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How to get Local heat transfer coefficient

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Old   April 16, 2020, 13:13
Default How to get Local heat transfer coefficient
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je young kim
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Hello guys.
Currently, I am simulating rectangular tube with inconsistent heat flux along the fluid direction.
What I wanna do is to calculate local heat transfer coefficient (hx)
I generated few plane along the tube and try to calculate hx.
Based on my knowledge, local coefficient is calculated at surface of the wall using energy balance as below.

qs= -kf dt/dr at wall surface = hx (Ts -Tm) Tm: mean or bulk temp Ts: surface or wall temp.

I tried to plot temp gradient along the perimeter of the tube to get dt/dr at few points. In case that the heat flux is consistent along the radial direction such as circular pipe, it should be fine. However, if the geometry is too complicated, its not easy to consider which point I should take.

Another one is I tried to get wall heat flux at each predefined plane. But it didnt show any value. Probably, the plane is not surface. Is there any way to get local wall heat flux directly? Do I need to define surface or volume instead of plane?
I tried at CFD-POST with volume, it didnt show anything.

I would appreciate if someone comments on this matter.

Ps. I dont want to use surface or wall hear transfer coefficient from the Fluent since the reference temp is user dependent value or mesh dependent value.
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Old   April 16, 2020, 18:19
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Erik
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See the FAQs. in the Wiki on the top of the page (directions are for CFX, but the principle is the same)
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Old   April 17, 2020, 03:38
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Thanks evcelica for the prompt reply.

I already gone through the few threads regarding this matter and FAQ's as well.

Basically, I understood how it is calculated.

I am curious how technically I could assess the values that I need.

To clarify my problem, I want to get local wall heat flux at plane.

The attached figure is simple diagram. I generated one plane (perpendicular to the flow direction).

I would like to get the wall heat flux from the hot fluid. In the plane, the wall heat is transferred by its perimeter instead of cross-sectional area.

In Fluent and CFD-Post side, I couldn't get the wall heat flux.

For Cold fluid zone- metal zone, and hot fluid zone-metal zone, I set coupled wall.

Do I need to pre-set something before the simulation?

It seems that the wall heat flux is accessible only at wall condition.

Is there any way to get wall heat flux and wall temperature?

In the end, I would like to plot Nu or h along the pipe for each fluid zone.

Any idea or suggestions?
Attached Images
File Type: png simple diagram.png (12.3 KB, 18 views)

Last edited by jykim; April 17, 2020 at 07:24.
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Old   April 24, 2020, 23:12
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Of course "Wall Heat Flux" is only available at the wall.
If you need wall heat flux and Temperature, try the variables "Wall Heat Flux" and "Temperature" at the solid side of the interface.
What else do you not understand?
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Old   April 29, 2020, 04:30
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Quote:
Originally Posted by evcelica View Post
Of course "Wall Heat Flux" is only available at the wall.
If you need wall heat flux and Temperature, try the variables "Wall Heat Flux" and "Temperature" at the solid side of the interface.
What else do you not understand?
Let's say there is internal flow along the pipe.

I would like to calculate the local convective heat transfer coefficient and Nu number and plot them along the pipe.

In this case, how do I get heat flux from the wall to inner fluid at each location?

Can you give me advice more in details?
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Old   May 1, 2020, 23:10
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HTC and Nusselt are surface variables, not bulk flow variables.
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