[Gerry Kan]

Howdy People:

I have a seemingly trivial issue, but I have been stuck on this literally for weeks. I hope a different pairs of eyes would give me some insight.

Currently I have an inlet boundary, in which a mixture of air and a trace amount of another gas phase species enter my flow domain.

From our experimental observations, I have:

1) Mass flow rate of this trace species, in kg/s
2) Ambient density of the mixture at the inlet boundary

Note that I have no control over the experimental side of things so I am stuck with what I am given.

However, at least for OpenFOAM, I need to turn this into some kind of concentration flux rate. For that I need to somehow obtain the mass flow rate of the mixture, which I don't have. The question is how?

In the meantime I have tried the following with no avail:

a) Assume mixture mass by estimating the air volume using the first layer of cells adjacent to the inlet boundary. The end calculation simply gave me the mean cell height with variations due to mixture density

b) Assume unit volume and estimate the concentration flux. This led to a simple division ( y_species = m_species / rho_mixture, assuming volume of 1 cu m), attractive but dubious.

c) Assume constant mass fraction and work out the mass flow rate. This seems most plausible but more of the "rule-of-thumb" rather than the "scientific" variety.

d) Work out the mixture mass flow rate independently, but this requires more information than I have, and additional assumptions will risk going back to (c).

Any further ideas would be greatly appreciated,
Gerry.