Thermodynamic analysis of general heat engine cycle with finite heat capacity rates for power maximization

Abstract

In this study, the ideal cycles with finite heat capacity rates is investigated theoretically to maximize power generation using a sequential Carnot cycle model. Although the Carnot efficiency is important, it is limited to evaluating only in terms of heat source/sink temperatures. For the actual heat engine, maximization of power generation is more important than cycle thermal efficiency when utilizing low-grade heat sources such as a waste heat. In this study, power generation optimization is numerically simulated under the fixed conditions of heat source temperatures, heat source flow rate and heat sink temperature. Effect by two design variables, compressor exit temperature and evaporator size ratio, were evaluated during cycle optimization. The optimization was performed using the pattern search algorithm (PSA) under a given thermal capacitance rate ratios and size of heat exchanger (UA) conditions. As a result, designing compressor exit temperature for maximizing the heat received from heat sources does not always maximize the power, but the higher the UA makes the optimum temperature lower, and the power output higher. These idealistic approaches can be useful in designing of cycle where the power maximization is crucial.

Keywords

• Power maximization
• Sequential carnot cycle
• Waste heat recovery
• Pattern search algorithm
• Trilateral cycle