How to evalute Sherood number in Fluent

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  • Last Post 2 weeks ago
khalidb77 posted this 2 weeks ago

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 2 weeks ago

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 2 weeks ago

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 2 weeks ago

Have you got energy switched on? 

khalidb77 posted this 2 weeks ago

Have you got energy switched on? 

Yes it is 

rwoolhou posted this 2 weeks ago

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

abenhadj posted this 2 weeks ago

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

Best regards,

Amine

khalidb77 posted this 2 weeks ago

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 2 weeks ago

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

abenhadj posted this 2 weeks ago

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

Best regards,

Amine

khalidb77 posted this 2 weeks ago

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 2 weeks ago

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

Best regards,

Amine

khalidb77 posted this 2 weeks ago

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

Khalid

abenhadj posted this 2 weeks ago

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

Best regards,

Amine

khalidb77 posted this 2 weeks ago

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 2 weeks ago

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

Best regards,

Amine

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