Hello. I was working on a sample problem on my thermodynamics book about isentropic nozzles. Pressures, velocities, and temperatures of steam entering to a non isentropic nozzle and exiting it are known. The question asks me to find the velocity of the steam exiting, if the nozzle were isentropic. I find the amount of irreversibilities using entropy data and then find the specific entropy of the exiting steam. Here is my question: The solution says the exiting pressure remains the same and the temperature decreases if the nozzle were isentropic. What is the reason for that? Couldn't the pressure change and temperature remain the same? I hope you understand my question and thank you very much for your attention!