Review of certain key issues in indirect measurements of the mass flow rate of solids in pneumatic conveying pipelines

On-line mass flow measurement of particulate solids in pneumatic conveying pipeline is a technically challenging area, where mass flow measurement presents a range of problems. These problems are not normally relevant to a single phase flow, but are always involved in gas–solids two-phase flows, like inhomogeneous distribution of solids over the pipe cross section, irregular velocity profiles, variations in particle size, moisture content, and deposition of fine particles on the inner wall of the pipeline. These variables may affect the response of a solids flow meter in ill-defined ways. All of these make the design and the calibration of solids’ mass flowmeter more difficult. Based on a review of non-invasive mass flow measurements of particulate solids, this paper summarizes and highlights several key issues, which often rely on structures of sensors or measurement methods, in indirect mass flow metering of pneumatically conveyed solids. They are: (i) spatial filtering effect; (ii) averaging effect; (iii) measurement resolution and sensitivity of array structures in tomography sensors.     

超(超)临界疏水阀开阀水锤及管道振动

针对超(超)临界疏水阀开阀水锤及阀后管道振动问题,运用充液管道振动分析的流固耦合理论及特征线法,建立开阀水锤及管道振动的数学模型,求解得到疏水阀在不同流量特性及不同套筒层数下阀开启时水锤压力、流体流速、管道轴向内力和管道振速的时域曲线。研究结果表明:水锤压力取决于流体的流速与压力相互作用,管道内力受水锤压力影响较大,局部受管道振速影响;额定流量恒定时,线性流量特性下水锤峰值压力明显小于快开特性,流速大于等百分比特性,超(超)临界疏水阀宜选用线性流量特性;随着套筒层数增加,水锤压力峰值和管道轴向内力峰值减小,但开阀初始阶段流速波动和管道振动增加。     

A system to estimate coarse particle velocities at the pipe wall in settling slurry flow

Understanding and modelling of coarse particle (settling) slurries in laminar flow in pipes is still not complete. Better analytical procedures will enable more efficient pipeline operation which could result in significant power savings in the transport of coarse materials. The depth and velocity of the settled bed significantly affect the pressure gradients required to pump these slurries and knowledge of these parameters is of importance. Existing measurement techniques that can be used for monitoring of these complex fluid systems are either very expensive, not easy to implement or mostly used under controlled laboratory conditions. A new measurement system was developed that is capable of detecting the deposition of solids, the depth of a settled bed and the velocity of coarse particles at the pipe wall, around the pipe circumference. Particle velocities were determined by cross-correlating modulated signals from pairs of electrodes mounted flush with the pipe wall, in contact with the slurry. Tests were conducted using a mixture of acetal beads in water, at bulk velocities between 0.5 and 4 m/s. Estimated particle velocities from the cross-correlation analyses were compared with those obtained using a 30 fps video camera combined with visual inspection, and found to be within ±6%, thus validating the viability of the system. Particle velocity resolution using the cross-correlation technique is limited by block size, sample rate and the measurement distance between electrode pairs. Further test work with a range of real slurries (different particle sizes, solids concentrations and rheologies) needs to be conducted, along with more extensive verification of the results, to establish the limits of the system. Initial testing and evaluation of the system, which is capable of coarse particle flow monitoring in real time, showed significant potential for development of a new commercial sliding bed detector that can be used in a wide range of industrial applications in which particles are transported hydraulically.     

Design and evaluation of electrostatic sensors for the measurement of velocity of pneumatically conveyed solids

Electrostatic sensing technology in combination with correlation signal processing offers a promising solution to the on-line continuous measurement of velocity of particulate solids in pneumatic pipelines. This paper describes the fundamental mechanism of the electrostatic sensing and identifies the important aspects of the design of constituent elements of the sensor including electrodes, amplifiers and sensing heads. Experimental evaluation of a prototype commercial product called V-TESS 500 was conducted on 36 mm bore vertical and horizontal sections of a pneumatic conveyor circulating corn-flour and pulverised coal over a velocity range of 6 to 45 m/s for mass concentration of particles between 0.014 and 5.7 kg/m³. The performance of the instrument was quantified in terms of repeatability, linearity and response time. The uncertainty of the system was studied by comparing the measured solids velocity to the superficial air velocity in the pipeline. Effects of particles' accretion on the inner surface of the pipe wall on the measurement are also included. Results obtained demonstrate that the system is capable of providing solids velocity measurements with repeatability better than ±2% and response time less than 2.5 s.     

Flow imaging for multi-component flow measurement

For pseudo-homogeneous flows, measurements of density and mean velocity can give the component mass flow rate of a two-component mixture. However, for accurate measurement of non-homogeneous flow rate, the density and velocity distribution across the cross-section of the pipe must be known. The most practical way of obtaining this information is by using the flow imaging technique.

A recently developed capacitance system gives 60 frames per second images of oil/water flow in a 78 mm pipe. The target spatial resolution is one part in 20 by distance (one in 400 by area). The electrical properties of each imaged boundary are functionally related to the imaged value, so the component ratio of a two-component mixture within a boundary can be measured, although individual particles cannot be imaged. Design data shows how the basic system can be part of a complete system for component mass flow measurement.     

空间Z形管路液-固两相流冲蚀特性分析

空间Z形管路是油气开采过程典型的结构形式,在工程作业中受到高压高速液-固两相流的作用,容易导致管路系统产生冲蚀磨损失效。基于液-固两相流冲蚀磨损理论,选取合适的冲蚀磨损理论模型,讨论了流速、颗粒直径、质量流量、黏度以及重力等不同流体参数对管路系统弯头处的冲蚀磨损情况。结果表明:管路弯头处的冲蚀区域受内流场的影响存在明显差异,出口端弯头处的最大冲蚀率大于进口端弯管端。流速、颗粒直径、质量流量与整体管路最大冲蚀率呈正相关关系,黏度与整体管路最大冲蚀率呈负相关关系。分析了不同工况下空间Z形管路的冲蚀特性,获得了流体参数对管路冲蚀的影响规律,为工程实际复杂管路系统冲蚀磨损寿命预测提供技术参考。     

钻孔水力开采用气力提升装置的实验研究

为阐明进气方式对气力提升特性的作用规律,以普通河沙模拟井下矿层,利用小型输沙系统实验研究在恒定浸入率和供沙量下气孔数量与进气角度对扬水量、扬沙量及总效率的影响。结果表明:任一进气方式下扬水量、扬沙量及总效率并不随气量值增加呈现单调特性,前两者峰值所处位置大致接近,且较总效率峰值对应点右移。气孔数量和进气角度对扬水量及扬沙量影响较小,对总效率影响程度稍大。就整体而言,对应气孔数量和进气角度分别为4和90°时其扬沙量与总效率较其它进气方式上扬。另外,实验测得最高扬沙效率所对气相佛汝德数大致相同,约为2.5,且最佳扬沙效率所对应的气相佛汝德数随管径递增。     

A novel flowrate measurement method for small-diameter pipeline based on bidirectional acoustic resonance

Traditional acoustic flowmeters are difficult to use in small-caliber, low-velocity piping systems. In this study, a novel method for fluid velocity measurement in small-diameter pipelines is developed based on the characteristic of acoustic resonance and standing wave tube. This method solves the problem of mutual interference between bidirectional acoustic loops, and realizes the simultaneous measurement of bidirectional resonant frequency. The tiny variation of flow velocity in a small-diameter pipeline can be sensitive by measuring the difference in bidirectional high-order resonance frequency. Experimental results show that the measurement system with a 15 mm diameter pipe has good linearity and high sensitivity to low velocity. Hence, this new method widens the application scope of acoustic flowmeters, especially in small-diameter, low-velocity piping systems.     

水平管内以叶轮起旋的螺旋流的数值模拟

采用RNG k-ε模型对水平管内以叶轮起旋的螺旋流的流动特性进行了数值模拟研究,通过试验验证了数学模型的准确性和可靠性。研究结果表明:叶片旋流器产生的旋流场,切向速度分布具有近似Rankine组合涡结构的特点,径向速度最大值达轴向速度的0.5倍。雷诺数对旋流强度影响较大,Re数越大,旋流强度越大,且旋流强度的衰减速率越小。强旋流使轴向逆压力梯度足够大而引发轴向回流,从而产生了中心回流区域;能够增加反应介质的滞留时间,提高气液两相的传质和传热效率,促进水合物浆体快速生成,保障管道安全输送。     

Diagnostic flow metering using ultrasound tomography

For an accurate flow metering without considering the influences of flow control devices such as valves and elbows in closed conduits, velocity distribution in the cross-sectional area must be integrated. However, most flow meters, including multi-path ultrasonic, electromagnetic or Coriolis mass flow meters, require assumptions on the fully-developed turbulent flows to calculate flow rates from physical quantities of their own concern. Therefore, a long straight pipe has been a necessary element for accurate flow metering because the straight pipe can reduce flow disturbances caused by flow control devices. To reduce costs due to the installation of long straight pipes, another flow metering technique is required. For example, flow rates can be estimated by integrating velocity distributions in the crosssection of conduits. In the present study, ultrasound tomography was used to find the velocity distribution in the cross-section of a closed conduit where flow was disturbed by a Coriolis mass flow meter or a butterfly valve. A commercial multi-path ultrasonic flow meter was installed in the pipeline to measure the line-averaged velocity distribution in the pipe flow. The ultrasonic flow meter was rotated 180° at intervals of 10° to construct line-averaged velocity distributions in Radon space. Flow images were reconstructed by using a backprojection algorithm (inverse Radon transform). Flow diagnostic parameters were defined by calculating statistical moments, i.e., average, standard deviation, skewness, and kurtosis, based on the normalized velocity distribution. The flow diagnostic parameters were applied to flow images to find whether the parameters could discern flow disturbances in the reconstructed velocity distribution.     

Flow rate measurement in flows with asymmetric velocity profiles by means of distributed thermal anemometry

Flow rate in closed conduits is one of the most frequently measured parameters in industrial processes and in gas and water supply. For an accurate measurement, flow meters typically require a fully developed symmetric flow profile with preferably no radial or tangential velocity components. This is commonly secured by mounting flow meters in a pipe at a sufficiently long distance downstream any change in cross-section or pipe direction. In this paper, we introduce a new approach for flow rate measurement of gases or liquids that employs a novel spatially resolving fluid velocity sensor basing on thermal anemometry. The new principle allows accurate flow rate measurements for non-axisymmetric velocity profiles, even directly after pipe bends, T-junctions or other alterations in the pipe geometry. This is exemplified for air flow in three different pipe bend configurations.     

Dynamic response of rotating flexible cantilever pipe conveying fluid with tip mass

In this study the vibration system is consisted of a rotating cantilever pipe conveying fluid and a tip mass. The equation of motion is derived by using the Lagrange's equation. Also, the equation of motion is derived applying a modeling method that employs hybrid deformation variables. The influences of the rotating angular velocity and the velocity of fluid flow on the dynamic behavior of a cantilever pipe are studied by the numerical method. The effects of a tip mass on the dynamic behavior of a rotating cantilever pipe are also studied. The influences of a tip mass, the velocity of fluid, the angular velocity of a cantilever pipe and the coupling of these factors on the dynamic behavior of a cantilever pipe are analytically clarified. The natural frequencies of a cantilever pipe conveying fluid are proportional to the angular velocity of the pipe and a tip mass in both axial direction and lateral direction.     

Velocity distribution of liquid phase at gas-liquid two-phase stratified flow based on particle image velocimetry

Horizontal gas-liquid flows are commonly encountered in the production section of the oil and gas industry. To further understand all parameters of the pipe cross-section, this paper use particle image velocimetry to study the circular pipe cross-section liquid velocity distribution rule. Firstly the focus is on the software and hardware combination of image correction system, to solve the influence of different refractive indexes of medium and pipeline curvature caused by image distortion. Secondly, the velocity distribution law of the corrected stratified flow (the range of liquid flow of 0.09-0.18 m³/h, and gas flow range of 0.3-0.7 m³/h) cross-section at different flow points of the pipeline cross-section at x=0 and in the Y direction at the maximum liquid velocity is studied. It is found that these distribution laws are caused by the influence of the interphase force of the gas-liquid interface and the resistance of the pipe wall. The current measurements also produce a valuable data set that can be used to further improve the stratified flow model for gas-liquid flow.     

Characterization of swirling-flow behavior in complex pipeline using bubble trajectory method with stereo particle tracking/image velocimetry

To understand the swirling-flow behavior in a complex pipeline geometry comprising an elbow and orifice, a quantitative flow visualization technique is introduced into the flow-field observation using a bubble trajectory method combined with stereo particle tracking/image velocimetry. For the chosen bubble sizes of approximately 2 mm un a pipe of 56 mm in diameter, their motion is correlated with the mean swirling flow, and when analyzed in a straight swirling flow, the bubbles cluster close to the point of maximum axial velocity for swirl intensities larger than 0.3. Subsequently, this experimental technique is applied to the characterization of a swirling flow in the Mihama pipeline model, for which the streamwise variation of the location of the maximum axial velocity and its magnitude are measured over the full range of the pipeline model. A spiral swirling flow is observed downstream of the elbow owing to the combined effect of the swirling and secondary flows in the elbow. The spiral swirling flow persists in the following straight pipe down to the orifice, where a highly accelerated flow with a high turbulence is generated towards the top wall of the pipe. This result agrees closely with the observation of pipe-wall thinning in the prototype Mihama pipeline.     

超声多普勒谱修正的油水两相流流速测量

针对水平管道油水两相流流速的无扰动测量问题,提出一种基于超声/电学双模态传感器的流速测量方法。测量系统由连续波超声多普勒传感器和基于电容与电导的电学传感器构成,分别用于获取两相流流速和分相含率。由于连续波多普勒的测量区域集中于管道中心,受流速剖面、含率分布影响,所测得流速并非流体的总表观流速。在假设含率分布满足高斯分布的前提下,建立相含率加权的多普勒能量谱模型,将含率分布的影响因素引入总表观流速的测量,并建立总表管流速和分相表观流速的计算模型。在试验基础上,分别确定水连续和油连续时总表观流速计算模型的参数。试验表明,通过模型计算出的表观流速与实际测量的流速能够较好吻合,总表观流速的相对误差小于6.32%,分相表观流速的方均根误差小于5.64%。     

Dynamic analysis of Coriolis flow meter using Timoshenko beam element

Coriolis mass flow meter (CFM) is used to measure the rate of mass flow through a pipe conveying fluid. In the present work, the Coriolis effect produced in the pipe due to a lateral excitation is modeled using the finite element (FE) method in MATLAB©. The coupled equation of motion for the fluid and pipe is converted to FE equations by applying Galerkin technique. The pipe conveying fluid is excited at its fundamental natural frequency. The time lag observed between symmetrically located measurement points which are equidistant from the point of excitation, is utilized to predict the mass flow rate. The results predicted by the present code is validated using the experimental, and numerical results published in the literature. The main contribution is the development of a FE model, using three node Timoshenko beam element to analyse the dynamics of fluid conveying pipes subjected to external excitation. The direction of the Coriolis force is perpendicular to the plane containing the velocity of flow vector and angular velocity vector of the pipe. Hence a three dimensional FE model is essential. This model can include curved geometry, damping, velocity and gyroscopic effects for three dimensional flexible tubes. The reduced integration used for overcoming shear locking in two node elements, will result in the formation of spurious modes leading to an incorrect prediction of natural frequencies and velocity. These modes will not occur while using three node elements. Influence of spatial as well as temporal discretisation on the time lag and frequency are also discussed. The sensitivity analysis shows that the time lag varies linearly with the mass flow rate.     

超声波气体流量计检测精度影响因素分析

在天然气的管道运输过程中,提高气体流量测量的精度是提高运输效率、避免安全事故发生的关键技术。利用流体力学仿真（CFD）方法建立组合双弯管及变径管道模型,定量计算修正系数,对双声道超声波流量计结构和安装位置对于管道内气体速度场的影响进行研究。通过仿真得出超声波流量计的最优声道位置,并结合实验验证了仿真结果的可信性。模拟结果表明,双弯管和变径管与超声波流量计的安装位置至少为10D才能保证流体充分流动;通过修正系数随雷诺数的变化情况得出双声道超声波流量计的最优声道位置为距管道截面中心0.25D处。研究结论对于不同性质气体的流量检测同样适用,为工业中气体运输检测精度的提高以及超声波流量计的优化提供了依据。     

多孔介质单元区域的流场模拟及分析

利用三维软件对多孔介质排气管道进行模拟,通过CFD软件STAR-CCM+对多孔介质单元区域进行数值模拟,得到多孔介质单元区域的流场(速度流场、压强流场).结果表明:管道中间的多孔介质区域吸收了一部分气体,使得管道内部的压强降很小,同时管道内部的气体流速也在减小,说明多孔介质区域的吸附作用很强.为今后废气的排气管道的研究提供参考.     

A new method for field test of the heating capacity of air source heat pumps

The operation performance measurement of the air source heat pumps in the field, in which conditions are complicated and the accuracy could not be ensured, is very crucial for its performance evaluation and improvement. In this investigation, a novel method for measuring the heating capacity of the air source heat pump is established. An auxiliary electric heater is installed along the pipeline between the compressor and the condenser, and the refrigerant temperature difference caused by the heater is gathered to calculate the refrigerant mass flow rate based on the energy conservation. The heating capacity is calculated with the measured data of the refrigerant enthalpy at the inlet and outlet of the condenser and the refrigerant mass flow rate of the compressor discharge pipe. The validation results in laboratory tests show that the measured heating capacity accuracy is within 9.2%. It is also found that the impact of the novel test method on the heating capacity of the air source heat pumps is below 1.7%, and the power consumption of the tested units is increasing of within 1.8% compared with it when the electric heater is off. The refrigerant enthalpy difference method with an electric heater presented in this research can be applied to measure the heating capacity of different air source heat pump air heaters accurately in the field, which will be much helpful to improve the performance for cleaning heating in northern China.     

气固两相管道输送分支流动阻力特性的研究

在水平T型分支管道中用压缩宅气对平均粒径为0．5mm砂石进行了气力输送试验,对气固两相分支管道输送的阻力性能进行了研究。试验结果表明,在发送压力基本保持不变的情况下,当输送气速下降时各分支管的单位长度压差在开始时逐渐减小;但当气速下降到一定程度后,单位长度压差下降趋势减缓,其中局部阻力相对较大的分支管路则开始增大。当分支管流量控制阀开度差值由小变大时,两分支管各自的压差曲线逐渐远离,局部阻力较大的分支管路的临界速度增大。