Influence of compression ratio in compressed extended graphite on thermo-physical properties of composite phase change material: An experimental investigation

Graphite-based phase change material (PCM) composites improve thermal transport in latent heat storage systems by enhancing the system's thermal conductivity. The composite PCM is created by saturating the compressed expanded graphite (CEG) matrix with molten PCM, while the CEG is prepared by compressing expanded graphite (EG). This study investigates how the compression ratio in compressed expanded graphite (CEG) affects key properties of composite PCM, including pore volume fraction, PCM mass fraction, effective thermal conductivity, and latent heat capacity, using paraffin as the PCM. CEG's porosity is determined using liquid volume displacement, while differential scanning calorimetry (DSC) assesses the paraffin-CEG composite's effective latent heat capacity and melting temperature. The composite PCM's effective thermal conductivity is measured using a transient plane source (TPS) apparatus. The results show a 3 to 10 fold increase in the effective thermal conductivity of the composite compared to pure paraffin, depending on the CEG matrix compression ratio. A key finding from this experimental study is the incomplete impregnation of PCM within the CEG matrix, which reveals the presence of inaccessible air voids that prevent molten PCM from infiltrating under standard atmospheric pressure conditions. Empirical relationships are established to correlate the compression ratio with parameters like porosity, PCM mass fraction, and effective thermal conductivity. © 2024