Paraffin based composite phase change materials for thermal energy storage: Thermal conductivity enhancement

Paraffin wax (PW) has been widely used as a phase change material for thermal energy storage due to relatively high thermal energy storage density and other desirable properties. However, it has a low thermal conductivity (TC), leading to a long charging and discharging time. To address the issue, carbon nanotubes (CNTs) were mixed with PW to form PW-CNTs composites. As CNTs are highly thermally conductive, the use of such a material is expected to give a good level of thermal conductivity enhancement. To further enhance the heat transfer process, metal meshes were placed in the interior of the PW-CNTs composites. Experimental results show that the addition of 10% CNTs by mass leads to a thermal conductivity enhancement of 31.4% and 40.2% respectively in the solid and liquid states. The results also show that the use of metal meshes shortens the charging and discharging durations by at least 40.3% and 30.2%, respectively. Heating and cooling cycling tests have also been carried on the PW-CNTs composites and the results show a large decrease in the thermal conductivity after a few cycles due to severe aggregation of CNTs in PW-CNTs composites.