Comparison of Particle Dynamics Analyzer (PDA) and SetScan Optical Patternator Results

The primary goal of this study was to determine when patternation information derived from Particle Dynamics Analyzer (Dantec Dynamics dual-PDA) measurements of volume flux, velocity and mean drop size agreed with corresponding values measured using an optical patternator (En’Urga, Inc SetScan OP-600). To achieve this, data from each instrument was transformed into spatially resolved absorptances (equivalent to drop surface area per unit volume) and compared. The secondary goal of this study was to explain the cause of any discrepancies in comparison of the two absorptance sets when they occurred. Key conclusions drawn from this study are: absorptance agreement to within 20% can be achieved in many cases; however, the difference between the PDA-calculated and optical patternator-measured absorptances becomes larger as the drop arrival rate increases, as the drop size decreases, and when a significant drop size-velocity correlation is present. These discrepancies are attributed to an underestimation of the volume flux (which becomes more important with increasing droplet arrival rate), an over-reporting of the mean drop diameter (which is the result of the restrictive data acquisition scheme applied when ensuring mass closure), the limited PDA dynamic range (which can preclude simultaneously accounting for both the largest and smallest drops in the spray), and by the optical patternator’s number-density based measurement scheme (which will not yield the same results as the flux-based PDA when a drop size-velocity correlation is present).