一种用于在线测量的电容层析成像图像重建算法

提出了一种新的、快速的电容层析成像算法。在分析极小范数解的基础之上针对ECT逆问题的特点对其进行改进,并利用奇异值分解定理证明这种改进的数值稳定作用,从而从极小范数解的角度解决了ECT逆问题数值解的唯一性和稳定性问题;在此基础上从最优化的角度推导出进一步提高重建图像质量的公式;数值实验表明这种改进是有效的,其图像重建时间近似LBP,然而成像质量比LBP、Tikhonov和Landweber迭代法要好。     

电容层析成像技术研究进展

在介绍了电容层析成像技术原理及组成部分的基础上,详细阐述了电容层析成像技术的研究现状,包括微小电容检测与数据采集系统、图像重建算法和应用研究,总结了电容层析成像技术在多模态成像、图像重建算法及成像质量评价等方面面临的挑战,并指出了未来努力的方向。     

电容层析成像技术在线测量气固流化床空隙率的研究

基于电容层析成像技术，提出了一种在线测量气固流化床空隙率的新方法。建立了相应的12电极电容层析成像气固流化床空隙率测量系统，可同时实现气固 流化床空隙率分布的在线显示和整体空隙率测量。选择加权反投影算法进行图像重建以保证空隙率分布显示的实时性和有效性。采用Tikhonov正则化原理和ART算法相结合的组合型新图像重建算法来实现整体空隙率的测量。Tikhonov正则化原理用于克服图像重建过程中的不适定问题，ART算法用于提高最终重建图像的质量。研究表明以上提出的空隙率测量新方法是有效的。空隙率分布在线测量的速度可达25幅／秒以上，整体空隙率测量的最大误差可小于5％。     

用于两相流流型显示和空隙率测量的电容层析成像技术

引　言两相流流型的实时显示和空隙率的在线测量对两相流系统的控制、运行乃至机理研究等均具有重要意义 ,一直是两相流领域中重要的研究方向 .现已提出多种实现流型显示和空隙率测量的方法 ,例如用于流型显示的核辐射线法和光学法 ,用于空隙率 (或浓度 )测量的机理估算法、核辐射线法、电学法、光学法、微波法、热学法和核磁共振法等 ,但是总的来讲还未能满足应用要求 ,实际应用的例子也较少[1] .电容层析成像 (ｅｌｅｃｔｒｉｃａｌｃａｐａｃｉｔａｎｃｅｔｏｍｏｇｒａｐｈｙ ,简记ＥＣＴ)技术由于可在不干扰流场的情况下获取反映两相流…     

电容层析成像测量气固两相流的影响因素

气力输送管道内经常出现的磨损现象和被测介质的不透明性,使得运用常规方法测量固体流动时的参数困难重重。ECT作为最先进和最有效的方法之一,可在线测量流动管道内固体横截面浓度分布和固体速度,便可计算得到固体质量流量。然而在大部分实际应用中,存在许多因素会影响管内固体的横截面浓度分布和固体的湿度值,使计算质量流量时产生误差。本文通过探讨找到解决此问题的方法,使得计算误差减小到可以忽略,结果更贴近实际情况。     

基于数据驱动的卷积神经网络电容层析成像图像重建

针对电容层析成像技术的图像重建问题,提出了基于数据驱动的卷积神经网络图像重建方法。根据气固两相流的流型特点,通过数值模拟的方法随机生成了60000组介质分布图像,并利用有限元法计算了与之对应的电容向量,从而建立了一个“电容向量-介质分布”数据集;然后根据电容层析成像图像重建特点建立了卷积神经网络模型,对数据集中的训练集进行学习和训练,并利用测试集对训练结果进行了验证与评价。在此基础上,对获得的ECT图像重建卷积神经网络模型进行了静态实验和流化床测试实验研究。模拟和实验结果表明：所建立的卷积神经网络能较好地实现ECT图像重建,可直接用于流化床内的颗粒浓度分布测量。     

基于电容层析成像多相流检测的动态重建算法研究

为了提高ECT图像重建质量,提高ECT在线监测的精确性,提出了一种广义动态图像重建算法(DR),集合了ECT测量信息和流动对象的物理演变信息。该算法同时考虑被测对象的空间约束、时间约束以及动态变化信息的目标功能。动态实验研究表明,该算法成功解决ECT逆问题,有效突破了ECT图像重建的数值不稳定性,其成像质量明显好于一般的静态图像重建算法。     

非规则结构电容层析成像填补法测量的敏感场特性及重构算法改进

利用填补的方式将不规则区域转为规则成像区,可拓展电容层析成像的测量范围。首先分析了填补法对应的敏感场特性,然后分别研究了敏感场、归一化电容、填充区介电常数和图像重构算法对填补法成像的影响。并利用特定的填充区边界条件对Landweber算法进行改进,提出两种改进方法:变换矩阵和拆分矩阵的Landweber图像重构方法。结果表明,填充区使电容信号绝对值增强,非线性程度增加。不同背景的敏感场对成像影响较小,但填充区充满时的敏感场可强化环状流成像。去除填充区噪声的归一化电容矩阵有利于图像重构。填充物质的介电常数与测量区高介电常数相近时成像最佳。拆分矩阵法降低了求解维度,缩短了计算时间,对各种流型成像整体效果较好,基于松弛因子改进还可进一步优化重构图像。最后,在一般非规则结构中对改进方法的可靠性进行了测试验证。研究表明,改进方法可以用于一般性不规则结构的相分布测量,未来还可以用于因高温、腐蚀等无法直接进行电极安装的工业场合中,具有改进多相流测量方法的普遍意义。     

利用电容层析成像技术快速测量油气两相流空隙率的研究

基于12电极阵列式电容传感器电容测量信息,提出了一种油气两相流空隙率测量的新方法.该方法在实际测量过程中,首先对当前流型进行辨识,然后应用相应的空隙率测量模型计算空隙率.空隙率测量模型本质上是不同流型下对空隙率测量敏感的多个测量电容的最佳组合,该组合采用改进的遗传算法并辅以偏最小二乘获得,而流型辨识的结果则是采用电容层析成像技术结合模糊模式识别技术获得.实验结果表明,提出的空隙率测量新方法是有效的,测量精度满足工业应用的要求.     

采用二阶导数阵作为正则化的电容成像图像重建算法

Tikhonov正则化方法是解决病态逆问题的常用方法,正则化项的引入能改善问题的病态性。利用Laplace算子对正则化项中所包含的图像信息进行锐化处理,可提高电容成像图像重建的质量。仿真结果表明,相对于标准形式的Tikhonov正则化方法,采用正则算子为二阶导数算子的正则化方法图像重建结果边缘及轮廓清晰,对于各种设定流型均具有良好的适应能力,且图像重建结果对初始设定解不敏感,图像重建结果质量更高。     

Investigation of fluidized bed behaviour using electrical capacitance tomography

The temporal and cross-sectional distributions of particles in a 127 mm diameter fluidized bed have been obtained using a new generation, high-speed electrical capacitance tomography. Two planes of eight electrodes were used and mounted at 160 and 660 mm from the gas distributor which was a 3 mm thick porous plastic plate (maximum pore size of 50-70 μ m). 3 mm diameter, nearly-spherical polyethylene granules made up the bed. Experiments at sampling frequencies of 200-2000 cross-sections per second and gas superficial velocities from just below the minimum fluidization to 83% above minimum fluidization velocities were used. The time series of the cross-sectional average void fractions have been examined both directly and in amplitude and frequency space. The last two used probability density functions and power spectral densities. The information gathered shows that the fluidized bed was operating in the slugging mode, which is not surprising given the size of the particles. It has been found that an increase in the excess gas velocity above the minimum fluidization velocity resulted in an increase in the mean void fraction, an increase in the length and velocity of the slug bubbles as well as the bed height, and a slight decrease in the slug frequency. The results are presented in a level of detail suitable for comparison with later numerical simulation.     

电容层析成像在高压浓相煤粉气力输送中的应用

Electrical capacitance tomography (ECT) was applied to dense-phase pneumatic conveying of pulverized coal, including the visualization of gas-solid flows in a horizontal pipeline.The pressure of experimental setup was up to 4.0 MPa, the solid-gas ratio was up to 11.73 kg·kg-1, and the diameter of conveying pipeline was 10 mm.The pipeline thickness of 8-electrode ECT system was 5 mm.An improved AC-based capacitance measuring circuit was developed.Single channel capacitance measuring circuit was adopted to si...     

电容层析成像技术在分离器料腿浓度测量中的应用

Accurate solid concentration measurement plays a key role in the process industry. Measurements analyzed offline can be used to estimate process efficiencies, to identify problems in a flow, and to validate computational models. Online measurements can be used for active control. Electrical capacitance tomography (ECT) is a unique measuring technique with great potential in multiphase flow measurement. Experimental studies are carried out on a solid concentration measurement in a cyclone separator dipleg, using ECT. In this experiment eight electrodes are selected for the ECT sensor that is placed on the straight tube of the dipleg. The fluctuating characteristics according to the screw feeder and the effect of the airflow rate from the top of the cyclone are analyzed. The feasibility and reliability of the method are verified by the experimental results.     

Measurement of particle concentration in a Wurster fluidized bed by electrical capacitance tomography sensors

It is essential to measure and monitor the particle flow characteristics in a Wurster fluidized bed to understand and optimize the coating processes. In this article, two electrical capacitance tomography (ECT) sensors are used to measure the particle concentration in different regions in a Wurster fluidized bed for the “cold” particle flows. One ECT sensor has a 12‐4 internal‐external electrodes and another has eight electrodes. The 12‐4‐electrode ECT sensor is used to measure the particle concentration in the annular fluidization region (outside of the Wurster tube) and the eight‐electrode ECT sensor is used to measure the particle flow in the central region (inside the Wurster tube). The effect of particle type, particle moisture, fluidization velocity, and geometrical parameters on the Wurster fluidization process is studied based on the two ECT measurements. The radial particle concentration profiles in the annular fluidization and central flow regions with different operation parameters are given. Fast Fourier Transform analysis of the particle concentration in the Wurster tube is performed with different superficial air velocities. The optimum operating ranges of the Wurster fluidization process for different particles are given. In the end of the article, computational fluids dynamics simulation results are given and used to compare with the measurement results by ECT for a typical Wurster fluidized bed. © 2014 American Institute of Chemical Engineers AIChE J 60: 4051–4064, 2014     

A simple method for identifying bubbling/jetting regimes transition from large submerged orifices using electrical capacitance tomography (ECT)

The bubbling–jetting transition regimes from large orifice submerged in water were investigated for various orifice diameters. A simple and fast way for identifying the regime transition was successfully developed using electrical capacitance tomography (ECT). In all the experiments deionised water was liquid phase and air was gas phase. Orifice gas velocity (V_N) and orifice diameter (d_o) were varied from 0.8 to 186 m/s and 4–21 mm, respectively. It was found that the V_N,trans. strongly depends on the orifice diameter. In the small orifice diameter (d_o < 10 mm), V_N,trans. greatly decreases with the increase of orifice diameter. However, in the large orifice diameter (d_o > 10 mm), the effect of orifice diameter on the transition velocity is insignificant. Finally, the data obtained by ECT compares with other works and the dimensionless orifice Reynolds number (Re_o ～11,000) is preferred to identify the bubbling–jetting transition regimes.     

基于ECT和蚂蚁算法的油气两相流空隙率在线测量

基于电容层析成像系统（ECT）和蚂蚁算法,提出了一种油气两相流空隙率在线测量的新方法。该方法利用电容层析成像系统12电极电容传感器所获取的66个测量电容信息,首先根据电容层析成像系统所获取的流型辨识结果确定对应流型下的实际空隙率测量模型参数f和b,然后利用蚂蚁算法的信息素信息,找到当前测量状态下对空隙率起主要作用的组合电容集合和相应的权重系数,从而实现空隙率测量。与流型相对应的空隙率测量线性模型参数f和b基于先验数据通过最小二乘方法确定。油气两相流的实验结果表明,该方法对空隙率的在线测量是有效的,避免了复杂的图像重建计算,实时性能佳,测量时间小于0.08 s。在几种典型流型下,提出的空隙率测量方法与常用的快关阀方法相比最大测量偏差小于5.5%。     

Reconstruction of electrical capacitance tomography images based on fast linearized alternating direction method of multipliers for two-phase flow system

Electrical capacitance tomography (ECT) has been applied to two-phase flow measurement in recent years. Image reconstruction algorithms play an important role in the successful applications of ECT. To solve the il-posed and nonlinear inverse problem of ECT image reconstruction, a new ECT image reconstruction method based on fast lin-earized alternating direction method of multipliers (FLADMM) is proposed in this paper. On the basis of theoretical analysis of compressed sensing (CS), the data acquisition of ECT is regarded as a linear measurement process of permittivity distribution signal of pipe section. A new measurement matrix is designed and L1 regularization method is used to convert ECT inverse problem to a convex relaxation problem which contains prior knowledge. A new fast alternating direction method of multipliers which contained linearized idea is employed to minimize the objective function. Simulation data and experimental results indicate that compared with other methods, the quality and speed of reconstructed images are markedly improved. Also, the dynamic experimental results in-dicate that the proposed algorithm can fulfil the real-time requirement of ECT systems in the application.