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Overall Heat Transfer Coefficient

 

Overall Heat Transfer Coefficient Formulas

1UA=1h1A1+l1kA+1h2A2 

U=11h1+l1k1+1h2     (heat transfer through the plane wall and disregarding radiation)

U=11h1+l1k1+l2k2+1h2     (heat transfer through the plane composite wall, no thermal contact resistance and disregarding radiation

Symbol English Metric
U  = overall heat transfer coefficient  Btu/hrft2F   W/m2K 
A = contact area for each fluid side ft2 m2
A1 = contact area for one of the fluids ft2 m2
A2 = contact area for the other fluid ft2 m2
h1 = individual heat transfer convection coefficient for one of the fluids Btu/hr W
h2 = individual heat transfer convection coefficient for the other fluid Btu/hr W
k = thermal conductivity of the material Btuft/hrft2F W/mK
l1 = wall thickness in mm
l2 = wall thickness in mm

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.      

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