I'm working on a project about cooling and heating, and have a couple of questions needing answers/clarification: Entropy in refrigeration: The pV-diagram for the phase change refrigerator is that of the reversed Otto cycle. This cycle contains two adiabatic and two isochoric processes. The last two being irreversible. Thus the cycle has an entropic increase - since only a Carnot cycle conserves entropy, right? But when is the maximum value of entropy for the refrigeration reached - if it is reached at all? Equilibrium and steady state in a cooling system: Is equilibrium and steady state condition in a cooling system the same? I have understood steady state as the condition where the thermodynamic cycle is in equilibrium (e.g. when a refrigerator has been turned on for a small amount of time). Energy loss in cooling systems: How does energy loss occur in cooling systems? I think friction in the compressor (and maybe the extension valve) accounts for most of the lost energy from the power input, when work is done on the surroundings and not the working substance (e.g. freon). But flow turbulence of the substance plays a part too. But are there other energy loss sources of importance?