This paper describes an experimental study on the effect of tube diameter on the mechanism of flooding in vertical gas-liquid countercurrent annular flow. Flooding experiments were conducted with three different tube inner diameters, namely, 25, 67 and 99 mm with smooth inlet and outlet conditions for air and water. The results indicate that the mechanism of flooding is qualitatively different in the small and the large diameter test sections. While flooding in the 25 mm diameter section occurred essentially by the upward movement of large waves created near the liquid outlet, no such waves could be seen in the 67 and the 99 mm diameter test sections. Here, flooding occurred by droplet carryover or by an unstable, churn-like motion in the liquid film. The results are compared with existing correlations. The effect of test section length on flooding was also investigated. © 2001 Elsevier Science Ltd. All rights reserved.

Sreenivas Jayanti

Department Of Chemical Engineering

M. Vijayan

Arcot R. Balakrishnan

Pipe flow

Tubes (components)

ANNULAR FLOW

Multiphase flow

COUNTERCURRENT FLOW

experimental study

Flood

GAS-LIQUID TWO-PHASE FLOW

pipe

size

IIT Madras is a public technical and research university located in Chennai, Tamil Nadu. Founded in 1959, it is recognised as an Institute of National Importance.

IIT Madras has been ranked as the top engineering institute in India for four years in a row by the National Institutional Ranking Framework of the MHRD

It currently offers undergraduate, postgraduate and research degrees across 16 disciplines in Engineering, Sciences, Humanities and Management. About 596 faculty belonging to science and engineering departments and centres of the Institute are engaged in teaching, research and industrial consultancy.

IIT Madras

Effect of tube diameter on flooding

International Journal of Multiphase Flow

Transient response of two-phase flow is important in many analyses of nuclear reactor accident scenarios. In the present work, we study the response of vertical annular flow to a sudden or gradual pipe contraction. The three component fields of gas-liquid annular flow, namely, the liquid film, the entrained liquid droplets and the gas core, show different behaviour as they pass through an area change section because of their very different inertias. Pressure variation through the contraction is a result of the integrated effect of these responses. In order to throw light on these, pressure profiles along the upstream and downstream sections of the contraction have been measured in air-water flow through a vertical converging pipe section for diameter ratios of 1.5 and 2.0 and for half-cone angles of 8° 15° and 90°. The gas-droplet field interaction has been studied using computational fluid dynamics simulations while the gas-film flow interaction has been studied using an analytical model for film flow. These studies highlight the role of droplet inertia as the principal contributor to the pressure change in the contraction. A semi-empirical model has been developed for the pressure loss coefficient in the contraction. © 2019

Annals of Nuclear Energy

Study of gas-liquid upward annular flow through a contraction

Gas-liquid annular flow through a vertical circular pipe is well-understood and detailed phenomenological models exist in the literature. In the present work, the case of flow through a diverging section is studied experimentally and theoretically. Experiments have been carried out in air-water flow through a vertical diverging pipe section with a diameter ratio of 1.5 and 2.0. Pressure profiles have been recorded upstream, across and downstream of the diverging section for the cases of sudden expansion and gradual expansion with included half-angles of 8° and 15° for the diverging section. These show that the pressure variation is characterized by a strong pressure recovery downstream of the expansion which is in turn influenced by the smoothness of the expansion and the interfacial friction. The non-dimensionalized pressure loss across the expansion, which has been determined by extrapolating the pressure variations upstream and downstream, is found to vary systematically with the diameter ratio, the angle of the expansion and the ratio of superficial liquid-to-gas Reynolds numbers. A method, which uses the equilibrium annular flow model and an empirically determined expansion pressure loss coefficient, has been developed for the prediction of the pressure variation across the diverging section. © 2014 Elsevier Ltd.

Experimental and modelling studies of gas-liquid vertical annular flow through a diverging section

Systematic experiments were conducted to study the postflooding situation in air - water countercurrent flow in a tube of 0.025 m internal diameter with smooth inlet and outlet conditions for the two phases. The downflow rate of water and the pressure gradient were measured over a range of flow rates for test-section lengths of 0.6, 1.2 and 2.0 m. Additional experiments were conducted with increasing and decreasing water flow rates at a constant air flow rate. The length of the test section or the way the flooding point was approached did not significantly affect the onset of flooding. The data show that, as the gas flow rate is increased, the pressure gradient can fall significantly in the postflooding situation due to depleting the downflow rate of liquid. Dimensionless correlations are proposed to calculate the downflow rate and the pressure gradient given for overall flow parameters.

AIChE Journal

Investigation of Postflooding Conditions in Countercurrent Gas-Liquid Flow

Experiments have been conducted on countercurrent flow of air and water in tubes of 25, 67 and 99 mm diameter. Measurements of the pressure gradient, film thickness and down flow rate were made for a range of air and water flow rates under pre- and post-flooding conditions. The data showed that the pressure gradient did not increase appreciably until just before the onset of flooding. The mean film thickness under pre-flooding conditions was also predicted well by the falling film correlations. However, both quantities showed significant deviations from this pattern under post-flooding conditions. Existing correlations for predicting the pressure drop under post-flooding conditions gave poor prediction of the present data as well of the data from the literature. New correlations are presented for the pressure gradient and the mean film thickness under post-flooding conditions. © 2001 Published by Elsevier Science Ltd.

Experimental study of air-water countercurrent annular flow under post-flooding conditions

Calculations have been performed using the CFDS-FLOW3D computational fluid dynamics code to determine the force exerted on a standing wave by gas flowing over it. It is found that the drag on the wave is mainly due to the pressure variation around it and that it is a strong function of the channel dimensions. Extension of these results to typical flooding conditions in countercurrent flow in vertical tubes shows that the gas velocity required to transport waves upwards increases significantly as the tube diameter increases. It is suggested therefore that the mechanism of flooding depends on the diameter of the tube and that flooding is induced by upward transport of waves from near the bottom of the tube in small diameter tubes whereas in large diameter tubes, it may occur due to entrainment and carryover of droplets near the liquid entry.

Theoretical investigation of the diameter effect on flooding in countercurrent flow

Experimental study of the effect of pipe length and pipe-end geometry on flooding

Prediction of the slug-to-churn flow transition in vertical two-phase flow

Proceedings of the Royal Society of London. Series A: Mathematical and Physical Sciences

The prediction of turbulent flows over roughened surfaces and its application to interpretation of mechanisms of horizontal annular flow

Countercurrent gas-liquid annular flow, including the flooding state

Journal	International Journal of Multiphase Flow
ISSN	03019322
Open Access	No