Thermal delay of drop coalescence

Abstract

We present the results of a combined experimental and theoretical study of drop coalescence in the presence of an initial temperature difference T 0 between a drop and a bath of the same liquid. We characterize experimentally the dependence of the residence time before coalescence on T 0 for silicone oils with different viscosities. Delayed coalescence arises above a critical temperature difference T c that depends on the fluid viscosity: for T 0 > T c , the delay time increases as T 2/3 0 for all liquids examined. This observed dependence is rationalized theoretically through consideration of the thermocapillary flows generated within the drop, the bath and the intervening air layer.

Mixing Versus Stirring

“…Heuristics: The present ideas and methods are not limited to passive scalars. They were successfully applied to evaporating dense sprays , Marangoni flows (Geri et al 2017;Néel & Villermaux 2018), and should contribute…”

Surfing of drops on moving liquid–liquid interfaces

“…For example, a temperature difference at ∆T = 30 • C between two drops of 5 cSt silicone oil can delay coalescence for 1 hour until ∆T reduces below a critical value of ∆T c = 3.0±1.0 • C (Dell'Aversana et al 1996). Geri et al (2017) found that the delay increased monotonically with the initial temperature difference ∆T 0 . The thermal induced Marangoni effect was considered to be responsible for preventing coalescence in such cases (Napolitano et al 1986).…”

Inertial impedance of coalescence during collision of liquid drops

“…A situation that is related to that studied in the present paper arises in applications such as sprays and combustion where two drops collide in a gas (Qian & Law 1997) or when a drop falls through a gas onto a bath of the same liquid as the drop (Couder et al 2005;Geri et al 2017). In these problems also, the thin lubricating air layer between the two drops or the drop and the bath must drain to a critical thickness before coalescence is initiated by intermolecular forces.…”

“…2005; Geri et al. 2017). In these problems also, the thin lubricating air layer between the two drops or the drop and the bath must drain to a critical thickness before coalescence is initiated by intermolecular forces.…”