A heat exchanger is a component that allows the transfer of heat from one fluid (liquid or gas)
to another fluid. Reasons for heat transfer include the following:
1. To heat a cooler fluid by means of a hotter fluid
2. To reduce the temperature of a hot fluid by means of a cooler fluid
3. To boil a liquid by means of a hotter fluid
4. To condense a gaseous fluid by means of a cooler fluid
5. To boil a liquid while condensing a hotter gaseous fluid
Regardless of the function the heat exchanger fulfills, in order to transfer heat the fluids involved
must be at different temperatures and they must come into thermal contact. Heat can flow only
from the hotter to the cooler fluid.
In a heat exchanger there is no direct contact between the two fluids. The heat is transferred
from the hot fluid to the metal isolating the two fluids and then to the cooler fluid.