# How to calculate percentage mass flux using AcuProbe?

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Hi,

I have created an arbitrary surface in my air duct model to calculate mass flux using AcuProbe, however this returns total mass flux through the surface.

I have a system with two inlets (Inlet 1, Inlet 2) and three outlets (Outlet 1, Outlet 2, Outlet 3).

Is it possible to quantify the amount of air from Inlet 1 only that flows through this arbitrary surface?

I have created a surface in Acu console and did not apply any BCs. Only checked surface output.

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You may try using the Species equation, with the values different for the two inlets - for example Species1 = 0 at Inlet 1 and Species1 = 1 at Inlet 2.  Then you can look at species values on the surface and correlate that with the mass flux percentage for the species.  I would suggest something with that approach - basically using Species as an 'inert' scalar.

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Hi acupro,

Could you please check if this is the correct method. All inlets/outlets consist of identical fluid - air.

I have run my simulation again with the following settings:

Species equation turned ON Advective Diffusive.

Number of Species = 1.

Inlet 1: Species1 = 0

Inlet 2: Species1 = 1

Is it correct to assume that approximately 95 percent of Inlet 2 flows through this arbitrary surface? Is this volume fraction?

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The species equation is using mass fraction, not volume fraction.

The surface integrated value at that point in time gives information about that location - 95% coming from Inlet2 (where Species1 = 1).  It doesn't say anything about where else the flow from Inlet2 might be going.

This also brings up the question of initial conditions.  To what value of Species1 did you initialize the domain?  You may want to track two species instead of one.  You could initialize Species1 and Species2 to zero in the entire domain, then have Inlet1 with Species1 = 1 and Species2 = 0, and Inlet2 with Species1 = 0 and Species2 = 1.  This could help to clarify if any regions in the flow still have results from the initial condition.

There could also be some diffusion, so you may want to include diffusivity models, with a diffusivity value of 0, for the species, in attempt to minimize diffusion.

You may also want to work with your local Altair support team.

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