Development of convection in binary mixture with soret effect

This paper demonstrates the influence of low Rayleigh vibration on thermodiffusion measurement in microgravity environment. The goal is to show how the variation of certain parameters such as frequency and amplitude of translational vibrations would impact the results obtained from the ISS experiment. Precisely, impact of change in low Rayleigh vibration on the separation of a component is studied for each experimental run. ISS experimental data are obtained based on optical digital interferometry in a reduced gravity environment. The experiment is done in a cubic cell containing an aqueous solution exposed to a lateral temperature gradient. A mixture of water and isopropanol of different initial concentrations with positive and negative Soret coefficient is chosen as the test fluid. Collected data are analysed by image processing. Results show maximum separation of components for the case without any forced vibration. Moreover, an increase in Rayleigh number corresponds to decrease in the separation of components.

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“…Experimental cell. [9] splitter. Finally, interference fringes are captured by a charge coupled device (CCD) camera 1280 × 1024 pixels sensors.…”

Section: Methodsmentioning

confidence: 99%

Experimental evidence of low rayleigh vibration on mixture during thermodiffusion experiment

2013

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“…Chacha et al [5] investigated the role of thermal diffusion phenomena on compositional variation in a binary mixture of methane and normal butane in the presence of a fluctuating acceleration field, in experiments on board the International Space Station (ISS). Shevtsova [6] proposed a new approach to simultaneously measure diffusion and the Soret coefficient. A binary mixture of water and isopropanol was chosen as the working liquid.…”

Section: Introductionmentioning

confidence: 99%

A new process for the determination of the Soret coefficient of a binary mixture under microgravity

Mojtabi

2020

International Journal of Thermal Sciences

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In the presence of a gravity field or under microgravity, pure thermo-diffusion leads to very weak species separation in binary mixtures. To increase the species separation in the presence of gravity, many authors use thermo-gravitational diffusion in vertical columns (TGC). For a given binary mixture, the species separation between the top and the bottom of these columns depends on the temperature difference, ΔT, imposed between the two vertical walls facing each other, and the thickness, H, between these two walls (annular or parallelepipedic column). These studies show that, for a fixed temperature difference, the species separation is optimal for a thickness, H opt , much smaller than one millimetre. The species separation decreases sharply when the thickness H decreases with respect to this optimum value. It decreases progressively as H increases with respect to H opt. In addition, for mixtures with a negative thermo-diffusion coefficient, the heaviest component migrates towards the upper part of the column and the lightest one towards the lower part. The loss of stability of the configuration thus obtained leads to a brutal homogeneity of the binary solution. The objective of this study in microgravity was to increase the optimum of species separation. For this purpose, the binary fluid motion was provided by uniform velocities imposed on the two walls of the cavity facing each other. This forced flow led to species separation between the two motionless walls of the cavity. In this case, the fluid motion generated in the cavity was not dependent on the imposed temperature difference, ΔT contrarily to the case of thermogravitational column. Under these conditions and for a given column of thickness H, there are three independent control parameters: ΔT and the two velocities of the walls facing each other. Using the parallel flow approximation for a cell of large aspect ratio, the velocity, temperature and mass fraction fields within the cavity were determined analytically. Thus the parameters leading to optimal species separation were calculated. The analytical results were corroborated by direct numerical simulations. The present paper thus proposes a new process for the determination of the Soret coefficient, the thermodiffusion coefficient and mass-diffusion coefficient.

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“…In the material processing industry, the crystal growth process is an important example that the qualities of the crystal materials are closely affected by the flow instabilities resulting from the buoyancy and thermal-solutal convections, since the oscillatory flow induces impurity striations in the crystals [3,4]. Especially, under microgravity conditions, the effect of gravity is minimized [5] and the effect of thermal-solutal capillary flow generated by surface tension gradient is highlighted [6][7][8]. Czochralski (Cz) crystal growth technology is an important method for producing crystals, where a rod-mounted seed crystal dipped into melt and carefully pulled out by controlling the thermal and concentration gradients, crystal rotation and pulling rates [9,10].…”

Section: Introductionmentioning

confidence: 99%

Flow Instabilities of Coupled Rotation and Thermal-Solutal Capillary Convection of Binary Mixture in Czochralski Configuration

Yuan

2019

Crystals

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In order to understand the flow instabilities of coupled rotation and thermal-solutal capillary convection of binary mixture in a Czochralski configuration subjected to simultaneous radial thermal and solutal gradients, a series of three-dimensional direct numerical simulation have been conducted. The capillary ratio of the silicon-germanium mixture is −0.2. The rotation Reynolds numbers of crystal and crucible, Res and Rec range from 0 to 3506 and 0 to 1403, respectively. Results show that the basic flow is axisymmetric and steady. It has rich flow structures in the meridian plane, depending on the competitions among the driving forces. With the increase of thermocapillary and rotation Reynolds numbers, the basic flow will transit to three dimensional oscillatory flow. For different combination of rotation rate and thermocapillary Reynolds number, the oscillatory flow can be displayed as spoke patterns which is steady in time but oscillate in space, spoke patterns propagate in azimuthal direction, rotational waves or coexistence of spokes and rotational waves. The crucible rotation has an inhibitory effect on the flow instability, inducing the monotonically increase of critical value for flow transitions, however, for crystal rotation, the critical thermocapillary Reynolds number increases at first and then decreases. When the rotation rate is large, two flow transitions are captured.

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Development of convection in binary mixture with soret effect

Cited by 13 publications

References 3 publications

Experimental evidence of low rayleigh vibration on mixture during thermodiffusion experiment

Experimental evidence of low rayleigh vibration on mixture during thermodiffusion experiment

A new process for the determination of the Soret coefficient of a binary mixture under microgravity

Flow Instabilities of Coupled Rotation and Thermal-Solutal Capillary Convection of Binary Mixture in Czochralski Configuration

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