mass sink as a function of concentration

ranjith · May 7, 2010, 02:19

Hi,
I am simulating flow and oxygen consumption by cells in a bioreactor. My fluid is water with oxygen dissolved in it. I am modelling the cells as a mass sink for oxygen. The problem is that the amount of mass consumed by the cells is a function of the oxygen concentration in the vicinity of the cells .When I look at CFX I can only specify constant flux rates for a boundary sink. Please advice on how I can model the sink as a function of the oxygen concentration. Would it be better if I introduce an additional variable...

Ranjith

ghorrocks · May 7, 2010, 07:39

Isn't it a volume mass fraction sink, not a boundary sink? I am not sure what restrictions volume sinks have but I think you will be able to make it a function of the local mass fraction. Not sure, just try it. If not then your suggestion of using an additional variable might be a good work around. What this will probably do is to make the additional variable lag the mass fraction by an iteration which may improve numeric stability.

ranjith · May 7, 2010, 23:50

Thanks Glenn for your reply. I have infact completed the simulation. CFX does take expressions for boundary sources as a function of local mass fraction.

Thank you
Ranjith

ghorrocks · May 8, 2010, 06:46

I thought so. But don't you want a volumetric source, not a boundary source?

ranjith · May 9, 2010, 23:26

True, it is a volumetric sink. But I just converted it into a boundary sink...I just took the the volume function multiplied it by the volume of the cells and then divided it by the area.... I hope that is ok...

May 7, 2010, 02:19	mass sink as a function of concentration	#1
ranjith New Member ranjith Join Date: Dec 2009 Posts: 19 Rep Power: 16	Hi, I am simulating flow and oxygen consumption by cells in a bioreactor. My fluid is water with oxygen dissolved in it. I am modelling the cells as a mass sink for oxygen. The problem is that the amount of mass consumed by the cells is a function of the oxygen concentration in the vicinity of the cells .When I look at CFX I can only specify constant flux rates for a boundary sink. Please advice on how I can model the sink as a function of the oxygen concentration. Would it be better if I introduce an additional variable... Ranjith

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May 7, 2010, 07:39		#2
ghorrocks Super Moderator Glenn Horrocks Join Date: Mar 2009 Location: Sydney, Australia Posts: 17,710 Rep Power: 143	Isn't it a volume mass fraction sink, not a boundary sink? I am not sure what restrictions volume sinks have but I think you will be able to make it a function of the local mass fraction. Not sure, just try it. If not then your suggestion of using an additional variable might be a good work around. What this will probably do is to make the additional variable lag the mass fraction by an iteration which may improve numeric stability.

May 7, 2010, 23:50		#3
ranjith New Member ranjith Join Date: Dec 2009 Posts: 19 Rep Power: 16	Thanks Glenn for your reply. I have infact completed the simulation. CFX does take expressions for boundary sources as a function of local mass fraction. Thank you Ranjith

May 8, 2010, 06:46		#4
ghorrocks Super Moderator Glenn Horrocks Join Date: Mar 2009 Location: Sydney, Australia Posts: 17,710 Rep Power: 143	I thought so. But don't you want a volumetric source, not a boundary source?

May 9, 2010, 23:26		#5
ranjith New Member ranjith Join Date: Dec 2009 Posts: 19 Rep Power: 16	True, it is a volumetric sink. But I just converted it into a boundary sink...I just took the the volume function multiplied it by the volume of the cells and then divided it by the area.... I hope that is ok...