Melting in Vertical Cylinders During Thermal Energy Storage

The present study numerically investigates the process of melting in a hollow vertical cylinder, filled with a phase change material (PCM). The PCM used is sodium nitrate, which expands upon melting. Therefore, the cylindrical shell is partially filled with the PCM and the remaining volume is occupied by air. The influence of cylinder shape on the melting and heat transfer rate is analyzed. The numerical model takes both conductive and convective heat transfer into account during the melting process. For the problem being considered here, the dimensionless numbers that characterized the process are the Grashof, Stefan, and Prandtl numbers. The Aspect Ratio (AR) is used to characterize the shape of the cylinder, which is defined as the ratio of the height to the diameter of the cylinder. In this study, a range of AR values from 0.25 to 10 are investigated. Cylinders with small AR, corresponding to high Grashof numbers, lead to lower melting times compared with cylinders with high AR. The partially melted PCM shape differed between the high and low AR cases. The molten PCM stream function was also influenced greatly by the variation in solid PCM shape.