A thermodynamic cycle used in refrigeration systems. It has no moving parts and energy is supplied as heat either by an electric heater or a gas burner. Ammonia is usually used as the refrigerant. The absorption cooling cycle has three phases: the liquid refrigerant is evaporated to a vapour thereby extracting heat from its surroundings providing the refrigeration effect; the vapour is then absorbed into another liquid; the refrigerant-containing liquid is regenerated by heating, releasing the refrigerant. The adsorption refrigerator was invented by French engineer Ferdinand Philippe Edouard Carré (1824–1900).