Sorry if the formulation is imprecise, I'm a biology major trying to study some physics. The question is: So far, my reasoning is: I make an assumption in Step (2) that decreasing the pressure will decrease the temperature. But I'm not sure what the justification is. I only know of the ideal gas law, and I'm not sure if the behavior is the same for incompressible fluids. Maybe incompressibility means fluid is similar to ideal gas behavior, or maybe it holds in general and the incompressibility assumption can be removed? Or maybe it's dependent on the fluid? Thanks for any clarification!