Coalescence of drops on the free-surface of a liquid pool at elevated temperatures

Abstract

The coalescence dynamics of ethanol drops injected from a needle on the free-surface of an ethanol pool maintained at a higher temperature than the drop is experimentally studied using a high-speed imaging system. The drop is always kept at 25 ○ C, and the temperature of the ethanol pool is varied using a heater. The coalescence behavior depends on the size of the drop, the height of the needle tip from the freesurface, and the temperature of the ethanol pool. A parametric study is carried out by varying these parameters. The drop exhibits a residence period at low impact velocity, when it floats on the free-surface before the coalescence begins. Subsequently, the complete coalescence and partial coalescence dynamics are observed for different sets of parameters considered. It is found that increasing the temperature of the ethanol pool reduces the residence time of the drop. This phenomenon is explained by analyzing the forces acting on the drop and the capillary waves generated due to the temperature gradient between the drop and the ethanol pool. During partial coalescence, we also observed that the diameter of the daughter droplet decreases as the size of the primary drop and pool temperature are increased. As expected, due to the gravity effect, increasing the size of the drop also decreases the residence time. A regime map designating the complete coalescence and partial coalescence dynamics is plotted in the pool temperature and drop impact height space.

The dynamics of bouncing, partially coalescing, liquid metal droplets in a viscous medium

“…2019; Kirar et al. 2020) which is the focus of this study. At planar surfaces coalescence can occur in two ways: partial or full coalescence.…”

“…The study of coalescing fluids has allowed for advances in microfluidics (Prakash & Gershenfeld 2007), additive manufacturing in microgravity (Huang et al 2020), bioprinting of living tissue (Murphy & Atala 2014), the inkjet printing of electronics (Zhu, Wang & Zhu 2020) and even the study of natural phenomena such as rain (D'Adderio, Porcù & Tokay 2018). Coalescence can largely be separated into drop-drop coalescence (Yuan et al 2015;Duchemin, Eggers & Josserand 2003;Gebauer et al 2016), bubble coalescence (Liu et al 2019;Cui et al 2016;Feng et al 2016;Han et al 2016), the study of onset (Neitzel & Dell'Aversana 2002;Geri et al 2017) and drop-planar coalescence (Politova et al 2017;Zhang et al 2019;Kirar et al 2020) which is the focus of this study. At planar surfaces coalescence can occur in two ways: partial or full coalescence.…”

Electrohydrodynamic-induced partial coalescence between a droplet and a liquid–air interface

“…2019 a ), a falling drop on a heated pool (Kirar et al. 2020) or a larger-viscosity pool (Alhareth & Thoroddsen 2020). Additionally, the coalescence processes of two drops or bubbles have been comprehensively studied (Eggers, Lister & Stone 1999; Thoroddsen et al.…”

A study of two unequal-sized droplets undergoing oblique collision

“…[3][4][5][6][7] Several researchers have also investigated the coalescence dynamics of a liquid droplet on a flat liquid pool (see, e.g., Refs. [8][9][10][11][12][13][14]. Different collision outcomes have been observed when two equal-sized droplets undergo collision depending on the Weber number.…”