Heat exchanger:

A heat exchanger is an element which permits the transfer of heat from one fluid (liquid or gas) to another fluid. Purpose for heat transfer involves the following:

1. To heat a cooler fluid through means of a hotter fluid

2. To reduce the temperature of a hot fluid through means of a cooler fluid

3. To boil a liquid through means of a hotter fluid

4. To condense a gaseous fluid through means of a cooler fluid

5. To boil a liquid although condensing a hotter gaseous fluid

Regardless of the function the heat exchanger fulfills, in sequence to transfer heat the fluids included must be at dissimilar temperatures and they must come into thermal contact. Heat could flow only from the hotter to the cooler fluid.

In a heat exchanger there is no direct contact among the two fluids. A heat is transferred from the hot fluid to the metal isolating the two fluids and after that to the cooler fluid.