Abstract
An irreversible cycle model of a Braysson heat engine operating between two heat reservoirs is used to investigate the thermoeconomic performance of the cycle affected by the finite-rate heat transfer between the working fluid and the heat reservoirs, heat leak loss from the heat source to the ambient and the irreversibility within the cycle. The thermoeconomic objective function, defined as the total cost per unit power output, is minimized with respect to the cycle temperatures along with the isobaric temperature ratio for a given set of operating parameters. The objective function is found to be an increasing function of the internal irreversibility parameter, economic parameters and the isobaric temperature ratio. On the other hand, there exist the optimal values of the state point temperatures, power output and thermal efficiency at which the objective function attains its minimum for a typical set of operating parameters. Moreover, the objective function and the corresponding power output are also plotted against the state point temperature and thermal efficiency for a different set of operating parameters. The optimally operating regions of these important parameters in the cycle are also determined. The results obtained here may provide some useful criteria for the optimal design and performance improvements, from the point of view of economics as well as from the point of view of thermodynamics of an irreversible Braysson heat engine cycle and other similar cycles as well.
Highlights
The Braysson cycle is a hybrid power cycle based on a conventional Brayton cycle for the high tempe rature heat addition while adopting the Ericsson cycle for the low temperature heat rejection as proposed and investigated by Frost et al [1] using the first law of thermodynamics
The objective function is optimized with respect to the cycle temperatures for a given set of operating parameters
The minimum objective function and the corresponding power output as well as some other important parameters are calculated for a typical set of operating conditions
Summary
The Braysson cycle is a hybrid power cycle based on a conventional Brayton cycle for the high tempe rature heat addition while adopting the Ericsson cycle for the low temperature heat rejection as proposed and investigated by Frost et al [1] using the first law of thermodynamics. One can analyze the optimal performance of an irreversible Braysson heat engine cycle It is seen from Eq(12) that the objective function is a function of two variables (T1, T3 ) for given values of the isobaric temperature ratio x and other parameters. The optimal value of T1 at the minimum objective function is greater than that of T1 at the corresponding maximum power output, i.e. where T1,max are the maximum obtainable temperatures for a given set of operating parameters. Because the larger the internal irreversibility parameter R and the isobaric temperature ratio x are, the larger the total irreversibility in the cycle and the smaller the corresponding power output and the larger will be the cost of the system and the large value of the objective function. The objective function goes up as any one of the economic parameters increases but the effects of k 2 and k3 are more than those of k 1 on the objective function at the same set of operating condition
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