How can I know the propotion of the natural convection of the gas ?

hotboy · March 6, 2016, 06:40

Dear friends!
Now I was modeling the heat transfer of gas in a closed domain.My geometry is natural convection.jpg.
The gas in the closed domain is air .
After the result is converged.I know the total heat transfer rate,but how can I know the propotion of the natural convection of the gas ?
Thank you in advance!
your sincerely hotboy!

LuckyTran · March 6, 2016, 10:16

Do you mean what part of the total surface heat transfer is caused by natural convection?

Take the total surface heat flux and subtract the radiation heat flux.

Or if you mean locally at each point in the fluid?

The natural convection rate is just the advection rate (velocity * internal energy) plus the conduction rate (Fourier's law).

hotboy · March 10, 2016, 00:36

Quote:

Originally Posted by LuckyTran

Do you mean what part of the total surface heat transfer is caused by natural convection?

Take the total surface heat flux and subtract the radiation heat flux.

Or if you mean locally at each point in the fluid?

The natural convection rate is just the advection rate (velocity * internal energy) plus the conduction rate (Fourier's law).

Dear LuckyTran！
Thank you very much for your help!But I can't understand !
1.A face not only emit radiation to other faces but also absorb radiation from other faces.How can I know the net radiation of every face?
2.You said "The natural convection rate is just the advection rate (velocity * internal energy) plus the conduction rate (Fourier's law)".I really can't understand!
I do a simple 2D case about this problem,could you explain the meaning in my case?
The case is there .https://drive.google.com/folderview?...W8&usp=sharing
Thanks again for your help!

LuckyTran · March 10, 2016, 07:54

[QUOTE=hotboy;588934]2.You said "The natural convection rate is just the advection rate (velocity * internal energy) plus the conduction rate (Fourier's law)".I really can't understand!
/QUOTE]

I'm not sure why understanding basic definitions is difficult.

Convection = Advection + Conduction
This is the definition of convection

Conduction rate comes from Fourier's law: q"|conduction = -k grad(T), i.e. -k*dT/dx

This comes from the law of heat conduction

Advection = (advection velocty) * (property being advected)
q"|advection = u * (cp * phi), where phi can be temperature, internal energy, enthalpy, whatever your transport property is

This is a transport mechanism

March 6, 2016, 06:40	How can I know the propotion of the natural convection of the gas ?	#1
hotboy Member wanghuo Join Date: Aug 2014 Posts: 89 Rep Power: 11	Dear friends! Now I was modeling the heat transfer of gas in a closed domain.My geometry is natural convection.jpg. The gas in the closed domain is air . After the result is converged.I know the total heat transfer rate,but how can I know the propotion of the natural convection of the gas ? Thank you in advance! your sincerely hotboy!

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March 6, 2016, 10:16		#2
LuckyTran Senior Member Lucky Join Date: Apr 2011 Location: Orlando, FL USA Posts: 5,674 Rep Power: 65	Do you mean what part of the total surface heat transfer is caused by natural convection? Take the total surface heat flux and subtract the radiation heat flux. Or if you mean locally at each point in the fluid? The natural convection rate is just the advection rate (velocity * internal energy) plus the conduction rate (Fourier's law).

March 10, 2016, 07:54		#4
LuckyTran Senior Member Lucky Join Date: Apr 2011 Location: Orlando, FL USA Posts: 5,674 Rep Power: 65	[QUOTE=hotboy;588934]2.You said "The natural convection rate is just the advection rate (velocity * internal energy) plus the conduction rate (Fourier's law)".I really can't understand! /QUOTE] I'm not sure why understanding basic definitions is difficult. Convection = Advection + Conduction This is the definition of convection Conduction rate comes from Fourier's law: q"\|conduction = -k grad(T), i.e. -kdT/dx This comes from the law of heat conduction Advection = (advection velocty) (property being advected) q"\|advection = u * (cp * phi), where phi can be temperature, internal energy, enthalpy, whatever your transport property is This is a transport mechanism