Exploring the impact of inner and middle channel geometries on the melting rate of PCM-metal foam composition in a triplex tube heat exchanger

Abstract

Triplex tube heat exchangers (TTHXs) are devices suitable for storing thermal energy with PCM because they shorten the melting and solidification periods. Studies in literature have revealed that pipe geometries significantly affect the melting performance of PCM in thermal energy storage with TTHX. In the pipe designs carried out in these studies, convection in the heat transfer fluid (HTF) and the heat transfer surface areas of the pipes were considered. However, in addition to convection in the HTF, heat transfer by conduction and convection within the PCM also significantly affects the melting performance. The novelty of this study was to investigate the effects of inner and middle channel combinations with different geometries in TTHX on conduction and natural convection mechanisms in PCM combined with metal foam. Numerical analyses were carried out for nine inner-middle channel combinations with three different metal foam porosity values (epsilon = 0.85, 0.90 and 0.95). At porosity values of 0.85 and 0.90, the highest melting rate was achieved with the triangle-triangle inner-middle channel combination within a certain period, and the charging time was shortened by 16.67 % and 14.44 %, respectively, compared to the base case (circle-circle). For the porosity value of 0.95, it was observed that the most suitable channel combination for melting performance was circle-circle, as natural convection flow became more dominant in heat transfer in liquid PCM. At the porosity value of 0.95, the charging time with TTHX containing the circle-circle combination decreased by values ranging from 29.75 % to 59.86 % compared to other combinations.