MEASUREMENT OF PARTICLE CLOUD DENSITY AND VELOCITY USING LASER DEVICES

Determination of instantaneous local particle velocity and density of a fluid-particle suspension based on time-averaging requires that both the time scale relation and the volume scale relation be satisfied. S mall measuring volumes in laser facilities in comparison to particle s izes calls for averaging based on the continuum counterpart of time-av eraging. This procedure was validated by comparing particle cloud dens ity obtained from simultaneous velocity and mass flux measurements to the laser phase Doppler measurements. Based on the center-of-mass fram e of reference, the local instantaneous velocity of a cloud of particl es is given by the mass flux of the particle cloud divided by its dens ity. It was shown that to measure the velocity of a particle cloud wit h a distribution of particle diameters, both laser Doppler velocimetry and phase Doppler analysis are needed. The latter provides an absolut e standard for the measurement of cloud density and velocity with part icle size distribution. This is in spite of the requirement of spheric al particles and the preference for no more than one particle in the m easuring volume.