# boussinesq approximation when temperature difference is large

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 June 24, 2019, 23:11 boussinesq approximation when temperature difference is large #1 New Member   HakminLee Join Date: Jun 2019 Posts: 3 Rep Power: 6 I'm studying on the natural convection of spent fuel in the dry storage system. I understand that boussinesq approximation can be used only when the temperature difference is small. If the temperature range is 300K-500K for example, is it right to simply use an incompressible ideagl gas law that uses the p=rho*R*T law? Or can i just use the boussinesq approximation? i don't know about these. Thank your reply.

 June 25, 2019, 11:38 #2 Senior Member   Erik Join Date: Feb 2011 Location: Earth (Land portion) Posts: 1,171 Rep Power: 23 That temperature range is too large for Boussinesq. I've heard 10% density difference maximum. Ideal gas is not incompressible, it is definitely compressible, and using that for density would be much more appropriate.

June 25, 2019, 20:20
#3
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HakminLee
Join Date: Jun 2019
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Quote:
 Originally Posted by evcelica That temperature range is too large for Boussinesq. I've heard 10% density difference maximum. Ideal gas is not incompressible, it is definitely compressible, and using that for density would be much more appropriate.
Thankyou so much!

September 15, 2020, 15:07
#4
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Sai Krishna
Join Date: May 2018
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Quote:
 Originally Posted by evcelica That temperature range is too large for Boussinesq. I've heard 10% density difference maximum. Ideal gas is not incompressible, it is definitely compressible, and using that for density would be much more appropriate.
Hi evcelica,
I have a doubt regarding coefficient of thermal expansion which we use in boussinesq approximation.
I am doing simulation for natural convection for a pcb in an enclosure. the freestream temp is 322K. i read bousinesq approximation is valid iff
beta * (T-T_ref) <0.05. in this for beta what should I consider. my fluid is air and as its an ideal gas beta = 1/T. so here what temperature should I use.

Thanks for the help

 Tags boussinesq approximation, natural convection