Entransy analysis on optimization of a double-stage latent heat storage unit with the consideration of an unequal separation

A double-stage Latent Heat Storage (LHS) unit is transformed from a single-stage LHS unit, by separating the unit into two portions filled with different Phase Change Materials (PCMs). In this paper, a double-stage LHS unit is optimized with entransy analysis, with the consideration of an unequal separation. The criterion formulas of optimum separation as well as the distribution of coefficient c is derived. The valid range of melting temperature Tm_1 in the first portion is determined. The influence of Tm_1 on the performance of the optimal double-stage LHS unit is discussed. It is concluded that entransy dissipation rate is reduced with the optimum distribution. With the increase of Tm_1, the optimum c decreases in the first portion and increases in the second portion. The optimum c in the first portion is larger than that in the second portion, at the low end of Tm_1; while it is smaller, at the high end of Tm_1. The melting temperature Tm_2 in the second portion varies with Tm_1 as a U-shape curve. An equal separation is the best for a double-stage LHS unit. However, when the melting temperature available deviates from the designated value, the optimum distribution of c should be considered.