Planar laser-based measurements of droplet size, volume fraction, and velocity in flow-blurring sprays

We employ advanced laser-based diagnostics to investigate the spray characteristics of a custom-designed flow-blurring (FB) atomizer. Structured Laser Illumination Planar Imaging (SLIPI)-based methods are utilized to obtain two- and three-dimensional (2D–3D) maps of the droplet Sauter Mean Diameter (SMD) and planar liquid volume fraction, while the conventional particle image velocimetry is used to measure droplet velocities within the spray in 2D. Water and ethanol sprays are investigated across a range of air-to-liquid mass ratios (ALRs = 2–5). The SLIPI-based fluorescence/scattering ratio maps of droplet relative SMD are calibrated and compared using the Phase Doppler Particle Analyzer data, demonstrating strong agreement with a low mean absolute percentage error (MAPE), especially at lower ALR. However, at higher ALR, the optically dense sprays result in increased multiple scattering effects, leading to higher MAPE values. SLIPI effectively captures the transient and polydisperse nature of FB sprays, with droplet size distributions closely following a gamma function. Additionally, a correlation for SMD is developed in terms of key non-dimensional groups, which represent the geometric parameters, physical properties of the working fluid, and spatial locations within the spray. The relevant dimensionless groups in the SMD correlation based on the geometric and physical properties are Laplace number (300-9700), liquid Reynolds number (\(\text{Re}_l=95\) and 140), and Ohnesorge number (\(\text{Oh}=0.0027\) and 0.0065).