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The optimization design of the double-layered material tank is essential to improve the material mixing efficiency and quality in chemical engineering and lithium battery production. The draft tube structure and double-layered impellers affect the flow patterns of the fluid–solid transfer process, and its flow pattern recognition faces significant challenges. This paper presents a fluid–solid mixing transfer modeling method using the CFD-DEM coupling solution method to analyze flow pattern evolution regularities. A porous-based interphase coupling technology solved the interphase force and could be used to acquire accurate particle motion trajectories. The effect mechanism of fluid–solid transfer courses in the double-layered mixing tank with a draft tube can be obtained by analyzing key features, including velocity distribution, circulation flows, power, and particle characteristics. The research results illustrate that the draft tube structure creates two major circulations in the mixing transfer process and changes particle and vortex flow patterns. The circulating motion of the double-layered impellers strengthens the overall fluid circulation, enhances the overall mixing efficiency of the fluid medium, and reduces particle deposition. Numerical results can offer technical guidance for the chemical extraction course and lithium battery slurry mixing. [ABSTRACT FROM AUTHOR]

Visualization experiments were conducted to clarify the operational characteristics of a polymer pulsating heat pipe (PHP). Hydrofluoroether (HFE)-7100 was used as a working fluid, and its filling ratio was 50% of the entire PHP channel. A semi-transparent PHP was fabricated using a transparent polycarbonate sheet and a plastic 3D printer, and the movements of liquid slugs and vapor plugs of the working fluid were captured with a high-speed camera. The video images were then analyzed to obtain the flow patterns in the PHP. The heat transfer characteristics of the PHP were discussed based on the flow patterns and temperature distributions obtained with thermocouples. Before starting heating, because of high wettability, large liquid slugs positioned at the evaporator section of the PHP. After starting heating, since the occurrence of boiling divided the large liquid slugs, oscillatory flow of smaller liquid slugs and vapor plugs was found in the PHP. Clear circulation flow of liquid slugs and vapor plugs was observed when the power input to the PHP was larger than 12.0 W. The flow patterns and temperature distributions confirmed that the circulation flow enhanced the heat transfer from the evaporator section to the condenser section of the PHP. In the circulation flow mode, large growth and contraction of vapor plugs were found one after another in all even-numbered PHP channels. However, the analysis of flow patterns clarified that the phase-change heat transfer rate by large growth and contraction of vapor plugs was 19% of the total heat transfer rate of the PHP. Although the generation of large vapor plugs was found in the PHP, most of the heat was transferred by the sensible heat of the working fluid. [ABSTRACT FROM AUTHOR]

A three-dimensional flow of a viscous heat-conducting gas in a rapidly rotating straight circular cylinder in the presence of axial temperature gradients is studied. At the initial stage, gas-dynamic and thermal boundary layers on a rotating extended disk are considered. When taking into account the temperature change in density, the Dorodnitsyn transformation is used, which makes it possible to reduce the solution of the problem to the integration of a system of ordinary differential equations. Taking into account inertial effects, an approximate analytical solution of the problem is obtained in the case of small values of the Prandtl number, when the thermal boundary layer thickness exceeds the thickness of the hydrodynamic layer. The result of the calculation for an extended disk is used to estimate the intensity of the axial circulation flow in a rotating cylinder of finite dimensions. The influence of the intensity of temperature perturbation on the radial profile of circulation in a rotor is studied. [ABSTRACT FROM AUTHOR]

In this article we prove a linear inviscid damping result with optimal decay rates of the 2D irrotational circulation flow around an elliptical cylinder. In our result, no components of the asymptotic velocity field vanish, and the asymptotic flow lines are no longer an ellipse. [ABSTRACT FROM AUTHOR]

The performance of a uranium gas centrifuge which is used in the uranium enrichment industry depends strongly on the gas flow field. The computer simulation is vital to examine the gas flow field. Therefore, in the present study, the capabilities of OpenFoam software for simulating the gas flow inside the rotor for total reflux thermal drive-in axisymmetric mode has been investigated. The results corresponding to the OpenFoam ssimulation have been validated with those of analytical Olander’s model, numerical solution of the Harada’s study, and simulation using Fluent. The simulation results for gas flow inside the rotor of centrifuge showed that the density-based solver was properly chosen and the number of cells, 160×170, was compatible with mesh. The numerical results show that OpenFoam software was capable to examine the gas flow inside the rotor. Also, the simulation of the distribution of Knudsen number confirms the presence of the molecular region near the axis of rotation. OpenFoam is open-source software and there is the ability to solve the molecular region as well as the coding for coupling the continuous and molecular region, the feature which does not exist in the fluent software. The use of open foam is therefore recommended to simulate gas flow inside the rotor.

The circulation flow of a viscous incompressible fluid in the cylindrical containers bounded by the ends with the rotating and fixed disks are explored. The main goal of the research is aimed to study influence of rotation of casing and end disk on a circulation flow in a cylinder/disk device. This problem relates to inducing a circulation flow in a mechanical centrifuge for mixture separation. To solve this complex problem, an approximate calculation approach is proposed. It is based both on the integral relationships reducing to the balance of the azimuthal moment friction forces acting on the rotating volume and continuity of a circulation flow. To evaluate the friction forces at the ends of a cylinder, the case of infinitely extended disks is considered. For this case, the approximate analytical solutions of the hydrodynamic problem for the turbulent boundary layers on the rotating and fixed extended disks are obtained. In contrast to the previously published works, the inertial convective term associated with the angular momentum transfer from the external flow to the boundary layer in the equations of motion and the symmetrical radial velocity profile are taken into account. • The mechanical drive in the rotating disk/cylinder device is investigated. • We take into account the inertial convective term in the motion equations. • The approximate approach is used for engineering calculation and quick estimates. • Friction force in the boundary layers is calculated for the turbulent flow. [ABSTRACT FROM AUTHOR]

To improve the cavitation performance of the centrifugal pump, a new kind of centrifugal pump impeller with slot is proposed. The slot is on the impeller shroud near the suction side of the blade leading edge. So, the fluid with high energy in the impeller front side chamber is drained to the lowest pressure area. The jet flow would compensate the blade inlet flow with a certain energy. With numerical simulations, the pump's inner flows for 5 different slot sizes and their hydraulic performances are compared with those of the prototype pump. The slot jet would result in the increase of the impeller flow rate and the volute area ratio, leading to the head decrease within the whole flow rate range. The slot jet can suppress the reverse flow remarkably at a low flow rate, and the pump efficiency is improved. The slot jet improves the pump cavitation performance effectively, especially at a low flow rate. To some extent, the smaller the slot size is, the better the pump cavitation performance is. The cavitation performance of the slot impeller with a size of 2 mm×1.75 mm is much better than that of the prototype impeller. Compared with the prototype impeller, the lowest pressure near the slot impeller blade inlet and even the pressure in all forepart regions are improved significantly. The slot impeller is shown to be effective in suppressing the cavitation, and the available net positive suction head is improved. [ABSTRACT FROM AUTHOR]

The influence of the piston effect in subway tunnels depends on a train speed, the geometry of a tunnel and a train, the types of air flow caused by mechanical ventilation and other variable characteristics. Tables and graphs of changes in air flows generated by the effect of the piston are presented depending on the speed of a train and the degree of fill rate of a tunnel. It is noted that the piston effect is characterized by two phases. At the first stage, the piston effect and the processes of changing physical fields are non-stationary whereas at the second stage, the processes become stable. The speed of the circulation flow created by the piston effect, in accordance with the fill factor of a tunnel, is characterised by a linear relationship; the degree of its growth is directly proportional to the speed of a train. Based on the results from the present paper it is possible to calculate the velocity and consumption of an air flow in an underground space. The maximum value of air flow carried out by the piston effect does not exceed 90-100 m3/s. It corresponds to the stationary phase of motion, when the tunnel filling factor a = 0.35 and train speed is in the range of 40-45 km/h. Based on the obtained numerical simulation results, technological parameters for metro ventilation systems can be calculated more accurately. [ABSTRACT FROM AUTHOR]

[Display omitted] • Proposing five cyclones with diverse tilt angles for enhanced flow characteristics. • The formation mechanism of short-circuit flow are analyzed by numerical simulation. • Comparing Euler numbers for various cyclones through experiments and CFD. • Cutoff diameter and grade efficiency of different cyclones are evaluated. Short-circuit flow and circulation flow are important secondary flows in a cyclone, which have a negative impact on separation performance. This work proposed new cyclones (VH cyclone), incorporating volute-helical inlets with five tilt angles based on the characteristics of short-circuit flow and circulation flow, in order to enhance separation efficiency without a significant pressure drop compared to a Lapple-type cyclone with a tangential inlet (TI cyclone). The separation performance and Euler number of six cyclones are obtained by experiments and analytical models. The simulation is utilized to explore characteristics of short-circuit flow and circulation flow, with a focus on the impact of these flow patterns on particle motion. The result shows that proportion of short-circuit flow increases initially and then decreases with the increase of the tilt angle, while circulation flow is continually weakened. The cutoff diameter increases first and then decreases while the trend of Euler number is opposite for new cyclones. By considering both separation performance and Euler number, VH4 cyclone (Tilt angle of volute-helical inlet is 6.5°) exhibits optimal performance, with a cutoff diameter 20.41% lower than that of TI cyclone, while their Euler numbers are similar. [ABSTRACT FROM AUTHOR]

The upper reach of the Yellow River from Daliushu to Shapotou consists of five bends and has complex topography. A two-dimensional Re-Normalisation Group (RNG) k-ε model was developed to simulate the flow in the reach. In order to take the circulation currents in the bends into account, the momentum equations were improved by adding an additional source term. Comparison of the numerical simulation with field measurements indicates that the improved two-dimensional depth-averaged RNG k-ε model can improve the accuracy of the numerical simulation. A rapid adaptive algorithm was constructed, which can automatically adjust Manning's roughness coefficient in different parts of the study river reach. As a result, not only can the trial computation time be significantly shortened, but the accuracy of the numerical simulation can also be greatly improved. Comparison of the simulated and measured water surface slopes for four typical cases shows that the longitudinal and transverse slopes of the water surface increase with the average velocity upstream. In addition, comparison was made between the positions of the talweg and the main streamline, which coincide for most of the study river reach. However, deviations between the positions of the talweg and the main streamline were found at the junction of two bends, at the position where the river width suddenly decreases or increases.

The aim of this study is to investigate the flow field characteristics in ABL (Atmospheric Boundary Layer) flow over multiple hills and valleys in two-dimensional models under neutral conditions. Active turbulence grids and boundary layer generation frame were used to simulate the natural winds in wind tunnel experiments. As a result, the mean wind velocity, the velocity vector diagram and turbulence intensity around the hills were investigated by using a PIV (Particle Image Velocimetry) system. From the measurement results, it was known that the average velocity was increased along the upstream slope of upside hill, and then separated at the top of the hills, the acceleration region of U / U ref > 1 was generated at the downstream of the hill. Meanwhile, a large clockwise circulation flow was generated between the two hill models. Moreover, the turbulence intensity showed small value in the circulation flow regions. Compared to 1 H model, the turbulence intensity in the mainstream direction showed larger value than that in the vertical direction. This paper provided a better understanding of the wind energy distribution on the terrain for proper selection of suitable sites for installing wind farms in the ABL. [ABSTRACT FROM AUTHOR]

[Display omitted] • Eight novel bottom profiles of cylindrical hydrocyclone are designed. • Bottom profiles affect the grade efficiency of intermediate and coarse particles. • The particle content in the circulation flow can be altered by the bottom profile. • Separation performance can be improved by controlling particle circulation flow. The cylindrical hydrocyclone has been increasingly used in coarse classification due to its reduced fine particle entrainment, but the loss of coarse particles to overflow remains an intractable problem. Based on the notion that the strong circulation flow caused by the flat bottom structure bears primary responsibility for the problem, this study designs eight unique bottom profiles to regulate the particle circulating flow and attempts to correlate particle circulation flow with classification performance. The effects of the bottom profile on flow field characteristics, particle spatial distribution, circulation flow rates, and grade efficiency are explored in detail using validated models in a Φ200 mm cylindrical hydrocyclone. The findings suggest that bottom profiles have the greatest effect on the axial velocity near the bottom and the grade efficiency of intermediate and coarse particles, while all unique designs have the potential to lower turbulence intensity. An ascending segment near the wall or a descending segment near the axis can help to mitigate the misplacement of coarse particles by reducing particle circulation flow without affecting the entrainment of fines appreciably. Additionally, two circles are found on each side of the cut plane, which is conducive to releasing coarse particles from the circulation flow. Regulation of particle circulation flow by adjusting bottom profile parameters can improve separation performance. [ABSTRACT FROM AUTHOR]

The circulation flow, in light dispersion hydrocyclones and the effects of various parameters on this flow were studied quantitatively through measurements of the axial velocity field. A phase Doppler particle analyzer (PDPA) system was developed to measure the axial velocity field in axial cross sections in ∅ 35 mm hydrocyclones with various vortex finders lengths, overflow orifice diameters, cone angles, inlet flow rates, and split ratios. The results showed that the zero-axial-velocity wave zone (ZAVWZ), which is responsible for the coupling of circular and closed flow in most axial cross sections, is caused by the velocity gradient and can be described as the location of the circulation flow. The mechanism of circulation flow and cyclone separation was revealed by the formation mechanism of the circulation flow. A new equation for calculating the circulation flow rate is proposed. By studying the effects of the geometric and operating parameters on the circulation flow, it was observed that smaller distribution areas and rates of circulation flow usually result in higher separation efficiency in a hydrocyclone. [ABSTRACT FROM AUTHOR]

The errors of multiblock computational technologies realized in different versions of the VP2/3 package and involving the use of structured computational meshes of the H and O types with superposition were methodically investigated by the example of solving the problem on a circulation flow of an incompressible viscous fluid in a square cavity with a moving cover at a moderate Reynolds number of ~10. A comparison of the numerical estimations of the integral and extremum local characteristics of the indicated flow, made with the use of composite and multiblock meshes with varying densities and near-wall steps, has shown that it is reasonable to use multiblock computational technologies with linear interpolation in the calculations with conversion of parameters from mesh to mesh. [ABSTRACT FROM AUTHOR]

The unidiameter deadleg refers to the lateral branch of a three-way pipe with the same diameter, and generally, one end of the lateral branch, namely, the deadleg, is closed. In this paper, the characteristics of fluid flow in unidiameter deadlegs were numerically studied. The effects of deadleg length to diameter ratio (H/D) and the inlet flow velocity of the main pipe on the flow pattern and velocity distribution of the deadlegs were investigated. The results indicated that the inlet velocity is the primary factor for the development of mixing zone in the deadleg, and is proportional to the length and the intensity of the mixing zone which consists of a series of opposite circulation flow. Additionally, at the same inlet velocity, although increasing the total length of the deadleg favours of the growth of the mixing zone and circulation flow, it will lead to a longer stagnant zone, which brings enormous challenges to industrial applications. Furthermore, to verify the numerical method adopted, flow visualisation experiment was conducted under three different lengths to diameter ratios. The comparison between the results photographed and calculated shows a good agreement. [ABSTRACT FROM AUTHOR]

Abstract: Membrane bioreactor (MBR) processes for the treatment of municipal and industrial wastewater have been extensively investigated in the past years. For this purpose, synthetic model feeds containing dissolved macromolecules and/or suspended solids were used to allow for a stable and reproducible feed composition. Lab-scale setups equipped with single membrane filaments and pilot plants containing single-bundle configurations were applied. Despite the fact that numerous of the corresponding findings were successfully transferred to large-scale MBR processes, it is expected that the filterability of activated sludge differs significantly from that of common model substances. Moreover, phenomena linked to the highly complex multi-phase flow of liquid, suspended solids and dispersed air bubbles which physically interacts with the membrane filaments make downsizing difficult. Therefore, the overall objective of this study was to evaluate the transferability of lab-scale microfiltration results to large-scale MBR processes. Our investigations have shown that the rheology of a model feed containing silica particles is similar to that of activated sludge with MLSS⩽3.5g/L. A noticeable sub-critical fouling was observed, but was removable by an intensive chemical cleaning using sodium hypochlorite. Lower fouling rates when increasing the aeration frequency with the same net aeration rate were found for both single-fibre and single-bundle tests, but are more pronounced on the larger scale. A macroscopic circulation flow affects the filtration performance of full-scale MBRs, but is difficult to mimic on a smaller scale. Fibre motion enhances the filtration performance, but is insensitive to packing density variations for bundles of up to four filaments. [Copyright &y& Elsevier]

Surface wave dynamics of falling film on the surface of periodic rectangular wall under monochromatic-frequency flowrate forcing disturbances is studied via numerical simulation. Waveforms formed on the periodic rectangular wall are different from those on the flat plate. At low frequency, the perturbation introduced at the inlet first undergoes a steady flow region and then develops into solitary waves. When the frequency becomes higher, solitary waves disappear. Film deformations in the steady flow region and characteristics of solitary waves are studied as the film travels down. There are circulations at the depression of periodic wall which are dependent on the local film characteristics and geometry of the corrugation. Moreover, the flow rate and geometry of the corrugations can also affect the evolvement of the monochromatic perturbation. [ABSTRACT FROM AUTHOR]

A toluene oxidation system is developed using an adsorbent and a nonthermal plasma (NTP) flow that consists of a surface discharge and a circulation flow. The liquid toluene is vaporized in the circulation line connected with a blower, the adsorbent, and the surface discharge plasma reactor in series, and the toluene gas is adsorbed by the adsorbent. Hydrophobic zeolite pellets are used as the adsorbent. After the toluene adsorption, ozone generated by the surface discharge is supplied to the adsorbent, and adsorbed toluene is oxidized on the surface of the adsorbent. Because the gas is circulated during toluene oxidation, ozone is used to oxidize toluene effectively and without waste. As a result, adsorbed toluene is efficiently converted to \COx\ (\CO + \CO2) using the NTP flow; 88% and 43% conversion ratios of toluene to \COx are achieved when 1 and 6 mL of toluene are oxidized for 90 and 150 min, respectively. In addition, \CO2 selectivity of more than 89% is obtained when 1 and 6 mL of toluene are oxidized. The conversion rate of toluene to \COx and the energy efficiency of the toluene-to-\COx conversion increase with the amount of adsorbed toluene. [ABSTRACT FROM AUTHOR]

Based on the solution of unsteady Reynolds equations (URANS) closed with the aid of differential equations for shear stresses transport (MSST), the evolution of the vortex structure in a square cavity with a moving lid and an unsteady turbulent heat transfer in the air medium are computed while maintaining constant temperatures of the hot moving and cold motionless walls (Re = 5·104). The phases of the development of dynamic and thermal processes are analyzed. [ABSTRACT FROM AUTHOR]