Wall temperature define in fluent

zdz198728 · September 22, 2009, 11:53

Hi, guys:
If I put adiabatic wall temperature boundary condition, combustion happened around the wall. Should the wall temperature equal to fluid temperature when the case reach to steady state? From my case , the answer is no. So Could anyone help me to explain this?thanks

ztdep · September 22, 2009, 23:58

radiation?

zdz198728 · September 23, 2009, 10:14

I keep radiation on, however, the emissivy I set is zero.

Charles Rundle · November 19, 2009, 00:37

Hello,

If I may ask, is there any reason that you set the wall's emissivity to zero? I am assuming that the radiation model was left on to account for radiation given off by the combustion and the medium is treated as participating.

I would expect that the default radiation settings would probably use the emissivity for the absorptivity as well. Which means that your walls are being treated a perfect reflector. Any radiation generated will be reflected back thought the fluid until the fluid absorbs it all again. This may be exactly what you are looking for in which case ignore this part. As I mentioned before combustion is not my area of expertise.

Also how uniform is your fluid temperature? The net radiation flux is zero; to be adiabatic the wall only has to be the same temperature as the fluid adjacent to the wall. There may be a very sharp gradient in temperature near the wall which allows for a substantial difference between bulk fluid temperature and wall temperature despite being adiabatic.

I hope this is helpful and I haven't covered material you already know. Have a good day.

CAR

September 22, 2009, 11:53	Wall temperature define in fluent	#1
zdz198728 New Member Dezhi Zheng Join Date: Sep 2009 Posts: 8 Rep Power: 16	Hi, guys: If I put adiabatic wall temperature boundary condition, combustion happened around the wall. Should the wall temperature equal to fluid temperature when the case reach to steady state? From my case , the answer is no. So Could anyone help me to explain this?thanks

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September 22, 2009, 23:58		#2
ztdep Senior Member p ding Join Date: Mar 2009 Posts: 427 Rep Power: 19	radiation?

September 23, 2009, 10:14		#3
zdz198728 New Member Dezhi Zheng Join Date: Sep 2009 Posts: 8 Rep Power: 16	I keep radiation on, however, the emissivy I set is zero.

November 19, 2009, 00:37		#4
Charles Rundle New Member Charles Rundle Join Date: Oct 2009 Posts: 9 Rep Power: 16	Hello, If I may ask, is there any reason that you set the wall's emissivity to zero? I am assuming that the radiation model was left on to account for radiation given off by the combustion and the medium is treated as participating. I would expect that the default radiation settings would probably use the emissivity for the absorptivity as well. Which means that your walls are being treated a perfect reflector. Any radiation generated will be reflected back thought the fluid until the fluid absorbs it all again. This may be exactly what you are looking for in which case ignore this part. As I mentioned before combustion is not my area of expertise. Also how uniform is your fluid temperature? The net radiation flux is zero; to be adiabatic the wall only has to be the same temperature as the fluid adjacent to the wall. There may be a very sharp gradient in temperature near the wall which allows for a substantial difference between bulk fluid temperature and wall temperature despite being adiabatic. I hope this is helpful and I haven't covered material you already know. Have a good day. CAR