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.     

Flaw inspection of welded joints in titanium alloys by the eddy current method

The eddy current transducer (ECT) of the transformer type is used to construct a sensor for investigating titanium sheets joined by a welded joint. The characteristics of the ECT are presented. The measurement method for controlling the occurrence of defects in the welded joints in titanium alloys is described. The experimental results obtained by the ECT on two welded titanium sheets are presented. The depth of penetration of the field of eddy currents into the investigated object is determined and the dependences describing the response of the ECT at different depths of the defect are outlined. The relationships can be used for evaluating the quality of welded joints and determining the reliability of welding.     

Enhancement of Evaporation in Presence of Induced Thermocapillary Convection in a Non-Isothermal Liquid Bridge

This paper examines the evaporation rate through the interface of a evaporating—convecting non-isothermal cylindrical column (liquid bridge). The liquid phase is subject to a vigorous thermocapillary convection. Experiments were performed in a wide range of the imposed temperature difference. The obtained data are compared to a theoretical model of mass transport that does not account for the bulk fluid flow. The analytical results obtained for the real experimental conditions reveal an important role of the convective heat and mass transport in evaporization. The convective process is found responsible for enhancing the evaporation rate by several times with respect to the conductive regime.     

Thermovibrational Convection in Microgravity: Preparation of a Parabolic Flight Experiment

This work describes the preparation of the future experiments on thermovibrational convection in microgravity during parabolic flights. The experimental setup for observing thermovibrational flows is designed. It consists of a cubic cell with liquid, which is subjected to controlled vibration, and equipment for registering velocity and temperature fields with a help of optical digital interferometry. The question of choosing working liquid and control parameters of the experiment is addressed. A 3D numerical simulation of thermovibrational convection in a cubic cavity is performed for real parabolic flight conditions. The study is aimed at estimating the values of physical quantities that manifest the presence of thermovibrational flows and can be experimentally measured during short microgravity time (20 s).     

Overlimiting mass transfer through cation-exchange membranes modified by Nafion film and carbon nanotubes

Eight cation-exchange membranes different in the surface morphology and the degree of hydrophobicity were studied by contact angle, voltammetry and mass transfer rate measurements. One series of membranes was prepared starting from heterogeneous MK-40 membranes, and another, from homogeneous Nafion? 117 membranes. Coating a membrane with a thin film of Nafion resulted in increasing surface hydrophobicity, while the doping of the Nafion surface film with carbon nanotubes (CNT) led to an unexpected decrease in hydrophobicity. It was found however that after 100 h operation of a Nafion? 117 membrane coated with a Nafion film doped with CNT, the contact angle increased from 51 to 81°. This increase in the surface hydrophobicity was accompanied by a significant rise in overlimiting transfer rate, more than 1.5 times, under the same voltage. High correlation between the overlimiting mass transfer rate and the degree of hydrophobicity was observed also in all studied cases: more hydrophobic surface leads to a higher mass transfer rate. The effect is explained by increasing electroconvection occurring as electroosmosis of the second kind: the slip of water over a hydrophobic surface enhances the tangential velocity of electroconvective vortex having its maximum at a distance of several hundreds of nm from the surface.     

Aspects of the formation of sulfide inclusions and their effect on the quality of low-alloy structural steels

Metallurgist - Results are presented from an analysis of the mechanical properties of forgings made of low-alloy structural steels cast in a vacuum. These forgings sometimes have substandard...     

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.