Heat pump and refrigeration cycle

Thermodynamic heat pump cycles or refrigeration cycles are the conceptual and mathematical models for heat pumps and refrigerators. A heat pump is a mechanical system that allows for the transference of heat from one location (the 'source') at a lower temperature to another location (the 'sink' or 'heat sink') at a higher temperature. Thus a heat pump may be thought of as a 'heater' if the objective is to warm the heat sink (as when warming the inside of a home on a cold day), or a 'refrigerator' if the objective is to cool the heat source (as in the normal operation of a freezer). In either case, the operating principles are identical. Heat is moved from a cold place to a warm place. Thermodynamic heat pump cycles or refrigeration cycles are the conceptual and mathematical models for heat pumps and refrigerators. A heat pump is a mechanical system that allows for the transference of heat from one location (the 'source') at a lower temperature to another location (the 'sink' or 'heat sink') at a higher temperature. Thus a heat pump may be thought of as a 'heater' if the objective is to warm the heat sink (as when warming the inside of a home on a cold day), or a 'refrigerator' if the objective is to cool the heat source (as in the normal operation of a freezer). In either case, the operating principles are identical. Heat is moved from a cold place to a warm place. According to the second law of thermodynamics heat cannot spontaneously flow from a colder location to a hotter area; work is required to achieve this. An air conditioner requires work to cool a living space, moving heat from the cooler interior (the heat source) to the warmer outdoors (the heat sink). Similarly, a refrigerator moves heat from inside the cold icebox (the heat source) to the warmer room-temperature air of the kitchen (the heat sink). The operating principle of the refrigeration cycle was described mathematically by Sadi Carnot in 1824 as a heat engine. A heat pump can be thought of as a heat engine which is operating in reverse. Heat pump and refrigeration cycles can be classified as vapor compression, vapor absorption, gas cycle, or Stirling cycle types.