Abstract
Air-water two-phase flow in pipes introduces a noticeable challenge due to the complexity of the fluids. Thus, to estimate the best design and reasonable financing cost of the transportation pipelines where the bends are presenting a part of their accessories, the investigators should have been able to estimate the flow regime occurring at different directions. An experiment was carried out by using a 90o bend fixed with two pipes where the flow was upstream from a vertical to a horizontal pipe which were representing the bend inlet and outlet respectively. Two wire-mesh sensors were used for obtaining the data of the void fractions (α) at water superficial velocities (Usl) which changed from 0.052 to 0.419m/s, and air superficial velocities (Usg) from 0.05 to 4.7m/s. Furthermore, the characterization of flow regimes of the air-water flow at both bend inlet and outlet were competed accurately by using void fraction analysis of the time series, Power Spectral Density (PSD), tomographic images observed by the sensor program, and the Probability Density Function (PDF) method. The flow regimes of vertical flow lines at the bend inlet were observed as bubbly, cap-bubble, slug, and churn flow, whereas the flow regimes of the horizontal flow line at the bend outlet were characterized as having stratified, stratified wavy, bubbly, plug, slug, wavy annular, and semi-annular flow due to the gravity and bend effects.
Highlights
Two-phase flow exists in a wide scope of mechanical applications and can be noticed in many scientific fields [1]
The following methods were utilized to classify the flow regimes occurring at the bend inlet in the vertical pipe and at the bend outlet in the horizontal pipe: the time series of void fraction, the tomographic images of the Wire-Mesh Sensor (WMS) program, Power Spectral Density (PSD), Probability Density Function (PDF), and mean void fraction and liquid holdup (H)
By increasing the Usg value to 0.28m/s at the bend inlet, the mean void fraction fluctuated frequently under the values of 0.2 and 0.7 (Figure 3(a)) The PDF plot exhibits two peaks at PDF values 0.01 and 0.05 (Figure 3(b)), while the PSD plot shows a single peak with a maximum of about 60 at 1.75Hz (Figure 3(c))
Summary
Two-phase flow exists in a wide scope of mechanical applications and can be noticed in many scientific fields [1]. The experimental study in [9] exhibited the identification of air-water flow in a 50mm horizontal pipe by using PDF and the void fraction of time series under different water and air superficial velocities according to the analysis estimated in [10]. They observed the following flow regimes in the horizontal pipe: annular-wavy, slug, bubbly, and stratified flow under air superficial velocities from 0.23 to 10.5m/s and water superficial velocities from 0.05 to 1.7m/s by using WMS to obtain the void fraction values. The comprehension of the air-water flow properties accounts on the knowledge of the flow patterns occurring inside the pipes, the exact prediction of the two-phase flow pattern is the starting point for designing systems able to save energy and diminish system collapse by calculating the void fractions and estimating the bend effect on the air-water flow regimes of the vertical riser pipe to the horizontal flow line
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