A Joule-Thomson or Isenthalpic Expansion
A gas at pressure P_{1} \text { and temperature } T_{1} \text { is steadily exhausted to the atmosphere at pressure } P_{2} through a pressure-reducing valve. Find an expression relating the downstream gas temperature T_{2} \text { to } P_{1}, P_{2} \text {, and } T_{1}. Since the gas flows through the valve rapidly, one can assume that there is no heat transfer to the gas. Also, the potential and kinetic energy terms can be neglected.