Mohammed Hussein you can refer to this

https://www.youtube.com/watch?v=tLkze27-9HE

it is very helpful

First of all, go to the reference tab and put the dimension of your hydraulic diameter value in the place of L value. Then You need to draw 10-20 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 [K].

Tf = local bulk temperature [K].

(You can use the local bulk temperature as a reference temperature to compute the local heat transfer coefficient and Nusselt number.)

Dh = Hydraulic diameter [m].

k = thermal conductivity [W /( m⋅K)].

For, average Nu, do the integration.

I can tell you for average Nu and average heat transfer coefficient.

In the bottom of the Fluent option tree, there is Report section. There click surface integral. Choose facet average, temperature, wall temperature, choose the plane of interface of solid and Fluid and click calculate. That will be Tw. (Local wall temperature).

For Tf (local bulk temperature), click volume integral then volume average, temparature, then click calculate.

Other values of k, q, Dh are already known so you can calculate average Nu and h from there.

Fluent uses the reference temperature as bulk temperature. So, in theory, it will calculate the global Nusselt using the bulk temperature as input. But, you can create a report to calculate the volume average temperature and use it after the solution as the bulk temperature and create a new variable to calculate the heat transfer coefficient. To calculate the local Nusselt, you can cut your geometry with planes, and calculate the local Nusselt using the cut positions.

Hi Mohammad,

The original formulation is the best way to assess the NU and heat transfer ratio as it finds in enormous high-quality papers. For example, to calculate Nu make use of NU=hD/k. So it would help if you calculate h based on the formulation(Q=mct and ...). For T calculation in the inlet and outlet, use mass average or surface average temperature in the software. See when it gives a closer answer to your experimental trends. Also, for Wall temperature use surface average temperature.

Best,

You can calculate h_local and N_local from:

h=q''/(Tb-Tw).

Nu is the ratio of heat transfer coefficient (W/m² K)  times a hydraulic diameter (pipe diameter for example) to thermal conductivity (W/m/K). Nu=hDh/k

K is the thermal conductivity

See the following video and the tutorial it can help you,

https://www.youtube.com/watch?v=tLkze27-9HE&t=680s