Process Equipment and Plant Design
Fouling factor must be included in the calculation of over all design heat transfer coefficient, when the liquid

Is highly viscous
Containing suspended solids flows at low velocity
Containing suspended solids flows at high velocity
Is of high specific gravity

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Process Equipment and Plant Design
In the case of a shell and tube heat exchanger, the logarithmic mean temperature difference

May be either more or less than geometric mean and arithmetic mean value depending upon whether the flow of stream is co-current or counter-current
Is always less than arithmetic mean value, but more than geometric mean value
Is always less than arithmetic average value
Is always more than arithmetic mean value and the geometric mean value

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