RheoHeat - Calculation example

Example

The overall heat transfer coefficient k [W/m²·K] for the conditions shown in the figure to the right is calculated as:

where λ [W/m·K] is the wall thermal conductivity, α₁ and α₂ [W/m²·K] are the respective individual heat transfer coefficients and k [W/m²·K] is the overall heat transfer coefficient.
Assuming the following numerical values: α₁ = 2,000 W/m²·K α₂ = 20 W/m²·K w = 2 mm λ = 20 W/m·K the result is:


i.e. the overall heat transfer coefficient is almost equal to the individual heat transfer coefficient on side 2. Even with a 100% increase on side 1, i.e. α₁ = 4,000 W/m²·K the k value is still 20 W/m²·K. This is a case which might be at hand when the fluid on side 2 is extremely viscous thus giving very bad heat transfer conditions. If instead α₂ = 200 W/m²·K the k value becomes 179 W/m²·K and with α ₂ = 2000 W/m²·K the k value becomes 909 W/m²·K. If in this case the thickness of the wall is decreased by 50%, i.e. to 1 mm instead of 2 mm, the k value becomes 952 W/m²·K.