(577h) Breakage of Single Drops and Bubbles in a Turbulent 2-D Orifice Flow

Authors: 
Ko, D. I., University of Maryland
Calabrese, R. V., University of Maryland
Much of the existing literature on droplet break-up deals with either non-inertial (Stokes flows) or turbulent flows with droplets in the inertial or viscous subranges. The current work examines the break-up of single macroscale droplets and bubbles in turbulent flows due to short-term high-intensity deformation events. Information from both experimental observations and computational simulations are combined to develop break-up criteria and determine the probability of droplet break-up.

The experimental apparatus consists of a parallel plate channel with a 25%-open slit orifice, creating a 2-D planar orifice flow in the center plane. Water was used as the continuous phase, with Reynolds numbers ranging from approximately 8,000 to 19,000. Oil droplets and air bubbles were injected upstream of the orifice using a variety of capillary tubes, generally resulting in droplet diameters between 200 and 1200 microns, much larger than the Kolmogorov microscale. The path and behavior of the droplets and bubbles were recorded using high speed digital imaging.

To understand the local conditions of the droplet prior to break-up, computational simulations of the orifice were performed for each Reynolds number case. The channel flows were simulated using 3-D RANS equations with the realizable k-ε turbulence model. The droplet path from the experimental images was then compared to the simulated deformation field to construct the deformation history of the droplet as it passed through the orifice. The synthesis of this experimental and computational information led to the development of breakage probability and regime plots that can be correlated using an appropriately defined turbulent Weber number.