Abstract

Utilization of waste heat from an energy conversion process is a key step in improving the overall energy system conversion efficiency and reducing the cost of energy. Since a supercritical CO2 Brayton power cycle is being considered as an important cycle for the conversion of solar energy to power, we propose to utilize the heat rejected from this cycle to feed a bottoming thermodynamic cycle. Goswami cycle can utilize the low temperature waste heat to produce both power and cooling in the same loop. Moreover, refrigeration and space cooling are usually more expensive than heating in most applications. This paper describes the modeling and simulation results of the combined Brayton and Goswami cycles. The mass flow ratio of the two cycles is determined by the heat exchanger effectiveness method, constraining the minimum allowed temperature difference. The operating parameters that yield the best performance in terms of overall cycle efficiency, net work, and cooling outputs were found through the optimization of a numerical model developed in MATLAB. The cooling production in the Goswami cycle is maximized at the expense of the net work in order to produce the maximum refrigeration output. A maximum combined efficiency for power and cooling generation above 45% can be found when the inlet temperature at the Brayton cycle is set at 700 °C.

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