Sensitivity studies on the multi-sensor conductivity probe measurement technique for two-phase flows

Abstract

The objective of this study is to advance the local multi-sensor conductivity probe measurement technique through systematic investigation into several practical aspects of a conductivity probe measurement system. Firstly, signal "ghosting" among probe sensors is found to cause artificially high bubble velocity measurements and low interfacial area concentration (a i) measurements that depend on sampling frequency and sensor impedance. A revised electrical circuit is suggested to eliminate this artificial variability. Secondly, the sensitivity of the probe measurements to sampling frequency is investigated in 13 two-phase flow conditions with superficial liquid and gas velocities ranging from 1.00-5.00m/s and 0.17-2.0m/s, respectively. With increasing gas flow rate, higher sampling frequencies, greater than 100kHz in some cases, are required to adequately capture the bubble number frequency and a i measurements. This trend is due to the increase in gas velocity and the transition to the slug flow regime. Thirdly, the sensitivity of the probe measurements to the measurement duration as well as the sample number is investigated for the same flow conditions. Measurements of both group-I (spherical/distorted) and group-II (cap/slug/churn-turbulent) bubbles are found to be relatively insensitive to both the measurement duration and the number of bubbles, as long as the measurements are made for a duration long enough to capture a collection of samples characteristic to a given two-phase flow system (or a statistical ensemble). Fourthly, investigation into the orientation of a double-sensor probe in the pipe indicates that the sensors should be oriented parallel to the pipe wall to ensure symmetric bubble velocity measurements. Lastly, Monte Carlo simulations are performed to study the effects of the axial (s) and lateral (d) probe sensor separation distances. In addition to

Prediction of Bubble Size Distribution above the Bubble-Breaking Plate

“…Using this frequency for measurements ensures that the quantization error of the statistical results is at least less than 10% of the average value. However, the measurement results are not more accurate as the frequency increases because the signal overlap phenomenon becomes more pronounced at higher measurement frequencies, which significantly impacts the measurement results . Therefore, the highest measurement frequency of the instrument, 20 kHz, was not used in this experiment, but a relatively high accuracy of 10 kHz was chosen.…”

Local Distributions of Bubble Velocity and Interfacial Area in the Slender Particle-Containing Scrubbing–Cooling Chamber of an Entrained-Flow Gasifier

“…Sampling time and frequency have been validated in Peng et al 13 as well. It is worth noting that Worosz et al 63 found that the interfacial area measurement strongly depends on the selection of the sampling frequency. Only when the sampling frequency is larger than 100 kHz can the measured interfacial area within ±5% of the values at 250 kHz be guaranteed.…”

Advanced Deep Learning-Based Bubbly Flow Image Generator under Different Superficial Gas Velocities

“…Some invasive detection methods, such as the conductance needle method, have limited application scope because of their interference with the movement of the bubbles in a flow field. 7 In recent years, the rapid development of high-speed photography and digital image processing technology provides new possibilities for noncontact measurements. Based on these techniques, many researchers, such as Mohagheghian and Elbing 8 and Feng et al, 9 have analyzed the bubbly flow characteristics in gas−liquid two-phase flow under different working conditions.…”

“…As bubbles often appear in clusters in the liquid phase, it is difficult to accurately capture the morphology and size distribution characteristics of bubbles. Some invasive detection methods, such as the conductance needle method, have limited application scope because of their interference with the movement of the bubbles in a flow field . In recent years, the rapid development of high-speed photography and digital image processing technology provides new possibilities for noncontact measurements.…”