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In
addition to heating up or cooling down fluids in
just a single phase, heat exchangers can be used
either to heat a liquid to evaporate (or boil) it or
used as condensers to cool a vapor and condense it
to a liquid. In chemical plants and refineries,
reboilers used to heat incoming feed for
distillation towers are often heat exchangers.
Distillation set-ups typically use condensers to
condense distillate vapors back into liquid.
Power plants which have steam-driven turbines
commonly use heat exchangers to boil water into
steam. Heat exchangers or similar units for
producing steam from water are often called boilers
or steam generators.
In the nuclear power plants called pressurized water
reactors, special large heat exchangers which pass
heat from the primary (reactor plant) system to the
secondary (steam plant) system, producing steam from
water in the process, are called steam generators.
All fossil-fueled and nuclear power plants using
steam-driven turbines have surface condensers to
convert the exhaust steam from the turbines into
condensate (water) for re-use.
In order to conserve energy and cooling capacity in
chemical and other plants, regenerative heat
exchangers can be used to transfer heat from one
stream that needs to be cooled to another stream
that needs to 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 a the heat
exchanger to accept additional heat. One example
where this has been investigated is for use in high
power aircraft electronics. |
