Rate of Heat Transfer in Heat Exchangers

\[Q = U A\; \Delta T_{m}\] Where, \(U\) is overall heat transfer coefficient.

For thin-walled tubes, where \(A_1 = A_2\), we can write, \[\frac{1}{U} = \frac{1}{h_1} + \frac{x_w}{k_w} + \frac{1}{h_2}\] \(A\) = heat transfer area = \(\pi D L\)

\(\Delta T_{m}\) = mean temperature difference between the two fluids.