Thermal Energy Storage Properties Research Articles

Conch shell derived bio-carbon/Paraffin as novel composite phase change material with enhanced thermal energy storage properties for photovoltaic module cooling systems

Phase change materials (PCM)-based photovoltaic module cooling systems (PVCS) are essential in lowering module temperatures and improving overall efficiency. The use of conch shell-based composite PCM in PVCS for improved thermal management has not been reported. This study uses thermally conductive calcium compounds enriched aqua bio-mass based carbonized conch shell porous carbon (CSC) as an organic form stabilizer to produce a composite Paraffin PCM (CPN) and explores its thermal energy storage capabilities for PVCS. The effect of carbonization temperature on the development of CSC frameworks is investigated by assessing morphology, graphitization degree, crystalline nature, functional elements, and surface characteristics. The composite CPN samples are then produced using a vacuum impregnation process with different mass proportions (43:57, 50:50, 57:43, and 64:36) of Paraffin PCM and CSC form stabilizer. Non-carbonized conch shell powder based composite PCM samples are produced using the former process and use as reference samples. The leakage assessment study demonstrates that the composite CPN with a proportion of 64:36 offers better anti-leak tendency before and after thermal cycling. The composite CPN sample is further evaluated for thermal conductivity, phase transition properties, thermal stability, and chemical stability. Experimentation on phase change rate assessment of the composite CPN demonstrates its capability for PVCS. The cycled composite CPN sample possesses a better loading efficiency (90.71 %), enhanced thermal conductivity from 0.214 to 0.433 W/mK, improved thermal stability up to 204oC, melting/freezing energy density (206.3/191.2 J/g), and thermal storage capability (96.82 %), making it a viable anti-leak material for improving PVCS operational performance.

Pickering emulsions stabilized by cellulose nanofibers with tunable surface properties for thermal energy storage

Cellulose nanofibers (CNFs) have been widely used as a renewable emulsifier to stabilize two immiscible liquids due to their intrinsic amphiphilicity and excellent emulsifying ability. However, it remains challenging to fully understand the effects of carboxylate group content and surface charge density on the emulsifying ability of CNFs and the stability of Pickering emulsion. Herein, carboxymethylated CNFs were extracted from bleached kraft pulp using etherification reaction and high-pressure homogenization, allowing for easy surface charge density and size adjustment by changing sodium chloroacetate content and homogenization cycles. The optimizing CNFs possessed a high Zeta potential (−71.2 mV) and a suitable carboxylate group content (1.81 mmol/g), which enabled CNFs to irreversibly adsorb at the hydrophobic paraffin wax (PW) droplet surface and form interfacial steric barriers, providing large electrostatic repulsion between the PW droplets against coalescence. Thus, the CNF-stabilized PW emulsions could be stored for more than 6 months. Moreover, the phase change enthalpy of the freeze-dried emulsion is as high as 193.7 J/g, which provides the emulsion to reversibly store and release heat. This work provides a comprehensive insight into the interfacial stability mechanism of CNFs as stabilizers and facilitates the potential application in thermal energy storage.

Ag nanowires modified expanded graphite based composite phase change materials with enhanced thermal conductivity, light/electro-to-thermal performances

Phase change materials with excellent thermal energy storage property displayed great potential application in many fields, such as lithium battery thermal management, energy saving building and waste heat utilization. In this paper, a novel composite phase change material of Ag nanowires modified expanded graphite/lauric-myristic-palmitic acid (AgNWs@EG/LMP) with the function of photo/electro-thermal conversion property was prepared which the AgNWs@EG was acted as the matrix material and LMP was the phase change material. The composite exhibited high latent heat of 118.42 J/g at the phase change temperature of 33.62 °C with the LMP supporting ratio of 76.18%. The thermal conductivity of AgNWs@EG/LMP reached 4.23 W/(m∙K) which enhanced 1914% than that of LMP. The photo-thermal conversion efficiency reached 88.01% and the electro-thermal conversion efficiency was 65.4% with an input voltage of 1.5 V. Further results showed the composite AgNWs@EG/LMP possessed good chemical compatibility, good thermal stability and reliability. Therefore, the novel composite of AgNWs@EG/LMP with good thermal property and multi-energy conversion functions will process potential application in energy storage system and thermal management fields.

Green building material with superior thermal insulation and energy storage properties fabricated by Paraffin and foam cement composite

In the field of architecture and construction, foam cement has been gradually gaining popularity due to its outstanding attributes of reduced weight, carbon footprint, and potential thermal insulation effects. However, relying solely on the thermal insulation provided by the foam in foam cement lacks the capability to store and release heat. In this paper, a novel approach is proposed by directly incorporating paraffin into foam cement with non-continuous pores, creating a phase change foam cement. The addition of paraffin to foam cement, facilitated by the presence of surfactants in foam, allows the paraffin to disperse. In contrast, if paraffin is directly added to cement without the foam, it tends to aggregate. The internal pore structure, thermal performance, phase change temperature, and relaxation distributions were investigated through equipment such as scanning electron microscope (SEM), thermal conductivity meter, differential scanning calorimetry (DSC), and H1 nuclear magnetic resonance (NMR). Results indicate that paraffin/foam cement plays a dual function, effectively storing and releasing energy, significantly enhancing its thermal insulation performance. Particularly, the incorporation of 10 vol% paraffin content results in a notable 21.8 % reduction in the thermal conductivity, for foam cement with a density of 600 kg/m3. This is attributed to the heat storage capability of the phase-change paraffin, which absorbs heat as the surrounding temperature rises, synergistically collaborating with the foam. This presents a novel perspective for the development of green and energy-efficient building materials, contributing to the realization of sustainable energy utilization in the construction industry.

Advancing thermal control in buildings with innovative cementitious mortar and recycled expanded glass/n-octadecane phase change material composites

This study delves into the role of phase change materials (PCMs) in bolstering energy efficiency, particularly in response to escalating global energy consumption in construction. The research focuses on integrating recycled expanded glass (REG) as a support material for shape-stabilized PCMs, specifically emphasizing n-octadecane (nOD) in cement mortars. With nOD exhibiting a melting point around 27 °C and a high latent heat thermal energy storage (TES) capacity of 241 J/g, various analyses, including DSC, FT-IR, SEM, TGA, and thermoregulation tests, assess the impact of different nOD/REG concentrations on TES properties. Alterations in physico-mechanical properties of mortar mixtures are noted with increasing REG/nOD content, impacting porosity and water absorption. The incorporation of REG/nOD PCMs decreases thermal conductivity, from 0.3620 W/mK (no PCM) to 0.1494 W/mK (full replacement). Thermo-regulation tests highlight PCM’s ability to counteract temperature fluctuations, surpassing results from other studies. Temperature difference outcomes (−10.60 °C daytime cooling, 4.00 °C nighttime heating) establish REG/nOD as promising for sustainable construction. The research evaluates PCM-infused concrete’s impact on building energy efficiency, noting significant heat demand reductions across climates and wall thicknesses. Carbon emissions decrease notably, especially with coal as the fuel source. Customized material thickness in PCM-integrated walls shows potential for substantial energy savings. These findings contribute valuable insights to the viability of REG/nOD composites in mitigating heating and cooling loads, advancing sustainable building solutions.

Preparation and Properties of a Composite Carbon Foam, as Energy Storage and EMI Shield Additive, for Advanced Cement or Gypsum Boards

This article explores the cutting-edge advancement of gypsum or cement building boards infused with shape-stabilized n-octadecane, an organic phase change material (PCM). The primary focus is on improving energy efficiency and providing electromagnetic interference (EMI) shielding capabilities for contemporary buildings. This research investigates the integration of these materials into construction materials, using red-mud carbon foam (CCF) as a stabilizer for n-octadecane (OD@CCF). Various analyses, including microstructural examination, porosity, and additive dispersion assessment, were conducted using X-ray microtomography and density measurements. Thermal conductivity measurements demonstrated the enhancement of composite boards as the OD@CCF content increased, while mechanical tests indicated an optimal additive content of up to 20%. The thermally regulated capabilities of these advanced panels were evaluated in a custom-designed room model, equipped with a homemade environmental chamber, ensuring a consistent temperature environment during heating and cooling cycles. The incorporation of OD@CCF into cement boards exhibited improved thermal energy storage properties. Moreover, the examined composite boards displayed efficient electromagnetic shielding performance within the frequency range of 3.2–7.0 GHz, achieving EMI values of approximately 18 and 19.5 dB for gypsum and cement boards, respectively, meeting the minimum value necessary for industrial applications.

Polymer‐based supporting materials and polymer‐encapsulated phase change materials for thermal energy storage: A review on the recent advances of materials, synthesis, and characterization techniques

AbstractPhase change materials (PCMs) can be classified as smart materials having its applications in varied fields like domestic and commercial refrigerators, solar absorption chillers, air conditioning, free and radiative cooling, solar air heaters, solar stills, solar absorption cooling, electric and electronic devices for cooling purposes and in textiles. Here, in this review, the various polymer‐based and encapsulated PCMs used for fulfilling the above applications are discussed along with their varied synthesis/fabrication methods. Furthermore, chemical characterization is discussed by FTIR for understanding the chemical structure along with functional groups present in the materials. The thermogravimetric analysis (TGA) is also critically discussed for understanding the thermal stability of the Polymer PCM or the phase change composites and the latent heat of PCM melting was also explored by differential scanning calorimetry (DSC) for various PCM which gives insight into the thermal energy storage capability and property. The inbuilt surface structure of the polymer PCM was also tried to be investigated by scanning electron microscopy (SEM) which when understood gives a clear picture about the structure–property relationship.Highlights Polymeric supporting materials and polymer encapsulation on PCM were reviewed. The materials used and the synthesis of polymeric PCM were studied in depth. Chemical characterization was reviewed for chemical structure. Thermal stability checks by TGA and latent heat prediction was done by DSC. Morphology was reviewed using SEM for the structure–property relationship.

Enhancing sustainability with waste hemp-shive and phase change material: Novel gypsum-based composites with advanced thermal energy storage properties

This study addresses the rising demand for sustainable construction by introducing composite materials from natural and renewable resources: gypsum, hemp, and phase change materials (PCMs). These materials cater to the growing preference for eco-friendly building solutions. Incorporating hemp enhances sustainability while integrating PCMs into the porous hemp structure ensures adequate thermal energy storage and release without leakage. Firstly, the agricultural waste hemp shives and lauryl alcohol (LA) PCM were mixed to create shape-stabilized hemp/PCM composites. The highest PCM ratio was determined in shape-stabilized composites exhibiting non-leakage properties, which was 45 wt %. These composites were then incorporated into gypsum materials at loadings of 7.5 %, 15 %, 22.5 %, and 35 wt % to produce the final composites. Morphological, thermal, and chemical characteristics of shape-stabilized composites were examined using SEM, TGA, and DSC, while the solar thermoregulation tests assessed the gypsum matrix composites. The phase change temperature of PCM was determined as 20.24 °C with a melting enthalpy value of 224.4 J/g. The hemp/PCM shape-stabilized composites demonstrated an impressive melting enthalpy value of 100.2 J/g, with only a slight reduction to 99.5 J/g after 750 test cycles. When the ambient temperature exceeded 50 °C, the central temperature of the cabins containing PCM composites was found to be at least 4 °C cooler than those containing only gypsum. Conversely, when the ambient temperature dropped to around 20 °C, it was observed that the central temperature of the cabins with PCM composites was approximately 2 °C warmer than those with only gypsum. This study introduces a novel approach to creating environmentally friendly gypsum/hemp/PCM composites for thermal energy storage systems.

Excellent interfacial compatibility of phase change capsules/polyurethane foam with enhanced mechanical and thermal insulation properties for thermal energy storage

The incorporation of phase change microcapsule (microPCMs) substantially augmented the temperature regulation capacity of foams, endowing it with outstanding application potential in numerous industrial domains. However, interfacial compatibility issues between the capsule and the substrate always exist and affect foam performance. In this study, a milli-meter macrocapsule (macroPCMs) containing microPCMs was prepared using calcium alginate gel as the second layer wall to physically improve the interfacial compatibility. And poly (N-hydroxymethyl acrylamide) was in situ polymerized in the gel layer and provided active alcohol hydroxyl groups to form chemical grafting with the polyurethane raw materials, which further chemically improved the interfacial compatibility. These measures created a significantly improved foam microstructure and a greatly increased foaming capacity, which thus endow the composite foam with excellent thermal insulation performance and mechanical strength. Compared with conventional microPCMs-based foam, the foaming capacity of the macroPCMs-based foam increased by 40 folds, the temperature regulation duration increased by 7 folds, and the mechanical performance increased by 3 folds. Moreover, the insulated incubator fabricated with the macroPCMs-based foam exhibited two-fold greater thermal insulation efficiency than conventional models containing internal ice incubator, which validated the potential of employing macroPCMs-based polyurethane foam in cold chain logistics applications.

Effects of graphene doping on shape stabilization, thermal energy storage and thermal conductivity properties of PolyHIPE/PEG composites

The development of clean and renewable energy sources has been necessitated by the ever-increasing energy consumption, increasing environmental degradation caused using fossil fuels and concerns over the rise in CO2 spreading. Functional phase change materials (PCMs)' energy storage capacity is appealing owing to their environmental friendliness, superior thermal energy storage (TES) capacity, and capability to improve energy efficiency. A series of hierarchical porous high internal phase emulsion polymer (PolyHIPE) materials with high PCM impregnation capacity were synthesized in this investigation. It has been achieved to encapsulate 80 % by mass of polyethylene glycol (PEG) into the PolyHIPE structure. However, the efficiency of energy storage and conversion systems is affected by a wide variety of factors; one of them is poor thermal conductivity. The development of carbon-based materials like graphene is particularly promising in the disciplines of energy storage and conversion. With this intention, the synthesis of composite PCMs in which the heat conductivity has been enhanced with graphene at three different ratios (wt% 3, 5, and 10) has been performed, conducting comprehensive investigations. The produced composite PCMs have an energy storage capability of over 120 J·g−1 and high thermal and structural stability. In the polyHIPE/graphene structures produced in the absence PCM, the thermal conductivity value exhibits a notable enhancement of up to 125 % due to the increased amount of graphene compared to the polyHIPE material. Following the impregnation of PolyHIPE@Graphene with PEG, it was observed that the thermal conductivity value improved by up to 51.2 % in comparison to PCM. The addition of graphene also gradually shortened the heat storage-release time. In short, herein a series of PCM composites with high energy storage capacity, capable of trapping different PCMs within their structure, has been proposed for TES applications. The manufactured composite PCMs have the potential to be used for a wide range of things, like maintaining the temperature of batteries and photovoltaic solar cells, packaging perishable foods, and providing thermal comfort in textiles and medicinal materials.

Investigation on low-carbon shape-stable phase change composite by steel slag and carbide slag for solar thermal energy storage

Resources utilization of a variety of industrial solid wastes including steel slag (SS) and carbide slag (CS) is an effective measure that reduces environmental destruction and greenhouse gas emissions. In this work, seven shape-stable phase change materials (SSPCMs) with different mass fractions were prepared by cold compression-hot sintering (CCHS) method utilizing SS and CS as the skeleton material (SM) and NaNO3 as the phase change material (PCM). Research on critical properties of SSPCMs including thermal energy storage properties, microscopic morphology, mechanical properties, chemical compatibility, and economic properties was undertaken. Results indicated that various properties were optimized when the mass ratio of SS, CS, and NaNO3 was 2.5:2.5:5 (SC4). The mechanical strength of sample SC4 was 131.2 MPa, and the optimum thermal energy storage (TES) density in the temperature range of 100 °C–400 °C was 371.1 J/g. The maximum thermal conductivity of sample SC4 was 1.263 W/(m·K) after 1307 heating and cooling cycles. The sample SC4 exhibited favorable chemical compatibility and the elements were uniformly distributed in the sample SC4.

Mitigating supercooling in microencapsulated phase change materials by incorporating compatible polyethylene wax as a nucleating agent

Microencapsulated phase change materials (MicroPCMs) have been investigated as thermal storage materials for decades, due to their benefits in storage container protection and PCM leakage prevention. For improved thermal storage properties, the elimination of supercooling, where the micro-sized PCMs crystallize at temperatures significantly below their designated melting point, or over a broad temperature range, has been targeted in many researches. However, most successful methods either compromise the protective shell or reduce the storage enthalpy. In this work, a relatively high-melting-point polyethylene wax (PE-W) that exhibits good compatibility with PCM n-octadecane (n-Oct) was introduced to mitigate the supercooling. MicroPCMs containing n-Oct core materials incorporated with PE-W, were prepared using emulsion polymerization, resulting in cross-linked shell poly(methyl methacrylate-co-allyl methacrylate) denoted as P(MMA-co-AMA). The MicroPCMs with PE-W present consistent sizes ranging from 1 to 5.5 μm, maintained a regular spherical shape, and retained uniform morphologies. The quantity incorporated is exceptionally minimal, constituting merely 2.5 ‰, owing to the effective dispersion, which arises from their intrinsic compatibility. The addition of PE-W nucleating agent significantly reduced the degree of supercooling from 8.0 °C for reference MicroPCM to 1.7 °C for MicroPCM with PE-W. Additionally, the enthalpy associated with heterogeneous nucleation saw a substantial increase, rising from 0% in the reference MicroPCM to 58% in that containing PE-W. The heat resistance of MicroPCM encapsulated by P(MMA-co-AMA) has been greatly improved by 90 °C. The endurance of the MicroPCM highlights the remarkable durability and the sustained effectiveness of PE-W in eliminating supercooling over 100 heating and cooling cycles. Furthermore, in a thermal load scenario, the MicroPCM demonstrated exceptional thermal storage and protective characteristics. The outstanding thermal energy storage properties make them promising candidates for use in textiles, preservation, and transportation applications.

Preparation and thermal energy storage properties of shaped composite phase change materials with highly aligned honeycomb BN aerogel by freeze-vacuum drying under the control of a temperature gradient

Preparation and thermal energy storage properties of shaped composite phase change materials with highly aligned honeycomb BN aerogel by freeze-vacuum drying under the control of a temperature gradient

Optimization of PCM Properties for Thermal Energy Storage in Solar Parabolic Trough Systems: A Review

Abstract: Solar Parabolic Trough Systems (PTS) are highly efficient solar thermal technologies for converting concentrated solar radiation into thermal energy. However, their intermittent energy production, primarily due to variations in solar availability, underscores the necessity for effective thermal energy storage (TES) solutions. Phase Change Materials (PCMs) have emerged as a promising means to store and release thermal energy efficiently. This study focuses on the critical task of optimizing PCM properties to enhance thermal energy storage within Solar Parabolic Trough Systems. The selection and fine-tuning of PCM properties are paramount to achieving superior TES performance. Parameters under scrutiny include the melting temperature, latent heat of fusion, thermal conductivity, and cost-effectiveness. Each of these factors plays a pivotal role in the overall efficiency and economic viability of PCM-based TES systems integrated with PTS. Through a thorough review of existing research and recent advancements in the field, this study sheds light on the profound impact of tailored PCM properties. It demonstrates how optimizing these properties can lead to substantial improvements in energy storage capacity, system efficiency, and overall cost-effectiveness. Such optimizations are crucial not only for enhancing the competitiveness of solar thermal technology but also for promoting sustainable energy utilization. The investigation presented herein underscores the significance of PCM property optimization as a strategic pathway toward advancing solar thermal technology. By maximizing energy storage capacity, minimizing thermal losses, and optimizing cost factors, we can unlock the full potential of PTS, making them more reliable and accessible for meeting the world's growing energy demands. This research serves as a valuable resource for engineers, researchers, and stakeholders working towards the integration of PCM-based TES with solar thermal systems. Ultimately, it contributes to the realization of a cleaner, more sustainable energy future, addressing the urgent need to reduce greenhouse gas emissions and our reliance on non-renewable energy sources

Charging characteristics of finned thermal energy storage tube under variable rotation

Solar photovoltaic-thermal (PVT) systems effectively offset the drawbacks of intermittent solar and low photovoltaic conversion efficiency. Thermal energy storage (TES) tanks of PVT systems with high charging efficiency and consistent thermal safety might achieve efficient utilization of solar energy for building. A new variable rotational strategy has been proposed to optimize the charging characteristics for TES tubes, taking into consideration the non-uniformity of melting. A series of simulations based on the volume-averaged model are conducted to investigate the thermal energy storage property of TES tubes under variable rotary mechanism. Qualitative and quantitative comparisons are made between variable rotation (ω = 1.5–0.5, 1.5–1.0, 1.5–2.0 rad·s−1), constant rotation (ω = 1.5 rad·s−1), and stationary systems. The focus of the comparison is melting efficiency, temperature distribution, and natural convection. The results indicate that rotation effectively shortens charging time, with a 57.62% and 15.73% reduction with variable rotary mechanisms of 1.5–1.0 rad·s−1 when compared with stationary and constant rotating tubes. Meanwhile, in the final moment, the greatest medium-temperature (55–65 °C) proportion of 90.58% and less low-temperature (25–55 °C) and high-temperature (65–70 °C) paraffin occupation of 4.67% and 4.75% could be obtained, reflecting the completed latent heat storage and stable thermal safety. The optimal variable rotation achieves improvements of 47.84% and 106.73% in time-integral Grashof number (Gr) and heat storage rate, compared with traditional stationary tubes.

Developing Wallpaper/Dodecyl alcohol composite phase change materials as new kind of wall covering elements for building interior thermoregulation

This study introduces a novel wall-covering element consisting of wallpapers (WP) impregnated with Phase Change Material (PCM), with the aim of enhancing thermal properties and providing effective thermal regulation performance in interior spaces. The study conducts practical investigations into the thermal attributes of wallpapers (WPs) impregnated with Dodecyl alcohol (DDA) as the chosen PCM, culminating in a leakage-free WP/DDA wall covering element. The process of impregnating involved applying liquid DDA to the back side of the WP using a manual coating apparatus. Four distinct DDA ratios, ranging from 0% to 20% by mass of WP, were applied. The chemical compatibility of the developed WP/DDA composite was explored using Fourier Infrared Spectroscopy (FTIR). The thermal energy storage (TES) properties were assessed through Differential Scanning Calorimeter (DSC) analysis, and the thermo-regulative performance of the WP/DDA composite was evaluated in laboratory-scale test rooms under real weather conditions. The DSCoutcomesexposed that melting temperature and latent heat capacity of WP/DDA were 21.78 °C and 26.9 J/g, respectively.The thermoregulation tests showed that the prepared WP/DDAsignificantly reduce interior room temperature fluctuation and can maintain indoor temperature longer in comfortable temperature ranges. The largest difference between the reference room and test room was observed to be about 2℃. The room temperature was cooler for about 9 h 53 min during day times for the DDA case.The results designated that the developed WP/DDA composite could be evaluated as a promising new kind of building wall covering element for reducing the cooling load of room.

Studies on the thermal characteristics of nano-enhanced paraffin wax phase change material (PCM) for thermal storage applications

The purpose of this research is to improve the thermal energy storage properties of paraffin wax by adding nanoparticles, such as Multi-Walled Carbon Nanotubes (MWCNTs) and nano SiO2.Dispersing MWNCTs and SiO2 nanoparticles at weight percentages of 0.5 and 1.0 respectively, in paraffin wax resulted in mono and hybrid nanoparticles enhanced PCM (HnPCMs). Transmission Electron Microscopy, Field Emission Scanning Electron Microscopy, and X-ray Diffraction were used to characterize the nanoparticles and fabricated PCMS. Differential Scanning Calorimetry, Thermogravimetric Analysis, and Thermal Conductivity Measurement are employed to investigate how hybrid nanoparticles impact the thermo physical characteristics of paraffin wax. The weight fraction of nanoparticles dispersed in the PCMs is directly proportional to the improvement of the heat conductivity of the composite. To get the most benefit from an increase in thermal conductivity, use a weight fraction of hybrid nanoparticles that is equal to or >1 %. The results of the analysis indicate that the fusion of SiO2 and MWNCTs nanoparticles with paraffin wax was homogeneous and the nanoparticles enhanced the thermal conductivity of the paraffin wax to 32 %, 40 %, and 46 %, respectively with HnPCM 2 to HnPCM 4. The melting and solidification temperatures of PCM can be lowered and raised, respectively, by dispersing nanoparticles, as demonstrated experimentally. Other properties, such as latent heat, specific heat, and viscosity may be impacted by the dispersion of excessive nanoparticles. These promising findings demonstrated that nanoparticles, specifically MWCNT and SiO2 might be employed to improve paraffin wax's thermal characteristics for thermal energy storage.

Preparation of novel hollow metal organic framework for enhancing flame retardancy of paraffin/EP thermal energy storage materials

AbstractParaffin is a potential thermal energy storage material, but leakage and flammability are the two major problems affecting its storage and safe use. Here, a novel flame retarded paraffin/epoxy resin composite was developed by using paraffin, epoxy resin and hollow metal organic framework (W‐UiO66‐PPA) as thermal energy storage material, supporting material and flame retardant, respectively. The thermal energy storage and flame retardancy performances were examined with differential scanning calorimetry, vertical burning, limiting oxygen index and cone calorimeter tests. The results show that the paraffin/epoxy resin retains intact without leakage when the content of paraffin reaches 40 wt%, and this material exhibits high melting latent heat and remarkable thermal recycling property. In addition, the flame retarded paraffin/epoxy resin shows excellent flame retardancy, which is attributed to the following three aspects: (1) the hollow structure with open vertices of W‐UiO66 is capable of absorbing and collecting the combustible gasses produced by the combustion of epoxy resin; (2) the Zr and W elements of W‐UiO66 can facilitate catalytic charring and form a dense char layer; (3) phosphorous‐containing free radicals are able to capture OH· and O· free radicals during the combustion of paraffin and epoxy resin, thus interrupting the combustion chain reaction. On the whole, the flame retarded paraffin/EP possesses excellent thermal energy storage, thermal recycling, and flame retardancy properties. Our work provides a fantastic inspiration for the rational design of other flame retarded form‐stable phase change materials.

Improved thermal, dielectric, and mechanical properties of acrylate composites with diethylene glycol and silane-treated ternary hybrid fillers via three-dimensional vat photopolymerization

Rapid advances in electronic devices have led to the production of highly integrated structures, which are prone to the thermal accumulation problem. Accordingly, polymer-based composites have been introduced to solve the thermal dissipation problem and endow energy storage properties. In this study, an acrylate polymer-based composite with boron nitride (BN), barium titanate (BT), and carbon nanotubes (CNTs) ternary fillers was fabricated via three-dimensional (3D) vat photopolymerization (VPP). To improve the processability of the printing, diethylene glycol (DEG) was added as a viscosity reducer, and ternary fillers were surface-treated with silane functional groups. The surface-treated ternary composite improved tensile strength, thermal conductivity, and dielectric constant compared to a composite composed of raw ternary fillers. Furthermore, the composites with silane-treated BN and CNTs showed thermal conductivity of 2.796 W/(m∙K) and thermal conductivity enhancement of 1153% compared to the acrylate matrix. The dielectric constants and electrical insulation of the composites were also investigated. The proposed method ushers a new era in polymer-based composites with improved thermal conductivity and energy storage properties as well as desired and controlled complex structures through swift and sophisticated 3D VPP printing.

Nanoadditives induced enhancement of thermal energy storage properties of molten salt: Insights from experiments and molecular dynamics simulations

Current concentrated solar power (CSP) plants use molten salts as heat storage and heat transfer medium. The thermal property enhancement of molten salts can increase the efficiency and lower the investment cost of CSP plants. In this study, the experiments and molecular dynamics (MD) simulations were employed to investigate the effect of doping Al2O3, SiO2 nanoparticles or multi-walled carbon nanotubes (MWCNTs) on the specific heat capacity (SHC) of ternary carbonate salt. The results show that the SHC of molten salt can be enhanced by adding nanoadditives. The addition of MWCNTs has the largest SHC enhancement in both solid and liquid states. Based on MD simulations, the radial distribution functions, number density distribution and vibrational density of states were further analyzed to reveal the effect of nanoadditive, base salt and interface thermal resistance between them on SHC at different temperatures. It is found that the nanoadditive agglomeration, the ion spacing of base salt, and the thermal resistance between base salt and nanoadditive is independent on temperature and cannot result in the enhanced SHC of liquid nanocomposites. Moreover, the thickness of interfacial layer changes with temperature. The thicker interfacial layer leads to the higher SHC of liquid nanocomposites. The interfacial layer also has a decisive influence on SHC of solid nanocomposites. The scanning electron microscopy images show that the layered, needle-like, and network-like interfacial layers are observed in Al2O3, SiO2 and MWCNT nanocomposites, respectively. The present findings are helpful to understand the mechanisms governing thermal energy storage, and provide guidelines for the performance optimization of molten salt based nanocomposites.