Field Of Thermal Energy Storage Research Articles

Thermal storage performance of a novel shell-and-tube latent heat storage system: Active role of inner tube improvement and fin distribution optimization

This study presents a numerical analysis of the melting process in a shell-and-tube latent heat thermal energy storage (LHTES) system, featuring a twisted elliptical inner tube with annular fins. Utilizing paraffin as the phase change material (PCM) and water as the heat transfer fluid (HTF), this research examines the impact of varying twist degrees, fin quantity and fin distribution on the system's thermal performance during melting process. The analysis of the melting process includes complete melting time, temperature, and the contour of the solid-liquid interface. Notably, the study identifies that both fin quantity and distribution play a significant role in the melting process. The findings indicate that an optimal configuration, comprising a 720° twisted degree, 11 fins, and a base number a of 0.80, enhances the melting efficiency of the LHTES system by 156.44 % and reduces ineffective heat loss by 41.36 %. These results highlight the potential advantages of the twisted elliptical inner tube structure and propose an innovative approach with an exponentially non-uniform fin distribution, marking an advancement in the field of thermal energy storage.

A review of flame aerosol synthesis technology for the synthesis of nanoparticles and functional energy materials

The outstanding performance of nanomaterials in chemical, magnetic, electrical, catalytic, and mechanical properties has paved the way for the huge market in material fabrication, energy storage, electronics, and many other industries. Traditional synthesis methods are relatively stunted in industrial applicability and scalability due to complex manufacturing processes and long preparation times, hampering the development and commercialisation of nanomaterials. On the other hand, the flame synthesis method emerges as an inexpensive, efficient, and easily scalable method for the commercial production of nanoparticles. The present review aims to highlight the research status and applications of the nanomaterials synthesised by the flame aerosol method. The advancement of flame aerosol synthesis technologies is reviewed, with emphasis on the state-of-the-art flame reactor configuration and design. Critical flame parameters that govern the formation of nanoparticles in the flame are reviewed to provide an understanding of the formation criteria and growth of nanomaterials in the flame environment. The properties and characteristics of carbon-based, platinum group metal, metal oxide, bimetallic nanoparticles, perovskite and high entropy oxide nanomaterials produced by flame synthesis are extensively reviewed. In addition, commercial manufacturing of flame-synthesised materials along with applications of the nanomaterials in the field of thermal or photocatalytic energy storage, fuel cells, and gas sensing are presented.

Modification of steel slag to prepare chlorides based composite phase change materials with shape stability for high-temperature thermal energy storage

Using steel slag to prepare high-temperature (>500 °C) PCMs was an effective way to achieve its high value-added utilization as a potential heat storage medium in a variety of applications, such as solar energy storage, power peak shaving, and industrial waste heat recovery. However, the complex solid waste of steel slag might be corrosive to salt-based PCMs at high temperature. To address this issue, steel slag was firstly modified with another solid waste (i.e., CFA), which was then used to microencapsulate NaCl-KCl to prepare shape-stabilized C-PCMs in this work. Thermophysical and mechanical properties of C-PCMs were analyzed. Results showed that CFA modification greatly improved chemical compatibility between steel slag and eutectic salt through phase reconstruction. Steel slag modified with 30 wt% CFA at 1100 °C was identified as the optimum skeleton. The prepared C-PCMs containing 50 wt% salt showed a phase transition temperature of 653 °C with a high latent heat of 139 J/g and an excellent cycling stability. Additionally, its thermal conductivity reached 1.46 W/(m·K), 180 % higher than of pure salt. Compressive strength of the composite could be as high as 119 MPa, superior to other salt-based C-PCMs. A heat storage device was further designed to allow the numerical investigation of thermal performance of the prepared C-PCMs in practical conditions. Attributed by reasonable arrangement of bricks, the heat storage device possessed a uniform temperature distribution over the vertical cross-section of HTF, which contributed to a quick completion of charging and discharging process. This work could potentially lay a foundation for application of steel slag in the field of high-temperature thermal energy storage.

A Mini Review on Sewage Sludge and Red Mud Recycling for Thermal Energy Storage

Sewage sludge and red mud, as common industrial waste, have become a research hotspot in the field of achieving carbon peaking and carbon neutrality, reducing carbon emissions, and solving environmental problems. However, their treatment and disposal have always been a difficult problem in the environmental field. Utilizing these two materials for thermal energy storage can not only improve energy utilization efficiency but also further reduce carbon emissions during their treatment process, providing a new approach for sustainable development in the industrial sector. This article summarizes the research progress for the resource recovery of sewage sludge and red mud for direct thermal energy recovery and composite phase change energy storage. After proper treatment, sludge and red mud can be directly used as energy storage materials. In addition, sludge and red mud can be combined with phase change materials to prepare composite materials with an excellent energy storage performance. This composite has broad application prospects in fields such as solar energy utilization and building energy efficiency. However, there are still some challenges and issues in this resource recovery and utilization, such as potential environmental pollution during the treatment process, the long-term stability of energy storage materials, and cost-effectiveness, which require further research and resolution. The purpose of this paper is to evaluate the potential of sewage sludge and red mud as energy storage materials, to explore their feasibility and advantages in practical applications, and to reveal the research progress, technical challenges, and future development directions of these two materials in the field of thermal energy storage.

Preparation of mono-sized high sphericity Al-Si alloy particles for thermal energy storage materials by pulsated orifice ejection method

The demand for Al-Si particles with high sphericity and narrow size distribution is growing in the field of thermal energy storage. In this study, a novel pulsated orifice ejection method (POEM) was successfully employed to produce different-sized Al-Si alloy particles. The analysis indicates that such particles exhibit high sphericity, with each particle having a sphericity exceeding 0.9. The particles are precisely size-controllable and mono-sized, thereby ensuring that they have the identical thermal history. The combination of cooling rate calculation and particle structure analysis indicates that the particles prepared by POEM exhibit higher cooling rates through rapid solidification, resulting in finer and more uniform microstructures. The thermal analysis results demonstrate that the Al-Si alloy particles prepared in this study have high melting latent heat (approximately 500.87 J/g) and solidification latent heat (approximately 467.26 J/g), showcasing their potential as high-efficiency phase change materials for high-temperature thermal energy storage.

Enhancement of Polyacrylic Acid/Silicon Carbide Nanocomposites’ Optical Properties for Potential Application in Renewable Energy

Composites made from polymers and nanoparticles have promise to be effective solar collectors and thermal energy storage devices due to benefits including improved thermal characteristics and increased structural stability. This study intends to fabricate polyacrylic acid/silicon carbide (PAA−SiC) nanocomposites and examine the optical properties for use in solar collectors and thermal energy storage (TES) fields. The optical properties of PAA−SiC nanocomposites are investigated within the wavelength between 340 and 840 nm. The findings indicate that an increase in SiC concentration in the PAA aqueous solution to 50 g/L at a wavelength of λ = 400 nm causes an increase in the absorption by 50.2% besides a reduction in transmission by 6%. Furthermore, the energy band gaps were reduced from 3.25 eV to 2.95 eV to allow for the transition, and subsequently reduced from 3.15 eV to 2.9 eV to allow for forbidden transition as a result of the increasing SiC concentration from 12.5 g/L to 50 g/L. The optical factors of energy absorption and optical conductivity were also enhanced with a rising SiC concentration from 12.5 to 50 g/L. Specifically, an improvement of 61% in the melting time of PAA−SiC−H2O nanofluids is concluded. Accordingly, it can be said that the PAA−SiC−H2O nanofluids are suitable for renewable energy and TES systems.

Multistage Porous Carbon Derived from Enzyme-Treated Waste Walnut Green Husk and Polyethylene Glycol for Phase Change Energy Storage.

The thermal storage performance, cost, and stability of phase-change materials (PCMs) are critical factors influencing their application in the field of thermal energy storage. Porous carbon, with its excellent support, thermal conductivity, and energy storage properties, is considered one of the most promising support matrix materials. However, the simple and efficient synthesis of high-performance and highly active bio-based materials under mild conditions still faces challenges. In our work, a novel method for preparing new functional composite phase-change materials based on enzyme treatment technology and using waste walnut green husk biomass and polyethylene glycol as raw materials was developed. The enzymatic treatment method exposes the internal structure of the walnut green husk, followed by the adjustment of the calcination temperature to increase the adsorption sites of the biochar, thereby stabilizing polyethylene glycol (PEG). The porous properties of walnut green husk biochar effectively regulate the phase-change behavior of polyethylene glycol. In the biochar carbonized at 600 °C, the PEG loading reached 72.09%, and the absorption heat of the solid-solid phase-change material (SSPCM) reached 194.76 J g-1. This work not only enriches the application of biomass in heat storage but also demonstrates the broad prospects of SSPCMs in solar thermal utilization.

High value utilization of waste peanut shell: Prepared novel shape stable composite phase change materials with high thermal conductivity

To address the leakage and low thermal conductivity issues of phase change materials (PCMs), this study aims to prepare high thermal conductivity shape stable composite phase change materials (sscPCMs) using waste peanut shell. Employing pyrolysis technology, waste peanut shell has been successfully converted into high-performance framework materials. In addition, it also compared the thermal energy storage performance of shape stable composite stearic acid/peanut shell biochar (ss-cSA/PSC) with that of shape stable composite stearic acid/peanut shell (ss-cSA/PS). Excitingly, the thermal energy storage performance of ss-cSA/PSC has been significantly improved. Specifically, the thermal conductivity of ss-cSA/PSC reached 0.527 W/(m·K), which is 3.2 times higher than that of pure SA and 2.4 times higher than that of ss-cSA/PS. In addition, the phase change latent heat of ss-cSA/PSC can reach 70.59 J/g, which is 27.2% higher than that of ss-cSA/PS. The high thermal conductivity and phase change latent heat highlighted its significant superiority in the field of thermal energy storage. Furthermore, ss-cSA/PS and ss-cSA/PSC have been characterized by SEM, FTIR, XRD, and TGA. The results indicated that both two kinds of sscPCMs have excellent chemical compatibility, thermal reliability, and thermal stability. In summary, PSC is an economical, environmentally friendly, and sustainable framework material which used to prevent the leakage of PCMs and improve the thermal performance.

Cellulose nanocrystal stabilized copper nanoparticles for grafting phase change materials with high thermal conductivity

Phase change materials (PCMs) have recently garnered significant attention for thermal energy storage applications. However, widely used PCMs, such as polyethylene glycol (PEG), suffer from low heat conductivity, poor thermal stability, and a tendency to leak, limiting their practical use. Therefore, the objective of this study is to develop a highly thermally conductive composite PCM using PEG and a thermally conductive nanomaterial, specifically cellulose nanocrystals supported by copper nanoparticles (CNC@Cu-NPs). The CNC@Cu-NPs nanocomposite material was used as a matrix to support polyethylene glycol (PEG), resulting in a shape-stable phase change material termed PEG/CNC@Cu-NPs. The obtained PEG/CNC@Cu-NPs were characterized using various analytical techniques. Fourier transform infrared spectroscopy (FTIR) analysis revealed the chemical linkages between PEG and cellulose nanocrystals through a radical polymerization reaction. Polarizing optical microscopy (POM) images of PEG/CNC@Cu-NPs exhibited spherocrystal morphology with smaller sizes compared to pure PEG, suggesting that CNC inhibited PEG side-chain mobility. According to differential scanning calorimetry, the suggested PEG/CNC@Cu-NPs demonstrated a temperature transition between 0.51 °C to 24.5 °C with enthalpies of fusion and crystallization measured at 92.19 and 98.54 J/g, respectively, while also exhibiting excellent cycling stability after 60 heating/cooling cycles. The addition of a modest amount of copper nanoparticles resulted in a remarkable improvement (>50 %) in the thermal conductivity of the PCM. Thermal imaging using an infrared camera showed that PEG/CNC@Cu-NPs exhibited a delay of 10 min in heating compared to pure CNC, confirming the good heat retention capacity of the developed composite material. Based on the aforementioned findings, the proposed PEG/CNC@Cu-NPs PCM offers promising application possibilities in the field of thermal energy storage.

Efficient solar thermal storage of foamy bamboo charcoal-based composite phase change materials

Solid/liquid phase change materials (PCMs) with high phase change latent heat have been widely used in thermal energy storage in recent years, but their own disadvantages such as poor light-absorbing capacity, easy leakage, and low thermal conductivity seriously limit their practical use in solar thermal storage applications. In this study, a series of biomass-derived porous carbons (CB400, CB550, and CB700) were synthesized by combining the template method with the activation method through high-temperature carbonization using bamboo as raw material and Ca(OH)2 as precursor. 1-octadecanol (OC) is selected as the PCM, and four different composite photothermal phase change thermal storage materials (CB550-85, CB550-80, CB550-75 and CB550-70) were prepared by using CB550 as the photosensitizer and support material. The phase change enthalpy of CB550-85 with 85 wt% OC content was 299.8 J/g, the thermal conductivity of CB550-70 with 70 wt% OC content was 0.71 W·m−1·K−1, which is 184 % higher than that of 1-octadecanol. CB550-OC has good thermal and shape stability, excellent solar energy absorption capacity and photothermal conversion performance. This study provides a new technological pathway for the utilization of biomass. CB550-OC has a broad application prospect in the field of solar thermal utilization and thermal energy storage.

Fluidized bed reactor sizing using manganese aluminium spinel for thermochemical storage

In the field of high-temperature thermal energy storage, the use of reacting systems that reversibly decompose and regenerate, absorbing and releasing heat on demand, is becoming more and more attractive. It is essential in the perspective of achieving high thermal energy density storage, appearing potentially suitable for long-term applications too.Thermochemical Systems (TCS) can contribute to increasing the dispatchability of thermal storage, potentially even on a seasonal timescale. So far, most of this field's scientific works have focused on the conventional concept of fixed-bed reactors. To improve the heat transport phenomena involved in TCS storage, a fluidized bed solution was considered in this article. At this aim, a manganese aluminium spinel, which is a low toxic, low pollutant and very cost-effective is proposed for this application. It was synthesized in the form of properly sized (150–200 μm of diameter) particles to be effectively adopted for fluidizing beds.The present work deals with the sizing of the reactor and its coupling with a Concentrating Solar Thermal (CST) system using the Solar Central Receiver (SCR) technology with air as Heat Transfer Fluid (HTF). Imposing realistic boundaries, an optimal configuration was established, with an operating HTF pressure of 4 bar and a thermal discharging power of about 16 MWth. A volumetric energy density of 170 kWhth/m3 was achieved and, despite a relatively low TES reaction enthalpy, the resulting specific cost of 33 €/kWh demonstrates the suitability of this configuration even for the current thermal storage commercial solution, and shows the high potentiality of this type of storage systems.

Lightweight, robust, porous heterocyclic para‐aramid aerogel hollow fibers for multifunctional applications

AbstractIn nature, many fibers with warmth‐retention properties, such as the hair of polar bears and rabbits, both have a hollow cross‐section structure. The static air in fiber cavities can effectively inhibit heat conduction and serve as an effective thermal insulator. In this work, the high‐performance heterocyclic para‐aramid polymer was selected as the spinning solution, and aerogel hollow fiber was prepared by coaxial wet spinning and freeze‐drying techniques. The effects of spinning solution concentration and lyophilized solvent on the micromorphology, mechanical properties, and specific surface area of heterocyclic para‐aramid aerogel hollow fiber (HPAAHF) were systematically studied. The produced HPAAHF possessed excellent mechanical properties (tensible strength ~3.85 MPa), high specific surface area (~ 260.90 m2 g−1), and lightweight advantages. The thermal conductivity of HPAAHF was only 0.0278 W m−1 K−1, indicating its excellent thermal insulation properties. The aerogel fabric exhibited outstanding flame retardancy properties, with a total heat release of only 0.7 MJ m−2 in the cone calorimetric experiment, making it a self‐extinguishing fabric. In addition, phase change material was injected into the hollow structure to obtain aerogel‐phase change material composite fibers, which exhibited great energy storage prospects. As a result, the high‐performance heterocyclic para‐aramid polymer‐based aerogel hollow fiber was successfully prepared and had multifunctional applications in thermal insulation, flame retardancy, and heat energy storage fields.

A novel bio-based composite phase change material with excellent photo-thermal conversion capability for solar energy harvesting and energy storage

Organic solid-liquid phase change materials (PCMs) have been widely studied in the field of photo-thermal conversion and thermal energy storage. However, problems such as easy leakage and low efficiency of photo-thermal conversion limit their applications. To solve these problems, this study developed a shape-stable composite phase change material (CPCM) using sponge tissue of discarded corn stem (STCS), polyethylene glycol (PEG), pyrrole (Py), and multi-walled carbon nanotube (MWCNT). PPy and MWCNT enable the CPCM to have excellent photo-thermal conversion capability and thermal conductivity. With 0.2 % MWCNT content, the CPCM achieved a thermal conductivity of 0.4609 W/m·K and a photo-thermal conversion efficiency exceeding 95.3 %. It also demonstrated high enthalpy and relative enthalpy efficiency (152.2 J/g, 96.01 %). Moreover, the CPCM exhibited remarkable shape and thermal stability, with no pyrolysis below 340 °C and nearly unchanged enthalpy after 100 cycles. Meanwhile, this CPCM also showed excellent ability in promoting seawater desalination. This work provides a new idea for recycling of agricultural waste and storage of solar energy as well as desalination of seawater.

The spider web of modified wheat bran captured PEG to form stabilized phase change composites for temperature regulation and waste heat storage

Biomass based phase change composites (PCCs) have potential application prospects in the field of thermal energy storage (TES). Environmentally friendly development could be realized by recycling and reusing wheat bran (WB) of the agricultural and forestry waste. Distinguished from conventional biomass derivatives and/or carbonization methods, multi-walled carbon nanotubes (MWCNT/OH) modified wheat bran aerogels (MWB) with 3D entanglement structure was fabricated by utilizing physical pasting incorporating chemical cross-linking and functional modification, and then followed by freezing method. The fabricated MWB exhibited a graded and “spider web” entangled special porous structure, which could adsorb polyethylene glycol (PEG) effectively to form stabilized PCCs (MWB/PEG). This non‑carbonized, thermally conductive biomass PCCs play a positive role in energy and environmental recycling. Experimental results indicated that MWB possessed 87.9 % adsorption efficiency and excellent anti-leakage property. Enthalpy efficiency embodied through thermal storage capacity reached 86.5 %. Besides, the outstanding temperature regulation and heat transfer characteristics were verified by thermal infrared imaging. Two clear phase transition buffers appeared as well as the temperature distribution mainly concentrated in the phase transition temperature range from vertical view during heating/cooling process. Thermal conductivity and thermal diffusion coefficient of MWB/PEG increased to 0.26 W/m·K and 0.19 mm2/s from 0.15 W/m·K and 0.11 mm2/s for pure PEG, respectively. The MWB/PEG could store thermal energy by illumination and corresponding photothermal conversion rate reached up to 80.4 %. This composite showed a remarkable waste heat storage and/or reuse through electrothermal testing with integrated conductive fabrics, which would provide a potential development of green and high performance of TES technology in wearable flexible sensors and other fields.

Advancements in Phase Change Materials: A Path to Sustainable Energy Solutions in China

With the rapid development of China, the country's demand for energy has significantly increased. According to the "World Energy Outlook 2020," China's annual average growth rate of primary energy consumption is 1.9%, and it is predicted that China's energy consumption will account for over 20% of global energy consumption by 2050. In the energy budget, 90% is allocated to thermal energy conversion, transmission, and storage. Facing an impending energy crisis, enhancing energy production while minimizing energy loss has become a matter of widespread concern. Phase Change Materials (PCMs), also called phase change energy storage materials, have garnered attention as a novel energy-efficient and environmentally friendly material. PCMs refer to substances that undergo a change in state and provide latent heat without changing their temperature. Phase change thermal storage materials utilize phase transitions during heat exchange processes to store energy by means of these phase changes. Compared to chemical energy storage materials, PCMs offer high thermal efficiency and energy storage density, maintain constant temperature, and are more easily controllable. They hold great potential as a promising material in the field of thermal energy storage and have been widely applied in areas such as solar energy, lithium batteries, building insulation, and medical applications. This article offers a comprehensive overview of the principles and classification of Phase Change Material (PCM), including organic PCM, inorganic PCM, and composite PCM. It discusses their applications in solar thermal energy storage, cooling of photovoltaic panels, building materials, and industrial waste heat recovery. The article also highlights China's research and development efforts in these areas, emphasizing the country's significant contributions to advancing PCM technology.

Characterization and performance investigation of UiO-66 for low-grade thermochemical adsorption heat storage

Thermochemical energy storage can improve low-grade energy utilization efficiency, thereby reducing buildings' operating energy consumption. However, common thermochemical thermal storage materials have poor stability and low energy storage density. To this end, it put forward to use UiO-66 as a novel low-grade thermal energy storage material. It was synthesized and characterized, and its thermal conductivity, optimal activation temperature and time, adsorption kinetics and thermal energy storage density were also comprehensively studied. The results showed that the thermal conductivity of UiO-66 was 0.282 W/(m·K) at 30 °C. The optimal activation temperature and time for UiO-66 were 100 °C and 1.5 h taking into account the balance between the high water uptake and energy saving. The water uptake of UiO-66 at 30 °C and 80% RH reached 0.410 g/g, 2.1 times that of Zeolite 13X. The adsorption behavior of water vapour in UiO-66 was accurately described by the pseudo-second-order kinetic model. The thermal energy storage density of UiO-66 was 818 kJ/kg, which was 1.6 times higher than that of Zeolite 13X (515 kJ/kg), demonstrating excellent thermal storage performance. To sum up, the research results showed that UiO-66 had application potential in low-grade thermal energy storage fields such as heat from solar collector and industrial waste heat.

Preparation and characterization of quinary nitrate salt based composite phase change material with low melting point for low and medium temperature thermal energy storage

This work concerns the development of a shape-stable molten salt based composite phase change material (PCM) for low and medium temperature thermal energy storage. The composite is fabricated by using a cold compression and hot sintering method with the employment of a eutectic quinary nitrate salt of NaNO3-NaNO2-KNO3-KNO2-LiNO3 as PCM, halloysite nanotube (HNT) as skeleton supporting material and natural graphite as thermal conductivity enhancement additive. A sequence of characterizations is performed to investigate the composite microstructure, chemical and physical compatibility, thermal stability, phase change behaviour, and thermal conductivity as well as cycling performance. The results indicate that an excellent chemical compatibility has been achieved among the ingredients of quinary salt, HNT and graphite within the composite. A mass concentration of 50 wt% HNT endows the composite with the optimal formulation in which 10 wt% graphite can be successfully accommodated and a thermal conductivity around 1.31 W/m·K can be acquired. Moreover, in such a formulation, the composite presents a considerably low melting temperature of 72.4 °C and a high thermal decomposition temperature of 530 °C, which achieves the composite a relatively high energy storage density nearly 500 kJ/kg at a temperature range of 25–510 °C. The results presented in this work demonstrate that the quinary salt-HNT-graphite composite with fairly low phase transition temperature and a splendid combination of thermal properties and cycling performance could be a promising candidate to replace the conventional organic based PCMs utilized in low temperature thermal energy storage fields.

Low cost and eco-friendly form stable phase change material based on fly ash-expanded graphite binary supporting materials for large-scale application

The high cost and relatively complex packaging technology constrain the use of phase change materials (PCMs) in the field of thermal energy storage. Hence, in this study, the form-stable phase change materials (FSPCMs) of lauric acid (LA)/raw fly ash (RFA)-expanded graphite (EG) with a low cost were prepared via simple direct impregnation method by impregnating LA into RFA and EG, which was used to further enhancing heat transfer and package efficiency. Thus, the binary supporting materials-based eco-friendly FSPCMs were synthesized by using cheaper supporting materials RFA-EG for large-scale preparation of PCM. Subsequently, the fabricated FSPCMs have been characterized by analysis techniques such as SEM (scanning electron microscope) and BET (Brunauer-Emmet-Teller), FT-IR (Fourier transform infrared spectroscopy), DSC (different scanning calorimetry), and TGA (thermogravimetry analysis) to determine the microstructure, chemical compatibility, thermal properties, and thermal stability. The results show that the maximum mass fraction of LA absorbed into RFA without leakage was up to 50 wt%. The SEM analysis showed that LA could cover the surface of RFA particles and the EG was dispersed in the space among RFA particles. And, the heat storage and release efficiency of LA/RFA-EG exhibited higher heat transfer efficiency than that of LA and LA/RFA. The phase change temperature and latent heat of LA/RFA-EG FSPCM were 45.73 °C and 85.34 J/g, respectively. The TGA demonstrated that LA/RFA-EG FSPCM presented good thermal stability. Compared to pure LA, the thermal conductivity of LA/RFA-EG (10 wt%) was up to 0.933 W/m·k, which increased by 478.46 % due to the introduction of 10 wt% EG and RFA. The heat-storing or releasing time of LA/RFA-EG was decreased by 60 % for the melting process and 76.92 % for the freezing process than that of LA, respectively. Using solid waste as the supporting material, the eco-friendly LA/RFA-EG with high absorption capacity and high latent heat was a promising candidate for the large-scale application of FSPCMs in thermal energy storage.

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.

Nitrate salt-halloysite nanotube (HNT) composite phase change materials for thermal energy storage: The feasibility of material fabrication by using HNT as skeleton substance and its thermal properties

This work concerns the fabrication of a salt based form-stable phase change composite by employing halloysite nanotube (HNT) as ceramic supporting material (CSM). The HNT has been broadly reported for preparation of low-temperature organic composites but very little has been done in medium and high temperature thermal energy storage fields. Herein we demonstrate for the first time with the use of HNT as skeleton substance for the fabrication of salt composite by cold compression and hot sintering technology. The feasibility of material fabrication is confirmed by evaluating a case containing a salt of sodium nitrate as phase change material and HNT as CSM. The effect of preheating treatment of HNT on the microstructure and phase change behaviours as well as cycling performance of the composite is investigated. The results show that HNT can be wetted by the liquid nitrate salt at elevated temperatures, verifying the viability of the present strategy by using HNT as SSM for the synthesis of salt composite. A stable chemical structure is achieved in the salt-HNT composite, which confirms a preeminent chemical stability and compatibility between the HNT and nitrate salt. The hollow tubular structure of HNT could not only be able to provide extra surface for accommodating liquid salt to form a dense composite, but also strengthen the thermal stability of the nitrate salt. The preheating treatment of HNT at 300 °C and 500 °C respectively causes the occurrence of dehydration and dehydroxylation process, which in turn leads to the morphology and microstructure change of HNT, and hence affects the cycling performance of the composite. In comparison with the composite made from HNT preheated at 500 °C where a serious pulverization and deformation has been observed after 100 thermal cycles, the composite containing HNT preheated at 300 °C presents more stable structure and excellent cycling performance, revealing that the HNT is only suitable for the accommodation of inorganic salt that having application temperature limit less than 500 °C.