Phase-change of paraffin inside heat exchangers: an experimental study

The article presents an experimental investigation of the charging of phase change material (PCM) inside a concentric annular cavity of horizontal and vertical heat exchangers. A heat transfer fluid (HTF) passes through the inner pipe at three temperatures of 60, 70 and 80 degrees C. The experimental results exhibited that conduction dominates the initial stages of the charging process. As time advances, the buoyancy-driven convection develops and speeds up the charging at the upper portion of the two heat exchangers' orientations. It is also observed that the charging rate is influenced by the inlet water temperature and the orientation of the heat exchangers. The melting times are reduced by about 27.5%, 46.3% for an inlet temperature change from 60 to 70 degrees C and 60 to 80 degrees C, respectively, in the horizontal heat exchanger. The melting time decreases by 32.6% and 50.2% in the vertical heat exchanger for the same temperature differences. In addition, the transient Nusselt number has the same behaviour for two orientations and changes positively with an inlet temperature of HTF. Moreover, the stored energy within PCM increases with the amount of transferred energy from HTF and its temperature.