Editing Refrigeration (section)

====Vapor-compression cycle====
{{See also|Vapor-compression refrigeration}}
[[File:Refrigeration.png|frame|right|Figure 1: Vapor compression refrigeration]]
[[File:RefrigerationTS.png|frame|right|Figure 2: Temperature–Entropy diagram]]
The vapor-compression cycle is used in most household refrigerators as well as in many large commercial and [[Industrial refrigerator|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 analyzed on a diagram<ref>[http://web.me.unr.edu/me372/Spring2001/Vapor%20Compression%20Refrigeration%20Cycles.pdf The Ideal Vapor-Compression Cycle] {{webarchive|url=https://web.archive.org/web/20070226113352/http://web.me.unr.edu/me372/Spring2001/Vapor%20Compression%20Refrigeration%20Cycles.pdf |date=2007-02-26}}</ref> as shown in Figure 2. In this cycle, a circulating refrigerant such as a low boiling hydrocarbon or [[hydrofluorocarbons]] enters the [[gas compressor|compressor]] as a vapour. From point 1 to point 2, the vapor is compressed at constant [[entropy]] and exits the compressor as a vapor at a higher temperature, but still below the [[vapor pressure]] at that temperature. From point 2 to point 3 and on to point 4, the vapor travels through the [[condenser (heat transfer)|condenser]] which cools the vapour until it starts condensing, and then condenses the vapor into a liquid by removing additional heat at constant pressure and temperature. Between points 4 and 5, the liquid refrigerant goes through the [[thermal expansion valve|expansion valve]] (also called a throttle valve) where its pressure abruptly decreases, causing [[flash evaporation]] and auto-refrigeration of, typically, less than half of the liquid.

That results in a mixture of liquid and vapour at a lower temperature and pressure as shown at point 5. 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 vapour returns to the compressor inlet at point 1 to complete the thermodynamic cycle.

The above discussion is based on the ideal vapour-compression refrigeration cycle, and does not take into account real-world effects like frictional pressure drop in the system, slight [[thermodynamic reversibility|thermodynamic irreversibility]] during the compression of the refrigerant vapor, or [[ideal gas|non-ideal gas]] behavior, if any. Vapor compression refrigerators can be arranged in two stages in [[cascade refrigeration]] systems, with the second stage cooling the condenser of the first stage. This can be used for achieving very low temperatures.

More information about the design and performance of vapor-compression refrigeration systems is available in the classic ''[[Perry's Chemical Engineers' Handbook]]''.<ref>{{cite book|author1=Perry, R.H. |author2=Green, D.W. |name-list-style=amp |title=Perry's Chemical Engineers' Handbook|edition=6th |publisher=McGraw Hill, Inc.|year=1984|isbn=978-0-07-049479-4|title-link=Perry's Chemical Engineers' Handbook}} (see pp. 12-27 through 12-38)</ref>