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Natural Convection around two spheres in a box - chtMultiRegioSimpleFoam

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Old   January 14, 2015, 17:47
Default Natural Convection around two spheres in a box - chtMultiRegioSimpleFoam
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Hello guys,

i want to share with you my case. I am making a new post because i did not find anything from all the threads i saw in this Forum, i really hope that someone will be interesting to solve problem together!

I USE SALOME 6.6.0 FOR MESHES AND OPENFOAM 2.3.X

I have to study a simple heat transfer between two spheres suspended in the air in a box (or room) as you can see from the pictures in the following link:

http://imagizer.imageshack.us/a/img661/3933/3stE7n.png
http://imageshack.com/a/img537/559/couMpy.png

The sphere 1 is at 300K the bridge (blue cylinder) at 400 K and the sphere 2 at 400 K and they are suspended in the air for example in a room or in a box.

I want to study the heat transfer from the sphere 2 to the sphere 1 through the bridge which shares the two surfaces with them .

I started making a search and i found that a good solver for this case could be chtMultiRegion. I chose chtMultiRegionSimpleFoam so i started with the a simple case (1 sphere suspended in the air) with a flow over the sphere and it works perfectly, but in this case which i am sharing with you i have natural convection...

So my case is actually a natural convection let's say in a room or box due to the heat transfer between the sphere 1 and sphere 2

(in my domain i defined 4 fixedWall which are the walls of the room)

My BC on the walls are:


fixedWall

T : zeroGradient
P: zeroGradient
P_rgh: zeroGradient
U: fixedValue
uniform (0 0 0)

in the folder costant i changed the direction of g (9.81) and it is directed downwards as the z axe (the longer side of the box).

So finally my questions are:

1. Why do not i get i good result with these BCs ?
2. Do you think that should i change the solver ? But as you can see
http://imageshack.com/a/img901/7827/AGlbOE.png
the cht is made also for buoyant cases
3. What do you think about my case ?

I wanna remark that i am just interested to study the heat transfer between the spheres without convective flux (natural convection)

Please i would like to have same help because i worked for weeks getting anything good. I did not upload my whole case, if are interested i ll send you by email or i ll attach here as a attachment.

Thank you in advance

best regards

Salvo
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Old   January 15, 2015, 04:34
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Michael Leck
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Hy,

can you explan your Problems exactly? What isn't good?

In the P-file I would put all parameters to "calculated".

I sent you an message to send me your file. I'll have a look on it.

Quote:
Originally Posted by salvo-K61IC View Post
Hello guys,

i want to share with you my case. I am making a new post because i did not find anything from all the threads i saw in this Forum, i really hope that someone will be interesting to solve problem together!

I USE SALOME 6.6.0 FOR MESHES AND OPENFOAM 2.3.X

I have to study a simple heat transfer between two spheres suspended in the air in a box (or room) as you can see from the pictures in the following link:

http://imagizer.imageshack.us/a/img661/3933/3stE7n.png
http://imageshack.com/a/img537/559/couMpy.png

The sphere 1 is at 300K the bridge (blue cylinder) at 400 K and the sphere 2 at 400 K and they are suspended in the air for example in a room or in a box.

I want to study the heat transfer from the sphere 2 to the sphere 1 through the bridge which shares the two surfaces with them .

I started making a search and i found that a good solver for this case could be chtMultiRegion. I chose chtMultiRegionSimpleFoam so i started with the a simple case (1 sphere suspended in the air) with a flow over the sphere and it works perfectly, but in this case which i am sharing with you i have natural convection...

So my case is actually a natural convection let's say in a room or box due to the heat transfer between the sphere 1 and sphere 2

(in my domain i defined 4 fixedWall which are the walls of the room)

My BC on the walls are:


fixedWall

T : zeroGradient
P: zeroGradient
P_rgh: zeroGradient
U: fixedValue
uniform (0 0 0)

in the folder costant i changed the direction of g (9.81) and it is directed downwards as the z axe (the longer side of the box).

So finally my questions are:

1. Why do not i get i good result with these BCs ?
2. Do you think that should i change the solver ? But as you can see
http://imageshack.com/a/img901/7827/AGlbOE.png
the cht is made also for buoyant cases
3. What do you think about my case ?

I wanna remark that i am just interested to study the heat transfer between the spheres without convective flux (natural convection)

Please i would like to have same help because i worked for weeks getting anything good. I did not upload my whole case, if are interested i ll send you by email or i ll attach here as a attachment.

Thank you in advance

best regards

Salvo
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Best regards
Michael
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Old   January 16, 2015, 13:19
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Alex
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zfaraday will become famous soon enough
You chose the proper solver for your case, but remember: chtMultiRegionSimpleFoam is for steady state and chtMultiRegionFoam is for time-depending evolutions.

What kind of bad results are you getting with this configuration?

Cheers,

Alex
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Web site where I present my Master's Thesis: foamingtime.wordpress.com

The case I talk about in this site was solved with chtMultiRegionSimpleFoam solver and involves radiation. Some basic tutorials are also resolved step by step in the web. If you are interested in these matters, you are invited to come in!
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Old   January 16, 2015, 14:23
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Hi zfaraday,

thank you for your reply!

I am not sure with the BCs that i used... I do not know if in this room a have to use 6 walls or i have to use inlet and outlet and 4 walls to make it converge, but actually i am just interested the the heat transfer from the hot sfere to the cold sphere. Which BCs do u suggest me? if u want to have a look i can send u the case

thank you in advance

best regards
salvo
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Old   January 16, 2015, 14:27
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Alex
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Send me your case and I will take a look when I have time (I don't know if I will be able to do it this weekend...).

alexx.roque@gmail.com
__________________
Web site where I present my Master's Thesis: foamingtime.wordpress.com

The case I talk about in this site was solved with chtMultiRegionSimpleFoam solver and involves radiation. Some basic tutorials are also resolved step by step in the web. If you are interested in these matters, you are invited to come in!
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