Heat exchangers are devices built for efficient heat transfer from one fluid to another and are widely used in
engineering processes. Some examples are intercoolers, preheaters, boilers and condensers in power
plants. By applying the first law of thermodynamics to a heat exchanger working at
steady-state condition, we obtain:
mi hi=0
where, mi= mass flow of the i-th fluid hi= change of specific enthalpy of the i-th fluid
There are several types of heat exchanger:
recuperative type, in which fluids exchange heat on either side of a dividing wall
regenerative type, in which hot and cold fluids occupy the same space containing a matrix of material that works alternatively as a sink or source for heat flow
evaporative type, such as cooling tower in which a liquid is cooled evaporatively in the same space as coolant.
The recuperative type of heat exchanger which is the most common in practice may be designed according
to one of the following types:
mi 
hi=0