Formation Of Convective Flow Research Articles

Urban environment as a factor in the formation of the area microclimate

The growth of the leading countries’economies leads to the rapid development of megacities and changes in urban areas. Currently, more and more modern high-rise civil buildings are being built, resulting in an increasing density of urban areas and the activity of transport infrastructure. This causes major changes in the structure of urban development, which leads to a change in aeration and microclimatic conditions in urban areas. Solar radiation plays an active role in shaping the microclimate of the urban space, which aggravates the heat and wind regime of the urban environment. This is especially acute in the southern cities with hot climatic conditions. The article analyzes modern urban areas and factors affecting their microclimate. The role of temperature inversions in the formation of microclimatic conditions is indicated. Using the example of the yard space in Dushanbe, measurements and field studies were carried out; graphs of the climatic indicators of the urban area were plotted. The role of solar radiation in the formation of convective flows and microclimatic conditions of urban space is discussed.

Experimental and numerical study of the natural convection in dispersed systems in a heated rectangular cell

In this work, we study the appearance and development of convective flows in a dispersed medium by the experimental methods and mathematical modeling. An experimental study of the dynamics of thermoconvective flows is carried out in a specially designed cell, which is a rectangular vertical cavity with the possibility of heating the walls. A series of experiments were carried out at different temperature gradients. Various modes of convective flow have been obtained. To simulate the dynamics of convective flows in a rectangular cavity, a mathematical model based on the equations of thermal convection in the diffusion approximation has been created. Convective flow patterns for a dispersed medium have been obtained. Numerical calculations coincide with the experimental results. Numerical simulation of the problem allows us to estimate the distribution of velocities, temperature, and concentration of the dispersed phase inside the cell during the formation of convective flows and the established convection regime.

Numerical simulation of hydrodynamics and heat transfer in the technological reservoir with the heat pump

The mathematical modeling of mixed convection of viscous incompressible fluid in a rectangular reservoir with the sources of input and output of mass has been carried out. Is studied the influence of heat sink as a result of the work of heat pump and its position on the formation of convective flows and a change in the temperature conditions. Are revealed basic laws governing the heat transfer in the small environment of heat pump. The analysis of the influence of Reynolds numbers on the intensity of the heat exchange is carried out.

Investigation of the oxide phase convective homogenization while vacuum-arc with hollow cathode remelting of steel

Discussion of the requirements for the placement of ZrO 2 powder in the cathode, which must be taken into account in the production of ODS steel by vacuum-arc remelting in order to provide the high level of homogenization of the oxide particle is presented. The description of the experimental setup and the cathode structure for vacuum-arc remelting of steel, alloyed with oxide nano-powder is given. The role of convective processes in the homogenization of nano-particles in the production of ODS steel is highlighted. The convective flow of liquid metal captures ZrO 2 powder particles and carries them throughout its volume. The use of the elementary cylindrical convective cell with mixed boundary conditions is proposed for the description of homogenization of the oxide particles. The structure and spatial distribution of the convective mass transfer in the cylindrical convective cell with the cosinusoidal bottom profile are provided. Spatial distribution of convective flow in the cell is described by the Stokes lines, which are concentrically arranged smooth closed lines, which indicates the formation of convective flow in the form of a single vortex in the cell with mixed boundary conditions. Near the bottom, the Stokes lines reflect the curved cosine bottom profile. Criteria of vacuum-arc melting and convective mixing of ZrO 2 nano-particles are formulated. Drops of the liquid material of the cathode with ZrO 2 nano-particles penetrate to the central vertical flow of the convective cell. Then, near the wall of the crystallizer, the particles are subjected to vertical forces: Archimedes force (always directed in vertical direction, i.e. upwards); gravity force (always directed downwards); friction force (Stokes force) (directed along the liquid velocity vector) on these particles. The Archimedes force depends on the volume, i.e. size, of the particle. Thus, the less the nano-particle size, the lower the buoyancy force. The criterion of overcoming the Archimedes force allows determining the sizes of the particle at which their uniform distribution in the cell volume is possible. Criteria of convective homogenization ZrO 2 nanoparticles are the following: – droplets of cathode material penetrate into the cylindrical convective cell on a circular line which corresponds to the inner circumference of the hollow cathode; – drops of the cathode material penetrate to a depth of convective cells, consistent with its half-height; – ZrO 2 particles with sizes less than 90 nm will be stored for a long time in the melt, and homogenized in volume of the melt as a result of convective mass transport.

Investigation of the oxide phase homogenization in the convective cell while producing vacuum-arc remelting

Discussion of the requirements for the placement of ZrO 2 powder in the cathode, which must be taken into account in the production of ODS steel by vacuum-arc remelting in order to provide the high level of homogenization of the oxide particle is presented. The description of the experimental setup and the cathode structure for vacuum arc remelting of steel, alloyed with oxide nano-powder is given. The role of convective processes in the homogenization of nano-particles in the production of ODS steel is highlighted. The convective flow of liquid metal captures ZrO 2 powder particles and carries them throughout its volume. The use of the elementary convective cell with free boundary conditions is proposed for the description of homogenization of the oxide particles. The structure and spatial distribution of the convective mass transfer in the elementary convective cell with the non-planar bottom profile are provided. Spatial distribution of convective flow in the cell is described by the Stokes lines, which are concentrically arranged smooth closed lines, which indicates the formation of convective flow in the form of a single vortex in the cell with free boundary conditions. Near the bottom, the Stokes lines reflect the curved cosine bottom profile. The scenario of vacuum arc melting and convective mixing of ZrO 2 nano-particles is formulated. Drops of the material of the cathode with ZrO 2 nano-particles fall to the central vertical flow of the ECC. Here, the particles are subjected to the action of the convective flow, which will result in the impact of multidirectional forces: Archimedes force (always directed upwards); gravity force (always directed downwards); friction force (Stokes force) (directed along the liquid velocity vector) on these particles. The Archimedes force depends on the volume, i.e. size, of the particle. Thus, the less the nano–particle size, the lower the buoyancy force. The criterion of overcoming the Archimedes force allows determining the sizes of the particle at which their uniform distribution in the cell volume is possible. It is necessary to provide such conditions: – the deeper the drops get into the cell, the more evenly ZrO 2 particles are distributed in the cell volume; – even distribution of ZrO 2 particles in the sample volume should be observed for sizes less than 80–100 nm.

The Effect of Differences in the Diffusion Coefficients of Components on the Onset of Convection in Isothermal Multicomponent Systems

Two series of experiments on the formation of convective flows in multicomponent liquid and gaseous mixtures are considered. In the first series, the convective structures arising during the diffusion of a binary aqueous solution of salt and sugar in an aqueous solution of pure salt were studied using the schlieren method. The observed behavior of convective cells corresponds to the instability similar to the "finger structures". In the second series, the experiments were conducted to determine the effective diffusion coefficients as a function of pressure in gas mixtures 0.5504 CH4 + 0.4496 Ar – N2 and 0.5994 H2 + 0.4006 Ar – N2. Our experiments have shown that the onset of convective flows both in liquid and gaseous multicomponent mixtures is due to the difference in the interdiffusion coefficients of the components. The experimental data for the ternary gas mixtures are described in the framework of the linear theory of stability.

Formation of the orogen-foredeep system: A geodynamic model and comparison with the data of the northern Forecaucasus

The disturbance of mechanical and thermal equilibria in the upper shell of the Earth as a result of mantle or local within-plate processes related to periodic tectonic activity gives rise to the formation of convective flows in the low-viscosity asthenosphere. These flows affect the lithosphere and create domains of subsidence and uplift, which can continue to develop long after the cessation of active periods. If the density of the lithosphere does not decrease with depth, then small-scale flows increase uplift in zones of compression of the continental lithosphere and create domains of extension at their margins. In our opinion, small-scale convection is the main geodynamic factor that forms foredeeps. The results of detailed numerical modeling of foredeep formation at the margins of adjoining orogens are presented in the current paper. In order to set the initial conditions for the stage of continental collision, the precollision stages of the foldbelt evolution are considered, including the stage of trough formation on the thinned continental crust or on the oceanic lithosphere and the stage of sedimentary basin formation; depending on the degree of extension, this can be an inner sea or a passive continental margin. Such initial conditions were used in modeling of the compression stage (continental collision), when the orogen-foredeep system is formed. The parameters of the model and the tectonic processes are chosen so as to bring the results of numerical computation in line with the data on the Greater Caucasus and northern Forecaucasus, including the thickness of the crustal layers and sedimentary cover, structure of the foredeeps, rate of tectonic subsidence, heat flow, etc. Comparison of the numerical modeling results with the formation history of the Caucasus foredeeps confirms that the first stage of regional compression of the Greater Caucasus took place before the deposition of the Maikop sediments. At least three compression stages followed: 16.6–15.8 Ma (Tarchanian), 14.3–12.3 Ma (Konkian-early Sarmatian), and 7.0–5.2 Ma (Pontian). The next stage of regional compression is apparently occurring at present.

Space and Time Correlations in a Dissipative Structure Emerging in an Electrochemical System with a Cation-Exchange Membrane

The mechanism of electromasstransfer in a system containing a cation-exchange membrane at a current density exceeding the limiting diffusion current is studied by analyzing the electric potential fluctuations. An experimental setup is designed for measuring fluctuations simultaneously at 16 points in a galvanostatic mode. The fluctuations are found to form in a near-membrane diffusion layer of electrolyte depleted of carriers. As the current density increases, spectra of resonance fluctuations turn into flicker-noise spectra; this process is studied in great detail. Use of space and time difference moments for processing noise signals allowed us to estimate such parameters as the correlation time, space correlation length, and components of the propagation velocity for perturbations in the dissipative structure forming in the membrane system. The data point to the formation of convective flows thermally induced in a diffusion layer of electrolyte under the action of Joule heating at a current density approaching a limiting value.

Effect of temperature on diffusional instability

It is shown that in the case of unstable diffusion, the process tends to become more stable with an increase in temperature. A reduction in temperature in a stable system may result in the formation of convective flows, and the system will change over to the unstable state.