Layer Vortices Research Articles

Study of Properties of Water-Dispersion Paint and Varnish Compositions with the Content of Modified Mineral Filler

This article presents the results of research work devoted to improving the characteristics of paint and varnish coatings based on aqueous dispersions of polyacrylates; it is proposed to modify them by introducing mineral raw materials as fillers and hydrated lime, with subsequent processing in a vortex layer apparatus. The introduction of activated diatomite does not cause the deterioration of covering power, adhesion or an increase in the porosity of the paint material. The modification of coatings contributes to an increase in their operational properties, which can be associated with a reduction in the free volume in the composite and the formation of polymer boundary layers with modified physical and chemical properties. The aim of this study is to obtain a water-dispersion paint and varnish composition containing modified diatomite on a polyacrylate basis and, subsequently, study its main physical and mechanical parameters. The work has been carried out by the following method: determination of porosity, adhesion, elasticity and covering power of the control composition; determination of porosity, adhesion, elasticity and covering power of the obtained composites using modified filler; investigation of the influence of radiation on the infrared spectrum of the paint coating surface using a FLIRB620 thermal imager. As a result of this research work, it was noticed that the modification of water dispersions with silica-activated diatomite helps to eliminate the main disadvantages of materials and coatings based on acrylate binders—low water resistance and low physical and mechanical characteristics. The introduction of modified diatomite into water-emulsion paint on an acrylate base does not lead to the deterioration of the main performance characteristics of paint coatings—porosity, adhesion, elasticity and covering.

Energy efficiency of hydrogen production during dark fermentation

It is widely known that most of the world's energy is produced from non-renewable energy sources such as crude oil and coal. Hydrogen is an ideal fuel candidate with a high energy content and clean combustion product. Biohydrogen is an environmentally friendly, renewable biofuel with high energy density, making it a viable alternative to fossil fuels in the future. At the same time, despite the large number of articles on the intensification of both dark fermentation and anaerobic bioconversion in general, the operating costs of the proposed intensification methods are not well covered in the literature. The goal of the work was to estimate the conversion coefficient of thermal and electrical energy spent on the functioning of the process of dark fermentation of various organic wastes into the energy of produced hydrogen. A block diagram of the energy flows of the dark fermentation system and the structure of the energy consumption of the system were developed. The obtained literature and experimental data suggest that the conversion coefficient of energy into biohydrogen in the process of dark fermentation is less than 1, so to obtain 1 kWh of hydrogen it is necessary to expend more than 1 kWh of energy. At the same time, the use of a vortex layer apparatus for dark fermentation of the food waste model made it possible to increase the energy output of the process by more than 7 times, thereby bringing the values of the conversion coefficients of thermal and electrical energy closer to 1. Despite the fact that the energy efficiency of most known methods for producing hydrogen is higher than the energy efficiency of dark fermentation, it is worth noting that the raw material for producing hydrogen in the dark fermentation process is organic waste, and not high-energy fuel (natural gas, methane, coal) or water in the case of electrolysis. In addition, the use of a vortex layer apparatus for pre-treatment of the dark fermentation substrate made it possible to achieve electricity conversion coefficient values 40% higher than with water electrolysis.

Applications of partial differential equations to transient heat and mass transfer in MHD flow over a porous medium

The flow problem discussed in this research is an investigation of compressible viscous fluid in an unstable 2D MHD laminar driven vortex and stable boundary layer flow, passing a heated stretched sheet at varying speeds via a porous medium exposed to a magnetic field with viscous dissipation, thermal diffusion, thermal radiation, chemical reaction and Dufour effects. With the aid of similarity transformations, PDEs that come out in governing equations of this formulations are converted into non-linear sets of ODEs. Well-defined bvp4c technique used to numerically solve these converted equations. With use of various graphs, the consequences of different factors on the distributions of velocity, temperature and concentration were examined numerically and graphically. Physical parameters for this issue are also discussed.

Large-amplitude steady gravity water waves with general vorticity and critical layers

Large-amplitude steady gravity water waves with general vorticity and critical layers

Direct numerical simulation of 45° oblique flow past surface-mounted square cylinder

Comprehensive coherent structures around a surface-mounted low aspect ratio square cylinder in uniform flow with an oblique angle of $45^{\circ }$ were investigated for cylinder-width-based Reynolds numbers of 3000 and 10 000 by direct numerical simulation based on a topology-confined mesh refinement framework. High-resolution simulations and the critical-point concept were scrutinized to reveal for the first time the reasonable and compatible topologies of flow separation and complete near-wall structures, due to their extensive impact on various engineering applications. Large-scale horseshoe vortices are observed at two notable foci in the viscous sublayer. Within this layer, a wall-parallel jet is formed by downflow intruding into the bottom surface at the half-saddle point, then deflecting in the upstream direction and finally penetrating the bottom surface until the half-saddle point. A pair of conical vortices on the cylinder's top surface switch themselves on two sides of the square cylinder, where the switching frequency is identical with that of the sway of the side shear layer. The undulation of the Kelvin–Helmholtz instability is identified in the instantaneous development of a conical vortex and side shear layer, where the scaling of the ratio of the Kelvin–Helmholtz and von Kármán frequencies follows the power-law relation obtained by Lander et al. (J. Fluid Mech., vol. 849, 2018, pp. 1096–1119). Large-scale arch-shaped vortex is often detected in the intermediate wake region of a square cylinder, involving two interconnected portions, such as the leg portion separated from leeward surfaces and head portion rolled up from the top surface. The leg portion of the arch-shaped vortex was rooted by two foci near the bottom-surface plane.

Mechanisms of influence of confluence containing spur-dike on microplastic transport and fate

The issue of microplastic pollution is an urgent and undeniable global ecological concern. Due to the intricate three-dimensional (3D) hydrodynamic properties, the confluence is highly susceptible to microplastic contamination, particularly in the presence of spur dike disturbance. The present research goal is to elucidate the underlying mechanism governing the impact of the spur dike on transport and retention fate of microplastic at the confluence. A 3D hydrodynamic-microplastic transport model was developed at the confluence, and the Computational Fluid Dynamics (CFD) coupled with Discrete Element Method (DEM) method was employed to conduct the simulation. The concentration distribution, residence time, and trajectory of microplastics with different sizes and materials, as well as the effect of various angles of the spur dike on them were explored. The results indicate that (i) Large quantities of polyamide and polystyrene microplastics (less than 1 mm in diameter) with a residence time greater than 70 s are present in the flow stagnation zone, flow separation zone, the vicinity of spur dike, and downstream of the flow separation. (ii) The layout of the spur dike will lead to an increase in microplastic concentrations upstream of the spur dike and downstream of the flow separation. (iii) Vorticity and mixing layer thickness play crucial roles in the retention of microplastics within the flow separation and spur dike field. (iv) The dimensionless angles of the spur dike (αN) exhibit a linear and inverse relationship with the dimensionless standard deviations (σN) within the spur dike field. This study will expand our understanding of the transport and retention mechanisms of microplastics, and provide valuable insights for accurately identifying pollution hotspots of microplastic pollution at confluences with spur dikes.

Joule heating for structure reconstruction of hard carbon with superior sodium ion storage performance

Hard carbon anode for sodium ion batteries still remains many challenges including insufficient cycling life and initial Coulombic efficiency (ICE), weak rate capability and poor compatibility in common ester electrolytes. Here, we propose a Joule heating post-treatment including multifield sintering method to reconstruct the structure of hard carbon from thick graphene layers to more disordered vortex layer structure composed of thin and curved graphite-like domains. The molecular dynamics simulation and differential charge density distribution demonstrate the crucial effect of electric field in strengthening the interaction between the polar molecule groups and the graphene layer, leading to the distortion and expanding of graphene layer. This is a universal and highly efficient strategy to modify various hard carbons within minutes. The optimized hard carbon anode exhibits exceptional rate capability and cycling stability with a high retention rate of 88.4% after 15,000 cycles at 10C in ether electrolyte. It also displays remarkably improved reversible capacity, initial Coulombic efficiency ICE of 89.5% and cycling stability in ester electrolyte. It is revealed by in-situ electrochemical impedance spectroscopy and atomic force microscopy that the spontaneous formation of a thin, stable and inorganic substance-rich solid electrolyte interface layer with significantly improved mechanical property is largely responsible for the outstanding sodium-ion transport kinetics and long lifespan.

Analysis of interfacial effect and boundary layer for forced convection on the macroscopic hydrophilic-hydrophobic hybrid surface: A large eddy simulation

Hydrophilic-hydrophobic hybrid surfaces are developed to solve the flow and heat transfer performance contradiction. However, hybrid surfaces often have micro- or nano-scale featured sizes and are used in phase change heat transfer because hydrophilic regions contribute to droplet nucleation, and hydrophobic regions contribute to bubble nucleation. In this study, large eddy simulation is used to investigate the forced convection on macroscopic hydrophilic-hydrophobic hybrid surfaces where only the surface local wettability is changed. Three hybrid surfaces with different hydrophilic-hydrophobic ratios and two homogeneous wettability surfaces are designed, and representative flow Reynolds numbers of 4000, 6000, 10 000, and 40 000 are explored to achieve different turbulent styles. The transient parameters of kinematics, vorticity, and boundary layer are analyzed to clarify the mechanism of turbulence change and eddy generation and explain the causes of variations in flow and heat transfer performances. It proves that macroscopic hydrophilic-hydrophobic hybrid surfaces are suitable for forced convection due to the drag reduction on hydrophobic regions, backflows at hydrophilic-hydrophobic interfaces, and eddies at hydrophobic-hydrophilic interfaces, which can enhance the internal disturbance and harmonize the flow and heat transfer performances. The mechanism has a profound significance in broadening the application of hydrophilic-hydrophobic hybrid surfaces and designing the arrangement of hydrophobic regions.

Flow-induced vibration of the drilling pipe with internal flow under the combination of control rods and rotation

The effect of a combination of control rods and rotations on the fluid induced vibration (FIV) response of pipes with internal flow is numerically investigated. A numerical simulation method for a pipe with internal flow was established according to a strip theory. The results show that the control rod arrangement does not change the vortex shedding on the noninternal flow pipe. As the rotation rate α increases, the pipe vortex layer is deflected, increasing the influence of the control rod. The pipe vortex shedding stops at α = 0.75, and the dimensionless cross-flow amplitude reduction (RAy) reaches 0.95. For the pipe with an internal flow velocity of V = 1 m/s, the vortex shedding stops earlier. As the α increases from 0 to 0.5, the RAy of noninternal flow pipe increases from 0.07 to 0.85. The internal flow has an enhanced effect on FIV suppression. The control rod–rotation combination provides more stable FIV suppression of the pipe than the two-dimensional elastically mounted cylinders.

Development and Verification of an Improved Wake-Added Turbulence Model in FAST.Farm

We introduce a generalized wake-added turbulence (WAT) model in the multiphysics, multiturbine simulation tool FAST.Farm. The WAT model introduces additional small-scale turbulence that represents the breakdown of vortical structures and shear layers in the wake. The article describes the development, implementation, calibration, and verification of the model. The novelties of the model include support for wake asymmetry, buildup of WAT across the wind farm, and secondary effects of wake-induced turbulence (e.g., wake meandering) driven by smaller-scale turbulence structures that arise from wake breakdown. Large-eddy simulations were run to support the calibration of the WAT parameters and verification of the model. Previous studies hypothesized that the lack of WAT modeling was the source of underprediction of fatigue loads, in particular for cases at low turbulence intensities and/or stable atmospheric boundary layers. This study confirms that the newly implemented WAT model enhances the loads predictions in these cases.

Multiscale interaction analysis of Landfall Typhoon Lekima (2019) based on vorticity equation diagnosis

To investigate the multiscale interaction characteristics of Landfall Typhoon Lekima (2019), this study analyzed the characteristics of the different scale vortex structure and interactions among different scales based on vorticity equation diagnosis. The analysis is based on the simulation results of the WRF model which has been thoroughly verified. The main results are as follows: the original vorticity dominated by the meso-α scale vorticity increases with height and then decreases, with maximum vorticity distributed at 900 hPa. The meso-β scale vorticity varies significantly with altitude, while the meso-γ scale vorticity field exhibits obvious positive vorticity below 850 hPa. The meso-α scale vorticity tendency primarily maintains negative, contributing significantly to the overall reduction in the original vorticity field over time. The increase in mid-to-upper-level (above 550 hPa) original vorticity is mainly related to the variations in the meso-β and meso-γ scale vorticity fields. The original vorticity dominated by the meso-α scale vorticity increases with height and then decreases, and the whole layer vorticity decreases over time. The meso-β scale vorticity varies significantly with altitude and time, while the meso-γ scale vorticity field consistently exhibits significant positive vorticity below 850 hPa. The vorticity equation diagnosis revealed that the primary source terms of the vorticity tendencies are the twisting and stretching terms, and the main sink terms being horizontal and vertical vorticity transport terms below 900 hPa. The source terms and sink terms exchange above 850 hPa. Scale separation results show that the primary contributions of all impact factors originate from the meso-α and meso-γ scale fields (accounting for over 80% of the total), with the contribution of the meso-α scale being less than that of the meso-γ scale and a notable contribution over 35.5% of the interactions between different scales.

Evaluation of the influence of an aggressive environment on the durability of the cement stone

The paper proposes methods for assessing the durability of building materials and structures based on Portland cement when exposed to aggressive environments that mimic the products of the vital activity of bacteria on building materials. To determine the main parameters of the model of degradation of building materials under the action of aggressive environments, a mathematical model has been developed in the form of integral and differential relations connecting these parameters. A technique for identifying the mechanical characteristics included in these models based on the solution of inverse biodegradation problems has been developed. The analysis of changes in the structure of the cement stone was carried out using the results of computed tomography, and the regularities of the distribution of pores in the cement stone from the time of exposure were obtained. Based on experimental and numerical studies, it has been established that the mechanism of destruction of cement stone obtained by the traditional method and activation in the vortex layer apparatus is different. The difference lies in the greater accumulation of cement stone interaction products in the activated sample, which is confirmed by a shift in porosity to less than 0.5 mm and a lower solubility value compared to the control composition. The compressive strength of the samples as a result of exposure for 28 days decreased by 37% and 20% for the control and activated compositions. The mass of the studied samples as a result of exposure decreased by 49% and 21%, respectively. On the basis of this mechanism, a mathematical model of the process of material degradation in an aggressive one is developed, taking into account changes in porosity and acidity concentration, and dependence of material strength reduction are obtained.

Effect of Tip Gap Size on the Tip Flow Structure and Turbulence Generation in a Low Reynolds Number Compressor Cascade

Abstract Efficient and compact axial compressors are currently undergoing rapid development for use in microcooling systems and small-scale vehicles. Limited experimental work concentrates on the inner flow field of the compressors working at such low Reynolds numbers (Re∼104). This study examines the vortical structures and the resulting turbulence production in the transitional flow over a C4 compressor blade at a Reynolds number Re of 24,000, with a specific focus on the impact of tip clearance. The particle image velocimetry measurements reveal the tip flow structures in detail, including the tip leakage vortex (TLV) and its induced complex vortical structures. The tip secondary flow at the low Reynolds number can be divided as the tip leakage flow (TLF)/vortex and transitional boundary layer both at the end walls and the blade surfaces. The TLV propagates at the highest spanwise positions and farthest pitchwise positions at the middle tip gap size (τ/C = 3%) for the three tip gap sizes investigated. The tip flow fluctuations decrease from τ/C = 5% to τ/C = 3% and then increase from τ/C = 3% to τ/C = 1%. The spatial distribution, streamwise evolution, and individual Reynolds normal stress components contributing to the turbulent kinetic energy (TKE) are discussed. The primary contributors to the turbulence generation are examined to elucidate the flow mechanism leading to the distinct anisotropic turbulence structure in the tip region with various tip gap sizes.

Contour Dynamics and Global Regularity for Periodic Vortex Patches and Layers

Contour Dynamics and Global Regularity for Periodic Vortex Patches and Layers

The Contact Angles of Quartz and Caustic Dolomite Powders after Mechano-Magnetic Treatment

The determination of the surface free energy (SFE) is currently achieved using an instrumental method, one of which is «sessile drop». The surface free energy of quartz and caustic dolomite powders was defined before and after mechano-magnetic activation in the Vortex layer device. Free surface energy was identified by the well-known models proposed by the Owens–Wendt–Rabel–Kaelble (OWRK) and Van Oss–Chaudhury–Good (VOCG). The determination of the surface free energy (SFE) based on the presented model provides a good convergence: due to experimental assumptions, the deviation in calculation results is 14–16%. It was shown that mechano-magnetic treatment increased the adhesion of quartz powder by 86% (from 73 to 136 J/m2) and caustic dolomite by 217% (from 884 to 2800 J/m2). The mechano-magnetic treatment of study materials can significantly improve the interaction of the liquid with solid. This is evident from comparison of two attributes: the amount of change of specific interphase surface energy of a solid at the boundary with the gas per to change of specific surface of the powder and the change in the cosine of contact wetting angle per to a change in specific surface of the powder. This means the first value that represents the intensity of the interaction between liquids and solids multiplу greater than an integral characteristic of the interaction at the boundary of three phases. Such changes in geometric characteristics and surface properties are effective factors in structure formation control, especially hydration hardening.

Pretreatment of anaerobic fermentation feedstock in a vortex layer apparatus: Effect of the working chamber ferromagnetic core on biogas production

Currently, the volume of waste generation is growing at a high rate. Anaerobic digestion is an effective way to process organic waste to produce biogas. To increase the bioavailability and efficiency of mass transfer between feedstock particles and microorganisms, it is advisable to pretreat organic waste using various methods. One of the most promising and energy-efficient methods for preparing a feedstock for anaerobic bioconversion is its processing in a vortex layer apparatus (VLA). However, there are some limitations in the VLA operation. Therefore, to exclude the stagnant central zone from the volume of the VLA working chamber and increase the magnitude of the magnetic field in the VLA working chamber, a ferromagnetic core in the form of a steel pipe was coaxially mounted. Thus, the purpose of this work is to experimentally study the effect of the ferromagnetic core of the VLA working chamber on the production of biogas during anaerobic bioconversion of a model of organic waste from the agricultural sector. To achieve this goal, an experimental plant was developed and created. The experimental data obtained suggest the high efficiency of pretreatment of the feedstock in VLA with a ferromagnetic core in the working chamber before anaerobic bioconversion. The developed anaerobic bioconversion system made it possible to increase the methane production rate by 287 % at hydraulic retention time (HRT) of 4 days and by 3.5 times at HRT of 2 days compared to the control. At the same time, the methane yield at HRT of 4 days increased by 43 %, and at HRT of 2 days it decreased by 14 %. The hydrogen sulfide content in biogas also increased more than three times, while no hydrogen was detected in the biogas. Thus, pretreatment of the feedstock in VLA with a ferromagnetic core to produce biohythane in a one-stage anaerobic bioconversion system at 55.1 °C is impractical.

Magnetic field suppression characteristics in interaction process between shock wave and light gas cylinder

Based on ideal compressible magnetohydrodynamics (MHD) equations, the interface instabilities induced by the interaction between planar shock wave and the light gas (Helium) cylinder under the influence of the magnetic fields with different directions are investigated numerically by using the CTU(corner transport upwind)+CT (constrained transport) algorithm. The numerical results elucidate the evolution of flow field characteristics and wave structures with and without magnetic field. Moreover, we examine the influence of the magnetic field direction on a characteristic scales (including the length, height and width of the central axis of gas cylinder), as well as the volume compressibility. Then, the mechanism of the magnetic field direction affecting the interface instability is studied in depth by integrating the analyses of the circulation, energy, velocity and magnetic force distribution within the flow field. The core of this study, is to explore the suppression mechanism of interface instability by magnetic field force. The results show that the magnetic pressure plays a crucial role in driving vorticity away from the interface, thereby reducing its deposition on the density interface. Simultaneously, it adheres to the divided vortex layer, thereby effectively isolating the influence of Richtmyer-Meshkov instability on the interface. On the other hand, the magnetic tension adheres to the separated vortex layer, and its direction is opposite to that of the vorticity generated by the shear of interface velocity. This action effectively suppresses the Kelvin-Helmholtz instability and the rolling-up of vortices on the density interface. Additionally, under the control of a longitudinal magnetic field, the direction of magnetic tension is opposite to the direction of the central jet, effectively suppressing the development of Rayleigh-Taylor instability.

ПОВЫШЕНИЕ ЭНЕРГОЭФФЕКТИВНОСТИ СИСТЕМЫ ОБРАБОТКИ ПОБОЧНЫХ ПРОДУКТОВ ЖИВОТНОВОДСТВА, ОСНОВАННОЙ НА ИХ АНАЭРОБНОЙ БИОКОНВЕРСИИ

One of the anaerobic bioconversion process’s significant disadvantage at organic waste and animal by products’ treatment is the limiting stage, namely hydrolysis existing. A number of wellknown methods of livestock organic waste and by products before methane fermentation’s pretreatment are described. To eliminate this disadvantage and hydrolysis process accelerating, it was proposed to use an improved vortex layer apparatus with an integrated ferromagnetic core located coaxially in the apparatus vortex layer’s working chamber pretreatment system using. This system allows to accelerate not only hydrolysis, but also to introduce additionally iron particles into the substrate, which are a catalyst for methanogenesis using. In addition, the iron particles anaerobic oxidation products are nutrients for methanogenic microorganisms. At the same time, it is known that the vortex layer apparatus consumed energy significant part into waste heat, that can be disposed by a pump’s compression heat using is converted. An experimental installation was developed and created, and its operation’s description is given. The energy consumption’s investigated system structure for animal by products processing based on their anaerobic bioconversion was also determined. By the response surface methodology using, key factors’ influence was studied, namely, of the initial substrate’s pumping rate, the vortex layer apparatus cooling system for pumps’ circulation supply and electromagnetic field in the vortex layer apparatus’ coil frequency on the coolants’ temperatures in the heat pump’s compression evaporator and condenser and the initial substrate’s temperature’s changing and, as a result, the energy efficiency process preprocessing. By the central composite experiment’s design using, these factors’ optimal values with an electricity coefficient conversion into heat optimized value based on previously defined optimization’s criteria were found. The obtained experimental data allow to talk about in both the electricity conversion’s coefficient spent on the ABC operation and the energy system’s efficiency as a whole increasing.

Innovative organic waste pretreatment approach for efficient anaerobic bioconversion: Effect of recirculation ratio at pre-processing in vortex layer apparatus on biogas production

Agricultural waste, called biomass, is of great interest as a renewable energy source. The purpose of this work was to determine the optimal recirculation rate (RR) values of the solid digestate when applying a new approach to the intensification of anaerobic conversion, providing a high quality biogas yield. This approach includes solid digestate recirculation and pre-processing a mixture of raw waste and solid digestate in a vortex layer apparatus. For this, the operation of an experimental biogas plant without recirculation and with recirculation was considered, starting from very low RR values, from 0.034 to 1, to ensure a high methane production rate (MPR) and methane yield (MY). From the point of view of MPR and MY, the recirculation ratios of 0.034 and 0.071 look the most attractive, however, with a recirculation ratio of 0.5, the content of hydrogen sulfide de-creased to 14 ppm with a simultaneous increase in MPR by 12 % compared to the control.

Phase Composition of Hydration Products of Portland Cement Mechanically Activated in a Vortex Layer Apparatus with Additives of Various Nature

Phase Composition of Hydration Products of Portland Cement Mechanically Activated in a Vortex Layer Apparatus with Additives of Various Nature