多路热气流量控制及其在防除冰试验中的应用

流量精确控制是保证结冰风洞热气防除冰试验成功的关键,针对传统调节阀控制存在受下游影响大和多路流量控制耦合的问题,设计了一套多路热气流量控制系统,采用背压阀对各支路流量控制单元入口压力进行精确控制,通过电作动筒改变各支路针阀喉道流通面积,结合临界流文氏管流量计流量测量,实现多路流量解耦控制。试验表明,多路热气流量控制系统可实现多路流量解耦控制,调节速度快,10 s左右即可达到目标流量,控制精度高,稳定后最大相对误差小于0.6%,该系统可为我国后续飞行器防除冰试验系统验证与适航审定提供有力支撑。     

新型煤粉流量调节阀性能研究

在煤粉密相输送实验装置中,研究了工业规模级管径的新型煤粉流最调节阀性能.通过改变阀门参数和操作条件,观察阀芯结构对煤粉输送特性的影响.在对不同阀芯结构的阀门进行系统测试与分析的基础上,得出了优选的阀芯结构.研究结果表明.在相同煤粉流量下,不同阀芯结构的阀门所获得的固气比大致相等;在优选的阀芯结构下,当节流面积变化范围为12%～100%,与之对应的煤粉流量调节范围为50%～96%;随着节流面积的减小,煤粉输送稳定性变弱.     

基于PID的流量调节阀的设计

针对流量控制,设计了一种结构简单、控制方便、精度高的基于PID的流量调节阀。流量调节阀主要由手动平衡阀、流量传感器、步进电机和控制器四部分组成,控制器采用PID算法控制步进电机。检测步进电机电流的大小不仅能确定手动平衡阀是否到达了极限调节值,也可以防止过电流损坏电机。实验测试中,用PC机对输出流量值进行设定和对流量调节阀的控制效果进行分析。通过反复试验,证明了输出的流量值能准确快速的跟随设定值的变化而变化。研究表明,基于PID的流量调节阀能实现高精度的流量控制。     

压力位差式层流流量传感元件数值模拟研究

层流流量计具有量程比宽、测量准确、响应快等优点,适用于气体微小流量测量。但是传统层流流量元件取压点之间并不完全是充分发展段层流流动,所测得差压中存在非线性压力损失。本文介绍了可以将非线性压损予以消除的压力位差式(PPD)层流流量传感技术,采用计算流体力学方法对PPD传感元件两条支路内部流动进行仿真分析,得到了各支路内部流速场和压力场,两条支路的流动阻力特性,以及压力位差与体积流量关系曲线。结果表明,PDD层流流量传感单元两条支路流阻特性一致,压力位差与流量具有理想的线性关系,验证了PDD原理的正确性,相对于传统层流传感元件,PDD层流流量传感元件可以有效将非线性压损消除,能够获得更高的测量精度和更大的量程比。     

“调节阀选用技术”讲座——第二讲 调节阀口径的选择

调节阀最佳口径的选择是调节阀选择中的重要内容之一。调节阀能否正常地运转以及调节阀性能的好坏都与调节阀口径选择得是否正确有着密切的关系。一、调节阀计算压差的选择调节阀对流体流量进行调节时,必然会产生一定的压力损失,也就是说调节阀前后应有一定的压差。压差的选择关系到调节阀口径计算的正确性、调节性能的好坏和设备动力的经济性,因此是调节阀计算中最关键的问题之一。从全装置的经济投资及节约能源出发,希望调节阀上的压力损失尽可能地小,这样可以选择小扬程的泵以节约动力。但从工作特性分析知道,调节阀在系统中必须占有一定的压差才有较好的调节     

一种新型三相流测量系统的研制

利用成熟的单相流测量仪的基本原理 ,研制了一种新的三相流在线检测仪及其系统。应用热扩散法来测量气液比 ,设计的灵巧电容探头来测量油水比 ,该仪器可适合各种不同生产条件的油田的三相流测量     

离心机控制电路改进

对KCWL系列离心机控制电路进行改进,增加了对三通调节阎的控制电路,实现了离心机正常停机或故障停机时控制三通调节阀自动切换到旁通管路的功能.     

计算机在调节阀选择和计算中的应用

在研究IEC和ISA调节阀选择计算方法的基础上,设计了一个汉化软件包,用计算机选择调节阀流量特性,计算局部阻力损失、调节阀压降、阀阻比、流量系数等,并对相对行程、可调比和允差等进行验算。     

变面积临界流文丘里喷嘴特性研究

针对目前气体流量计量领域临界流文丘里喷嘴临界流量不可调节或调节困难的情况,提出一种喉部过流面积可调节的变面积临界流喷嘴.通过结构分析、建模计算、流体力学Fluent仿真等方式,对棒状节流体、锥状节流体、台锥状节流体三种不同调节方式进行研究分析.结果表明:采用三种不同节流体的变面积临界流文丘里喷嘴均能实现临界流流量的调节,在背压比小于最大允许背压比后,流量保持一稳定值,基本不变.建模计算得到的理论值与Fluent仿真到的数据较为符合.     

基于文丘里流量传感器的湿气两相流量模型研究

研究旨在通过计算流体动力学(CFD)仿真技术预测的湿气气、液两相流量.以双差压长喉颈文丘里流量传感器为测量手段.模拟压力范围0.4,0.6,0.8,1.0,1.2 MPa,气相体积流量范围为140～283 m3/h,温度范围23 ～30℃,含液率范围0.5％～1.5％.文丘里流量传感器口径为DN100,节流比为0.55.多相流模型采用离散相模型(DPM),利用欧拉壁面(EWF)模型以模拟管壁上的薄液膜.分析得出压力、气相流速和液相体积含率(LVF)对液膜厚度的影响规律.根据仿真结果建立基于双差压比值法的气、液两相流量预测模型.将仿真值与实验值进行比较,气相流量模型预测的均方根误差为1.8％,且液相流量模型预测的均方根误差为6.1％.     

可压缩流体流量系数计算公式的分析与比较

本文介绍了目前调节阀选择时所使用的几种主要的可压缩流体流量系数计算公式,通过对其进行分析和比较,给出了各自不同的适用范围,对正确选择调节阀有一定的指导作用.     

基于区域权函数理论的多电极电磁流量计电极设计

基于Shercliff权函数提出区域权函数概念,设计多电极电磁流量计,通过测量管道截面不同位置的弦端电压,计算各区域的轴向平均速度,实现速度分布与体积流量的测量。着重研究了流量计电极设计,选取不锈钢平头方案的多电极电磁流量计,对于阀门下游的非轴对称单相流体积流量测量精度高于±1.0%,倾斜管固—液两相流实验证明:该设计对于两相流非轴对称的速度分布测量具备可靠性。     

柴油机可调涡流比燃烧过程三维仿真

在柴油机进气歧管前安装蝶形涡流调节阀,通过调整直气道侧的有效流通面积改变缸内涡流强度。在稳流吹风试验平台,研究涡流调节阀角度对进气道流量因数和涡流比的影响,并结合粒子图像测速（particle image velocimetry,PIV）分析缸内涡流的形成过程。采用计算流体力学（computational fluid dynamics,CFD）评估涡流调节阀角度对缸内混合气体形成过程的影响,计算结果可复现三维 PIV测量的缸内流场结构和相似的涡心位置。随着进气门关闭,涡流比从0.57提高到2.05,油气在周向的相互作用增强,从而加速预混燃烧阶段的放热速度,促使燃烧重心提前、燃烧持续期缩短。在相同进气流量条件下,强涡流运动也促使累积放热量增加。     

A vapor based microfluidic flow regulator

We introduce a flow regulating technology that uses trapped air bubbles in a hydrophobic microfluidic channel. We present basic designs for flow regulators and flow valves using trapped air. Experiments have successfully demonstrated the capability of this technique for delivering constant and varying flow rate, and for on-off valving. This approach to valving provides a simple, yet effective way to monolithically integrate flow and valve control on polymer Lab-on-Chip devices.     

Development of micro-vibrating flow pumps using MEMS technologies

In the present paper, we propose a micro-vibrating flow pump (micro-VFP), which is a novel micropump. The micro-VFP is constructed using an actively vibrating valve that has a cantilever-like structure fixed on a wall of a microchannel and a slit orifice downstream. The slit orifice is designed to make the flow asymmetric around the vibrating valve and to effectively generate a net flow in one direction. At the same time, the valve works as an actuator to induce liquid flow in the microchannel. Since the valve is made of a flexible material including magnetic particles, it is manipulated by changing the magnetic field from outside the micro-VFP. This design allows external operation of the micro-VFP without any electrical or mechanical connections. In addition, the micro-VFP, which realizes pumping with a chamber free design, is advantageous for implementation in a small space. In order to demonstrate its basic pumping performance, a prototype micro-VFP was fabricated in a microchannel with a cross section of 240?μm?×?500?μm using microelectromechanical systems technologies. The vibration characteristics of the valve were investigated using a high-speed camera. The pump performance at various actuation frequencies in the range of 5 to 25?Hz was evaluated by measuring the hydrostatic head and the flow rate. The proposed micro-VFP design exhibited an increase in performance with the driving frequency and had a maximum shut-off pressure of 3.8?±?0.4?Pa and a maximum flow rate of 0.38?±?0.02?μl/min at 25?Hz. Furthermore, in order to clarify the detailed pumping process, the flow characteristics around the vibrating valve were investigated by analyzing the velocity field based on micron-resolution particle image velocimetry (micro-PIV). The validity of the hydrostatic measurement was confirmed by comparing the volume flow rate with that estimated from micro-PIV data. The present study revealed the basic performance of the developed micro-VFP.     

Controlling capillary-driven surface flow on a paper-based microfluidic channel

This paper describes two methods for controlling capillary-driven liquid flow on microfluidic channels. Unlike flow driven by external forces, capillary-driven flow is dominated by interfacial phenomena and, therefore, is sensitive to the channel geometry and chemical composition (surface energy) along the channel. The first method to control fluid flow is based on altering surface energy along the channel through regulation of UV irradiation time, which enables adjusting the contact angle along the fluid path. The slowing down (delay) of the liquid flow depends on the stripe length and its position in the channel. Using this technique, we generated flow delays spanning from a second to over 3 min. In the second approach, we manipulated the flow velocity by introducing contractions and expansions in the channel. The methods used herein are inexpensive and can be incorporated to the microfluidic channel fabrication step. They are capable of controlling liquid flow with precise time delays without introducing the foreign matter in the fluidic device.     

A liquid-triggered liquid microvalve for on-chip flow control

This work introduces a novel surface tension and geometry based liquid-triggered liquid microvalve for on-chip liquid flow control. The simultaneous presence of two liquid plugs at the uncomplicated valve junction triggers the further movement of the liquids and overcomes the stop valve function of the device, thereby providing a precise means of timing liquid movement on-chip. The generic structure was shown to successfully function and forms the basis for several novel and useful functions, including fluidic AND gates, contactless on-chip liquid sample control, timing of independent processes on the same microchip, bubble-free joining of liquids, all of which pose great challenges in the area of microfluidics. The device may be applied to chemical analysis, drug discovery, medical diagnostics and biochemistry.     

中性点不接地系统配网三相解耦潮流

针对中性点不接地系统无零序通路的特点,提出了一种三相解耦潮流计算方法。该方法忽略零序分量的影响,使得不对称的三相负荷引起的相间耦合解耦,从而实现按相潮流计算。该算法将现有配网三相潮流算法中的3n阶节点电压方程分解为三个n阶节点电压方程,这样无论采用哪种算法都可以大大的节约了内存和计算量,为配电网实现按相分析提供了一种好方法。本文对以36节点的系统进行验证,计算结果表明该方法能充分计及负荷的三相不平衡的影响,有较好的运算速度和准确度。     

Mixing and flow regulating by induced-charge electrokinetic flow in a microchannel with a pair of conducting triangle hurdles

The induced-charge electrokinetic flow (ICEKF) in a rectangular micorchannel with a pair of conducting triangle hurdles embedded in the middle is investigated in this paper. A correction method is suggested to numerically estimate the induced zeta potential on the conducting surface. Two-dimensional pressure-linked Navier-–Stokes equation is used to model the flow field in the channel. The numerical results show flow circulations generated from the induced non-uniform zeta potential distribution along the conducting hurdle surfaces. It is demonstrated numerically that the local flow circulations provide effective means to enhance the flow mixing between different solutions; by adjusting the electric field applied through the microchannel with a non-symmetric triangle hurdle pair, an electrokinetic flow regulating effect can be obtained and this effect depends on the dimensions of the conducting converging–diverging section. The mixing and flow regulating using ICEKF described in this paper can be used in various microfluidics and lab-on-a-chip (LOC) applications.     

Critical pressure for capillary valves in a Lab-on-a-Disk: CFD and flow visualization

Capillary valves are used as pressure barriers to control flow sequencing in microfluidic devices. Influence of valves height on liquid flow pattern and critical pressure are studied through flow visualization and CFD predictions (Gambit® 2.2.30 and FLUENT® 6.2.16). Both hydrophilic and hydrophobic walls are studied. Results show that the surface tension plays a major role in the liquid progress through the microchannel/valve and also in the valve filling process. Critical pressure varies linearly with the valve hydraulic diameter in the range 0.91 < D_h < 3.5 [mm] according to: P = 14.14 · D_h + 47.42 [Pa].