Overall Heat Transfer Coefficient

Written by Jerry Ratzlaff on . Posted in Thermodynamics

Overall heat transfer coefficient, abbreviated as 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

\(\large{   \frac{ 1 } { U \; A }  =   \frac{ 1 } { h_1 \; A_1 }  +  \frac{ l_1 } { k \; A }  +  \frac{ 1 } { h_2 \; A_2 }    }\)

\(\large{ U  =  \frac{1}{ \frac{1}{h_1} + \frac{l_1}{k_1} + \frac{1}{h_2}  }   }\)     (heat transfer through the plane wall and disregarding radiation)

\(\large{ U  =  \frac{1}{ \frac{1}{h_1} + \frac{l_1}{k_1} + \frac{l_2}{k_2} +  \frac{1}{h_2}  }   }\)     (heat transfer through the plane composit wall, no thermal contact resistance and disregarding radiation)

Where:

\(\large{ U }\)  = overall heat transfer coefficient 

\(\large{ A }\) = contact area for each fluid side

\(\large{ A_1 }\) = contact area for one of the fluids

\(\large{ A_2 }\) = contact area for the other fluid

\(\large{ h_1 }\) = individual heat transfer convection coefficient for one of the fluids

\(\large{ h_2 }\) = individual heat transfer convection coefficient for the other fluid

\(\large{ k }\) = thermal conductivity of the material

\(\large{ l_1 }\) = wall thickness

\(\large{ l_2 }\) = wall thickness

 

Tags: Equations for Heat Transfer Equations for Coefficient Equations for Heat