Konstantin Kostarev | Institute of Continuous Media Mechanics UrB RAS (original) (raw)

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Papers by Konstantin Kostarev

ВЕСТНИК ПЕРМСКОГО УНИВЕРСИТЕТА. ФИЗИКА

One of the promising directions in modeling of mass transfer in microgravity is the use of hetero... more One of the promising directions in modeling of mass transfer in microgravity is the use of heterogeneous fluid systems with the same initial density. However, in most cases the application of this approach is prevented by the contraction effect, which is a non-additive variation of the mixture volume (and, accordingly, mixture density) due to a change in the concentration of one of its components. The cause of the contraction is the appearance of compounds made up of the solute molecules / ions and solvent molecules due to the formation of hydrogen bonds and electrostatic interaction. Unfortunately, the prediction of the contraction effect is complicated by the lack of the relevant information for most liquid systems. To eliminate this drawback, the contraction of the most well-known aqueous solutions was determined. The obtained data are systematized and analyzed, and for a number of solutions a correlation between their contraction and other physicochemical properties has been est...

Microgravity Science and Technology, 2016

In this work, we focus on the processes which accompany a frontal neutralization reaction occurri... more In this work, we focus on the processes which accompany a frontal neutralization reaction occurring between two miscible fluids filling a vertical Hele-Shaw cell. We have found that chemically-induced changes of reagent concentrations coupled with concentration- dependent diffusion (CDD) can produce spatially localized low density areas which are sensitive to the external inertial field. In the case of static gravity we have demonstrated both experimentally and theoretically that it can give rise to the development of perfectly periodic convective structure. This scenario is strikingly different from the irregular density fingering, which is typically observed in the miscible systems. When the system is under the influence of the periodic low-frequency vibrations perpendicular to the reaction front, we found numerically the excitation of a mixed-mode instability combining the double-diffusion instabilities and the Rayleigh-Taylor mechanism of the convection within the low density areas.

The paper presents the results of experimental study of solutocapillary Marangoni convection aris... more The paper presents the results of experimental study of solutocapillary Marangoni convection arising in a non-uniform fluid mixture with a vertical gradient of concentration of dissolved surfactant around a stationary air bubbles immersed in the solution. The Fizeau interferometer-based technique was used for studying the convective flow structures and concentration field evolution. The tests revealed the periodic disturbances of the surfactant distribution caused by the abrupt outbursts and decays of the intensive solutocapillary flow at the bubble surface. The ground of the oscillations is conditioned by the specific competition of two different mechanisms of convective mass transfer namely the Marangoni convection which mixing up the solution and gravitational concentration motion restoring the destroyed surfactant stratification. The time dependences of the oscillations period were analyzed in relation to the average solution concentration, the surfactant concentration gradient ...

The Marangoni convection is a fluid motion caused by the action of capillary forces arising at th... more The Marangoni convection is a fluid motion caused by the action of capillary forces arising at the interface as a result of nonuniform surface tension distribution. Since Newtonian fluids have no a yield strength, the free surface motion is supposed to occur at any indefinitely small difference of the surface tension along an interface. From the other hand, in the case of gas bubbles and drops the onset of surface flow takes place only after the appreciable (up to several percents) surfactant concentration difference at the interface is reached [1]. Moreover, for drops, initiation of the interface flow is observed already after a surfactant has penetrated through the interface into the drop and an initial surfactant distribution has been formed. Most probably, the observed threshold in the development of the Marangoni convection is related with the existence of uncontrolled substances (impurities), which are surface-active against a test liquid and which therefore can form adsorbed ...

Micromachines, 2018

Continuous-flow microreactors are an important development in chemical engineering technology, si... more Continuous-flow microreactors are an important development in chemical engineering technology, since pharmaceutical production needs flexibility in reconfiguring the synthesis system rather than large volumes of product yield. Microreactors of this type have a special vessel, in which the convective vortices are organized to mix the reagents to increase the product output. We propose a new type of micromixer based on the intensive relaxation oscillations induced by a fundamental effect discovered recently. The mechanism of these oscillations was found to be a coupling of the solutal Marangoni effect, buoyancy and diffusion. The phenomenon can be observed in the vicinity of an air–liquid (or liquid–liquid) interface with inhomogeneous concentration of a surface-active solute. Important features of the oscillations are demonstrated experimentally and numerically. The periodicity of the oscillations is a result of the repeated regeneration of the Marangoni driving force. This feature i...

The paper is concerned with a comparative analysis of the results of experimental and theoretical... more The paper is concerned with a comparative analysis of the results of experimental and theoretical investigations of thermocapillary and solutocapillary phenomena observed at the interface of Newtonian fluids. These phenomena occur due to formation of the surface tension difference caused by a non-uniform distribution of temperature or surfactant concentration at the interface. The arising capillary forces set in motion of the surface and of the nearby fluid layers in the direction of higher surface tension. As a rule these are the regions with lower temperature or lower concentration of the surfactant. If the interface belongs to a freely floating inclusion, such as a drop or a gas bubble, its displacements cause the inclusion to move in the opposite direction (capillary drifting). If, for some reasons, the inclusion is unable to move, the motion of its surface initiates in the surrounding fluid an intensive convective motion called the Marangoni convection. The existence of the com...

Physical Review E

We report shock-wave-like structures that are strikingly different from previously observed finge... more We report shock-wave-like structures that are strikingly different from previously observed fingering instabilities, which occur in a two-layer system of miscible fluids reacting by a second-order reaction A + B → S in a vertical Hele-Shaw cell. While the traditional analysis expects the occurrence of a diffusion-controlled convection, we show both experimentally and theoretically that the exothermic neutralization reaction can also trigger a wave with a perfectly planar front and nearly discontinuous change in density across the front. This wave propagates fast compared with the characteristic diffusion times and separates the motionless fluid and the area with anomalously intense convective mixing. We explain its mechanism and introduce a new dimensionless parameter, which allows to predict the appearance of such a pattern in other systems. Moreover, we show that our governing equations, taken in the inviscid limit, are formally analogous to well-known shallow-water equations and adiabatic gas flow equations. Based on this analogy, we define the critical velocity for the onset of the shock wave which is found to be in the perfect agreement with the experiments.

Results of the numerical and laboratory modeling of free thermal convection in a gap between two ... more Results of the numerical and laboratory modeling of free thermal convection in a gap between two coaxial cylinders under microgravity conditions are presented. The numerical study was carried out by the finite difference method using convection equations in the Boussinesq approximation. The laboratory simulation employed a high-viscosity fluid (epoxy resin). A comparison of thermal front propagation data for different Rayleigh numbers demonstrates good agreement between the results of numerical and laboratory modeling.

Physical Review Fluids

This paper presents an experimental and numerical study on the structure and stability of a solut... more This paper presents an experimental and numerical study on the structure and stability of a solutal advective flow in a horizontal shallow layer. The flow is induced by the initial longitudinal steplike density distribution caused by inhomogeneous solute concentration. It is shown that, when the density difference or the channel thickness increases, the main flow instability in the form of longitudinal convective rolls occurs in the near-wall region. This phenomenon originates from the Rayleigh-Taylor instability, which develops near both the upper and lower horizontal boundaries, where the unstable density stratification occurs due to no-slip boundary conditions. It is established that the solutal Péclet number, a measure of the relative strength of advection and diffusion, must exceed the critical value Pe * ≈ 300 for the instability to set in. Moreover, the Péclet number uniquely determines the spatiotemporal characteristics of the secondary flow, namely, its wavelength and formation time. The results of the laboratory experiments are in good agreement with the numerical predictions.

The Journal of Physical Chemistry B

The concentration convection in an isothermal liquid with a surfactant concentration gradient, ar... more The concentration convection in an isothermal liquid with a surfactant concentration gradient, arising near a fluid drop clamped between the vertical walls of a horizontal channel is studied numerically within the framework of simple mathematical model with the surface phase at the drop-liquid interface formed by adsorption /desorption process. The interaction between the buoyancy and the Marangoni convective flows is

Physical review. E, Statistical, nonlinear, and soft matter physics, 2015

We report on chemoconvective pattern formation phenomena observed in a two-layer system of miscib... more We report on chemoconvective pattern formation phenomena observed in a two-layer system of miscible fluids filling a vertical Hele-Shaw cell. We show both experimentally and theoretically that the concentration-dependent diffusion coupled with frontal acid-base neutralization can give rise to the formation of a local unstable zone low in density, resulting in a perfectly regular cell-type convective pattern. The described effect gives an example of yet another powerful mechanism which allows the reaction-diffusion processes to govern the flow of reacting fluids under gravity conditions.

Physical Review E, 2015

Comptes Rendus Mecanique

The solutocapillary Marangoni convection around a gas bubble in the inhomogeneous binary mixture ... more The solutocapillary Marangoni convection around a gas bubble in the inhomogeneous binary mixture of miscible fluids with a vertical surfactant concentration gradient was studied experimentally. A new phenomenon, the oscillatory instability of the surfactant mass transfer, near the bubble boundary, was detected and investigated. The interpretation of this effect as an interaction between the surfactant adsorption at the bubble free surface and solutocapillary and buoyancy convective mechanisms is proposed. The experimental data on oscillation period in relation to bubble dimensions, time, liquid layer thickness, physico-chemical fluid parameters and concentration gradients are presented and discussed. To cite this article: K. Kostarev et al., C. R. Mecanique 332 (2004).

Physics Procedia, 2010

The paper deals with the results of experimental studies made to examine the behavior of a thin h... more The paper deals with the results of experimental studies made to examine the behavior of a thin horizontal layer of a ferrofluid, lying on a liquid substrate and subjected to the action of differently oriented magnetic fields. It has been found that a nonhomogeneous magnetic field normal to the layer surface can cause the deformation and rupture of the layer. As soon as the action of the field ceases the rupture can collapse or remain open if the initial layer thickness is below the critical value. However, the existing stable rupture of the layer can be closed by a homogeneous magnetic field applied to the layer in the longitudinal direction.

Frontal photopolymerization of polyacrylamide gel is theoretically and experimentally investigate... more Frontal photopolymerization of polyacrylamide gel is theoretically and experimentally investigated under conditions of microgravity. With the help of optical methods, the conversion field of monomer is visualized in the course of the experiment, and the pattern of a reaction front motion is determined. The comparison of the properties of flight and laboratory samples of gel allows us to conclude that carrying out polymerization onboard an orbital station in order to obtain homogeneous polymeric materials is promising.