Visualization and size-measurement of droplets generated by Flow Blurring® in a high-pressure environment

Flow Blurring (FB) atomization is a highly efficient method to produce aerosols. It originates from an unexpected turbulent back flow motion in the interior of the atomizer. The onset for the appearance of such pattern is dictated by a geometrical parameter, phi, that is, the ratio of the distance from the tip of the liquid feeding tube to the discharge orifice (H), and the diameter of the discharge orifice (D). In this work, a FB atomizer with a nominal phi = 1/6 was used to produce water and ethanol droplets into pressurized environments (>1 MPa). The droplet size distributions and mean droplet speeds were investigated using (1) direct visualization with an ultra-high-speed video camera coupled with an automated droplet measurement (ADM) program and (2) using a light scattering instrument. Light scattering measurements, with water and ethanol, varying the driving pressure to produce the aerosol (Delta P), indicate a power dependence of similar to 2/5 of the dimensionless mean droplet diameter ((D) over bar /D-o) on the dimensionless liquid flow rate (Q/Q(o)). At higher liquid flow rate, the optical resolution of the droplets is improved compared to lower volumetric flow rates, thus facilitating analyses with the ADM program. The approach outlined herein provides a guideline for characterization and implementation of the FB technology in high-pressure applications.