Latent Enthalpy Research Articles

Optimizing thermal performance of sodium acetate trihydrate phase-change-materials through synergistic effects of binary graphene nanoadditives for prolonged hot beverage maintenance

Sodium acetate trihydrate (SAT) is a promising candidate for thermal energy storage due to its high latent enthalpy and economic viability. However, limitations like supercooling and low thermal conductivity hinder its practical application. Herein, these challenges are addressed by developing a novel SAT-based composite phase change material (PCM) through incorporation of binary nanoadditives—graphene oxide (GO) and graphene nanoplatelets (GNP) to mitigate supercooling and enhance thermal conductivity, respectively. Notably, the optimal composite, SAT/0.25GO/0.75GNP, identified through systematic formulation optimization, retains a high latent enthalpy (281.09 J/g), comparable to pure SAT (290.47 J/g), with improved thermal conductivity and substantially reduced supercooling and phase separation issues. The combined effects of GO and GNP, likely due to noncovalent interactions, enhanced heat transfer in the composite, which was further tested in a vacuum mug. The SAT/0.25GO/0.75GNP composite achieved ideal drinking temperatures (60–50 °C) for hot water in just 4 minutes–18 times faster than the PCM-free control mug and 6 times faster than the Mug containing pure SAT. While the PCM-free mug maintains hot water within this interval for only 49 min, MugPCM, encapsulating pure SAT, retains heat for 76 min, and that with SAT/0.25GO/0.75GNP keeps remarkably hot for as long as 100 min.

Prediction of pure and mixture thermodynamic properties and phase equilibria using an optimized equation of state – part 1: Parameter estimation

This study presents a novel three-parameter equation of state (EOS) wherein attraction parameter polynomial coefficients are optimized to enhance predictive capabilities. The performance of the proposed EOS is systematically compared with established models including Peng-Robinson, Patel-Teja, and Twu-Coon-Cunningham equations. Through comprehensive evaluation, it is demonstrated that the proposed EOS exhibits superior accuracy in vapor pressure and latent enthalpy predictions, while maintaining comparable precision in liquid density estimations. Notably, the fugacity expression of the proposed EOS closely resembles that of a two-parameter equation, resulting in significantly reduced computational overhead. Additionally, a comprehensive table of equation of state parameters for all four equations is available in an online repository, facilitating easy implementation and comparison. Furthermore, a reliable generalized polynomial correlation is provided for the proposed EOS parameters against the true compressibility factor and acentric factor, leveraging data accessibility and enhancing its applicability and versatility. These findings underscore the potential of the optimized attraction parameter polynomial coefficients approach in advancing the accuracy and efficiency of EOS modeling, thereby offering promising avenues for diverse applications in thermodynamics and process engineering.

Fabrication and building energy-saving performance evaluation of polyethylene glycol/polymethyl methacrylate/expanded graphite thermal enhanced shape-stable phase change material

Integrating Phase Change Material (PCM) with building envelope is a promising way to reduce building energy consumption. However, leakage and insufficient PCM loading rate for existing encapsulation strategies limit its further application. In this work, a safer and easier way to fabricate Shape-Stable Phase Change Material (SSPCM) is proposed, whose products combine the outstanding leakage-proof property and high PCM loading rate. With the method of in-situ polymerization, not only the Polyethylene Glycol (PEG) is packaged by Polymethyl Methacrylate (PMMA), but the Expanded Graphite (EG) also has a chance to be added as the property regulator. The prepared SSPCMs are proved to be shape-stable over melting temperature with a leakage rate under 1 %. The characterization test reveals that with EG mass fraction increase from 0 to 2.5 %, the thermal conductivity augments from 0.23 to 1.73 W/(m·K) while the phase change latent enthalpy changes from 85.11 kJ/kg to 116.10 kJ/kg. Notably, the EG is more than a thermal conductivity enhancer, it also plays an important role in the modification of comprehensive properties. To optimize the building energy-saving performance of SSPCMs, the factors affecting building cooling electricity consumption like deployment position and thermal properties are evaluated in detail. The simulation results show that the optimum strategy is employing SSPCM with 2.0 wt% EG in the middle of the envelope, the cooling electricity consumption can be reduced by 8.64 % compared with the benchmark. The physical mechanism of energy-saving is also discussed from multiple angles. From a statistical view, sensitivity and uncertainty analysis of the simulation results is completed, to identify the influence of input parameters and validate the reliability of the simulation results. Finally, an economic analysis is carried out, proving the economic feasibility for further application. This research provides valuable insights for SSPCM’s application and design of energy-efficient buildings.

X-ray computed tomography analysis of calcium chloride hexahydrate solidification

Latent Thermal Energy Storages (LTESs) are receiving increasing interest, since they offer many advantages to the field of Thermal Energy Storages (TESs), such as a nearly isothermal solid–liquid phase transition and a high energy storage density. To boost the transition towards a climate-neutral future, a lot of work is surely needed on Phase Change Materials (PCMs) which are used inside LTESs. Salt hydrates, a particular class of PCMs, are very attractive in terms of cost and volumetric latent enthalpy but present drawbacks that still limit their effective deployment in real applications, such as supercooling and phase separation (or segregation). The current work assesses the suitability of X-ray Computed Tomography (XCT) as a novel technique in the field of LTESs to study the solidification of phase-change materials. In this study, calcium chloride hexahydrate (CaCl2·6H2O) is chosen as a representative PCM and the results derived are shown to be repeatable. For the first time, the direct measurement of the volumetric liquid fraction is correlated to temperature measurements allowing for the visualisation of supercooling and the validation of an enthalpy-porosity numerical model, which could be useful in the design of LTES. XCT methodology offers unmatchable features as compared to the other method to measure the volumetric liquid fraction. Given its accuracy and the rigorous protocol, it can be considered as a benchmark for new liquid fraction measurement technologies but it also permits to study how the different PCMs melt and solidify, giving new insights on the mechanisms at the basis of the most crucial challenges, among those: subcooling, segregation, and metastable phase change.

Graphene oxide modified sodium alginate/polyethylene glycol phase change material hydrogel scaffold composite with photothermal temperature control for potential bone tissue regeneration

The challenge of precisely regulating temperature during the photo-thermal bone promotion remains unresolved. Phase change material (PCM), capable of undergoing a phase transition at a specific temperature, offers a solution by photothermal temperature regulation through the storage and release of heat. This study incorporated biocompatible polyethylene glycol (PEG) with specific phase transition points as PCM. A phase change hydrogel scaffold was then synthesized through semi-crosslinking PEG with calcium-ion-chelated sodium alginate (SA) acting as the structural framework. Additionally, the newly developed graphene oxide (GO) modified composite scaffolds (GO-PHSC), featuring 0.5 wt% GO, not only demonstrated outstanding photothermal conversion efficiency and an optimal phase change temperature (42.2 °C) but also exhibited desirable values for latent enthalpy (100 J/g) and latent heat recovered (LHR) (93.3%). Moreover, the form-stability test demonstrated the PCM scaffolds' exceptional resistance to leakage and maintenance of shape stability even at elevated temperatures (70 °C). Beyond achieving passive temperature control in photothermal therapy, experimental findings highlighted that the phase change hydrogel, incorporating calcium ions and GO, met various requirements such as physicochemical properties, microstructure, mechanics, mineralization, biocompatibility, and cell affinity. These collective attributes suggest that GO-PHSC emerges as a promising scaffold composite candidate for temperature-controlled photothermal therapy in bone regeneration.

Efficient-thermal conductivity, storage and application of bionic tree-ring composite phase change materials based on freeze casting

Thermal energy storage, management, and utilization with phase change materials have received increasing attention in industrial fields such as photo-thermal-electric conversion and integrated circuit cooling. However, the inherent low thermal conductivity and melting leakage are long-term bottlenecks that prevent their widespread commercial application. Herein, a novel composite phase change material (CPCM) with high-thermal conductivity and stability based on bionic porous SiC skeleton is proposed, which is oriented by optimized freeze casting to design vertical tree-ring porous structure for fast photo-thermal conversion and storage. The results demonstrate the novel bionic SiC skeleton can regulate the porosity (50%–70%) by changing the slurry solid content, which also exhibits good anisotropic thermal conductivity. SiC/paraffin CPCM's mass and latent enthalpy of attenuated merely by 0.87% and 1.5% after 200 repeated heat storage/exhaustion cycles, confirming its excellent longevity and stability. The high-temperature SiC/NaCl-MgCl2-KCl CPCM has a thermal conductivity of 12.54 W‧m−1‧K−1, an effective thermal-storage density per production cost of 74.5 kJ‧CNY-1, and a high photo-thermal storage efficiency of 91.8%. Finally, a variable-power chip dissipation experimental system was built to verify the thermal performance of the CPCM module in the paper. It could dissipate heat rapidly and maintain a lower temperature. This work provides a promising strategy for photo-thermal utilization and thermal management of electronic devices.

Fabrication and characterization of microencapsulated dimethyl adipate phase change material with melamine-formaldehyde shell for cold thermal energy storage in coating

Abstract Microencapsulated phase change material (MPCM) was synthesized by using the in-situ polymerization technique. Dimethyl adipate (DMA) and melamine-formaldehyde were used as core and shell material for polymerization respectively. Sodium laureate sulphate (SLS) is used as a surfactant. The thermal properties were characterized by using a differential scanning calorimeter (DSC) and thermogravimetry analysis (TGA). Fourier transform infrared spectroscopy (FT-IR) was used to confirm the chemical structure. The morphology of microcapsules was studied by using, scanning electron microscopy. DSC result of MPCM has been observed to melt at 10.09 °C with melting latent enthalpy 88 J/g and crystallizes at 4.69 °C with crystallization latent heat 89.50 J/g. TGA analysis confirms increases in the thermal stability of MPCM. The decorative coating was prepared with 0, 5, 10, 15, and 20 % MPCM loading, and the prepared paint was tested for pencil hardness, gloss, and stain resistances. The thermal energy transfer rate was used to measure how much time coated panel took to reach the equilibrium temperature of 25 °C. Coating with 20 % MPCM loading revealed good thermal storage capacity but other general coating properties deteriorate.

Preparation and Characterization of Bio-Based PLA/PEG/g-C3N4 Low-Temperature Composite Phase Change Energy Storage Materials.

As energy and environmental issues become more prominent, people must find sustainable, green development paths. Bio-based polymeric phase change energy storage materials provide solutions to cope with these problems. Therefore, in this paper, a fully degradable polyethylene glycol (PEG20000)/polylactic acid (PLA)/g-C3N4 composite phase change energy storage material (CPCM) was obtained by confinement. The CPCM was characterized by FTIR and SEM for compatibility, XRD and nanoindentation for mechanical properties and DSC, LFA, and TG for thermal properties. The results showed that the CPCM was physical co-mingling; when PLA: PEG: g-C3N4 was 6:3:1, the consistency was good. PEG destroys the crystallization of PLA and causes the hardness to decrease. When PLA: PEG: g-C3N4 was 6: 3: 1, it had a maximum hardness of 0.137 GPa. The CPCM had a high latent enthalpy, and endothermic and exothermic enthalpies of 106.1 kJ/kg and 80.05 kJ/kg for the PLA: PEG: g-C3N4 of 3: 6: 1. The CPCM showed an increased thermal conductivity compared to PLA, reaching 0.30 W/(m·K),0.32 W/(m·K) when PLA: PEG: g-C3N4 was 6: 3: 1 and when PLA: PEG: g-C3N4 was 3: 6: 1, respectively. Additionally, the CPCM was stable within 250 °C, indicating a wide appliable temperature range. The CPCM can be applied to solar thermal power generation, transportation, and building construction.

Experimentally based testing of the enthalpy-porosity method for the numerical simulation of phase change of paraffin-type PCMs

The enthalpy-porosity method is generally applied as an economical resort for the numerical simulation of phase change materials (PCMs). However, having been developed strictly for metals, its suitability for the task is unclear, nor is the rationale for assigning its internal parameters, e.g., latent enthalpy and the constant of the momentum source term representing the “mushy” region. We first experimentally and exhaustively characterize a paraffin-type PCM, including differential scanning calorimetry (DSC) at several heating rates, T-history, and fusion visualization. Then, we develop a numerical model and systematically run simulations under different internal parameters and thermophysical properties of the PCM. Simulation results exhibit significant disagreement with experiments that cannot be reduced by any strategy for combining different material properties and model parameters. Among other effects, the constant of the momentum source term, which has to be assigned somewhat arbitrarily, has more relevance in the accuracy than any set of properties obtained by DSC and other experimental techniques. Thus, a rather negative, although interesting, conclusion is suggested: the enthalpy-porosity method may fail to model the phase change of paraffin-type PCMs. This is, of course, of paramount importance for the studies of their utilization in practical systems since it puts a fundamental point of uncertainty in any numerical study or lumped-type model derived thereof. The paper concludes with a tentative discussion of the possible causes of this failure and perspectives for developing more proper models.

Preparation and characteristics of paraffin/silica aerogel composite phase-change materials and their application to cement

In this study, microencapsulated paraffin/silica aerogel composite phase-change materials (MPCMs) were developed and incorporated into cement to impart heat storage/release capabilities. First, the hydrophilically modified MPCMs were subjected to a leakage test. Using a simple stirring method, the composite with an aerogel: paraffin mass ratio of 22:78 was demonstrated to have the best adsorption capacity. Transmission electron microscopy, scanning electron microscopy, Fourier-transform infrared spectroscopy, and X-ray diffraction analyses revealed that the paraffin was stable and physically encapsulated by the aerogel. The differential scanning calorimetry results showed that the encapsulated MPCMs had a fusion latent enthalpy of 94.45 J/g and phase-change temperature range of 20.8–34.4 ℃. The enthalpy was reduced by only 3.87% after 1000 freezing–thawing cycles. In the second part of the experiment, heat-storage cement (HSC) specimens were prepared to investigate the effect of MPCMs modified with silane coupling agents. The proportion of MPCMs and curing temperature were varied, and the effects of these variations on the compressive strengths of HSC stones were investigated. The compressive strength of the HSC samples was improved by adding multiwall carbon nanotubes (MWCNTs) to paraffin to form paraffin/aerogel composite MWCNT micro-encapsulated phase-change materials (CMPCMs). The results show that adding 1.53 wt% MWCNTs increases the thermal conductivity by 50.6% and refines the pore size and strength of the HSC stone. Furthermore, the 7-day strength of the HSC stone increased to 8.6 MPa by adding MWCNTs to 30 wt% modified CMPCM, meeting the requirement standard. Cement hydration calorimetry, performed using a TAM AIR isothermal calorimeter, revealed that MPCMs prolong the induction period of cement hydration, reduce the rate during the acceleration period of cement hydration, and absorb the heat of hydration. Moreover, the thermal regulation behaviour of 10 mm thick HSC plates was tested. The highest temperature difference was determined to be 2.36 ℃ and 1.92 ℃ during the heating and cooling processes, respectively, compared with that of plain cement plate, at the same time. Therefore, HSC panels have potential applications in building thermal management.

Phase Change Materials for Life Science Applications

AbstractPhase change materials (PCMs) are a class of thermo‐responsive materials that can be utilized to trigger a phase transition which gives them thermal energy storage capacity. Any material with a high heat of fusion is referred to as a PCM that is able to provide cutting‐edge thermal storage. PCMs are commercially used in many applications like textile industry, coating, and cold storage typically for heat control. These intriguing substances have recently been rediscovered and employed in a broad range of life science applications, including biological, human body, biomedical, pharmaceutical, food, and agricultural applications. Benefiting from the changes in physicochemical properties during the phase transition makes PCMs also functional for barcoding, detection, and storage. Paraffin wax and polyethylene glycol are the most commonly studied PCMs due to their low toxicity, biocompatibility, high thermal stability, high latent enthalpy, relatively wide transition temperature range, and ease of chemical modification. Current challenges in employing PCMs for life science applications include biosafety and/or engineering difficulties. The focus of this review article is on the life science applications, evaluation, and safety aspects of PCMs. Herein, the advances and the potential of employing PCMs as a versatile platform for various types of life science applications are highlighted.

Development of carbon-coated aluminosilicate nanolayers composite shape-stabilized phase change materials with enhanced photo-thermal conversion and thermal storage

Latent heat thermal energy storage (LHTES) system that centers on organic phase change materials (PCM) is regarded as an efficient strategy for the utilization of solar energy. The leakage problem and insensitivity to the sunlight of organic PCM significantly limit the large-scale application in the solar energy storage field. In the current study, a composite shape-stabilized phase change material (ss-PCM) for solar energy utilization was fabricated by incorporating stearic acid (SA) into the carbon-coated aluminosilicate nanolayers developed through intercalation of kaolinite with potassium acetate and then calcination. The resulting composite ss-PCM without leakage possesses excellent encapsulation ability (63.8%) and high latent enthalpy (132.0 J/g), which are ascribed to the higher specific surface area and pore volume of the carbon-coated aluminosilicate nanolayers, and good compatibility. The photo-thermal conversion efficiency of the final composite ss-PCM is up to 92.1%. After 500 heating-cooling cycles, the number of thermal cycles does not show an apparent effect on the enthalpy of the composite ss-PCM, implying its outstanding thermal cycle stability. The mechanism of leakage proof and photo-thermal conversion performance enhancement of composite ss-PCM were explored. The leakproof ability of composite ss-PCM is not only related to the solid capillary force and surface tension of carbon-coated aluminosilicate nanolayers but also the strong chemical bond between SA molecules and these nanolayers. The carbon layers of the supporting material provide an excellent light absorption property. Hence, this work may offer a new idea for designing and constructing the clay mineral (kaolinite) with a special nanolayer structure for preparing composite ss-PCM with superior photo-thermal conversion and solar energy storage capacity.

Ni@rGO into nickel foam for composite polyethylene glycol and erythritol phase change materials

The exploitation of shape-stabilized composite phase change materials (CPCMs) with high solar-thermal conversion efficiency, thermal storage capacity and thermal conductivity has attractive prospects for solar energy utilization. In this work, reduced graphene oxide (rGO) nanosheets decorated with Ni nanoparticles (Ni@rGO) are successfully filled into the nickel foam (NF) skeletons by acidic graphene oxide solution impregnation and subsequent thermal reduction methods. The obtained NF/Ni@rGO supports with controllable Ni@rGO content are used as the carrier for loading polyethylene glycol (PEG) and erythritol (ET) to prepare CPCMs. The Ni@rGO hybridization enhances the interaction of the carrier framework with the PCM, which can effectively increase the PCM loading and prevent its leakage. As compared with bare NF supported CPCMs, the NF/Ni@rGO supported CPCMs have better shape stability, far higher thermal storage density, and better recyclability. The optimized CPCMs with PEG and ET show high latent enthalpies of 125.30 J·g−1 and 280.66 J·g−1, respectively. It is also found that the thermal conductivity of CPCMs is significantly improved to 0.9199 W·m−1K−1 for NF/Ni@rGO-10/PEG and 0.9146 W·m−1K−1 for NF/Ni@rGO-10/ET, which is 344 % and 35 % higher than that of PEG and ET, respectively. In addition, the decoration of Ni nanoparticles on the rGO support (i.e., NF/Ni@rGO-10) could further improve the thermal conductivity, solar-thermal conversion efficiency (95.74 %) and electro-thermal conversion efficiency (71.39 %) of CPCMs. This research furnishes the basis for the development of high performance CPCMs. Moreover, it has great potential and broad application prospects in the efficient utilization of solar energy and thermal management of electronic devices.

Loading phase change material in a concrete based wall to enhance concrete thermal properties

In this study, energy analysis was performed to improve the thermal behavior of the concrete-based wall of the building in the presence of phase change material (PCM). PCMs have low conductivity, acceptable specific capacity, and high latent enthalpy, which makes them a superior candidate for building applications. Considering the thermal properties of concrete in the range of 100–200 mm, PCM was added to the concrete. At concrete thickness of 100 mm, the impact of PCM was maximized so that the combination of PCM with concrete significantly reduced heat load (by 71.5%) as well as cold load (by 61%). Annual analysis showed that in the concrete thickness of 100 mm–200 mm, the presence of PCM reduces energy demand. At a thickness of 100 mm, the energy consumption was reduced by 64.1% while at the thickness of 150 and 200 mm, energy demand reduction was 59% and 56.8%. Due to loading PCM into concrete, an annual energy-saving of 231.6 kWh/m2 at the concrete thickness of 100 cm was achieved. This value at 150 cm and 200 cm was 176.5 and 156.3 kWh/m2, respectively.

Construction of Three-Dimensional Network Structure in Polyethylene-EPDM-Based Phase Change Materials by Carbon Nanotube with Enhanced Thermal Conductivity, Mechanical Property and Photo-Thermal Conversion Performance.

High thermal conductivity and good mechanical properties are significant for photo-thermal conversion in solar energy utilization. In this work, we constructed a three-dimensional network structure in polyethylene (PE) and ethylene-propylene-diene monomer (EPDM)-based phase change composites by mixing with a carbon nanotube (CNT). Two-dimensional flake expanded graphite in PE-EPDM-based phase change materials and one-dimensional CNT were well mixed to build dense three-dimensional thermal pathways. We show that CNT (5.40%wt)-PE-EPDM phase change composites deliver excellent thermal conductivity (3.11 W m−1 K−1) and mechanical properties, with tensile and bending strength of 10.19 and 21.48 MPa. The melting and freezing temperature of the optimized phase change composites are measured to be 64.5 and 64.2 °C and the melting and freezing latent enthalpy are measured to be 130.3 and 130.5 J g−1. It is found that the composite phase change material with high thermal conductivity is conducive to the rapid storage of solar energy, so as to improve the efficiency of heat collection.

Thermo-physical and mechanical investigation of cementitious composites enhanced with microencapsulated phase change materials for thermal energy storage

This paper reports a comprehensive experimental investigation of cement pastes enhanced with Microencapsulated Phase Change Materials (MPCM) for Thermal Energy Storage (TES) purposes. The experimental plan considers three water-to-binder ratios and three MPCM volume fractions, for a total of nine different MPCM paste mixtures. The water-to-binder ratios of the pastes are 0.33, 0.40 and 0.45, which were mixed with a commercial MPCM, namely Nextek 37D® having a melting/solidification temperature of 37 °C, with volume percentage substitutions of 0%, 20% and 40%, respectively. Thermal, physical and mechanical tests were performed to investigate the effect MPCM have on the resulting TES, strengths and conductive properties of the considered mixtures by employing DSC, Hot-Disk, and mechanical tests. The measured latent heat of MPCM was 197.3 J/g and 194.6 J/g for heating and cooling, respectively. The volumetric latent enthalpies for the MPCM-based composites showed an almost constant average of 20–25 MJ/m3 for samples with 20% MPCM and 55–60 MJ/m3 for samples with 40% MPCM, independently of the w/b ratio. Thermal conductivity values measured at 25 and 45 °C ranged between 0.93 and 0.44 W/m × K. MPCM substitution turned out to significantly affect the overall porosity of the composite resulting in a lower thermal conductivity for the MPCM-pastes in comparison to the plain cement matrix. Finally, mechanical tests were conducted that showed a strength loss due to either increasing w/b ratios or for enhanced amounts of MPCM (e.g., up to a 74% and 69% of strength loss were registered for bending and compression, respectively). The thermo-physical and mechanical characterizations were conducted according to an experimental plan that provided a wide set of research results for both sole MPCM and MPCM-cement systems analyzed by SEM, EDS/elemental mapping, contact angle tests, particle size distribution analysis and Mercury Intrusion Porosimetry technique.

Transforming polymorphs, melting, and boiling during cookoff of PETN

Transforming polymorphs, melting, and boiling are physical processes that can accelerate decomposition rates during cookoff of PETN and make measurements difficult. For example, splashing liquids from large bubbles filled with decomposition products clog pressure tubing in sealed experiments. Boil over can also extinguish thermal excursions in vented experiments making ignition difficult. For better measurements, we have modified the Sandia Instrumented Thermal Ignition (SITI) experiment to obtain better sealed and vented cookoff data for PETN by reducing the sample size and including additional gas space to prevent clogged tubing and boil over. Ignition times were not affected by 1) increasing the gas space by a factor of 3 in sealed SITI experiments or by 2) venting the decomposition gasses. That is, thermal ignition of PETN is not pressure dependent and the rate-limiting step during PETN decomposition likely occurs in the condensed phase. A simple decomposition model was calibrated using these observations and includes rate acceleration caused by melting and boiling. The model is used to predict internal temperatures, pressurization, and thermal ignition in a wide variety of experiments. The model is also used with SITI data to estimate the previously unreported latent enthalpy (5 J/g) associated with the α (PETN-I) to β (PETN-II) polymorphic phase transformation of PETN.

Synthesis and Characteristics of Microencapsulated Decanol with TiO2 Shell as Composites for Cold Energy Storage

A novel microencapsulated phase change materials for cold energy storage was synthesised through sol-gel means using decanol as phase change material and titanium dioxide (TiO2) as encapsulated material. The micromorphology and composition of microcapsules were observed by field emission scanning electron microscope (FE-SEM), Fourier transformation infrared spectrometer (FT-IR).Using differential scanning calorimeter (DSC) and thermogravimetric analyzer (TGA) thermal properties of microcapsules were characterized. Results of FE-SEM and FT-IR indicated that micro sized decanol droplets were encapsulated with TiO2 to form the well-developed core-shell structure, which was only physical coating between them. Furthermore, the chemical and thermal stability of the microcapsules were improved and the inflammability of the microcapsules was lowered using TiO2 as shell material. The DSC result of the desirable ones melt at 3.87 ℃ with a latent melting enthalpy of 61.12 J·g-1 and solidified at – 1.32 ℃ with a latent solidification enthalpy of 59.54 J·g-1. In general, the prepared microcapsules have potential for cold energy storage.

Preparation, characterization and performance of paraffin/sepiolite composites as novel shape-stabilized phase change materials for thermal energy storage

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.

High-Temperature Chloride-Carbonate Phase Change Material: Thermal Performances and Modelling of a Packed Bed Storage System for Concentrating Solar Power Plants

Molten salts eutectics are promising candidates as phase change materials (PCMs) for thermal storage applications, especially considering the possibility to store and release heat at high temperatures. Although many compounds have been proposed for this purpose in the scientific literature, very few data are available regarding actual applications. In particular, there is a lack of information concerning thermal storage at temperatures around 600 °C, necessary for the coupling with a highly efficient Rankine cycle powered by concentrated solar power (CSP) plants. In this contest, the present work deals with a thermophysical behavior investigation of a storage heat exchanger containing a cost-effective and safe ternary eutectic, consisting of sodium chloride, potassium chloride, and sodium carbonate. This material was preliminarily and properly selected and characterized to comply with the necessary melting temperature and latent enthalpy. Then, an indirect heat exchanger was considered for the simulation, assuming aluminum capsules to confine the PCM, thus obtaining the maximum possible heat exchange surface and air at 5 bar as heat transfer fluid (HTF). The modelling was carried out setting the inlet and outlet air temperatures at, respectively, 290 °C and 550 °C, obtaining a realistic storage efficiency of around 0.6. Finally, a conservative investment cost was estimated for the storage system, demonstrating a real possible economic benefit in using these types of materials and heat exchange geometries, with the results varying, according to possible manufacturing prices, in a range from 25 to 40 EUR/kWh.