Water was employed as the heat transfer fluid because of its high thermal capacity and excellent thermal conductivity. The inner tube and fins are made of copper, while the outer tube is insulated.
The simulation conditions were set as follows: the heat transfer fluid (H.T.F.) temperature is 300 K for melting and 360 K for solidification. The mass flow rate is 0.25 kg/sec, and the initial temperatures are 360 K for melting and 300 K for solidification. The duration of the run is 3600 seconds for melting and 7200 seconds for solidification, reflecting the slower pace of the solidification process compared to melting.
The mesh size was meticulously chosen after numerous evaluation tests to attain the optimal balance between accuracy and time efficiency. It consists of 1,200,000 elements, with each time step test taking approximately 30 seconds. The time step, set at 1 second, was determined through time step evaluation tests during the mesh size selection process. The solution control parameters were adopted from previous studies for consistency.
Result and discussion
The results were visualized in plots displaying the heat transfer rate (q), the volume-averaged liquid fraction, and PCM temperature over time. These plots were complemented by visual observations of liquid fraction and temperature contours, providing valuable insights into the melting and solidification processes. They also highlight the significant role of natural convection in each phase.