Interferometric single particle sizing methods

Abstract

The theoretical description of light scattering interferometry and the Phase Doppler method are reviewed. In particular, the possible difficulties associated with the combined light scattering by reflection and refraction were addressed. Reflection and refraction are detected when using large off-axis light scatter detection. This is necessary when applying single particle counters to sizing particles in high number density environments. The use of laser beams with Gaussian intensity distributions used to measure drops on the order of the focused beam waist must be considered as nonuniformly illuminated. As such, the relative intensities of the light scattered by reflection and infraction depends on the drop trajectory through the beam. Depending on the technique used, measurement errors associated with the ambiguous combination of light scattered by reflection and refraction can occur. Experiments using monodispersed drop streams directed on random trajectories were conducted to prove that a properly designed Phase Doppler instrument did not produce erroneous measurements resulting from nonuniform drop illumination. Measurement of spray in complex turbulent flows showed large differences in drop velocity and angle of trajectory with change in drop size. Small drops were measured as moving in a reversed direction where large drops had a relatively large forward velocity. These results emphasized the need for sophisticated instrumentation.The theoretical description of light scattering interferometry and the Phase Doppler method are reviewed. In particular, the possible difficulties associated with the combined light scattering by reflection and refraction were addressed. Reflection and refraction are detected when using large off-axis light scatter detection. This is necessary when applying single particle counters to sizing particles in high number density environments. The use of laser beams with Gaussian intensity distributions used to measure drops on the order of the focused beam waist must be considered as nonuniformly illuminated. As such, the relative intensities of the light scattered by reflection and infraction depends on the drop trajectory through the beam. Depending on the technique used, measurement errors associated with the ambiguous combination of light scattered by reflection and refraction can occur. Experiments using monodispersed drop streams directed on random trajectories were conducted to prove that a properly des...