$\frac{1}{U_0}=\frac{1}{h_o}+\frac{r}{k}(\frac{A_o}{A_{lm}})+\frac{1}{h_i}(\frac{A_o}{A_i})+R_{f,0}+R_{f,i}$

Example:

Given:

Questions:

Which resistance governs?

What are your recommendations to improve the performance of this exchanger?