Intermittent flow initiation in a horizontal tube: quantitative visualization and CFD analysis

Abstract

The onset of slugging in stratified gas-liquid flow in a 26.4-mm ID horizontal pipe was investigated experimentally using a high-speed digital video processing technique. Spatio-temporal displacement maps were produced to show the evolution of two-phase flow structures (waves, slug precursors and liquid slugs) in the flow entrance region of the air-water mixture flow. The two-phase distribution derived from the visualization technique was in good agreement with measurements performed using non-intrusive capacitance sensors. Numerical results from a hybrid CFD approach that combined the twofluid model and volume-of-fluid method to track the position of the large-scale interface in time and space also agreed well with the quantitative flow visualization data for phase distribution, slug length and slug frequency. The relative errors between the flow structure velocities calculated by cross-correlating the numerical and experimental (image analysis) phase distribution signals were 6.8 and-7.4% for the slug and plug flow cases, respectively. Keywords Intermittent flow Á Slug initiation Á Image analysis Á Liquid holdup Á CFD analysis List of symbols F Frequency (Hz) g Acceleration of gravity (m s À2) j Superficial velocity (m s À1

The effect of air velocity on slugs in a confined channel

“…They concluded that using the VOF model, the formation and propagation of the slug flow regime along horizontal circular pipes is successfully described and validated against the experimental results. Costa et al [35] worked on a horizontal pipe with an inside diameter of 26 mm using the VOF method. Parameters such as slug velocity and slug length were in good agreement with the experimental results, with relative errors of less than 8% for the slug velocity.…”

Quantifying interfacial parameters of upward and downward annular flow condensation from high-speed visualization

“…The majority of them were focused on accurately determining film thickness, phase fractions and/or intermittent flow parameters (e.g., slug velocity, frequency and size) in adiabatic (air-water) flows [4,5]. Comparisons against more established experimental techniques [6,7] and numerical simulations have been carried out [8]. Among the most widely investigated methods, one can cite edge detection, watershed segmentation [9], ensemble averaging [10] and "blob" extraction [11].…”

Numerical Investigation of Two-Phase Flow Induced Local Fluctuations and Interactions of Flow Properties Through Elbow

“…Experimental studies [5][6][7] have been conducted in attempt to explore the transient interactions between phases in two-phase flows. A more detailed study investigated the evolution of slug and churn gas pockets using a multivariate pseudo Wigner distribution together with multivariate multiscale entropy to analysis the measured data [5].…”