Particle velocity and mass flow measurement in pneumatic conveyors

Abstract

A new method is described for measuring the mass flow of powder in a pneumatic conveyor without obstructing the flow of the material or using moving parts. Mass flow is a function of powder loading and velocity. Tile velocity is derived from the transit time of the naturally occurring flow noise pattern between capacitance transducers at two positions along the axis of the conveyor. The transit time is determined by cross-correlating the transducer outputs with an one-line digital computer. Loading can be measured by nucleonic absorption, or it can be derived from the cross-correlation. The method has been tested with soft flour in a 6-in-dam. pneumatic conveyor; the accuracy was ±2% full scale deflection over a mass flow range from 45 lb/h to 800 lb/h. The computer loading for each flow reading using a typical digital computer is, computation time 0.3 s and a block of 295 data values from each of two transducers is read at sampling intervals of 0.5 ms.