Binary collisions of drops of immiscible liquids

Abstract

International audienceThis experimental and theoretical study is devoted to the investigation of head-on collisions of two drops of immiscible liquids. In the experiments, pairs of drops are made to collide at well-defined kinetic and geometric conditions. The sizes and relative velocity of the colliding drops close to the point of impact are measured by means of image processing. The deformed states after the impact, their evolution with time, and their stability are studied by visualization. The theory considers the dynamics of the rim formed at the edge of a radially spreading lamella due to capillary forces at the free surfaces of the lamella and at the liquid/liquid interface. The equations of the rim formation and motion are obtained from the volume, mass and momentum balance equations which account for the inertial, viscous and capillary effects. The theory predicts the evolution of the main geometrical parameters of the liquid mass formed by the drop collision: thickness of the lamella, diameter, and size of the rim cross-section. The theoretical predictions agree well with the experimental data, although no adjustable parameters are used in the model

Drop spreading at the impact in the Leidenfrost boiling

“…In principle, values of A slightly different from 1 are also possible. However, as pointed out by Roisman et al, 26 these would lead to solutions where f (ξ) rapidly diverges from unity as ξ increases.…”

“…The general solution of this non-linear ODE is given by Eq. (4.10) in Roisman et al 26 As ξ approaches 0 (i.e., for large times and small radii), the function f (ξ) tends toward the integration constant A and the radial velocity in the sheet can be expressed as the asymptotic solution,…”

“…The model for the drop spreading is adapted from an approach developed by Roisman et al to describe the spreading of drops on dry and wetting surfaces, 24,25 and the binary collisions of drops 26 given the similarities between these different processes. It should be noted that the definition for the Weber and Reynolds numbers is generally different in the head-on collisions of equal drops.…”

Edge effect: Liquid sheet and droplets formed by drop impact close to an edge

“…Previous studies focused on the crown dynamics and droplet ejection in axisymmetric configurations [33][34][35][36][37]. Increasing attention has also been paid to impacts on small solid targets of size comparable to that of the drop diameter [38][39][40][41][42] or binary drop collision [43,44]. In the crescent-moon impact scenario, an intrinsic horizontal asymmetry leads to a nonaxisymmetric liquid sheet [19].…”

Common Approaches in Description of Ordinary Liquids

“…From the analysis of the recent theoretical and experimental results for the collisions of liquid droplets [74][75][76] together with the BUU [64] and nuclear fluid dynamics (NFD) [40] results for HIC, it is suggested that there should be four distinct stages of the collision [ Fig. 11].…”