Optimal Condition of Finite Number of Heat-Recovery Cycles for a Non-Isothermal Heat Source

This study analyzes a temperature condition that produces maximal power from a non-isothermal heat source under a finite number of heat-recovery thermodynamic cycles. Some previous studies have theoretically analyzed a system utilizing thermal energy from heat sources under multiple thermodynamic cycles assuming a constant heat-source temperature. However, many heat sources for heat-recovery thermodynamic cycles are non-isothermal, where the temperature changes considerably during heat exchange with the cycles. Therefore, it is necessary to consider the temperature change of the heat source. First, a condition that maximizes the power generated by a combination of single/multiple Carnot cycles from constant-specific-heat heat sources is analyzed, and the optimal temperature is derived analytically. Subsequently, simulations of the Rankine cycle and several patterns of the Kalina cycle are compared with those of the analytical model. These comparisons reveal that the proposed model effectively estimates the condition for heat-recovery cycles that produce maximal power from a non-isothermal heat source. Using the proposed method, the required number of cycles and their operating conditions under a given heat source condition are estimated, without any information about cycle configurations, types of working fluids, and iteration of simulation calculation under inappropriate conditions, and a systematic exploration of the optimal system is ensured.