Viscous to Inertial Crossover in Liquid Drop Coalescence

TL;DR

This study investigates the transition from viscous to inertial forces during liquid drop coalescence, revealing a late crossover time influenced by flow geometry, which challenges existing theories.

Contribution

It introduces a new understanding of the viscous-inertial crossover timing in drop coalescence, considering flow geometry effects not previously accounted for.

Findings

Late crossover time observed at low velocities

Flow geometry influences the viscous-inertial transition

Electrical and high-speed imaging methods used

Abstract

Using an electrical method and high-speed imaging we probe drop coalescence down to 10 ns after the drops touch. By varying the liquid viscosity over two decades, we conclude that at sufficiently low approach velocity where deformation is not present, the drops coalesce with an unexpectedly late crossover time between a regime dominated by viscous and one dominated by inertial effects. We argue that the late crossover, not accounted for in the theory, can be explained by an appropriate choice of length-scales present in the flow geometry.