Hi everyone,
I would be very grateful if someone could help me in calculating the local and average Nusselt number in a rectangular microchannel, as the default magnitude of the Nusselt number in fluent is incorrect. I know the Nusselt number equation (Nu = h*Dh/kf), but I want the procedures used to calculate it in FLUENT.
With my best wishes.
Dr. Ahmed F. Al-Neama
First of all, go to the reference tab and put the dimension of your diameter value in the place of L value. Then calculate the local bulk temperature across the height of the channel in various sections. You can use the local bulk temperature as a reference temperature to compute the local heat transfer coefficient and Nusselt number.
By integrating or averaging the local Nusselt number along the microchannel, the averaged Nusselt number is calculated.
Ahmed Fouad Al-Neama
You need to draw like 5-6 planes along the cross-section, and compute the following:
Local Nusselt number = [q˙/(Tw−Tf)]*Dh/k
Where:
q˙= local heat flux [W/m2].
Tw= local wall temperature (or maximum temperature at this point) [K].
Tf = local fluid temperature (or the average temperature) [K].
Dh = Hydraulic diameter [m].
k = thermal conductivity [W /( m⋅K)].
For, average Nu, just do the integration.
I would just like to add to Omar's answer, that 5 to 6 planes seems low. Try having more planes near the inlet (to capture the developing flow influence). In the fully-developed region, you can have equally spaced planes less in number.
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