Understanding the means and processes behind the creation of fluid particles motion (bubbles/droplets) is of great significance in both industry and academia. One of the many ways of producing motion is by the use of interfacial flows and in particular, are referred to as thermocapillary flows if these flows are induced by temperature variation. This technique takes advantage of the temperature dependency of the surface tension to produce the flow and is one of the simplest ways to generate motion. Preliminary interest in the use of this technique is to simulate the effects of buoyancy in microgravity. Later, several studies have followed in finding ways to leverage its ability in the area of microfluidics.

In the present work, we use an in-house solver in OpenFOAM to model different thermocapillary phenomenon problems, and three droplet motion areas are selected in particular. The first area deals with droplet motion inside the ambient fluid, while the second area deals with motion inside a capillary tube, and finally, the third area deals with motion caused by a temperature gradient on the surface. Although a quantum of work is conducted both numerically and experimentally in the field of droplet motion inside the ambient fluid, we have observed that there is a research gap where motion near the wall is not adequately studied. We validated our solvers with various experimental and numerical field benchmark cases and analyzed the motion of a single and pair of droplets with a wall proximity effect. The characteristics of the migration of droplets have been found to be affected, and various factors influencing migration have been studied. The most prominent findings are droplets are seen to deviate towards or away from the wall on the basis of the operational set of parameters and in the case of a pair of droplets, there is a possibility of interaction even though a small droplet is trailing a larger droplet.

With respect to the migration of droplets within the capillary tube, the thermocapillary motion of a perfectly wetting silicone oil slug is experimentally studied and a mechanistic model to explain migration is suggested. As far as the numerical investigation of motion is concerned, there is an intrinsic challenge in modelling all the physics of perfectly wetting droplets, and we thus choose a study in literature where the thermocapillary motion of the partially wetting droplet is examined for validation. The migration properties of a partially wetting droplet are similar, as seen in our in-house experiments with a perfectly wetting droplet, and thus we proceeded with a computational analysis of slug undergoing a reciprocating motion between two frequently triggered heaters. The dynamics studied, and the effect of the parameters studied will assist in constructing simplified microfluidic systems in a capillary tube where droplets can be moved, retained or reciprocated to incr ease mixing.

Droplet motion on the surface using thermocapillary forces has a wide range of applications in open-surface microfluidics, condensate removal, lubrication systems, etc. The migration characteristics predicted by the solver are comparable with previous numerical and experimental investigations, and one of the primary objectives in the field is to increase the thermocapillary migration velocity. Our in-house experiments with the migration of silicone oil on a narrow-width surface have shown that the migration velocity is improved for a fixed-volume droplet due to lateral-spread containment. Taking advantage of this effect, the numerical investigations of the migration of droplets are carried out on a hydrophilic track where the lateral spread is reduced due to the difference in wettability. The spreading characteristics are related to thermocapillary dynamics, and the study found that the enhancement was seen up to width and depreciation of migration velocity was seen subsequen tly.

The entire research was carried out in order to explain and extend thermocapillary migration to different facets of science and technology while also designing methodologies to model the problem and reveal the unexplored mechanics behind the motion of the droplet.