Optimization of multistage latent heat storage unit under unsteady inlet temperature based on entransy theory

摘要

Thermodynamic analysis and optimization of a multistage latent heat storage (LHS) unit with unsteady heat transfer fluid (HTF) inlet temperature were performed based on the entransy theory. The expressions of the optimum phase change material (PCM) melting temperatures (T_(m,opt)) were derived. The results indicate that with the increase of stage number (n), T_(mn,opt) increases and T_(mn,opt) decreases, which extends the selection range of PCM. For fixed entransy dissipation condition, increasing n will not change the fluctuation of the HTF outlet temperature; however, a nearly uniform HTF outlet temperature can be obtained by increasing unit length (L). The unsteady HTF inlet temperature has great effects on the optimum phase change temperature. For a 3-stage LHS unit, the optimum phase change temperature of each stage increases by 14.9 K, 26.4 K and 38.0 K respectively with respect to the values obtained by steady method, which causes the heat storage capacity decreases by 6.1% and entransy dissipation decreases by 10.6%. The greater the temperature fluctuation is, the greater the effects will be. The present work can provide guidance for the design of the multistage LHS unit with unsteady HTF inlet temperature.