Trifonov Y.,RAS Institute of Thermophysics
Physics of Fluids | Year: 2014
The paper is devoted to a theoretical analysis of the linear stability of the viscous liquid film flowing down an inclined wavy surface. The study is based on the Navier-Stokes equations in their full statement. The developed numerical algorithm allows us to compute both the steady state solution of the nonlinear equations and the rates of growing or damping in time of the arbitrary two-dimensional disturbances of the solution which are bounded in space. The wall corrugations have a great influence on the disturbances behaviour. There is a critical Reynolds number Recr when the steady-state viscous flow over an undulated surface becomes unstable. It is found that the value of Recr depends essentially both on the topography parameters and the liquid's physical properties. In the case of the flat plate, the critical Reynolds number depends only on the value of the inclination angle. For different values of the Kapitza number, the inclination angle, and the Reynolds number we obtained the regions of the corrugation's parameters (amplitude and period) where all two-dimensional disturbances decay in time. © 2014 AIP Publishing LLC.
Misyura S.Ya.,RAS Institute of Thermophysics
Chemical Physics Letters | Year: 2013
The dissociation of methane hydrate under external pressure of 1 bar is studied experimentally. Non-isothermal dissociation is fundamentally different from the quasi-isothermal case. The increase in the density of heat flux from 255 to 13 700 W m 2 results in 9-fold increase in the dissociation rate of methane hydrate. Different variations of clathrates dissociation may be observed depending on the heat flux magnitude: (1) without self-preservation (high heat fluxes), (2) a partial self-preservation with one minimum of dissociation rate, and (3) a partial self-preservation with two minimums (low heat fluxes). When describing dissociation kinetics of the spherical granules, it is important to know the time dependence of the ice layer thickness growth. It is shown that not the curvature, but the heat flux value regulates the dissociation rate and the change in diffusion. A drastic change in dissociation rate is caused by a pressure decrease in pores. © 2013 Elsevier B.V. All rights reserved.
Trifonov Y.Y.,RAS Institute of Thermophysics
AIChE Journal | Year: 2010
The article is devoted to a theoretical analysis of counter-current gas-liquid wavy film flow between vertical plates. We consider two-dimensional nonlinear waves on the interface over a wide variation of parameters. The main interest is to analyse the wave structure at the parameter values corresponding to the onset of flooding observed in experiments. We use the Navier-Stokes equations in their full statement to describe the liquid phase hydrodynamics. For the gas phase equations, we use two models: (1) the Navier-Stokes system and (2) the simplified Benjamin-Miles approach where the liquid phase is a small disturbance for the laminar or turbulent gas flow. With the superficial gas velocity increasing and starting from some value of the velocity, the waves demonstrate a rapid decreasing of both the minimal film thickness and the phase wave velocity. We obtain a region of the gas velocity where we have two solutions at one set of the problem parameters and where the flooding takes place. Both the phase wave velocity and the minimal film thickness are positive numbers at such values of the velocity. We calculate the flooding point dependences on the liquid Reynolds number for two different liquids. The wave regime corresponding to the flooding point demonstrates negative u-velocities in the neighbourhood of the interface near the film thickness maximum. At smaller values of the superficial gas velocity, the negative uvelocities take place in the neighbourhood of the film thickness minimum. © 2009 American Institute of Chemical Engineers.
Trifonov Y.Y.,RAS Institute of Thermophysics
Fluid Dynamics Research | Year: 2012
This paper is devoted to a theoretical analysis of nonlinear two-dimensional waves using both the Navier-Stokes equations in their full statement and two integral approaches: Shkadov's approach and 'the regularized integral model'. We found the steady-state travelling waves and carried out an analysis of their linear stability and bifurcations using the Floquet theory. We found that thesolutions of the Navier-Stokes equations are qualitatively different from the solutions of Shkadov's integral approach starting from some values of the Kapitza number Ka. It is found that the solutions of all models considered here have an internal vortex at moderate Reynolds numbers Re. A linear stability analysis with respect to the periodic disturbances of the same wavelength L as a period of the nonlinear solution allows us to calculate the bifurcation lines of the nonlinear waves on the plane of two parameters (wavelength L and Re/Ka) for different values of Ka. These lines form a multi-fold and multi-sheet surface where we can compute the different types of solutions at one set of parameters by using the continuation principle and starting the computations with small values of Re/ Ka. We found that most of the solutions are unstable. © 2012 The Japan Society of Fluid Mechanics and IOP Publishing Ltd.
Misyura S.Y.,RAS Institute of Thermophysics
Experimental Thermal and Fluid Science | Year: 2016
Various evaporation regimes were studied experimentally in a wide range of droplet sizes and wall temperatures at a change in thermal-physical and geometrical characteristics of the wall. With the increasing diameter of the wetting spot of a water sample from 1 to 30 mm, the width of the transition region of boiling crisis increases. Dynamics of large droplets boiling is determined not only by wall overheating, but also by the droplet shape. Evaporation of droplets on the surfaces, whose longitudinal dimensions are much larger than the droplet diameter, should take into account free convection of gas and thickness of diffusion boundary layer, which depends on the droplet diameter. Wall surface polishing causes a multiple increase in evaporation time within the transitional boiling region, in contrast to the rough wall. For We≈. 0 and polished surface of the wall, the time of evaporation and Leidenfrost temperature in the transitional boiling region increase many times, in contrast to the rough wall (for high We number the result is opposite). To assess the effect of wall thickness on the rate of evaporation, it is important to consider the ratio of the droplet diameter to the wall thickness, depth of solid wall cooling, ratio of wall thermal conductivity to conductivity of liquid, and values of dimensionless Bio (Bi) and Fourier (Fo) numbers. © 2015 Elsevier Inc.