I am simulating a single flow in a 2D tube with a uniform heat flux applying on the outer surface.
I found difficulties finding the Nusselt Number or in other words a correct way to obtain acceptable results, where I'm trying to validate my results with a previous research paper.
if anyone has experience in calculating Local and Average Nusselt Number using Fluent ANSYS or an information that can serve the purpose.
I will appreciate the Help.
Hi,
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://youtu.be/3YJhB7VmVEw
Follow this video, you can find how to calculate the local Nu and Average Nu:
https://www.youtube.com/watch?v=tLkze27-9HE&t=680s
Youcef Attou Your example is not correct for this situation as he asks for flow inside tube.
Mahmoud Haj Ibrahim Please read this conversation..
https://www.researchgate.net/post/How-do-I-calculate-the-heat-transfer-coefficient-in-Fluent#view=558072415f7f7149de8b45cb
I agree with M. H. Shedid. The suggested conversation is very useful.
The steps on how to calculate Nu are listed.
Hi,
The correct way is to calculate the Nu number manually, but some researchers report it directly from ANSYS Fluent.
In the first way, you should do the following steps:
1- Report wall heat flux and wall temperature in some sections.
2- Create isosurfaces in those sections to get the fluid bulk temperature.
3- Put them in the following equation to get the local Nu number.
Nu_x = D * q''/ (kf*(Tb-Tw)).
4- Finally, by averaging the local Nu numbers, you can calculate the average Nu number.
In a direct way, you should use correct reference values (tube diameter as reference length, inlet flow temperature as reference temperature) and get the surface Nu number from the ANSYS Fluent report.
Note that the second gives the correct answer when the fluid bulk temperature is close to the inlet temperature.
So the answer to your question depends on the method used by the reference paper.
Be careful.
The physical properties of a working fluid, which are generally temperature and pressure-dependent, are used to calculate dimensional characteristics. For the precise calculation of these characteristics, it is necessary to clearly define the temperature at which the physical properties of the fluid are taken.
The temperature of the boundary layer changes from Twall on the surface of the plate (tube) to the free fluid temperature at the outer layer of the boundary. The properties of the fluid depend on the temperature and they are changing analogous to the boundary layer. In order to take into account the change in properties with temperature, the properties of the fluid are usually defined for the temperature of the boundary layer. The properties of the fluid are then considered to be constant in these values throughout the heat exchanger.
Nu number is calculated for the temperature of the boundary layer.
The temperature of the boundary layer can be taken to be approximately equal (Twall + Tbulk) / 2
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