# Mass flow rate through a surface towards specified direction

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 September 3, 2019, 13:04 Mass flow rate through a surface towards specified direction #1 New Member   Can Unsal Join Date: Sep 2019 Posts: 14 Rep Power: 6 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, 18:26 #2 Super Moderator   Glenn Horrocks Join Date: Mar 2009 Location: Sydney, Australia Posts: 17,771 Rep Power: 143 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, 14:26 #3 New Member   Can Unsal Join Date: Sep 2019 Posts: 14 Rep Power: 6 That's the point, ı don't want to include back flow

 September 4, 2019, 19:18 #4 Super Moderator   Glenn Horrocks Join Date: Mar 2009 Location: Sydney, Australia Posts: 17,771 Rep Power: 143 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 6, 2019, 12:28 #5 New Member   Can Unsal Join Date: Sep 2019 Posts: 14 Rep Power: 6 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?

 September 7, 2019, 07:01 #6 Super Moderator   Glenn Horrocks Join Date: Mar 2009 Location: Sydney, Australia Posts: 17,771 Rep Power: 143 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.

 Tags mass flow rate inlet