text: A domestic refrigerator is an example of a heat pump: a heat engine in reverse. Work is used to create a heat differential. Many cycles can run in reverse to move heat from the cold side to the hot side, making the cold side cooler and the hot side hotter. Internal combustion engine versions of these cycles are, by their nature, not reversible.
  Refrigeration cycles include:
  *Air cycle machine
  *Gas-absorption refrigerator
  *Magnetic refrigeration
  *Stirling cryocooler
  *Vapor-compression refrigeration
  *Vuilleumier cycle