Helium is used as the working fluid in a brayton cycle with regeneration. the pressure ratio of the cycle is 8, the compressor inlet temperature is 300 k, and the turbine inlet temperature is 1800 k. the effectiveness of the regenerator is 75 percent. determine the thermal efficiency and the required mass flow rate of helium for a net power output of 60 mw, assuming both the compressor and the turbine have an isentropic efficiency of (a) 100 percent and (b) 80 percent.