Impingement and Coalescence Phenomena of Gallium-based Liquid Metal Drops in a Viscous (Non-Oxidizing) Environment

Abstract

The thesis focuses on the transport phenomena of liquid metal (LM) drops in a viscous, non-oxidizing environment, specifically using eutectic alloys of gallium (Ga) like Galinstan (68.5% gallium, 21.5% indium, and 10.0% tin). Ga-based LMs have enabled advancements in bio-devices, flexible circuits, and actuators. However, significant gaps exist in understanding the spatial-temporal behaviour of LM drops, particularly in impingement, splashing, and planar coalescence. A computational approach using C++ OpenFOAM libraries was adopted to address these gaps. Experimental analysis of LMs is challenging due to spontaneous oxidation and opacity, complicating imaging and fluid dynamics study. Extensive testing ensured reliability by comparing findings with existing numerical models. For drop impingement, the study utilized the Weber number (We) and Ohnesorge number (Oh) to examine aspects like temporal spreading factor, maximum spreading factor, and contact time on surfaces. Various droplet behaviours, including deposition, rebound, and splash, were observed, identifying a mechanism for bubble entrapment during the recoiling phase. For drop splashing, the onset of splashing in a viscous medium was explored, examining features like droplet diameter, ejection time, and ejection angle. For drop planar coalescence, the mechanisms for partial coalescence were studied, identifying critical parameters distinguishing partial from complete coalescence at the liquid-liquid interface. The potential occurrence of vortices during partial coalescence, drop reduction ratio, and time of coalescence were investigated. The bubble entrapment phenomenon was characterized and compared with existing entrainment modes, with additional tests assessing the influence of the surrounding medium on coalescence dynamics.