A relation between the design parameters of an internally and externally irreversible radiative heat engine is presented to find the maximum power and the efficiency at maximum power output. It was found that the ratio of the reservoir temperatures must be less than half of the cycle-irreversibility parameter and the ratio of area of the heat exchangers must be less than 1.0 for optimum thermal efficiency and maximum power output. Increasing the cycle-irreversibility parameter and the heat-transfer area of the cold side improve thermal efficiency and maximum power output.

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Using the theory of finite-time thermodynamics, an optimal petformance analysis of an internally and externally irreversible Carnot-like single heat engine was studied to determine the maximum power and the efficiency at the maximum power output. Based on this study, the maximum power and the efficiency at the maximum power output of an irreversible combined heat engine (two single irreversible heat engines in a cascade) were obtained for steady state operation The optimal performance of the combined cycle was expressed in terms of two design parameters. The effects of these parameters on the petformance of the combined cycle were examined. The upper and lower bounds to the maximum power and the efficiency at the maximum power were determined. These results were compared with those obtained for a single cycle. It was shown that it is ~ possible to design a combined engine which generates more power and is more efficient than a single cycle.

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