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-   -   Heating of a metal piece in a furnace (http://www.cfd-online.com/Forums/fluent/70791-heating-metal-piece-furnace.html)

 Paulik December 6, 2009 06:42

Heating of a metal piece in a furnace

Hello everyone,

I am trying to view the heating profile of a metal piece within a furnace using Fluent. I've built the geometry in Gambit and now I wanna solve this problem in Fluent but I have a problem: it doesn't work. I can see the heating profile in the furnace and I can see that the metal piece is disturbing the "natural" flow, but I cannot see the profile inside it (no conduction). Does anyone have any idea how to "activate" conduction or how to include that piece in the calculus ?

 JohannV December 7, 2009 02:28

Hi Paulik,
Did you choose the solid property for your metal piece?
And did you selected the coupled option in the wall between the fluid and the metal piece?

 Paulik December 7, 2009 09:55

Heating of a metal piece in a furnace

Yeah, I set all the properties. I also have the wall set to coupled. Look, uploaded a photo with the boundary conditions. Maybe the geometry isn't good. I don't know why it isn't working. The flow near the metal piece is deviated but the temperature inside in constant.
http://www.eucred.ro/profil.jpg
As you can see, the metal piece is neutral.

 JohannV December 7, 2009 10:41

Hi,

I did a mistake last week. May be you have the same one. In my case I expected a clear temperature distribution, but because of the different heat capacities the temperature distribution was vely smooth inside of my metal pice.

Please try to plot the temperature distribution from the wall of the metal pice to several milimeters inside. May be it helps.

If you allredy done this, I have no other sugestions.

Good luck

 Paulik December 7, 2009 10:48

Heating of a metal piece in a furnace

:(( I've already done this. I have made a XY Plot (Temperature vs Lenght inside the body) to see if there is any heat at the boundary but nothing and I also changed the thermal conductivity coefficient for the metalic piece with a value closer to the one of the fluid.

Thanks a lot Johann for trying to help me.

If maybe there are any other person that could help me?

 JohannV December 8, 2009 03:36

Hi paulik,

whats about your y+ value. I read in a anothe forum that this value should be between 1 and 3.

 Paulik December 8, 2009 08:58

Heating of a metal piece in a furnace

Where can I see the y+ value?
I know about the Yplus of the turbulence model but only for plotting and its value is 0 constant.

 JohannV December 8, 2009 10:16

You can find it in:
Display->Contours->Contours of: Turbulence and Wall Yplus

 Paulik December 8, 2009 10:18

Yeah, that one is 0. I have nothing inside. Any suggestion ?

 JohannV December 8, 2009 10:43

As I understood, you have only buoyant flow. Do you consider the gravity and the temperature dependent density?

 Paulik December 8, 2009 10:45

Nope. No gravity and no temp-dens dependence

 JohannV December 8, 2009 10:49

I'm not shure, but could you post a picture with your mesh at the wall?

 Paulik December 8, 2009 10:56

 JohannV December 8, 2009 11:05

I think it has somethink to do with der wall funktion(boundary layer).
If you look at the exuiations of the heat transport (fluent documentation), and the exuiation of y+, there is alwais a term for turbulenc. And if you have only boujant flow, may be there is no turbulence.

 JohannV December 8, 2009 16:00

Hi I just calculated your case and there was the same problem, no heat flux to the metal piece. But after a patch of the turbulent kinetic energy there was a heat flux.

So I think you need some turbulence to transfer the heat.(see the equations in fluent documentation)

I think you can solve the problem with a UDF.

Please let me know if you have successful calculated the case.

 Paulik December 9, 2009 07:26

First of all I want to THANK you so much for helping me and secondly I think I'm screwed up in the head. It doesn't work to me. I Initialize the Turbulent Kinetic Energy Patch to the both interiors but I see no changes. I think I did something wrong from the beginning.
Let me tell you what I defined and maybe you can see the problem from this, if it worked for you.
So, I defined the following:

Boundary Conditions:
• big_interior(inside the furnace) - Interior - Fluid - No source terms and fixed values;
• small_interior(inside the metallic body) - Interior - Solid - No source terms and fixed values;
• up/down walls - Wall - Temperature (300K);
• metallic_walls - Wall - Coupled;
• metallic_walls_shadow - Wall - Coupled;
• left/right walls - Wall - Heat Flux 10 W/m2 and HGR 10W/m2
Models: Energy Ecuation Activated
Viscous: Viscous Heating Activated + Viscous Model K-epsilon
Materials: Aluminum (solid) and Air (fluid)

and the Initialization from the left/right walls.

This is what I am using. If you think something's not right, please let me know.

Once again,
Thanks a lot dude for helping,

Paul

 JohannV December 9, 2009 08:44

hi,

i have the same BC's and additionaly I activated the gravity. I also use temperature dependent density and heat capacity of the air.
But this is not the problem, the velocity distribution on the fluid seems to be physical allright.

I used the laminar solver, because there is no turbulence in the computational domain.

The question is: how is the heatflux calculatet in a laminar case?:confused:

I'm now trying to find it out.:mad:

 Piotrek December 9, 2009 09:36

Hi,

I was reading your post and I do not understand one thing. In your geometry you have heatflux on side walls. Top and bottom walls are set to 300K - constant temperature. Up to this point it is ok.

Than you define all walls of the box to be 300K. If this is a boundary condition, than the surface will simply cool the fluid around, and that is what I see on the picture.

I think that you should set this side wall of the box with zero (0) heatflux instead of temperature condition. Maybe specify tempeature at the bottom of the box, than you should have heat transfer in solid. Correct me if I am wrong. Good luck

 Paulik December 9, 2009 11:35

Still not working

Now the walls of the metallic body are set to Coupled and 0 on Heat Generation. I also set the Laminar Solver.
I now have this profile:

http://www.eucred.ro/noulprofil.jpg

Which is also abnormal because now I have constant temperature inside the body. This is a messed-up problem.
Another strange thing is the temperature profile inside. Take a look at this XY Plot:
http://www.eucred.ro/noulprofilxy.jpg
I understand something happens there. I have a temp. drop on the down corners of the body.

Oh, and I also included the Gravity (y=-9.81) as Johann recommended.

 JohannV December 10, 2009 07:36

Hi Paulic,

I yust calculated your problem again and I have some good results.

I have a heatflux through the aluminum wall and the temperature is slowly inkreasing. We were to impatient;), the result apears after some xK iterations.

Now its up to you to evaluate the physiks of the modell.

Give me your e-mail and I will send you the case file.

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