Effect of inner-tube spacing on charging and discharging performance of latent energy storage heat exchangers

•The charging and discharging progress of the horizontal dual-inner-tube heat exchanger is explored.•The effect of the inner-tube spacing on the performance is explored.•The relationship between HTF’s initial temperature and the effect of inner-tube spacing on the performance is discussed. The inner-tube arrangement has an important impact on the performance of latent thermal energy storage heat exchangers, but the effect of inner-tube spacing on the performance has not been widely concerned. This study simulated numerically the charging and discharging processes of the horizontal dual-inner-tube heat exchangers and researched the effects of inner-tube spacing on the performance parameters of the heat exchangers. The studied performance parameters included the phase change time of phase change material, the charging rate, and the discharging rate. The results show, as the inner-tube spacing increases, the phase change time decreases first and then increases, and both the charging rate and discharging rate increase first and then decrease. Moreover, the inner-tube spacing has a more pronounced effect on the discharging process than the charging process. Among all cases, the performance parameters are optimal when inner-tube spacing is 20 mm. Compared with the case whose inner-tube spacing is 5 mm, the melting time mostly shortens by 5.78%, and the charging rate increases by 5.48% for the heating temperature of 80℃. Additionally, the solidification time mostly shortens by 38.68% and the discharging rate mostly increases by 60.49% when the cooling temperature is 20℃. Furthermore, the heating temperature doesn’t affect the effect of inner-tube spacing on the charging performance, and the effect of inner-tube spacing on the discharging performance also can’t be influenced by the cooling temperature. The research results have a certain reference value for the optimal design of the heat exchangers and its engineering application.