Simultaneous measurement of particle size and particle velocity by the spatial filtering technique

The objective of this study was to compare the measuring results of a fiber-optical probe based on a modified spatial filtering technique with given size distributions of different test powders and also with particle velocity values of laser Doppler measurements. Fiber-optical spatial filtering velocimetry was modified by fiber-optical spot scanning in order to determine simultaneously the size and the velocity of particles. The fiber-optical probe system can be used as an in-line measuring device for sizing of particles in different technical applications. Spherical test particles were narrow-sized glass beads in the range 30 - 100 mum and irregularly shaped test particles were limestone particles in the range 10-600 mum. Particles were dispersed by a brush disperser and the measurements were carried out at a fixed position in a free particle-laden air stream. Owing to the measurement of chord lengths and to the influence of diffraction and divergent angle, the probe results show differences from the given test particle sizes. Owing to the particle-probe collisions, the mean velocity determined by the probe is smaller than the laser Doppler mean velocity.