A mass flowmeter includes a hollow flow tube with a contoured longitudinal bore. Inserted into the contoured longitudinal bore are preferably four rods. The rods establish stable axial vortices within the hollow flow tube. Pressure pulses on the flow rods produced by the vortical flows are measured by...http://www.google.com.au/patents/US6058787?utm_source=gb-gplus-sharePatent US6058787 - Mass flow measuring device
