The effects of geometry and heating rate on thermocapillary convection in the liquid bridge

Abstract

The experimental study on thermocapillary convection in liquid bridges of large Prandtl number has been carried out on Tiangong-2 in space. The purpose of these experiments is to study the oscillation instability of thermocapillary convection, and to discover and recognize the mechanism of destabilization of thermocapillary convection in the microgravity environment in space. In this paper, the geometry of a half-floating-zone liquid bridge is featured by the aspect ratio Ar and volume ratio Vr, and its influence on critical conditions of oscillatory thermocapillary convection is studied. More than 700 sets of space experiments have been finished. The critical conditions and oscillation characteristics of thermocapillary convection instability in the Ar-Vr parameter space have been fully obtained under microgravity conditions for the first time. It is found that the Ar-Vr parameter space can be divided into two regions of different critical conditions and oscillation characteristics: the region of low frequency oscillation, and the region of high frequency oscillation. More importantly, we obtain the complete configuration of these two stability neutral curves, and find that the low frequency mode is a ' ' type curve. Based on this, we discuss the influence of heating rate on the oscillation mode. It is found that the heating rate affects the selection of critical mode, which results in a jump change of critical temperature difference. The findings of this study are helpful to better understand the critical modes and transition processes of thermocapillary convection in liquid bridges with different configurations.

Rayleigh–Bénard convection in viscoelastic liquid bridges

“…Kang et al. 2019; in the following, we will refer to the ‘classical’ waveforms corresponding to standing and travelling waves as ‘SW’ and ‘TW’, respectively).

Figure 11.Three-dimensional streamlines ( a – d ) coloured according to the magnitude of the axial component of velocity (red and blue corresponding to rising and falling fluid, respectively) and three-dimensional isosurfaces ( e – h ) of non-dimensional azimuthal velocity w φ (four snapshots equally spaced in time within the oscillation period): travelling wave with m = 1 (TW1) emerging for A = 1, Ra = 3000 and θ = 0.1.

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“…the so-called 'silicone oils') have been used in these studies as surrogates of the real melts owing to their transparency to visible light, the high thermal stability and the ability to be liquid at ambient temperature (see, e.g. the experiments conducted in space by Kang et al 2019). This configuration has attracted so much attention that it has become over the years an inexhaustible source of inspiration for the understanding of the properties of different types of convection at a very fundamental level (typically for the so-called thermocapillary or 'Marangoni' flow since the seminal work by Schwabe & Scharmann (1983), and, later, also for thermal buoyancy convection or mixed thermocapillary-thermogravitational flow, see Wanschura, Kuhlmann & Rath 1996;Lappa, Savino & Monti 2000;Lappa, Yasuhiro & Imaishi 2003;Melnikov, Shevtsova & Legros 2005;Shevtsova, Melnikov & Nepomnyashchy 2009).…”

“…Here we focus on the liquid bridge with the multi-fold intention to: (i) enrich the existing literature on the oscillatory states of Newtonian fluids in floating zones driven by surface-tension effects in space (pure Marangoni convection, see, e.g. Kang et al 2019), with heretofore unseen information about the time-dependent solutions that can be produced in these configurations when three-dimensional viscoelastic fluids are considered in terrestrial conditions (pure buoyancy convection); (ii) highlight related analogies and differences; (iii) complement the existing information on viscoelastic Rayleigh-Bénard convection constrained by solid lateral walls (Park et al 2009;Park & Lim 2010;Park 2018) with new findings about domains with 'free' boundaries; (iv) extend earlier investigations where buoyancy convection in cylindrical geometries was examined for Newtonian fluids only (e.g. Wanschura et al 1996;Borońska & Tuckerman 2010a,b) to cases where elasticity plays a significant role; (v) determine the structure of the emerging flow (in terms of magnitude and wavenumber) and (vi) provide new details about the effective patterning behaviour in the nonlinear regime, i.e.…”

Hydrothermal waves in a liquid bridge subjected to a gas stream along the interface

“…One of the objectives is to study the effect of an external coaxial gas stream on the Marangoni convection in LBs (Shevtsova et al 2014). Several LB experiments have recently been conducted on the International Space Station (ISS) in the Japanese module KIBO (Sato et al 2013; and in Space lab Tiangong-2 (Kang et al 2019) but without forced gas flow. In the context of the JEREMI experiment, which is planned to be carried out at the ISS in the KIBO module, some preparatory experimental and numerical studies are currently going ahead with the present work among them.…”

Particle accumulation structures in noncylindrical liquid bridges under microgravity conditions

“…The interest in this problem is still alive as witnessed by the studies being produced nowadays [25,26].…”