Sound Speed for Doppler Setup

Hi, all!

I'm trying to set up a strap on Doppler to measure flow of digested wastewater sludge. We've got lab data on most of the parameters we need, but I'm struggling to come up with a value for sound speed. We're looking at roughly a 7-8% dry solids measurement.

I've tested out the meter just running the sound speed of water, but the reading came back in the thousands of gpm instead of in the hundreds. (Compared with our inline flow meter, should be roughly 175gpm.)

We're testing it on a line with a known working flow meter in hopes that we can then use it to compare to a suspected faulty flow meter in a different location.

Any thoughts on how to derive this value? My Google skills are failing me.

Thanks for the help!

Welcome to the "Realities of Doppler Club"

My 10 year experience with clamp-on ultrasonic is that transit time technology, correctly applied, can be fabulously accurate, whereas doppler is a merely a poor means of relative indication of which direction the fluid is flowing and its relative flow rate magnitude which manifests as more or less than the previously indicated, but without any meaningful connection to an absolute value, unless you 'calibrate' to an already installed flow meter. Typical errors I've seen were from +40% to +200% of assumed flow rates, frequently a flow rate higher than the pump could produce.

I do wish you the best, and if your experience with doppler eventually contradicts mine, please come back and inform me and the forum of your success. I'd be interested in a doppler flow meter that is capable of guessing better than me (pump's on, pressure's where it should be, no catastrophic breaks/leaks so flow should be about X) at what's happening.

As to a sonic velocity, isn't that what the meter is supposed to measure? That's a rhetorical question, why buy a meter when you have to tell it how fast the fluid is flowing?

The meter probably wants to know the sonic velocity for the fluid, water, which is temperature dependent.

There are some tables here for sonic velocity:
http://www.engineeringtoolbox.com/sound-speed-water-d_598.html

Dan