Question

A simple ideal Brayton cycle without regenera- tion is modified to incorporate multistage compression with intercooling and multistage expansion with reheating, without changing the pressure or temperature limits of the cycle. As a result of these two modifications,
(a) Does the net work output increase, decrease, or remain the same?
(b) Does the back work ratio increase, decrease, or remain the same?
(c) Does the thermal efficiency increase, decrease, or remain the same?
(d) Does the heat rejected increase, decrease, or remain the same?

Answer 1

Answer 2

(a) The net work output would increase. When multistage compression with intercooling and multistage expansion with reheating are incorporated into the Brayton cycle, the compression process becomes more efficient as intercooling reduces the temperature and pressure at each stage. This allows for higher work extraction during expansion, leading to an overall increase in net work output.

(b) The back work ratio would decrease. The back work ratio represents the ratio of work required for compression to the net work output of the cycle. With multistage compression and intercooling, the work required for compression is reduced due to the lower temperature and pressure at each stage. As a result, the back work ratio decreases.

(c) The thermal efficiency would increase. Thermal efficiency is a measure of the ratio of net work output to the heat input. With multistage expansion and reheating, the expansion process becomes more efficient as reheating increases the temperature and pressure at each stage. This allows for better utilization of the heat input, leading to an increase in thermal efficiency.

(d) The heat rejected would remain the same. The heat rejected in the Brayton cycle is primarily dependent on the temperature difference between the working fluid at the turbine inlet and the cooling medium. The modifications of multistage compression with intercooling and multistage expansion with reheating do not affect this temperature difference. Therefore, the heat rejected would remain the same.