I do have a photo of the demo apparatus that we are going to use. There is a sketch of the configuration also in the appendix of the "unveil" package. I'm not sure I can easily post the photos I have in this 'forum', so in the meantime see if this will do:
The air source is a shop vacuum we plan to run in reverse (I have included the specifications in the "unveil" package. The Gas (or air) then flows through a flowmeter and exit pipe that connects to the inlet of your prototype.
In order to avoid errors, I'll refer you again to the "unveil" package for the sizing of the exit pipe as it is specified there.
About the Archimedes number - check your densities; for salt the particle density is over a thousand times larger than the gas density so the difference between the two is positive. The viscosity is positive so the Archimedes number should be positive as well. If you get stuck, EMail me your calculation along with the units you are using for each variable to firstname.lastname@example.org
Is it possible for our group to also submit our numbers for confirmation because we have some doubt in our calculations and assumptions? Our pressure drop calculations are off the graph presented in the last page of the package.