The fundamental optimal relations and the bounds of the allocation of heat exchangers and efficiency for a non-endoreversible brayton cycle

Abstract

In this paper we analyze a Brayton cycle with external and internal irreversibilities. The external ones come from heat transfer with counterflow heat exchangers in the cold and hot sides; the internal irreversibilities are given by the isentropic efficiencies of the compressor and turbine. Optimization is carried out with respect to the pressure ratio and the total inventory of the heat transfer units, using the $\varepsilon$-NTU method. We show the analytical expressions for the efficiency that mazimizes work and the optimal allocation (size) of heat exchangers. We also analyze the asymptotic behavior of these expressions. The results obtained extend a Bejan's model and are more general and useful.