Latent heat thermal energy storage enhancement in triplex tube heat exchangers: A comparative study on different tree-shaped fin structures

Abstract

This study introduces an innovative tree-shaped fin structure (TSFS), named bidirectional TSFS (TSFSi↔o), employed in the middle layer of a triplex tube heat exchanger (TTHE) containing the phase change material RT82. The purpose is to reduce both the completed melting time (CMT) and the completed solidification time (CST) during the charging and discharging stages. This arrangement attaches TSFs to the inner and outer walls sequentially. The novelty lies in filling the gap between the two main branches of the adjacent fins with the sub-branches of the opposite fins. A numerical comparison was conducted among three configurations: 1. common unidirectional TSFS (TSFSi→o), 2. The proposed structure, and 3. Unidirectional radial fin structure (RFS) (RFSi→o), with varying fin counts of 6 and 8. The effects of number, shape, and arrangement of fins on the CMT and CST are investigated. Results demonstrate that TSFSi↔o reduces both CMT and CST by 11.45%/2.54% and 12.45%/4.34%, respectively, in cases with 6/8 fins, compared to TSFSi→o. These amounts of relative changes suggest a relation of RFSi→o > TSFSi→o > TSFSi↔o concerning CMT and CST criteria. The performance improvement achieved by the proposed structure increases as the number of fins decreases, due to the larger gap in configurations with fewer fins.