(419e) Breakage of Single Drops in an Inertial Laminar 2-D Orifice Flow

Authors: 
Ko, D. I., University of Maryland
Calabrese, R. V., University of Maryland
Fundamental studies in laminar flows have traditionally considered the deformation and break-up of single drops in uniform prototypical Stokes flows first established by Taylor (1934). More recently, advances in computational methods have led to numerical simulations of drop break-up in inertial shear flows. The current work adds to the existing body of drop break-up knowledge by investigating the effect of short-term high-intensity deformation events on the break-up of large single drops in inertial laminar flow through a 2-D slit orifice. Information from both experimental observations of the trajectory, deformation, and break-up of single drops and computational simulations of the flow field are combined to develop break-up criteria based on the conditions along the drop trajectory and determine the potential for drop 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. Two oils were used as the continuous phase, resulting in Reynolds numbers ranging from 110 to 600. Water drops were injected upstream of the orifice using a variety of needles, generally resulting in droplet diameters between 200 and 1200 microns. The path and behavior of the drops were recorded using high speed digital imaging. Observations of the various modes of break-up will be presented. High fidelity CFD simulations were performed to acquire the velocity and deformation fields (in the absence of the drop) in the vicinity of the orifice.

To understand the conditions experienced by the drop prior to break-up, the experimental drop trajectories were combined with the flow field simulation to create a deformation history for each drop. By analyzing these results, the appropriate velocity, length, and time scales for laminar break-up were extracted. Based on these analyses, two new forms of local, trajectory-dependent Weber number are suggested. Each form includes recommended critical Weber number thresholds for break-up.