(1) Assuming one side wall temperature based on the temperature of cold and hot fluids;
(2) Calculate the heat transfer coefficient on this side using the criterion relationship equation;
(3) Calculate the heat exchange rate q1 per unit area on this side using the formula q1=a1 (t1 tw1);
(4) Calculate the wall temperature tw2 on the other side using the formula tw2=tw1-q1Rp based on the thermal resistance Rp of the plate heat exchanger plate;
(5) Calculate the heat transfer coefficient a2 on the other side using the criterion relationship equation;
(6) Calculate the heat exchange rate q2 per unit area using the formula q2=a2 (tw2-t2). If the assumed wall temperature is correct, then q1=q2 should be used; If q1 ≠ q2, the wall temperature should be re assumed before calculation until q1 and q2 are basically equivalent.
For accurate and fast calculation, computers can be used; Alternatively, graphical calculation can be used, assuming multiple wall temperatures, to plot the calculated q1 and q2, where the intersection point of q1 and q2 is the wall temperature.