An experimental research on surface oscillation of buoyant-thermocapillary convection in open cylindrical annuli

Abstract

An experiment is carried out on the surface oscillation of buoyant-thermocapillary convection in an open cylindrical annulus. When the radial temperature difference ΔT reaches a critical value ΔT c , a regular oscillation appears and soon disappears on the open surface, which varies when the liquid layer's thickness h and temperature difference ΔT are varied. With growth of ΔT , dominant frequency of the visible oscillation will grow too but is found within certain frequencies. Driving forces, buoyance and thermocapillarity, are responsible for this phenomanon and the "balance" point is considered to exist when h is between 4.5-5.0 mm. Surface oscillation region is also found restricted within a narrow gap when Bo is smaller than 3.7.Keywords Cylindrical annulus · Buoyant-thermocapillary convection · Surface oscillation · Critical temperature difference Inner radius of the cylindrical annuli, mm

The volume ratio effect on flow patterns and transition processes of thermocapillary convection

“…As the thermal motion in the pool continues to accelerate, the frequency can be expressed as a function of Ma. In figure 11, Ma for various Vr shows a monotonically increasing behaviour, which is in good agreement with the ground experimental result (Zhang et al 2014). The linear fitting slope of the frequency with the variable is in the range 0.001-0.002, and there is no notable difference between the results of different volume ratios.…”

“…The volume ratio also seriously affects the critical temperature difference, frequency, wavenumber, etc., exhibiting nonlinearity in their relationships. It has been confirmed that the frequency and wavenumber are much smaller than those of terrestrial experiment results (Zhang et al 2014). The wavenumber in space no longer decreases as the liquid layer thickens (Schwabe 2002;Schwabe & Benz 2002), but decreasing first, then increasing and finally decreasing, which is influenced by the flow state.…”

“…With further increasing Ma above 1.22Ma c , in Rg 4, far away from the critical oscillation state, rather than directly translating into chaos (Zhang et al 2014), a unique flow pattern is firstly recognized in the temperature field. Maintaining the wavenumber in Rg3, the amplitude and frequency of the periodic oscillation are further amplified.…”

“…The volume ratio effect on thermocapillary convection was firstly proposed by Hu in a study of a liquid bridge, which has been proved theoretically and experimentally (Tang & Hu 1994). The volume ratio effect in annular LPs has not been explored in depth, as the temperature field with large volume ratios is impossible to build under gravity conditions (Zhang, Duan & Kang 2014), where several other influential factors such as deformation, natural convection in the pool and natural convection in the ambient gas are unavoidably present. A long-period microgravity environment can provide idealistic conditions for the study of the volume ratio effect on instability mechanisms.…”

Experimental research on thermocapillary migration of drops by using digital holographic interferometry

“…The investigation of thermocapillary flow is important for basic research, as well as for material sciences, chemical engineering, and space manufacturing (Zhu et al 2011;Zhang et al 2014). When the gravity effect is greatly reduced, the interfacial phenomenon becomes important.…”