Thermal property measurement and heat transfer analysis of acetamide and acetamide/expanded graphite composite phase change material for solar heat storage

As a phase change material (PCM), acetamide (AC) can be a potential candidate for energy storage application in the active solar systems. Its utilization is however hampered by poor thermal conductivity. In this work, AC/expanded graphite (EG) composite PCM with 10 wt% (mass fraction) EG as the effective heat transfer promoter was prepared; its thermal properties were studied and compared with those of pure AC. Transient hot-wire tests showed that the addition of 10 wt% EG led to about five-fold increase in thermal conductivity. Investigations using a differential scanning calorimeter revealed that the melting/freezing points shifted from 66.95/42.46 °C for pure AC to 65.91/65.52 °C for AC/EG composite, and the latent heat decreased from 194.92 to 163.71 kJ kg−1. In addition, heat storage and retrieval tests in a latent thermal energy storage unit showed that the heat storage and retrieval durations were reduced by 45% and 78%, respectively. Further numerical investigations demonstrated that the less improvement in heat transfer rate during the storage process could be attributed to the weakened natural convection in liquid (melted) AC because of the presence of EG.

Thermal characterization of AC (a) and AC/EG composite (b) at the heating/cooling rates of 10 °C min−1 by differential scanning calorimeter.Figure optionsDownload as PowerPoint slideHighlights
► Acetamide (AC)/expanded graphite (EG) composite PCM was prepared for solar heat storage.
► Thermal conductivity of AC/EG composite PCM with 10 wt% EG (mass fraction) showed a five-fold increase, and the melting/freezing points and latent heat were characterized by the differential scanning calorimeter tests.
► Heat storage tests were conducted and the results indicated that heat storage and retrieval durations were reduced by 45% and 78%, respectively.
► Thermo-fluidic phenomena associated with melting/freezing were numerically investigated.