Harry R Cripps
Optimising heat exchanger approach temperaturesThe amount of heat recovered in a heat exchangers increases the smaller the approach temperature but this makes the exchanger increasingly expensive.
Before a project is finalised, the exchanger approach temperatures should be optimised with regard to energy costs savings, capital cost and return on investment required.
Because optimisation may require a significant amount of work, it is normal practice to assume representative (rule of thumb) approach temperatures for preliminary investigation.
For individual heat exchange duties, economical approach temperatures may vary from as low as 5 deg C for easy to handle liquids, eg clean water etc, up to 50 deg C or more for difficult fluids.