16. Overall Heat Transfer Coefficient including Fouling Coefficients

\[\boxed{\frac{1}{U_1A_1} = \frac{1}{h_1A_1} + \frac{1}{h_{1,d}A_1} + \frac{x_w}{k_wA_m} + \frac{1}{h_{2,d}A_2} + \frac{1}{h_2A_2}}\]

where \(h_{1,d}\) and \(h_{2,d}\) are fouling coefficients.