Numerical study of thermal performance of a PCM in a modifying tube-bundle latent heat thermal storage

Abstract

The main aim of this study is to numerically investigate the thermal performance of a newly designed modifying tube-bundle Latent Heat Thermal Storage (LHTS). The new LHTS design proposed a half-cylindrical tube attached to the Heat Transfer Fluid tube, which implies making the PCM indirect contact with the HTF tube. This reduces the heat transfer resistance by eliminating the metal construction of the tubes. For this purpose, a 3D numerical model was developed based on mass, momentum and energy conservations using ANSYS Fluent software. After validating the model developed by comparing numerical results with those obtained experimentally by a published study, the PCM liquid fraction and amount of power stored during the melting and solidification were studied. Water and lauric acid as a working fluid and PCM were implemented in the model. In addition, three different Heat Transfer Fluid (HTF) inlet temperatures 15°C,20°Cand25°C, and HTF’s flow rates in terms of Reynolds number 1000,1500and2000 were tested. The thermal behaviour of the present LHSU design was compared with that of the same volume double pipe LHTS unit. Results showed that the melting and solidification processes of the proposed storage were very uniform, with convection and conduction heat dominating PCM melting and solidification, respectively. The increase in the heat transfer contact area between the HTF and the tube bundle contributed significantly to the PCM melting and solidification acceleration, making each tube bundle behave as a single storage unit. Therefore, the time required for complete melting and solidifying of the PCM was half (50%) of the time needed for the same amount in the double pipe LHTS. Similarly, the melting and solidification time in the preset storage was shortened by about 22% and 41.6%, respectively, compared with the regular tube LHTS unit.