The transition boundaries between interaction regimes of liquid droplets colliding in a gas

Abstract

In this research, we use two different approaches to distinguishing the interaction regimes of liquid droplets in a gas environment. The first one distinguishes the following regimes: coalescence (parent droplets merge), bounce (parent droplets approach each other and then move away from each other), separation (impact produces two new droplets of a similar size as the initial ones), and disruption (two initial droplets break up into more than two fragments). The second approach distinguishes the following regimes: coalescence (merging of initial fragments), bounce (merging and consecutive splitting into two fragments of similar size as the initial ones), stretching separation (fragmentation due to the stretching of the merged droplet), and reflexive separation (fragmentation due to the tendency of each fragment to take spherical shape). Experimental results for different slurries, emulsions, solutions, and single-component compositions allowed us to distinguish transition boundaries of collision regimes using the Weber and Ohnesorge number, as well as angular and linear interaction parameters. Mathematical expressions are obtained for the boundaries, describing the variation ranges of droplet interaction parameters as well as their properties required for the consistent transition from one collision regime to another. The expressions are second order polynomials with droplet size ratio, Weber number, Ohnesorge number, and interaction parameters as variables. A database of empirical coefficients is obtained for general mathematical expressions that can be used to predict the transition boundaries of droplet collision regimes. Any of the two approaches to distinguishing the regimes is equally viable for this matter.