Assessment of latent heat thermal storage systems operating with multiple phase change materials

Abstract

Abstract Latent heat thermal storage (LHTS) systems employing phase change materials (PCMs) offer several advantages compared to sensible heat storage units. However, they exhibit an inherent poor thermal performance owing to poor heat transfer, poor thermal conductivity of PCMs, and so on. Methods such as replacing single PCMs with multiple PCMs, addition of fins, micro/macro/nano-encapsulated composite PCMs and dispersion of high conductivity particles to PCMs have been suggested and studied in the past by different authors as a means for performance enhancement of LHTS systems. While extensive literature is available on the last three methods, studies on multiple PCMs are very limited. It is rather difficult at this stage to conclude on the benefits and merits/demerits of the method, given the limited data available in the open literature. Therefore, there is a need for consolidation and compilation of the existing literature to understand and assess the performance of LHTS units operating with multiple PCMs. An attempt is made in this paper to assess the performance of multiple PCM based thermal storage systems by carrying out a comprehensive review of available literature on the topic. Studies have evinced that single PCM units replaced with multiple PCMs offered superior performance with enhanced charging/discharging rates and better energy/exergy efficiencies. Also, past investigations reveal optimal melting temperatures of PCMs, optimal melting temperature difference between PCMs, optimal mass and so on to obtain an optimal performance of multiple PCM systems. Relevant published data were compared and discussed to understand the research trend over the years. Discussions were extended covering the challenges involved with multiple PCMs highlighting the scope for further research. An overall summary based on the survey has been presented for a concise understanding of key findings published in the open literature.