Transparent Boundary

Hitch8 · August 3, 2010, 04:04

Dear CFX experts,

I'm modeling the radiation exchange within a cavity at high temperatures. The cavity has a opening at the top. I'm not sure how to define the boundary conditions at the opening that radiation emitted inside the cavity is lost trough this opening. Should I use the option "local temperature"?

Thank you very much in advanced!

Philipp

stumpy · August 3, 2010, 14:03

No, local temperature would mean that the incoming radiation is based on the local fluid temperature at that boundary. You should set an External Black Body Temperature and specify the far field temperature.

Hitch8 · August 4, 2010, 02:33

Thank you very much Stumpy!
One more question: What would be the best way to model a transparent window (emissivity = 0, reflectivity = 0.06 and transmissivity = 0.96)?

Regards,
Philipp

ghorrocks · August 4, 2010, 06:30

Is it inside the simulation or a boundary condition?

If inside the domain it should be a solid domain. If you are in V12 you may also be able to do it as a thin surface/interface. If it is a boundary then forget the window and place whatever gets through the window as the boundary.

Hitch8 · August 6, 2010, 09:46

It is a boundary. I defined now an external black body temperature.

Thank you very much Glenn!

Philipp

August 3, 2010, 04:04	Transparent Boundary	#1
Hitch8 New Member Philipp Join Date: Apr 2010 Posts: 27 Rep Power: 16	Dear CFX experts, I'm modeling the radiation exchange within a cavity at high temperatures. The cavity has a opening at the top. I'm not sure how to define the boundary conditions at the opening that radiation emitted inside the cavity is lost trough this opening. Should I use the option "local temperature"? Thank you very much in advanced! Philipp

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August 3, 2010, 14:03		#2
stumpy Senior Member Join Date: Apr 2009 Posts: 531 Rep Power: 21	No, local temperature would mean that the incoming radiation is based on the local fluid temperature at that boundary. You should set an External Black Body Temperature and specify the far field temperature.

August 4, 2010, 02:33		#3
Hitch8 New Member Philipp Join Date: Apr 2010 Posts: 27 Rep Power: 16	Thank you very much Stumpy! One more question: What would be the best way to model a transparent window (emissivity = 0, reflectivity = 0.06 and transmissivity = 0.96)? Regards, Philipp

August 4, 2010, 06:30		#4
ghorrocks Super Moderator Glenn Horrocks Join Date: Mar 2009 Location: Sydney, Australia Posts: 17,703 Rep Power: 143	Is it inside the simulation or a boundary condition? If inside the domain it should be a solid domain. If you are in V12 you may also be able to do it as a thin surface/interface. If it is a boundary then forget the window and place whatever gets through the window as the boundary.

August 6, 2010, 09:46		#5
Hitch8 New Member Philipp Join Date: Apr 2010 Posts: 27 Rep Power: 16	It is a boundary. I defined now an external black body temperature. Thank you very much Glenn! Philipp