Investigations on a complex Brayton cycle under maximum economic and maximum thermodynamic conditions

SYNOPSIS: A complex Brayton cycle is investigated under maximum economic and maximum thermodynamic conditions. The economic function (which is defined as the power output divided by the total cost) and cycle efficiency are optimised with respect to the cycle temperatures, reheat and intercooling pressure ratios for a typical set of operating conditions. It is found that there are optimal values of the turbine outlet temperature, intercooling, reheat and cycle pressure ratios at which the cycle attains the maximum objective function and maximum efficiency. But the optimal values of these parameters corresponding to the maximum economic function are different from those corresponding to the maximum efficiency for the same set of operating conditions. The maximum economic point and the maximum thermodynamic point exist but the economic function corresponding to the maximum efficiency is found to be lower than that which can be attained and vice-versa. Again, all the performance parameters are further enhanced as the component efficiencies, effectiveness of different heat exchangers and the heat capacitance rates of the external reservoirs are increased, while the reverse is found in the case of the working fluid heat capacitance rate. Also the effects of reheat pressure ratio are found to be greater than those of the intercooling pressure ratio while at the same set of operating conditions, the optimal values of reheat pressure ratio are found to be lower than those of the intercooling pressure ratios for all the performance parameters.