Development of optical digital interferometry technique for measurement of thermodiffusion coefficients

The paper presents the development of an experimental technique based on optical digital interferometry for measuring thermodiffusion (Soret) coefficients. The experiments are performed in a cubic cell containing an aqueous solution and being heated from above. This is the first report on the method that allows to record the temperature and concentration fields in the entire cell rather than just between two points. Such information is not only available at the steady state, but within the whole diffusion process. The time-dependent evolution of the concentration field allows the measurement of molecular diffusion coefficient in addition to the Soret coefficients. The measurements of transport coefficients have been performed in water/ethanol mixture and water/isopropanol mixtures.     

Some special features of thermoconvective motion in multilayer liquids

Thermocapillary convection is considered in multilayer systems of liquids at whose interfaces surface tension forces act. It is assumed that the liquids are immiscible and a linear temperature distribution is maintained at the lower solid boundary.Institute for Problems of Mechanics, Russian Academy of Sciences, Moscow. Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 65, No. 2, pp. 144–151, August, 1993.     

Influence of interfacial heat exchange on the flow organization in liquid bridge

The appearance and development of thermoconvective oscillatory flows in a cylindrical column with a free lateral surface (so-called liquid bridge) filled with 5 cSt silicone oil are investigated experimentally. The experiments were carried out under terrestrial conditions for a wide range of volumes of liquid bridges. Heat transfer from the interface changed the threshold of socillatory instabilities. The sensitivity of thermo-convective flows to the interfacial heat exchange was found to be strongly depending on the liquid bridge volume. Slender liquid bridges (under filled zone with respect to the straight cylinder) are rather stable to external disturbances. On the contrary, fat liquid bridges are extremely sensitive to the thermal environment in the gas phase.     

Digital Interferometry Applied to Thermogravitational Technique

In this work, we have applied Optical Digital Interferometry approach to thermogravitational micro-column technique. By the new analysis, we examine the entire height of the micro-column and determine the complete concentration profile inside. The measurements were carried out by two lasers with different wavelength λ =?633nm and λ =?470nm. The system was validated with binary subsystems of the THN-IBB-C12 ternary mixture at equal mass fractions. The results were compared with values of Benchmark Fontainebleau and they showed an excellent agreement.     

Mixing Under Vibrations in Reduced Gravity

The aim of this study is to analyze the physical mechanism by which vibrations affect the mixing characteristic of two initially stratified miscible fluids. The translational periodic vibrations of a rigid cell filled with different mixtures (Sc?=?7125) are considered. The vibrations with a constant frequency are imposed parallel to the initially planar interface. The ability of the applied vibrations to enhance the flow is examined. At the early stage after imposing the vibrations the Kelvin-Helmholtz instability is observed in absence and at low level of gravity. Later in time the system undergoes a transition to Rayleigh-Taylor instability. With increasing of gravity level the life-time of Kelvin-Helmholtz instability is decreased. We found the critical value of Gr above which this instability do not developed.     

Origin of Axially Running Waves in Liquid Bridges

A supercritical three-dimensional thermoconvective flow in a long non-isothermal liquid bridge with aspect ratio Γ?=?1.8 is numerically investigated under terrestrial conditions. Study of the flow regimes shows that the instability sets in as an axially running wave with zero wave number, m?=?0, which is a two-dimensional unsteady flow. Further increasing the applied temperature difference results in bifurcation of m?=?1 wave traveling azimuthally with a slightly higher frequency. The two waves co-exist within a certain range of the temperature difference values, and finally the m?=?0 wave is suppressed while the azimuthal one gets stronger.     

Open Questions on Reliable Measurements of Soret Coefficients

This study was motivated by experimental problems arising in the design of optical digital interferometry for measurements of Soret coefficients in laboratory conditions. Our attention is mainly focused on thermal design of the set-up. The goal is to establish a linear temperature profile inside the experimental cell while heating from above. The measures for preventing deleterious convection inside the working liquid and outside the experimental cell (in the surrounding gas) are carefully examined. It is pointed out that both convection in the liquid and in the surrounding gas have a strong negative effect on the quality of optical measurements.     

Preparation of JEREMI Experiment: Development of the Ground Based Prototype

This study has been performed in the frame of preparing the space experiment JEREMI (Japanese and European Research Experiment on Marangoni Instabilities). The use of forced coaxial gas flow is proposed as a way to stabilize the Marangoni convection in liquid bridges, which might have important technological applications in the floating zone technique. A new set-up is under development and all sub-systems have passed severe tests. Here we present the design of this set-up and preliminary results of experiments for shear-driven two-phase flows in a confined volume of liquid under conditions of normal gravity. The geometry corresponds to a cylindrical liquid bridge concentrically surrounded by an annular gas channel with external solid walls. Gas enters into the annular duct, flows between solid walls and upon reaching the liquid zone entrains initially quiescent liquid. The test liquids are ethanol, n-decane and 5?cSt silicone oil, which have different degrees of viscosity and of volatility. The gas flow along the interface strongly enhances the evaporation and, correspondingly, affects the interface shape. Silhouette measurements are used for optical determination of the interface shape. From the digital images the variation of the liquid volume as a function of flow rate is calculated.