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Both electrostatic and capacitance sensing techniques have been increasingly attractive for gas solid flow measurement. Although independent flow monitoring can be achieved by either an electrostatic sensor or a capacitance sensor, the fusion of them could provide diversified flow information with simplified sensor structure when used for gas solid flow measurement. In this paper, a novel electrostatic coupled capacitance sensor is proposed for gas solid flow measurement, which could simultaneously act as an electrostatic sensor and a capacitance sensor and thus acquires electrostatic and capacitance information within the same sensing space. Through an in-depth theoretical analysis of the sensor principle based on a pair of concave electrodes, a corresponding interface circuit is designed for signal conversion and extraction. Experiments carried out on a single particle test rig and a belt-pulley rig verify that the electrostatic and capacitance signals can be simultaneously obtained from the proposed sensor through the designed interface circuit. Furthermore, a sensor prototype with a three-electrode configuration is designed to measure the particle velocity, concentration, mass flow rate and charge level on a gravity-fed solids flow rig, demonstrating the potential application of the developed electrostatic coupled capacitance sensor for the gas solid flow measurement. [ABSTRACT FROM AUTHOR]

The ac-based electrical capacitance tomography (ECT) system has been successfully used for visualizing gas–solid flow in various industrial processes, such as pneumatic conveyor and fluidized bed. However, the solid particles in gas–solid systems are charged due to the collisions between particles and pipe wall. The particle charging decreases the image reconstruction accuracy of the ac-based ECT system and even leads to the reconstruction image distortion. In this paper, the electrostatic effect on ECT by particle charging is first investigated theoretically, and then experiments on a belt conveyor rig are performed to verify the electrostatic effect. Experimental results showed that the particle charging causes the additional output of the ac-based C/V conversion circuit. When the additional output makes the output of the circuit in its saturation region, the reconstruction image from the ac-based ECT system is completely distorted. However, the particle charging has no effect on the ac-based ECT system when the output signal of the C/V conversion circuit is within its allowable output range. By choosing a suitable amplifier and appropriate feedback resistance and capacitance values ( R\!f and C\!f ), the saturation of the output signal of the $C/V$ conversion circuit is avoided, and so, the electrostatic signal superimposed on the output capacitance signal of the $C/V$ circuit can be completely removed by a bandpass filter due to their distinct frequency characteristics. As a consequence, the electrostatic effect on the ac-based ECT system can be eliminated by optimizing ac-based $C/V$ conversion circuit. [ABSTRACT FROM PUBLISHER]

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. [ABSTRACT FROM AUTHOR]

In this paper, a measurement system for the local mean velocity of pneumatically conveyed particles is proposed and developed. It mainly consists of electrostatic sensor arrays, signal conditioning circuits, and a digital signal processor (DSP)-based data acquisition and processing unit. Electrostatic sensor arrays are used to detect the charge on particles in its sensing zone and further make the local particle mean velocity measurement in conjunction with cross-correlation method. The sampling frequency is determined from theoretical analysis of the bandwidth of electrostatic signal and accuracy of correlation velocity calculation. Experiments are carried out on a belt conveyor and a gravity-fed particle rig to determine the optimized sampling number of the electrostatic signal through analyzing the measurement error of the transit time. The results showed that the more sampling numbers, the higher stability of measurement results. The repeatability of the measurement system is less than ±2.2% and the linearity is better than ±4.9% over the velocity range of 5.50–21.98 m/s. Experiments are also performed on a high-pressure dense-phase pneumatic conveying system of pulverized coal, indicating that the measurement system is capable of achieving local mean velocity measurement of pneumatically conveyed particles with the relative standard deviation less than 5.5%. [ABSTRACT FROM PUBLISHER]

Highlights: [•] The spatial sensitivity of the ESM is presented. [•] The spatial filtering effect of ESM is analyzed. [•] A dimensionless calculation model for the sensitivity of the ESM is suggested. [•] The analytical results are verified on a gravity-fed particle rig. [ABSTRACT FROM AUTHOR]

The signal quality and accuracy of the spatial filtering method for solid particle velocity measurement based on a linear electrostatic sensor array (LESA) are dependent on the spatial filtering characteristics of the LESA and particle distribution in a pneumatic conveying pipeline. In this paper, the charge induced on a circular LESA with different geometric sizes from a single particle having a unity charge is mathematically modeled. Furthermore, a dimensionless computation model of the sensitivity of the LESA is suggested based on a fitted cosine function to the finite-element calculation results of the mathematical model, and the spatial filtering characteristics and spatial selectivity of the LESA are quantitatively investigated based on the computation model. Experimental work was performed on a purpose-built particle flow test rig to verify the dimensionless computation model and the modeling results. Results obtained reveal that the LESA acts as a narrow-bandpass filter in the temporal and spatial frequency domains, and its spatial selectivity is closely related to the number, spacing, and width of the electrode. These results provide an important basis for the performance improvement and optimized design of the LESA for particle velocity measurement. [ABSTRACT FROM PUBLISHER]

Abstract: Particle velocity is one of the important parameters describing the flow state of gas–solid two-phase systems. In this paper, a novel spatial filtering method based on an electrostatic sensor matrix (ESM) is proposed for local particle mean velocity measurement in a gas–solid two-phase pipe flow. The sensing zone of each linear sensor array in the ESM is analyzed using a finite element method. The relationship between the frequency spectrum characteristics of the output signals of the ESM and local particle mean velocity is obtained. A local particle mean velocimeter based on the ESM is further designed and established. Performance of the velocimeter is evaluated on a gravity-fed particle flow rig. Experimental results demonstrate that the standard deviation of the measured velocities by the velocimeter is less than 11.1%. [Copyright &y& Elsevier]

Abstract: Particle charging generated by particle-wall, particle–particle and particle–gas contacts in pneumatic transport pipelines contain rich information on gas–solid flow hydrodynamics. In this paper, experiments were performed in a dense phase pneumatic conveying system, and electrostatic fluctuation signals were detected by a ring-shape electrostatic sensor that is based on electrostatic induction theory. Power spectrum analysis and Hilbert–Huang transform (HHT) were applied to the electrostatic fluctuations, namely outputs of the electrostatic sensor, to extract and characterize the intrinsic features of dense-phase gas–solid flow. Results show that the dominant peak of the power spectrum of the electrostatic fluctuations moves toward higher frequency with the increasing gas superficial velocity. The Hilbert–Huang transform reveals the non-linear and non-stationary intrinsic nature of the electrostatic fluctuations. By using the non-linear and non-stationary signal processing method (HHT), non-linear inter-modulation characteristics in the dense phase gas–solid flow were analyzed, and the relations between the energy distribution transmissions in intrinsic mode functions (IMFs) with different orders and the flow characterization of the dense phase gas–solid flow, was investigated as well, which can represent the behavior, stability and regime transitions of the gas–solid flow in the dense-phase pneumatic conveying system at high pressure. [Copyright &y& Elsevier]

Abstract: The fundamental measurement theory of an electrostatic probe and cross-correlation velocity measurement method are introduced in this paper. The effects of the probe''s geometric parameters, including the length of the probe; the thickness, length and relative permittivity of the dielectric pipe; the radius of the screen on the dimensionless calibration coefficient (k), and the statistical error of the transit time (τ m) of the correlation velocity measurement system using electrostatic probes were investigated theoretically. Finally the measurement system was applied in a 10 mm bore horizontal section of a dense-phase pneumatic conveying system under high pressure circulating pulverized coal over a superficial air velocity range of 0.5–7 m/s for a particle concentration 0.052–0.141 m3/m3. The experimental results that were obtained demonstrate that the system is capable of providing solid particle velocity measurements with repeatability better than 10% under the given experimental conditions. [Copyright &y& Elsevier]

This article describes the characteristics of ring-shaped electrostatic pulverized fuel meters and their applications. At the University of Teesside, UK, the electrostatic technique has been used to measure pulverized fuel flow concentration, velocity, and mass flow rate under lean-phase condition. The mathematic model has been developed to express the relationship between the root-mean-square (rms) value of the meter's output voltage and solids mass flow rate. The effects of solids velocity and particle size on measurements have also been reflected in the model. Furthermore, the model presents the sensitivity variations over the cross-sectional area of meter and along the pipe axis. The article also introduces the research carried out at Southeast University in China, where the technique has been extended to measure dense-phase flow of pulverized coal, which is common in gasification and blast furnaces. [ABSTRACT FROM AUTHOR]

Abstract: In gas–solid two-phase flow, the charge distribution is a very important process parameter which is useful to the study of electrostatic adhesion. Electrostatic tomography (EST) is a relatively new non-intrusive technique which can be used to acquire charge distribution. However, due to limited measurements, the quality of image reconstruction is poor. In this paper, a dual-mode sensor technique based on electrical capacitance tomography (ECT) and EST is proposed. The theoretical analysis and the numerical simulation results reveal that the permittivity distribution obtained from ECT can provide a priori knowledge for the inversion calculation of EST, so that the accuracy of spatial sensitivity calculation in EST can be improved. This proposed technique is expected to be prospective in industrial applications and will also be beneficial to the research on the fluid dynamics of gas–solid two-phase flow. [Copyright &y& Elsevier]