In the framework of the complete formulation of the conjugate problem, the liquid–gas flow structure arising upon local heating using thermal sources is investigated numerically. The two-layer system ...is confined by solid impermeable walls. The Navier–Stokes equations in the Boussinesq approximation in the ‘streamfunction–vorticity’ variables are used to describe the media motion. The dynamic conditions at the interface are formulated in terms of the tangential and normal velocities, while the temperature conditions at the external boundaries of the system take into account the presence of local heaters. The influence of the number of heaters and heating modes on the dynamics and character of the appearing convective regimes is analysed. The steady and commutated heating modes for one and two heaters arranged at the lower boundary are investigated. The heating initiates convective and thermocapillary mechanisms causing the fluid motion. Transient regimes with the successive formation of two-vortex, quadruple-vortex and two-vortex flows are observed before the stabilization of the system in the uniform heating mode. A stable thermocapillary deflection appears at the interface above the heater. The commutated mode of heating entails oscillations of the interface with a change in the deflection form and the formation of travelling vortices in the fluids. The impact of particular mechanisms on the flow patterns is analysed. The paper presents typical distributions of the velocity and temperature fields in the system and the position of the interface for the considered cases.
In this paper, we compare the Marangoni effect and the effect of the Prandtl number variation on features of the liquid film rupture under the action of a thermal load and show a principal difference ...between these two effects. Results of computational analysis allow us to make the following conclusions. When affecting on the free surface of the plane liquid film by thermal beam, in order to obtain the initial holes of the same size in films with various thermal physical properties, one should apply a thermal load of a certain well-defined type, more specifically, concentrated thermal load, which provides the predetermined temperature at least on one of the film boundaries. In this case the size of the holes will depend only on the width of a thermal beam applied to the film free surface. Paper presents the solutions of the model problems.
The kinetics of oxidation of allyl alcohol to glycidol in the presence of extruded titanium silicalite was investigated. Based on the experimental data obtained, a kinetic model of the process was ...developed and the activation energies of the target and side reactions, the rate constants and the adsorption equilibrium were determined. Testing of the process of allyl alcohol epoxidation was carried out and the adequacy of the proposed kinetic model was evaluated at the bench laboratory installation of continuous action.
Graphic Abstract
The paper deals with the development of convective flows in a complex system of thin liquid layers occurring under the effect of thermal load. To study this process a mathematical model which is ...based on the decomposition of complex problem into unitary elements (modules) with some set of rules allowing their linkage with each other was constructed. Each module represents a monotypic local model. The fluid flow and heat transfer in each of these modules are described by the Navier-Stokes and thermal conductivity equations. The boundary conditions required to solve these systems of equations are represented explicitly and written in the form of conservation laws. The numerical analysis of effect of thermal load on the characteristics of the liquid layers movement depending on the Marangoni number is carried out. It is shown that physical and thermophysical properties of liquid layers play the decisive role. It is exactly they control the convective flows in layers and determine the position and shape of interfaces. The results of model problem solutions are presented.
This paper describes the study of a problem of thermocapillary convection in a flat bounded region filled with liquid and gas in contact along the interfacial interface under weak evaporation. ...It is proposed to investigate the heat and mass transfer processes and the parameters of phase transitions during local heating using a two-sided mathematical model based on the Oberbeck–Boussinesq equations. The characteristics of mass transfer through a thermocapillary interface due to evaporation and vapor content in the gas layer are analyzed with account for the influence of the Soret and Dufour effects. The results of a numerical study of the evolution of the interface and unsteady flows in a cell are presented. The calculation of the main characteristics of the liquid — gas system and the position of the interface at each time is carried out using a specially developed numerical algorithm. The model presented in this study makes it possible to describe the formation of characteristic thermal and concentration structures and the transition modes of cellular convection with a complex configuration of flows in layers.
The problem of thermocapillary convection under the conditions of weak evaporation in a plane confined volume is studied. The mathematical model to investigate the processes of heat- and mass ...transfer and phase transition parameters in a bilayer system subjected to local heating is suggested. A two-sided model based on the Boussinesq approximation of the Navier–Stokes equations is formulated in the “stream function–vorticity” terms. It includes governing equations and boundary conditions on the interface which are the consequences of the conservation laws and conditions on the outer boundaries of a cuvette. Special attention is given to the study of the effects of evaporation at the thermocapillary interface. The conditions of the heat and mass balance at the deformable interface with respect to the diffusive-type evaporation are assumed to be fulfilled. The temperature relations on the solid walls of a cell take into account the presence of thermal elements of finite size. The Dufour and Soret effects are considered in the interface conditions and in the governing equations describing the fluid motion in a gas-vapor mixture. A numerical algorithm is developed to calculate the basic characteristics of the liquid–gas system and interface location at any time. The results of the numerical study of the interface evolution and non-stationary flows in a cavity being under normal gravity conditions are presented. The possibility of intensifying the evaporation due to the arrangement of additional thermal elements is discussed. The proposed approach allows one to reliably feature the basic characteristics of convective regimes, to evaluate amplitude of the interface deformations and to forecast parameters of vapor content in a gas phase.
Phase diagrams of the polyphenylsulfone (PPSU)
–
polyethylene glycol (PEG)
–
N-methyl-2-pyrrolidone (NMP) system have been plotted as a function of PEG molecular weight. For 15 wt % PPSU solutions ...containing 15 wt % of PEG with molecular weight of 6000
–
40 000 g mol
–1
, the occurrence of an upper critical solution temperature (UCST, solution
–
gel transfer (gel point)) and a lower critical solution temperature (LCST) was found. According to the phase diagrams analysis, a method for the preparation of high flux PPSU membranes using the systems with UCST and LCST in an experimentally attainable temperature range has been proposed. The method involves casting solution processing at a temperature of the existence of a one-phase homogeneous solution (UCST < T < LCST), and the use of a coagulation bath at a temperature between UCST (gel point) and LCST. Membranes prepared from 15 wt % PPSU solutions with the addition of PEG-20000 were found to have the highest pure water flux (500–1000 L m
–2
h
–1
at 0.1 MPa), and a human serum albumin rejection of ca. 90%.
In the current study, extensive Orbitrap mass spectrometry analysis was conducted for skin strain Micrococcus luteus C01 planktonic cultures and biofilms after 24 h and 72 h of incubation either in ...the presence of epinephrine or without any implementations. The investigation revealed the complex and conditionally extensive effect of epinephrine at concentrations closer to normal blood plasma concentrations on both planktonic cultures and biofilms of skin strain M. luteus C01. The concentrations of hundreds of proteins changed during the shift from planktonic growth mode to biofilm and hundreds of proteins were downregulated or upregulated in the presence of epinephrine. Ribosomal, TCA, and cell division proteins appear to be the most altered in their amounts in the presence of the hormone. Potentially, the regulatory mechanism of this process is connected with c-di-GMP and histidine kinases, which were affected by epinephrine in different samples. The phenomenon of epinephrine-based biofilm regulation in M. luteus C01 has wide implications for microbial endocrinology and other research areas.
The free surface of a liquid film exposed to a laser beam is deformed and suffers a rupture. Depending on the thermal load intensity and the thermal properties of the liquid the rupture can be ...accompanied by the formation of secondary droplets over the film crown. This process is investigated using a mathematical model describing the motion of the thin layer of a viscous nonisothermal liquid. The model is based on the two-dimensional Navier–Stokes equations. The boundary conditions at the film-gas and film-liquid interfaces necessary for the solution of these equations are derived in the explicit form. The results of the solution of model problems are presented.
Nowadays the water management measures are ineffective. The field trips of 2017-2018 are carried out. The Lower Volga is drained by 37 watercourses, 34 of them belong to small rivers. The right bank ...tributaries of the Volga are short and flow in deep channels - 76% of all tributaries of its lower reaches. Left bank waterways are long, flowing in shallow channels - 24%. This is due to the location of the right bank of the Volga within the Volga Upland with a developed ravine-net system and a zone of dry steppes. The left bank of the lower reaches of the Volga River lies in the semi-desert zone, where the ravine-gully network is poorly developed. Factors affecting the state of these rivers: the flow of wastewater from industrial enterprises; pollution by fertilizers, pesticides; flow regulation; irrevocable withdrawal of river runoff for household, industrial, agricultural needs. Measures to address these problems: the transition to modern water-saving technologies; cleaning of domestic, agricultural and industrial waste; toughening control over compliance with the norms of discharge of pollutants into rivers; the establishment of water protection and sanitary zones for all reservoirs; clearing channels, coasts and floodplains from debris; tight control over livestock grazing in floodplains; planting forest belts along the river channels.
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