Formation Of Vortex Flow Research Articles

Progress in the creation of long-lived atmospheric luminous formations in a pulsed electric discharge with an electrolytic electrode

This work presents an analysis of the research conducted in many countries in recent years on the so-called Gatchina discharge. The findings indicate that the Gatchina discharge exhibits the majority of the characteristics of natural ball lightning, making it the most effective method for reproducing and studying this phenomenon. To a large extent, our new results are based on experiments performed for the first time to visualize dust particles arising in an erosive emission, as well as the formation of vortex flows. These experiments make it possible to explain the ability of the Gatchina discharge to maintain its shape for a long time in the afterglow.

Increasing the efficiency of coagulation in resonant gaps due to acoustic flow formation

Relevance. The urgent need to eliminate environmental pollution from industrial emissions of various solid particles. At the same time, maximum attention is paid to cleaning exhaust gases from particles of 2.5 microns in size or less. One of the most promising ways to increase the efficiency of existing gas purification equipment in capturing such particles is their coagulation by exposing the gas flow to high-intensity acoustic vibrations of ultrasonic frequency. However, at low concentrations, even at the maximum permissible sound pressure level, the coagulation efficiency of particles smaller than 2.5 microns is insufficient to increase the recovery rate of gas cleaning equipment. Therefore, there is an urgent need to find new ways to further improve the efficiency of ultrasonic coagulation of particles smaller than 2.5 μm. Aim. To determine the conditions for the formation of vortex flows in ultrasonic fields with the maximum ultrasonic influence in terms of sound pressure level. Conducting comparative studies of the coagulation of particles with a size of 2.5 microns with and without vortex flows. This will make it possible to determine the real values of increasing the efficiency of ultrasonic coagulation during turbulization of a gas-dispersed flow by acoustic flows in comparison with coagulation in a uniform ultrasonic field and without it. Objects. Coagulation of particles under the influence of homogeneous and inhomogeneous ultrasonic fields. Methods. Computer modeling of the formed ultrasonic field by the finite element method using harmonic acoustic analysis. The paper considers the experimental method for studying the process of combining particles under the influence of ultrasonic vibrations. To determine the characteristics of an aerosol during experimental studies, a TIPAS-1 meter based on the small-angle scattering method and the spectral transparency method was used. Results. The paper introduces the results of studies of coagulation of particles with a size of 2.5 microns or less in an ultrasonic field formed in resonant gaps by oscillating disk emitters. The authors proposed to increase the efficiency of coagulation in resonant gaps through the use of ultrasonic disk emitters capable of forming alternating zones of maximum and minimum amplitude oscillations in the resonant gaps. The creation of such zones ensured the formation of vortex-type acoustic flows capable of moving particles within the nodal regions of a standing wave and between them. The involvement of small particles in the formed flows made it possible to increase the probability of their collision. It was established that more effective ultrasonic coagulation provides an increase in the degree of inertial capture for particles of 2.5 microns in size by 6% – from 89 to 95%, for particles of 1.5 microns in size by 7% – from 85 to 92%, and for particles of 0.5 microns by 9% – from 76 to 85%.

Initial stage of formation of vortex flow in an inductor with counter-rotating magnetic fields

In this article, unsteady flows of electrically conductive fluid in a cylindrical cavity under the action of differently directed rotating magnetic fields are investigated. The relevance of the study is due to the presence of such a flow in the flow meter for liquid-metal heat carrier which is currently under development. The subject of study is the process of formation of the spin-up flow stage in a combined inductor of a rotating magnetic field. The acceleration or the spin-up stage is characterized by a significant change in the angular velocity of the liquid and begins with the formation of low pressure areas due to centrifugal forces. The alternation and movement of low and high pressure areas lead to velocity pulsations. For small values of the control parameter, which is the Taylor number, the flow energy gradually increases. In this case, the steady flow consists of two azimuthal and several poloidal vortices with clearly defined structures. When the Taylor number exceeds a critical value, strong pulsations occur in the flow, resulting in the decay of large-scale vortices. The intensity of the current is characterized by the Reynolds number. A power-law relationship with an exponent of 1.57 has been established between the Reynolds and Taylor numbers. It has been found that the time of formation of a steady flow varies from several seconds to tens of seconds, depending on the value of the Taylor number. The estimates of the control parameters have been obtained for a flowmeter operating in a typical mode. It has been shown that for the correct measurement of flow velocity in the flowmeter, it is necessary that that the Taylor numbers be higher than 108. The study is carried out using mathematical modeling and the obtained results are verified by experiment. The average calculated profiles are located within the confidence intervals of the experimental profiles.

CFD simulation and optimization of an industrial cement gas–solid air classifier

An air classifier is one of the main and effective devices in cement industry. In this study, a three-dimensional, steady and two-phase (solid-gas) computational fluid dynamics (CFD) simulation was performed to optimize the performance of this device in the Kerman Momtazan cement plant, Iran. After the validation of CFD results, the air flow field and air path lines between fixed blades were checked carefully and the non-uniformity in velocity distribution and the formation of vortex flows between the blades close to particle inlets were observed. The study tried to improve the device efficiency by changing the method of entering particles into the device, resulting in a reduction in air classifier electrical energy consumption (from 41 to 35 (kW h)/t) and an increase in production rate (from 203 to 214 t/h). Additionally, the study investigated the effects of other modifiable operating conditions like rotary cage rotation speed, pressure difference, and inlet air temperature on the particle size distribution and classifier efficiency. The results showed that increasing the cage rotation speed decreased the product rate and the product particles mean diameter while increasing pressure difference or increasing temperature increased the product rate and the product particles mean diameter. It was concluded that these modifiable operating conditions can significantly affect the performance of the air classifier in the cement industry.

The influence of needle eccentric motion on injection and spray characteristics of a two-layered eight-hole diesel injector

To meet the increasingly stringent emission regulations nowadays, the quality of injection and spray must be high. The eccentric displacement of an injector needle during injection influences fuel flow characteristics within the nozzle (in-nozzle) and the injection and spray characteristics from the nozzle holes. In this study, the effect of the needle (within a double-layered eight-hole nozzle) on in-nozzle flow, injection and spray was analyzed and characterized. The model was validated by comparing simulation and experimental results from each hole (hole-to-hole). The hole-to-hole internal flow characteristics, injection characteristics, and spray characteristics under various needle eccentricities and radial displacements (needle deflections) were also analyzed. From the results, different asymmetric fuel flow characteristics were noted. Nozzle holes close to the needle deflection formed spray jets with wider cone angles and shorter penetration whereas nozzle holes at the opposite side of the needle deflection, formed spray jets with relatively smaller cone angle and higher penetration. As the needle lift got closer to the maximum lift, the effect of the eccentricity on in-nozzle fuel flow decreased. The direction of the needle eccentricity (needle deflection) dictated the flow dynamics within the holes which then affected the type of cavitation. The holes closer to the needle developed string type cavitation due to the formation of vortex flow in the nozzle. The eccentric effect of the needle was felt more by the lower layer nozzle holes than the upper layer holes.

Turbulence-driven vortex-flow around a magnetic island

We predict a new state of plasma self-organization, in the presence of magnetic islands, namely turbulence-driven island vortex-flows, which are non-axisymmetric flows. The interaction between an E × B sheared vortex-flow and the drift-wave (DW) turbulence driving it, is derived in the presence of a coherent static magnetic island. The turbulence is driven by a 3D density profile due to quasi-linear island-induced profile flattening, and the DWs thus follow the local electron diamagnetic drift along the island. The metric tensor is introduced, making the analysis easier in island geometry. An extended Charney–Hasegawa–Mima equation describes the DW turbulence—flow interaction, from which a wave-kinetic equation is obtained in island geometry. This yields a turbulence-vortex-flow predator–prey model which predicts a nonlinear threshold for island vortex-flow formation. The vortex-flow threshold decreases with increasing island-width as , which shows that wider islands may more easily drive vortex-flows.

Experimental evaluation of the energy dissipation efficiency of the vortex flow section of drop shafts

In urban wastewater collection and drainage networks, vortex structures are recruited to transfer fluid between two conduits with significant level differences. During the drop shaft, in addition to preventing the fluid from falling due to vortex flow formation, a significant amount of the fluid energy is dissipated due to wall friction of vertical shaft. In the present study, by constructing a physical model with a scale of 1:10 made of Plexiglas, the energy dissipation efficiency in the vertical shaft has been investigated. In this way, the performance of dimensional analysis indicates that the flow Froude number (Fr) and the ratio of drop total height to shaft diameter (L⁄D) are parameters affecting the efficiency of flow energy dissipation in the vertical shaft (ηs). This research considers four levels of Fr factor (1.77, 2.01, 2.18, and 2.32) and three levels of L⁄D factor (10, 13, and 16). Additionally, four replications for 12 possible combinations allow us to carry out 48 experiments and the full factorial method. The results demonstrated that the energy dissipation efficiency in the vertical shaft changes varies from 10.80 to 62.29%. Moreover, ηs values decrease with an increase in Fr whereas the efficiency increases with increasing L⁄D ratio. Furthermore, the regression analysis gave a second-order polynomial equation which is a function of Fr and L⁄D to accurately estimate the flow energy dissipation efficiency in the vertical shaft.

INVESTIGATION OF THE FUEL-AIR FLOW INSIDE A VORTEX FURNACE WITH A FLUIDIZED BED USING A SPECIAL AIR-DISTRIBUTING NOZZLE

The article presents the results of an experimental study of the fuel-air flow inside a vortex furnace with a fluidized bed using a special air distribution nozzle. Nowadays, the issue of dependence on fossil energy resources is the most important problem for the countries of Europe. One of the promising solutions to this problem is the use of vortex solid fuel furnaces for burning low-calorie types of fuel, such as waste from the woodworking and agricultural industries. Our country has developed agricultural and woodworking sectors of the economy, so the amount of waste from these industries is significant, which allows them to be used to cover the energy needs of the state. At the same time, there is a significant number of solid fuel boilers on the territory of Ukraine that can be used for this task. The main difficulties in burning low-grade fuels in solid-fuel boilers are the low level of efficiency of these vortex furnaces and insufficient theoretical information about this. To conduct the experiment, a special installation in the form of a cylinder with a nozzle inside is used. The nozzle has a plate inclination of 15 °, which does not exceed 10% of the total live cross-sectional area of the chamber of the experimental setup. In the course of the experiment, the boundary conditions for the formation of a vortex flow at different amounts of fuel and different air flows were determined, and the values of pressure loss and flow velocity were shown. The results are presented in graphical and tabular form. For example, for 2.9 kg of sawdust, the maximum speed of vortex flow formation is 0.72 m/s, for 5.8 kg this value is 0.57 m/s. The obtained results make it possible to formulate recommendations for the improvement of existing solid fuel furnaces due to the use of special nozzles for the intensification of combustion processes. This creates prospects for the development of the country's energy sector. Keywords: fuel combustion, vortex furnaces, furnace aerodynamics, special nozzle.

Hourly population exposure index for PM2.5 in urban street canyons

Vehicle emissions are among the primary sources of fine particulate matter (PM2.5). Assessing population exposure levels to PM2.5 from traffic emissions in street canyons is imperative. Accordingly, this study developed an hourly population exposure index (HPEI) by combining PM2.5 concentration distributions determined using computational fluid dynamics–based simulations, outdoor/indoor (O/I) concentration ratios of PM2.5 determined experimentally, and population distributions determined through an investigation. The results indicated that strength of vehicle emission sources and meteorological conditions affected the PM2.5 concentration distributions in the examined street canyon. The mean PM2.5 concentration in the middle of the street was higher than the concentrations at other positions, and PM2.5 concentrations on the leeward sides of buildings were higher than those on the windward sides. Moreover, three to five peaks of PM2.5 concentrations were observed at different measurement positions on the street and were attributed to the formation of vortex flows. The O/I concentration ratios of sulfur in PM2.5 in home, office, school, bus, and car microenvironments were 0.47, 0.50, 0.51, 0.77, and 0.61, respectively. The HPEI most closely reflected the population distribution at 7:00; however, it was derived using the PM2.5 concentration distributions and population distributions observed at 10:00. These results may help researchers understand the population exposure distribution and improve urban environmental management strategies.

Study on the influence of auxiliary electrode and magnet on electrochemical machining of SS304 using NaCl and NaNO3

SS304 is a potential material for the use in defense, medical, aerospace, and automotive industries owing to its excellent mechanical and chemical properties. Machining of SS304 is a topic of great research interest and complex shapes can be produced effectively using Electrochemical machining (ECM). However stray corrosion is a problem in ECM that has a negative impact on the process. Moreover, acids are widely used as electrolytes in ECM. The use of eco-friendly electrolytes saves the operator and the environment from the threats associated with the use of acids as electrolytes. Hence in this study, eco-friendly electrolytes (NaCl and NaNO3) are used. This paper presents a study to reduce the adverse effect of stray corrosion using a magnet, an auxiliary electrode, and a combination of both on two eco-friendly electrolytes using SS304 as workpiece. The evaluation was done based on Taper angle, Radial overcut, MRR, Surface roughness, and Radial-Stray current affected zone. The magnet was placed below the workpiece using a 3D-printed fixture. From the experiments conducted it has been found that the use of Aluminum as an auxiliary electrode is effective when using NaCl as an electrolyte. Up to 37% decrease in taper angle and a 63% reduction in surface roughness was observed when machining was done under the influence of a magnet using NaCl, due to the formation of vortex flow in the machining zone.

Novel transonic nozzle for Ranque-Hilsch vortex tube

The process of the vortex flow formation in the Ranque-Hilsch vortex tube is studied. Starting from deficiencies of the existing vortex tubes, a novel type for the transonic nozzle is suggested and designed. The proposed nozzle is different from the existing classical ones by the presence of additional supersonic section placed after the blades. This section creates controlled conditions for acceleration of the vortex flow to supersonic speed. Analysis of the gas flow in the transonic nozzle using 3D RANS simulations showed that slightly improper selection of nozzle dimensions may lead to destabilization of the vortex flow and deterioration of the vortex tube performance. Simplified semi-one-dimensional model of swirling gas flow was derived and utilized for correction of the nozzle dimensions in order to stabilize the flow. Detailed validation of this model against full 3D RANS simulations demonstrated its applicability for preliminary engineering computations. It was demonstrated that application of the novel transonic nozzle extends the region in the energy separation chamber occupied by the supersonic vortex. This results in increase of both temperature separation effect and vortex tube energy efficiency. Main advantages and disadvantages of the novel transonic nozzle are summarized in the concluding section.

Numerical analysis and experimental characterization of vortex flow at the gas-liquid interface in porous structure

Due to open-cell foam materials have extensive application foreground in medium-low pressure drop reactors or reactive distillation with low liquid load operation, it has been a hot spot in this field to explore the liquid phase flow inside the pores of foam materials. The present investigation addresses the formation conditions of the vortex flow in matrix porous structure (MPS) that is made from 3D printing technology. An experimental system consisting of a high-speed camera with a macro lens and particle tracking system was used to investigate the effect of the liquid flow rate and the liquid viscosity on the vortex flow formation in MPS. The numerical analysis based on the CFD modeling was used to calculate the vortex flow behaviors and characteristics. This model is validated and compared with the results of experimental campaigns performed in MPS with the formation of stable vortex flow. It was also found that the radius and swirling velocity of the vortex can be decreased by increasing the liquid viscosity and it would be slightly affected by main flow velocity with 10mL/min – 100mL/min, which is helpful to construct the gas-liquid interface with the formation of vortex flow for realizing process intensification.

A novel curved-corrugated channel model: Thermal-hydraulic performance and design parameters with nanofluid

In this study, flow structure and heat transfer characteristics of the novel channel, namely: the curved-corrugated channel, are numerically studied using ZnO-water nanofluid and the presence of E-shaped baffles. The influences of corrugations, baffles, and geometric parameters; gap ratio (GR = 0.2,0.3,0.4, and 0.5), blockage ratio (BR = 0.2,0.25,0.3, and 0.35), and pitch angle (β = 10°, 12.5°, and 15°) at different Reynolds number (8000–32,000) and volume fraction of ZnO particles (0–4%) are evaluated using thermal-hydraulic performance method. The results reveal that the formation of vortex flow and increased turbulence due to effects of corrugations and baffles can improve the heat transfer enhancement. Tested channel with baffle is superior to the other without baffle in thermal-hydraulic performance factor (THPF), and at lowest pitch angle 10° provides the best THPF. Reducing the gap ratio and increasing the blockage ratio, i.e. 0.2 and 0.35, yields the best THPF at 2.57. New correlations for Nusselt number and friction factor for baffled curved-corrugated channel with using nanofluid are also reported.

Thermal-hydraulic performance and design parameters in a curved-corrugated channel with L-shaped baffles and nanofluid

High heat generation is seen as a major issue in most mechanical and manufacturing industries, carrying with huge sub-problems. One of the possible cooling techniques is the combination of two or more passive methods, in particular for those parts with complex geometry. In this study, flow structure and heat transfer characteristics of the novel channel namely: curved-corrugated channel are numerically studied with using ZnO-water nanofluid and presence of L-shaped baffles. The influences of corrugations, baffles manner arrangement, and geometric parameters; corner angle (γ= 30°,45°,60°, and 90°) and blockage ratio (BR=0.25,0.3. 0.35, and 0.4), at different Reynolds number (8000–32000) and volume fraction of ZnO particles (0–4%) are evaluated using thermal-hydraulic performance method. The multi-phase mixture and the κ-ε model are used to simulate turbulent nanofluid flows inside the curved-corrugated channels at constant temperature condition (T = 355 K). The results reveal that the formation of vortex flow and increased turbulence due to effects of corrugations and baffles can improve the heat transfer enhancement. Inline arrangement of baffle is superior to the staggered arrangement in thermal-hydraulic performance (PEC), and at lowest angle 30° provide the best PEC. Regarding the friction ratio and compared to those of a plain channel, the effect of blockage ratio is considerable as it yields a multiplier impact of the corner angle. Reducing the blockage ratio and the corner angle, i.e. 0.25 and 30°, yields to the best PEC at 1.99. New correlations for Nusselt number and friction factor for baffled curved-corrugated channel with using nanofluid are also reported.

Numerical analysis of the hydraulic characteristics of modified labyrinth weirs

Labyrinth weirs increase the discharge rate by increasing the effective length of the weir within a confined width. In this paper, an attempt was made to improve the hydraulic performance of labyrinth weirs by both notching the weir wall and inclining the weir crest edge. To simulate the free flow surface, the volume of fluid (VOF) method, and the turbulence, the RNG k-e model was adopted in the FLOW-3D software. To validate the numerical model with the experimental data, the results indicate that the maximum relative error is 4.8%, which confirms that the numerical model is fairly well to predict the specifications of flow over on the labyrinth weir. Numerical simulation results showed that for low HT/P ratios (HT: approach flow head, P: weir height), modifying the geometry using either methods improved the discharge coefficient and discharge capacity over the labyrinth weir compared to a conventional weir. By increasing lc/wc (lc: the weir cycle length and wc: the weir cycle width) for low ratios of HT/P, the flow magnification ratio Q/Qn (Q: weir discharge, Qn: conventional weir discharge) increases. By increasing the HT/P ratio, the flow magnification ratio and the flow rate both decrease significantly, that is because of the vortex flow formation, the rejection of the flow upstream, and local submergence of entry cycles with a high HT/P ratio. Therefore, modifying the labyrinth weir geometry at low HT/P ratios (HT/P < 0.2) results in a better hydraulic performance, a higher discharge coefficient, and larger discharge values.

Vortex Flow Formation by a Melting Ice Block

The phenomenon of spontaneous rotation of melting ice on a solid substrate and on the surface of water has been confirmed by experiments in this work. The rotation velocity was found to increase with the temperature of the reservoir. Using the dying technique, a vortex flow was determined to appear directly under the ice block in experiments placing an ice block on the free surface of a resting liquid. A recorded vortex flow causes ice to rotate. The rotation parameters were measured, and the critical value of the depth of the resting fluid layer, necessary for the start of ice block rotation, was obtained.

Flow and mixing processes in a passive mixing microfluidic chip: Parameters’ estimation and colorimetric analysis

Objectives. The development of microfluidic systems is one of the promising areas of science and technology. In most procedures performed using microfluidic systems, effective mixing in microfluidic channels of microreactors (chips) is of particular importance, because it has an effect on the sensitivity and speed of analytical procedures. The aim of this study is to describe and evaluate the major parameters of the flow and mixing processes in a passive microfluidic micromixer, and to develop an information-measuring system to monitor the dynamics of flow (mixing) of liquids.Methods. This article provides an overview of the concept of microfluidic mixing chips (micromixers) and their classification, and analyzes the kinds of points of mixing and microfluidic channels for mixing. The article presents the description and calculations of the hydrodynamic similarity criteria (Reynolds, Dean and Peclet numbers), which are the critical parameters for creating and optimizing micromixers (for example, straight and curved channels in the flow rate range between 100 and 1000 µl/min). We have developed an information-measuring system to monitor the dynamics of flow (mixing) of liquids in a microfluidic channel, which consists of a microscope with a digital eyepiece (LOMO MIB, Russia), an Atlas syringe pump (Syrris Ltd., UK) and a passive mixing microfluidic chip of interest (made of clear glass). This system was designed to quickly illustrate the principles of mixing in microfluidic channels of different configurations.Results. The developed system has allowed carrying out a colorimetric analysis of the modes and dynamics of mixing two liquids (5% aqueous solution of azorubine dye and water) at the T-shaped mixing point, at the straight and curved (double-bend shaped) sections of the microfluidic channel of the passive-type micromixer with flow rates varying from 100 to 400 µl/min.Conclusions. According to the obtained calculations, the share of the advective mixing processes (formation of vortex flows and increase in the contact area of the mixed substances) in flowing liquids is significantly higher in curved microchannels. The developed information-measuring system to monitor the dynamics of flow (mixing) of liquids in a microfluidic channel is a convenient tool for optimizing the mixing modes in the channels of micromixers, and for designing new configurations of channels in microchips. It would allow intensifying processes and increasing the performance of microfluidic systems.

Mixing of fluids in vortex T-mixer with two and four non-aligned inlet microchannels

Mixing of fluids at microscale is an indispensable stage required on the microfluidic systems. Large number of micromixer designs aimed with efficient mixing has been reported by many researchers. In this work numerical study has been executed out on vortex T-mixer. This mixer has two and four non-aligned inlet channels. The inlet channels are aligned tangentially to the main microchannel at one end. The objective was to examine mixing and fluid flow for a broader range of Reynolds numbers. The results were correlated with simple T-mixer (inlet channels in-planar with the main microchannel). Vortex T-mixer with two inlet channels show better mixing performance among the three designs due to vortex flow. Vortex T-mixer with four inlet channels show the formation of vortex flow. However, such flow are depicted at much higher Reynolds number. The study reveals vortex T-mixer with two inlet channels quite promising design as compared to T-mixer with four inlet channels.

INVESTIGATION OF HEAT DISTRIBUTION PROCESSES ON THE INNER SURFACE OF THE ENCLOSING STRUCTURE, TAKING INTO ACCOUNT THE MOVEMENT OF AIR IN THE BOUNDARY AREA BETWEEN THE DEVICE AND FENCING

A study was made of the nature of the movement of air mass in the space between the device that warms the room and the confining outer wall of the room. The hydrodynamic motion of the air mass was simulated on the basis of the two-dimensional in space Navier-Stokes equations and the convective heat conduction equation to find out a detailed picture of the physical processes that occur. Also for some particular cases, analytical solutions were obtained for the conjugate problem, where the movement of air is caused by its thermal expansion and the action of gravity in areas with different densities (Archimedes' forces). The simulation of more complex types of air movement with the formation of vortex flows using numerical methods and the corresponding program codes written in C++. It was found that the movement of air mass in the space between the device and the fence strongly depends not only on the temperature of the device, the wall, and the outside air. It was revealed that hydrodynamics and heat transfer are significantly influenced by two geometrical parameters: the distance between the device and the wall, and the distance from the flooring to the bottom of the device. In particular, a thin layer of the downward flow of cold air along the fence and above the floor is possible. The condition for the occurrence of such a downward flow has been found, it is determined by the ratio of the temperature of the wall, the device, and the average temperature in the room.

Thermomechanically Excited Vortical Flow in a Hybrid-Oriented Nematic Channel

In this paper, we described numerically several scenarios of formation of vortex flows (VF) in microsized hybrid-oriented liquid crystal (HOLC) channels with orientation defects using a nonlinear generalization of the classical Ericksen–Leslie theory that allows taking into account termomechanical contribution, both in the expression for the shear stress and in the entropy balance equation. An analysis of the numerical results showed that there are two or one vortices in the HOLC channel although two vortices directed towards each other are generated at the initial stage of the VT formation Thermomechanically Excited Vortical Flow.