Bubble rise in a non-isothermal self-rewetting fluid and the role of thermocapillarity

Abstract

We report on the motion of a buoyancy-driven bubble in a vertical micro-channel and the significant role of thermocapillarity. A series of experiments have been carried out using a circular micro-channel filled with pure liquids (pure water and pure 1-butanol) and a selfrewetting fluid (water -1-butanol 5% vol.) under isothermal and non-isothermal controlled conditions. In both cases, different mass fluxes and heat fluxes were applied on the microchannel within the same temperature gradient field (18 o C to 75 o C) which was increasing linearly in the same direction with the liquid flow. We have shown that the behaviour of the bubbles in a self-rewetting fluid departed considerably from that of pure liquids. The anomalous property of the alcohol mixture, i.e. the quasi-parabolic dependence of the surface tension with the temperature, drastically modified the movement (promoted or inhibited) and the shape (spherical or deformed) of the migrating bubbles. These phenomena were explained in terms of the location of the bubble associated with the well-defined surface tension 2 minimum, and as a function of dimensionless numbers. Heat transfer coefficient calculations in the single and two-phase flows were acquired for all the liquids used. We demonstrated that the presence of Marangoni stresses resulted in the enhancement of the heat transfer distribution in the self-rewetting fluid flows compared to the pure liquids.

Unsteady motion of a long bubble or droplet in a self-rewetting system

“…where f M , f G and f B are given by (38), (39) and 40 Note that, once again, the behaviour described in this Section is qualitatively different from that for ordinary fluids for which σ is a linearly decreasing function of T studied by Wilson [25]. In the latter case b and L are constants and the Marangoni contribution to dc/dt is independent of c, and hence dc/dt is constant (i.e.…”

“…These studies show that the behaviour of a bubble or droplet in or of a self-rewetting fluid can be qualitatively different from that for an ordinary fluid. Specifically, the theoretical studies by Karapetsas et al [35] of the motion of a droplet on a heated substrate, and by Tripathi et al [36] of the rise of a bubble in a vertical channel, as well as the experimental studies by Shanahan and Sefiane [37] of the motion of a bubble in a mean flow, by Mamalis, Koutsos and Sefiane [38] of the motion of a droplet on a heated inclined substrate, by Mamalis, Koutsos and Sefiane [39] of the rise of a bubble in a vertical micro-channel, and by Mamalis, Koutsos and Sefiane [40] of the spreading of a droplet on a heated substrate, all demonstrate this. In the present work we seek to bring further insight into this problem by formulating and analysing a theoretical model for the unsteady motion of a long bubble or droplet in a self-rewetting system in a non-uniformly heated tube.…”

Nonisothermal Spreading Dynamics of Self-Rewetting Droplets

“…In this case, the convection mechanism is driven by the reverse Marangoni effect 59,60 . Therefore, the induced Marangoni convection flows may play an important role in energy transport phenomena 21,61,62 . Multiphase flows coupled with heat transfer mechanisms still pose many experimental and theoretical challenges.…”

“…59,60 Therefore, the induced Marangoni convection flows may play an important role in energy transport phenomena. 21,61,62 Multiphase flows coupled with heat transfer mechanisms still pose many experimental and theoretical challenges. In this work, we study for the first time the spreading dynamics of selfrewetting droplets, which partially (90°> θ eq > 0°) wet a flat uniformly heated substrate under nonisothermal conditions.…”

“…The presence of liquid–vapor gradients (concentration and/or temperature) in the vicinity of the triple contact line leads to spontaneous liquid inflows directed from the colder region to the hotter side, for temperatures above the minimum of the surface tension (Figure ). In this case, the convection mechanism is driven by the reverse Marangoni effect. , Therefore, the induced Marangoni convection flows may play an important role in energy transport phenomena. ,, …”