Heat exchangers transfer heat between two or more streams of fluid that flow through the apparatus. A major characteristic of heat exchanger design is the relative flow configuration, which is the set of geometric relationships between the streams.
Counter flow Heat Exchanger
In a counter-flow heat exchanger, the two fluids flow parallel to each other, but in opposite directions. The two fluids flow respectively within the inner tube and through the annular space that separates the two tubes. In practice, a large number of tubes can be inserted within a single surrounding tube, of much larger diameter, known as the shell
Parallel flow Heat Exchanger In a parallel-flow heat exchanger, the two fluids flow parallel to each other, and in the same direction Parallel-flow exchangers make poor use of the available temperature difference when both fluids change appreciably in temperature, in which case they are not used if efficiency is the most important factor in design. They do, however, tend to have more uniform wall temperatures than do counter-flow exchangers