# Overall Heat Transfer Coefficient

Written by Jerry Ratzlaff on . Posted in Thermodynamics

## Overall Heat Transfer Coefficient

Overall heat transfer coefficient ( $$U$$ ) is the heat transfer between items like walls in buildings or across heat exchangers for the conduction within materials.

### Overall Heat Transfer Coefficient Formula

$$\frac{ 1 } { U \;\dot\;\; A } \;=\; \frac{ 1 } { h_1 \;\dot\;\; A_1 } \;+\; \frac{ dx } { k \;\dot\;\; A } \;+\; \frac{ 1 } { h_2 \;\dot\;\; A_2 }$$

Where:

$$U$$  = overall heat transfer coefficient

$$A$$ = contact area for each fluid side

$$h_1$$ = individual heat transfer convection coefficient for one of the fluids

$$h_2$$ = individual heat transfer convection coefficient for the other fluid

$$A_1$$ = contact area for one of the fluids

$$A_1$$ = contact area for the other fluid

$$k$$ = thermal conductivity of the material

$$dx$$ = wall thickness