Abstract
Phase change materials (PCMs) are gaining increasing attention and becoming popular in the thermal energy storage field. Microcapsules enhance thermal and mechanical performance of PCMs used in thermal energy storage by increasing the heat transfer area and preventing the leakage of melting materials. Nowadays, a large number of studies about PCM microcapsules have been published to elaborate their benefits in energy systems. In this paper, a comprehensive review has been carried out on PCM microcapsules for thermal energy storage. Five aspects have been discussed in this review: classification of PCMs, encapsulation shell materials, microencapsulation techniques, PCM microcapsules’ characterizations, and thermal applications. This review aims to help the researchers from various fields better understand PCM microcapsules and provide critical guidance for utilizing this technology for future thermal energy storage.
Highlights
Phase change materials (PCMs) have a high heat of fusion in general and can store/ release a large amount of energy during melting/solidifying processes [21, 22]
Organic PCMs are further described as paraffin and nonparaffin materials [31, 32]. e paraffin, one of the by-products of petroleum refinery, consists of carbon and hydrogen atoms joined with the general formula CnH2n+2, where n is the number of carbon (C) atoms [33]
Salt hydrates can be considered as alloys of inorganic salts and water forming a typical crystalline solid with the general formula M · nH2O. ey suffer from several problems, which limit their applications in TES facilities [37,38,39]
Summary
With the surrounding environment, microencapsulation of the PCMs has been widely used in recent years. Alkan et al reported that n-eicosane microencapsulated with polymethylmethacrylate (PMMA) shell had good thermal stability [67] It is a three-step degradation process during thermogravimetric analysis (TGA) tests, and the phase change temperature remained mostly unchanged after 5000cycle DSC tests. Inorganic shells generally have higher rigidity, higher mechanical strength, and better thermal conductivity [52]. E obtained microcapsules showed spherical shape with a uniform diameter of around 5 μm and had good thermal conductivity, thermal stability, anti-osmosis properties, and serving durability. Crystalline metal oxides, such as ZnO and TiO2, have multifunctional properties including catalytic, photochemical, and antibacterial characteristics. Contrasted to the microcapsules without SiC, heat transfer rate of the microcapsules with 7% SiC had a significant enhancement, and thermal conductivity improved by 60.34%
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