Margin for Fouling of Heat Transfer Surfaces

Adequate fouling factors should be considered (depending on fluid properties, operating condition, etc.). 

Orientation of inlet and outlet nozzles should be veiy carefully decided, especially on the shell side. The possibility of short-circuiting (when inlet and outlet nozzles ate on the same side of the axis of a single-pass heat exchanger) is always there. In the case of multiple-pass heat exchangers (on shell side), there is a possibility of idle pockets at comers of baffles. 

A typical example is the gas-to-gas heat exchanger used in a sulphuric acid plant for reheating the return gasses from intermediate absorption tower before admitting into next converter stage. 

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