Changes

===Gas cycle===

===Gas cycle===

Gas cycle systems are similar to vapor compression cycle systems, but use the reverse Rankine cycle.  The main functional difference from vapor compression is that the refrigerant remains a gas throughout the entire process.  For this reason, a specially formulated refrigerant is not usually needed.  Regular [[nitrogen]]-dominant air is usually sufficient.  However, this system is also less efficient than vapor compression, and also much larger.<br />

Gas cycle systems are similar to vapor compression cycle systems, but use the reverse Rankine cycle.  The main functional difference from vapor compression is that the refrigerant remains a gas throughout the entire process.  For this reason, a specially formulated refrigerant is not usually needed.  Regular [[nitrogen]]-dominant air is usually sufficient.  However, this system is also less efficient than vapor compression, and also much larger.<br />

Gas cycle refrigeration is used in some cases where high-pressure air is readily available, or chemical refrigerants (like ammonia) are considered too dangerous.  One place this system is popular in aircraft, since both of these criteria are met.<ref>http://www.brighthubengineering.com/hvac/20589-methods-of-refrigeration-gas-cycle</ref>

Gas cycle refrigeration is used in some cases where high-pressure air is readily available, or chemical refrigerants (like ammonia) are considered too dangerous.  One place this system is popular is in aircraft, since both of these criteria are met.<ref>http://www.brighthubengineering.com/hvac/20589-methods-of-refrigeration-gas-cycle</ref>

===Magnetic refrigeration===

===Magnetic refrigeration===