Most unfired heat exchangers, operating with fluids that do not change phase, are of baffled shell-and-tube design, by which is meant that one of the fluids flows within straight or hairpin-bent tubes, whereas the other flow between and around those tubes, within an ah-confining shell, being guided in its path by baffles. These baffles serve to hold the tubes apart, so that the shell-side fluid can flow between them; they also control the path of that fluid to some extent.
Many different designs are used; the choice depends on the relative importance, for the fluids and the application in question, of such factors as the following
- Capital (construction) cost
- Running (especially pumping) cost
- Clean ability
- Tendency to corrosion
- Pressure differences to be sustained
- Dangers associated with leakage
- Temperature range, and liability to thermal stress
Tendency to tube vibration and subsequent fatigue