#### Heat Transfer

Q.

Fouling factor for a heat exchanger is given by (where, U1 = heat transfer co-efficient of dirty surface U2 = heat transfer co-efficient of clean surface)

A. U_1 - U_2
B. 1/U_1 - 1/U_2
C. 1/U_2 - 1/U_1
D. U_2 - U_1