Coaxial Cylinders Research Articles

Scattering of water waves by a wave energy device consisting of a pair of co-axial cylinders in a uniform water having finite channel width

We consider a device which consists of a floating structure over a cylindrical plate placed at a finite height from the impermeable ocean floor. This paper developes the interaction of linear water waves with such a device. The whole fluid domain is divided into a number of sub-domains and boundary value problems are formulated for each identified sub-domain. The channel multipoles, separation of variables and matched eigenfunction expansion methods allow us to solve boundary value problems for the diffracted velocity potentials in each sub-domain. We investigate the wave forces exerted on the proposed device. Consequently, the effects of the various parameters, e.g., drafts, radii, the gap between the cylinders and mainly channel width of the device on the wave forces exerted by the cylinders are presented graphically. We observe a small oscillation nature near the peak value of the exciting force for the particular value of channel width w=2.4m. The peak value of the exciting forces occurs near the wavenumber kr1=1.0 for different width of the channel walls. The obtained results are compared with some available results, and it shows a good agreement between the obtained and available results.

Modeling of soil dumping based on a modified Upwind Leapfrog difference scheme

The difference scheme is developed for the diffusion-convection problem numerical solution at large grid Peclet numbers. The scheme based on linear combination of the Upwind and Standard Leapfrog difference schemes (LCUSLDS) with weight coefficients obtained by minimizing the approximation error at small Courant numbers. The proposed approach takes into account the function of cell fullness, which allows to increase the accuracy of modeling on the area with complex geometry. The proposed modification of the Upwind Leapfrog difference scheme for the diffusion-convection problem numerical solution has better accuracy compared to other schemes considered in the article for grid values of Peclet numbers in the range 2 ≤ Pe ≤ 20. The problem of substances transport between two coaxial cylinders for large and small values of grid Peclet numbers is considered to test the proposed difference scheme. This movement of the water medium in hydrodynamics is called the Couette-Taylor flow. The steady fluid flow between two infinitely long coaxial circular cylinders is considered.

Effects of Halide Anions on Water Desalination based on Crystallization Methods: Freezing and Tetrahydrofuran Hydrate formation

In this study, the water desalination was performed using the freezing method and Tetrahydrofuran hydrate formation in a stationary reactor. The experimental setup includes two coaxial cylinders, which ice crystals deposit outside the cool inner cylinder; thus the salt concentration increases in the residual brine. In order to evaluate the performance of these methods, the removal percentage of salt was measured by the electrical conductivity instrument. The results show that the removal efficiency decreases with an increasing salt concentration in the freezing method while the different trend is observed in the hydrate formation method. As an important result, the salt removal efficiency of the hydrate formation method was higher than the freezing process. Also, to investigate the effect of the anionic size on the salt removal efficiency, the experiments were performed with NaCl, NaBr, NaF, and NaI, which have the same cations. The results show that the performance of desalination improves by increasing anionic radius. So the dissolved mineral components are removed in the following order. The removal of salts with a higher size is further by the hydrate-based and freezing desalination.

Effect of sedimentation on the rheological properties of cement pastes

Rheology has been widely used to describe the flow properties of fresh cement-based suspensions. Nevertheless, the characterization and understanding of the rheological behavior of cement-based materials have become essential with the recent introduction of novel applications like digital construction in the field of civil engineering, among others. It has been well documented that concrete and mortar may suffer stability problems (i.e. the ability of the mixture to maintain homogeneous). At the scale of cement paste, this phenomenon can still arise and affect the rheological properties of the measured paste. Therefore, inaccuracies during the measurements and incorrect interpretation may occur, resulting in erroneous conclusions. This study explores the impact of sedimentation of cement particles when characterizing the rheological properties of cement paste. The w/c employed in the pastes were 0.45 and 0.35 with the addition of superplasticizer to obtain a dispersed system. The rheological properties were measured using a coaxial cylinder configuration and followed up to 180 min after the contact between cement and water. Repeated measurements were executed with and without a homogenization procedure after each application of a measuring procedure. Comparing the results shows a clear influence of sedimentation on the evolution of rheological properties with time, and the effect is more pronounced for the mixtures with high w/c and for the procedure with the larger shear rate. Therefore, it is strongly recommended to keep a measuring procedure sufficiently short in duration.

Hydrodynamic force and wave run-up due to diffraction of ocean water waves by a surface-piercing bottom-mounted compound partial-porous cylinder

Here we consider the case of a train of linear water waves incident on a bottom-mounted surface-piercing compound partial-porous cylinder consisting of two coaxial cylinders of which the upper cylinder is hollow with a thin porous side wall and the lower cylinder, with radius greater than that of the upper one, is rigid. Subsequently, we examine the associated hydrodynamic forces. Using linear water wave theory and eigenfunction expansion, the problem is developed in terms of suitable velocity potentials. The important boundary condition on the porous boundary is defined with the aid of Darcy’s law. The matching conditions across the linear interface between successive fluid domains arising due the continuity of pressure and velocity are suitably used. Thereafter, a system of linear equations arises in terms of the unknowns solving which the hydrodynamic force and wave run-up for the compound partial-porous cylinder are calculated. Various numerical experiments show the effect of different parameters, such as porosity of the upper cylinder, draft ratio, the ratio of radii of the upper and lower cylinders and the depth of water on hydrodynamic force and wave run-up. It is observed that the wave force takes higher values corresponding to lower values of radius ratio, draft and porous coefficients. Further, for fixed values of radii, porosity and depth, the wave run-up is observed to be more when the wavenumber takes increasing values. The obtained results establish that different parameters may be suitably chosen in order to design useful ocean structures which may be installed as wave-absorbers for various activities in ocean including capturing of wave energy. Further, such structures can also act as the base of windmills installed in oceans to extract wind energy. The efficiency of the model developed is validated by comparing it with an available established result from which an excellent agreement is observed.

Investigation of the tangential discontinuities formation in the glycerol under shear load

The work is devoted to the study of the formation of tangential discontinuities of glycerol parameters under shear load. The studies were carried out using a modified coaxial cylinder viscometer. The experiment was inspired by the work of Ya. I. Frenkel, in which it was noted that “… liquids, being condensed media, should exhibit effects that are more characteristic of solids than gases …”, while the thermodynamic and kinetic properties should be determined by structural “variables”, traditional for both “liquid” and solid state. These studies will further help in explaining the anomalous momentum transfer regimes caused by the mechanisms of instability that are realized under the conditions of the “decay” of multiple metastable states, usually observed under intense (dynamic and shock-wave) loading in liquids and solids.

Air Supply Mode Effects on Ozone Production of Surface Dielectric Barrier Discharge in a Cylindrical Configuration

We investigated the air supply mode effects on ozone production of the surface dielectric barrier discharge in the cylindrical configuration. The air into the discharge volume between two coaxial cylinders was supplied through four nozzles axially or tangentially. Using tangential air supply, the vortex flow in the part of the discharge chamber was created. Because the active electrode was in the form of interconnected rings on the outer surface of the glass tube, we changed the airflow orientation concerning this electrode. The existence of vortex airflow affects the plasmachemical processes taking part in the discharge, and therefore, it affects discharge ozone production. We also paid attention to ozone concentration and temperature of output air measurements as a function of the duration of the experiment for both tangential and axial air supply modes. We found that the time required for the stabilization of generated ozone concentration depends on the discharge power, and for our experimental conditions, it smaller than approximately 70 s. Besides, in the case of tangential air supply into the discharge chamber, the concentration of ozone produced by the discharge is for higher discharge power increased in comparison with the concentration for the axial air supply mode.

The flow behavior of raw Jojoba oil in comparison with some traditional lube oils

To evaluate the possibility of utilizing the raw Jojoba oils for lubricating purposes in internal combustion engines, the flow behavior of raw Jojoba oil was investigated experimentally. Three customary lube oils of Diesel-, Petrol-, and Motorcycle-engines were employed in comparison with the raw Jojoba oil. Rheometer type of Fann Model of 50SL with coaxial cylinders device was used for this investigation. This investigation reveals that the shear stress of the raw Jojoba oil increases gradually with shear rate in the range of 10–500 s−1 in a linear relationship. At constant shear rate, the shear stresses of the raw Jojoba oil decrease steadily with temperature range of 30−90 C°. The well-known Herschel-Bulkley model can be used to describe sufficiently the flow behavior of the raw Jojoba oil measurement data. The raw Jojoba oil shows flow behavior index equals almost one with slight apparent yield stress. The apparent flow viscosity of the raw Jojoba oil can be analyzed by Arrhenius relationship to show the effect of the applied temperature. At higher operating temperature of 90 °C the raw Jojoba oil exhibits better performance and show higher viscosity values than all the examined lube oils within the range of 10–100 s−1 with viscosity index of 233 which is much higher than the commercial examined oils (range 130–140).

Effect of bio-based flow improver on the microscopic and low-temperature flow properties of waxy crude oil

Wax formation creates flow assurance problems in the production and transportation of waxy crude oil. Flow improvers are added to waxy crude in order to reduce handling cost. Bio-based flow improvers derived from cheap renewable resources are attractive as cost-effective, eco-friendly alternatives to the conventional additives. Natural cashew nut shell liquid extracted from waste biomass (Anacardium occidentale shells) was derivatized and applied as flow improver for waxy crude oil. Effect of the additive on wax formation in crude oil was studied by cross-polarized microscopy, while the change in oil flow properties was evaluated using a rotational coaxial cylinder viscometer. Micrographs of the waxy crude were processed and analyzed with image J software. The microscopic properties of the wax crystals were characterized using Feret diameter, crystal area, aspect ratio, circularity, solidity and boundary fractal dimension. The pour point of doped crude oil was depressed by − 18 °C and the wax area fraction reduced by 40% due to wax inhibitive effect of the additive. The presence of the additive resulted in evolution of smaller, rounder and more regular wax crystals with smoother and more even surfaces indicated by reduction in the Feret diameter, aspect ratio and boundary fractal dimension of wax crystals in doped oil, and an increase in crystal circularity and solidity. The shear stress and viscosity of doped oil were reduced by 86.8% and 85.0%, respectively. The flow improvement effect of the CNSL derivative is linked to its effect on morphology and microstructure of wax crystals in the crude oil.

Investigation of thermal conductivity of orange and tangerine juices in non-stationary state

Thermal conductivity is one of the main thermophysical properties of liquid food products, including fruit and vegetable juices. Known experimental installations measure the thermal conductivity of stationary liquids. This results in significant deviations from the actual numbers. A method of determining the thermal conductivity of a fluid in motion and an experimental installation implementing the proposed method are suggested. The developed experimental installation consists of two coaxial cylinders: internal and external. A gap between cylinders is filled with analysed liquid. The object of the study was the juices of subtropical fruits, such as oranges, tangerines grown in the subtropical regions of the Republic of Azerbaijan. In this work, the thermal conductivity of juices was also investigated during forced movement on an installation also consisting of two coaxial cylinders. Experimental measurements of thermal conductivity for orange and mandarin juices were carried out. Experiments were carried out at frequencies from 50, 100, 150 and 200 s-. A general description of the dependence of thermal conductivity on temperature, dry matter concentration and rotational speed made it possible to develop a model, in particular for orange juice. The described method and experimental installation for measuring the thermal conductivity of a liquid in a non-stationary state made it possible to develop a mathematical model describing the dependence of thermal conductivity on temperature, dry matter content and cylinder speed.

Micropolar fluid between two coaxial cylinders (numerical approach)

The paper describes the flow of a suspension which is a mixture of two phases: liquid and solid granules. The continuum model with microstructure is introduced, which involves two independent kinematic quantities: the velocity vector and the micro-rotation vector. The physical analogy is based on the movement of the suspension between two coaxial cylinders. The inner cylinder is stationary and the outer one rotates with constant angular velocity. This physical analogy enabled a mathematical model in a form of two coupled differential equations with variable coefficients. The aim of the paper is to present the numerical aspect of the solution for this complex mathematical model. It is assumed that the solid granules are identically oriented and that under the influence of the fluid they move translationally or rotate around the symmetry axis but the direction of their symmetry axes does not change. The solution was obtained by the ordinary finite difference method, and then the corresponding sets of points (nodes) were routed by interpolation graphics.

Forced Convection inside a Vertical Circular Cylinder with an Inner Coaxial Rectangular Cylinder

In this work, we performed a numerical simulation of laminar forced convection and, in an annular space inside a vertical circular cylinder with an inner coaxial rectangular cylinder having an aspect ratio (height/radius) γ=2, filled with a liquid metal (Pr = 0.0023). Six annular gaps R =0.9, 0.8, 0.7, 0.6, 0.5 and 0.4 were studied. The governing equations are solved using the ANSYS Fluent code which is based on the finite volume method. SIMPLE algorithm is employed for the pressure-velocity coupled momentum equations. Two cases of the rotating parts of the cylinders are investigated and the effect of Reynolds number on the flow are examined. The obtained results of the forced convection show that the increase of the Reynolds number Re affects straightly on the structure of the flow wherever the velocity field are destabilized and the strongest stabilization of the velocity field occurs when the flow generated by the rotating of the circular cylinder and the rectangular cylinder.Keywords: forced convection, annular gap, circular cylinder, rectangular cylinder, co-rotating.

Energy Consumption of Self‐Compacting Concrete during Mixing and Its Impact on the Yield Stress Measured in the Ready‐Mix Concrete Plant

To find the energy required during the mixing process of self‐compacting concrete in a ready‐mixed concrete plant and correlate the results with the yield stress of concrete. Power consumption required during the mixing of concrete is measured with a wattmeter connected to the mixing unit’s power supply. A coaxial cylinder viscometer is used to measure the yield stress of concrete. The clamp meter measures the power when the impeller rotates inside the coaxial cylinder viscometer, which is filled with concrete. When the impeller rotates in a coaxial cylinder filled with concrete, the power is measured by a clamp meter. Torque is obtained through the power relationship, which is an essential factor in determining the yield stress. The cost of a rheometer is so high that all construction industries, research institutions, and researchers cannot measure rheological parameters. Nowadays, all rheometers are automated; hence, the cost is very high. Tattersall’s approach of power requirement in mixing the concrete and calculating the yield stress reduces the complexity in determining the rheological parameter.

Review on Electrolytic Conductivity Sensors

Electrolytic conductivity (EC) sensors are widely used in diverse industries, including: pharmaceuticals, food, power, manufacturing, and environmental monitoring. This article presents an overview and analysis of EC sensors used in these industries from the lowest to the highest range of conductivities and in applications, where there are strong requirements for accurate and traceable conductivity measurements of water and electrolyte solutions. Included are reported sensor designs based on two- and four-electrodes with parallel plates, coaxial cylinders, van der Pauw configurations, planar and miniature configurations, and contactless inductive or capacitive coupling. A comprehensive list of exact analytical formulas for computation of cell constants for the configurations is provided. The advantages and disadvantages of using frequency domain or time domain measurement schemes in these sensors are discussed, and the reader is guided to select the suitable method of sensor calibration among the methods available, computing uncertainty budgets, ensuring traceability to the International System of Units (SI) and compliance with standards, such as Pharmacopeias. Finally, trends in the development of EC sensors and the related challenges in relation to calibration and compliance with standards are presented. This article also introduces the reader to the EC cell of a sensor, which can be modeled by solving the Poisson-Nernst-Planck equations or using appropriate equivalent circuit diagrams. It is stepwise described how the models can be extended to include effects such as electrode polarization and steric effects of ions, and it is illustrated by means of an ideal EC cell, where guards eliminate fringe fields, that the simplest equivalent circuit with a single resistor and a single capacitor models electrolytic sensor data very well in the lower range of electrolytic conductivities.

Stability Criteria to the Incompressible Inviscid Linear Fluid between Two Rotation Coaxial Cylinders

The stability and instability phenomenon coupled with the rotation effect and the thermal convection between two concentric cylinders was studied. By means of the Normal-Modes method, the stability or instability criteria for the linearized system in terms of the oscillation frequency, the axial wavelength and the background thermal gradient are proved. Besides, some numerical simulation for the axisymmetric perturbations is presented.

МОДЕЛЮВАННЯ АНАЛІТИЧНОГО РОЗВИТКУ ФОРМ ГОТСЬКОГО МАЙБУТНЬОГО ЧАСУ

The purpose of this article is to give the model, which demonstrates the development of the Future tense forms in the Gothic language. The initial stage of modelling the Future tense development includes the description of components according to their constituent features. It gives the possibility of tracing the gradual analytisation of corresponding grammatical form, and finding out latent features, which are characteristic for differentiated grammatical forms creating and building the set of Germanic future tense formal structures. The subject of the investigation are peculiarities of formation mechanism of temporal verb forms for projecting the action into the future. To describe the future action the Gothic language used forms of the Present tense involving phrase or upper phrase context. Within the Present tense forms a prefixal word formation model was found. The Greek future tense was translated involving prefixal and present forms in the Gothic language. The Gothic optative was involved to render the future tense. The present tense forms gain future meaning under the influence of aspect-tense specificity, which is recognized as futurelizing factor. Functions of the aspect-tense specificity may be performed with phrase or upper phrase context and syntactical structures with definitely represented semantics. Distinguished present tense constructions create the primary pivot, which is a basis for further development of the Gothic future tense forms. Gothic analytical structures with participle or infinitive were formed involving inchoative, strong, preterite present verbs. These structures are recognized as compound verbal predicates. Analytical structures cover the pivot creating coaxial cylinders. The whole model may be recognized as divergent-rotational because representing the Gothic future tense forms model itself "moves" along the temporal axis. Multilevel model structure demonstrates the fact that analytical forms are changeable in the gravitation. The comparison of divergent-rotational model components and peculiarities of their arrangement indicates and the caudal development of the Future tense forms in the Gothic language. Tendencies found and distinguished as initial, primary in the Gothic language happen in the process of development of the Old Germanic languages. These tendencies are reflected in the Modern Germanic languages, too.

Detection Mechanism of Water Content in Oil–Water Emulsions by Coaxial Double Cylinder Electrodes

This article proposes a new method for detecting water content in oil-water emulsions by a coaxial double cylinder electrodes system. An equivalent circuit model of the system is developed that consists of the electrical double layers, sample solutions, and electrodes. The impedance response is analyzed for different frequency ranges, and the effect of the electrode surface-sample solution interface is also investigated. A coaxial double cylinder electrodes system is designed and fabricated to conduct measurement experiments. The results verify the validity of the model and uncover a linear relationship between the water content and the electrical properties. Combined with the back propagation artificial neural network, the impedance spectral data also show a strong correlation with water content. We also demonstrate how the method can contribute to determining the water content of an oil-water emulsion system.

Сравнительное изучение кинетики свертывания крови и тромбообразования реологическими и электрореологическими методами.

Цель исследования: изучить механизмы формирования и тромбодинамические свойства кровяного сгустка при тромбообразовании in vitro и представить сравнительное исследование кинетики тромбообразования с помощью реологических и электрореологических методов в условиях постоянного и осциллирующего сдвигового вискозиметрического течения; оценить свертывание цельной и консервированной крови, ее вязкоупругие свой ства и влияние фибриногена и декстранов на формирование сгустка. Материалы и методы. Вязкость и удельную электропроводимость нормальной и консервированной с CPD-A1-адениновым раствором крови измеряли ротационным вискозиметром Low Shear 30 Contraves (LS30) с коаксиальными цилиндрами и копией измерительной системы MS1/1 со встроенными электродами (разработана на базе LS30) в условиях постоянного сдвигового потока и в электрическом поле. Вязкоупругие свойства нормальной цельной крови исследовали с помощью реометра Physica MCR 301 (Anton Paar, Austria) в условиях осциллирующего синусоидального потока. Результаты. Представлены результаты кинетики динамической вязкости и удельной электропроводимости консервированной крови в процессе коагуляции в условиях постоянного сдвигового потока и в электрическом поле. Исследованы вязкоупругие свойства цельной крови в условиях синусоидального осциллирующего вискозиметрического течения и представлены зависимости упругого модуля G' (storage modulus) и модуля потерь G'' (loss modulus), а также нормальных сил как функция времени при свертывании. Приводятся данные эффекта фибриногена и декстрана на упругий модуль G' и на модуль потерь G'' цельной крови в процессе коагуляции. Заключение. В условиях вискозиметрического течения при низких скоростях сдвига кинетика тромбообразования характеризуется начальным этапом постепенного увеличения кажущейся вязкости и уменьшения удельной электропроводимости крови и периодом интенсивной коагуляции, характеризирующимся экспоненциальным ростом вязкости и параллельным уменьшением удельной электропроводимости исследуемого образца. Установлено, что коагулирующая цельная кровь обладает нелинейными вязкоупругими свойствами. Кинетика образования сгустка в условиях осциллирующего вискозиметрического течения крови характеризуется увеличением упругого модуля G' и модуля потерь G'' со временем. Одновременно зарегистрирована и отрицательная нормальная сила исследуемого образца в зазоре между пластинами при постоянной толщине зазора. Повышение содержание фибриногена ускоряет коагуляцию и увеличивает значения упругого модуля G' и модуля потерь G'', а также и нормальной силы коагулирующей цельной крови. Objectives: to study the mechanisms of thrombus formation and thrombodynamic properties of a blood clot during coagulation in vitro and to present a comparative study of clot kinetics formation under conditions of steady and oscillating shear viscometric flow and at electric field by rheological and electrorheological methods; to evaluate the coagulation of whole and preserved blood, its viscoelastic properties and the effect of fi brinogen and dextrans on clot formation. Materials/ Methods. The viscosity and electrical conductivity of normal blood and blood preserved with CPD-A1-adenine solution were measured with a Low Shear 30 Contraves (LS30) rotational viscometer with coaxial cylinders and with a copy of the measuring system MS1 / 1 with builtin electrodes at a steady viscometric shear flow and in an electric field too. The viscoelastic properties of normal whole blood were investigated using a Physica MCR 301 rheometer (Anton Paar, Austria) at an oscillating sinusoidal flow. Results. Kinetics of the dynamic viscosity and electrical conductivity of preserved blood during coagulation at a steady shear flow and at electric field were obtained. The viscoelastic properties of whole blood were investigated under conditions of sinusoidal oscillating viscometric flow. The dependences of the elastic (storage) modulus G' and the loss modulus G'', as well as the normal coagulation forces as a function of time are presented. The effect of fibrinogen and dextran on the elastic modulus G' and the loss modulus G'' of whole blood during coagulation are presented. Conclusions. The kinetics of blood coagulation at low shear rates is characterized by a gradual increase of the apparent viscosity and a decrease in blood conductivity at the initial stage and an exponential increase in viscosity during intensive coagulation and a parallel decrease of conductivity too. It was established that coagulating whole blood exhibit nonlinear viscoelastic properties under conditions of sinusoidal blood flow. The kinetics of thrombus formation is characterized by increasing the elastic modulus G' (storage modulus) and the loss modulus G'' with time. The negative normal force in the gap between the plates is also registered at a constant thickness of the gap. An increase in fibrinogen content accelerates coagulation and increases the values of elastic modulus G' and loss modulus G', as well as of the normal force of coagulating whole blood.

Three-dimensional flip-flopping flow around a pair of dual-stepped circular cylinders in a side-by-side arrangement

Three-dimensional direct numerical simulations of flow around a pair of dual-stepped circular cylinders in a side-by-side arrangement and a proximity interference region are presented. The dual-stepped cylinders consist of two coaxial cylinders with a larger-to-smaller diameter ratio of 2. The Reynolds number and the side-by-side gap ratio, based on the larger (smaller) diameter, are 200 (100) and 1 (3), respectively. Two flip-flopping flow regimes A and B are observed behind the dual-stepped cylinders, exhibiting temporal variations of hydrodynamic drag and lift force coefficients. The flow regime B is featured by the flip-flopping, higher vortex-shedding frequencies and greater flow instability than those in the flow regime A. Half-loop and direct connections of vortices take place frequently in the narrower wake, while the vortex reconnection and multiple connection predominate the wider wake. This suggests that the dual-stepped cylinder with the narrower wake behaves similarly to a single dual-stepped cylinder. The dynamic mode decomposition analysis reveals pitchfork and Hopf bifurcation (in-phase and anti-phase synchronization) modes in the larger cylinder wake, with the interaction of these bifurcations originating from the flip-flopping flow pattern. However, the pitchfork mode is not found in the smaller cylinder wake, suggesting that its flip-flopping flow behavior is not self-originated but triggered by the flip-flopping flow mechanism of the larger cylinder.

On numerical modeling of natural convection based on the OpenFOAM solver

This work considers numerical modelling of natural incompressible convection problems in the gravity field in the Boussinesq approximation using OpenFOAM. A mathematical model of natural convection in the gravity field, using Boussinesq approximation, was considered. The built-in solver was identified and modified. The exact solution, theoretical data and experiment were used to verify the solver. A numerical study of natural convection in a horizontal liquid layer was performed. Natural convection in a fluid layer between coaxial cylinders was considered.