radiation in CFX

aleghfeli · May 17, 2013, 08:20

Dear topsedar, I am simulating the same case and i don't know how to design the vacuum between two solids where only heat radiation occurs. Did you assume it is as solid and what are the material properties? or is there another way to setup the vacuum? I really appreciate your help. Thank you.

ghorrocks · May 17, 2013, 08:30

My posts tell you exactly how to do it. Model it as a transparent solid with an almost zero thermal conductivity.

aleghfeli · May 17, 2013, 08:49

Dear ghorrocks, how can i make the solid transparent and what are the suggested values of the solid material properties as shown in the attachment. I appreciate your help and thank you

ghorrocks · May 17, 2013, 10:20

The tab you are showing is for a fluid. You need to make it a solid.

In the radiation properties make absorption coeff=0. Now it does not absorb, that is it is transparent.

aleghfeli · May 17, 2013, 10:38

This photo is for the material properties which its thermodynamic state is chosen to be solid. It solid domain will be chosen when applying boundary condition as shown in the attached photo "CFD2.jpg". If I am still doing it wrong please tell me what is the correct way. Otherwise will you please give me the best properties approximation that represents the vacuum material as shown in the first attached "CFD.jpg". In term of "Molar mass, Density, Specific heay capacity, Ref. Spec. Enthalpy, Entropy, Dynamic Viscosity, Thermal Conductivity, Refractive Index, Absorption Coefficient, Scattering Coefficient, Thermal Expansivity"

aleghfeli · May 17, 2013, 15:10

Will you please look into my question? The submission is soon and I need to be done with it. Thank you

ghorrocks · May 17, 2013, 20:12

Almost all of those parameters are irrelevant. Some require values just to keep the solver happy. I will leave it as an exercise for you to work this out. If you are not sure whether a parameter is important or not then do a sensitivity check (run a value then 10x the value and see if it makes a difference) to find out.

And just a comment - do not rush people on a free open forum like this. If you are in a hurry you should pay for support from ANSYS. On a free forum you get help when we get around to it.

sumagaji · January 10, 2019, 10:36

Quote:

Originally Posted by topsedar

Yes I calculated the Flux Distribution of Sun Radiation on the glass and absorber by SolTrace Software. this means that i know the radiation Flux on outer surface of glass and absorber. you are right. i guess in this situation activing Radiation model only in vacuum space and setting some sources on the absorber and glass would complete radiation modeling in my case.

Topsedar, can you help me how you resolve this problem. I am using fluent in the same case with your's and I find it very difficult to simulate Annulus using radiation (surface to surface) and also want to know if I can consider the vacuum space as solid or fluid.

ghorrocks · January 10, 2019, 18:13

Setting up radiation is very different between CFX and Fluent. So if you want help on radiation modelling in Fluent then post on the Fluent forum.

May 17, 2013, 08:20	Radiation	#21
aleghfeli New Member Abdalla Join Date: May 2013 Posts: 4 Rep Power: 13	Dear topsedar, I am simulating the same case and i don't know how to design the vacuum between two solids where only heat radiation occurs. Did you assume it is as solid and what are the material properties? or is there another way to setup the vacuum? I really appreciate your help. Thank you.

January 10, 2019, 18:13		#29
ghorrocks Super Moderator Glenn Horrocks Join Date: Mar 2009 Location: Sydney, Australia Posts: 17,871 Rep Power: 144	Setting up radiation is very different between CFX and Fluent. So if you want help on radiation modelling in Fluent then post on the Fluent forum. __________________ Note: I do not answer CFD questions by PM. CFD questions should be posted on the forum.

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May 17, 2013, 08:30		#22
ghorrocks Super Moderator Glenn Horrocks Join Date: Mar 2009 Location: Sydney, Australia Posts: 17,871 Rep Power: 144	My posts tell you exactly how to do it. Model it as a transparent solid with an almost zero thermal conductivity.

May 17, 2013, 10:20		#24
ghorrocks Super Moderator Glenn Horrocks Join Date: Mar 2009 Location: Sydney, Australia Posts: 17,871 Rep Power: 144	The tab you are showing is for a fluid. You need to make it a solid. In the radiation properties make absorption coeff=0. Now it does not absorb, that is it is transparent.

May 17, 2013, 15:10		#26
aleghfeli New Member Abdalla Join Date: May 2013 Posts: 4 Rep Power: 13	Will you please look into my question? The submission is soon and I need to be done with it. Thank you

May 17, 2013, 20:12		#27
ghorrocks Super Moderator Glenn Horrocks Join Date: Mar 2009 Location: Sydney, Australia Posts: 17,871 Rep Power: 144	Almost all of those parameters are irrelevant. Some require values just to keep the solver happy. I will leave it as an exercise for you to work this out. If you are not sure whether a parameter is important or not then do a sensitivity check (run a value then 10x the value and see if it makes a difference) to find out. And just a comment - do not rush people on a free open forum like this. If you are in a hurry you should pay for support from ANSYS. On a free forum you get help when we get around to it.