Hydrodynamic Situation Research Articles

Механизм влияния электрического поля на процесс модифицирования серого чугуна

A diagram of an experimental installation for measuring the electrical resistance of a gray cast iron melt is presented, where a gauge based on a Kelvin double bridge is used. It is shown that the value of the specific electrical resistance of gray cast iron varies depending on the type of conditioning agent. Experimental data on the difference in specific resistivity values for various gray cast iron nucleating agents are presented. Changes in the values of electrical resistance under the influence of electric field treatment of inoculated cast iron melt are also given. Comparison of the strength values of gray cast iron with its values of the electrical resistivity of the cast iron melt after the electrical field exposure showed their simultaneous change. The decrease in the values of the electrical resistance of hot iron due to the electric field exposure is shown and it corresponds to an increment in the strength of inoculated cast iron. The effectiveness of the electric field exposure on the process of inoculation is determined by thermal ionization of the chemical elements included in the conditioning agent. The maximum increase of these parameters after electric field exposure when using FS75 nucleating agent is shown. The mechanism of the influence of an electric field on the cast iron solidification for the inoculation process of FS75, containing 75 % silicon in its composition, is described. The dependence of the efficiency of electric field exposure on the composition of the nucleating agent for gray cast iron is shown. A physical model of the effect of an electric field exposure on the process of cast iron inoculation is found. The possibility of influencing the hydrodynamic situation in the melt of gray cast iron and changing the rate of dissolution of nucleating agent particles by means of electric field exposure is given

Application of computational fluid dynamics for simulation of stirred bioreactors in Ansys Fluent

Stirred bioreactors are widely used in the pharmaceutical industry to produce various active substances for the treatment of cancer, heart and vascular diseases, viral and bacterial infections. Despite the widespread use of bioreactors with a stirrer, the optimization of mixing conditions remains an urgent task. In bioreactors of this type, continuous mixing of cells in a medium with a high rotation speed should be carried out. The manuscript considers an example of the use of computational fluid dynamics to study and model the process of cultivation Escherichia coli bacterial cells in a batch bioreactor (NLF, 30 l.). Computational fluid dynamics was used to analyze the hydrodynamic conditions in a bioreactor with a double Rushton turbine stirrer. To describe the movement of flows and evaluate turbulence in a batch bioreactor, the multiphase Euler model and the k-𝜀 turbulence model, respectively, were used, the built-in Ansys Fluent software package. A geometric model was built with the original dimensions of the bioreactor with an NLF 30 stirrer. Based on the geometric model, a computational grid was created for the working volume of the bioreactor and the optimal parameters for constructing the computational grid were selected. As a result of modeling the hydrodynamic regime, the distribution profiles of the turbulence kinetic energy over the volume of the bioreactor were obtained and the velocities of cell movement were found at different speeds of rotation of the stirrer. The obtained results show the possibility and applicability of the Ansys Fluent software package for calculating the hydrodynamic situation in a bioreactor with a stirrer at different stirring rates and at different cell volume fractions.

Magnetized flow of naturally convective viscous fluid in permeable rhombus-shaped annulus by executing FEM simulations

The present work is deliberated to investigate the flow and thermal behavior of viscous fluid flow in permeable rhombic-shaped enclosure. Annular region lying below inner and outer rhombuses is the area of concentration during this study. Magnetic field is employed in horizontal direction to envision aspects of Lorentz field. Governing equations are developed in dimensional form of partial differential setup. Numerical experiments via finite element approach are capitalized to find solution. Grid convergence test is executed to show domain distribution along with decision about mesh level at which computations are to conducted. Streamlines and isothermal maps are sketched to show comprehensive change in associated flow fields against governing parameters. Kinetic energy and average heat flux coefficient are evaluated in comparative manner for magnetic and hydrodynamic situations. Through attained outcomes, it is concluded that kinetic energy and heat flux coefficient enhances reduction against Hartmann number.

On the Influence of Hydrodynamic Conditions during Coking on the Structure of the Resulting Coke

The production of a highly anisotropic structure of needle coke depends not only on the quality of the raw material, but also on the hydrodynamic situation in the coke chamber formed as a result of shear stresses of the mesophase matrix by the flows of released steam-gas products of coking distillate and continuous supply of raw materials. The paper presents the resultsof studies on the quality of needle coke obtained during coking in static and dynamic conditions. It is shown that the microstructural organization of coke can differ quite a lot depending on the coking technology.

Study on the hydrodynamic characteristics of swirl flow device

The work examined the hydrodynamic situation, which is created by the interaction of reciprocal twisted flows and the distribution of axial velocity along the radius of the primary and secondary flow inputs and the radius of the exhaust pipe in order to create a complete physical picture. Determination of the radius distribution of the static pressure values determined by the height of the apparatus and the static pressure distribution in the exhaust pipe.

Mathematical description of the processes occurring during active grain ventilation

The subject of the study is the process of active ventilation of wheat grain with variable heat supply. The purpose of the work is a mathematical description of the nature of the flows of matter and energy in the process of active ventilation of wheat grain. Thanks to the selected original design of the exhaust coolant outlet unit, made in the form of a mesh spiral tube, it was possible to optimize the hydrodynamic situation in the layer of dried grain. The developed mathematical model, as a mathematical description, consists of equations of material, thermal balances, equations of hydrodynamics in steady and unsteady states. This mathematical model is the basis for creating a material model of the process and conducting an experiment with subsequent data processing. As a result, it is possible to obtain criteria equations of processes that make it relatively easy to calculate processes under various technological modes.

Preparation of aurum chloride complex and its use for industrial acetylene hydration catalyst process

The use of a modern homogeneous metal complex catalyst for the hydration of acetylenes is being investigated. The process is relevant both for the industry of basic organic synthesis and for the perfume industry. The analysis of existing processes used in industry for the production of acetaldehyde was carried out. Significant shortcomings of existing processes are revealed: low environmental friendliness and high energy consumption. To solve this problem, the reaction of hydration of an acetylene compound was studied using a modern homogeneous catalyst based on gold, which is not toxic. The study was conducted by selecting aliquots during the reaction. Using the 1H NMR spectroscopy method, the conversion values of phenylacetylene were calculated for the time values corresponding to the moments of aliquot sampling. The reaction order with respect to phenylacetylene was calculated and the reaction constant under the reaction conditions was calculated. When reacting in the presence of the proposed catalyst, a conversion of phenylacetylene of 86.96 % is achieved in 3 hours. The data obtained provide grounds for carrying out the process of catalytic hydration of acetylenes, namely phenylacetylene, with the production of acetophenone, which is important for use in the perfume industry. The data obtained can be applied to the process of hydration of acetylene with the formation of acetaldehyde, which is widely used in the industry of basic organic synthesis. For the process of catalytic hydration of acetylene compounds, a hardware design is proposed, a gas-liquid reactor with a changing hydrodynamic situation, which, together with the product separation column, is combined into a single installation. Using an optimized method, a catalyst based on gold chloride was synthesized from a gold alloy.

Genetic diversity of inlet systems along non-tidal coasts: examples from the Black Sea and Sea of Azov (Ukraine)

In the coastal zone of the oceans, coastal barriers are quite widespread. Within their limits, inlets periodically arise and exist for a certain time, which is of great geological, hydrological, ecological, and navigational significance. Along the coasts where tidal fluctuations predominate, tidal inlets stand out, which are quite well studied in terms of genesis, morpho-, hydro- and litho-dynamics. Inland, semi-isolated marine basins, where tidal fluctuations do not reach a significant amplitude, are called non-tidal seas. Within the coastal barriers of non-tidal seas, channels periodically arise and develop, which are called breaches or prorvas. Breaches are quite often mentioned in the specialized literature along the coasts of non-tidal seas, but they have not been purposefully studied. In this article, we tried to analyze the conditions for the formation of prorvas within non-tidal seas based on many years of research. We have identified four hydrodynamic situations in which breaches are formed. The presented variety of situations allows us to identify and describe four genetic types of prorvas: storm-generated, storm-surge-generated, wind-stress-generated, and river-stress (fluvially induced). The presented article is the first attempt to analyze the genetic characteristics of the breaches.

Effect of fluid hydrodynamic situations on enzymatic hydrolysis of mixed microalgae: Experimental study and simulation

The enzymatic hydrolysis of microalgae has already been studied for bioethanol production. However, the enzymatic hydrolysis of microalgae under various fluid hydrodynamic conditions has not been simulated yet. Accordingly, the present study investigated the effect of various stirrer speed values, impeller types, and the presence of baffles on glucose extraction from the mixed microalgae using cellulase. The Michaelis-Menten kinetic constants of enzymatic hydrolysis were calculated in the AQUASIM and were used for simulation in COMSOL. The simulated values agreed with the experimental results and revealed that the low stirring speed reduced glucose extraction through undesirable enzyme distribution and the formation of regions with a high concentration of hydrolysis products to inhibit the enzyme's operation. The higher uniformity of glucose concentration at higher stirring speeds compared to lower stirring speeds ensured the higher efficiency of the mixing process in this reactor. The study findings suggested that a sufficient understanding of the mixing effects in the enzymatic hydrolysis could improve the economic feasibility of the process. Furthermore, compared to the unbaffled reactor, the proper mixing in the baffled reactor increased the enzymatic hydrolysis rate. It was found that altering the impeller type leads to a negligible change in the enzymatic hydrolysis rate.

Sensitivity of phytoplankton to climatic factors in a large shallow lake revealed by column-integrated algal biomass from long-term satellite observations

There are some uncertainties of using chlorophyll a (Chla) concentrations in water surface to address phytoplankton dynamics, especially in large shallow lakes, because of the dramatic vertical migration of phytoplankton. The column-integrated algal biomass (CAB) can reflect the whole water column information, so it is considered as a better indicator for phytoplankton total biomass. An algal biomass index (ABI) and an empirical algorithm were proposed previously to measure algal biomass inside and outside euphotic zone from the Moderate Resolution Imaging Spectrometer (MODIS) data. A long-term CAB time series was generated in this study to clarify the temporal and spatial changes in phytoplankton and address its sensitivity to climatic factors in Lake Chaohu, a shallow eutrophic lake in China, from 2000 to 2018. Overall, the CAB for Lake Chaohu showed significant temporal and spatial dynamics. Temporally, the annual average CAB (total CBA within the whole lake) was increased at rate of 0.569 t Chla/y, ranging from 62.06±8.89 t Chla to 76.03±10.01 t Chla during the 19-year period. Seasonal and periodic variations in total CAB presented a bimodal annual cycle every year, the total CAB was highest in summer, followed by that in autumn, and it was the lowest in winter. The pixel-based CAB (total CAB of a unit water column), ranging from 112.42 to 166.85 mg Chla, was the highest in the western segment, especially its northern part, and was the lowest in the central parts of eastern and central segments. The sensitivity of CAB dynamics to climatic conditions was found to vary by region and time scale. Specifically, the change of pixel-based algal biomass was more sensitive to the temperature change on the monthly and annual scales, while wind speed impacted directly on the short-term spatial-temporal redistribution of algal biomass. High temperature and low wind speed could prompt the growth of total CAB for the whole lake, and the hydrodynamic situations affected by wind and so on determined the spatial details. It also indicated that Lake Chaohu may face more severe challenges with the future climatic warming. This study may serve as a reference to support algal bloom forecasting and early warning management for other large eutrophic lakes with similar problems.

Hydrodynamics of a reactor with updated structure of frame mixing device

This article is devoted to computer simulation of the hydrodynamic situation in a reactor with a standard design and an upgraded design of a frame stirrer. A comparative analysis of the hydrodynamics of fluid flows occurring in the volume due to the use of classical and modernized design was performed. An upgraded design of a frame stirrer for homogenizing the medium in a reactor has been proposed.
 The aim of this work was to study the influence of the geometry of the stirrer blades and their location in space on the speed and direction of flows in the reactor.
 The basis for the new design of the mixing device was the standard design of the frame mixer with two horizontal jumpers. Installation of additional blades and their placement at a certain angle to the vertical and horizontal planes and relative to each other was considered as one of the methods of improving the design.
 For this work, the study was conducted in the universal software system of finite element analysis ANSYS. Computer simulation is used to analyze complex systems and processes based on a computer model.
 The simulation was performed to analyze the influence of the geometry of the mixing device on the speed and direction of fluid flow in the apparatus. To conduct the study, 3D-models of two different types of geometry of the mixing device were built, physicomechanical parameters of the environment in the reactor were set and on the basis of these data the mixing process in the apparatus was modeled. In this work, the influence of plate geometry and their location in space on hydrodynamics is investigated. The basis of the proposed design of the mixing device is the task of intensifying the mixing process by increasing the mixing efficiency along the height of the apparatus.
 A comparative analysis of the direction of fluid flow, its velocity and temperature change using a standard and upgraded design of the mixing device was performed.
 It was found that when installing additional plates that are located at an angle to the horizontal and vertical planes in the reactor there are additional axial and radial fluid flows, which improves homogeneity and increases the intensity of mixing.

Study of the hydrodynamic structures of opposite flows of phases during the final distillation of miscella of vegetable oil

Oil production technology includes a large number of processes in its cycle, such as extraction, pressing, extraction, evaporation of miscella is one of the most complex and energy-intensive processes. Intensification and optimization of these processes, increasing the efficiency of distillation units is a very urgent task. The study of heat and mass transfer in gas-liquid streams, taking into account the hydrodynamic situation in distillation units, makes it possible to objectively assess the advantages and disadvantages of devices, contributes to more targeted developments in the field of rational design of technological units. An increase in the productivity and optimization of the distillation processes of oil miscalls can be achieved by organizing a rational structure of phase flows, which ensures the maximum gradients of temperatures, concentrations and intensification of heat and mass transfer.

Climate change impact assessment under data scarcity by hydrological and hydrodynamic modeling in Izmit Bay/Turkey

To assess climate change impact on the hydrology of Izmit Bay, a coupled model chain using the results of four combinations of Global Climate Models (GCMs) and Regional Climate Models (RCMs) and consisting two hydrological models (mGROWA and PROMET) and one hydrodynamic model (MIKE 3HD) was established. Climate model data of the 4 GCM-RCM combinations were applied to both hydrological models. The resulting 8 streamflow data of the hydrological models were then applied to the MIKE 3HD to assess possible hydrodynamic situations in Izmit Bay. Related model results indicate a range of possible future streamflow regimes suitable for the analysis of climate change impact on Izmit Bay. In order to evaluate the effects of the hydrological changes only on the bay, the bay was considered as closed in terms of hydrodynamics. There is a clear indication that the climate change induced impacts on streamflow may influence the sea level in the Bay to a minor extent. However, climate change induced water exchange processes in the Bay may have a much bigger influence. Hence, it is suggested that further simulations should be run once the hydrologic regime of the Marmara Sea has been assessed in a broader macro-scale study.

Mathematical modeling of the droplet formation process in a microfluidic device

The results of droplet formation modeling in a microfluidic device based on the force balance method are described in the paper. The Navier-Stokes and continuity equations in an axisymmetric formulation were used to describe the hydrodynamic situation in a liquid film between a growing droplet and a channel wall. Shear stresses, pressure gradient along the droplet, as well as interfacial tension forces were included in the force balance. The obtained results allow to analyze the influence of phase flow rates and the properties of both phases on the flow regimes boundaries. It is shown that the continuous phase flow rate significantly determines the hydrodynamic situation both in the formed droplet of the dispersed phase and in the continuous phase film. On the other hand, the effect of the dispersed phase viscosity on the position of the flow regimes boundaries is much stronger than the viscosity of the continuous phase.

Studying the hydrodynamic conditions of fluids in reservoir conditions and assessing their influence on the accumulation and placement of hydrocarbon deposits

The article discusses the study of the behavior of reservoir fluids and the influence of the hydrodynamic situation on the accumulation and conservation of hydrocarbon deposits in the explored structures of the Beshkent trough. The main attention is paid to studying the value of the potential energy of fluids by mapping them at different points in the reservoir to determine the path of formation water and the possible hydrocarbon deposits associated with them. The places of their most probable accumulation are forecasted and recommendations are given for the implementation and adoption of optimal decisions on the targeted conduct of prospecting and exploration.

Перспективи нафтогазоносності нижньосарматських відкладів північно-західної частини Зовнішньої зони Передкарпатського прогину (за гідрогеохімічними та гідродинамічними ознаками)

The hydrogeochemical parameters of the Lower Sarmatian aquifer of the north-western part of the Outer Zone of the Carpathian Foredeep have been studied. The waters of the chloride-calcium type (according to the classification of V. O. Sulin) are dominated. Other types of water are distributed locally. On the basis of the calculated genetic coefficients, the conclusion on sedimentogenic conditions of their forming during a geological history of the region is made. It is established that the general tendency for the deposits of the Outer Zone is increasing of TDS of water with depth and stratigraphy. The waters of the north-western part of the Outer Zone are characterized by reduced values of sulfate content and sulfation coefficient rSO42– • 100/rCl–, indicating the conditions of hydrogeological closed structures. The genetic index of formation water metamorphism (rNa+/rCl–) is mainly inversely dependent on TDS. Its values greater than one are inherent in waters of hydrocarbonate-sodium and sulfate-sodium types, which are not typical for the hydrocarbon deposits. The nature of fluctuations in the values of the chlorine-bromine coefficient is fully consistent with other hydrochemical parameters and the results of paleohydrodynamic reconstructions. A detailed analysis of the current hydrodynamic situation of Lower Sarmatian aquifer in combination with geochemical features and paleohydrodynamic reconstructions allowed to identify the perspective structures of the studying region. Our forecasts for the gas potential of the Krukenychy depression are consistent with the forecasts of researchers of Ivano-Frankivsk National Technical University of Oil and Gas. The results of their research are based on gravitational field anomalies.

Разработка системно-поэлементной методологии исследования и экологической модернизации технологического оборудования

For solving problems of analysis, calculation, optimal design and control of technological processes, a powerful system-logical and formal-mathematical apparatus is the system-element methodology. This methodology has been developed to describe the processes of coagulation and sedimentation in multiphase turbulent flows. From the standpoint of systems analysis, it includes three stages: qualitative analysis of the structure of the physicochemical system (PCS); synthesis of the structure of the functional diagram of physical and chemical effects; identification and evaluation of system parameters based on experimental data. Considering the totality of physicochemical effects and phenomena, six types were identified - from phenomena at the molecular level to the totality of processes that determine the hydrodynamic situation in the apparatus as a whole. Approximately to the general case, in the future, a system-element methodology was proposed, designed to create an ecologically perfect unit and including 10 stages, starting with the formulation of the problem and the choice of initial data and ending with the design task. We have proposed a more advanced system-element methodology for research and environmental modernization of technological equipment, the stages of which do not describe the specifics of a particular process, but at the same time reflect the integrity and logical sequence of the research.

Effect of Hydrodynamic Conditions in an Impinging-Jet Microreactor on the Formation of Nanoparticles Based on Complex Oxides

The effect of the hydrodynamic situation (mainly conditions of mixing of the solutions of the reagents) on the composition and sizes of the nanoparticles being formed in an impinging-jet microreactor (IJMR) upon the impinging of the jets of the reagents—aqueous solutions of lanthanum nitrate and ammonium dihydrogen phosphate—is studied. Unique conditions are generated in the IJMR providing a short-term contact of the jets of the solutions that move at a high velocity (of about 10–20 m/s). The characteristics of turbulence in the IJMR are calculated. It is shown that the rate of dissipation of turbulent kinetic energy in the zone of impinging of the jets may reach 107–109 W/kg, which is comparable to the level of dissipation of energy in ultrasonic baths and is several orders of magnitude higher when compared to almost any other type of reactor. The effect of the region that has a size of the minimum Kolmogorov turbulence scale, i.e., a self-organizing “nanoreactor,” on the size of the particles being formed upon the deposition of particles with a complex composition is determined. Comparing the results of the calculation with the experimental data shows that, in some cases, the volume of the nanoreactor, taking into account the concentration of the solutions, determines the weight and size of the particles being formed. An explanation for the effect of a different influence of the velocity of impingement of the jets on the size of the nanoparticles being formed during the microreactor mixing of the reagents, depending on the characteristic features of the mechanisms of chemical reactions under the conditions of “soft” chemistry, is provided.

Multifractality in the general cosmological solution of Einstein’s equations

We demonstrate the scale invariance of the vacuum Bianchi type IX equations and use this to argue for the possibility of multifractal turbulence as a realisation of the suggestion by Belinski that there will be a fragmentation of local regions of inhomogeneous Mixmaster chaos on approach to an initial inhomogeneous cosmological singularity. Differences between the gravitational and hydrodynamical situations are outlined. Various potential obstacles to this picture of gravitational turbulence are discussed.

Gas-hydrodynamic characteristics of aerotanks

The purpose of the research was to determine the hydrodynamic indicators of aerotanks determining the depth and effectiveness of wastewater treatment. The study of technological parameters of the aeration tank was carried out on a physical model representing a transverse vertical section of the aerotank. The hydrodynamic similarity in the model and industrial aerotank determined by the identical values of the Reynolds, Froude, and Euler criteria. The study of similar indicators on an industrial aeration tank is very difficult and costly. The model and experimental setup make it possible to vary in a wide range the intensity of air aeration, the design and location of the aerator, control the speed of hydrodynamic flows and the concentration of freely floating sludge in the facility with aeration. To study the gas-hydrodynamic indicators in the aerotank model, original methods based on the laws of physical chemistry have been developed and used. The contact surface of the phases “liquid - gas” from the intensity of air aeration was determined using a chemical method for aerated biological wastewater treatment facilities. The dependences of the specific contact surface of the phases “liquid - gas”, referred to the unit of the working area of the aerator, on the intensity of aeration and the depth of immersion of the aerator are obtained. The oxidizing ability of a fine bubble aerator was determined for various aeration intensities. The dependences of the oxidizing ability on the contact surface of the phases ‘liquid - gas” in aerotanks were obtained for the first time. It is shown that the oxidation ability of the aerotank is determined by the phase contact surface and, to a large extent, by the hydrodynamic situation in the aerotank, which forms the fields of freely floating activated sludge.