Local Void Fractions and Bubble Velocity in Vertical Air-Water Two-Phase Flows Measured by Needle-Contact Capacitance Probe

Abstract

Multiphase flow measurements have become increasingly important in a wide range of industrial fields. In the present study, a dual needle-contact capacitance probe was newly designed to measure local void fractions and bubble velocity in a vertical channel, which was verified by digital high-speed camera system. The theoretical analyses and experiments show that the needle-contact capacitance probe can reliably measure void fractions with the readings almost independent of temperature and salinity for the experimental conditions. In addition, the trigger-level method was chosen as the signal processing method for the void fraction measurement, with a minimum relative error of −4.59%. The bubble velocity was accurately measured within a relative error of 10%. Meanwhile, dynamic response of the dual needle-contact capacitance probe was analyzed in detail. The probe was then used to obtain raw signals for vertical pipe flow regimes, including plug flow, slug flow, churn flow, and bubbly flow. Further experiments indicate that the time series of the output signals vary as the different flow regimes and are consistent with each flow structure.

Hydrodynamic Study of a Hybrid Electro-Flotation Column

“…Several techniques have been developed that aim to measure the volumetric gas fraction in a two-phase flow. Among them are capacitance sensors [31], magnetic resonance [32,33], ultrasonic methods [34,35], radiation attenuation techniques [36,37], and wire mesh sensors [38,39]. The void fraction in a two-phase flow can also be measured by applying acoustic emission technology for measuring acoustic emission signals.…”

Gas Void Fraction Measurement of Gas-Liquid Two-Phase CO2 Flow Using Laser Attenuation Technique

“…A variety of typical methods, including capacitance sensors [6,7], wire-mesh sensors [8,9], radiation attenuation techniques [10,11], magnetic resonance [12,13] and ultrasonic techniques [14,15] have been applied to measure the gas void fraction of the gas-liquid two-phase flow. The sensing principle of the capacitance sensors makes use of different electrical permittivities of the phases.…”

“…Such sensors have the advantages of a structural simplicity and low cost. Huang et al [6] designed a dual needle-contact capacitance probe to measure the local void fractions and bubble velocities of the air-water two-phase flow. Li et al [7] developed a method for the gas void fraction measurement and flow pattern recognition of the gas-oil two-phase flow based on a capacitance sensor and the least-squares support vector machine (LS-SVM) technique.…”