Extended phase Doppler anemometer for sizing particles smaller than 10 μm

Abstract

Simultaneous measurements of size and velocity of spherical particles smaller than 10 μm in diameter are considered. For such an application, the standard phase Doppler anemometer (PDA) requires an excessively large angle between the laser beams and yet the system response remains non-monotonic and results in large uncertainties in the measurement. An alternative optical layout, referred to as planar layout, is introduced herein, whereby the beam angle is kept small (less than 10°) and the fluctuations in the response curves are suppressed significantly. The effect of the remaining fluctuations is eliminated by employing additional detectors and taking simultaneously two or more phase measurements. Each measured combination of signal phases is compared with the theoretical response curves using the joint probability method, which yields the most probable particle diameter and minimizes the measurement uncertainties. The use of planar layout and the joint probability method is demonstrated through measurements with monosize latex particles and the droplets produced by electrosprays.