The Refrigerator

Surprisingly, a refrigerator can be considered a heat engine. This statement almost sounds like a paradox, but no, a fridge is actually a heat engine that does negative work. A heat engine is a system where heat is transferred into a "tank" where the pressure caused an increase in volume which pushes a piston up, causing it do work (force times displacement). in conventional heat engines such as those in cars, the system does positive work as more heat enters the system as leaves (work =Qin- Qout). In a refrigerator negative work is done as more heat flows out than in causing the piston to move in a direction that opposes the force (Qin-Qout=negative). Work is also equal to Q-deltaU so if Qnet is negative Work is negative, the system cools, and a refrigerator is formed. I think it is pretty cool that a heat engine and refrigerator work the same way, just opposite. A car engine and refrigerator both do work but one is positive and the other is negative.