Assessment on the effect of longitudinal fins upon melting process in a latent heat thermal energy storage unit

Abstract

Latent heat thermal energy storage(LHTES) unit are an effective technical means to balance the demand and supply of energy. To enhance the heat transfer efficiency of the phase change material(PCM) in the LHTES unit, a series of novel three-tube heat exchangers with longitudinal fins was designed. The study was carried out in terms of the number, length, thickness, and arrangement of fins. Results demonstrate that the thickness change of fins has a significant effect on reducing the melting time of the whole PCM. The thin long fins have a higher melting rate. The complete melting time of the thin long fins was 10.6 % faster than that of the short thick fins. By studying the effect of fin length on the heat storage performance, it was found that the structure appeared to be more reasonable at L = 30 mm and the heat storage time was shortened by 18.0 %. In addition, the use of the lower long and upper short fin arrangement can strengthen the heat transfer. Considering that the amount of heat storage capacity decreases as the number of fins increases, N = 20 is considered as the best fin number. Therefore, we give an optimal combination of fin design parameters (N = 20, L = 30, W = 1), which shortens the total melting time of PCM by 71.2 %. To be conclusive, it is more beneficial to add fins to heat transfer enhancement than to have no fins, saving more energy charging time.