Thermal characteristics of paraffin in a spherical capsule during freezing and melting processes

The objective of the present study was to investigate the thermal characteristics of paraffin in a spherical capsule during freezing and melting processes. Experiments were performed with paraffin, i.e., n-tetradecane, and a mixture of n-tetradecane (40%) and n-hexadecane (60%) and water. The parameters were the Reynolds number and the inlet temperature during the freezing process and initial temperature during the melting process for a PCM-thermal-storage system. The phase-change period for the capsule at the edge of a storage tank was shorter than that at the center of the storage tank due to smaller porosity at the center than the edge of the storage tank. Water showed a bigger of subcooling than paraffin. It took longer for water to reach the dimensionless thermal-storage capacity of 1 during the freezing process, and shorter during the melting process than that for paraffin. The average heat-transfer coefficients were affected by the inlet or initial temperature and Reynolds number more during the melting process than during the freezing process due to a natural-convention effect during the melting process. The average heat-transfer coefficients for paraffin were larger by a maximum of 40% than those for water during the freezing and melting processes.