Entransy analysis on the performance of the counter-flow heat exchangers for a double evaporating temperature chiller

The double evaporating temperature (DET) chiller has been considered as a credible method to realize temperature and humidity independent control (THIC). Energy performance optimization is of great significance for the extensive application of the DET chiller. In this paper, entransy method is employed to analyze heat transfer performance of heat exchangers based on the extremum principle of entransy dissipation (EPED) and the minimum entransy dissipation-based thermal resistance (EDTR). The entransy dissipation rate and EDTR are discussed in detail to indicate the impacts of t_l,c, t_h,c (i.e., temperature of low temperature chilled water, high temperature chilled water), MC(R32): MC(R236fa) (i.e., mass concentration ratio of R32 to R236fa), and structural parameters on heat transfer performance of heat exchangers. The results indicate that the lowest entransy dissipation rate of heat exchangers are achieved when MC(R32): MC(R236fa) is 40%: 60%. The design t_l,c/t_h,c are suggested to be set at 7/16 °C to reduce the entransy dissipation rate and EDTR of heat exchangers, which is beneficial to strengthen energy utilization of the chiller for energy saving. Considering the significant effect of heat capacity ratio of two steams on the EDTR, m_r (i.e., mass flow rate of refrigerant) and m_l,c/m_h,c/m_c (i.e., mass flow rates of low/high temperature chilled water/cooling water) should be increased and decreased, respectively.