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％.     

湿气计量中旋进旋涡流量计信号特征与精度补偿

针对气体旋进旋涡流量计在湿气计量中测量精度低,无法判别管道内是否含水的问题,提出了一种基于脉冲串时间长度变化率的湿气状态识别及气相流量测量精度补偿方法。通过湿气实验分析旋进旋涡流量计旋涡进动的信号特征,对比了干气和湿气条件下旋涡进动信号的时域特征、频域特征和“虚低”特征,发现了脉冲串时间长度变化率和体积含液率FVL的关系。在体积含液率小于 0.5％时,脉冲串时间长度变化率小于1.0％,并以此对管道内湿气状态进行识别和补偿。通过脉冲串时间长度变化率与仪表系数的变化规律,建立气相流量测量精度补偿模型。补偿后,97％的数据气相流量相对误差在±2％以内。     

新型内外管差压流量计湿气测量模型研究*

针对湿气的在线不分离测量,课题组提出了一种新型内外管差压式流量计,针对该流量计在天津大学油、气、水三相流实验装置上进行了测试,实验压力定为0.1MPa和0.2MPa,选取了与本实验工况相近的经典湿气测量模型对其虚高值进行了预测,预测结果显示“Bizon模型冶预测效果最佳,但直接应用于内外管差压式流量计,测量误差仍不满足要求,因此,将理论分析与数据融合思想结合,进行了内外管差压流量计的湿气新测量模型拟合,建立湿气虚高值与其特性参数之间的非线性关系式。误差分析验证表明,新测量模型平均误差在1.6%以内,且误差波动性较小,比较稳定,能够满足工业生产中湿气的测量要求。     

基于总线技术的井下流量采集传输系统设计

文章介绍了一种井下流量采集传输系统设计和实现方案。针对油田分层注水井需要实时监测每层油层注水量以及压力温度等参数,设计了基于文丘里流量计原理和485总线通信的井下流量采集传输系统,该井下流量采集传输系统实时采集文丘里流量计入口和出口处压力差,根据测量压力差及文丘里管尺寸,通过能量守恒定律--伯努力方程和流动连续性方程计算实时流量,并对时间进行积分计算出总流量,通过485总线实时将流量等参数上传至地面测控计算机,具有参数上传实时性强、流量采集精度高、抗干扰能力强、尺寸小等特点。实验结果表明,井下流量采集传输系统满足注水井流量等参数实时监测的要求。     

基于狭缝文丘里管的气液两相流测量

提出了一种新的气液两相流测量系统-狭缝文丘里气液两相流测量系统.理论分析表明,狭缝文丘里管利用对称结构可以减小或消除摩阻压降的影响,中间狭缝处垂直于水平流向的重位压降的测量同样避免了沿程摩擦阻力的影响.提出了基于狭缝文丘里测量系统的气液两相流非分离测量方案,并进行了实验研究.利用狭缝文丘里重位压降信号在三类流动下的特性,可以直接识别流型,在不同的流型下用相应的测量模型求解气液两相的流量.结果表明该方法是可行的.     

低压气体流量标定技术研究

热式质量流量传感器用于测量35～41 kPa(绝压)的气体流量,需在该工况下对其进行标定.采用文丘里喷嘴作为标准器,在被测流量传感器处构建调压系统,调节压力可至40±0.1 kPa(绝压),建立低压气体流量标准装置,通过比较流量传感器输出值与文丘里喷嘴标准流量,标定流量传感器.对常压下校准的喷嘴在35～41kPa(绝压)条件下是可以作为标准器进行了分析,试验证明:装置的稳定性为0.6%,重复性为0.13%,临界背压比为0.5,低压气体流量标定方法科学可行.     

粉尘浓度测量装置利用涡流发生效应的优化研究

对现阶段电荷感应法测量粉尘浓度不够精确的问题进行了研究。依据涡流发生效应和文丘里效应,对现有环状粉尘传感器的测量管道进行改造。通过在文丘里管道的喉道中间段不同对称位置加入三片三角形涡流发生器,使气流通过管道时不易产生气体分离效应;在发生器尾部产生空气旋涡,使得环式静电传感器所感应的电荷量增大。利用PROE 5.0软件建立所设计管道3D模型,并利用Fluent软件对改进的管道进行气固两相流仿真,获得改进管道内粉尘颗粒速度分布云图及喉道段内粉尘的速度值。使用环形静电传感器的数学模型,分别计算了文丘里管道和改进管道在不同粒径比下的感应电荷量。结果表明:改进管道的结构在实验中使得感应电荷量大幅提高,在各阶段测得感应电荷量提高20%以上。通过试验可知,在各个浓度情况下测量精度得到了较大的提升,大气监测和燃煤电厂粉尘浓度在线测量精度都有所提高。     

临界流文丘里喷嘴测量不确定度分析

介绍了临界流文丘里喷嘴的工作原理,以及用pVTt法气体流量标准装置检定临界流文丘里喷嘴流出系数时的不确定度分析。对于检定过程的不确定度问题,列出了理想条件下的临界流量、实际条件下的临界流量以及喷嘴流出系数不确定度等的数学模型。并对检定过程中喷嘴流出系数的相对拓展不确定度进行了详细的评定,分析了各个因素的来源,便于我们在实际工作中分析影响测量不确定度的主要因素,从而提高我们校准工作的准确度和可靠性。     

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.     

压力位差式层流流量传感技术气体测量适用性研究

压力位差式(PPD)层流流量传感技术应用于气体测量时,需要对流体可压缩性的影响进行验证和评估.本文采用计算流体力学方法,分别采用不可压缩和可压缩流体模型对PPD传感元件内部流动进行仿真分析.结果显示,质量流量相同情况下,采用可压缩模型时,毛细管内部流动总压下降速率比不可压缩模型大,说明气体可压缩性对流动和压损产生比较明显的影响;另一方面,尽管存在压缩性影响,但PPD传感元件中两条支路总压降基本相同,其流阻特性是一致的,说明PPD技术的假设条件是合理的,该新型传感技术对气体流量测量具有适用性.对比传统层流元件和PPD层流元件计算数据,后者流量测量误差减小至少一个量级,能够很大程度上消除非线性影响.在对气体膨胀修正系数Kexp取值的研究中,发现Kexp=1时计算得到的流量与真实流量偏差最小,验证了前人研究结果.文中还通过实验测试对数值计算结果进行了验证.     

改进的NURBS曲线预估校正插补方法

现行的NURBS曲线参数预估校正插补方法不能预估最开始的两个参数,而且不能控制预估参数迭代修正的次数。提出改进的NURBS预估校正插补方法,该方法预估插补点参数,根据最大进给步长约束、轮廓误差约束以及法向加速度约束,判定预估参数与实际参数的误差,当误差在允许范围内,则对参数步长增量进行调整,否则进行迭代修正。仿真实验结果表明,新方法通过对参数步长增量的调整,使得预估参数更加接近实际参数,较现有方法有效减少了参数迭代修正的次数,利于实时插补的实现。     

Non-isothermal flow of rarefied gas through a long pipe with elliptic cross section

A non-isothermal rarefied gas flow trough a long tube with an elliptical cross section due to pressure and temperature gradients is studied on the basis of the S-model kinetic equation in the whole range of the Knudsen number covering both free molecular regime and hydrodynamic one. A wide range of the pipe section aspect ratio is considered. The mass flow rate is calculated as a function of the pressures and temperatures on the tube ends. The thermomolecular pressure effect has been modeled and the coefficient of the thermomolecular pressure difference has been calculated in whole range of the Knudsen number and in wide range of the pipe section aspect ratio.     

差压式流量计干气体流量检测示值修正关系图

节流装置前后产生的差压决定于流过节流装置的气体工作状态参数。在推导示值修正公式时应注意三种工作状态流量：设计状态流量，即人为设定的工作状态流量；流过节流装置的工作状态流量，即管道中的实物流量；检测出的工作状态流量，即检测出未修正的差压代表流量，该流量是三者中最为关键的。应用图解法分析了差压式流量计干气体流量检测与示值修正公式。该公式也可用于喷嘴、文丘利管、阿牛巴、威力巴、弯头等差压式流量计示值的修正。     

激光测径仪温度测量误差修正的研究

针对激光测径仪随温度变化而易造成测径误差的问题,采取了线性补偿和非线性补偿相结合的温度误差修正方案.研究了温度与误差数据的关系,通过给激光管加热,测试在温度影响下激光测径仪的误差数据.针对误差数据建立线性补偿和非线性补偿相结合的修正方案,设计了相应的温度误差修正系统.研究结果表明,经过温度误差补偿后,激光测径仪的精度大大提高,最大相对误差由修正前的0.39％减小到修正后的0.04％,且随着温度的变化,测量数据无明显波动.     

A Venturi microregulator array module for distributed pressure control

Pressure-driven flow control systems are a critical component in many microfluidic devices. Compartmentalization of this functionality into a stand-alone module possessing a simple interface would allow reduction of the number of pneumatic interconnects required for fluidic control. Ideally, such a module would also be sufficiently compact for implementation in portable platforms. In our current work, we show the feasibility of using a modular array of Venturi pressure microregulators for coordinated droplet manipulation. The arrayed microregulators share a single pressure input and are capable of outputting electronically controlled pressures that can be independently set between ±1.3 kPa. Because the Venturi microregulator operates by thermal perturbation of a choked gas flow, this output range corresponds to a temperature variation between 20 and 95°C. Using the array, we demonstrate loading, splitting, merging, and independent movement of multiple droplets in a valveless microchannel network.     

Rarefied isothermal gas flow in a long circular tube due to oscillating pressure gradient

The time-dependent isothermal fully developed rarefied gas flow in a circular tube driven by harmonically oscillating pressure gradient is investigated, based on the linearized unsteady BGK kinetic model equation. The flow is characterized by the gas rarefaction parameter, which is proportional to the inverse Knudsen number and the oscillation parameter, defined as the ratio of the collision frequency over the pressure gradient oscillation frequency. Computational results of the amplitude and the phase angle of the flow rates and the velocity distributions, as well as of the periodic time evolution of these macroscopic quantities, are provided, covering the whole range of the two parameters. The kinetic results properly recover the limiting solutions in the slip and free molecular regimes for low- and high-speed oscillations. At low frequencies, the time-dependent flow becomes quasi-steady and gradually tends to the corresponding steady-steady one, which is reached faster when the flow is more rarefied. As the frequency is increased, the amplitude of the macroscopic quantities is decreased and their phase angle lag with respect to the pressure gradient is increased approaching asymptotically the limiting value of \(\pi /2\). In terms of the gas rarefaction, there is a non-monotonic behavior and the maximum flow rate amplitude may be observed at some intermediate value of the gas rarefaction parameter depending upon the oscillation parameter. At high frequencies, the flow consists of an inviscid piston flow in the core and the frictional Stokes wall layer with a velocity overshoot. These effects, well known in the viscous regime, are also present here in the transition regime and depend on both the gas rarefaction and oscillation parameters. As the gas rarefaction is increased, higher oscillation frequencies are needed to trigger these phenomena. Oscillatory rarefied flows are of main interest in sensors, controllers and resonators, which may be present in various microfluidic applications (e.g., microcooling, microseparators and micropropulsion).     

管道综合参数检测系统

本文采用CD3激光位移传感器,运用三角测距原理进行圆周半径测量,并采用二维PSD位置传感器完成机械振动的误差修正。通过螺旋采集数据获取足够的信息,运用特殊算法,重建管的三维图形,显示在模拟监视器上。并计算出管的各个参数,与产品标准比对判别成品是否合格,将数据处理结果和判别结论显示在计算机屏幕上。     

基于MSP430罗茨气体流量积算仪的设计与实现

针对目前工业现场天然气计量情况.设计基于16饽嵌入式微处理器MSP430F157为核心的罗茨流量积算仪.采用非线性校正算法实现对流量传感器非线性特征的校正,扩大流量积算仪的量程比:采用多周期测频法,提高传感器输出信号频率测量的精度;通过引入气体压缩因子,修正流量补偿计量公式.积算仪能够更精确地实时温压补偿.文中详细介绍了积算仪的硬件和软件设计方案,经测试和实际运行表明,该流量积算仪稳定可靠,测量精度高.量程比宽,具有一定的实用价值.     

V型锥流量计的原理及应用

传统的流量计主要是差压式流量计,距今已有百年的历史。事实上,其中有很多弊端难以在文丘里管为代表的第一代流量计中解决,无法满足现代工业的需求。而且经实验证明,文丘里管流量计有诸如测量精度低、压差阻力大等缺点[1]。如果我们将V型锥流量计大量的使用到工业现场中,将会大大改善流量计量精度,以达到现代工业现场所要求的范围。同时呼吁尽快制定V-Cone流量计的国家标准。     

Effect of operating conditions and liquid physical properties on the size of monodisperse microbubbles produced in a capillary embedded T-junction device

The aim of this study was to investigate the effect of operating parameters such as liquid flow rate, gas inlet pressure, and capillary diameter as well as the influence of the physical properties of the liquid, in particular viscosity, on the generation of monodisperse microbubbles in a circular cross section T-junction device. Aqueous glycerol solutions with viscosities ranging from 1- to 100 mPa s were used in the experiments. The bubble diameter generated was studied for systematically varied combinations of gas inlet pressure, liquid flow rate, and liquid viscosity with a fixed capillary inner diameter of 150 μm for the liquid and gas inlet channels as well as the outlet channel. In addition, the effect of channel geometry on bubble size was studied using capillaries with inner diameters of first 100 and then 200 μm. In all the experiments the distance between the coaxial capillaries at the junction was set to be 200 μm. All the microbubbles produced in this study were highly monodisperse (polydispersity index <1 %) and it was found, as expected, that bubble formation and size were influenced by the ratio of liquid to gas flow rate, capillary size, and liquid viscosity. The experimental data were then compared with empirical scaling laws derived for rectangular cross-section junctions. In contrast with these previous studies, which have found bubble size to be dependent on either the flow rate ratio (the squeezing regime) or capillary number (the dripping regime), in this experimental study bubble size was found to depend on both capillary number and flow ratio.