Investigating the Characteristics of Two-Phase Flow Using Electrical Capacitance Tomography (ECT) for Three Pipe Orientations

Abstract

Experiments of gas–liquid flow in a circular pipe for horizontal and inclined positions (upward/downward) are reported. The characteristics of two-phase flow in terms of liquid holdup (ε(L)) and induced flow patterns are studied using three experimental techniques; time-averaged ε(L) from permittivity profiles using electrical capacitance tomography (ECT), instantaneous ε(L) using two fast-closing valves (TFCV), and high-speed camera images (HSCI) to capture/identify the formed flow patterns. Thus, this experimental setup enables the development of more well-defined flow patterns in gas–liquid two-phase flow and allows for multi-technique verification of the results. Taken from experimental measurements, a model is proposed to predict ε(L) for high and low situations. The correlations are a function of the hydrodynamic dimensionless quantities which provide hydrodynamic similarity. Regarding different pipe orientations, ε(L) predictions are comparable to ε(L) from experimental measurements with accepted accuracy: 88% of the predictions are within ±5–15% and 98% are below ±20%. The correlations also were validated by reported results and against correlations available in the literature and show higher prediction accuracy. It is confirmed that the kinematic similarity which is achieved by the gas–liquid velocity ratios and the inertial forces influence the flow pattern and the liquid holdup.

A Simplified Numerical Approach to Examine the Sensitivity of Two-Electrode Capacitance Sensor Orientation to Capture Different Gas–Liquid Flow Patterns in a Small Circular Pipe

“…The experimental operating conditions consist of (a) different combinations of gas–liquid (i.e., air and water) superficial velocities, and (b) different tested inclination angles (i.e., 0°, +15°, +30°). The configuration of this setup and the initial operating conditions allowed the development of all the well defined multiphase gas–liquid flow patterns [ 28 , 32 , 33 ]. The setup was designed to operate with water as the liquid phase at the superficial velocity between 0 and 1.06 m/s, and with air as the gas phase the superficial velocity is between 0 and 5.0 m/s.…”

“…In other words, for example, the simulated small-bubbles/slug flow pattern is the same in structure for all inclination. The only two differences are (1) the combination of gas–liquid superficial velocities at which these flow patterns were induced due to the effect of gravity and inclination, and (2) some flow patterns did not form or develop in a certain inclination (i.e., the plug flow pattern at a horizontal 0°, and the stratified wavy at all upward inclined angles [ 28 , 32 ]).…”

“…Simply, the working principle of any capacitance sensor is that the capacitance output is the result of the variation in the two phases’ concentration as they pass the electrodes domain and its corresponding outcome on the dielectric constant [ 21 ]. Capacitance sensors come with a minimum number of two electrodes and up to 16 electrodes [ 25 , 28 , 29 ]. For constructing tomography images and calculating the liquid holdup with a high accuracy (as presented in Table 1 ), most of the capacitance sensors that were used had at least eight electrodes or more.…”

“…For constructing tomography images and calculating the liquid holdup with a high accuracy (as presented in Table 1 ), most of the capacitance sensors that were used had at least eight electrodes or more. However, as stated by Reinecke et al (1997), Bangliang et al (2000), and Almutairi et al (2020), more than two-electrode sensors requires the following supporting equipment; an acquisition system, immediate iteration method, multiplexer, an efficient resistance analyzer (or impedance), and a relatively high-speed processer with a display unit to reconstruct the produced images [ 28 , 30 , 31 ]. Moreover, apparent disadvantages were raised by many scientific researchers such as the blaring and distorted nature of the reconstructed images, the nonlinearity of the measurements, the severe disturbance of the electromagnetic field due to the length of the connected wires, and this approach is considered complex and expensive, which requires regular calibration [ 21 , 32 ].…”

Liquid-Liquid Flow Pattern Prediction Using Relevant Dimensionless Parameter Groups

“…(q,r) Larger elongated or spherical bubbles of one liquid in the other (SLo, Bo or SLw, Bw) [2]. For an accurate prediction of the multiphase flow features, it is essential to identify the flow pattern, because uncertainties in flow pattern determination greatly affect the liquid-hold up and pressure drop predictions [23]. Therefore, the flow pattern is a defining feature of multiphase flow.…”