Velocity distributions in moving powders by microwave Doppler radar

Abstract

Analysis of the Doppler signals produced by the reflections of microwaves from moving powders, using a fast Fourier transform technique, gave a power spectrum of the various frequencies, and hence velocities, present in the signal. The width of this spectrum, which is an estimate of the range of velocities present within the flowing powder, was calculated for powders of various sizes and shapes flowing on an inclined chute. The effect of particle size and shape on the spectral width produced during flow down smooth and sand-roughened chutes was investigated for angles of chute inclination between 30° and 65°. Spectral widths for flow on chutes inclined at angles well above the minimum necessary to support flow were reasonably constant down the length of the chute and were larger for flow over a sand-roughened surface than over a smooth surface. At angles close to the minimum angle to support flow, where there was a fast-moving upper layer shearing over a slower or stationary base layer, the spectral width increased considerably.