page_title: Heat pump and refrigeration cycle
section_title: Vapor-compression cycle
hierarchical_section_title: Heat pump and refrigeration cycle / Thermodynamic cycles / Vapor-compression cycle
caption_attribution_description: en:Image:RefrigerationTS.jpg with JPEG artifacts removed by a four-line Python program. Hooray, python-imaging!
context_page_description: Thermodynamic heat pump cycles or refrigeration cycles are the conceptual and mathematical models for heat pump, air conditioning and refrigeration systems. A heat pump is a mechanical system that allows for the transmission of heat from one location at a lower temperature to another location at a higher temperature. Thus a heat pump may be thought of as a "heater" if the objective is to warm the heat sink, or a "refrigerator" or “cooler” if the objective is to cool the heat source. In either case, the operating principles are close. Heat is moved from a cold place to a warm place.
context_section_description: The vapor-compression cycle is used in most household refrigerators as well as in light commercial, commercial, and industrial refrigeration systems. Figure 1 provides a schematic diagram of the components of a typical vapor-compression refrigeration system. 
   The thermodynamics of the cycle can be analysed on a diagram as shown in Figure 2. In this cycle, a circulating working fluid commonly called  refrigerant such as Freon enters the compressor as a low pressure and low temperature vapor. The vapor is compressed at constant entropy and exits the compressor superheated. The superheated vapor travels through the condenser which first cools and removes the superheat and then condenses the vapor into a liquid when releasing additional heat at constant pressure and temperature. The liquid refrigerant goes through the expansion valve (also called a throttle valve) where its pressure abruptly decreases, causing flash evaporation and auto-refrigeration of, typically,a small portion of the liquid.
   That results in a mixture of liquid and vapor at a lower temperature and pressure. The cold liquid-vapor mixture then travels through the evaporator coil or tubes and is completely vaporized by cooling the warm air (from the space being refrigerated) being blown by a fan across the evaporator coil or tubes. The resulting refrigerant vapor returns to the compressor inlet to complete the thermodynamic cycle.
  The above discussion is based on the ideal vapor-compression refrigeration cycle, and does not take into account real-world effects like frictional pressure drop in the system, slight thermodynamic irreversibility during the compression of the refrigerant vapor, or non-ideal gas behavior (if any).
caption: Figure 2:Temperature–Entropy diagram of the vapor-compression cycle.
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