D. A. Nekrasov

Modeling of boiling of subcooled water and ethanol under conditions of pulsed heat generation in a wall

Results of experimental investigation and mathematical modeling of boiling of subcooled water and ethanol under pulsed heat generation in a heater wall are presented. The defining steps of boiling, i.e., warming-up of the wall area, development of the vapor phase, and formation of the pressure wave, are considered. Beginning from some values of surface warming rates (∼3000 K/s) and underheating (∼20 K), the mechanisms of boiling of water and alcohol are demonstrated to be different.

Peculiarities of diffusion in gels

An optical method was applied to study the peculiarities of diffusion in gel: this method provides real-time visualization of spreading of solutes brought into the gel. It was shown that spectral characteristics of reflected light give additional information about nature of diffusive spreading of solutes and about state of the gel. Gels with different densities and lifetime were studied. These parameters have strong influence on the velocity of diffusion. The study demonstrated critical differences for diffusion process in gels with true solutions and with solutions with nanoparticles. Experiments discovered the anisotropy in 3D diffusion of solutes in gels; physical explanation of this phenomenon was proposed.

Development of convection in near-wall granular bed during nonstationary heating

Based on the developed and realized optical method of the polarization of temperature fields, the results of experiments on the visualization of temperature fields and the development of convective flows during the nonstationary conductive heating of the cell wall involving a layer of pebble beds placed in liquid are presented. Upon variations in the heat physical properties of liquid and particles (pebbles) of the granular bed, as well as the value of the supplied heat flow, the mechanism of the pebble-bed effect on the time and character of the formation of free convection close to the wall heated from below has been studied. The calculation model of the process has been suggested.

Peculiarities of unsteady mass transfer in flat channels with liquid and gel

The rate of the unsteady mass-transfer process in horizontal flat channels filled with viscous liquid (water) and in channels filled with gel has been measured experimentally. It has been established that the rate of propagation of a substance through a channel under the unsteady one-dimensional mass transfer conditions depends on its width and exceeds the value corresponding to the rate of diffusion. The measured mass transport rate in an open channel is less than in a closed channel. The reason for the increased mass-transfer rate with regard to the diffusion mechanism is the slow convective flow of liquid caused by the difference between the densities of a diffusing substance and water. The presence of the surface concentration gradient of liquid gives rise to the appearance of surface forces that significantly affect the mass transport rate. The similarity of the mass-transfer behavior in channels filled with pure liquid and gels is found experimentally, which allows one to talk about their presence, as well as of convective transport in them.

Experimental and numerical simulation of interphase mass transfer of gas bubble in granular backfill and gel

An experimental and numerical study of the process of interphase mass transfer has been performed upon the motion of gas bubble in the granular layer saturated with liquid at different tilt angles of the tube and in the case of movement in the channel between the gel layers. The dependences of the coefficient of effective dimensionless mass transfer have been obtained depending on the tilt angle of the tube and backfill diameter. The relationship between the coefficient of effective dimensionless mass transfer and the rate of the free-floating gas bubble has been established.

Modeling slug flow and mass transfer in inclined pipes

An experimental and numerical study of the gas projectile mass transfer when moving in an inclined pipe has been carried out. The mathematical model is based on the smoothed particle hydrodynamics method and verified by experimental data. The dependence of the velocity of the gas projectile motion and effective dimensionless mass transfer coefficient on the pipe inclination angle has been found. The simulated and calculated from experimental data bubble profiles have been compared.

Hydrodynamic peculiarities of concentrated water suspensions in smooth pipe

The numerical simulation of the pulp motion in direct pipe has been held on the basis of the developed mathematical model of motion for the mixture of liquid and solid particles using the lattice Boltzmann equations. The model was verified by the original experimental data on the hydraulic resistance coefficients at the pulp motion in pipe at outlet from disintegrator. The dependences of the hydraulic resistance coefficient on the concentration ratio of water and solid particles including highly saturated suspensions have been obtained. The intrinsic velocity profiles for the motion of suspensions with various Reynolds numbers have been determined.