Overall Heat Transfer Coefficient Formulas |
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1U⋅A=1h1⋅A1+l1k⋅A+1h2⋅A2 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) |
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Symbol | English | Metric |
U = overall heat transfer coefficient | Btu/hr−ft2−F | W/m2−K |
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 | Btu−ft/hr−ft2−F | W/m−K |
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.