Micro- and nano-encapsulated metal and alloy-based phase-change materials for thermal energy storage.

Macro-encapsulation of metal balls prepared by waste aluminum cans in ceramic capsules with reserved space

Effect of structural characteristics and surface functional groups of biochar on thermal properties of different organic phase change materials: Dominant encapsulation mechanisms

Review on thermal conductivity enhancement, thermal properties and applications of phase change materials in thermal energy storage

What about greener phase change materials? A review on biobased phase change materials for thermal energy storage applications

A phase-change material (PCM) thermal energy storage (TES) has been studied as part of a project to develop a solar-based room-heating system for extreme cold areas using ANSYS Fluent. The purpose of using a PCM thermal storage is to overcome the intermittency of solar and provide room heating during nighttime as a sustainable and clean solution. A computational fluid dynamic (CFD) model is developed for a cubical TES unit having an array of cylindrical rods of stainless steel filled with inorganic PCM as thermal storage media. Heat-transfer fluid (HTF) selected for this study is water. In the present study, the diameter of cylindrical rods is optimized by comparing the melting characteristics of PCM with three different diameters, and thermal performance of the selected option is investigated and discussed. ANSYS Fluent software is used for numerical modeling of a commercially available inorganic PCM material Save-HS48 (Pluss Advanced Technologies, India) and the results were validated using experimental data provided by the PCM manufacturer. 3D transient option with solidification and melting in Ansys Fluent software is selected for the investigation. A four-hour charging time is assumed for the numerical modeling and discharging for a particular case was studied with suitable assumptions for full-cycle analysis. Thermo-physical properties of Save-HS48 PCM are found to be suitable for solar room-heating application and effectiveness of all the cases simulated in the present study provides suitable results for further experimental study of a PCM-TES unit.

Latent heat storage systems consisting of phase change materials (PCMs) offer the advantage of a large thermal energy storage density as compared to sensible heat storage systems. Most recent work has focussed on organic and inorganic PCMs which have problems of subcooling and phase segregation. Metallic PCMs are a recent innovation for medium to high temperature applications due to their high thermal conductivities, high volumetric storage capacities and their low degrees of sub-cooling during the release of latent heat. For medium temperature applications like cooking of food, very limited work has been done on metallic PCMs for energy storage. Solder based PCMs have rarely been investigated for medium temperature applications thus it is necessary to carry out an experimental study on the use of a solder as PCM candidate. No work has ever been reported using the eutectic solder (Sn63/Pb37) as a PCM. Its use is justified since it is low cost and locally manufactured solder worldwide. Another recent innovation is cascaded thermal energy storage (TES), whereby two PCMs with different melting temperatures are used in a single storage tank to improve the efficiency of energy storage. No work has also appeared in recent literature involving metallic solders in cascaded systems. In a bid to investigate the suitability of the eutectic solder as a PCM for medium temperature applications, two eutectic solder (Sn63/Pb37) based systems are experimentally evaluated during discharging cycles. The first system is a single PCM system composed of a packed bed of spherically encapsulated eutectic solder capsules. The other system is a two PCM cascaded system comprising of eutectic solder spherical capsules at the top and erythritol spherical capsules at the bottom in a storage ratio of 50 %: 50 %. Discharging experiments are carried with three different discharging flow-rates to investigate the effect of the flow-rate on the thermal performance. The three discharging flow-rates used are 4 ml/s, 6 ml/s and 8 ml/s. For both storage systems, an increase in the discharging flow-rate increases the peak discharging energy and exergy rates. For both storage systems, an increase in the discharging flow-rate increases the peak discharging energy and exergy rates. The single PCM system shows higher energy and exergy rates for most of the discharging duration compared to the cascaded system. An increase in the flow-rate increases the peak energy and exergy discharging rates for the single PCM and the cascaded PCM storage systems. The single PCM system out-performed the cascaded system during the discharging tests possibly due to the lower melting temperature and lower thermal conductivity of the bottom PCM (erythritol) in the cascaded system. However, for the higher flow-rates (6 ml/s, 8 ml/s), the cascaded system shows a slightly better or comparable performance at the start and at end of discharging.

This paper presents the work carried out in ‘SEHRENE’ (Horizon Europe Project) to select suitable materials of construction for MgCl2.6H2O-based PCM (phase change material) thermal energy storage system. Commonly used construction materials, such as carbon steels, often have corrosion rates that limit their use in industrial PCMs. Metals that form passivating oxide films, such as Al, may give lower corrosion rates if fluxing of the oxide does not occur in the molten PCM. There have been suggestions to use Al alloy construction materials in PCM-based thermal energy storage (TES) systems where better heat transfer is essential, and carbon steel where structural integrity and cost-effective construction material is more suitable. This philosophy forms the core of the TES design in the above mentioned project. However, galvanic corrosion between the two dissimilar metals is a concern. To understand this further, carbon steel substrates were coated with Al, cut to expose Al-steel interface, and exposed to molten MgCl2.6H2O. The galvanic corrosion performance was determined by examining the cross-sections of specimens post-exposure. The cross-sectional metallographic analysis revealed that corrosion was detectable. However, no significant effect was discernable. The experimental work demonstrated that MgCl2.6H2O could be a potential PCM candidate for thermal energy storage system. The study also indicated coatings, such as thermally sprayed aluminum (TSA), could be considered for such applications to mitigate the corrosion issues based on the ease of application, availability, and cost.

Domestic hot water (DHW) and space heating (SH) are occupying more than 65% of carbon dioxide emissions in the residential sector.As global warming is critical issue, reducing carbon dioxide emissions is essential by decreasing fossil fuel energy use and improving energy efficiency.Air source heat pumps (ASHPs) are promising technologies that can provide DHW and SH with higher energy efficiency with less carbon dioxide emissions than conventional gas boiler systems [1].Recently, heat pumps (HPs) integrated with photovoltaic thermal modules (PVT), referred to as PVT-HP or solar-assisted heat pump (SAHP), have gained attention.PVT system can reduce HP operation time and power consumption, resulting in increased overall efficiency.However, owing to the imbalance between energy demand and the supply of renewable energy in these systems, thermal energy storage (TES) is required.Additionally, TES acts as a buffer tank, contributing to a reduction in the heating capacity required from the HP [2].Various studies have been conducted on SAHP and TES.Bae et al.[3] experimentally investigated the effect of the PVT-ASHP integrated with two water storages for DHW and space heating.The coefficient of performance (COP) of the system improved by approximately 52% compared to the ASHP system.Huan et al. [4] found that the parallel SAHP achieved 34.4% higher COP than the serial SAHP during the annual operation of a hot water supply system at a university in Xi'an, China.For TES, phase change materials (PCMs) have been gaining attention owing to their significant latent heat during phase transition.Cunha et al. [5] denoted that a SAHP with PCM TES system could store more energy within narrower temperature range than water storage, resulting in 56% reduction of annual CO 2 emissions, and energy savings of 76% compared to the conventional gas boiler system.However, research on PVT-ASHP system integrated with PCM TES is limited.In this study, the annual energy performances of DHW systems are analysed using the dynamic simulation program TRNSYS.Parallel solar-assisted air source heat pump (SAASHP) integrated with two different TESs, PCM TES and water storage, are selected as the analysed system.DHW load profile is set according to the 210 L water tank load profile in the European standard EN 16147[6].For the solar source, a PVT module with 1.58 m 2 absorber area is selected.System COP, electrical power, and thermal energy are primarily used as energy performance parameters.As a result, the SAASHP with PCM TES shows 9.2% higher system COP than the SAASHP with water storage through a year.The annual electricity generations of the PVT module for both cases are 931 MJ.The thermal energy generation of the PVT module of the PCM TES case is 8.1% higher than that of the water storage case owing to PCM TES's superior thermal characteristics.PCM TES demonstrates an isothermal characteristic during charging and discharging, which contributes to a lower temperature of the circulating water through the condenser of ASHP and PVT module compared to that of water storage.The lower circulating water temperature results in higher ASHP COP and larger thermal energy generation from PVT, leading to better overall system COP compared to the water storage case.However, the total amount of thermal energy from PVT is only 0.5% of the energy demand for DHW owing to the limited PVT area.Further optimization of the PVT module area can lead to more effective system configuration.

Form-stable phase change materials with high phase change enthalpy from the composite of paraffin and cross-linking phase change structure

Research on phase change material (PCM) for thermal energy storage is playing a significant role in energy management industry. However, some hurdles during the storage of energy have been perceived such as less thermal conductivity, leakage of PCM during phase transition, flammability, and insufficient mechanical properties. For overcoming such obstacle, researchers have been concentrating on composite PCM, where PCM is combined with metal or non-metal particles, fibrous materials, expanded or porous materials, and flame retardants. The main purpose of the current paper is to review the properties enhanced paraffin-based composite PCM. In the literature review, paraffin is selected as a thermal energy storage material, which is mixed with property-enhancing material to prepare composite. Structural and thermal properties of composite have been explored with the help of scanning electron microscope, X-ray diffractometer, transmission electron microscope, polarizing optical microscope, Fourier transform infrared spectroscopy, thermogravimetric analysis, and differential scanning calorimetry. Mechanical properties of the material are also portrayed using different testing techniques. Nevertheless, numerical methods have also been adopted for characterization of composite. It is found from the literature review that with incorporation of property-enhancing material, thermal conductivity, phase transition rate, and shape stability of PCM increased at the same time flammability, heat storage capacity, and mechanical properties reduced.

Recent development on heat transfer and various applications of phase-change materials

A novel form-stable composite as phase change material (PCM) for thermal energy storage was prepared by absorbing stearic acid (SA) into halloysite nanotube (HNT). The composite PCM was characterized by TEM, FT-IR and DSC analysis techniques. The composite can contain SA as high as 60 wt% and maintain its original shape perfectly without any SA leakage after subjected to 50 melt–freeze cycles. The melting temperature and latent heat of composite (SA/HNT: 60/40 wt%) were determined as 53.46°C and 93.97 J g−1 by DSC. Graphite was added into the SA/HNT composite to improve thermal storage performance, and the melting time and freezing time of the composite were reduced by 65.3 and 63.9%, respectively. Because of its high adsorption capacity of SA, high heat storage capacity, good thermal stability, low cost and simple preparation method, the composite can be considered as cost-effective latent heat storage material for practical application. Copyright © 2011 John Wiley & Sons, Ltd.

The building sector is known to make a large contribution to total energy consumption and CO2 emissions. Phase change materials (PCMs) have been considered for thermal energy storage (TES) in buildings. They can balance out the discrepancies between energy demand and energy supply, which are temporally out of phase. However, traditional PCMs need special latent storage devices or containers to encapsulate the PCM, in order to store and release the latent heat of the PCM. The proper design of TES systems using a PCM requires quantitative information and knowledge about the heat transfer and phase change processes in the PCM. In Korea, radiant floor heating systems, which have traditionally been used in residential buildings, consume approximately 55% of the total residential building energy consumption in heating. This article reviews the development of available latent heat thermal energy storage technologies and discusses PCM application methods for residential building using radiant floor heating systems with the goal of reducing energy consumption.

Heat transfer study of phase change materials with graphene nano particle for thermal energy storage

Catastrophe theory and its applications : Tim Poston and Ian Stewart, Fearon-Pitman, Belmont, Calif., 491 p., 1978.