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-   -   wall b.c's (http://www.cfd-online.com/Forums/fluent/32300-wall-b-cs.html)

eric October 10, 2003 07:45

wall b.c's
 
Hi,

What happens in a combustion simulation with heat transfer, if there are no conditions set at the walls?

Will fluent still calculate the temperature of the walls?

Thanks

Eric

Jin-Wook LEE October 12, 2003 21:49

Re: wall b.c's
 
Default wall BC for the energy is 'no heat flux'. If you do not apply any BC, then Fluent calculates the wall temperature.

Sincerely, Jinwook


eric October 13, 2003 07:22

Re: wall b.c's
 
Hi Jinwook,

Thanks for your reply. The reason i ask this question is because i know the wall temperatures in my kiln but i don't know the burner operating conditions i.e. fuel and air massflow rates.

So what i'm going to do is take a guess of what they might be and solve for those conditions. If i get the wall temperatures i want in the solution, then i know i've got the right burner operating conditions. This why i want fluent to solve the wall temperatures. Does this method sound right to you or am i wrong?

My explaination is not very clear but hopefully you'll understand what i'm trying to say, any help is much appreciated,

Regards,

Eric

Jin-Wook LEE October 13, 2003 20:20

Re: wall b.c's
 
I can understand your intention. Your task seems to be very difficult.

I think that one of the possible way is,

1) include solid region.

2) solve conjugate heat transfer with convection and radiation wall BC at the outer wall.

3) get the wall temperature from the solution.

Sincerely, Jinwook


eric October 14, 2003 11:14

Re: wall b.c's
 
Hi Jinwook,

Yes this is exactly what i'm trying to do.

I have included the solid region in my simulation so that there's the internal fluid region, boundary wall, solid region and then outer wall. I have created this as follows

Two concentric pipes and split the outer pipe with the inner pipe to allow the heat transfer through the wall. I hope this is what you mean 'conjugate heat transfer'.

You tell me to apply 'convection and radiation wall BC at the outer wall', can you explain to me how i'd get the heat transfer coefficient for the convection BC?

I don't know the appropriate free stream temperature for my conditions , as it will depend on the wall temperature, so how can I input the free stream temperature, will I take a guess?

Thanks for your help,

Eric

Jin-Wook LEE October 15, 2003 23:59

Re: wall b.c's
 
Heat transfer coefficient is system dependent. You may found the coefficients for similar case from the 'heat transfer handbook'. Otherwise you should have another simulation with free stream condition to get heat transfer coefficient.

As far as I know, free stream temperature does not mean 'near wall temperature'. It means the temperature of 'FREE STREAM', far field from the wall. It may be atmospheric temperature for many cases.

Sincerely, Jinwook



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