Mass flow rate through a surface towards specified direction

Battousai07 · September 3, 2019, 14:04

Hi, I need to calculate mass flow rate or velocity through a surface towards specified direction. This surface represents inlet of a sack (closed volume). There is a reverse flow at this surface (towards out of the sack) I need to calculate mass flow rate in to the sack. Is it possible?

ghorrocks · September 3, 2019, 19:26

Yes, the massFlow() CEL expression works it out for you, and includes the effect of any backflow.

Battousai07 · September 4, 2019, 15:26

That's the point, ı don't want to include back flow

ghorrocks · September 4, 2019, 20:18

In the documentation (CFX Reference guide, massflow CEL function) it states that the approximate mass flow can be evaluated by "areaInt_x(Velocity u * Density)@myLoc + areaInt_y(Velocity v * Density)@myLoc + areaInt_z(Velocity w * Density)@myLoc". You can modify this equation by setting the velocity at regions of reverse flow to zero velocity.

Battousai07 · September 6, 2019, 13:28

Hi, first of all thanks for your attention and help. I have tried what you have suggested unfortunately did not work out for me. I need to calculate only velocity (+w). Thanks to you now i am able to monitor towards an axis, is it possible to specify (+w) or (-w) as well?

ghorrocks · September 7, 2019, 08:01

It appears you missed the sentence which read "You can modify this equation by setting the velocity at regions of reverse flow to zero velocity."

It is always better if you figure these things out for yourself, but now I know you want positive w only and not negative w and u and v can be ignored, the equation becomes "areaInt_z(absVal(Velocity w) * Density)@myLoc". (I am not sure about the "absVal" function and cannot look it up as I am not at work. You will have to check this is the correct function in the CFX reference manual, the section on CEL Functions)

September 3, 2019, 14:04	Mass flow rate through a surface towards specified direction	#1
Battousai07 New Member Can Unsal Join Date: Sep 2019 Posts: 14 Rep Power: 7	Hi, I need to calculate mass flow rate or velocity through a surface towards specified direction. This surface represents inlet of a sack (closed volume). There is a reverse flow at this surface (towards out of the sack) I need to calculate mass flow rate in to the sack. Is it possible?

September 3, 2019, 19:26		#2
ghorrocks Super Moderator Glenn Horrocks Join Date: Mar 2009 Location: Sydney, Australia Posts: 17,871 Rep Power: 144	Yes, the massFlow() CEL expression works it out for you, and includes the effect of any backflow. __________________ Note: I do not answer CFD questions by PM. CFD questions should be posted on the forum.

September 4, 2019, 20:18		#4
ghorrocks Super Moderator Glenn Horrocks Join Date: Mar 2009 Location: Sydney, Australia Posts: 17,871 Rep Power: 144	In the documentation (CFX Reference guide, massflow CEL function) it states that the approximate mass flow can be evaluated by "areaInt_x(Velocity u * Density)@myLoc + areaInt_y(Velocity v * Density)@myLoc + areaInt_z(Velocity w * Density)@myLoc". You can modify this equation by setting the velocity at regions of reverse flow to zero velocity. __________________ Note: I do not answer CFD questions by PM. CFD questions should be posted on the forum.

September 7, 2019, 08:01		#6
ghorrocks Super Moderator Glenn Horrocks Join Date: Mar 2009 Location: Sydney, Australia Posts: 17,871 Rep Power: 144	It appears you missed the sentence which read "You can modify this equation by setting the velocity at regions of reverse flow to zero velocity." It is always better if you figure these things out for yourself, but now I know you want positive w only and not negative w and u and v can be ignored, the equation becomes "areaInt_z(absVal(Velocity w) * Density)@myLoc". (I am not sure about the "absVal" function and cannot look it up as I am not at work. You will have to check this is the correct function in the CFX reference manual, the section on CEL Functions) __________________ Note: I do not answer CFD questions by PM. CFD questions should be posted on the forum.

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September 4, 2019, 15:26		#3
Battousai07 New Member Can Unsal Join Date: Sep 2019 Posts: 14 Rep Power: 7	That's the point, ı don't want to include back flow

September 6, 2019, 13:28		#5
Battousai07 New Member Can Unsal Join Date: Sep 2019 Posts: 14 Rep Power: 7	Hi, first of all thanks for your attention and help. I have tried what you have suggested unfortunately did not work out for me. I need to calculate only velocity (+w). Thanks to you now i am able to monitor towards an axis, is it possible to specify (+w) or (-w) as well?