Fouling factor in heat exchangers

More about heat exchangers, and in particular let’s face the topic of fouling factor in heat exchangers. This is a relevant topic in order to ensure the proper thermal transfer efficiency in exchangers, as I’m often asked about it. Fluids flowing inside heat exchangers can indeed contain particles that lay down in sediments in the long term, sticking on heat transfer surfaces and lowering the exchanger’s thermal efficiency.

The fouling factor is a sizing up coefficient to be applied while engineering a heat exchanger. In fact, a higher margin must be accounted in the sizing of a heat exchanger, counteracting the fouling on heat transfer surfaces due to the settling of fouling particles.

The evaluation of the coefficient relies on the kind of flowing movements involved in the heat exchangers, impacting the quantity of particles that can buildup on thermal transfer surfaces. The fouling factor then varies depending on the kind of heat exchanger, being different for a shell & tube exchanger or a plate heat exchanger. The effective fouling factor values for a plate heat exchanger are ten times lower than the ones applicable to shell & tube heat exchangers, because fluids in a plate heat exchanger have a much more turbulent flow.

A turbulent flow of the fluid within plate heat exchangers allows to drag the particles that have the potential to settle on heat transfer surfaces, thus requiring a lower oversizing coefficient of the exchanger. Another reason is represented by the construction of the kind of heat exchanger itself: a shell & tube exchanger, once it’s manufactured, cannot be expanded, while a plate heat exchanger allows to vary and increase the number of plates, boosting its thermal transfer efficiency in case of fouling fluids or different operating conditions compared to design parameters.