Editing Heat exchanger (section)

===Phase-change===
[[Image:Kettle reboiler.svg|thumb|right|Typical kettle reboiler used for industrial distillation towers]]
[[Image:Surface Condenser.png|thumb|right|Typical water-cooled surface condenser]]

In addition to heating up or cooling down fluids in just a single [[phase (matter)|phase]], heat exchangers can be used either to heat a [[liquid]] to evaporate (or boil) it or used as [[Condenser (heat transfer)|condensers]] to cool a [[vapor]] and [[Condensation|condense]] it to a liquid. In [[chemical plant]]s and [[Petroleum refinery|refineries]], [[reboiler]]s used to heat incoming feed for [[distillation]] towers are often heat exchangers.<ref>{{cite book|author=Kister, Henry Z.|title= Distillation Design|edition=1st |publisher=McGraw-Hill|year=1992|isbn=978-0-07-034909-4|title-link= Distillation Design}}</ref><ref>{{cite book|author1=Perry, Robert H.  |author2=Green, Don W.|title=Perry's Chemical Engineers' Handbook|edition=6th| publisher=McGraw-Hill|year=1984|isbn=978-0-07-049479-4|title-link=Perry's Chemical Engineers' Handbook}}</ref>

Distillation set-ups typically use condensers to condense distillate vapors back into liquid.

[[Power plant]]s that use [[steam]]-driven [[turbine]]s commonly use heat exchangers to boil [[water]] into [[steam]]. Heat exchangers or similar units for producing steam from water are often called [[boiler]]s or steam generators.

In the nuclear power plants called [[pressurized water reactor]]s, special large heat exchangers pass heat from the primary (reactor plant) system to the secondary (steam plant) system, producing steam from water in the process. These are called [[Steam generator (nuclear power)|steam generators]]. All fossil-fueled and nuclear power plants using steam-driven turbines have [[surface condenser]]s to convert the exhaust steam from the turbines into condensate (water) for re-use.<ref>[http://www.epa.gov/oar/oaqps/eog/course422/ce6b3.html Air Pollution Control Orientation Course] from website of the Air Pollution Training Institute</ref><ref>[http://kolmetz.com/pdf/ENERGY%20EFFICIENCY%20IMPROVEMENT.pdf Energy savings in steam systems] {{webarchive|url=https://web.archive.org/web/20070927225000/http://kolmetz.com/pdf/ENERGY%20EFFICIENCY%20IMPROVEMENT.pdf |date=2007-09-27 }} ''Figure 3a, Layout of surface condenser'' (scroll to page 11 of 34 PDF pages)</ref>

To [[Energy conservation|conserve energy]] and [[cooling capacity]] in chemical and other plants, regenerative heat exchangers can transfer heat from a stream that must be cooled to another stream that must be heated, such as distillate cooling and reboiler feed pre-heating.

This term can also refer to heat exchangers that contain a material within their structure that has a change of phase. This is usually a solid to liquid phase due to the small volume difference between these states. This change of phase effectively acts as a buffer because it occurs at a constant temperature but still allows for the heat exchanger to accept additional heat. One example where this has been investigated is for use in high power aircraft electronics.

Heat exchangers functioning in multiphase flow regimes may be subject to the [[Ledinegg instability]].