Annular Channel Research Articles

Theoretical and Experimental Flow Characteristics of a Large-Scale Annular Channel in Terms of Deformation Gradient, Eccentricity, and Water Compressibility

Hydraulic water plunger pumps have come to be widely used in coal mining, seawater desalination, and oil exploitation due to their high output pressure and large flow characteristics. In a high-pressure large-flow plunger pump, the leakage of the annular channel of the plunger pair is an essential factor affecting volume efficiency. The axial pressure gradient exists in the fluid inside the annular channel, resulting in the plunger and plunger sleeve forming similar funnel-like shapes. Moreover, the characteristics of large diameter, high working pressure, and low fluid viscosity of the plunger pump will lead to the complicated flow of the annular channel. The influence of eccentricity and structural deformation on leakage is difficult to evaluate. Therefore, considering the deformation gradient and eccentricity of the plunger pair and the compressibility of the water, the deformation equations and leakage equations of the annular channel under the laminar and turbulent flow state are derived in this study. The eccentricity and leakage of the annular channel under different pressure conditions are measured using a built sealing test bench. It is proved that the discrepancy between the calculated model and the experimental results is less than 6% under different pressures, which effectively predicts the sealing performance of plunger pumps. The results show that under the laminar flow condition, the effects of eccentricity, structural deformation, and medium compressibility on leakage are 148%, 4.92%, and 0.92%, respectively. In turbulent conditions, they were 31%, 2.84%, and 1.19%, respectively. Besides, the reasonable material pairing of the plunger friction pair can reduce the variation of leakage due to structural deformation.

Genetic optimization design for aerodynamic structure of oblique flow compressor radial inlet chamber in compressed air energy storage system

AbstractThe compressor plays a significant role in the compressed air energy storage (CAES) system, and its performance directly determines the overall efficiency of the system and the economy of energy storage. Internal flow losses and outlet distortion due to poor design of its radial inlet chamber (RIC) geometry can degrade the performance of downstream components and reduce compressor unit performance. In this article, a multiobjective optimization design is carried out for the RIC of the oblique flow compressor in CAES system, and a parametric optimization design method of the RIC annular convergent channel meridian profile is developed. The optimal Latin hypercube experimental design (opt LHD) method is used to generate the sample library, and the radial basis function neural network (RBFNN) is used to establish the surrogate model of each design parameter and RIC performance. The multiobjective optimization is executed by the second‐generation non‐dominated sorting genetic algorithm (NSGA‐II). After optimization, the area of the annular convergent channel of the RIC is expanded, the transition of the meridian profile is smoother, the distortion coefficient of the RIC is reduced by 0.58%, and the total pressure loss coefficient is reduced by 16.45%. By using the optimized RIC, the performance of oblique flow compressor has been improved. Compared with the original model, the total pressure ratio and isentropic efficiency of the whole machine at the design point have been increased by 0.6% and 0.32%, respectively.

Effect of turbulence modulation caused by thread structure on coaxial air-blast atomization

This study aims at investigating the influence of turbulence modulation caused by a thread structure on coaxial air-blast atomization by means of high-speed flow visualizations and droplet particle size techniques. The medium in the central channel of an atomizer is water while the annular channel is airflow. The results show that the thread structure added to the inner surface of an annular channel plays an important role in atomization effect. The generated liquid ligaments on the jet present more structures, which grow shorter and breakup faster than that without thread. To compare the difference in jet breakup length and droplet diameter caused by the thread structure, we establish a new breakup length model and then use the ratio of structure factors to describe the change in the droplet diameter. The results in this experiment confirm the improvement of atomization performance brought by optimization design of the thread structure.

Critical heat flux of water in vertical annular channel with a short heated rod under low pressure and low flow conditions

An experimental study on critical heat flux (CHF) has been conducted in a vertical annulus channel with a short heated rod at low pressure and low flow conditions. The heated rod of the test section was made of Inconel-625 with a diameter of 37.2 mm and a heated length of 390 mm. The pressure, inlet temperature and mass flux were varied in the range of 103–170 kPa, 63 −90℃and 59.6–131.9 kg m2 s−1. The CHF phenomenon was observed through the transparent quartz glass. It was found that the CHF positions firstly appeared in a small zone on the heated rod wall and the dry-out area would further expand if the power was not cut off immediately. The experimental results showed that most of CHF data were firstly detected at the upper thermocouple position near the outlet, while CHFs data were observed at lower positions with low mass flux. And based on Mishima and Ishii’s flow regime map, the analysis of experimental flow regime indicated that most of the CHF occurred in slug-churn and churn-annular flow regimes. Finally, the measured CHF data were compared with the results predicted by four commonly used correlations and the method of CHF look-up table, and a new correlation was developed. It was found that the new correlation can be better predicting experimental data with an error within ± 15%.

Study of beam divergence and thrust vector eccentricity characteristics of the Hall thruster based on dual Faraday probe array planes and its applications

The accurate knowledge of the thrust vector eccentricity and beam divergence characteristics of Hall thrusters are of significant engineering value for the beneficial integration and successful application of Hall thrusters on spacecraft. For the characteristics of the plume bipolar diffusion due to the annular discharge channel of the Hall thruster, a Gaussian-fitted method for thrust vector deviation angle and beam divergence of Hall thrusters based on dual Faraday probe array planes was proposed in respect of the Hall thruster beam characteristics. The results show that the ratios of the deviation between the maximum and minimum values of the beam divergence angle and the thrust vector eccentricity angle using a Gaussian fit to the optimized Faraday probe dual plane to the mean value are 1.4% and 11.5%, respectively. The optimized thrust vector eccentricity angle obtained has been substantially improved, by approximately 20%. The beam divergence angle calculated using a Gaussian fitting to the optimized Faraday probe dual plane is approximately identical to the non-optimized one. The beam divergence and thrust vector eccentricity angles for different anode mass flow rates were obtained by averaging the beam divergence and thrust vector eccentricity angles calculated by the dual-plane, Gaussian-fitted ion current density method for different cross-sections. The study not only allows for an immediate and effective tool for determining the design of thrust vector adjustment mechanisms of spacecraft with different power Hall thrusters but also for characterizing the 3D spatial distribution of the Hall thruster plume.

Modeling of Turbulent Convective Heat-Transfer Characteristics in a Concentric Annular Channel

Turbulent convective heat-transfer characteristics in a concentric annular channel with both walls heated are theoretically modeled and numerically computed in this article. Generalized algebraic predictive models and equations for heating over a single wall are first reviewed by summarizing the well-known methods in the literature. These methods are then scrutinized according to the most recent investigations such that new viewpoints and corrections are introduced accordingly. Moreover, the application of superposition in temperature is used in the current work instead of the Nusselt number as seen in the literature. The numerical integration method is applied to the generalized equations to obtain the solutions, which are found to be in decent agreement with the direct numerical simulation (DNS) data in the literature. The results in this work also indicate that the wall heat flux density ratio and the annular radius ratio are two key factors that have a great influence on the heat-transfer characteristics of the case with both walls heated.

Study on the structural design and performance of magnetorheological (MR) valve with hybrid supply magnetic source and double annular channels

Valve plays an important role in achieving precise position control for the hydraulic lift system. In order to improve the performance of hydraulic lift in precise motion, this paper proposes an MR valve with hybrid supply magnetic source and double annular channels. In addition, a structural model was established to perform pressure drop analysis. According to its working principle, it is proposed that this MR valve has two channels that work separately. There are three working modes in which the two channels work together, and the pressure drop of the MR valve can be calculated in different ways. Therefore, the MR valve with hybrid supply magnetic source and double annular channel performance test system is constructed, and the magnetic field inside the valve is simulated by performing magnetic field finite element analysis. Finally, a test bench of vehicle maintenance elevators is built to analyze whether the MR valve with hybrid supply magnetic source and double annular channels can achieve accurate control on the vehicle maintenance elevators. According to the experimental and simulation results, the pressure drop of the MR valve with hybrid supply magnetic source and double annular channels is affected by the current and channel operating mode, while the load makes little difference to the pressure drop. The worse the rising response time performance increases with increasing current, but the response time performance decreases without being affected by current. When a current greater than 1.5A is applied to the coil, the response time of the lifting platform is basically maintained at 6 s with the increase of current. The position accuracy is ±1 mm for the experimental platform of the vehicle maintenance lift table based on the MR valve with hybrid supply magnetic source and double annular channel hydraulic system.

Air rumbling for online fouling mitigation of calcium carbonate aqueous solution under subcooled flow boiling heat transfer

In this research, increasing the shear stress by injecting air into the working system was implemented to mitigate crystallization fouling of calcium carbonate (CaCO3) aqueous solution. For this purpose, various experiments were conducted under subcooled flow boiling condition for analysing the effect of air injection on reduction of fouling formation inside a vertical annular channel with upward flow. These experiments were conducted at different operating conditions including air injection rate of 2–10 l/min, air injection freqency (f) of 0.5–2 h−1, heat flux of 52–83 kW/m2, fluid flow rate of 2–4 l/min, fluid bulk temperature (Tb) of 30–55 °C, and at a constant CaCO3 concentration of 0.2 g/l. The results showed that by increasing f from 0.5 to 2 h−1, the rate of fouling formation decreased. Also, the air rubmbling was more effective when Tb increased from 30 °C to 55 °C, by decreasing the fouling resistance from 38% to 57% comparing with no-mitigation experiment. When the heat flux was 83 kW/m2, air rumbling could decrease the fouling resistance by 57%. On the other hand, at lower heat flux of 52 kW/m2, air injection not only failed to reduce the fouling resistance, but increased it by about 20%. Also, when the air injection rate increased from 2 to 10 l/min, fouling resistance increased slightly. This environmentally friendly method has not received much attention before. Hopefully, the results presented in this research can pave the way for more research works on the mitigation of crystallization fouling using air injection.

Fuel distribution of sub- and supercritical kerosene jets into swirling air in an annular mixing channel

The uniformity of fuel/air mixture in the mixing channel of the lean premixed and prevaporized injector is important for NOx emissions reduction in aircraft engines. In the present study, an optical annular mixing channel is designed to investigate the effects of heated RP-3 fuel on fuel/air mixing at liquid, gas, and supercritical injections. Planar laser-induced fluorescence is employed to obtain multiple cross-sectional fuel distributions along the axial direction of the mixing channel. The results show that for the liquid injections, the droplets tend to move closer to the outer wall due to the effect of the centrifugal force. Increasing air temperature in the range of 450 K to 670 K can promote liquid evaporation and suppress the centrifugal effect, and result in a 70 % increase in the fuel dispersion area. Compared with liquid injections, the gaseous injections are more evenly distributed and closer to the inner wall. And the displacement of the fuel is mainly determined by the fuel–air momentum ratio. Interestingly, the near-critical and supercritical fuel injections in the range of 638–700 K and 2.2–2.5 MPa show bimodal fuel distributions along the radial direction. The fuel distributed close to the outer wall is from the condensed part which moves under centrifugal effect, while the fuel distributed close to the inner wall is from the gaseous part which is mainly affected by injection penetration.

Study of the influence of temperature dependent viscosity on fluid flow in annular channels

For all liquids, a change in viscosity depending on temperature is characteristic. In most cases, this dependency is commonly overlooked; however, when studying the flow of liquids under conditions of intense heat exchange, the temperature-dependent viscosity can have a significant impact on mass and heat transfer processes. It should be noted that for some liquids, such as polymer solutions or biological fluids, the temperature dependence of viscosity can be extremely complex and nonlinear. In such cases, ignoring this dependence can lead to inaccurate results and errors. Annular channels find wide applications in various technical systems, including heat exchangers and hydraulic devices. Understanding the factors influencing the fluid flow and discharge in such channels is a key aspect of optimizing their design and operation. One of the main factors influencing the flow process and fluid discharge in annular channels is the temperature-dependent viscosity of the fluid. This work investigates the influence of the thermo-viscous parameter with monotonic and non-monotonic temperature-dependent viscosity, as well as the geometric parameter of the annular channel on the fluid flow process and discharge. The mathematical model includes the continuity equation, Navier-Stokes equations, and the temperature equation. The method of control volume and the SIMPLE algorithm, modified to account for the variable viscosity coefficient, were applied for the numerical solution of these equations. It is shown that in the case of liquid flow in an annular channel with a monotonic dependence of viscosity on temperature, the steady-state discharge closely approaches the discharge at maximum viscosity. However, in the case of a liquid with non-monotonic viscosity dependence on temperature, the discharge significantly depends on the thermo-viscous parameter.

Investigation of eigenfunctions of perturbation of the radial component of flow velocity

The flow of a thermoviscous model fluid in an annular channel with a given temperature field is considered. The problem of the stability of the flow of a thermoviscous fluid is solved on the basis of a generalized equation by the spectral method of expansion in Chebyshev polynomials of the first kind. The influence of taking into account the exponential dependence of fluid viscosity on temperature and channel geometry on the spectral characteristics of the equation of hydrodynamic stability of incompressible fluid flow in an annular channel is investigated. The eigenvalue spectra were obtained numerically. The spectral characteristics determine the structure of the eigenfunctions and the critical parameters of the flow of a thermoviscous fluid. In this case, the eigenfunctions demonstrate the behavior of transverse velocity disturbances, their possible growth or decay over time. Graphs of the eigenfunctions of the generalized flow stability equation in an annular channel have been constructed. It is shown that the structure of the spectra largely depends on both the properties of the liquid, determined by the functional dependence of viscosity, and on the geometry of the channel. The stability of the flow of a thermoviscous fluid depends on the presence of an eigenvalue with a positive imaginary part among the entire set of found eigenvalues for fixed parameters of the Reynolds number and wave number. It has been established that at small values of the thermoviscosity parameter the spectrum is comparable to the spectrum for isothermal fluid flow in a flat channel, however, as it increases, the number of eigenvalues and their density increase, that is, there are a greater number of points at which the problem has non-zero amplitudes of transverse velocity disturbances. It is worth noting that the diversity of eigenvalue spectra corresponds to the diversity of eigenfunctions, which have a nontrivial distribution of the oscillation amplitude over the cross section in each case. Smooth curves are obtained for a narrow channel, as for the case of a flat channel. However, as the ratio of the channel radii increases, “jumps” appear. Also, note that the eigenfunctions do not have the property of symmetry; this follows from the fact that the velocity profile in the unperturbed state also does not have symmetry. The maximum values of the eigenfunctions are shifted to the right from the center of the channel, which corresponds to the fact that disturbances arise and grow intensively near the hot wall.

Investigation of multi loop linear magnetic circuits of electromagnetic flow converters with ring channels

Mathematical models of single and multiloop magnetic circuits of electromagnetic flow transducers with an annular channel are designed taking into account the parameters of the magnetic circuit. The possibility of compensating the difference in magnetic resistances of coaxially located concentric ferromagnetic cores and the difference in their circumference by selecting the thickness of the cores is shown. It has been installed that the magnetic flux in ferromagnetic cores is distributed along the angular coordinate. The magnetic induction in the annular channel is unevenly distributed along the radial coordinates. It was found that with an increase in the value of the attenuation coefficient of the magnetic field in the magnetic circuit, the degree of magnetic induction in the annular channel increases along the angular coordinate, while it remains constant along the radial coordinate.

An overview on thermal exchange and crisis of heat transfer release in the annular channels with flow swirl

An overview on thermal exchange and crisis of heat transfer release in the annular channels with flow swirl

Numerical study of nonisothermal flow of polymer melt with undermelted granules in an annular channel of a disk extruder

A computational experiment was carried out on the basis of the created model of melt flow with undermelted granules in a straight annular channel, which takes into account the design characteristics of a pilot-industrial disk extruder. A polymer composition based on high-pressure polyethylene (PE 15803-020) was chosen as a model object. The calculation procedure is presented in an analytical form at disk speeds of minimum value – 120, nominal value – 150, and maximum value – 180 rpm.

Simulation of strain waves evolution in the walls of coaxial annular and circular channels filled with viscous fluid and made from incompressible material with fractional physical nonlinearity

Simulation of strain waves evolution in the walls of coaxial annular and circular channels filled with viscous fluid and made from incompressible material with fractional physical nonlinearity

Research of the process of air separation of grain material in a vertical zigzag channel

The aim of the research is to determine ways to improve the efficiency of grain materials pneumatic separation based on the study of the interaction mechanism of grains with the air flow in the channel elements, which are inclined sections of the air duct. The paper considers a modified separation method that separates the grain material according to the aerodynamic properties of the components in a vertical zigzag air channel in an aerodynamic and gravitational field. The studies were carried out by means of mathematical modeling followed by experimental confirmation of the modeling results. A computer mathematical model was created in the MathCad 13 application package to determine the parameters of the zigzag aspiration channel. This model describes the influx of parameters in the channel (width, height, cut of the zigzag ledge to the horizon, edge of the zigzag ledge) on the nature of the grain trajectory. As a result of the numerical simulation process using the mathematical package Mathematica, dependence was obtained to determine the trajectory of motion depending on the angular velocity. An increase in the pneumatic separation effect during the grain mixtures division due to the influence of the Magnus effect was established as a result of experimental studies. The design of a zigzag separator with an annular channel section has been improved based of the research carried out.

Longitudinal waves in the walls of an annular channel filled with liquid and made of a material with fractional nonlinearity

Purpose of this paper is to study the evolution of longitudinal strain waves in the walls of an annular channel filled with a viscous incompressible fluid. The walls of the channel were represented as coaxial shells with fractional physical nonlinearity. The viscosity of the fluid and its influence on the wave process was taken into account within the study. Metods. The system of two evolutionary equations, which are generalized Schamel equations, was obtained by the two-scale asymptotic expansion method. The fractional nonlinearity of the channel wall material leads to the necessity to use a computational experiment to study the wave dynamics in them. The computational experiment was conducted based on obtaining new difference schemes for the governing equations. These schemes are analogous to the Crank–Nicholson scheme for modeling heat propagation. Results. Numerical simulation showed that over time, the velocity and amplitude of the deformation waves remain unchanged, and the wave propagation direction concurs with the positive direction of the longitudinal axis. The latter specifies that the velocity of the waves is supersonic. For a particular case, the coincidence of the computational experiment with the exact solution is shown. This substantiates the adequacy of the proposed difference scheme for the generalized Schamel equations. In addition, it was shown that solitary deformation waves in the channel walls are solitons.

Problem solution analysis on finding the velocity distribution for laminar flow of a non-linear viscous flushing fluid in the annular space of a well

Modern drilling fluids are non-linear viscous media with an initial shear stress. In classical scientific works on hydromechanical modeling of drilling fluids motion in pipes and annular channels the Shvedov – Bingham approximation and Ostwald – de Waale power-law model were used, which did not fully account for behavior of technological fluids in a wide range of shear rates. This article presents a numerical solution for a mathematical model of drilling fluid motion of the three-parameter Herschel – Bulkley rheological model in the annular space of the well. The Herschel – Bulkley model in the rheological equation takes into account the presence of initial shear stress and a tendency for viscosity to change with shear rate, which distinguishes it from the Ostwald – de Waale and Shvedov – Bingham models. The target function in solving the equation of motion is the velocity distribution in the radial direction of the upward flow of the flushing fluid. The analysis of obtained solution is based on the theory of velocity profile influence on quality of cuttings removal during wellbore cleaning. Due to peculiarities of mathematical statement of the task, which supposes necessity of differential equation of motion solution, Wolfram Mathematica computational software has been used as a calculation tool. The analysis of numerical solution allowed to draw conclusions about the possibility of its application in evaluation of velocity profile when drilling fluid moves in annular space of the well. The possibility for application of modified excess coefficient as a relative quantitative parameter for evaluation of velocity profile uniformity was substantiated.

Расчет конструктивных параметров мультицилиндрового теплового генератора на основе течения Куэтта–Тэйлора

Direct conversion of wind energy into heat is a relevant direction for the development of alternative heat power engineering. The paper considers an efficient wind heat generator that consists of two rotors nested in each other's annular gaps and forming a system of cylindrical coaxial annular channels filled with a viscous working fluid. Depending on the properties of the working fluid, the velocity of the rotors, the number of annular channels and their geometry, there are combinations of parameters for the optimal design of the heat generator. The proposed method for selecting the design parameters of coaxial rotors makes it possible to directly select the optimal design of rotors for a given power of the heat generator and the properties of a viscous working fluid. The design of the multi-cylinder system of the heat generator, which uses the annular Couette–Taylor flow, is presented in the form of an equivalent single annular gap, which made it possible to generalize the results of investigations carried out with different working fluids under various conditions, in the form of a single dependence of the dimensionless power of the heat generator on the number Reynolds. The obtained dependence is well approximated by a linear function in the experimentally studied range of Reynolds numbers. An algorithm for calculating the geometric design parameters of a multi-cylinder annular system is proposed. As an example, calculations of the structural dimensions of nine variants of heat generators for three power values are given: 10 kW, 20 kW and 50 kW.

Study on Convective Heat Transfer of Supercritical Water in Annular Square Channel

Supercritical water, known for its abrupt changes in fluid properties near the pseudocritical region, has always posed a design challenge, leading to enhancement or deterioration in heat transfer. Additionally, the lack of complete understanding of the thermodynamic behavior of supercritical water near the pseudocritical zone, unlike in the subcritical zone, highlights the necessity of a systematic study. Hence, this paper focuses on characterizing the convective upward flow and heat transfer characteristics inside a vertical smooth annular square channel. The numerical analysis uses a steady-state, pressure-based, compressible, Newtonian solver with body force term and two-equation turbulence model to study the influence of variation in pressure, heat flux, and heat-to-mass flux ratios. The flow characteristics and heat transfer behavior of deteriorated, normal, and enhanced heat transfer modes are studied. The heat transfer deterioration is suppressed with the increase in pressure; however, it increases with the increase in inlet bulk temperature. The supercritical boiling number that determines the heat transfer mode is calculated and analyzed for the square annulus section. The evolution of the flow in different heat transfer modes differs based on the effect of buoyancy on the velocity field and the turbulence. The calculated Nusselt numbers match the existing Jackson and Hall correlation well with a maximum absolute error of 9.91%.