Effect of increasing number and arrangement of hot fluid tube on melting behavior of Phase Change Material in a triplex tube heat exchanger

In this paper three dimensional numerical study of melting of phase change material (PCM) in a triplex tube heat exchanger is studied. Water is used as heat transfer fluid (HTF) which flows through the inner and outer tubes while the shell side is filled with RT35 as the PCM. The main purpose of this study is to investigate the effect of increasing number of inner hot fluid tube and its arrangement on melting behavior of PCM. Also a comparison between triplex and double tube heat exchanger is done. Enthalpy porosity method is used for modeling the phase change process. The result shows that at the initial steps of the melting process, the major mechanism of heat transfer is conduction while afterward natural convection will be main heat transfer mechanism. Increasing number of inner tubes increases heat transfer surface thus the natural convection intensifies in shell side which considerably diminishes the melting time. Increasing number of inner tube in a triplex tube heat exchanger from 1 to 4 leads to 29 percent decrease in melting time. Arrangement of inner tubes in distributed case intensifies the melting. In a triplex tube heat exchanger in comparsion with double pipe melting time is 80 percent less.