Numerical investigations of the effect of the flip method on charging/ discharging performance of a vertical shell-and-tube latent heat thermal energy storage unit

To address the issues of uneven heat transfer and low heat storage rate in the vertical shell-and-tube latent heat thermal energy storage (LHTES) unit, in the paper, the flip method is proposed to be applied to melting and solidification processes of units, aiming at prolonging the time for natural convection to work, while alleviating the temperature stratification phenomenon, so as to strengthen thermal performance. The melting and solidification characteristics of vertical units with flipping are revealed by numerical simulation methods. More importantly, the effect of the dimensionless flipping time t* on the charging and discharging processes is explored. Results show that the implementation of flipping significantly boots both charging and discharging rates, with maximum reductions in melting and solidification times of 33.44 % and 13.31 %, respectively, compared with units without flipping. Furthermore, with the increase of t*, the melting and solidification time both show a trend of first decreasing and then increasing, where the optimal melting tm* and solidification ts* are 0.5 and 0.25, respectively. In this mode, the melting-solidification full cycle time is shortened by 14.93 %. The present study provides new ideas for optimal designs and engineering applications of LHTES units.