Hi all, I've been asked to search for a way, cost isn't that big of an issue, to measure flow rate in real-time of small, fast, abrasive particles (AlO2). These particles are, on average, 50 microns in diameter, and are shot out of a nozzle, itself just a bit bigger than 50 microns. Another requirement is that this detection system be non-invasive, i.e. it does not obstruct the flow itself. So far, I've looked into using Cavity Ringdown Spectroscopy (CRDS), but it doesn't seem suitable because the method employed is tracking particles in the air, which are very small and very low speed. I've also looked at a multi-pass optical cell, but that's more tailored towards analysis of exhaust gases and the like. I'm currently looking at Continuous Opacimeters [pdf], where they shoot light across the direction of the flow, and based on the attenuation, certain characteristics can be shown. Any ideas on how to measure the mass flow rate of small AlO2 through a tube/nozzle?