The highest possible exit temperature would be if we did not get any work out, i.e. the turbine broke down. Now we have a throttle process with constant h assuming we do not have a significant exit velocity.
Exit: 200 kPa, h = hin = 3476.28 kJ/kg ⇒ T = 495°C
Efficiency: η = w/ws = 0
Remark: Since process is irreversible there is no area under curve in T-* diagram that correspond to a q, nor is there any area in the P-v diagram corresponding to a shaft work.
