How to evalute Sherood number in Fluent

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  • Last Post 10 January 2020
khalidb77 posted this 06 January 2020

Hello 

I have a double diffusion (Heat and Mass transfer) problem within a cavity utilizing air+H2O vapor. I am trying to evaluate Sherwood number in Fluent from the relation

 

here I need to evaluate the concentration derivative then integral it to obtain the number but I do not know how to do that? knowing that X and Z are non-dimensional coordinates? any suggestions please?

Regards,

Khalid

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abenhadj posted this 07 January 2020

You need to get the gradients of the concentration at the surface x=0. Refer to the customization manual to access the gradients of other variables rather velocity.

Best regards, Amine

khalidb77 posted this 07 January 2020

thanks for the reply. I added some derivatives to the menu of variables using the command line in Fluent but I am not sure if concentration derivative with them? if you see picture below there are two derivatives drho-dX & drh0-dy are these derivatives for concentration or enthalpy? knowing that its units in kg/m^4?

rwoolhou posted this 07 January 2020

Have you got energy switched on? 

khalidb77 posted this 07 January 2020

Have you got energy switched on? 

Yes it is 

rwoolhou posted this 07 January 2020

Turn it off and see if the data is still there. 

abenhadj posted this 07 January 2020

You need the derivative of mass fractions to have the gradients of the concentrations.

Best regards, Amine

khalidb77 posted this 07 January 2020

Turn it off and see if the data is still there. 

Yes the derivative of drh0-dX & drho-dY is still exist just temperature derivatives disappear? I think the term rho is referes to density of mixture? So can I transform it to concentration derivative?

 

 

 

 

rwoolhou posted this 07 January 2020

Possibly. You may be better off using a UDF, the gradients are available directly there. 

abenhadj posted this 07 January 2020

Read the Manual as it tells what to do to have species gradients.

Best regards, Amine

khalidb77 posted this 07 January 2020

Read the Manual as it tells what to do to have species gradients.
I  need to ask if I multiply the derivate of density drho-dX by the mass fraction of species can I get the concentration derivative using a custom field function?
Khalid

abenhadj posted this 07 January 2020

No you need the species mass fraction gradients to deduce the molar concentration gradient.

Best regards, Amine

khalidb77 posted this 09 January 2020

Can I use CEL expression in CFD-post to evaluate the mass fraction gradient? is it possible to do that?

Khalid

abenhadj posted this 09 January 2020

Yes it is possible. Do expect different results due to interpolation. I recommend to do everything in Fluent.

Best regards, Amine

khalidb77 posted this 09 January 2020

Thanks for the reply. I tried in Fluent but I did not find anything related with UDF for gradient in the UDF user guide. I am so grateful if you send me the number of section concerned with UDF for gradients in data postprocessing.

Khalid

abenhadj posted this 10 January 2020

Check paragraph from Customization manual: Gradient (G) and Reconstruction Gradient (RG) Vector Macros. 

Best regards, Amine

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