Measurement of Particle Rotational Velocity Using a Laser Anemometer

An electrodynamic balance and a frequency shifted Laser Doppler Anemometer (LDA) were used to obtain rotational velocity data from nonspherical particles undergoing pure rotation. A charged oil shale particle (150μm × 150 μm × 60 to 80 μm thick) was suspended in an electric field and rotated at a constant velocity by subjecting it to a vertical air jet. The measuring volume of the LDA was located on the particle, and Doppler bursts were observed from both stationary and rotating particles. This observation suggests that micron‐sized surface irregularities can act as individual scattering sources for LDA measurements. Signal analysis was performed with a counter type processor and a PDP‐11 computer. The particle motion was recorded on video tapes from which the true rotational velocity and maximum radius of rotation were obtained. Within the experimental uncertainties, the maximum rotation‐induced surface velocity measured with the LDA agreed well with that obtained from video tapes.