CFD Online Discussion Forums - Gas Mixing Measurements

Hi!

I took the liberty of creating a new thread.

My case is pretty straight forward. I have two parallel pipes. The smaller one located inside the bigger one. Eventually the smaller pipe ends and the mixing of nitrogen (bigger pipe) and helium (smaller pipe) begins. The flow rates are controlled by the inlet velocities (1% helium, 99% nitrogen).

What I'm going to investigate is the level of mixing. I've been told that the CoV (Coefficient of Variation = standard deviation / mean) represents how well the mixture has blended.
CoV = 1 means no mixing, while CoV = 0 indicates a perfect mix?

With this being said I think I'm ready to define my problem. As you can see in the code below (functions output in controlDict), the CoV is greater than one. This means that the difference in concentration at a given measurement point is significantly higher or lower than the mean concentration of the cross section at the majority of measurement points? I.e. there is definitely not a uniform mix?
Also, the flow rates given by my initial conditions doesn't seem right either (0.01-0.99). The inlet conditions have been verified several times. I could try changing from a velocity condition to a flow rate condition, although I can't see how this will change anything.

The plane1/2 output is taken from a plane right before the outlet.

the faceObje1/2 output is taken from my patch "outlet".

Any thoughts?

Code:

faceSource plane1 output:

    areaAverage(sampledSurface) for He = 0.00162516212296

    areaAverage(sampledSurface) for T = 352.574410291

    areaAverage(sampledSurface) for N2 = 0.998374837877



faceSource plane2 output:

    CoV(sampledSurface) for He = 1.29855814792

    CoV(sampledSurface) for T = 0.00170251695443

    CoV(sampledSurface) for N2 = 0.00211380278868



faceSource faceObj1 output:

    areaAverage(outlet) for He = 0.00158949601069

    areaAverage(outlet) for T = 352.583244014

    areaAverage(outlet) for N2 = 0.998410503989



faceSource faceObj2 output:

    CoV(outlet) for He = 1.31250790071

    CoV(outlet) for T = 0.00168238393736

    CoV(outlet) for N2 = 0.00208954739943