CFD Analysis of Spiral Flow Fields in Proton Exchange Membrane Fuel Cells

Proton exchange membrane fuel cells(PEMFCs)are largely used in various applications because of their pollution-free products and high energy conversion efficiency.In order to improve the related design,in the present work a new spiral flow field with a bypass is proposed.The reaction gas enters the flow field in the central path and diffuses in two directions through the flow channel and the bypass.The bypasses are arranged incrementally.The number of bypasses and the cross-section size of the bypasses are varied parametrically while a single-cell model of the PEMFC is used.The influence of the concentration of liquid water and oxygen in the cell on the performance of different flow fields is determined by means of Computational fluid dynamics(COMSOL Multiphysics software).Results show that when the bypass number is 48 and its cross-sectional area is 0.5 mm^(2),the cell exhibits the best performances.

TWO DIMENSIONAL SUBSONIC AND SUBSONIC-SONIC SPIRAL FLOWS OUTSIDE A POROUS BODY

In this paper,we investigate two dimensional subsonic and subsonic-sonic spiral flows outside a porous body.The existence and uniqueness of the subsonic spiral flow are obtained via variational formulation,which tends to a given radially symmetric subsonic spiral flow at far field.The optimal decay rate at far field is also derived by Kelvin ’s transformation and some elliptic estimates.By extracting spiral subsonic solutions as the approximate sequences,we obtain the spiral subsonic-sonic limit solution by utilizing the compensated compactness.The main ingredients of our analysis are methods of calculus of variations,the theory of second-order quasilinear equations and the compensated compactness framework.

Experimental Research on Gas-Liquid Two-Phase Spiral Flow in Horizontal Pipe

In view of the importance of gas-liquid two-phase spiral flow and the few research reports at home and abroad,the gas-liquid two-phase spiral flow patterns have been researched in a horizontal pipe with different parameters investigated by means of observation and a high-speed camera.Since the appearance of spiral flow makes the distribution of twophase flow more complicated,the flow patterns appearing in the experiments were divided into the Spiral Wavy Stratified Flow(SWS),the Spiral Bubble Flow(SB),the Spiral Slug Flow(SS),the Spiral Linear Flow(SL),the Spiral Axial Flow(SA),and the Spiral Dispersed Flow(SD) by the observations and with reference to the predecessors' research achievements.A flow pattern map has been drawn up.The influence of velocity,vane angle and vane area on flow pattern conversion boundary and pressure drop has been studied,with a solid foundation laid for the future research work.

BASIC HYDRODYNAMICS CHARACTERISTICS OF CAVITY SPIRAL FLOW IN A LARGE SIZE LEVEL PIPE

Based on the observation of a model test and in combination with some theoretical analysis, the researches of some basic hydrodynamics characteristics of cavity spiral flow in a large size level pipe with a shaft-inlet is presented in the paper, which include the basic flow pattern, formation condition of the cavity spiral flow, discharge Q, cavity diameter d0, wall pressure coefficient Cpw, velocity distribution, total energy dissipation rate η etc. The results show that the basic flow patterns can be divided into three zones according to the variations in amount of ventilation Ф, cavity diameter d0 and gas pressure p0 within cavity spiral flow when the upstream and downstream water level changes and that the basic hydrodynamics characteristics change with the flow pattern and have the different behaviour.

TRANSPORT EFFICIENCY OF THE SPIRAL FLOW IN CIRCULAR PIPE

A concise definition of Transport Efficiency (TE) was given to examine the amount of transported grains in the pipe flow with certain energy consumption. The transport characteristics and the so-called 'roto-floating' characteristics were studied from the tests of sediment transport in the normal pipe flow and the spiral pipe flow, and hereby the energy gradients of the two kinds of pipe flows were obtained. By comparing the mean concentrations at the same gradient, it was concluded that the TE of the latter is several times to over ten times higher than that of the former, and the lift of the latter is 200 times larger than that of the former for the nearly same TE. The spiral flow in circular pipe is suitable for transporting fine grains of high concentration, and with sedimentation trend and coarse grains.

Predicting Endometrium Receptivity with Parameters of Spiral Artery Blood Flow

In order To evaluate whether the parameters of spiral artery blood flow, as measured by transvaginal color Doppler, may be used to assess endometrium receptivity prior to embryo transfer (ET), a retrospective study of 94 infertile women who had undergone ART treatments with different outcomes (pregnant or nonpregnant) was done. Subendometrial blood flow was evaluated. The resistance index (RI), systolic/diastolic ratio (S/D) and pulsatility index (PI) were significantly lower in those who achieved pregnancy as compared with those who did not: 0.62±0.04 vs 0.68±0.04 (P<0.001), 2.66±0.33 vs 3.19±0.39 (P<0.01) and 1.15±0.17 vs 1.34±0.22 (P<0.05), respectively. Furthermore, when RI>0.72, PI>1.6, and S/D>3.6, no pregnancy occurred. These data suggest that the parameters of spiral artery blood flow could be used as a new assay in predicting endometrial receptivity before ET.

Aspiration spiral-flow type centrifugal flotation machine

Aspiration spiral flow type centrifugal flotation machine takes full advantage of centrifugal force field and gravitational field, and strengthens flotation of coal slurry. As a new-type flotation machine of high efficiency, its key component is bubble generator. Which completes the process of ore pulp inflation and liberalization. The design, parameters and working principle of bubble generator provide the design of the same device in similar equipment with reference. The result of industrial operation shows that this machine is of such features as small occupational area, greater concentration ratio, high processing capacity, high efficiency and lower investment etc.

Study of Spiral Flow Generated through an Annular Slit

The effect of pressurized air inlets in the reservoir upstream of the annular slit on characteristics of the axial and tangential velocity components is investigated numerically, and the mechanism of occurrence of spiral nozzle flow is clarified. In simulations, Unified Platform for Aerospace Computational Simulation (UPACS) is used. The governing equations under consideration are the unsteady compressible Navier - Stokes. A second-order finite volume scheme with MUSCL (Roe scheme) is used to discretize the spatial derivatives, and a second order-central difference scheme for the viscous terms, and a MFGS (Matrix Free Gauss Seidel) is employed for time integration. Spalart-Allmaras model was used as a turbulence model. The results obtained are compared with velocity distributions in the experiment measured by the two-component fiber optic laser Doppler velocimeter system. The existence of discrete pressurized air inlets that leads to the occurrence of asymmetrical characteristics is a very important factor for the formation of spiral flow.

Hemodynamic effects of the spiral flow guider on small-diameter vascular graft

Small-diameter vascular grafts are in large demand for coronary and peripheral bypass procedures, but present products still fail in long-term clinical application. Hence, A new type of small-diameter vascular graft(SDVG) is designed with a spiral flow guider to induce spiral blood flow and thus improve the local hemodynamic performance. In present article, to investigated how the spiral flow guider influenced the hemodynam ic performance of this new SDVG, via computational fluid dynamics(CFD). The numerical results demonstrate that: 1) the spiral flow guider could indeed make the blood flow rotate; 2) the blood velocity near the vessel wall and wall shear rate(WSR) w ere greatly enhanced; 3) the number of the helical turns had obvious non-positive correlation with the hemodynamic performan ce of the new graft. It is believed that the increased blood velocity near the wall and the WSR are conductive to anti-throm bosis and anti-hyperplasia, hence the graft patency rate for long-term clinical use can be improved. Present study may also h elp better understand the optimal design of the spiral flow guider for the purpose of prolonging the long-term patency rate of th e SDVG.

Flow Dynamics of a Spiral-groove Dry-gas Seal

The dry-gas seal has been widely used in different industries. With increased spin speed of the rotator shaft, turbulence occurs in the gas film between the stator and rotor seal faces. For the micro-scale flow in the gas film and grooves, turbulence can change the pressure distribution of the gas film. Hence, the seal performance is influenced. However, turbulence effects and methods for their evaluation are not considered in the existing industrial designs of dry-gas seal. The present paper numerically obtains the turbulent flow fields of a spiral-groove dry-gas seal to analyze turbulence effects on seal performance. The direct numerical simulation （DNS） and Reynolds-averaged Navier-Stokes （RANS） methods are utilized to predict the velocity field properties in the grooves and gas film. The key performance parameter, open force, is obtained by integrating the pressure distribution, and the obtained result is in good agreement with the experimental data of other researchers. Very large velocity gradients are found in the sealing gas film because of the geometrical effects of the grooves. Considering turbulence effects, the calculation results show that both the gas film pressure and open force decrease. The RANS method underestimates the performance, compared with the DNS. The solution of the conventional Reynolds lubrication equation without turbulence effects suffers from significant calculation errors and a small application scope. The present study helps elucidate the physical mechanism of the hydrodynamic effects of grooves for improving and optimizing the industrial design or seal face pattern of a dry-gas seal.

Heat transfer characteristics of air cross-flow for in-line arrangement of spirally corrugated tube and smooth tube bundles

An experimental study on heat transfer and resistance coefficients of linearly arranged smooth and spirally corrugated tube bundles in cross-flow was performed. The heat transfer and resistance coefficients are presented in this paper with transverse and longitudinal tube-pitch and tube geometries taken into account. The experiment's results can provide technical guidelines for application to horizontal air preheater with arranged in-line spirally corrugated tube bundles, especially to the air preheater for CFBCBs (Circulating Fluidized Bed Combustion Boilers).

Fluid flow and heat transfer characteristics of spiral coiled tube: Effects of Reynolds number and curvature ratio

Numerical analysis was performed to investigate flow and heat transfer characteristics in spiral coiled tube heat exchanger. Radius of curvature of the spiral coiled tube was gradually increased as total rotating angle reached 12π. As the varying radius of curvature became a dominant flow parameter, three-dimensional flow analysis was performed to this flow together with different Reynolds numbers while constant wall heat flux condition was set in thermal field. From the analysis, centrifugal force due to curvature effect is found to have significant role in behavior of pressure drop and heat transfer. The centrifugal force enhances pressure drop and heat transfer to have generally higher values in the spiral coiled tube than those in the straight tube. Even then, friction factor and Nusselt number are found to follow the proportionality with square root of the Dean number. Individual effect of flow parameters of Reynolds number and curvature ratio was investigated and effect of Reynolds number is found to be stronger than that of curvature effect.

基于子宫内膜结构与子宫螺旋动脉血流参数构建人工授精妊娠预测模型及验证

背景:现子宫内膜结构及子宫螺旋动脉血流参数对夫精宫腔内人工授精(artificial insemination by husband,AIH)妊娠率的影响水平尚不明确,该研究通过校准其他混杂因素后,确定了其独立影响因素,并构建了预测模型,具有较好的临床应用效能。目的:基于子宫内膜结构及子宫螺旋动脉血流参数构建AIH临床妊娠预测模型及验证。方法:回顾性分析2017年1月至2021年1月于常州市妇幼保健院接受AIH助孕治疗患者共1299例,将其中1182例未临床妊娠者纳入未妊娠组,117例临床妊娠者纳入妊娠组;通过1∶1倾向评分匹配,妊娠组与未妊娠组各匹配成功93例;采用单、多因素分析筛选子宫内膜结构及子宫螺旋动脉血流参数对AIH结局的影响因素,通过受试者工作曲线确定各独立影响因素的最佳截断值,限制性立方样条法分析各独立影响因素对AIH妊娠影响的风险趋势,临床决策曲线与临床影响曲线对该联合预测模型的临床应用效能进行检验。结果与结论:①倾向评分后妊娠组与未妊娠组各非内膜因素均无显著统计学意义,数据具有较好的均衡性(P>0.05);②单因素分析结果显示,内膜下血管化指数、血流指数、血管化血流指数、子宫动脉阻力指数、子宫动脉搏动指数、收缩期最高血流速度/舒张期末血流速度、基底子宫内膜到外子宫肌层内层平均交界区、最大交界区厚度为AIH妊娠的影响因素(P<0.05);③多因素Logistic回归结果显示,基底子宫内膜到外子宫肌层内层平均交界区厚度、子宫动脉搏动指数、血管化血流指数为AIH妊娠的独立影响因素,影响大小依次为血管化血流指数>基底子宫内膜到外子宫肌层内层平均交界区厚度>子宫动脉搏动指数;④受试者工作曲线显示,血管化血流指数的曲线下面积为0.704(0.629,0.779),最佳截断值为6.26;基底子宫内膜到外子宫肌层内层平均交界区厚度的曲线下面积为0.660(0.582,0.739),最佳截断值为6.38;子宫动脉搏动指数的曲线下面积为0.642(0.563,0.721),最佳截断值为1.18;⑤限制性立方样条曲线显示,当血管化血流指数>6.24时,其对AIH妊娠具有显著的正影响趋势;基底子宫内膜到外子宫肌层内层平均交界区厚度≤6.55 mm时,其对AIH妊娠具有显著的正影响趋势;当子宫动脉搏动指数>1.27时,其对AIH妊娠具有负影响风险;⑥临床决策曲线与临床影响曲线显示,该联合预测模型在阈概率值为0.17-0.93时具有临床最大净获益,且在该阈概率范围内损失与获益的比值始终小于1,显示出该联合预测模型具有较好的临床效能;⑦结果表明,通过倾向评分与多因素Logistic回归校正子宫内膜外其他混杂因素后,基底子宫内膜到外子宫肌层内层平均交界区厚度、子宫动脉搏动指数、血管化血流指数为AIH妊娠的独立影响因素,通过对其最佳截断值的确定与风险趋势性评估,证实该联合预测模型具有较好的预测价值与临床应用效能。

静态混合器结构优化设计与流场特性分析

为油田高能效驱油以提高原油产量,针对SK型和SX型静态混合器混合单元结构,通过创新设计和三维建模开发多重螺旋混合单元静态混合器,基于静态混合原理,利用FLUENT数值模拟软件,采用有限体积法,对所开发混合器内流体的流场进行仿真分析,研究该结构静态混合器的流动特性,结果表明,该种静态混合器使流体产生剪切和正反向涡旋作用,流体被充分扰动,混合均匀,满足油田注聚驱油要求,可为油田开发新型高效静态混合器提供一定技术支持。

Middle or low water pressure direct spiral double helix converging nozzle structure optimization and flow field analysis

In order to solve the problem of using middle or low water pressure to form fine water mist,a new nozzle is proposed in fire rescue robot.Existing water mist nozzles are basically used for high pressure and in large size,complex structure and poor low pressure atomization effect in comparison with requirement of snake-like fire rescue robots.On the basis of comprehensive typical spray nozzles,a direct spiral double helix converging nozzle(DSDHCN) is proposed,which has the advantages of small volume,light weight,simple structure,and convenient installation.To make the spray nozzle have good performance,and meet the requirements of more efficient fire extinguishing,a numerical study is carried out to analyze the internal and external full flow field of nozzle.A gas-liquid two-phase flow is applied to simulate the external full flow field of nozzle with VOF model in fluent software.The simulation results show the real situation of water flow out of the atomization nozzle and the water jet trajectory.Some simulations about middle or low water pressure direct spiral double helix converging optimized nozzle have been done in 30 bar pressure.The simulation results show that the optimized nozzle structure not only makes the spray droplets have a good cone angle,but also have a sufficient axial velocity,which proves the structure rationality of the proposed optimized nozzle.

流动阻力对螺旋溜槽分选流场的影响

螺旋溜槽是一种应用广泛的流膜重力选矿设备,矿物的分选是在只有几毫米的薄层流体中完成的,分选流体的流态对矿物的分选有着重要的影响,而流动阻力是影响流体流态和流场特征的重要因素。在螺旋溜槽分选过程中,影响流动阻力的主要因素有槽面粗糙度及矿浆黏度,为了探明流动阻力对于螺旋溜槽流场特征的影响规律,借助CFD技术对直径为1200mm的螺旋溜槽槽内流体流态与螺旋槽面粗糙度、矿浆黏度之间的关系进行了研究。结果表明,随着槽面粗糙度、矿浆黏度的减小(即流动阻力的减小),内缘流膜厚度呈减小趋势而外缘流膜厚度呈增大趋势,流膜形态内缘薄外缘厚的特征进一步加强;溜槽内缘层流区域的占比呈增大趋势,但所能达到的最大雷诺数有所增大;溜槽外缘最大切向速度呈增大趋势;二次环流区域呈向槽外缘扩充趋势,二次环流的强度呈增强趋势。研究结果可为螺旋溜槽表面摩擦系数及矿浆黏度的选择提供参考。

叶顶间隙对螺旋混流式喷水推进泵内流及推进特性的影响

喷水推进泵是舰船泵喷推进系统的核心部件,喷水推进泵在工作过程中,叶顶间隙处所产生的泄漏流会严重影响混流泵的工作性能。为了探讨叶轮叶顶间隙对喷水推进泵推进特性的影响,本文定义了叶顶间隙系数τ,设计了六种不同叶顶间隙系数模型并使用Ansys进行仿真分析,最终得到叶顶间隙对于喷水推进泵内流以及推进特性的影响规律。结果表明:随着叶顶间隙系数的增大,叶顶间隙处泄漏流逐渐增加,泄漏涡影响范围变大,轴向推力随着叶顶间隙系数的增大呈负指数下降,叶顶间隙处泄漏量随指数上升,喷水推进泵内流损失增加,推进效率持续减小,并且在大流量工况下叶顶间隙对喷水推进泵推进特性影响最大,在设计的六套模型中,叶顶间隙系数为0.08,叶顶间隙为0.16mm时效率最高。通过本文的研究可以发现,叶顶间隙对于喷水推进泵内流以及推进特性影响较大,在设计时应尽量减小叶顶间隙。

A Numerical Study on Fully Developed Fluid Flow and Heat Transfer in a Spiral Finned Tube

In this paper, the standard k-εtwo-equation model is adopted to numerically simulate fully developed fluid flow and heat transfer in a spiral finned tube within a cracking furnace for ethylene manufacturing. By variable transformation, the orlglnal 3-D problem is converted into a 2-D problem in spiral coordinates. The algorithm of SIMPLEC is used to study the fully developed fluld flow and heat transfer in the spiral finned tube at constant periphery temperature and constant axial heat flux, The computed results agree pretty well with the experimental data obtained from the industry, Further studies on the fluid flows and temperature profiles at different Reynolds numbers within straight and spiral finned tubes are conducted and the mechanisms involved are explored. It is found that with the spiral finned tube, pressure drop increases to a great extent whereas heat transfer tends to be decreased.

逆流式双螺旋叶片气液固多相旋流分离特性

针对海洋平台空间的局限性和天然气水合物开采特殊工况,设计了一种结构紧凑、分离效率较高、维护成本低的逆流式双螺旋叶片气液固多相旋流分离器,以期实现海上平台天然气、泥质粉砂和海水多相混流的高效分离。综合高含气、高流量、小粒径等因素耦合作用,建立气液固多相分离湍流数学模型,采用SIMPLE压力-速度耦合算法进行求解,揭示螺距、螺旋叶片头数和螺旋圈数等叶片结构参数对气液固多相旋流分离性能的影响规律;并依据气液固多相旋流分离双螺旋叶片的单因素优化结果,量化分析入口流速、含气体积分数、泥质粉砂粒径等生产参数对气液固多相旋流分离性能的影响程度。研究结果表明:当螺旋叶片的螺距为70 mm、螺旋头数为2且螺旋圈数为3时,逆流式双螺旋叶片气液固多相旋流分离性能最佳;增大入口流速可有效提高分离效率,入口流速达到3.0 m/s时,气、固两相分离效率分别提高至98.6%和83.2%;而含气体积分数由30%增至45%时,气相分离效率由99.4%降至96.5%,且气相出口含气体积分数由81.1%增至91.9%;泥质粉砂的粒径尺寸会影响分离效率,粒径尺寸为70 um时,分离效率可达93.4%。所得结论可为适用于天然气水合物开采的气液固多相分离器的设计和优化提供参考。

黏度对管内螺旋流径向压差的影响规律研究

管内油水两相螺旋流的径向压差特性在多相流测量方面表现出非常好的应用前景。文章基于计算流体动力学(CFD)方法,研究不同流量(10~80 m3/d)、不同含水率(30%~90%)及不同油相黏度(50~15000 mPa·s)对管内油水两相流螺旋流径向压差特性的影响规律。分析不同工况下管内油水两相螺旋流流场特性,揭示油水混合流量、含水率与径向压差间的关系。研究结果表明:在油相黏度较低时,油水两相流通过旋流器后会形成稳定的“油核+水环”。当含水率和油水混合表观流速保持一定时,随着油相黏度增加,径向压差逐渐下降。当油相黏度超过10000 mPa·s后,径向压差与黏度无关,只取决于油水的混合流量。且发现径向压差与油水混合流量之间具有高度相关性,可以利用此机理,实现油水两相流流量测量。