Clean Coefficient, U_C and Fouling Resistance, R_d : Once film coefficients are known, clean coefficient for heat exchangers can be found. It is important to allow for fouling of exchangers. The relationships involved are listed in Table 5.7. Heat transfer resistance in a clean heat exchanger, 1/U_C:

Dirty (design) heat transfer resistance, 1/U_D:

Depending upon heat load and the type of arrangement, heat transfer area (A) can be calculated.

Module for calculation of Design Coefficient.

d_i		(Inside diameter, in)
d_o		(Outside diameter, in)
h_i		(Inside film coefficient, BTU per hr per ft² per deg F)
h_o		(Outside film coefficient, BTU per hr per ft² per deg F)
R_di		(Inside fouling factor, hr ft² deg F per BTU)
R_do		(Outside fouling factor, hr ft² deg F per BTU)
LMTD		(log mean temperature difference deg F)
Q		(Heat load, BTU per hr)