# How to Monitor Volume at specific value

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 April 15, 2014, 06:08 How to Monitor Volume at specific value #1 New Member   Marcin Join Date: Apr 2014 Posts: 4 Rep Power: 4 I have a question regarding CFX Pre. I would like to set a monitor in a following way: [*]Monitor volume (inside fluid domain) which is defined as Iso-volume at value (this can be done in POST - no clue if possible in PRE).[*]For instance I want to measure volume of air inside fluid domain, which has Temperature = 350K and I would like to monitor that in solver manager during simmulation Have you ever came accross such a problem? Any tips which way to go?

 April 15, 2014, 08:16 #2 Super Moderator   Glenn Horrocks Join Date: Mar 2009 Location: Sydney, Australia Posts: 12,709 Rep Power: 98 You cannot do isovolume in the solver. This series of expressions will get close to it: InTemperatureRange = if(T<351[K] && T>349[K],1,0) AirVFInTempRange = Air.Volume Fraction * InTemperatureRange AirVolumeInRange = volumeInt(AirVFInTempRange)@DomainName Then assign AirVolumeInRange to a monitor point.

 April 15, 2014, 09:10 #3 New Member   Marcin Join Date: Apr 2014 Posts: 4 Rep Power: 4 Thanks Glen! Another question though: Analogic to already posted - I want to monitor the Volume of methane at its Lower Explosive Limit (LEL=4.4% mol/mol) As I understood - If I use following: This defines cloud of CH4 at ~LEL and "rejects" volume which does not meet requirement InLELRange = if(CH4 Ideal Gas.Molar Fraction <0.045[mol/mol] && CH4 Ideal Gas.Molar Fraction>0.043[mol/mol],1,0) Definition of the volume meeting ~4.4% mol/mol CH4_VF_InLELRange = CH4 Ideal Gas.Molar Fraction * InLELRange Integration of defined CH4 volume in my Fluid Domain CH4VolumeInLELRange = volumeInt(CH4_VF_InLELRange)@DomainName Please Let me know if it makes sense. I will try to implement that in my model and will share if it worked.

 April 15, 2014, 09:47 #4 New Member   Marcin Join Date: Apr 2014 Posts: 4 Rep Power: 4 OK - After Introducing proposed expressions (for temperature) I am receiving an error message from PRE: The function 'volumeInt' referenced in parameter 'Expression Value' in object '/FLOW:Flow Analysis 1/OUTPUT CONTROL/MONITOR OBJECTS/MONITOR POINT:Cloud Size' has an invalid argument, 'AirVFInTempRange'. Only arguments that consist of a single recognised variable name are supported by the solver. Any Ideas how to fix that?

 April 15, 2014, 18:39 #5 Super Moderator   Glenn Horrocks Join Date: Mar 2009 Location: Sydney, Australia Posts: 12,709 Rep Power: 98 First of all - I used a volume integral over the volume fraction. This gives the total volume. Your post #3 does a volume integral of the molar fraction which is a different thing, and will not give volume. Second - The error message is clear, if cannot find the variable it is naming. Sometimes CEL gets the order of expressions mixed up as it is trying to evaluate the AirVFInTempRange expression after the volumeInt expression and this leads to an error as the volumeInt expression has undefined variables. Try putting the entire expression on one expression: AirVolumeInRange = volumeInt(Air.Volume Fraction * if(T<351[K] && T>349[K],1,0))@DomainName

 Tags cfx.pre.volume.monitor

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