Hi, I'm writing a small student-paper on heat pumps, and I'm not at the point where i explain the physics behind it. This is probably a silly question, but there's something I can't seem to understand about the throttling process. First off I get that the enthalpy is conserved through the throttling process, and that Upotential increases, causing the Ukinetic to decrease, which cause the liquid to cool. But this is my problem with the theory: Let's say that the throttle is 2 cm long. If you look at the liquid as it goes into the first cm of the throttle, you decrease the volume of the liquid, causing the temperature to increase. And if you then look at the process where it moves on through the last part of the throttle, it'll increase it's volume, thereby decrease it's temperature. So why aren't the liquid at the same temperature as when it went into the throttle?