Electrostatic sensors – Their principles and applications

Electrostatics of granules and granular flows: A review

Online continuous measurement of the mass flow rate of pneumatically conveyed solids is desirable in the monitoring and optimization of a range of industrial processes, such as food processing, chemical engineering, and power generation. This article introduces a technique for the mass flow rate measurement of pneumatically conveyed solids based on multimodal sensing and data-driven modeling. The multimodal sensing system is comprised of an array of ring-shaped electrostatic sensors, four arrays of arc-shaped electrostatic sensors, and a differential-pressure (DP) transducer. Data-driven models, including artificial neural network (ANN), support vector machine (SVM), and convolutional neural network (CNN), are established through training with statistical features extracted from the postprocessed data from the sensing system. Statistical features are shortlisted based on their importance by calculating the partial mutual information (PMI) between the features and the corresponding reference mass flow rate of solids. Experimental work was conducted on a laboratory-scale rig to train and test the models on both horizontal and vertical pipelines with particle velocity ranging from 10.1 to 36.0 m/s and mass flow rate of solids from 3.2 to 35.8 g/s. Experimental results suggest that the ANN, SVM, and CNN models predict the mass flow rate of solids with a relative error within ±18%, ±14%, and ±8%, respectively, under all test conditions. The predicted mass flow rate measurements with the ANN, SVM, and CNN models are repeatable with a normalized standard deviation within 14%, 8%, and 5%, respectively, under all test conditions.

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Mass Flow Rate Measurement of Pneumatically Conveyed Solids Through Multimodal Sensing and Data-Driven Modeling

Characterization of gas-solid flow in a cold fluidized bed from signals of a non-invasive electrical charge sensor

Flame monitoring of industrial combustors with high-reliability sensors is essential to operation security and performance. An ion current flame sensor with a simple structure has great potential to be widely used, but a weak ion current is the critical defect to its reliability. In this study, parameters of the ion current sensor used for monitoring flames on a Bunsen burner are suggested, and a method of further improving the ion current is proposed. Effects of the parameters, including the excitation voltage, electrode area, and electrode radial and vertical positions on the ion current, were investigated. The ion current grew linearly with the excitation voltage. Given that the electrodes were in contact with the flame fronts, the ion current increased with the contact area of the cathode but independent of the contact area of the anode. The smaller electrode radial position resulted in a higher ion current. The ion current was insensitive to the anode vertical position but largely sensitive to the cathode vertical position. Based on the above ion current regularities, the sensor parameters were suggested as follows: The burner served as a cathode and the platinum wire acted as an anode. The excitation voltage, anode radial and vertical positions were 120 V, 0 mm, and 6 mm, respectively. The method of further improving the ion current by adding multiple sheet cathodes near the burner exit was proposed and verified. The results show that the ion current sensor with the suggested parameters could correctly identify the flame state, including the ignition, combustion, and extinction, and the proposed method could significantly improve the magnitude of the ion current.

https://www.mdpi.com/1424-8220/21/3/697/pdf

Parameter Determination and Ion Current Improvement of the Ion Current Sensor Used for Flame Monitoring

The flame boundary is an important geometrical characteristic for the evaluation of flame properties such as heat release rate and radiation. Reliable and accurate measurement of the flame boundary is desirable for the prediction of flame structure and the optimization of combustion systems. Such measurement will inform the designers and operators of the combustion systems. This article presents for the first time a study of using an electrostatic sensor array for flame boundary measurement. The electrostatic sensor is placed in the vicinity of the flame to sense its movement through charge transfer. The principle, design, implementation, and assessment of a measurement system based on this methodology are introduced. Comparative experimental investigations with a digital camera conducted on a laboratory-scale combustion test rig show that the electrostatic sensor can respond to the variation of the distance between the electrode and the flame boundary. Reconstruction of the flame boundary is achieved using a set of distance measurements obtained from a sensor array. For diffusion flames over the range of fuel flow rate 0.60–0.80 L/min and premixed flames over the range of equivalence ratio 1.27–3.81, experimental results show that the measurement system is capable of providing a reliable measurement of the flame boundary. The correlation coefficients under all test conditions are mostly larger than 0.96, the mean relative errors within 7.4%, and the relative root-mean-square errors within 0.09. More accurate flame boundary measurements are achieved for diffusion flames. In addition, the overall polarity of charges in a flame can be determined from the polarity of the sensor signal.

/pdf/flame-boundary-measurement-using-an-electrostatic-sensor-2kt6kbcdto.pdf

Flame Boundary Measurement Using an Electrostatic Sensor Array

Oscillation frequency measurement of gaseous diffusion flames using electrostatic sensing techniques

The charge density in a flame contains important information about the combustion processes that is difficult to obtain due to fast, complex, and highly exothermic reactions. This paper presents a study of using electrostatic probes to measure the charge density in methane fired diffusion and premixed flames. The sensing principle, practical design, and performance assessment of the electrostatic probe are presented. Comparative experimental studies with a reference ion-current sensor carried out on a combustion test rig indicate that the fluctuation of the signal from the electrostatic probe arises from the variation in the charge density in a flame. A dimensionless index, combining the average of local peak values in the electrostatic signal with the flame oscillation frequency, is adopted as an indicator of the charge density. Experimental results demonstrate that the charge density in a methane diffusion flame has an increasing trend with the fuel flowrate varying from 0.80 L/min to 1.20 L/min. The charge density in a methane-air premixed flame yields a decreasing trend with the equivalence ratio ranging from 0.54 to 0.75, then increases and reaches a local peak at the equivalence ratio of 1.03, and continues to increase when the equivalence ratio varies from 1.03 to 3.50. The charge density in the inner cone is higher than that in the outer cone for diffusion and premixed flames. The results obtained suggest that the developed electrostatic probe and the index can be used to indicate the charge density in diffusion and premixed flames.

/pdf/measurement-of-charge-density-in-methane-fired-diffusion-and-v6q0lthlr9.pdf

Jiali Wu

Papers

Electrostatic sensors – Their principles and applications

Flame Boundary Measurement Using an Electrostatic Sensor Array

Oscillation frequency measurement of gaseous diffusion flames using electrostatic sensing techniques

Measurement of Charge Density in Methane Fired Diffusion and Premixed Flames Using Electrostatic Probes