUTHOR]

Herein, free cooling an application of thermal energy storage is investigated through theoretical observations of air being cooled after passing over encapsulated phase change material (PCM). The impact of encapsulation geometry changes from circular to; rectangular, square, and elliptical shapes is studied for the PCM solidification and melting cycles. The study is performed for sp24, sp26, and sp29 PCM types with and without the inclusion of CuO and Al2O3 nanoparticles (NPs). A transient mathematical model for heat transfer behavior of airflow over the encapsulation is constructed and solved using Ansys 20.2 software. It is found that the rectangular-shaped PCM encapsulation with CuO nano-enhanced PCM has the shortest complete melting (~ 1–2 h) and complete solidification times (~ 3–9.3 h). Nanoparticle enhancement improves the rate of melting by a maximum of 11.56% with Al2O3 NPs and by 6.12% with CuO NPs at an inlet airflow temperature of 313 K. A maximum outlet air-temperature drop of ~ 3.1 K occurs in the cylindrical geometry with CuO nano-enhancement and the highest Nusselt number is obtained at similar conditions. From this study it is recommended to use either sp24 or sp26 PCMs mixed with nano-alumina and encapsulated within rectangular containers for free cooling applications. [ABSTRACT FROM AUTHOR]

In this research, the effects of activated carbon from corncob (ACC) biomass as the supporting material were investigated on leakage problem and thermal properties of palmitic acid (PA) as a phase change material (PCM) for thermal energy storage, using the impregnation method. The leakage test demonstrated that the addition of ACC significantly reduced the leakage of PA. Furthermore, it was evident from ATR-FTIR spectra and XRD results that PA and ACC did not undergo any chemical reactions, and the crystal structure of PA was not changed, while the ACC was amorphous. According to the SEM result, ACC had a porous structure, and its increase in PA caused a larger pore volume and a higher specific surface area, which could prevent the leakage of PA. The thermal stability of the composites was measured by TGA. The results revealed that the addition of ACC slightly accelerated the pyrolysis of PA, improved the thermal conductivity of PA, and had enough thermal stability below 150 °C to be suitable for building and solar thermal energy storage applications. DSC analysis of the form-stable PCM showed a melting temperature of 61.25 °C and a melting latent heat of 81.57 J g−1, and demonstrated high thermal reliability after 10 cycles, indicating excellent energy storage capacity. The BET test revealed that the ACC with 1364.70 m2 g−1 have a great potential to use for supporting material, and the composites were mesoporous, which prevented the leakage of PA. [ABSTRACT FROM AUTHOR]

Solar energy is the most plentiful renewable energy source that has the capability to keep up with the growing demand. When the sun's energy is not available, thermal energy storage (TES) using phase change material (PCM) is a promising technique for storage and utilization. However, PCM's low thermal conductivity may limit its use. The use of nanomaterials to enhance the thermal conductivity is one of the prominent solutions to overcome this issue. This research work reports that graphene nanoparticles (0.1%, 0.3%, 0.5%, 0.7% and 1% mass) enhanced paraffin wax (PW) to improve the thermophysical properties and transmittance capability. Thermogravimetric analyzer (TGA), differential scanning calorimeter (DSC), Fourier transform infrared spectroscopy (FTIR) and ultra-violet visible spectroscope (UV–VIS) were used for the characterization of the base PCM and nano-enhanced phase change materials (NePCM) composites. A significant improvement of 110% in thermal conductivity was obtained at 0.7% mass ratio compared to base PW without compromising the prepared composites' latent heat storage (LHS) capacity. TGA and FTIR outcomes demonstrated excellent thermal and chemical stability, respectively. To check the thermal reliability of composite, the PW and nanocomposite were subjected to repeated thermal cycling. The outcome evidence that the NePCM composite had consistent thermal energy storage properties even after repeated thermal cycles. The composite's light transmission was drastically lowered by 56.34% (PW/Gr-0.5) compared to base PW, resulting in PW/Gr composite has better thermal reliability in relation to thermal conductivity and LHS than base PCM, which can be used specifically in photovoltaic thermal systems and TES. [ABSTRACT FROM AUTHOR]

Over the years, incredible evolution has been framed in developing particle-induced discrete simulation techniques over conventional continuum approaches. In particular, the lattice Boltzmann method (LBM) originated from a flexible and robust computational tool for scientific research and various practical applications. LBM is based on a mesoscopic approach that acts as a bridge between the microscale and macroscale, offering distinct features in the accuracy of simulations and numerical efficiency. LBM has been successfully employed over a broad aspect of disciplines, encompassing biomedicine, geothermal energy, flow physics, materials, chemistry, medical treatment, storage of energy, and several engineering disciplines. Meanwhile, phase change materials (PCMs) are extensively utilized in thermal energy storage (TES) systems as they can absorb and release heat throughout the phase change process. Moreover, phase change heat transfer (HT) has a substantial occurrence in industrial and domestic activities. It is expected to enhance the thermal transport rate between HT fluid and PCMs for the confinement of a larger amount of heat. This current work aims to provide a comprehensive review of LBM for thermo-fluids concentrating on thermal flows and PCM. It also enlightens a brief insight into the LBM formulation of heat transfer for PCMs under various external force conditions and the implementation of boundary conditions for PCMs. In addition, it also introduces the study and examination of the existing TES systems comprising PCMs for various applications. [ABSTRACT FROM AUTHOR]

This research demonstrates the performance of a novel parabolic trough collector (PTC) that uses a naturally circulated open loop, and it is evaluated experimentally for several classes of solar radiation data. A concentric absorber tube packed with phase change material (PCM) is used in the development of an indoor PTC system. A comparative study has been performed for both bare and PCM-based receiver tubes for various classes of solar radiation data. According to the findings, the overall thermal efficiency of the naturally circulated PTC system in bare receiver tubes is 0.66, 0.57, 0.63, 0.64, 0.66, and 0.63, respectively, at classes 2, 3, 5, 6, 8, 9, and 10. Meanwhile, the overall thermal efficiency of PCM-based receiver tubes is 0.70, 0.62, 0.69, 0.65, 0.68, and 0.66, respectively. However, the instantaneous thermal efficiency of the developed system at various classes of solar radiation can be predicted by using different machine learning (ML) models. These models include linear regression (LR), polynomial regression (PR), decision tree (DT), random forest (RF), artificial neural network (ANN), KNN regression, and Gaussian process regression (GPR). Among all of these, the GPR model is showing higher prediction performance (i.e. RMSE = 0.0049, R2 = 0.9977) than that of the remaining developed ML models. [ABSTRACT FROM AUTHOR]

The development of a new composite phase change material (PCM) was accomplished by using n-eicosane, which was belonging to the paraffins. For this goal, hexagonal boron nitride (h-BN)-loaded macroporous foams were synthesized by emulsion-templating method. The resulting foams were used as supporting materials in the preparation of n-eicosane-based composite PCMs that have improved thermal conduction property. The h-BN was synthesized as additive with the aim of thermal conductivity enhancement, and the porous supporting materials were obtained by polymerization of high internal phase emulsions (HIPEs) at various loadings of h-BN nano-fillers (0, 1, 5 and 9 mass/%). The h-BN, h-BN-loaded macroporous polyHIPE foams (MPFs) and composite PCMs were fully characterized by SEM, BET, FT-IR, TG and DSC analysis techniques. Furthermore, leak-proof and phase-change properties of composite PCMs were tested in addition to investigation of thermal behavior with a thermal performance test. The highest thermal energy storage (TES) capacity among the produced n-eicosane-based h-BN-loaded MPFs was belonging to 1 mass/% h-BN-loaded composite PCM having 79 J g−1 latent heat of melting and 38.79 °C melting temperature; the composite was also comprised of the supporting matrix with highest specific surface area. Based on the results, thermally conduction enhanced n-eicosane-based composite PCMs are promising materials for thermal management applications, such as electronic package and electronics cooling, with thanks to high latent heats (range between 72.2 and 79 J g−1) and convenient phase transition temperature as well as anti-leakage property. [ABSTRACT FROM AUTHOR]

The most common type of thermal energy storage material is phase change material (PCM). Because of their low thermal conductivity values and the liquid leaks caused by the transition phase from the solid to the liquid state, these materials have limited applications. To make these materials applicable in a variety of applications, their stabilization within a composite material must be improved. Lauric acid is a saturated fatty acid organic PCM with high latent heat, good chemical and thermal stability, and little supercooling and pollution. To address the leakage issue, expanded organophilic clay treated with cationic surfactant (CTAB) and lauric acid graft-modified cellulose nanofibers were added. In order to increase thermal insulation and lower energy consumption, composite materials based on cement, organophilic clay, and modified cellulose nanofibers were created in this study. These materials are used as shape-stable materials in the building industry. The thermal conductivity of the PCM composite samples increases in direct proportion to the percentages of organophilic clay added, according to research on the thermal behavior of the materials created. The findings indicate that the S5 sample has a thermal conductivity of the order of 0.115 (W m−1 K−1) and that the reduction in thermal conductivity reached 60%. This allows for the best thermal insulation performance due to the prepared material's stability heat, making the material promising for thermal energy storage. The results of the (DSC) thermal properties revealed that the fusion temperature and latent heat of the composite materials were 21.56 °C and 88.5 J g−1, respectively, and supercooling degrees for the nanofiber cellulose–lauric acid composite decreased to 13.99 °C compared to 20.28 °C for pure lauric acid. The FTIR and XRD techniques confirmed the production of the organophilic clay. The addition of clay to the nanofiber cellulose–lauric acid composite material solves the leakage impacts with the phase change material. [ABSTRACT FROM AUTHOR]

In this study, microcapsules based on Cu2O containing different phase change materials (PCM) were prepared and characterized. The elemental, structural and electronic properties of the Cu2O-based microcapsules were characterized using several techniques such as X-ray diffraction, X-ray photoelectron spectroscopy, scanning and transmission electron microscopy and Fourier-transform infrared spectroscopy. In addition, the thermal properties of the microcapsules prepared were characterized in order to analyse their possible application as a thermal energy storage medium. Heating/cooling cycles using a differential scanning calorimetry technique were performed, and the phase change temperature and enthalpy were estimated. We observed good stability after the cycles. Furthermore, the encapsulation efficiency was estimated from melting and crystallization enthalpy values, reaching a value of 14.8% for the paraffin wax-based microcapsules. Finally, isobaric specific heat was measured to evaluate the storage capability of the encapsulated PCMs with regard to pure Cu2O to evaluate their possible application as a thermal storage system. An increase of around 140% was found in the isobaric specific heat for the microcapsules based on paraffin wax with regard to pure Cu2O. [ABSTRACT FROM AUTHOR]

A thermal energy storage system combined with renewable energy sources or waste heat recovery will increase the dispatchability of the energy system. It also helps to reduce the gap between supply and demand. Among available techniques, latent heat thermal energy storage systems have been an attractive area of research. Selecting a phase change and construction material is vital in designing any storage system. In the present study, corrosion characterization was performed for erythritol used in the experimental prototype. The use of erythritol to develop a storage system requires understanding its corrosion behavior with storage container material and piping system to ensure the safety of construction and enhance the system's life. Corrosion rates were determined in stainless steel and mild steel sample by gravimetric tests, measuring the mass loss after 2000 h of immersion at 140 °C in two different test conditions. Simultaneously, surface morphology and corrosion products were analyzed by scanning electron microscopy (SEM) and energy-dispersive X-ray scanning (EDX). The experimental result confirms that stainless steel shows better corrosion resistance than mild steel for selected phase change material. SEM and EDX analysis shows no significant changes in the structure after 2000 h of immersion. Corrosion rates for open and closed crucible stainless steel sample have been observed at 0.003 mm y−1 and 0.004 mm y−1, respectively, whereas mild steel sample was more affected by PCM in both the open and closed crucible tests, giving 0.0221 mm y−1 and 0.0392 mm y−1. The study shows that further research is required in different operating conditions. [ABSTRACT FROM AUTHOR]

Mesoporous silica nanocomposites are a promising class of shape-stabilized phase change materials with high heat of fusion. We report the first study on the possibility of using FDU-12 mesoporous silica, which contains cubic ordered mesopores, as matrix for stearic acid and bismuth. Shape-stabilized nanocomposites which exhibit no macroscopic segregation of the liquid phase upon phase transition due to intercapillary forces, were obtained at 70% mass fatty acid or 50% mass metal loading. The matrix and PCMs were characterized by X-ray diffraction, infrared spectroscopy, thermogravimetric analyses and differential scanning calorimetry coupled with optical microscopy. The shape-stabilized PCM containing stearic acid exhibits a heat of fusion of 100 J g−1 and two distinct melting/freezing transitions, which correspond to interparticle and nanoconfined acid phases. The bismuth containing sample has a reversible transition enthalpy of 21.9 J g−1 and a melting point decreased by 1.6 °C with respect to bulk. The metal PCM is confined in the interparticle space, as confirmed by electron microscopy analyses. Both samples have good thermal reliability, retaining their heat of fusion values after 50 heating–cooling cycles. FDU-12 is a promising matrix for obtaining both organic and inorganic shape-stabilized phase change materials. [ABSTRACT FROM AUTHOR]

Thermoregulating composites were produced by using a thermoregulating slurry (NPCS) containing nanoencapsulated phase change material (NPCM) from poly(styrene-co-divinylbenzene) as shell and the commercial paraffin Rubitherm®RT27 as core material. These composites were synthesized by using the constitutive water of the slurry as setting water and changing the NPCM/Hemihydrate (NPCM/Hem) mass ratio within 0.0–0.41. It was found that nanoparticles were uniformly dispersed into the gypsum, and the gypsum crystal morphology was tuned by the addition of the slurry. Attending to the thermal properties, these materials can work either as insulating or thermal energy storage materials, decreasing the thermal conductivity up to ~ 50%, whereas the thermal energy storage (TES) capacity is enlarged in a ~ 140%, respect to the pure gypsum, when the maximum NPCM/Hem mass ratio was used. This composite had a latent heat of 30.2 J g−1 and a heat capacity of equivalent 3.5 J g−1 K−1. Composites from a NPCM/Hem mass ratio up to 0.15 satisfied European mechanical standard EN 13,279–1 for gypsum binders and gypsum plasters and all of them, presented a bulk density higher than 0.60 g cm−3. The addition of a 41% in mass of nanocapsules allowed to save 13.5 kWh m−3 and, reducing the CO2 emissions up to 3.4 kg of CO2 per operating cycle. The use of this new material would lead to significant energy and economic savings, as well as a considerable reduction in the emission of polluting gases into the atmosphere. [ABSTRACT FROM AUTHOR]

Water crisis has been emerged as major environmental issues at global level, which involves lack of cost-effective and efficient treatment facilities of wastewater and scarcity of drinking water. Commercially available technologies such as RO plants are too expensive to be used in rural areas or remote areas that lack of reliable power supply. Therefore, application of solar energy for water purification such as solar still is gaining much interest due to their efficient utilization for residential and commercial application for the treatment of saline as well as industrial wastewater. Presently, research work for the efficient design with productivity enhancement of the solar still is very much popular and focused area of work. This review article provides the technological advancements in different designs of solar still (active and passive) with the productivity of water. The assessment of thermal energy storage materials and the use of nanofluids for the energy and productivity enhancement for better utilization of solar still are discussed. Another aspect of this review article deals with the utilization of wastewater (industrial and non-portable) in solar still and their treatment applicability. It can be concluded from the present review article that the use of phase change materials and nanomaterials improves the heat transfer rate and productivity of solar still and makes it very effective for industrial use. [ABSTRACT FROM AUTHOR]

We investigated the impact of thermally expanded graphite (ExG) on thermal conductivity and charging/discharging time for pristine pentadecane (PD), a potential phase change material for low-temperature thermal energy storage applications. The expanded graphite is prepared using a high-temperature (~ 950 ℃) thermal shock on chemically treated natural graphite flakes and is vacuum impregnated in pentadecane. Four different 5, 10, 15, and 20 mass% expanded graphite and pentadecane (PD-ExG) composite samples are considered for intensive studies of their thermophysical properties using differential scanning calorimeter (DSC), temperature history (T-history), and transient plane source measurements. DSC measurements showed the reduction in latent heat of fusion of pentadecane with increased mass% of ExG, but the melting temperature remained nearly unaffected. Further, thermal conductivity of pentadecane-expanded graphite composites enhanced from ~ 0.18 W m−1 K−1 (for pristine pentadecane) to 1.1 W m−1 K−1, 2.6 W m−1 K−1, 4.7 W m−1 K−1, and 7.1 W m−1 K−1 for 5, 10, 15, and 20 mass% ExG composite samples, respectively. The discharge time for these PD-ExG composites reduced about 42.7 to 67.81% as compared to pristine PD sample. PD-ExG composite with 10% or more ExG also showed the shape stability of PD-ExG composites and thus reduced leakage of PD in liquid state. Thus, PD-ExG form stable phase change material composite with enhanced thermal conductivity and enhanced charge/discharge rate, making it a suitable PCM for low-temperature thermal energy storage system such as space cooling. [ABSTRACT FROM AUTHOR]

In this study, an attempt was made to extend the comfort of a passenger car cabin during the compressor off cycle using thermal energy storage (TES) in an HFO-1234yf mobile air conditioning (MAC) unit for idle stop/start vehicles. Fatty acid (OM08), as a phase change material (PCM), with 0.1–0.5 vol% of graphene nanoplatelets (GnPs) was used in this study. It was found that the inclusion of GnPs increases the thermal conductivity and dynamic viscosity of the liquid PCM nanocomposites by ~ 46% and ~ 53%, respectively, with 0.5 vol% of GnPs. During the pull-down cycle, the enhanced thermal conductivity outweighs the increased dynamic viscosity, resulting in a quicker decrease in PCM temperature. The test results revealed that the cabin temperature increases through the addition of TES, with a marginal decrease in the coefficient of performance. The addition of TES with the use of pure PCM increases the compressor power consumption of the MAC system by less than 1%. However, with the inclusion of graphene the power consumption increases with respect to the volume fraction. Without TES, the cabin comfort is extended by 78 s, 60 s, and 43 s for heating loads of 500, 1000, and 1500 W, respectively, and with the inclusion of TES, using pure PCM, the cabin comfort increased by up to 106 s, 87 s, and 63 s, respectively. The inclusion of 0.5 vol% GnPs extends the cabin comfort further by up to 189 s, 147 s, and 105 s for heating loads of 500, 1000, and 1500 W, respectively. Further, the CO2 equivalent emissions of the MAC system with TES using a pure PCM and a PCM nanocomposite are 10.54% and 5.64% lower than that of the system without TES, respectively. [ABSTRACT FROM AUTHOR]

The different MSEP/SA composite phase change materials were prepared by direct impregnation method with SEP-v, SEP-p, SEP-f as supporting material. The thermal stability of the composite phase change materials was analyzed and the differences in the thermal properties and thermal reliability were compared, and provided reference for the study of different SEP to adsorb stearic acid (SA). The results indicated that there is no chemical reaction during the preparation of the composite PCMs. SEP-f has great advantages as a supporting material and its composite (65SEP-f/SA) has a good leak-proof performance with remaining mass ratio is above 99% for leakage test of 50 h. Besides, melting and freezing latent heat of three composite PCMs are similar, For 65SEP-f/SA, the melting latent heat is 76.10 J g−1 corresponds to the phase change temperature of 344.15 K and the freezing latent heat is 75.59 J g−1 corresponds to the phase change temperature of 336.85 K. The 65SEP-f/SA has the highest thermal conductivity of 0.9460 W m−1 K−1. It can be conducted that 65SEP-f/SA have great application potential in the field for low temperature phase change energy storage. [ABSTRACT FROM AUTHOR]

Solar parabolic dish collectors are widely used for solar thermal energy conversion for various medium- and high-temperature applications. One of the problems being faced by the receivers of parabolic dish collectors is the short-time non-availability of solar radiation because of cloud cover. This affects the useful output and also results in a sudden change in the receiver temperature, which induces thermal stress in it. Hence receiver with short-term thermal energy storage is attempted to tackle this issue. A hemispherical cavity receiver is developed with a double-layered wall, and the space between the two layers is filled with a salt bath composed of a eutectic mixture of NaNO3 and KNO3 as phase change material. The heat transfer fluid flows through the copper tubes that are coiled in the gap between the two layers. The phase change material surrounds the copper tubes and acts as a storage as well as a heat transfer medium. Experimental results show that the integration of the storage medium to the receiver has a good impact on the thermal output, even during irregular radiation input conditions. The receiver has attained a net energy efficiency of 31.4% for an average irradiance of 561 Wm−2. [ABSTRACT FROM AUTHOR]

In this work, polyurethane (PU) insulating panels containing different amounts of a microencapsulated paraffin with a nominal melting temperature of 24 °C, used as phase change material (PCM), were produced. The resulting panels behaved as multifunctional materials able to thermally insulate and simultaneously storing/releasing thermal energy near room temperature. The panels were characterized from a microstructural, thermal and mechanical point of view. Viscosity measurements highlighted an increase in the viscosity values of the PU liquid precursors due to the addition of the capsules, and this could lead to some difficulties during the production stages, especially in the mixing and foaming phases. From optical microscopy micrographs and density measurements, it was observed that the introduction of paraffin tended to destroy the cellular structure of PU foams, and for PCM contents above 30 mass/% the foams were characterized by an open-cell morphology. SEM observations showed that PCM was preferentially distributed in the cell walls intersection, and a rather limited interfacial adhesion between capsules and PU could be detected. Thermogravimetric analysis evidenced that the introduction of the PCM tended to increase the degradation resistance of the foams, while from differential scanning calorimetry tests it was possible to conclude that PCM addition was able to impart good thermal energy storage properties to the foams, with specific melting enthalpy values of 70 J g−1 for a microcapsules concentration of 50 mass/%. As expected, thermal conductivity (λ) of the foams increased with PCM amount, but this enhancement was not directly related to the higher λ of the PCM itself, but rather than to the cell opening effect promoted by the PCM introduction. The microcapsules addition progressively increased the stiffness of the foams, reducing the failure properties both under quasi-static and impact conditions. Moreover, the mechanical properties were strongly affected by the testing temperature (i.e. the physical state of the wax contained in the microcapsules). [ABSTRACT FROM AUTHOR]

In this study, we focus on important global issue containing both environmental pollution control and energy saving. High density polyethylene (HDPE) is utilized as supporting material to load paraffin, while Al2O3 nano-powder is added into composite behaving as thermal conductivity enhancement to form composite phase change materials (paraffin-Al2O3/HDPE composite PCMs). By the adsorption test and differential scanning calomeritry (DSC) curves, the loading ratio of paraffin in paraffin/HDPE composite is 60%, via taking phase change enthalpy and thermal conductivity into integrated consideration, the adding ratio of Al2O3 is 3% in paraffin-Al2O3/HDPE composite. And CMT4304 universal tester results manifest paraffin-Al2O3/HDPE composites have high compressive strength. For paraffin-Al2O3/HDPE composite with 3 mass% Al2O3, Fourier transformation infrared (FT-IR) result indicates no chemical interaction among raw materials but physical combination. DSC results identify composite PCM happens solid–solid phase transition at 33.3 ºC with enthalpy value of 10.7 J g−1 and melts at 48.8 ºC with enthalpy value of 95.1 J g−1, and thermal cycling measurements demonstrate the form-stable composite PCM with adequate stability after 300 times melting/freezing cycles. Furthermore, the thermal conductivity of paraffin/HDPE composite is enhanced by 119.4% to attain 0.419 Wm−1 K−1 after addition of Al2O3. To sum up, form-stable and tough paraffin-Al2O3/HDPE composite PCMs look promising for application in building field as solar energy utilization materials. [ABSTRACT FROM AUTHOR]

At present, a series of poly(ethylene glycol)s (PEGs) are grafted to a microcrystalline cellulose material to employ them as solid–solid phase change materials (SSPCMs) for thermal energy storage (TES). The variations in the application temperatures are supplied with different molecular weight PEGs in such an extent. PEGs are grafted to a cellulose (PEG-g-C) backbone through urethane linkages formed by using isophorone diisocyanate for the first time. PEG-g-C samples are characterized by employing advanced surface analytical techniques such as FTIR-ATR, SEM, and POM. FTIR-ATR, SEM, and POM results of these PEGs-cellulose composites show that these composites are synthesized, successfully. Furthermore, TGA and DSC are performed to investigate the thermal properties of these composites. The TES property of the PEG-g-C samples such as phase transition temperature, enthalpy, and specific heat capacity (Cp) is investigated by using DSC. DSC curves indicate that the PEG-g-C samples have considerable thermal storage density at the corresponding phase transitions (28.0–164.1 J g−1 during heating and 28.3–146.5 J g−1 during cooling). In addition, phase transition temperatures are recorded as − 3.4 °C and 54.0 °C during heating and − 4.9 °C and 38.0 °C during cooling as minimums and maximums, respectively. As the result, PEG-g-C samples are found as SSPCMs for potential TES applications. [ABSTRACT FROM AUTHOR]

The low thermal conductivity of phase change materials has resulted in prolonged melting and freezing processes (charge and discharge) in these materials. This problem has limited the application of these materials in the field of thermal energy storage. In the present study, the effects of adding Fe3O4 magnetic nanoparticles at various concentrations as well as applying the magnetic field on the melting process of paraffin as phase change material have been experimentally studied. Thereupon, a cubic chamber in which the left wall applied a constant heat flux was used. At the optimum concentration of nanoparticles (1 mass%), the constant magnetic field with the intensities of 0.01 T and 0.02 T was applied and compared with the case of without field. It was inferred that using Fe3O4 magnetic nanoparticles, due to the increment of thermal conductivity, leads to a decrease in the temperature gradient in the horizontal direction and thus a decrease in melting time. Moreover, applying the magnetic field, due to the formation of high conductive clusters of nanoparticles, reduced the melting time and improved the heat transfer in paraffin. By using an optimum concentration of nanoparticles (1 mass%), in the absence and presence of the magnetic field, melting time is reduced by 8% and 12%, approximately. [ABSTRACT FROM AUTHOR]

In modern heat transfer systems, thermal storage not only causes the balance between demand and supply, but also improves the heat transfer efficiency in these systems. In the present study, a comprehensive review of the applications of micro- or nano-encapsulated phase change slurries (MPCMs/NPCMs), as well as their effects on thermal storage and heat transfer enhancement, has been conducted. MPCMs/NPCMs have a myriad of applications and various usages such as pipe and channel flows, photovoltaic/thermal, solar heaters, air conditioning systems, storage tanks and heat pipes that have been categorized and studied. It was found that there are many advantageous adding MPCM/NPCM to the base fluid. The most important effect is that the addition of PCMs to the base fluid can intensify the capacity of energy absorption in the base fluid. These materials can absorb a high proportion of received energy by changing their phase and prevent temperature increment of the base fluid. Thereupon, the specific heat of the fluid in the presence of the micro-/nano-capsules increases. Moreover, in most studies reviewed, heat transfer coefficient and Nusselt number increase by the addition of micro-/nano-capsules to the base fluid. Also, the addition of MPCM/NPCM to the base fluid could make this material pumpable, although increment in the concentration of micro-/nano-capsules raises the viscosity of the working fluid and thereupon the pumping power. On the other hand, for a same heat load, the pumping power decreases due to the lower required flow rate in comparison with pure working fluid. The most important factor that must be considered in the application of MPCMs/NPCMs is the complete phase change of the material. Given the favorable thermal and fluid characteristics of MPCMs/NPCMs, the utilization of these materials could be a promising method to transfer heat and store it with high efficiency and low pumping power. [ABSTRACT FROM AUTHOR]

A series of novel polymeric form-stable phase change materials (FSPCMs) composed of poly(trimethylolpropane trimethacrylate-stearyl methacrylate) (PTS) and stearic acid were synthesized via solvent-free bulk polymerization. Stearic acid was used as phase change component, and PTS acted as supporting material. The chemical structure, crystalline properties, phase change ability, thermal reliability, and stability were characterized by Fourier transform infrared spectroscopy, X-ray diffraction (XRD), polarizing optical microscopy (POM), differential scanning calorimetry (DSC), accelerated thermal cycling testing, and thermogravimetric analysis (TG), respectively. The DSC results revealed that the maximum freezing and melting latent heat can reach 143.5 and 146.7 J g−1. The POM and XRD results proved the existence of spherocrystal. Accelerating thermal test and TG demonstrated that FSPCMs had good reliability and stability in practical application. The prepared form-stable phase change materials with high enthalpy and proper phase change temperature have a promising prospect in thermal energy storage. [ABSTRACT FROM AUTHOR]

In the present investigation, a novel composite of Polyethylene glycol (PEG) with molecular weight 10,000 (10 k) and aluminum oxide nanoparticle were prepared for solar thermal energy storage system. A composite of nanoparticles of Al2O3 in different mass fraction (1%, 2%, 3%, 4%, and 5%) and PEG 10,000 was prepared. The thermal properties of these composites and their chemical stability were studied by DSC and FT-IR analysis. The XRD technique was adopted for analyzing the crystallization of prepared composite materials. The TGA curves was also obtained and utilized to check the thermal stability of nano-enhanced organic phase change materials (NEOPCMs). The chemical and thermal reliability was tested by conducting an aging test on an in-housed designed thermal cycler for 1500 melt/freeze cycles. The results show that the thermal properties of the NEOPCMs do not change considerably after the thermal cycle test. An increment of 52.09% in thermal conductivity was found in the developed composite with 5% incorporation of nanoparticles. On the basis of results obtained, it can be ascertained that the composites possess significant thermal properties and are a good candidate for the latent heat thermal energy storage systems having temperature requirement around 60 °C such as solar water heater, etc. [ABSTRACT FROM AUTHOR]

This paper presents the numerical analysis of the transient performance of the latent heat thermal energy storage unit established on finite difference method. The storage unit consists of a shell and tube arrangement with phase change material (PCM) filled in the shell space and the heat transfer fluid (HTF) flowing in the inner tube. The heat exchange between the HTF, wall and PCM has been investigated by developing a 2-D fully implicit numerical model for the storage module and solving the complete module as a conjugate problem using enthalpy transforming method. A comparative investigation of the total melting time of the PCM has been performed based on natural convection in liquid PCM during the charging process. The novelty of this paper lies in the fact it includes convection in PCM and this investigation includes a detailed parametric study which can be used as a reference to design latent heat storage. The results indicate that natural convection accelerates the melting process by a significant amount of time. In order to optimize the design of the thermal storage unit, parametric study has been accompanied to analyze the influence of various HTF working conditions and geometric dimensions on the total melting time of the PCM. Another important feature considered in this work is the influence of the inner wall of the tube carrying the HTF on the entire melting time of the PCM. An error of around 7.2% is reported when inner wall of the tube is ignored in the analysis. [ABSTRACT FROM AUTHOR]

Numerical simulations are performed to analyze the thermal characteristics of a latent heat thermal energy storage system with phase change material embedded in highly conductive porous media. A network of finned heat pipes is also employed to enhance the heat transfer within the system. ANSYS-FLUENT 19.0 is used to create a transient multiphase computational model to simulate the thermal behavior of the storage unit. Copper foam is the porous medium used to enhance the heat transfer and is impregnated with the phase change material, potassium nitrate (KNO3). The effects of the porosity of the metal foam and the quantity of heat pipes on the thermal characteristics of storage unit have been investigated. The results indicated that increasing the quantity of the embedded heat pipes leads to drastic acceleration of both charging and discharging process. Impregnating the copper foam with potassium nitrate phase change material significantly affects the total charging and discharging times of the storage unit. It was shown that the porosity of the metal foam plays a key role in the thermal behavior of the system during the charging and discharging processes. [ABSTRACT FROM AUTHOR]

Using palmitic acid (PA), expanded graphite (EG), and carbon fiber (CF) as raw materials, PA/EG/CF composite phase change materials (CPCMs) with diverse CF contents were invented by melt blending approach. The effects of different ratios on thermal properties were studied by experimental characterization and testing. Scanning electron microscopy images displayed that PA was adsorbed in the pores of the EG surface, while CF was disorderly but uniformly embedded in the interior and surface of pores. The chemical stability and thermal decomposition stability of CPCM at low temperature were proved by Fourier transform infrared spectrometer and thermogravimetric analyzer results, respectively. According to the law of heat storage/release time and latent heat variation, the optimal ratio scheme was determined, and its heat storage/release time was 65% and 59% lower than pure PA, respectively. The form-stable materials were prepared by compression forming method, and thermal cycling experiment results demonstrated that the higher the content of CF, the stronger the inhibition of mass loss. Based on the experimental results, the PA/EG/CF CPCM has the advantages of stable phase transition, strong stability, and fast heat storage and release rate, so it has a marvelous application prospect in the field of low-temperature heat storage engineering. [ABSTRACT FROM AUTHOR]

In this study, a series of gelators (Gn, n is the number of carbon atoms of used fatty alcohol, n = 2, 4, 6, 8, 10, 12, 14, 16 and 18) were synthesized by reacting 4,4′-diphenylmethane diisocyanate with fatty alcohols. Meanwhile, n-octadecane-based gels as form-stable phase change materials (FSPCMs) for thermal energy storage were prepared by introducing Gn into n-octadecane. The gel properties were confirmed by "tube testing method." The results show that Gn (n = 2, 4) were immiscible with n-octadecane, while a lower mass percentage content (≤ 6 mass%) of Gn (n = 6, 8, 10, 12, 14, 16, 18) can gelate the n-octadecane and the gel-to-sol transition temperature is higher than 100 °C. The chemical structures, morphologies and crystalline properties of prepared FSPCMs were determined by Fourier transform infrared spectroscopy, scanning electron microscope, X-ray diffraction and polarized optical microscope. It is found that Gn could self-assemble into lamellar three-dimensional network structure to restrict the leakage of melted n-octadecane. Differential scanning calorimetry analysis results indicate that prepared FSPCMs exhibit high latent heats and latent heat efficiency is greatly higher than that of other traditional FSPCMs. Moreover, thermal cycling test results confirm that the prepared FSPCMs have good thermal reliability and reusability. This study is attractive for preparation of FSPCMs with high latent heats. Prepared FSPCMs could be potentially applied in the field of thermal energy storage for thermal comfort. [ABSTRACT FROM AUTHOR]

Nanoencapsulated phase change material (NEPCM) was prepared with oleic acid as phase change material by its encapsulation into Ag2O nanoparticles (NPs)-based urea formaldehyde (UF) resin. NEPCMs were synthesized by in situ polymerization with different surfactants, to obtain a better shell material in terms of energy release, leak arrest and enhanced thermal properties. The morphology and particle size of the prepared NEPCM were analyzed by digital microscope and scanning electron microscope. Fourier transform infrared spectroscopy was used to determine the chemical structure. X-ray diffraction studies were carried out to ensure the presence of Ag2O NPs containing UF resin as shell material and its cubic crystal system. Thermo-physical properties were evaluated using differential scanning calorimetry (DSC), thermogravimetric analysis and thermal diffusivity analysis. DSC results revealed that the cationic surfactant-assisted synthesis of shell material has a comparatively good encapsulation ratio of 45.52%, and to further enhance the encapsulating capacity, Ag2O NPs was introduced. Addition of Ag2O NPs into the shell material shows improved encapsulation ratio of 54.82% with latent heat of 71.7 J g−1 for melting at 5.21 °C and hence better surface morphology, good thermal stability, better thermal conductivity and more suitability toward thermal energy storage in buildings. [ABSTRACT FROM AUTHOR]

In this paper, the melting properties such as the thermal energy storage capacity and phase-change temperatures of paraffin are investigated. The paraffin is also modified as nano-PCM by dispersing small fractions (0.2% and 0.5% mass fractions) of highly conductive nanoparticles. The material used in this study has a melting temperature of 22 °C, making it suitable for domestic building applications. Additionally, the thermal conductivity and heating rate of the paraffin and paraffin with multiwall carbon nanotubes (MWCNTs) are studied experimentally. The results show that the paraffin with 0.2% and 0.5% mass fractions of MWCNTs could increase the thermal conductivity by 35% and 49% with respect to pure paraffin. The maximum thermal conductivity of 0.203 W m−1 K−1 is observed for the paraffin with 0.5% mass fraction of MWCNTs. Additionally, the heat of fusion slightly reduced by increasing the mass fraction of MWCNTs. The result implies that the materials used in this study could be used for building applications. [ABSTRACT FROM AUTHOR]

This paper comprehensively reviews the use of phase change materials (PCMs) as latent heat storage systems to improve the productivity of solar stills. Previous studies on enhancing the productivity of active and passive solar stills with PCM are also presented. These studies show that a passive solar still with PCM shows a productivity improvement of up to 120% compared with a solar still without PCM. Meanwhile, the productivity improvement of an active solar still with PCM could reach as high as 700%. These results indicate that productivity increases along with an increasing PCM mass and a decreasing saline water mass. The PCM is also observed to be less effective in daytime than in night-time. It is also shown that organic PCMs (such as paraffin) were mostly used in studies on productivity improvement, whilst very few studies have examined the effects of inorganic and eutectic types of PCM. [ABSTRACT FROM AUTHOR]

The eight kinds of fatty acid binary and ternary eutectics such as capric–lauric acid (CL), capric–myristic acid (CM), capric–palmitic acid (CP), capric–stearic acid (CS), capric–lauric–palmitic acid (CLP), capric–myristic–palmitic acid (CMP), capric–myristic–stearic acid (CMS), and capric–palmitic–stearic acid (CPS) were selected as solid–liquid PCMs in this paper. The innovative electrospun fatty acid binary eutectic/polystyrene/fatty acid ternary eutectic (i.e., CL/PS/CLP, CM/PS/CLP, CP/PS/CLP, CS/PS/CLP, CL/PS/CMS, CM/PS/CMS, CP/PS/CMS, CS/PS/CMS, CL/PS/CPS, CM/PS/CPS, CP/PS/CPS and CS/PS/CPS) and fatty acid ternary eutectic/polystyrene/fatty acid ternary eutectic (i.e., CLP/PS/CMP, CLP/PS/CMS, CLP/PS/CPS, CMP/PS/CMS, CMP/PS/CPS and CMS/PS/CPS) form-stable phase change composite fibrous membranes (PCCFMs) were fabricated by co-electrospinning. The morphological structure, phase change temperatures, and enthalpies were investigated by scanning electron microscope (SEM) and differential scanning calorimetry (DSC), respectively. The SEM images showed that the PS-based phase change composite fibers were collected to form form-stable PCCFMs with the average fiber diameter of about 335–640 nm. The DSC analysis indicated that the melting peak temperatures of electrospun PS-based form-stable PCCFMs can be adjusted to 15–25 °C with the temperature interval of 1 °C by combining the both of fatty acid binary and ternary eutectics into the PS supporting fibers. These PS-based form-stable PCCFMs can be recommended for potential low-temperature thermal energy storage applications to regulate temperature and satisfy the human thermal comfortability. [ABSTRACT FROM AUTHOR]

In present study, the efficient parameters on thermal energy storage in a double-wall tank with phase-change materials have been investigated. At first, the effect of using fins in distribution of phase-change materials has been studied. Inside the tank where the inlet-heated water is there, the inlet temperature and Reynolds number have been investigated. Also, on tank walls where the phase-change materials are placed, the effect of using of fins and the type of phase-change materials has been investigated. By mounting fins on areas with phase-change materials, the melting time reduces significantly. Therefore, after mounting fins, the melting of phase-change materials has been reduced from 60 to 80% in approximately 8 h. In water zone, by increasing inlet temperature from 340 to 360 K, the melting time of phase-change material reduces significantly, in a way that, after approximately 8 h, the amount of melted materials changed from 67 to 87%; however, the change in Reynolds number does not have any considerable influence. In final section, the effect of thermophysical properties of phase-change materials on melting process has been studied. The obtained results reveal that using materials with lower specific heat and melting temperature causes the reduction of melting time, and hence, for melting 90% of phase-change materials with wax, 14 h is needed, while, by using SavEHS34, these materials change their phase in 5.5 h. [ABSTRACT FROM AUTHOR]

A practical use of phase change material (PCM)-based thermal energy storage (TES) system is effectively employed for mitigating the imbalance between energy demand and energy supply. Technological development of TES is essential to overcome the drawback of the poor thermo-physical property of many PCM's. Otherwise, the PCM-based TES system would exhibit poor thermal management. In this work, D-Mannitol (DM) sugar alcohol is considered as PCM and experimental attempts were made to accelerate the phase change behaviour of the chosen PCM by adding 1 and 2% mass fraction of micron-sized copper and aluminium metal powders. The phase change temperature and enthalpy of fusion of the plain DM and composite DM were determined by differential scanning calorimetry (DSC) measurements, and the thermal stability of composite PCM was analysed using thermogravimetric analysis (TGA). Further, charging and discharging processes were conducted for plain DM and composite DM using Therminol 55 heat transfer fluid (HTF) to study their thermal energy storage performance. The DSC results indicated superior enthalpy of fusion and phase transition temperature and TGA results depicted extended decomposition temperature with an increase of about 2 °C to 32 °C for composite DM, respectively, over plain DM. Further, from charge–discharge studies, it was identified that the total time taken for a complete phase change process for the case of DM-Cu 2% during charging process was 22% and 11% lesser compared to plain DM and DM-Al 2%, respectively. Similarly during discharging process, the total time taken for a complete phase change process of DM-Cu 2% was 16% and 10% lesser compared to plain DM and DM-Al 2%, respectively, indicating superior phase change behaviour of composite DM compared to the plain DM. Thus, when compared to plain DM and Al microparticle in DM, Cu microparticle added DM was found to be more suitable to store thermal energy at a medium temperature range. [ABSTRACT FROM AUTHOR]

The synthesis of phase change materials based on NaCl–CaCl2 molten salt mixture and mesoporous silica was investigated. The influence of mesoporous silica porosity and salt concentration on the thermal energy storage properties of the resulting materials is discussed. The nanocomposite samples were characterized by X-ray diffraction, differential scanning calorimetry, infrared spectroscopy, thermogravimetry, scanning electron microscopy and X-ray photoelectron spectroscopy. The mesoporous silica was found to act as a reactive matrix for the molten salts. Composite samples with up 95% wt. salt can be obtained and used as shape-stabilized phase change materials. The materials have heat of fusion values of up to 60.8 J g−1 and specific heat capacity between 1.0 and 1.1 J g−1 K−1. The samples exhibit thermal stability up to 700 °C and can be used for high-temperature thermal energy storage through both latent and sensible heat storage mechanisms. [ABSTRACT FROM AUTHOR]

Leakage issue and low thermal conductivity largely restrict feasibility of fatty acid in real application of thermal energy storage (TES). In this paper, a novel form-stable phase change material (FSPCM) capric acid/diatomite (CA/DT) for TES was prepared using direct impregnation method by using CA as PCM and diatomite as supporting material. The fabricated composites were investigated in detail via the leakage test to determine the optimization proportion, and the real mechanism of preventing leakage by diatomite was analyzed. The characterization techniques such as thermogravimetric analysis, differential scanning calorimetry, intelligent paperless recorder technology, Fourier transform infrared spectrometer and scanning electron microscopy were applied to systematically investigate the thermal properties, microstructure and thermal compatibility of the prepared composites. The results showed that the maximum mass ratio of CA adsorbed into DT without leakage is as high as 50 mass%, which is mainly ascribed to the porous structure of DT. The selected FSPCM has a melting point of 34.9 °C and latent heat of 89.2 J g−1. What is more, the CA/DT FSPCM exhibits a distinctly enhanced thermal stability by TG analyses. The heat transfer efficiency of the CA/DT FSPCM is higher than that of pristine CA. Due to the high adsorption capacity, high latent heat, good thermal stability as well as low cost, the CA/DT FSPCM can be considered as potential materials for thermal energy storage. [ABSTRACT FROM AUTHOR]

Utilization of renewable biomass to prepare phase change material (PCM) that can reversibly store renewable thermal energy is of great interest. Castor oil with functional hydroxyl groups is especially attractive for the preparation of polymeric materials. In this work, a novel castor oil-based polyurethane-acrylate oligomer (COPUA) was firstly synthesized through a two-step condensation reaction. Followed by in situ polymerization of COPUA in the presence of palmitic acid (PA), a novel biomass-based form-stable PCM was prepared, in which renewable PA serves as phase change functional ingredient and castor oil-based crosslinking network acts as encapsulation material. Tailoring the mass ratio of PA and COPUA provides the ultimate encapsulation ratio (70%) of PA in form-stable PCM. The chemical structure, crystalline property, thermal property of form-stable PCM were characterized using Fourier transform infrared spectroscopy, wide-angle X-ray diffraction, differential scanning calorimetry and thermogravimetric. Those results demonstrate that the prepared form-stable PCM possesses that good thermal storage capacity with the phase change enthalpy reaches 141.2 J g−1. Accelerated thermal cycling test was also performed to illustrate the thermal reliability of form-stable PCM. [ABSTRACT FROM AUTHOR]

In this study, the hollow glass microsphere (HGS)/stearic acid (SA) composites were prepared as form stable phase change materials (FSPCMs) for thermal energy storage via directly impregnation. In prepared FSPCMs, SA acted as the phase change substance and the HGS functioned as the supporting materials to prevent the leakage of melted SA. The special structure and large surface of HGS had strong absorption ability for SA. The chemical structure, surface morphology, crystalline properties, phase change properties, thermal reliability and stability of prepared FSPCMs were extensively studied by Fourier transform infrared spectroscopy (FTIR), scanning electron microscope (SEM), X-ray diffraction (XRD), differential scanning calorimetry (DSC), thermal cycling test and thermogravimetric analysis (TGA), respectively. FTIR results showed that only physical interaction occurs between HGS and SA, and the SEM images showed the SA is adhered on the surface and internal surface of HGS through physical interaction. The XRD pattern exhibited that the crystalline properties of FSPCMs are not affected by the introduction of HGS. FSPCMs also exhibited good phase change properties with the latent heat in the range of 48.77–133.8 J g−1 and the phase change temperature in the range of 50.20–51.54 °C, and the supercooling degree was lower than 2 °C. The special structure of HGS imparted FSPCMs with good thermal reliability reflected by slightly variation of latent heat and phase change temperature after 100 thermal cycles. TGA results showed the FSPCMs have good thermal stability, which will meet the requirement of application. In conclusion, the prepared FSPCMs had great value in the field of thermal energy storage. [ABSTRACT FROM AUTHOR]

In this research, the n-butyl palmitate was synthesized using the esterification reaction of the PA with n-butanol. The 1H nuclear magnetic resonance and Fourier transform infrared illustrated that the hydroxyl group and carboxyl group disappeared, and the ester bond appeared after the reaction, explaining that n-butyl palmitate was successfully fabricated. The differential scanning calorimetry indicated that the phase-transition temperature and latent heat are 12.6 °C and 127.1 J g−1, which was suited to use in low-temperature fields such as food, pharmaceutical, and biomedical. The thermogravimetric analysis suggested that it had great thermal stability during the phase change process. In addition, the thermal conductivity of the n-butyl palmitate was slightly higher than other fatty acid ester, and the 500 thermal cycles test results indicated that it had excellent thermal reliability. Therefore, the n-butyl palmitate is deduced to share great thermal energy storage ability in terms of latent heat thermal energy system applications. [ABSTRACT FROM AUTHOR]

Thermal energy storage systems provide efficiency in order to have better utilization of energy sources while protecting the environment. Thermal energy storage can be classified as sensible and latent heat storage. The storage of latent heat allows a greater density of energy storage with a narrow temperature range during phase change. Phase change materials (PCMs) are important novel materials, which are used as the storage of thermal energy as latent heat, and can provide utilization of waste heat energy. In this study, the capric acid and oleic acid mixture containing hexadecane were encapsulated as the core with styrene–divinylbenzene copolymer shell by emulsion polymerization technique. Thermal properties of fatty acid microcapsules were characterized by differential scanning calorimetry and thermogravimetric analysis and also their morphology and structure were examined by scanning electron microscopy, polarized optical microscopy and Fourier transform infrared spectroscopy (FT-IR), respectively. The heat storage property of microencapsulated PCM was tested in a horizontal air flow channel system equipped with a flat heating plate, air fan and air flow sensors. The microencapsulated PCM was prepared successfully, and results of the analysis presented that this material is promising candidate for potential heating and cooling system applications. [ABSTRACT FROM AUTHOR]

The thermo-physical properties of NaNO3/KNO3 (solar salt) added with Al2O3 and TiO2 nanoparticles as phase change material in thermal energy storage system were investigated. Initially the Al2O3 and TiO2 nanoparticles were added to NaNO3/KNO3 (60:40) with a concentration of 1%, 3% and 5 mass% using low-energy ball mill. The differential scanning calorimetry instrument is used to measure the thermal properties of the prepared PCM composites. It is found that the phase change temperature and latent heat capacity vary with Al2O3 and TiO2 nanoparticles loading levels. When the loading is not over 3 mass% of Al2O3, the phase change temperature drops, and the latent heat capacity increases up to 23.3%. When the loading is over 3 mass% of Al2O3, the phase change temperature increases, and the latent heat capacity drops to 14.23%. A significant increase in latent heat capacity is found around 3 mass% of Al2O3 loading. When the TiO2 nanoparticle concentration increases, the phase change temperature decreases, and the latent heat capacity increases up to 32.2%. When the TiO2 nanoparticle's concentration decreases, the phase change temperature increases, and the latent heat capacity decreases. The thermal conductivity of the composites was found to increase with the increase in the loading of nanoparticles. After adding 3% by mass of Al2O3 and TiO2 nanoparticles, the thermal conductivity was found to increase by 8.30 and 8.10%, respectively. From the characterization studies, we found that TiO2 helps to achieve the improved thermo-physical properties and heat storage characteristics for NaNO3/KNO3 which suggests their potential candidate of usage in the thermal energy storage system. [ABSTRACT FROM AUTHOR]

Phase change materials (PCMs) that can store the heat energy obtained from intermittent solar irradiation are very important for solar energy absorption cooling system. In this work, an organic compound that melts at the temperature of 368.2 ± 0.5 K was applied as PCM. The specific heat capacities of the PCM were measured by temperature-modulated differential scanning calorimetry from 198.15 to 431.15 K. The thermodynamic functions of [HT-H298.15] and [ST-S298.15] were then calculated based on the measured heat capacities data. Afterward, the long-term cyclic thermal energy storage stability and thermal stability of the PCM were investigated. The results show that the PCM melted and crystallized at about 368 and 364 K, respectively, with a phase change enthalpy (ΔtransH) of 21 kJ mol−1 (130 J g−1). Additionally, it exhibited good long-term cyclic thermal energy storage stability and thermal stability. Hence, the PCM could be applied as good PCM for solar energy absorption cooling. [ABSTRACT FROM AUTHOR]

Bone char (BC) is a promising porous material that can be used for preparing a form-stable composite phase change material (PCM). In this paper, form-stable polyethylene glycol (PEG 6000)/BC composite PCMs were prepared by impregnation method. The PEG was used as the phase change material, and two different particle sizes of BC (0.8-1 mm: BC-1; 0.25-0.8 mm: BC-2) were acted as the supporting materials. The phase composition and chemical structure of the composite PCMs (PEG/BC-1 and PEG/BC-2) were characterized using X-ray diffraction and Fourier transformation infrared. The results indicated that the PEG can be well impregnated into BC pores with good compatibility. Thermal properties and thermal stability of the composite PCMs were determined by differential scanning calorimeter (DSC) and thermogravimetry analysis (TGA). DSC results showed that the maximum impregnation percentage for PEG into BC-1 and BC-2 was 38.77 and 43.91%, respectively, without melted PCM seepage from the composites. The TGA analysis revealed that the composite PCMs had good thermal stability above their working temperature range. The thermal cycle test of 100 melting-freezing cycles showed that the composite PCMs have good thermal reliability and chemical stability. The form-stable composite PCMs can be used as thermal energy storage material for waste heat storage and solar heating system. [ABSTRACT FROM AUTHOR]

In this study, a series of the cross-linked polyurethane (PU)/PEG4000 blend was synthesized as novel form-stable phase change materials (FSPCMs) for thermal energy storage through a facile and solvent-free synthetic strategy. In the obtained FSPCM, the PU functioned not only as supporting materials but as phase change substance. The PEG in FSPCM acted as phase change substance. The influence of PEG4000 content on the crystalline properties, phase change properties, thermal reliability and stability was extensively studied by X-ray diffraction (XRD), differential scanning calorimetry (DSC), thermal cycling test and thermogravimetric analysis (TG), respectively. Moreover, the chemical and crystalline structure of obtained PU and FSPCM was confirmed by Fourier transform infrared spectroscopy (FTIR) and polarizing microscope (POM). XRD and POM results indicated that the obtained FSPCM has similar crystalline structure to PEG. DSC results showed that FSPCM appears superior phase change properties with the phase change temperature and the latent heat in the range of 27.73-48.94 °C and 72.19-113.4 J g, respectively. The thermal cycling test and TG verified the excellent thermal reliability and stability of FSPCM. The obtained FSPCM exhibited great potential in the field of TES such as the solar energy collection system, exterior wall thermal insulation systems and hot water circulation system. [ABSTRACT FROM AUTHOR]

Nine nucleating agents, calcium pimelate (CaPi), bicyclic [1, 2, 2]heptane di-carboxylate (HPN-68), a commercially obtained aryl amide nucleating agent (TMB-5), calcium salt of hexahydrophthalic acid (HPN-20E), 1,3:2,4-di-p-methylbenzylidene sorbitol (MDBS) and sodium, potassium, magnesium and calcium salt of benzene-1, 3, 5-tricarboxylic acid (NaBTC, KBTC, MgBTC and CaBTC, respectively), were applied to reduce the supercooling of erythritol, and their effects were investigated by cyclic differential scanning calorimetry (DSC). The results revealed that NaBTC and KBTC could not induce erythritol to crystallize under the experiment condition. MDBS could only make erythritol to crystallize at a temperature slightly higher than that of pure erythritol, and the effect was unstable. MgBTC, CaBTC and HPN-68 could induce erythritol to crystallize at relatively high temperature, but the peak temperature of crystallizing ( T ) and the phase change enthalpy of crystallizing (Δ H) decreased greatly as the melting-crystallizing cycles increased. HPN-20E-doped erythritol crystallized at a high temperature with the T of 69.3 °C at the first cycle, but the T and Δ H varied greatly during the melting-crystallizing cycles. CaPi and TMB-5 could induce erythritol to crystallize at a stable temperature with the T of about 69 °C and 64 °C, respectively, and with a stable Δ H of about 204 and 185 J g, respectively, in all melting-crystallizing cycles. Hence, CaPi- and TMB-5-doped erythritol could be used as PCMs and applied in thermal energy storage in which the energy was absorbed at a high temperature and released at a lower but stable temperature. [ABSTRACT FROM AUTHOR]

Novel microencapsulated phase change materials (MicroPCMs) in which palmitic acid (PA) acted as core material and polyaniline as shell material were prepared by in situ polymerization method without any emulsifier and doping agent. The effects of the preparation temperature, polymerization time, oxidant concentration and the acid dopants on the morphology and thermal properties of the MicroPCMs were investigated by field emission scanning electron microscope, differential scanning calorimetry and thermogravimetry. The results showed that spherical MicroPCMs could be obtained when the polymerization was initiated at a temperature higher than the melting point of PA with a medium oxidant concentration and then relatively slowly completed the polymerization at a low temperature without any acid dopant. The best preparation condition in this work was that the polymerization was initiated at 348 K for 2 h with the oxidant/aniline mole ratio of 0.75 and then completed at 303 K for 18 h. The prepared MicroPCMs showed spherical morphology with the phase change enthalpy of 106.3 J g. Furthermore, the evaporation of PA in the MicroPCMs was postponed due to that PA was fully encapsulated in the capsules, which is favorable for its application. [ABSTRACT FROM AUTHOR]

Solar absorption cooling is a wonderful method to provide cold energy by exploiting solar energy. Phase change materials (PCMs) that store latent thermal energy are indispensible in solar absorption cooling system. It is worthwhile to find new PCMs due to the demanding on the temperature of the stored thermal energy which in turn would power the absorption chiller. In this paper, two compounds: 1-bromo-2-methoxynaphthalene (compound 1) and 2,2′-diphenyl-4,4′-bi(1,3-dioxane)-5,5′-diol (compound 2), were selected as potential PCMs. Their thermal energy storage properties and thermal stability were characterized by differential scanning calorimetry and thermogravimetric analysis. The results showed that both compounds could be applied as good PCMs in solar absorption cooling systems. Compound 1 melted at 356.82 K with the Δ H of 98.81 J g, while compound 2 melted in a broad temperature range with the melting point of 466.26 K and the Δ H of 101.4 J g. Both compounds exhibited good thermal stability. Furthermore, the molar specific heat capacities of these two compounds were measured by temperature-modulated differential scanning calorimetry from 198.15 K to the temperature that they started to decompose, and the thermodynamic functions of [ H - H ] and [ S - S ] were calculated based on the specific heat capacities data. [ABSTRACT FROM AUTHOR]