1. The problem statement, all variables and given/known data I'm given three temperatures and four pressures for a heat exchanger. I am also given the mass flow rate, which is the same for both the inlets and outlets. There is no heat transfer between the heat exchanger and the surroundings. My task is to find the fourth temperature in the heat exchanger. Both fluids are air treated as an ideal gas. Air1 - (T1 = 610K, P1 = 10^5 Pa, T2 = 860K, P2 = 9.7*10^5 Pa) Air 2 - (T1 = 1020K, P1 = 1.1*10^5 Pa, P2 = 10^5 Pa, T2 = ????) 2. Relevant equations This is what I'm looking for 3. The attempt at a solution Solving for the fourth temperature: Air 2 T2 = P2*(T1/P1) I know this can't be right, but it's all I can think of. I'm drawing a blank on how to find this fourth temperature. Please help!