Development of soft eutectic phase change material modified with expanded graphite for thermal energy storage and human comfort applications

Organic phase change materials (PCMs) have gained huge importance for thermal energy storage systems, but their applicability is restricted due to their low thermal conductivity and hardness. The aim of this research work is to solve the problem by developing a novel organic binary eutectic PCM employing paraffin wax and coconut oil in the eutectic mixture (ratio 1:1) to soften the PCM for thermal comfort applications. 3D expanded graphite (EG) was used as a filler to enhance the thermophysical properties of eutectic-EG PCM composite formed by melt-mixing technique. The percolation limit of EG was 0.5 wt-% to form the thermal network in PCM matrix. The thermal conductivity of eutectic-EG PCM composite enhanced significantly from 0.2 W m(-1) K-1 to 0.55 W m(-1) K-1 at 2 wt-% of EG in pristine PCM. Differential scanning calorimetry (DSC) was carried out to analyse the energy storage enthalpies and temperatures of composites. The 50 consecutive thermal heating and cooling cycles performed by conventional heating system showed the good thermal reliability of the composite. The numerical 2D simulation was conducted to reveal the heat propagation behaviour in the developed composite with the post-EG addition and to validate the enhanced thermal conductivity results obtained experimentally. The cost analysis results reveals that the cost per mean power of the composite is composite is approximately 100% lower than the pristine PCM. The developed composite's outstanding energy storage property indicates its potential for developing the soft heating pads/cartridges for human comfort and also the solar thermal energy storage applications for medium temperature ranges.