Multicomponent bio-based fatty acids system as phase change material for low temperature energy storage

In this study, new multicomponent mixtures of fatty acids for low temperature thermal energy storage applications have been developed. The new mixtures were based on coconut oil fatty acids (CoFA) and commercial grades of oleic (OA) and linoleic acid (LA). Refined coconut oil (CO) was first converted into free fatty acids by alkaline saponification. The prepared CoFA were then mixed with OA or LA at various compositions to prepare stable bio-based phase change materials (BPCMs). The thermal behavior including melting/solidification temperatures, specific heat and enthalpy of the developed mixtures were investigated by means of differential scanning calorimetry (DSC) and T-history. Transient hot wire method was used to measure thermal conductivity of the PCMs. The chemical stability and thermal reliability of the mixtures were assessed stepwise from 100 to 700 melt/freeze cycles by attenuated total reflectance-Fourier transform infrared spectroscopy (ATR-FTIR) and DSC. Based on DSC and T-history results, the phase transition of the developed PCMs were in line with the range of human comfort temperatures i.e. 18-25 degrees C, with no incongruent melting and less than 0.6 degrees C super cooling, whereas specific heat and enthalpy of the new mixtures were in the range of 1-5 J/g K, and 40-100 J/g. The FTIR and DSC results indicated that the PCMs mixtures are chemically and thermally stable. The thermal conductivity of the mixtures were in average 0.2 W/m K, in liquid phase and 0.35 W/m K, in solid phase. Out of the different developed combinations, the mixture of LA/CoFA (20/80) showed distinguished performance and can be considered as potential BPCM for low temperature thermal energy storage applications.