Development, optimization, and characterization of shape stable conductive composite phase change materials for versatile thermal energy storage needs

In thermal energy storage (TES), the commercial adoption of phase change materials (PCMs) is hindered by challenges in thermophysical and structural properties and a lack of optimization of thermal characteristics based on specific needs. This study addresses these limitations by developing shape stable composite PCMs (CPCMs) of two kinds, using refined preparation methods, achieving superior performance compared to previously reported CPCMs. The rigid CPCM (RCPCM) formulation includes paraffin (PA), and expanded graphite (EG) for thermal conductivity enhancement, while the second one flexible CPCM (FCPCM) involves styrene-ethylene-butylene-styrene (SEBS) for leakage retention and shape adaptability, Silicon oil (SO) for structural uniformity and expanded graphite (EG). The characterization of CPCM has been conducted through detailed testing and analysis. To optimize these CPCMs for diverse TES needs, machine learning (ML) techniques are employed to optimize thermophysical properties. Furthermore, the anisotropic thermal conductivity (TC) behavior is examined as a critical factor for designing TES units. The results demonstrate that the RCPCM with only (EG) exhibits an exponential increase in TC, while the CPCM having (EG) and SEBS attain a maximum TC of 3.35 W·m⁻¹·K⁻¹, and a 26 % reduction in latent heat (LH), showcasing exceptional performance not previously reported. A tradeoff analysis optimizes thermophysical properties based on TC and LH priorities based on (EG) mass fraction. The tradeoff results reveal the properties for short-term TES (TC = 3.0–8.0 W·m⁻¹·K⁻¹, LH = 63–110 kJ/kg), moderate-term TES (1.0–3.5 W·m⁻¹·K⁻¹, 120–180 kJ/kg), and long-term TES emphasizing LH (170–240 kJ/kg, 0.4–1.0 W·m⁻¹·K⁻¹.