Droplet size distributions in liquid–liquid semi-batch Taylor vortex flow

Charlton Campbell,R Dennis Vigil,Michael G Olsen

doi:10.1063/5.0018065

Abstract

Optical methods were used to measure droplet size distributions in a liquid–liquid Taylor vortex reactor oriented vertically along its main axis and operated in a semi-batch fashion with continuous feed of the dispersed phase and no feed or removal of the continuous liquid. The effects of two operational parameters on droplet size distributions were considered, including the inner cylinder angular velocity and the dispersed phase inlet flow rate. Both the mean droplet diameter and the droplet size distribution were found to depend upon the jet Reynolds number and were independent of cylinder rotation speed up to the largest azimuthal Reynolds number investigated (60 000). The droplet size distribution underwent a transition from a unimodal distribution at low cylinder rotation speeds to a bimodal distribution at intermediate speeds. At the largest rotation speeds considered, the bimodal distribution became right-skewed. These observations provide support for the hypothesis that the mean droplet size and size distribution are determined primarily by jet breakage dynamics at the tips of inlet nozzles. Furthermore, the mean droplet size data collected from two geometrically distinct reactors can be collapsed onto a universal curve by plotting the Weber number against the jet Reynolds number.

Highlights

Taylor–Couette (TC) flow offers a canonical system for studying hydrodynamic instabilities, and as such, it has been explored extensively for a single fluid phase
Representative droplet size distributions (DSDs) for several experimental conditions are shown in Fig. 3, including examples of three characteristic DSD shapes that were observed
Panels (a) and (b) show the examples of unimodal DSDs exhibiting a single major scitation.org/journal/adv peak with little asymmetry—a shape observed for the smallest values of Rej investigated

Summary

INTRODUCTION

Taylor–Couette (TC) flow offers a canonical system for studying hydrodynamic instabilities, and as such, it has been explored extensively for a single fluid phase. While operating a horizontally oriented TC device in batch mode and with high dispersed phase hold-up (up to 50%), these investigators reported a decrease in droplet size with increasing inner cylinder rotation speed. Qiao et al.[9] took a different approach by observing temporal droplet size evolution in a vertically oriented batch TC system in which droplets were introduced immediately prior to commencing inner cylinder rotation. Aside from the practical chemical and biological applications that motivate this semi-batch vertically oriented configuration, flow patterns arising in this system have recently been characterized and shown to depend upon the inner cylinder rotation speed and the flow rate of the dispersed phase as primary variables.[19] For this reason, these two variables were varied systematically in this study, and their impacts on downstream droplet size distributions and mean droplet size were measured using optical methods

Fluid test section descriptions and operating procedure

Data acquisition and image processing

Classification of droplet size distributions

Mean droplet diameter dependence on Reθ and Rej

Similarity relation for droplet diameter

Conclusions