Overall Heat Transfer Coefficient

In the situation of combined heat transfer, it is general practice to associate the total rate of heat transfer (Q), the overall cross-sectional region for heat transfer (A_o), and the overall temperature difference (?T_o) by using the overall heat transfer coefficient (U_o). The overall heat transfer coefficient joins the heat transfer coefficient of the two heat exchanger fluids and the thermal conductivity of the heat exchanger tubes. U_o is particular to the heat exchanger and the fluids which are used in the heat exchanger.

Q - U_oA_o?T₀

Here:

Q = the rate heat of transfer (Btu/hr)  

U_o = the overall heat transfer coefficient (Btu/hr - ft²-^oF)

A_o = the overall cross-sectional area for heat transfer (ft²)

ΔT_o = the overall temperature difference (^oF)