CFX Liquid Evaporation Model

Jinx · January 25, 2010, 06:35

Hi all,
I am trying to model the spray drying of milk powder and have a question with regard to the Liquid Evaporation Model in CFX. As far as I can make out from the documentation, the evaporation rate from the droplet is based on the average moisture content - i.e. the droplet surface moisture level is assumed to be equal to the average moisture level.

For some food products, and definitely for milk when the moisture level falls below the 30-50% level, the presence of the solids causes a moisture gradient from the droplet centre to the surface, which reduces the actual evaporation rate below that corresponding to the average moisture level. This effect has been documented in published literature and has been included in CFD models through the implementation of user defined evaporation models.

My question is: does CFX have a straightforward way of modifying the evaporation model to take account of this reduced drying rate? If not, is there a work-around I can use get the same effect?

Thanks for any help you can give!

ghorrocks · January 26, 2010, 17:18

I have no experience in this area but hopefully you can define the evaporation rate as a CEL function then you can make it a function of whatever you like.

Jinx · January 27, 2010, 17:10

Thanks for the reply Glenn.
I'm familiar with CEL functions for pre and post processing, and for tracking convergence on user defined variables. However I do not have any experience with implementing CEL functions for incorporating in the solver itself - i.e. how to implement my own evaporation model. I haven't found anything really helpful in the standard CFX documentation pack.

Do you know of any documentation to help me with using CEL for implementing a user defined model in the solver?
Thanks again!

ghorrocks · January 28, 2010, 17:31

You can't do much CEL without looking in the documentation. The CEL documentation is in the CFX Reference Guide. (When they first moved it there I could not find it either!)

January 25, 2010, 06:35	CFX Liquid Evaporation Model	#1
Jinx New Member John Join Date: Apr 2009 Posts: 6 Rep Power: 17	Hi all, I am trying to model the spray drying of milk powder and have a question with regard to the Liquid Evaporation Model in CFX. As far as I can make out from the documentation, the evaporation rate from the droplet is based on the average moisture content - i.e. the droplet surface moisture level is assumed to be equal to the average moisture level. For some food products, and definitely for milk when the moisture level falls below the 30-50% level, the presence of the solids causes a moisture gradient from the droplet centre to the surface, which reduces the actual evaporation rate below that corresponding to the average moisture level. This effect has been documented in published literature and has been included in CFD models through the implementation of user defined evaporation models. My question is: does CFX have a straightforward way of modifying the evaporation model to take account of this reduced drying rate? If not, is there a work-around I can use get the same effect? Thanks for any help you can give!

January 27, 2010, 17:10		#3
Jinx New Member John Join Date: Apr 2009 Posts: 6 Rep Power: 17	Thanks for the reply Glenn. I'm familiar with CEL functions for pre and post processing, and for tracking convergence on user defined variables. However I do not have any experience with implementing CEL functions for incorporating in the solver itself - i.e. how to implement my own evaporation model. I haven't found anything really helpful in the standard CFX documentation pack. Do you know of any documentation to help me with using CEL for implementing a user defined model in the solver? Thanks again! Last edited by Jinx; January 27, 2010 at 18:33.

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January 26, 2010, 17:18		#2
ghorrocks Super Moderator Glenn Horrocks Join Date: Mar 2009 Location: Sydney, Australia Posts: 17,854 Rep Power: 144	I have no experience in this area but hopefully you can define the evaporation rate as a CEL function then you can make it a function of whatever you like.

January 28, 2010, 17:31		#4
ghorrocks Super Moderator Glenn Horrocks Join Date: Mar 2009 Location: Sydney, Australia Posts: 17,854 Rep Power: 144	You can't do much CEL without looking in the documentation. The CEL documentation is in the CFX Reference Guide. (When they first moved it there I could not find it either!)