Effect of aspect ratio of elliptical stirred vessel on mixing time and flow field characteristics in the absence of baffles

Elliptical tanks were used as an alternative to circular tanks in order to improve mixing efficiency and reduce mixing time in unbaffled stirred tanks(USTs). Five different aspect ratios of elliptical vessels were designed to compare their mixing time and flow field. Computational fluid dynamics(CFD) simulations were performed using the k–ε model to calculate the mixing time and simulate turbulent flow field features, such as streamline shape, velocity distribution, vortex core region distribution, and turbulent kinetic energy(TKE) transfer. Visualization was also carried out to track the tinctorial evolution of the liquid phase. Results reveal that elliptical stirred tanks can significantly improve mixing performance in USTs. Specifically, the mixing time at an aspect ratio of 2.00 is only 45.3% of the one of a circular stirred tank. Furthermore, the secondary flow is strengthened and the vortex core region increases with the increase of aspect ratio. The axial velocity is more sensitive to the aspect ratio than the circumferential and radial velocity. Additionally, the TKE transfer in elliptical vessels is altered. These findings suggest that elliptical vessels offer a promising alternative to circular vessels for enhancing mixing performance in USTs.

What induced the trend shift of mixed-layer depths in the Antarctic Circumpolar Current region in the mid-1980s?

An obvious trend shift in the annual mean and winter mixed layer depth(MLD)in the Antarctic Circumpolar Current(ACC)region was detected during the 1960–2021 period.Shallowing trends stopped in mid-1980s,followed by a period of weak trends.The MLD deepening trend difference between the two periods were mainly distributed in the western areas in the Drake Passage,the areas north to Victoria Land and Wilkes Land,and the central parts of the South Indian sector.The newly formed ocean current shear due to the meridional shift of the ACC flow axis between the two periods is the dominant driver for the MLD trends shift distributed in the western areas in the Drake Passage and the central parts of the South Indian sector.The saltier trends in the regions north to Victoria Land and Wilkes Land could be responsible for the strengthening mixing processes in this region.

Wax deposition modeling in oil-water stratified pipe flow

Wax deposition in oil-water stratified flow is commonly encountered onshore and offshore oil production pipe systems,and typically reduces transportation capacity of oil.The accurate predicted model of wax deposition has becomes an indispensable approach to design effective remediation strategies.However,a reliable mechanistic model for wax deposition prediction in oil-water two-phase stratified pipe flow is lacking to validate the deposition process.In this work,a three-dimensional(axial,radial,and angular)robust wax deposit model for oil-water stratified circular pipe flow was developed.The model of formation of a gel deposit based on the first principles of rheology was developed,associated with the results obtained from hydrodynamics and heat/mass transfer simulations.The predictions for wax deposition are found to compare satisfactorily with experimental data with two different oils for single phase and four different water cuts for oil-water stratified pipe flow.It can be seen from the wax gelation mechanism that an increase in water cut can help to reduce the wall/oil-deposit interface shear stress,thereby leading to an increase in the degree of gelation as well as the deposit rate.Furthermore,a local deposit analysis in the circumferential direction was conducted,for water cut 75%and total flow rate 5 m3/h,which provided insights to understand that the thickness on pipe wall was roughly uniformly distributed locates near the top of the pipe and the nearer the position gets close to two points,where the oil-water interface contacts the inner wall,the deposition thickness quickly dropped to 0.It was attributed to the fact that a roughly uniformly thickness far away from the oil-water interface contact the inner wall resulted in the slowly changes temperature along the circumferential pipe wall wetted by oil.

Effect of Mixed Vegetation of Different Heights on Open Channel Flows

Vegetation of different heights commonly grows in natural rivers, canals and wetlands and affects the biodiversity and morphological process. The role of vegetation has drawn great attention in river ecosystems and environmental management. Due to the complexity of the vegetated flow, most previous research focuses on the effect of uniformed one-layered vegetation on the flow structure and morphological process. However, less attention was paid to the impact of the mixing vegetation of different heights, which is more realistic and often occurs in natural riverine environments. This paper aims to investigate the effect of mixing three-layered vegetation on flow characteristics, particularly the velocity distrbution, via a novel experiment. Experiments were performed in a titling water flume fully covered with vegetation of three heights (10, 15 and 20 cm) arranged in a staggered pattern, which is partially submerged. Velocities at different positions along a half cross-section were measured using a mini propeller velocimeter. Observed results showed that the velocity has a distinct profile directly behind vegetation and behind the vegetation gap. The overall profile has two distinct reflections about ? below or near the top of short vegetation (h): the velocity remains almost constant in the bottom layer ( h) the velocities directly behind the middle after short vegetation increase much faster than those directly behind the short after tall vegetation. The finding in this study would help river riparian and ecosystem management. .

Sap flow characteristics and physiological adjustments of two dominant tree species in pure and mixed plantations in the semi-arid Loess Plateau of China

It is essential to understand the water consumption characteristics and physiological adjustments of tree species under drought conditions,as well as the effects of pure and mixed plantations on these characteristics in semi-arid regions.In this study,the normalized sap flow(SFn),leaf water potential,stomatal conductance(gs),and photosynthetic rate(Pr)were monitored for two dominant species,i.e.,Pinus tabuliformis and Hippophae rhamnoides,in both pure and mixed plantations in a semi-arid region of Chinese Loess Plateau.A threshold-delay model showed that the lower rainfall thresholds(RL)for P.tabuliformis and H.rhamnoides in pure plantations were 9.6 and 11.0 mm,respectively,and the time lags(τ)after rainfall were 1.15 and 1.76 d for corresponding species,respectively.The results indicated that P.tabuliformis was more sensitive to rainfall pulse than H.rhamnoides.In addition,strong stomatal control allowed P.tabuliformis to experience low gsand Prin response to drought,while maintaining a high midday leaf water potential(Ψm).However,H.rhamnoides maintained high gsand Prat a lowΨmexpense.Therefore,P.tabuliformis and H.rhamnoides can be considered as isohydric and anisohydric species,respectively.In mixed plantation,the values of RLfor P.tabuliformis and H.rhamnoides were 6.5 and 8.9 mm,respectively;and the values ofτwere 0.86 and 1.61 d for corresponding species,respectively,which implied that mixed afforestation enhanced the rainfall pulse sensitivity for both two species,especially for P.tabuliformis.In addition,mixed afforestation significantly reduced SFn,gs,and Prfor P.tabuliformis(P<0.05),while maintaining a high leaf water potential status.However,no significant effect of mixed afforestation of H.rhamnoides was observed at the expense of leaf water potential status in response to drought.Although inconsistent physiological responses were adopted by these species,the altered water consumption characteristics,especially for P.tabuliformis indicated that the mixed afforestation requires further investigation.

Investigation of the oil-seawater mixed flow under an electromagnetic field

The electromagnetic separation method is a new approach to treat ship-based marine oily wastewater,in which oil droplets are dispersed in seawater(oil-seawater mixed flow).In order to clarify the separation process and determine the separation characteristics,the flow field and volume fraction of the oil droplets of the oil-seawater mixed flow under an applied electromagnetic field with different operating conditions were investigated by 2D numerical simulations with the Eulerian model.The results show that:(1)the downward Lorentz force causes seawater to flow downwards and the oil droplets to move upwards due to the electromagnetic separation force in the effective section of the separation channel;(2)the volume fraction of the oil droplets at the top of the outlet section increases with the current density,magnetic field,and the diameter of the oil droplet and decreases with the inlet velocity of the oily seawater.The results provide useful guidance for the design of electromagnetic separation devices of the oil-seawater mixed flow.

Application of the Modified nverse Design Method in the Optimization of the Runner Blade of a Mixed-Flow Pump

To improve the design speed and reduce the design cost for the previous blade design method, a modified inverse design method is presented. In the new method, after a series of physical and mathematical simplifications, a sail?like constrained area is proposed, which can be used to configure di erent runner blade shapes. Then, the new method is applied to redesign and optimize the runner blade of the scale core component of the 1400?MW canned nuclear coolant pump in an established multi?optimization system compromising the Computational Fluid Dynamics(CFD) analysis, the Response Surface Methodology(RSM) and the Non?dominated Sorting Genetic Algorithm?II(NSGA?II). After the execution of the optimization procedure, three optimal samples were ultimately obtained. Then, through comparative analysis using the target runner blade, it was found that the maximum e ciency improvement reached 1.6%, while the head improvement was about 10%. Overall, a promising runner blade inverse design method which will benefit the hydraulic design of the mixed?flow pump has been proposed.

Observed characteristics of flow,water mass,and turbulent mixing in the Preparis Channel

Preparis Channel is the very important exchange path of energy and materials between the northern Bay of Bengal and Andaman Sea(AS).A set of hydrographic measurements,a microstructure profiler,and a deep mooring were used to determine the characteristics of water masses,turbulent mixing,and flows in the Preparis Channel.The unprecedented short-term mooring data reveal that a deep current in the deep narrow passage(below 400 m)of the Preparis Channel flows toward the Bay of Bengal(BoB)with a mean along-stream velocity of 25.26 cm/s at depth of 540 m;above the deep current,there are a relatively weak current flows toward the AS with a mean along-stream velocity of 15.46 cm/s between 500 m and 520 m,and another weak current flows toward the BoB between 430 m and 500 m.Thus,a sandwiched vertical structure of deep currents(below 400 m)is present in the Preparis Channel.The volume transport below 400 m is 0.06 Sv(1 Sv=106 m^(3)/s)from the AS to the BoB.In the upper layer(shallower than 300 m),the sea water of the AS is relatively warmer and fresher than that in the BoB,indicating a strong exchange through the channel.Microstructure profiler observations reveal that the turbulent diffusivity in the upper layer of the Preparis Channel reaches O(10−4 m^(2)/s),one order larger than that in the interior of the BoB and over the continental slope of the northern AS.We speculate that energetic high-mode internal tides in the Preparis Channel contribute to elevated turbulent mixing.In addition,a local“hotspot”of turbidity is identified at the deep mooring site,at depth of about 100 m,which corresponds to the location of elevated turbulent mixing in the Preparis Channel.

Three-dimensional mixed convection stagnation-point fow past a vertical surface with second-order slip velocity

This study is concerned with the three-dimensional(3D)stagnation-point for the mixed convection flow past a vertical surface considering the first-order and secondorder velocity slips.To the authors’knowledge,this is the first study presenting this very interesting analysis.Nonlinear partial differential equations for the flow problem are transformed into nonlinear ordinary differential equations(ODEs)by using appropriate similarity transformation.These ODEs with the corresponding boundary conditions are numerically solved by utilizing the bvp4c solver in MATLAB programming language.The effects of the governing parameters on the non-dimensional velocity profiles,temperature profiles,skin friction coefficients,and the local Nusselt number are presented in detail through a series of graphs and tables.Interestingly,it is reported that the reduced skin friction coefficient decreases for the assisting flow situation and increases for the opposing flow situation.The numerical computations of the present work are compared with those from other research available in specific situations,and an excellent consensus is observed.Another exciting feature for this work is the existence of dual solutions.An important remark is that the dual solutions exist for both assisting and opposing flows.A linear stability analysis is performed showing that one solution is stable and the other solution is not stable.We notice that the mixed convection and velocity slip parameters have strong effects on the flow characteristics.These effects are depicted in graphs and discussed in this paper.The obtained results show that the first-order and second-order slip parameters have a considerable effect on the flow,as well as on the heat transfer characteristics.

Transient mixed convection flow arising due to thermal and mass diffusion over porous sensor surface inside squeezing horizontal channel

The double diffusion effect on the mixed convection flow over a horizontal porous sensor surface placed inside a horizontal channel is analyzed. With the appropriate transformations, the unsteady equations governing the flow are reduced to non-similar boundary layer equations which are solved numerically for the time-dependent mixed convection parameter. The asymptotic solutions are obtained for small and large values of the time-dependent mixed convection parameter. The results are discussed in terms of the skin friction, the heat transfer coefficient, the mass transfer coefficient, and the velocity, temperature, and concentration profiles for different values of the Prandtl number, the Schmidt number, the squeezing index, and the mixed convection parameter.

Efect of double dispersion on non-Darcy mixed convective flow over vertical surface embedded in porous medium

A numerical study of a non-Darcy mixed convective heat and mass transfer flow over a vertical surface embedded in a dispersion, melting, and thermal radiation is porous medium under the effects of double investigated. The set of governing boundary layer equations and the boundary conditions is transformed into a set of coupled nonlinear ordinary differential equations with the relevant boundary conditions. The transformed equations are solved numerically by using the Chebyshev pseudospectral method. Comparisons of the present results with the existing results in the literature are made, and good agreement is found. Numerical results for the velocity, temperature, concentration profiles, and local Nusselt and Sherwood numbers are discussed for various values of physical parameters.

EVOLUTION FILTRATION PROBLEMS WITH SEAWATER INTRUSION: TWO-PHASE FLOW DUAL MIXED VARIATIONAL ANALYSIS

Tow-phase flow mixed variational formulations of evolution filtration problems with seawater intrusion are analyzed. A dual mixed fractional flow velocity-pressure model is considered with an air-fresh water and a fresh water-seawater characterization. For analysis and computational purposes, spatial decompositions based on nonoverlapping multidomains, above and below the sea level, are variationally introduced with internal boundary fluxes dualized as weak transmission constraints. Further, parallel augmented and exactly penalized duality algorithms, and proximation semi-implicit time marching schemes, are established and analyzed.

Mathematical Modeling,Field Calibration and Numerical Simulation of Low-Speed Mixed Traffic Flow in Cities

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Effects of Meridional Flow Passage Shape on Hydraulic Performance of Mixed-flow Pump Impellers

During the process of designing the mixed-flow pump impeller, the meridional flow passage shape directly affects the obtained meridional flow field, which then has an influence on the three-dimensional impeller shape. However, the meridional flow passage shape is too complicated to be described by a simple formula for now. Therefore, reasonable parameter selection for the meridional flow passage is essential to the investigation. In order to explore the effects of the meridional flow passage shape on the impeller design and the hydraulic performance of the mixed-flow pump, the hub and shroud radius ratio (HSRR) of impeller and the outlet diffusion angle (ODA) of outlet zone are selected as the meridional flow passage parameters. 25 mixed-flow pump impellers, with specific speed of 496 under the design condition, are designed with various parameter combinations. Among these impellers, one with HSRR of 1.94 and ODA of 90° is selected to carry out the model test and the obtained experimental results are used to verify accuracies of the head and the hydraulic efficiency predicted by numerical simulation. Based on SIMPLE algorithm and standard k-ε two-equation turbulence model, the three-dimensional steady incompressible Reynolds averaged Navier-Stokes equations are solved and the effects of different parameters on hydraulic performance of mixed-flow pump impellers are analyzed. The analysis results demonstrate that there are optimal values of HSRR and ODA available, so the hydraulic performance and the internal flow of mixed-flow pumps can be improved by selecting appropriate values for the meridional flow passage parameters. The research on these two parameters, HSRR and ODA, has further illustrated influences of the meridional flow passage shape on the hydraulic performance of the mixed-flow pump, and is beneficial to improving the design of the mixed-flow pump impeller.

Effect of magnetic flow and external forcing current on mixed bursting in the pre-Botzinger complex

The pre-Botzinger complex(pre-BotC) in mammalian brainstem is essential for the generation of respiratory rhythms.Most dynamic studies on the pre-BotC neuron have been focused on its firing activities modulated by the ion conductances rather than that by the electromagnetic radiation or the external forcing current. In this paper, by adding the electromagnetic radiation and external forcing current to Park and Rubin’s model, we mainly investigate the influences of those two factors on the mixed bursting(MB) of single pre-BotC neuron. First, we explore how the variation of external forcing current affects the MB patterns of the system with non-vanishing magnetic flux. We classify the MB patterns and show their dynamic mechanism through fast-slow decomposition and bifurcation analysis. Then, by modifying the feedback coefficient, we further analyze the sole effect of electromagnetic radiation on the firing activities of the system. Our results may be instructive in understanding the dynamical behavior of pre-BotC neuron.

Experimental Study of the Influence of Flow Passage Subtle Variation on Mixed-flow Pump Performance

In the mixed-flow pump design, the shape of the flow passage can directly affect the flow capacity and the internal flow, thus influencing hydraulic performance, cavitation performance and operation stability of the mixed-flow pump. However, there is currently a lack of experimental research on the influence mechanism. Therefore, in order to analyze the effects of subtle variations of the flow passage on the mixed-flow pump performance, the frustum cone surface of the end part of inlet contraction flow passage of the mixed-flow pump is processed into a cylindrical surface and a test rig is built to carry out the hydraulic performance experiment. In this experiment, parameters, such as the head, the efficiency, and the shaft power, are measured, and the pressure fluctuation and the noise signal are also collected. The research results suggest that after processing the inlet flow passage, the head of the mixed-flow pump significantly goes down; the best efficiency of the mixed-flow pump drops by approximately 1.5%, the efficiency decreases more significantly under the large flow rate; the shaft power slightly increases under the large flow rate, slightly decreases under the small flow rate. In addition, the pressure fluctuation amplitudes on both the impeller inlet and the diffuser outlet increase significantly with more drastic pressure fluctuations and significantly lower stability of the internal flow of the mixed-flow pump. At the same time, the noise dramatically increases. Overall speaking, the subtle variation of the inlet flow passage leads to a significant change of the mixed-flow pump performance, thus suggesting a special attention to the optimization of flow passage. This paper investigates the influence of the flow passage variation on the mixed-flow pump performance by experiment, which will benefit the optimal design of the flow passage of the mixed-flow pump.

Mixed traffic flow modeling near Chinese bus stops and its applications

To determine how bus stop design influences mixed traffic operation near Chinese bus stops,a new theoretical method was developed by using additive-conflict-flows procedure.The procedure was extended from homogeneous traffic flow to mixed traffic flow.Based on the procedure and queuing theory,car capacity and speed models were proposed for three types of bus stops including curbside,bus bay and bicycle detour.The effects of various combinations of bus stop type,traffic volume,bus dwell time,and berth number on traffic operations were investigated.The results indicate that traffic volume,bus dwell time and berth number have negative effects on traffic operations for any type of bus stops.For different types of bus stops,at car volumes above approximately 200 vehicles per hour,the bus bay and bicycle detour designs provide more benefits than the curbside design.As traffic volume increases,the benefit firstly increases in uncongested conditions and then decreases in congested conditions.It reaches the maximum at car volumes nearly 1 100 vehicles per hour.The results can be used to aid in the selection of a preferred bus stop design for a given traffic volume in developing countries.

Convective heat and mass transfer in MHD mixed convection flow of Jeffrey nanofluid over a radially stretching surface with thermal radiation

Mixed convection flow of magnetohydrodynamic(MHD) Jeffrey nanofluid over a radially stretching surface with radiative surface is studied. Radial sheet is considered to be convectively heated. Convective boundary conditions through heat and mass are employed. The governing boundary layer equations are transformed into ordinary differential equations. Convergent series solutions of the resulting problems are derived. Emphasis has been focused on studying the effects of mixed convection, thermal radiation, magnetic field and nanoparticles on the velocity, temperature and concentration fields. Numerical values of the physical parameters involved in the problem are computed for the local Nusselt and Sherwood numbers are computed.

Dynamics of Motorized Vehicle Flow under Mixed Traffic Circumstance

为了学习混合交通的动力学，流动由组成机械化并且非机械化的车辆，一个汽车追随者模型基于免费、小心的碰撞的原则，开车被建议。侧面的磨擦并且重叠开车被介绍描述在机械化车辆和非机械化的车辆之间的相互作用。由数字模拟，流动密度关系，时间空间的动力学，和速度进化详细被调查。结果显示非机械化的车辆在机械化车辆流动上有重要影响并且引起最大的流动在大约 13% 衰退。非机械化的车辆能减少机械化车辆速度和原因速度摆动当机械化车辆密度是低的时。而且，非机械化的车辆在震荡的速度上看重要抑制效果密度是否是中等的，高度，和如此的效果是机械化了车辆密度增加变弱。结果也强调为分开的必要性从非机械化的车辆机械化了车辆。

AN EFFICIENT METHOD FOR SOLVING THE MIXED DIRECT-INVERSE PROBLEM OF THE TRANSONIC ROTATIONAL FLOW IN PLANE CASCADES

The method in [1] has been extended to the case of rotational flow in this paper. A new method for dealing with the shock wave is presented. This method has the advantages of both the shock-fitting and the shock capturing methods. The direct problem and the mixed direct-inverse prob- lem of the rotational flow in a transonic plane cascade at both design and off design conditions are solved, and the results show that the present method has rapid convergence rate and high accuracy even for the flow with moderately strong shocks. The calculations have been carried out on the DPS-8 computer, and for the direct problem, only 50-80 iterations are needed, and 50-80 seconds of CPU time are required.