On the thermocapillary motion of partially engulfed compound drops

Abstract

In this work the thermocapillary-induced motion of partially engulfed compound drops is considered. This phenomenon occurs in many natural and technological processes in which heat is exchanged between such hybrid drops and the medium around them through the interfaces. Two types of thermal fields and the resulting motions are studied; flow induced by an external temperature gradient and spontaneous thermocapillary motion. For the first flow type, it was found that, in general, the motion is induced in the direction of the temperature gradient. However, under certain physical conditions and drops' configuration a motion against the temperature gradient may be observed. In the second case, spontaneous thermocapillary motion, the compound drop moves due to surface tension gradients which result from the geometric non-uniformity of the system. Results are presented for several parameters such as configuration of the compound drop, viscosity, thermal conductivity ratio, the dependence of the various interfacial tensions on temperature and the volume ratio of the phases within the drop.

Thermocapillarity in Microfluidics—A Review

“…Droplet engulfment or encapsulation phenomenon has been a subject of investigation and application. Lavrenteva et al published the results of their theoretical studies on partial engulfment of slightly deformable (small Capillary number) compound droplets in an immiscible non-isothermal carrier fluid [ 167 , 168 ]. They showed that the partially engulfed droplets consist of three spherical surface segments which are subject to significant change due to droplet propagation in non-isothermal case ( Figure 19 ).…”

“… Streamline pattern of a compound drop moving with temperature gradient. Reproduced with permission of Cambridge University Press, from [ 168 ], L. Rosenfeld, O. Lavrenteva, and A. Nir, “On the thermocapillary motion of partially engulfed compound drops”, Journal of Fluid Mechanics, vol. 626, pp.…”

Dynamics and rheology of Janus drops in a steady shear flow

“…In general, it is insightful to have some knowledge of the flow at the microscopic level (individual particles or net-80 work structure) of complex fluids (colloidal dispersions, gels, emulsions, etc) to interpret the observed rheological behavior at the macroscopic scale. For compound multiphase drops, there has been considerable progress on the analytical treatment of axisymmetric flows in the limit of 85 low-Reynolds-number flows (Johnson and Sadhal, 1985;Sadhal and Oguz, 1985;Morton et al, 1990;Chervenivanova and Zapryanov, 1989;Vuong and Sadhal, 1989;Kan et al, 1998;Tsemakh et al, 2004;Rosenfeld et al, 2009). Numerical studies have principally addressed the problem of simulating large changes in shape and breakup of compound multiphase drops subject to external flows in confinement and open domains (Bazhlekov et al, 1995;Smith et al, 2004;Zhou et al, 2008;Qu and Wang, 2012;Hua et al, 2014).…”

Formation and breakup of compound pendant drops at the tip of a capillary and its effect on upstream velocity fluctuations

“…Compound drops have many promising applications in pharmaceutical and food industry, as well as waste water management. The behaviors of compound drops have been studied in various flow conditions, such as moving in quiescent flow [19], impact on flat surfaces [20], flow under thermocapillary force [21,22], formation in microcapillaries [23] and in microchannels [24], synthesis of polymeric microparticles [25,26]. However, to the best of our knowledge, compound pendant drops (CPDs), pendant drops with smaller drops or bubbles in them, have never been studied before.…”