Andrei Alexeievitch Vedernikov

Viscous fingering in miscible liquids under microgravity conditions

Viscous fingering was observed by injecting colored water into a Hele-Shaw cell preliminarily filled with a glycerin-water solution. We varied the viscosity ratio, the flow rate, the gap width, and the density ratio. The Peclet number was higher than 105. Some of the experiments were performed in microgravity conditions (parabolic flights) in order to eliminate the gravity influence on pattern formation. The video shows peculiarities of fingering in microgravity conditions for a gap width of 1.2 mm. The first sequence of two experiments shows the influence of the viscosity ratio, which was decreased by a factor of 10 from the first to the second experiment. The next sequence shows the influence of the flow velocity, which was decreased by a factor of two between the first and second experiments in this sequence.

Photogrammetric set-up for the analysis of particle motion in aerosol under microgravity conditions

An optical set-up to investigate the motion of aerosol particles under microgravity conditions has been designed and manufactured. It provides accurate measurement of 3D coordinates of up to 1000 particles, discrimination between particles of different nature and estimation of the angular velocity of small aerosol crystals. A photogrammetric technique is applied to track independently moving particles, using the acquisition and processing of stereoscopic image sequences. The optical scheme of the set-up is based on a unique objective that collects the light coming from different directions from the backand front-illuminated aerosol, and transfers it to four different cameras. Driving parameters for the optical head design and image quality are discussed. The set-up performance was verified on optical test objects, aerosol simulators and also real aerosol under microgravity conditions during parabolic flight. The set-up has been designed for use in the JET experiment on board the Maser 8 sounding rocket. The experiment aims at the first direct observation of the chemojet motion of free-flying small growing crystals. Investigation of chemojet motion along with elaboration of the image analysis technique is focused on the development of highly sensitive, real-time, non-perturbative analysis of the reactions on the surface of aerosol particles.

Thermophoretic measurements in presence of thermal stress convection in aerosols in microgravity conditions of drop tower

The aim of the work is getting reference data on thermophoretic motion eliminating gravity-induced perturbation, developing new instrumentation and procedures. A series of experiments on measuring phoretic velocities was performed in the Bremen drop tower providing 4.7 s of high quality microgravity conditions, which allowed making negligible particle sedimentation and buoyancy driven convection. Motion of aerosol particles was observed simultaneously at low resolution to control nongravity convective motion in the cell and at high resolution by the digital holographic velocimeter in order to register particle three-dimensional trajectories. By choosing appropriate cell size and experimental procedures the heat and mass transfer relaxation processes were reduced to less than 0.3 s thus allowing measurements of particle velocities during more than 4 s. Side-wall temperature creep created convective motion in the cell. Its influence was suppressed by choosing sufficiently flat cell geometry. The values of the measured thermophoretic velocities for Knudsen number in the range 0.047–0.89 were found to be between predictions of the classical models of Talbot et al [1] on one hand and Yamamoto and Ishiara [2] on the other hand. Particles of different thermal conductivities (paraffin and NaCl) had about the same velocities. No negative thermophoresis was observed at these conditions for NaCl.

Crystal separation from mother solution and conservation under microgravity conditions using inert liquid

The problem of the separation of crystals from their feeding solutions and their conservation at the end of the crystallization under microgravity is investigated. The goal to be reached is to propose an efficient and simple system. This method has to be applicable for an automatic separation on board a spacecraft, without using a centrifuge. The injection of an immiscible and inert liquid into the cell is proposed to solve the problem. The results of numerical modeling, earth simulation tests and experiments under short durations of weightlessness (using aircraft parabolic flights) are described.