On-stream particle size, concentration and velocity measurements by auto-correlation of scattered laser light

Abstract

With the increase in automatic control of powder processes there is now a need for on-stream or real time instrumentation to measure the size and solid concentration of particles in slurries. On-stream velocity, particle size and concentration have been obtained by the interrogation of sand-water slurries by two 5 mW HeNe laser beams. The scattered laser light, from concentrated slurries in the range 1.0 × 10 −4 −1.0% w/w flowing at velocities between 0.5 – 3.0 m sec −1 in a 2.5 cm diam. vertical pipe, is transduced by a photodetector into random fluctuating electrical signals. The individual signals are auto-correlated and the power spectra computed to determine the particle size range and concentration of the suspended particles while the velocity of flow is determined from cross-correlation of the signals obtained from the axially separated lasers. The change in particle concentration and size jointly affect the shape of both the auto-correlogram and the power spectral density of the photodiode signal. By improved methods of detection, instrumentation implementation and data analysis, the velocity, particle size and concentration in a flowing suspension can be separately evaluated.