Performance comparison of an irreversible closed variable temperature heat reservoir Carnot engine under maximum power density and maximum power conditions

Abstract

SYNOPSIS In this paper, power density, defined as the ratio of power output to maximum specific volume in the cycle, is taken as the objective for performance analysis and optimisation of an irreversible Carnot heat engine from the viewpoint of finite time thermodynamics. The engine, coupled to variable temperature heat reservoirs, includes three types of irreversibilities: finite rate heat transfer, heat leakage and internal irreversibility. The results obtained here are compared with those obtained by using the maximum power criterion. The design parameters under optimal conditions have been derived analytically and the effects of the irreversibilities on the general and optimal performances are investigated. The results show that the design parameters at maximum power density lead to smaller and more efficient heat engines. It is also seen that the irreversibilities have a greater influence on the performance at maximum power density conditions than that at maximum power conditions. Also in this analysis, the optimum conductance allocation parameter is analysed at both maximum power density and maximum power conditions by assuming a constrained total thermal conductance. The analytical expressions between the conductance allocation parameter and the thermal efficiency are obtained. The obtained results generalise the results of previous studies and provide guidance for optimal design in terms of power, thermal efficiency and engine sizes for real heat engines. When the heat transfers between the working fluid and the heat reservoirs are carried out ideally and the thermal capacity rates of the heat reservoirs are infinite, the results of this paper then replicate those obtained in recent literature.