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Engineering ToolBox > Overall Heat Transfer Coefficient
The overall heat transfer coefficient for a wall can be calculated as:
1 / U A = 1 / h1 A1 + dxw / k A + 1 / h2 A2 (1)
where
U = the overall heat transfer coefficient (W/m2K)
A = the contact area for each fluid side (m2)
k = the thermal conductivity of the material (W/mK)
h = the individual convection heat transfer coefficient for each fluid (W/m2K)
dxw = the wall thickness (m)
The thermal conductivity - k - for some typical materials: .
The convection heat transfer coefficient - h - depends on
Heat transfer coefficient for some common fluids:
The overall heat transfer coefficient can also be calculated by the view of thermal resistance. The wall is split in areas of thermal resistance where
Surface coatings or layers of "burned" product adds extra thermal resistance to the wall decreasing the overall heat transfer coefficient.
A single plate exchanger with media A transfers heat to media B. The wall thickness is 0.1 mm and the material is polypropylene PP, aluminum or stainless steel.
Media A and B are air with a convection heat transfer coefficient of hair = 50 W/m2K.
The overall heat transfer coefficient U per unit area can be expressed as:
U = 1 / (1 / hA + dxw / k + 1 / hB) (1b)
Using the values from above the overall heat transfer coefficient can be calculated to: