The flow rate of solids in a pneumatic conveying line can be measured on-line using acoustic waves in the audible frequency range. A prototype measurement instrument is described using four microphones attached to pressure taps along the wall of the pipeline. Conveying velocities were calculated from the difference between upstream and downstream propagation velocities and the solids volumetric concentration was correlated with the attenuation of the signal. A simple on-line calibration method using injection of a known mass of material was developed, and it fitted well to setady state test data over a wide range of conveying velocities. The system was tested in a three inch horizontal pipeline conveying 150 mum mean diameter sand particles in the dilute phase regime.
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