Thermal Energy Storage Applications Research Articles

Transient Thermal Performance of Phase-Change Material Infused in Cellular Materials Based on Different Unit Cell Topologies

Abstract Phase change material (PCM) employment in thermal management and energy storage applications is limited due to their inherently low thermal conductivity. Significant enhancement in the thermal performance of PCMs can be obtained when infused in porous media with high porosity and high solid-phase thermal conductivity. Earlier studies typically employ high porosity aluminum foams obtained via a conventional manufacturing process, commonly known as foaming. A typical representative unit cell of metal foams obtained via foaming process can be of tetrakaidecahedron shape. The conventional manufacturing process of high porosity metal foams offers limited flexibility over unit cell shape, porosity, and pore density. Metal additive manufacturing advancements have the potential to address this manufacturing limitation and provides freedom in the above design domain. To this end, we have explored four different unit cell topologies, viz., octet, tetrakaidecahedron, face-diagonal cube, and cube, for their role in enhancing the transient thermal performance when infused with PCMs. An enthalpy-porosity method has been employed to model the phase-change process for wide range of variables. It has been found that the presence of solid media results in significant enhancement in PCM's thermal performance, and the Octet-shaped unit cell outperformed the other unit cell topologies explored in this study.

Preparation and thermal properties of a novel ternary molten salt/expanded graphite thermal storage material

In thermal energy storage, the use of phase change materials (PCM) is a very efficient energy storage method. In the field of medium temperature thermal storage, nitrate PCM have always been a research hotspot, but their relatively high melting point and relatively low latent heat of phase change severely limit their application in thermal energy storage. In this paper, LiNO3 and NaCl with higher latent heat value were selected to improve the thermal properties of nitrate. A novel ternary mixed molten salt of NaNO3-LiNO3-NaCl with high latent heat was prepared and studied. NaNO3-LiNO3-NaCl/EG composite phase change material (CPCM) was prepared by selecting expanded graphite (EG) with a large thermal conductivity as the carrier adsorption material for molten salt. The thermophysical properties, thermal stability, and heat transfer ability of PCM and CPCM were tested. The composition and microstructure of the materials were also characterized. The experimental results showed that compared with pure NaNO3, the phase change temperature of NaNO3-LiNO3-NaCl was reduced by 45.3 °C, and the latent heat of phase change was increased by 59.4 J/g. NaNO3, LiNO3, NaCl and EG had good compatibility, without chemical reaction between them. From the microscopic morphology of the composite material, it can be seen that the PCM was uniformly dispersed into the porous structure of EG without agglomeration. The ternary new molten salt had higher thermal decomposition temperature and better thermal stability. When the addition ratio of EG was 20 %, the thermal conductivity of the ternary molten salt increased from 1.350 to 5.017 W/m·K. EG greatly improved the heat transfer capacity of PCM. And the PCM added with EG still had a high latent heat of phase change. The results show that NaNO3-LiNO3-NaCl/EG has broad application prospects in the field of medium and high temperature heat storage.

A Copolymer of Monomethoxy Poly(ethylene glycol)‐Polycaprolactone as Form‐Stable Phase Change Materials for Thermal Energy Storage

AbstractIn this work, a series of monomethoxy poly(ethylene glycol)‐polycaprolactone (mPEG‐PCL) copolymers with different mass percentages of mPEG was chemically synthesized as form‐stable phase change materials (FSPCMs) for thermal energy storage (TES) application for the first time. Their chemical structures, surface morphology, and thermal properties were studied in terms of nuclear magnetic resonance (NMR), Fourier transform infrared spectroscopy (FTIR), scanning electron microscopy (SEM), thermogravimetric analysis (TGA), and differential scanning calorimetry (DSC). 1H NMR, gel permeation chromatography (GPC), and FTIR results confirmed the successful ring‐opening polymerization of ϵ‐caprolactone with mPEG macromonomer, and the respective average molecular weight of the copolymers was obtained in the range of 9704–17346 g mol−1. DSC analysis results revealed that the copolymers have a phase change temperature and latent heat in the range of 52.8–57.9 °C and 88.8–114.4 J g−1 respectively and TGA analysis showed that they are thermally stable up to 150 °C. Leakage test results showed that the copolymers (mPEG)x‐(PCL)y displayed excellent form stability with minimal leakage while thermal cycling revealed good thermal reliability. In addition, the copolymers successfully demonstrated their ability to store and release heat for a prolonged period, making them suitable for TES applications like heating water storage tanks.

Synthesis, characterization and determination of thermal properties of shape stabilized n-pentadecane based composite phase change materials including graphitic carbon nitride/alumina fillers for latent heat storage applications

Recently, Phase Change Materials (PCMs) has attracted significant interest for thermal energy storage (TES), which is a rational and convenient energy storage method. In the present work, new composite PCMs were prepared by performing easy impregnation process in which n-pentadecane was selected as PCM. For this, emulsion templated porous polymer composites were synthesized and employed as the frameworks to obtain new composite PCMs. To improve the heat transfer characteristics, the support matrices were prepared by loading of 1 wt% thermal conduction enhancer fillers namely, graphitic carbon nitride (g-C3N4), graphitic carbon nitride/alumina (g-C3N4/Al2O3) and alumina (Al2O3). The chemical structure, thermal stability and specific surface area characteristics of the frameworks were examined by Fourier Transform Infrared Spectroscopy (FTIR), Thermogravimetry (TG) and Brunauer–Emmet–Teller (BET) surface area analyses. Furthermore, the morphology and distribution of the fillers were explored with Scanning Electron Microscopy (SEM) and energy dispersive X-ray spectroscopy (EDX). Additionally, improvements in the thermal conduction properties of the composite matrices were determined through the tests performed based on the T-history method. Moreover, the examinations on the thermal properties of the obtained composite PCMs were carried out using Differential Scanning Calorimetry (DSC). It was found that the reductions in supercooling temperatures (ΔT) were observed for the synthesized composite PCMs compared to degree of supercooling of pristine n-pentadecane. According to the obtained results, the synthesized composite PCMs can be employed in the cold thermal energy storage (TES) applications considering their appropriate properties and favorable TES capacities between 79.49 kJ/kg and 121.50 kJ/kg.

Experimental investigation for thermal performance of various heat sinks by alumina RT-70HC (NsPCM): Sustainable approach for thermal energy storage applications

This article explores the thermal management of three heat sinks with multiple topologies, such as the unfinned heat sink (US1), the square-finned heat sink (SS2) and the metallic porous foam-based heat sink (PFS3). The goal is to enhance their overall performance using smart nanomaterials to strengthen PCMs thermal conductivity with Al2O3/RT70HC, (NsPCM), under different transient heating loads (10–30 W) and varying nanomaterials saturation levels between 0.15 and 0.25 wt%. The results showed that the insertion of NsPCM lowered the bottom temperature of all heat sinks. The thermal performance of PFS3 was even better than US1 and SS2 at all Al2O3 saturation and heating loads, lowering the bottom temperature and achieving critical operational temperatures of 55 °C and 70 °C effectively. PFS3 has the highest surface area to volume ratio, exceptional thermal conductivity, and superior weight advantage compared to pin fin heat sinks. However, other highly conductive metallic foams instead of copper foam may be tested to avoid oxidation with alumina nanomaterials and enhance heat transfer. Therefore, adding nanomaterials into PCM is highly encouraged for sustainable advancement in electronic thermal management.

Preparation and characterization of lauric acid-stearic acid/fumed silica/expanded graphite thermally conductive enhanced composites

Fatty acid and fatty acid blend phase change materials (PCM) have issues with easy leakage and low thermal conductivity in thermal storage and exothermic processes. To overcome this issue, a novel low-temperature composite material, Lauric acid - stearic acid - fumed silica - expanded graphite (LA-SA-FS-EG), was fabricated by vacuum impregnation technique using lauric acid-stearic acid (LA-SA) as the phase change material (PCM), fumed silica (FS) as the support material, and expanded graphite (EG) as the thermal conductive material. Leakage tests indicated that the maximum adsorption of LA-SA by fumed silica was 75 wt%. Scanning electron microscopy (SEM) was employed to observe the microscopic morphology of the composites. The crystal structure and chemical composition of the composites were analyzed by X-ray diffraction (XRD) and Fourier infrared spectroscopy (FT-IR). The differential scanning calorimeter (DSC) data indicates that the melting temperatures of LA-SA-FS-EG 3 %, 5 % and 7 % were 33.38 °C, 33.32 °C and 33.13 °C respectively, with melting latent heats of 110.8 J/g, 114.3 J/g and 119.9 J/g, respectively. The thermal conductivity of LA-SA-FS-EG 7 % is improved by 454 % compared to the LA-SA-FS composite without the addition of EG. LA-SA-FS-EG7% composite showed excellent heat storage capacity. LA-SA-FS-EG7% has a 46.1 % increase in heat storage rate and a 59.4 % increase in thermal release rate compared to LA-SA-FS composite. Notably, the LA-SA-FS-EG7% composite retains good thermal properties even after 1000 heating and cooling cycles. Consequently, the LA-SA-FS-EG7% composites produced have potential applications in thermal energy storage and building energy efficiency.

Experimental analysis on thermal energy storage performance of micro-encapsulated stearic acid and stearyl alcohol PCM slurries; A comparative study

This study examined the thermal performance of a slurry containing micro-encapsulated phase change materials (me-PCMs) for thermal energy storage (TES) applications such as solar thermal or PVT systems. Specifically, the study focused on stearic acid (SAC) and stearyl alcohol (SAL) as the phase change materials, dispersed within an ethylene glycol aqueous solution. The research revealed that increasing the concentration of PCM in the slurry led to improved latent heat energies for both micro-encapsulated stearic acid (me-SAC) and micro-encapsulated stearyl alcohol (me-SAL) slurries during melting and solidification processes. Moreover, me-SAL slurries exhibited higher latent heat energies compared to me-SAC slurries at the same concentrations. The addition of CTAB surfactant positively influenced the stability of the slurry dispersion, ensuring a more even distribution of me-PCMs within the base fluid. These findings highlight the potential of me-SAC and me-SAL slurries as effective materials for TES applications. Significantly, me-SAL slurries outperformed me-SAC slurries in TES performance due to their greater latent heat energies during melting and solidification.

Thermal energy storage performance evaluation of bio-based phase change material/apricot kernel shell derived activated carbon in lightweight mortar

The synergy between phase change materials (PCMs) and activated carbon (AC) obtained from biomass is an energy-efficient method for creating composite materials with enhanced thermal performance. This study presents such a leak-proof composite with enhanced properties through the impregnation of bio-based lauric acid (L)-capric acid (C) eutectic mixture (LCEM) as a PCM in the AC derived from apricot kernel shells (AC-AKS) framework. The manufactured AC-AKS/PCM composite was subsequently incorporated into cement-pumice based mortar (CPM) in various proportions. This was done to produce energy-efficient construction materials aimed at increasing the thermal performance of buildings. Morphological, physical, thermal stability, mechanical strength, thermal energy storage (TES) and solar thermoregulation performances of the obtained leak-proof composite PCM were experimentally determined. The compressive strength of CPM samples with TES ability (TESCPM) was found 6.8 MPa, 4.3 MPa and 2.1 MPa for TESCPM1, TESCPM2 and TESCPM3, respectively. The relatively lower mechanical strength values can be accepted when considering their thermal regulation performances. The apparent porosity was around 26 %, while water adsorption around 24 % for TESCPM3. FTIR results proved the presence of well chemical compatibility between AC-AKS and PCM. The DSC results exposed that the AC-AKS/PCM composite had a melting temperature and a latent heat capacity of 21.58 °C and 126.8 J/g, respectively, while these values were within the range of 18.93–20.51 °C and 10.55–30.32 J/g for the TESCPMs. TGA results exposed that the functioning temperature of the AC-AKS/PCM was greatly lower than the limit temperature value measured for its thermal degradation. The solar thermoregulation performance test indicated that the fabricated TESCPM exhibited noteworthy advantages by providing the cooling effect throughout the daytime as well as the heating effect throughout the nighttime. All of these favorable properties make the proposed AC-AKS/PCM-integrated CPM promising materials for innovative TES applications in construction elements.

Best practices for characterization of High Temperature-Aquifer Thermal Energy Storage (HT-ATES) potential using well tests in Berlin (Germany) as an example

Application of Aquifer Thermal Energy Storage with High Temperatures (HT-ATES) ranging from 60–90 °C is a promising technique to store large amounts of energy in urban areas. However, these areas typically lack information on hydrogeological and thermal parameters of the subsurface to determine the potential for energy storage. Moreover, conventional exploration methods as pumping tests do not account for the variation in density caused by the high temperature gradients or changes in salinity as encountered in HT-ATES operation. The objective of this study is therefore to develop best practices for characterizing the hydrogeological and thermal properties of groundwater wells and their surrounding formation that determine the potential performance of HT-ATES-systems. In addition to conventional pumping tests, a set of Push–Pull tracer Tests (PPTs) with cold and hot water are proposed and scrutinized using Berlin as case study. There, the research well Gt BChb 1/2015, which is characterized by a reservoir temperature of 17 °C at a depth between 220 und 230 m below ground surface was tested.In 2017, seven Slug-Withdrawal Tests (SWTs), a Step-Rate-Test (SRT), a production tests, and two Push–Pull tracer Tests (PPTs) with hot and cold water were performed during a period of 40 days. These tests were accompanied by Distributed-Temperature-Sensing (DTS) monitoring. The temperature measurements provide indications of injection areas based on the warmback period during a PPT with 81 °C hot water.The determined aquifer transmissibility T=3.2×10−5m2/s, the related Productivity Index (PI=2.0m3/(h bar)), and maximum flow rates of about 5m3/h indicate that the aquifer has potential for HT-ATES. However, the PPT and the DTS monitoring revealed cross flow between the target aquifer and an overlying aquifer. Thus, a new well with a design avoiding cross flow is required to utilize the aquifer’s energy storage potential. A set of best practices for characterizing HT-ATES potential was derived from the experiences in this study.

Fabrication and characterization of nano-additives modified microencapsulated phase change materials with high thermal conductivity for thermal energy storage

Microencapsulation technology solves the problems that phase change materials (PCM) are easy to leak, difficult to transport, and vulnerable to contamination. However, the shell materials are mostly organic materials with low thermal conductivity, which limits their specific application in the field of thermal energy storage. In this regard, in order to enhance the thermal conductivity, a novel type of microencapsulated phase change materials (MicroEPCM) based on an n-eicosane core and a phenol-formaldehyde resin shell modified by nano-BN and nano-SiC, respectively, were fabricated via in-situ polymerization method. The effect of the mass fractions (2, 4 and 6 wt%) of nano-additives on the performance of MicroEPCM-BN and MicroEPCM-SiC was systematically investigated. The morphology, chemical structure and thermal properties of modified MicroEPCM were characterized by SEM, FTIR, XRD and DSC, respectively, to determine the optimum incorporation of nano-additives. Conclusions are as follows: modified MicroEPCM still had a spherical morphology with an average particle size range of 2–8 μm. Furthermore, the addition of nano-additives significantly improved the thermal conductivity of MicroEPCM, and the thermal conductivity gradually increased with the progressive increase in nano-additives content. MicroEPCM-4%BN and MicroEPCM-6%SiC had the best overall performance with phase change enthalpies of 145.83J/g and 131.30J/g, respectively, and the thermal conductivity increased by 61 % and 97 %, respectively, compared to that of MicroEPCM without nano-additives. They also showed excellent thermal cycling and degradation stability. Consequently, MicroEPCM modified by nano-additives will have great potential for thermal energy storage applications.

Improving the mechanical performance of phase change microcapsule/epoxy composites via alternately enhancing interface bonding and strength of microcapsules

Microcapsules containing phase change materials (MPCMs) can be integrated with polymeric matrices to develop intelligent thermoregulating composites for applications in temperature management and thermal energy storage. However, the mechanical properties of such composites can be severely compromised due to the weak interfacial adhesion and the poor microcapsule rupture strength. This paper aims to investigate the failure mode of microcapsule/epoxy composites and present corresponding implementable methods to improve their strength. The MPCMs/epoxy composite primarily fails due to poor microcapsule-matrix interface debonding resulting from the poor compatibility between MPCMs and epoxy resin. A silane coupling agent (EPTMS) was employed to modify the surface of MPCMs, forming E-MPCMs, and created a crosslinked interface network during the epoxy curing process. The tensile strength of composite containing 20 wt% E-MPCMs has been improved by 23.55 % while the failure mode switching to microcapsule rupture. Furthermore, the microcapsule shell enhanced by TiO2 nano-reinforcements achieves a 105.20 % improvement in microcapsule rupture strength. The incorporation of EPTMS modified TiO2-MF hybrid microcapsules (ET-MPCMs) resulted in a significant increase of 33.79 % in the tensile strength of ET-MPCMs/epoxy composite with the failure mode changing to microcapsule-matrix interface debonding again. The strategy of alternately enhancing subset properties derived from the competition failure mode of the composite opens new perspectives for the preparation of high-performance multifunctional composites.

Polyethylene Glycol Confined in SiO2-Modified Expanded Graphite as Novel Form-Stable Phase Change Materials for Thermal Energy Storage.

Form-stable phase change materials (FSPCMs) composed of poly(ethylene glycol) (PEG) encapsulated in SiO2-modified expanded graphite (EG@SiO2) were prepared and investigated for thermal energy storage behaviors. The modification of SiO2 on EG was done using a simple sol-gel method, and then the resulting EG@SiO2 was introduced to confine PEG at varying content (60-90 wt %). Surface properties (including microstructure, morphology, and functional groups), PEG adsorptivity, leakage-proof ability, and thermal energy storage of the prepared materials were thoroughly characterized and discussed. The EG@SiO2 with 15 wt % SiO2 outstandingly adsorbed PEG as compared to the pristine EG, showing up >80 wt % of PEG. As a result, PEG was well stabilized in EG@SiO2 porous network without leakage, owing to capillary force, surface tension, and hydrogen bonding interactions. The optimal 80 wt % PEG/EG@SiO2 composite possessed high crystallinity (93.5%), high thermal energy storage capacity (132.5 J/g), and excellent thermal conductivity (4.086 W/m·K). In addition, it exhibited good cycling durability after 500 repeated melting/crystallization cycles. The high thermal efficacy and inexpensiveness would make the PEG/EG@SiO2 FSPCMs suitable for scale-up applications in thermal energy storage.

Upcycling of PET plastics into diethyl terephthalate for applications as phase change materials in energy harvesting

Polyethylene terephthalate (PET) is an indispensable material in our everyday lives and upcycling of its waste has become a major area of research. Herein, the upcycling of PET waste into phase change materials (PCM) for thermal energy storage applications is presented. Hydrolysed and esterified PET waste affords diethyl terephthalate (DET), which when blended with UV-curing acrylic matrix, trimethylolpropane ethoxy triacrylate (TMPEOTA), forms a composite PCM. Chemical characterisation such as IR and NMR were conducted to confirm the presence of functional groups in the composites. The thermal properties of the composites, such as melting point and thermal degradation were obtained and DET exhibited a relatively high melting enthalpy of 94.1 J/g at about 39.9 °C. The form stability and thermal performance was studied for composites made of different DET loading weight percentages from 50 to 90 %. A loading rate of 80 % (D80) was found to provide best latent heat capacity while maintaining its form stability and minimizing leakage. Finally, to assess the performance of D80 as a thermal storage material, a thermal response test was performed and D80 was able to prevent significant rise in temperature for about 60s during its phase transition as opposed to TMPEOTA control.

Microencapsulation study of bioderived phase change material beeswax with ethyl cellulose shell for thermal energy storage applications

ABSTRACT The commercial shape-stabilized phase change material (PCM) products are obtained from synthetic raw materials. These materials are produced from carbon-intensive petroleum-refining processes. The carbon footprint can be minimized by using biobased products. Beeswax is a naturally available PCM with high phase transition enthalpy comparable to synthetic PCMs. In the previous literature studies, beeswax was shape-stabilized with synthetic materials. In the present study, beeswax was shape-stabilized with biopolymer ethyl cellulose by emulsion solvent evaporation method. The study aims to determine optimum microencapsulation process parameter levels for synthesizing microcapsules with high thermal energy storage (TES) capacity. The optimized process parameters for formulating microcapsules were 60:40 core/shell ratio, 2% PVA concentration, ethyl acetate solvent, and 40°C evaporation temperature. The microcapsules prepared with optimized process parameters were characterized using differential scanning calorimeter (DSC), T-history analysis, Fourier transform infrared (FTIR) spectroscope, and scanning electron microscope (SEM). FTIR and SEM analysis confirmed ethyl cellulose shell formation over the beeswax core. The optimized MPCM formulation possesses 115.8 J/g melting enthalpy with peak phase transition temperature of 58.2°C and thermal conductivity of 0.219 W/mK. The porous structure of the shell reduced melting enthalpy of optimized MPCM formulation to 84.6 J/g after 50 thermal cycles. The synthesized microcapsules comprise sustainable materials and have high TES capacity. The fabricated microcapsules can be used as TES additive in composite and coating formulations in food packaging.

Stability assessment of alumina and SiC based refractories in a high temperature steam environment as potential thermal energy storage materials

Solar energy can be utilized not only for electricity generation but also for synthetic fuel production, making it a versatile option in the transition to a low-carbon and sustainable energy system. However, to enable economically viable solar fuel production, the development of efficient thermal energy storage (TES) materials is crucial. Ceramic materials have been identified as a potential solution for high-temperature TES applications. In this study, two commercially available refractories, alumina coated recrystallized silicon carbide and alumina-based refractory were investigated for their stability under long-term steam corrosion tests to evaluate their suitability as TES materials for a potential TES unit. X-ray diffraction (XRD) revealed that recrystallized silicon carbide is composed of two different SiC polytypes (moissanite 6H and moissanite 4H) while alumina-based refractory contained corundum and mullite. Upon being exposed to steam, both materials exhibited distinct characteristics. SiC experienced significant mass gain, a subtle lightning of its surface color and erosion of a porous alumina coating on the SiC. Amorphous silica phases were detected as an indication of oxidation of SiC from X-ray diffractrograms. These remarkable changes clearly indicate that SiC is unsuitable for use in a potential thermal energy storage (TES) unit. On the other hand, there was no significant visual changes in the alumina-based refractory and the weight change was only marginal after corrosion tests. However, XRD indicated mullite completely disappeared after steam corrosion tests possibly due to its decomposition into Al2O3 and Si(OH)4.

Low-carbon cement manufacturing enabled by electrified calcium looping and thermal energy storage

Decarbonization of the cement industry is an important goal in the carbon neutralization vision. Calcium looping is a promising decarbonization method in the cement industry due to the well-established solid management system and the direct utilization of deactivated sorbent in cement manufacturing. Oxyfuel combustion is often used in the calcium looping to obtain high-purity CO2, yet results in large capital expenditures on the air separation unit and high electricity and fuel consumption. In this work, we propose an electrified calcium looping process which uses electric heating from renewables and thermal energy storage to replace fossil fuels. The CO2 generated in the calciner is directly separated with CO2 as the heat transfer fluid. The proposed process in a cement plant is assessed in the energy, environment, and economic aspects with both tail-end configuration and integrated configuration. Compared to conventional oxyfuel-based calcium looping, electrified calcination can reduce the primary energy consumption in cement manufacturing from 7458.0 MJ/t-clinker to 6484.0 MJ/t-clinker in the tail-end configuration and from 5320.9 MJ/t-clinker to 4996.6 MJ/t-clinker in the integrated configuration, at a CO2 capture efficiency of 90%. The reduced fuel consumption decreases CO2 emissions and capital expenditures for the CO2 capture system. Replacing oxyfuel with electrification and thermal energy storage brings only a limited reduction in the cost of CO2 avoidance in the integrated configuration, and the economic benefits can be significantly improved with lower-priced renewable energy. This work provides insights into the applications of cost-effective renewable energy, electric heating, and thermal energy storage in calcium looping-based industrial decarbonization.

Exploring the temperature-dependent thermal stability of nano-enhanced phase change materials: An experimental study using eicosane as the base material

Recently, studying phase change materials (PCMs) has brought many researchers' attention to be applied in thermal energy storage and battery thermal management (BTM) applications. Nano-materials have been used recently to improve the advantages of the PCM which makes them suitable materials to be used in thermal management systems. Moreover, the selection of the nanomaterials and the proper concentration of nano-particles in PCM affects the thermophysical characteristics of PCM. According to the fact that PCM requires to be thermally stable, the principal aim of this study is to analyze the thermal stability of PCMs composites by loading different mass fractions of CuO nano-particles. In order to add nano-particles to the eicosane-based PCM, a two-step method has been used. The thermal stability of the Nano-enhanced phase change materials (NePCM) has been measured by using the thermogravimetric analyzer. Results demonstrated that 0.5 wt% is the best value of additive nano-particle which showed a remarkable increment in thermal stability. Therefore, all the presented results indicate the importance of selecting an optimal PCM nano-composite for various applications including NePCM-based thermal energy storage and BTM systems. The brand and model of the device used in this study are Hitachi and STA7000 respectively.

Enhancing the performance of composite phase change materials using novel triply periodic minimal surface structures

Organic phase change materials (PCMs) are widely used in thermal management applications owing to their high latent heats of fusion and low cost. Unfortunately, their poor thermal conductivities severely hamper the thermal transport process. Hence, PCMs are often hybridized with high thermal conductivity materials that promote phase change for time-sensitive applications and potentially increase the power density of thermal energy storage (TES) devices. Optimized thermally conductive networks with high-latent-heat PCM matrices are critical in the thermal management of high heat flux applications. With advancements in additive manufacturing, it has become easier to create complex topologies, such as triply periodic minimal surfaces (TPMS), that can further augment the performance of composite PCMs. TPMS surfaces have shown great promise in improving thermal transport performance but investigations into their thermal properties remain limited. In this study, the thermal performances of PCM infused TPMS structures of wall thicknesses varying from 0.4 mm to 0.8 mm were systematically investigated. The TPMS structures were designed using level-set equations, and each system of structures was fabricated by selective laser melting, a metal additive manufacturing technique. Numerical investigations were performed to understand the phase change dynamics of PCM in TPMS cells and experiments were performed to determine their thermal properties and phase change performance for thermal energy storage applications. Our simulations revealed that for structures with uniform wall thickness of 0.4 mm, the novel Neovius structure resulted in the highest effective thermal conductivity enhancement. For a given thickness, it is thus hypothesized that more complex TPMS topologies have higher surface areas and volumes which enhance their thermal conductivities. However, the complex shape of the Neovius structure could not be further uniformly thickened without self-intersecting geometries. Ultimately, a balance of both the surface area and thickness of the TPMS cell determines the thermal conductivity enhancement. Overall, the 0.6 mm thick IWP cells had the highest thermal conductivity of 13.84 W/m K, which was consistently verified in experiments. This is likely due to the fact that it has a larger surface area than the P structure but is also thicker than the 0.4 mm Neovius structure. To further demonstrate the potential application of our PCM-based TPMS design, low temperature thermal cycling tests were performed. Our results showed the IWP cell structure promoted a more uniform temperature distribution as compared to the P cell. Phase change in the 0.6 mm thick IWP cell structure was completed 1.4 times faster than the 0.8 mm thick P cell and 1.8 times faster than the 0.6 mm thick P cell. The purpose of this study is to provide useful guidelines for the selection of TPMS structures for various applications such as battery packs and spacecraft and to open doors for the co-optimization of materials and device geometry for enhanced energy and power density.

Predicting and understanding corrosion in molten chloride salts

Molten chloride salts are stable at higher temperatures than many other salts, including nitrate salts, and are thus promising for heat transfer and/or thermal energy storage in concentrating solar power, nuclear power, and other thermal energy storage applications. However, corrosion in molten chloride salts remains a significant problem. While many studies have been devoted to evaluation of corrosion, we find that a comprehensive method for predicting corrosion in molten chloride salts is lacking. Here, we present an evaluation of corrosion in molten chloride salts using Ellingham diagrams and chloride-oxide stability diagrams, which enable prediction of alloy performance in molten chloride salts and allow corrosion results to be interpreted at a fundamental level.Graphical abstract

Investigation on Thermophysical Properties of Multi-Walled Carbon Nanotubes Enhanced Salt Hydrate Phase Change Material

Thermal Energy Storage (TES) is a valuable tool for improving the energy efficiency of renewable energy conversion systems. One of the most effective methods for harnessing thermal energy from solar sources is through energy storage using phase change materials (PCMs). However, the thermal performance of PCMs is hindered by their low thermal conductivity. This research focuses on enhancing the thermal performance of salt hydrate PCM using multi-walled carbon nanotubes (MWCNTs) and surfactants. Through experimental investigations, a salt hydrate PCM with varying concentrations of MWCNTs (ranging from 0.1% to 0.9%) was prepared using a two-step technique and their thermophysical properties were thoroughly characterized. Various techniques such as field emission scanning electron microscope, thermal conductivity analyzer, ultraviolet-visible spectrum, thermogravimetric analyzer, and Fourier transform infrared spectroscopy were utilized to study the effect of surfactant on the nanocomposites and examine their morphology, thermal conductivity, optical properties, thermal stability, and chemical stability. The results indicated that the inclusion of MWCNTs with salt hydrate significantly improved the thermal conductivity by 68.09% at a concentration of 0.7 wt %, compared to pure salt hydrate. However, this enhancement in thermal performance was accompanied by a reduction in optical transmittance in the developed nanocomposite PCM. Additionally, the formulated nanocomposite demonstrated excellent thermal and chemical stability up to temperatures as high as 468 °C. As a result, this nanocomposite shows great promise as a potential candidate for solar TES applications, offering favourable characteristics for efficient energy storage from solar sources.