The overall heat transfer coefficient can be used to calculate the total heat transfer through a wall or heat exchanger construction. The overall heat transfer coefficient depends on the fluids and their properties on both sides of the wall, and the properties of the wall and the transmission surface.
For practically still fluids - average values for the overall heat transmission coefficient through different combinations of fluids on both sides of the wall and type of wall - can be found in the table below:
|Fluid||Transmission Surface||Fluid||Overall Heat Transmission Coefficient|
|(Btu/ft2 hr oF)||(W/m2 K)|
|Water||Cast Iron||Air or Gas||1.4||7.9|
|Water||Mild Steel||Air or Gas||2.0||11.3|
|Water||Copper||Air or Gas||2.3||13.1|
|Water||Cast Iron||Water||40 - 50||230 - 280|
|Water||Mild Steel||Water||60 - 70||340 - 400|
|Water||Copper||Water||60 - 80||340 - 455|
Note that these coefficients are very rough. They depends on the fluid velocities, their viscosity, the condition of the heating surfaces, the size of the temperature differences and so on. For exact calculations - always check manufacturing data.