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Heat transfer between wall and air in Fluent

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Old   April 4, 2018, 10:05
Question Heat transfer between wall and air in Fluent
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Jimmy Lee
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Dear Friends:

I am focus on how to simulate Heat transfer between wall and air based on convection process.

1. I simulated wall surface temperature in energy-plus(other simulation software).And I import wall surface temperature based on Fluent's profile.

2. I turn on energy button and set standard k-e model.

3. I set wall boundary condition's Temperature used wall temperature profile. and Heat Transfer Coefficient as 11.2 and Free Steam Temperature used wall temperature profile.

4. I set gradient wind velocity in inlet boundary and outflow as the outlet boundary.

After simulation converged, I found the temperature of the area near the wall is really high, almost same with wall temperature. other area temperature is really low. So is my setting wrong to cause the wrong result?

I think that is because of the Heat Transfer Coefficient setting, I set 11.2. But I think the Heat Transfer Coefficient should be not constant.

So how to set Heat Transfer Coefficient? Does someone can give me any idea? Or someone has the same problems? Pls tell me~~THX~~~

Jimmy
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Old   April 4, 2018, 18:08
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Lucky Tran
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Quote:
Originally Posted by jimmy871013 View Post
3. I set wall boundary condition's Temperature used wall temperature profile. and Heat Transfer Coefficient as 11.2 and Free Steam Temperature used wall temperature profile.
This combination is wrong. You are simulating the fluid part right? Then you should be using the fixed wall temperature and using the imported wall temperature profile. Or you can import the wall heat flux and use that as the boundary condition. You shouldn't be "setting the heat transfer coefficient."

Last edited by LuckyTran; April 26, 2018 at 13:43.
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Old   April 26, 2018, 06:08
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Dear LuckyTran:

Thanks for your reply~~~

I want to simulate how the different wall temperature influenced the air. So I think you are right, I want simulate fluid part. So as you said I need set fixed wall temperature and wall temperature profile. But I cannot find how to set fixed wall temperature,I found I can only import profile and set wall temperature using profile....

And do i need to set Free Steam Temperature? Because when I did not set the Free Steam Temperature , the result has no different in the whole area even the surface temperature has very big different. On the other hand, when I set free steam temperature as same with the wall temperature, the result is much better. So could you tell me whether need to set free steam temperature or not?

Thx for your reply~~~I wish you have a nice day~~~

Jimmy
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Old   April 26, 2018, 13:40
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Your responses confuse the heck out of me, so here are step-by-step instructions.

First, import your temperature profile into Fluent.

Go to Boundary conditions, select your wall in the list and click Edit...

Then go to the thermal tab. Under thermal conditions choose temperature (the default is Heat Flux). In the Temperature(k) field instead of constant, you would choose the profile. Click OK. That's it. There is no heat transfer coefficient and no free stream temperature. Do not visit the Convection button in thermal conditions. You don't want that. Make sure you have selected Temperature in the thermal conditions and not anything else.

But I still have no idea what you are simulating. What do you hope to get as an output? The detailed temperature of the fluid and maybe the heat transfer coefficient?
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Old   April 26, 2018, 14:49
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Quote:
Originally Posted by LuckyTran View Post
But I still have no idea what you are simulating. What do you hope to get as an output? The detailed temperature of the fluid and maybe the heat transfer coefficient?
Dear LuckyTran:

Thanks for your reply. My idea is : 1. using Energy-plus to simulate wall surface temperature(Because Energy-plus has advantages in outdoor thermal simulation) 2. using ICEM to create mesh 3. using Fluent to get mesh point location and wall temperature(now all are 300K)profile 4. Based on the point location and wall surface temperature to change the profile(wall temperature) 4. import profile into Fluent 5. using Fluent to simulate how the heated wall (different temperature on the wall)influence the wind.

So my main idea is using Fluent to simulate how the heated wall influence wind(steady state and standard K-E model).

So is that possible to tell me the right process of setting? I did not find the similar case on Internet. THX for your helping~~~

Wishing you have a nice day~~~

Jimmy
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Old   April 26, 2018, 16:44
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So I've explained how to do the second last step, importing. I hope you can figure out how to set the turbulence model, the remaining boundary conditions, and then click the run button.

I can't follow what are steps 3 and 4. My understanding is you would get a wall temperature profile from Energy-plus (in step 1) and then import that into Fluent which is step 4.2. That is you need to provide the wall temperature to Fluent. How do you get a wall temperature from Fluent in step 3? And what is step 4 where you "change" the wall temperature? What are you changing it from and what would you change it to? I feel like you are trying to do another study and I just can't follow what it is.
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Old   April 27, 2018, 03:00
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Dear LuckyTran:

Thanks for your reply. I think I did not explain what I did very clearly,sorry~~

In step 1, I get wall temperature distribution (some wall surface location and these temperature).

In step 2, I got mesh which will be used in CFD simulation. Because I need mapping the temperature which I got in Energy-plus to the mesh, I need get the mesh location and default temperature.

So in step 3, I used Fluent to make profile(include mesh point X,Y,Z coordinate and wall temperature). After that, I change the wall temperature based on the mapping method(using the location to decide closest surface in Energy-plus and its temperature to the mesh point),then make a new profile(same X,Y,Z coordinate but new temperature)

so in step 4, I import new profile then simulate.

So that is my method to simulate how the heated wall influence wind. So could you give me some advise?

Thanks for your attention to my question~~~

Jimmy
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