Optimisation of a steady-flow carnot cycle with external irreversibilities for maximum specific output

A steady-how two-phase Carnot cycle is optimised for maximum specific work output for the case in which temperature differences exist between the cycle isotherms and the external reservoirs for a given heat exchanger standard (defined as the product of the surface area A and the heat transfer coefficient h(0)). When the heat transfer process between the cycle and the reservoirs is by convection obeying Newton's law the optimum efficiency is shown to be eta(opt) = 1 - root Tc/Th in which T-h and T-c are the temperatures of the hot and cold reservoirs, respectively. The efficiency is independent of the heat transfer process and is identical to the same expression for a similar non-how irreversible Carnot cycle as derived by Curzon and Ahlborn and ideal Joule-Brayton and Otto cycles when optimised for the same maximum work condition. For the case of both the heat transfer processes following the Stefan-Boltzmann law of thermal radiation the efficiency is dependent upon characteristics of the heat transfer process and can be greater than the Curzon-Ahlborn cycle efficiency. Results are also presented of an analysis of several cycles with the heat transfer processes being different combinations of radiation, condensation and convection processes. Copyright (C) 1996 Elsevier Science Ltd.