Thermal diffusion coefficient empirical formula

Chris S · May 14, 2018, 09:38

Hello,

The empirical formula for the thermal diffusion coefficient provided by Fluent when using the kinetic theory option for thermal diffusivity is supposedly derived from "Principles of Combustion" by K. K. Kuo (1986). I am sitting with the book in front of me and I cannot find anything that resembles this formula. Kuo mentions under the multicomponent diffusion equation that thermal diffusion was not considered. The link to the thermal diffusion coefficients page in the Fluent 17.2 manual is below:

https://www.sharcnet.ca/Software/Ans...diffusion.html

Is there somebody who can explain for me how they have arrived at the formula on this page? Thank you.

LuckyTran · May 14, 2018, 16:15

I don't have the book in front of me.

But if they mentioned that thermal diffusion was not considered, then you shouldn't expect to find the equation that would describe it. Look for the section that does have thermal diffusion (or Soret effects).

Also I think you have misunderstood something. The thermal diffusion coefficient (or thermodiffusion coefficient) is the mass diffusion coefficient which is attributable to thermal diffusion (diffusion of species concentration due to temperature gradients), hence it has the symbol D. This is not the thermal diffusivity (which is the heat diffusion due to temperature gradients), which normally has the greek symbol alpha.

Chris S · May 14, 2018, 18:30

It's strange that Fluent refers to Kuo if the formula is not there. That is if they haven't done some major derivation based on something in the book, or I just can't seem to find it. Would be nice with a page number for what they've used.

Chris S · May 15, 2018, 12:40

Anyone who has any thoughts on this? That'd be deeply appreciated.

Chris S · May 16, 2018, 12:32

A reference to the formula in litterature is all I need, anyone? Thanks

Chris S · May 17, 2018, 09:34

bump, please help

rsabatin · September 11, 2018, 19:49

I think this is the wrong reference. I found the formula in the book
"Applications of Turbulent and Multiphase Combustion" (page 248) also by Kuo.

Have you found other references?

May 14, 2018, 09:38	Thermal diffusion coefficient empirical formula	#1
Chris S New Member Chris Join Date: May 2018 Posts: 5 Rep Power: 8	Hello, The empirical formula for the thermal diffusion coefficient provided by Fluent when using the kinetic theory option for thermal diffusivity is supposedly derived from "Principles of Combustion" by K. K. Kuo (1986). I am sitting with the book in front of me and I cannot find anything that resembles this formula. Kuo mentions under the multicomponent diffusion equation that thermal diffusion was not considered. The link to the thermal diffusion coefficients page in the Fluent 17.2 manual is below: https://www.sharcnet.ca/Software/Ans...diffusion.html Is there somebody who can explain for me how they have arrived at the formula on this page? Thank you.

Similar Threads
Thread	Thread Starter	Forum	Replies	Last Post
Setting the height of the stream in the free channel	kevinmccartin	CFX	12	October 13, 2022 22:43
Compression stoke is giving higher pressure than calculated	nickjuana	CFX	62	May 19, 2015 14:32
Question about thermal expansion coefficient	side_attack	Main CFD Forum	0	December 20, 2013 09:15
Question about heat transfer coefficient setting for CFX	Anna Tian	CFX	1	June 16, 2013 07:28
Two-Phase Buoyant Flow Issue	Miguel Baritto	CFX	4	August 31, 2006 13:02

May 14, 2018, 16:15		#2
LuckyTran Senior Member Lucky Join Date: Apr 2011 Location: Orlando, FL USA Posts: 5,762 Rep Power: 66	I don't have the book in front of me. But if they mentioned that thermal diffusion was not considered, then you shouldn't expect to find the equation that would describe it. Look for the section that does have thermal diffusion (or Soret effects). Also I think you have misunderstood something. The thermal diffusion coefficient (or thermodiffusion coefficient) is the mass diffusion coefficient which is attributable to thermal diffusion (diffusion of species concentration due to temperature gradients), hence it has the symbol D. This is not the thermal diffusivity (which is the heat diffusion due to temperature gradients), which normally has the greek symbol alpha.

May 14, 2018, 18:30		#3
Chris S New Member Chris Join Date: May 2018 Posts: 5 Rep Power: 8	It's strange that Fluent refers to Kuo if the formula is not there. That is if they haven't done some major derivation based on something in the book, or I just can't seem to find it. Would be nice with a page number for what they've used.

May 15, 2018, 12:40		#4
Chris S New Member Chris Join Date: May 2018 Posts: 5 Rep Power: 8	Anyone who has any thoughts on this? That'd be deeply appreciated.

May 16, 2018, 12:32		#5
Chris S New Member Chris Join Date: May 2018 Posts: 5 Rep Power: 8	A reference to the formula in litterature is all I need, anyone? Thanks

May 17, 2018, 09:34		#6
Chris S New Member Chris Join Date: May 2018 Posts: 5 Rep Power: 8	bump, please help

September 11, 2018, 19:49		#7
rsabatin New Member Roberto Sabatini Join Date: Sep 2018 Posts: 1 Rep Power: 0	I think this is the wrong reference. I found the formula in the book "Applications of Turbulent and Multiphase Combustion" (page 248) also by Kuo. Have you found other references?