Influences of Co-Flow and Counter-Flow Modes of Reactant Flow Arrangement on a PEMFC at Start-Up

To investigate the influences of co-flowand counter-flowmodes of reactant flowarrangement on a proton exchange membrane fuel cell(PEMFC)during start-up,unsteady physical and mathematical models fully coupling the flow,heat,and electrochemical reactions in a PEMFC are established.The continuity equation and momentum equation are solved by handling pressure-velocity coupling using the SIMPLE algorithm.The electrochemical reaction rates in the catalyst layers(CLs)of the cathode and anode are calculated using the Butler-Volmer equation.The multiphase mixture model describes the multiphase transport process of gas mixtures and liquid water in the fuel cell.After validation,the influences of co-flow and counter-flow modes on the PEMFC performance are investigated,including the evolution of the current density,flow field,temperature field,and reactant concentration field during start-up,as well as the steady distribution of the current density,reactant concentration,andmembrane water content when the start-up stabilizes.Co-flow and counter-flow modes influence the current density distribution and temperature distribution.On the one hand,the co-flow mode accelerates the start-up process of the PEMFC and leads to a more evenly distributed current density than the counter-flow mode.On the other hand,the temperature difference between the inlet and outlet sections of the cell is up to 10.1℃ under the co-flow mode,much larger than the 5.0℃ observed in the counter-flow mode.Accordingly,the counter-flowmode results in a more evenly distributed temperature and a lower maximum temperature than the co-flow case.Therefore,in the flow field design of a PEMFC,the reactant flow arrangements can be considered to weigh between better heat management and higher current density distribution of the cell.

基于Web的工作流管理系统:co-Flow

讨论 Internet环境下协同产品开发的特征 ,研究它对工作流管理系统的要求 ;为适应这些要求 ,提出一个基于 Web的工作流管理系统软件体系结构 ;并详细介绍了该系统中的基于 XML的工作流过程定义和分布式工作流引擎间的互操作机制 .该系统的软件原型“co-Flow”能够适应

Formation of Copolymer-Ag Nanoparticles Composite Micelles in Three-dimensional Co-flow Focusing Microfluidic Device

A novel method was presented to create composite micelles of amphiphilic copolymers and Ag nanoparticles(NPs) in a three-dimensional co-flow focusing microfluidic device(3D CFMD). Self-assembly of the copolymers was initiated by the fast mixing of water and a blend dispersion of hydrophobic Ag NPs and amphiphilic copolymers. At the same time, the hydrophobic Ag NPs enter the core of copolymer micelles, based on the hydrophobic interaction. The copolymer-Ag NPs composite micelles have a core-shell structure with copolymer shell and Ag NPs core. COMSOL Multiphysics is used to simulate the concentration distribution of copolymers and Ag NPs under different flow rates. Co-assembly microfluidic conditions are determined based on simulation results. Under suitable microfluidic conditions, both block copolymers and gradient copolymers can co-assemble with hydrophobic Ag NPs to form composite micelles, respectively. This microfluidic coassembly method will have a good prospect in the preparation of composite micelles of amphiphilic copolymers and metal nanoparticles.

Hydrodynamics and Mass Transfer of Jet Co-flow Packing Tray

The jet co-flow packing tray(JCPT) with three different types of perforation in equal opening fraction was tested in two rectangular columns with 0.12m in width and 0.27m in length operated with air-water system. The influences of gas phase orifice F-factor and clear liquid height Hc on the amount of liquid lifted, Q, were examined. The corresponding correlation between Q with F-factor and equivalent diameter of perforated holes as well as Hc was obtained. Furthermore, the non-steady state mass transfer performance of JCPT was tested by the humidification of air with water. Finally, by the analysis of data and comparison, it was found that the JCPT tray with single cap and two holes exhibited the highest mass transfer efficiency and best performance.

The dynamic field in turbulent round jet discharging into a co-flowing stream

The effects of a co-flow on a spreading and entrainment rate of turbulent round jets have been studied numerically. The first and second order closure models are used and have been comp- ared with existing experimental data. The influence of theses models on the dynamic fields is examined. The results of the models in general agree well with the trends observed experiment- tally. The co-flowing imposed noticeable restri- ctions on the spreading and the turbulent mixing. Finally, an entrainment hypothesis has been introduced to describe the development of turbulent jets issuing into a stagnant or co-flowing air. It relates the mass flow rate of the surround- ing fluid entrained into the jet to the characteristic velocity difference between the jet and the co-flow. It is obvious that the co-flow decreases considerably the entrainment of air.

Numerical Study of Co-flow Jet Control on Corner Separation in Compressor Cascade

The design objectives of modern aircraft engines include high load capacity,efficiency,and stability.With increasing loads,the phenomenon of corner separation in compressors intensifies,affecting engine performance and stability.Therefore,the adoption of appropriate flow control technology holds significant academic and engineering significance.This study employs the Reynolds-averaged Navier-Stokes(RANS)method to investigate the effects and mechanisms of active/passive Co-flow Jet(CFJ)control,implemented by introducing full-height and partial height jet slots between the suction surface and end wall of a compressor cascade.The results indicate that passive CFJ control significantly reduces the impact of corner separation at small incidence,with partial-height control further enhancing the effectiveness.The introduction of active CFJ enables separation control at large incidence,improving blade performance under different operating conditions.Active control achieves this by reducing the scale of corner separation vortices,effectively reducing the size of the separation region and enhancing blade performance.

Numerical investigation of co-flow jet airfoil with parabolic flap

Both the Active Flow Control(AFC)and the variable-camber technology are considered as efficient ways to enhance the aerodynamic performance of an aircraft.The present study investigated the feasibility of the combination of a Co-Flow Jet(CFJ)airfoil and a parabolic flap,where the Reynolds Average Navier-Stokes(RANS)equations and the Spalart-Allmaras(S-A)turbulence model were exploited for the numerical simulation.Several significant geometric parameters,including the injection slot location,the suction slot location,the injection slot angle,the suction slot angle and the airfoil Suction Surface Translation(SST),were selected to study their effects on the aerodynamics of the proposed configuration.Then,an optimized design was created and compared with the baseline airfoil.The results show that the CFJ airfoil combined with the parabolic flap is more beneficial to the aerodynamic performance enhancement at small angles of attack.It is preferable to locate the injection slot at a 2%chord-wise location and the suction slot at a 75%chord-wise location.Both the decrease of the injection slot angle and the augmentation of the suction slot angle could reduce the drag.Furthermore,the SST of 0.5%chord is selected due to its high gain in the corrected aerodynamic efficiency at small angles of attack.Compared with the baseline,the optimized design could increase the lift coefficient and the corrected lift-to-drag ratio by 32.1%and 93.8%respectively at the angle of attack a=4°.

Experimental design for a novel co-flow jet airfoil

The Co-flow Jet(CFJ)technology holds significant promise for enhancing aerodynamic efficiency and furthering decarbonization in the evolving landscape of air transportation.The aim of this study is to empirically validate an optimized CFJ airfoil through low-speed wind tunnel experiments.The CFJ airfoil is structured in a tri-sectional design,consisting of one experimental segment and two stationary segments.A support rod penetrates the airfoil,fulfilling dual roles:it not only maintains the structural integrity of the overall model but also enables the direct measurement of aerodynamic forces on the test section of the CFJ airfoil within a two-dimensional wind tunnel.In parallel,the stationary segments are designed to effectively minimize the interference from the lateral tunnel walls.The experimental results are compared with numerical simulations,specifically focusing on aerodynamic parameters and flow field distribution.The findings reveal that the experimental framework employed is highly effective in characterizing the aerodynamic behavior of the CFJ airfoil,showing strong agreement with the simulation data.

服务创新网络中企业社会资本如何影响创新绩效——知识流耦合与知识共创的链式中介作用

基于社会网络理论与知识基础观,构建“企业社会资本—知识流耦合—知识共创—服务创新绩效”的链式中介模型,运用层次回归分析法对405份企业样本进行分析。研究发现:结构性、认知性、关系性社会资本均对服务创新绩效有显著正向影响,且影响程度依次减弱;知识流耦合、知识共创在企业社会资本与服务创新绩效之间起链式中介作用。研究可进一步夯实创新网络、社会资本理论基础,揭示企业社会资本通过知识作用路径影响服务创新绩效的内在机制,为服务企业提高创新绩效提供参考。

对置端曲面齿轮柱塞泵动态特性仿真研究

为了研究对置端曲面齿轮柱塞泵参数对泵动态特性的影响,根据端曲面齿轮柱塞泵工作原理,推导柱塞运动方程。利用Adams与AMESim软件建立对置端曲面齿轮柱塞泵联合仿真模型,通过联合仿真得到不同转速与偏心率下的柱塞泵出口流量与压力的相应曲线。结果表明:转速增大,泵出口流量与压力增大,脉动幅值与脉动频率增大;偏心率增加,泵出口流量与压力增大,脉动幅值增大,脉动频率不变。

进液量对气举式同向出流旋流器分离特性影响

为了提高旋流器的分离效率,提出一种气举式同向出流水力旋流器结构,通过注气的方式将旋流器轴心的油核举升至溢流口,加速油核向溢流口方向运动,进而提升旋流器的分离性能。基于雷诺应力模型(Reynolds Stress Model,RSM)与多相流模型(Mixture),模拟计算了入口进液量对气举式同向出流旋流器分离性能的影响,分析了进液量对旋流器内气核形态、速度场分布以及分离性能的影响规律。数值模拟结果表明:进液量分布在(3.6~8.4)m^(3)/h范围内时,随着进液量的增加,注气口处压力逐渐增大,混合液内各相介质的轴向速度与径向速度均有显著提高,旋流器轴心处的油相体积分数明显增大,旋流器的分离效率从64%增至77.9%。

旅游虚拟社区用户心流体验对价值共创的影响研究

旅游虚拟社区是用户实现分享旅游经历、获取旅游资讯和寻找出游同伴等功能的重要平台,也是企业实现精准营销的重要手段。企业和用户在虚拟社区共同投入、共同产出价值的过程称为价值共创。心流体验作为完全投入和集中注意力的积极心理状态,会影响用户与企业的契合程度,进而影响企业与用户之间的价值共创。文章通过对旅游虚拟社区用户数据进行采集与实证分析,揭示了用户心流体验对价值共创的影响机制。结果表明:内部动机和外部动机对用户产生的积极心理状态有显著正向影响;用户的积极心理状态及其与企业的契合程度对价值共创均有积极影响,且顾客与企业的契合程度在心流体验和价值共创过程中起部分中介作用。据此,文章提出了旅游虚拟社区企业可以通过提升用户参与动机,激发用户积极心理状态,强化顾客与企业之间密切关系,推动价值共创持续发展,实现引流交易和精准营销等管理启示。

改进7N喷头阻隔CO扩散有效性的模拟研究

为弥补常规组合式喷头存在的挡烟空隙不足,在普通7N喷头的基础上改进,设计出一种侧喷式7N喷头,并开展了数值模拟研究。通过对比下游截面处CO总质量通量、流场分布以及温度的变化情况,验证了改进喷头挡烟的有效性。在此基础上,分析了改进喷头在不同火源功率、流量、粒径下的作用效果。结果表明,普通喷头形成的雾幕能够有效降低通道温度,但并不能阻隔CO的扩散。在同样条件下,改进后的雾幕能够有效抑制CO蔓延,降温能力也有所提高,且其作用效果随喷头流量的增大更加显著。在流量为11.42 L/min时,下游CO质量通量及最高温度较改进前分别降低了71.64%、30.05%;即使火源功率增大至5 MW,改进后的雾幕仍能有效限制CO扩散;总体来看,粒径对CO的阻挡影响并不明显,对2 MW火灾的降温效果也在粒径200 m时达到最佳。

Aerodynamic performance enhancement forflapping airfoils by co-flow jet

Introducing active flow control into the design of flapping wing is an effective way to enhance its aerodynamic performance.In this paper,a novel active flow control technology called Co-Flow Jet(CFJ)is applied to flapping airfoils.The effect of CFJ on aerodynamic performance of flapping airfoils at low Reynolds number is numerically investigated using Unsteady Reynolds Averaged Navier-Stokes(URANS)simulation with Spalart-Allmaras(SA)turbulence model.Numerical methods are validated by a NACA6415-based CFJ airfoil case and a S809 pitching airfoil case.Then NACA6415 baseline airfoil and NACA6415-based CFJ airfoil with jet-off and jet-on are simulated in flapping motion,with Reynolds number 70,000 and reduced frequency 0.2.As a result,CFJ airfoils with jet-on generally have better lift and thrust characteristics than baseline airfoils and jet-off airfoil when Cμgreater than 0.04,which results from the CFJ effect of reducing flow separation by injecting high-energy fluid into boundary layer.Besides,typical kinematic and geometric parameters,including the reduced frequency and the positions of the suction and injection slot,are systematically studied to figure out their influence on aerodynamic performance of the CFJ airfoil.And a variable Cμjet control strategy is proposed to further improve effective propulsive efficiency.Compared with using constant Cμ,an increase of effective propulsive efficiency by22.6%has been achieved by using prescribed variable CμNACA6415-based CFJ airfoil at frequency 0.2.This study may provide some guidance to performance enhancement for Flapping wing Micro Air Vehicles(FMAV).

Numerical study of methane/air jet flame in vitiated co-flow using tabulated detailed chemistry

Two different combustion models,the autoignition(AI)model and flamelet/progress variable(FPV)model,have been applied to study the auto-ignition process of methane/air jet flame in vitiated co-flow.A priori study was conducted to test the validity of the two models.Results show that the different range of predicted reaction rates is mainly responsible for their different performances in large eddy simulation(LES)studies.In this paper,beta PDF was used to model the mixture fraction distribution,while two different shapes of PDF,delta function and beta function,were applied for the reaction progress.Compared to the FPV model,the AI model combined with beta function for reaction progress could capture the auto-ignition process and predict the exact lifted height.Also the results indicate that the variance of reaction progress plays an important role in predicting the flame lifted height.

Numerical investigation of dynamic stall suppression of rotor airfoil via improved co-flow jet

The decrease in aerodynamic performance caused by the shock-induced dynamic stall of an advancing blade and the dynamic stall of a retreating blade at low speed and high angles of attack limits the flight speed of a helicopter.However,little research has been carried on the flow control methods employed to suppress both the dynamic stall induced by a shock wave and the dynamic stall occurring at high angles of attack.The dynamic stall suppression of a rotor airfoil by Co-Flow Jet(CFJ)is numerically investigated in this work.The flowfield of the airfoil is simulated by solving Reynolds Averaged Navier-Stokes equations based on the sliding mesh technique.Firstly,to improve the effect of a traditional CFJ on suppressing rotor airfoil shock-induced dynamic stall,an improved CFJ—a CFJ-sloping slot is proposed.Research shows that the CFJsloping slot suppresses the shock-induced dynamic stall more effectively than a traditional CFJ.Moreover,the improved CFJ can also suppress the dynamic stall of rotor airfoil at low speed and high angles of attack.The improved CFJ proposed in this paper is an effective flow control method that simultaneously suppresses the dynamic stall of the advancing and retreating blades.The mechanism of the improved CFJ in suppressing the dynamic stall of the rotor airfoil is studied,and a comparison is made between the improved CFJ and the traditional CFJ in terms of dynamic stall suppression at high and low speed.Finally,the effect of improved CFJ parameters(the jet momentum coefficient,the position of the injection/suction slot,and the size of the injection/suction slot)on shock-induced dynamic stall suppression is analyzed.

Aerodynamic performance enhancement of co-flow jet airfoil with simple high-lift device

The present study performed a numerical investigation to explore the performance enhancement of a co-flow jet(CFJ)airfoil with simple high-lift device configuration,with a specific goal to examine the feasibility and capability of the proposed configuration for low-speed take-off and landing.Computations have been accomplished by an in-house-programmed Reynoldsaveraged Navier-Stokes solver enclosed by k-ωshear stress transport turbulence model.Three crucial geometric parameters,viz.,injection slot location,suction slot location and its angle were selected for the sake of revealing their effects on aerodynamic lift,drag,power consumption and equivalent lift-to-drag ratio.Results show that using simple high-lift devices on CFJ airfoil can significantly augment the aerodynamic associated lift and efficiency which evidences the feasibility of CFJ for short take-off and landing with small angle of attack.The injection and suction slot locations are more influential with respect to the aerodynamic performance of CFJ airfoil compared with the suction slot angle.The injection location is preferable to be located in the downstream of the pressure suction peak on leading edge to reduce the power expenditure of the pumping system for a relative higher equivalent lift-to-drag ratio.Another concluded criterion is that the suction slot should be oriented on the trailing edge flap for achieving more aerodynamic gain,meanwhile,carefully selecting this location is crucial in determining the aerodynamic enhancement of CFJ airfoil with deflected flaps.

回转窑中回收炉气与煤粉混合燃烧的数值模拟

针对回转窑-矿热炉工艺中工业炉窑的能耗大、废弃物排放量大且余热余能利用率低等问题,本研究设计了一款回转窑五通道燃烧器并将其用于炉气和煤粉混合燃烧,采用计算流体动力学(CFD)数值模拟的方法对回转窑内的气固两相燃料混合燃烧过程进行数值研究,分析了在气固两相燃料不同配比的工况下回转窑内温度场、流场、燃烧特性以及NO_(x)的变化规律。结果表明:掺入气体燃料有助于提高煤粉燃烧速率,改善窑内温度分布,降低NO_(x)排放量,火焰更加容易控制,呈现“棒槌形”。随着气体燃料的比例不断增加,高温区范围增大,焙烧区长度由9.16 m增加至14.17 m,炉窑出口处NO_(x)的含量由634 mg/m^(3)降低至29.8 mg/m^(3)。

电液伺服控制柱塞泵转速干扰及控制策略研究

为克服电机转速对电液伺服控制变量轴向柱塞泵输出特性产生的干扰问题,建立电液伺服控制轴向柱塞泵系统的Simulink-AMESim仿真模型,以恒流量为评价指标研究电机转速干扰条件下电液伺服控制变量柱塞泵恒流量控制的输出特性,分别利用传统PID及模糊自适应PID控制策略对电液伺服控制变量柱塞泵进行抗干扰控制,获得不同类型干扰情况下电液伺服控制变量泵系统的输出特性曲线。仿真结果表明:恒流量控制下,电液伺服控制变量柱塞泵的流量波动为3.80 L/min,当电机转速分别存在正弦波、方波及三角波脉冲扰动工况时,流量波动分别上升至9.34 L/min、9.59 L/min、4.52 L/min。分别利用PID及模糊自适应PID对电液伺服控制变量柱塞泵进行抗干扰控制,流量波动分别降低了3.41 L/min和5.90 L/min。

基于改进YOLOv8和多元特征的对虾发病检测方法

[目的/意义]对虾病害严重危害对虾养殖业。针对对虾病害发病快、死亡率高等特点,高密度的工厂化养殖等模式需要一种高效率对虾发病检测方法替代传统人工检查方法,实现对虾发病的及时预警。[方法]提出一种基于改进YOLOv8(You Only Look Once)和多元特征的对虾发病检测方法。首先利用改进YOLOv8网络从对虾夜间水面红外图像中进行前景提取,再利用Farneback光流法和灰度共生矩阵(Gray Level Co-occurrence Matrix,GLCM)提取对虾视频片段的运动特征与图像纹理特征,利用提取到的特征参数构建训练数据集,训练支持向量机(Support Vector Machine,SVM)作为分类器用于检测对虾视频片段,实现对正常与发病的对虾视频片段的检测分类。[结果和讨论]训练好的SVM分类器在300个测试样本上的表现为检测准确率平均值为83%,检测效果达到设计要求。检测误差主要是将发病片段错误地检测为正常片段。该误差主要受水面对虾数量和视频影响。[结论]本研究实现了对对虾发病的检测,提供了一种基于计算机视觉的检测方法。但受条件限制,仅在工厂化养殖环境下进行了实验,尚不能适用于多种养殖环境,仍有改进空间。