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For the calculation of Overall Heat transfer coefficient for fouling factor R, which one of the following expression do we use?

For the calculation of Overall Heat transfer coefficient for fouling factor R, which one of the following expression do we use? Correct Answer (hi-1+ho-1 + R)-1

When a heat exchanger is used with a fouling liquid, it leaves traces/deposits on the surface of the separating wall which reduces the overall heat transfer coefficient of the HE. This extra factor which reduces it is specified as the dirt factor (R), which is represented as H = (hi-1+ho-1 + R-1)-1.

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