Successive charging and discharging behaviour of a bio-organic sustainable phase change material and its instabilities

Abstract

A bio-organic phase change material (PCM) is a viable candidate for thermal storage systems because of its high latent heat capacity and sustainability. The present study is motivated by the aim of analysing the actual behaviour of an economical organic PCM with its instabilities to meet the thermal energy storage requirements. Successive charging and discharging experiments are conducted on coconut oil as PCM with varying heat transfer fluid (HTF) inlet temperatures of 50 °C, 40 °C, and 30 °C for melting and 5 °C, 10 °C, and 15 °C for solidification across different mass flow rates. PCM temperature distributions are measured radially, axially, and diametrically. Three distinct stages are observed during melting, marked by a notable temperature drop in the intermediate stage. The temperature dip during the melting is found to be prominent under higher HTF temperatures. An issue like supercooling occurs, which gets reduced under lower initial PCM temperatures and diminishes further under slower cooling rates. Adjusting the HTF inlet temperature proved more advantageous during coconut oil melting, with the 50 °C case storing 26.8 % more energy than the 30 °C case, while solidification at 5 °C stored 7.8 % more energy than at 15 °C. Meanwhile, the mass flow rate has a minimal influence, showing only 7.4 % and 5.8 % deviations in charging and discharging when halved. The analysis of the behaviour provides in-depth insights into the implementation of an organic-bio-friendly PCM.