基于双截面ECT的气/固两相流参数检测系统

为了实现多相流的流动过程在线监测和多参数测量,设计并研发了一套应用于气/固两相流检测的双截面8电极电容层析成像系统.采用交流法电容检测原理实现具有16个独立电容检测通道的电容测量电路,实测系统的成像速度为590帧/秒.将双截面电容层析成像系统用于气/固两相流的实时检测,并将两层截面的图像作相关计算,获取成像截面的固相速度分布.由固相速度和浓度最终算出气/固两相流的固相质量流量,从而实现气/固两相流浓度、速度、流量等多参数的综合检测.将双截面ECT传感器算得的质量流量与发料罐重力传感器获取的质量流量作对比发现,两者具有较好的一致性,流量测量误差小于8％.     

基于融合传感器的气固两相流参数检测系统设计

为了快速实现气固两相流输送过程中的多参数检测,设计了一种基于双圆环静电传感器和螺旋式电容传感器融合传感器的参数测量系统。采用螺旋电极电容传感器测量管内固相相对浓度,以降低电容传感器灵敏场不均匀对浓度测量的影响。将双圆环静电传感器的信号作互相关运算获得固相速度。由固相流速与相对浓度最终计算出固相质量流量,从而实现气固两相流的流速、浓度、流量等参数的综合测量。将系统测量的质量流量与重力传感器检测的质量流量相对比,两者误差小于7%,具有较好的一致性。     

一种新型浓度传感器的实验研究

介绍一种新型测量气／固两相流固相浓度的螺旋极板电容传感器，并通过实验得出提高传感器检测场灵敏度空间分布均匀性及克服边缘效应对检测精度影响的方法。     

电容式气固两相流的参数测量系统

为了实现气固两相流的多参数的测量和在线监测,设计并研发了一套基于直流充放电原理的气固两相流参数测量系统,其中主要包括与双螺旋式传感器相连接的2个电容检测通道的电容检测电路和实验平台,将双通道采集的电容数据通过相关算法的处理,获取截面固相速度,从而推算出气固两相流的固相质量流量,进而实现了气固两相流的多参数综合检测。将算得的质量流量与发料斗上的重力传感器获取的质量流量作对比,实验结果表明两者具有较好的一致性。     

基于静电传感器的气固两相流质量流量测量方法的研究

固相微粒的体积浓度和平均速度是测量两相流质量流量的2个关键参数。本文研究了基于静电传感器的双参数法测量质量流量的新方法。对体积浓度的测量,首先通过对系统等效电路的分析及求解泊松方程并结合体积浓度与空间电荷密度的关系,建立了传感器输出电压与体积浓度之间的数学模型,而对固相速度的测量则采用了波形法,记录通过上、下游传感器的时间差,计算出固相速度。在得到固相体积浓度与速度的基础上,由质量流量的计算公式即可得到两相流的质量流量。     

气固两相流固相浓度电容式传感器优化设计

本文建立了一种螺旋式电容传感器的数学模型,并基于该模型对传感器结构进行了优化设计。优化后的结构可以产生较均匀的灵敏场分布,实测结果表明,优化后的传感器电容值与固相浓度具有良好的线性关系,测量点的线性相对偏差小于0.8%,适用于气固两相流固相浓度的测量。     

一种参比电容传感器接口电路设计及性能评估

基于电容传感器的气固两相流测量技术被认为是最有前途的气固流测量技术,而电容传感器接口电路是电容传感器乃至电容法气固两相流测量技术研发和应用的关键.微小电容测量的难点在于杂散电容的存在以及电磁干扰,而张弛振荡电路可以通过差动结构消除待测电容两端的杂散电容,电路工作稳定性较高,电路还可以将电容值通过振荡的方式转化为只有高低电平的脉冲宽度,便于不受干扰的传输测量结果,同时使用合理的微处理器可实现对脉宽的高精度测量,从而提高测量电路整体的灵敏性与分辨力.为了应用于气固流相浓度测量,使用带参比电容的张弛振荡电路,并进行了性能测试.结果表明,带参比电容的张弛振荡接口电路迟滞误差为0.30％,非线性误差为0.30％,重复性误差为0.32％,可以在气固两相流相浓度测量中应用.     

三相流分相浓度测量平台的标定试验

根据多相流流动特性对固相质量流量及流速之间的依赖关系,通过在以气力输送系统为基础的煤粉/生物质/空气三相流分相浓度测量系统实验平台上,对固相质量流量及风速分别进行了标定试验.结合标定结果将固体颗粒质量流量转换成所需的固相体积浓度,最终达到测量系统的测试要求.     

用文丘里测量风粉混合物的浓度和流量

一次风煤粉浓度的可靠测量是电站锅炉燃烧优化和安全经济运行的前提条件.研究表明气固两相混合物流过文丘里时的差压与气体单独以相同流量流过文丘里时的差压存在一定的关系,这为气固两相文丘里流量计的研究提供了基础.气固两相文丘里流量计的应用与不断完善对提高锅炉参数的测量与控制水平具有重要的意义.     

双层电容层析成像传感器及应用

电容层析成像在气力输送过程中具有十分重要的应用地位，可进行固相浓度分布测量，流型判断。利用双层电容层析成像传感器不仅可以进行浓度测量还可以进行相关测速。基于这种思想，设计了一种双层电容传感器，与电容测量系统结合，用于气力输送过程固相浓度和速度的测量。     

High GVF and low pressure gas–liquid two-phase flow measurement based on dual-cone flowmeter

Parameter measurement of gas–liquid two-phase flows with a high gas volume fraction (GVF) has received great attention in the research field of multiphase flow. The cone meter, as a new proposed differential pressure (DP) meter, is increasingly being applied in flowrate measurement of gas–liquid two-phase flow. A dual-parameter measurement method of gas–liquid two-phase flow based on a dual-cone meter is proposed. The two-phase flow is investigated in a horizontal pipeline with high GVF and low pressure, and exists in the form of annular flow. By adding a second cone meter, both gas mass fraction (GMF) and mass flowrate are measured. The pressure drop performances of five different sized cones have been discussed to make a cooperating cone selection and efficiently position the dual-cone in the pipe. Dual-cone flowmeter experiments of 0.45 and 0.65 equivalent diameter ratio combination, and 0.65 and 0.85 equivalent diameter ratio combination are respectively carried out to analyze the linearity of two-phase flow multiplier with Lockhart–Martinelli parameter and obtain the dual-parameter measurement results. The relative experiment error of GMF, gas mass flowrate and total mass flowrate are respectively within ±7%, ±5% and ±10%. The relative error of the liquid phase is within ±10% when the liquid mass fraction is beyond 40%. The experimental results show that it is efficient to utilize this dual-cone method for high GVF and low pressure gas–liquid two-phase flow measurement.     

Comparison of throttle devices to measure two-phase flowrates of wet gas with extremely-low liquid loading

The online measurement of wet gas with extremely-low liquid loading (Lockhart-Martinelli parameter lower than 0.02) remains a challenge. In this study, three types of throttle devices, Venturi, orifice plate and cone, are compared experimentally with air-water two-phase flow in a horizontal pipe of inner diameter of 50 mm. High-precision correlations are established to measure the gas and liquid flowrates via a single throttle device. Results show that the two-phase mass flow coefficient (K) of the three throttle devices all increase linearly with the liquid densiometric Froude number and the K correlations are established respectively to correct the gas mass flowrate deviation. The pressure loss ratio (δ) for Venturi is sensitive and monotonous to the liquid loading, which contributes to the high accuracy of liquid flowrate measurement. By incorporating the K correlations, both the gas and liquid mass flowrates can be predicted precisely. The relative error of the gas mass flowrate predicted by the Venturi is within ±2.0% at 95% confidence level, and that of the liquid mass flowrate is within ±15% at 90% confidence level.     

An instrumentation system for multi-parameter measurements of gas-solid two-phase flow based on Capacitance-Electrostatic sensor

In this paper, an instrumentation system for the measurements of local solid volumetric concentration, local solid velocity, local solid mass flowrate and solid mass flowrate in gas-solid two-phase flow system is developed. It is based on a new type of a Capacitance-Electrostatic sensor (CES). The CES sensor is mainly composed of a capacitance electrode array and two electrostatic electrode arrays. The optimum design of the sensor is achieved by finite element method. The capacitance electrode array is employed to detect the solid distribution over the cross-section of the pipe, and the local solid volumetric concentration measurement is further derived. The electrostatic electrode arrays are used to measure the local solid velocities in conjunction with cross-correlation method. From the local solid velocity and local volumetric concentration, the solid mass flowrate and the local solid mass flowrate can be achieved. The developed system for the local solid volumetric concentration measurement is verified through analogue simulation experiments and static experiments. Finally, the system is employed to measure the local solid volumetric concentration, local solid velocity, local solid mass flowrate and solid mass flowrate on a belt conveyor. The experimental results show that the measurement error of the local solid volumetric concentration measurement results are less than 10.43% for solid local volumetric concentration ranging from 0.02 to 0.56, the standard deviations of the local solid velocity measurement results are less than 0.42 for solid velocity ranging from 3.5 m/s to 15.0 m/s, and the relative error of the solid mass flowrate is within −19.6% to +14.9% for solid mass flowrate ranging from 0.006 kg/s to 0.103 kg/s, indicating that the system is capable of achieving multi-parameters measurement in gas-solid two-phase flow system.     

阵列式静电-电容传感器灵敏度特性研究

结合静电和电容传感技术各自的特点,提出了阵列式静电-电容传感器用于气固两相流中固相颗粒的局部速度、局部浓度以及局部流量测量。利用静电极片阵列与电容极片阵列获取管道内颗粒的速度分布与浓度分布,进而计算出颗粒的局部流量。该阵列式传感器参数测量的准确性直接取决于它的空间灵敏度分布特性。对静电极片阵列和电容极片阵列的灵敏度特性进行了研究。首先,建立了静电极片阵列的三维静电场模型,通过有限元法分析静电极片阵列的结构参数(电极长度、电极覆盖角等)对传感器灵敏度特性的影响;然后根据电磁场理论建立电容极片阵列的数学模型,并对其进行数值计算,研究管道厚度、管道介电常数、电极覆盖角等参数对传感器灵敏度特性的影响;最后搭建了传动带装置进行了实验研究,实验结果证实了模拟结果的准确性,为阵列式静电-电容传感器的优化设计提供理论依据。     

A modified model for wet gas flowrate measurement considering entrainment downstream of a cone meter

To develop a reliable wet gas flowrate measurement model, the relationships between pressure drop characteristics and entrainment downstream of the cone are investigated experimentally. The equivalent diameter ratio of the cone is 0.45. The experimental fluids are air and tap water with X_LM in the range of 0–0.3. The two-phase mass flow coefficient and pressure loss ratio are employed to establish the measurement model. The piecewise characteristics of pressure loss ratio are disclosed innovatively, which is explained by the different intensity of entrainment downstream of cone caused by gas-liquid jetting. A simplified method for evaluating the degree of entrainment is proposed to facilitate the establishment of the modified measurement model. Under the present experimental conditions, the relative error of liquid fluctuates within ±20% when X_LM is larger than 0.02, and the relative error of gas flowrate is within ±5%. Compared with the model without piecewise consideration, the relative error of the liquid flowrate of the modified model reduces obviously under low wetness conditions (0.02<X_LM<0.1). The modified measurement model provides a reliable and cost-effective technology for wet gas flowrate measurement.     

Gas–oil two-phase flow measurement using an electrical capacitance tomography system and a Venturi meter

A new flowrate measurement method for gas–oil two-phase flow using an electrical capacitance tomography technique and a Venturi meter is reported in this paper. A hybrid image reconstruction algorithm combining the Tikhonov regularization and the Algebraic Reconstruction algorithm is used to obtain images. The cross-sectional void fraction is determined from the images. A Venturi meter is used as a velocity measurement device whilst five measurement models are introduced to predict the total mass flowrate of gas–oil two-phase flow. Experimental results obtained show that the performance of the proposed flowrate measurement system is effective.     

Compensation for Joule–Thomson effect in flowrate measurements by GMDH polynomial

The international standard for flowrate measurements ISO-5167 recommends the temperature sensor to be located downstream of the differential device what may cause a significant error in the measurement of the flowrate of natural gas, especially at high differential pressure, low temperature and low diameter ratio. The flowrate generally needs to be compensated for the temperature change due to the Joule–Thomson effect caused by the constriction of the metering device. The accurate compensation involves double calculation of both the natural gas properties and the flowrate. To decrease the computational load, an automatic correction of the flowrate by the GMDH polynomial surrogate is proposed. By using the compound measure of the approximation error and the execution time for model selection, the modified GMDH algorithm searches for the satisfactory model fulfilling the constraints of real-time application. The automatic correction of the flowrate measurements of a natural gas is simulated and the corresponding results are discussed. The derived model can be equally used for a natural gas specified by composition or by physical properties.     

气固两相流中基于神经网络的固相质量流量检测方法的研究

用神经网络的自学习算法对采样数据进行辨识得出固相质量流量的黑箱模型，实现固相质量流量的在线测量。实验结果，模型最大测量误差为１０％     

Gas–liquid two-phase flowrate measurement in pseudo-slug flow with Venturi

The importance of pseudo-slug flow research is becoming increasingly prominent in the petrochemical field. But the gas–liquid two-phase flowrate measurement in the pseudo-slug flow has not been properly understood and modeled. Based on the differential pressure of Venturi, this study proposes a new pseudo-slug flowrate prediction model. By means of Fast Fourier transform (FFT), the representative frequency range (3.125 Hz < f < 6.25 Hz) is determined. Then, the fourth detail component of the differential pressure after wavelet transform is selected as the flag to distinguish the liquid film region and the pseudo-slug body region. Based on the gas–liquid density ratio, a logarithmic model is established to predict the threshold value. In the liquid film region, the gas–liquid two-phase flow is regarded as wet gas and the flowrate is measured through the over-reading model. In the pseudo-slug body region, the volume gas holdup model is established based on the fluctuation information of the differential pressure. Then the gas–liquid two-phase flowrate can be obtained by solving the Bernoulli equation. Compared to the experiment, the confidence probability of ±10% relative deviation band is 97.78% for the gas, and the confidence probability of ±20% relative deviation band is 95% for the liquid.     

Stability-boundary effect in Coriolis meters

The Coriolis meter is used for measuring the mass flowrate and density of fluids. If a measuring range is not sufficiently far from the stability boundary of its measuring tube (critical flowrate), both measuring effects can no longer be independent. This paper discusses a mathematical model of the straight, slender tube meter, solved by the Galerkin method. Utilizing a power series expansion in fluid velocity, theoretical characteristics are derived, including the stability-boundary effect. Based on theoretical findings, a procedure is suggested to make corrections of the interaction between the mass flowrate and density measurement.