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.

Sreenivas Jayanti

Department Of Chemical Engineering

Computational fluid dynamics

Drag

Interfaces (materials)

Liquid waves

Pressure effects

Tubes (components)

ANNULAR FLOW

COUNTERCURRENT FLOW

DIAMETER EFFECT

flooding

GAS LIQUID FLOW

STANDING WAVES

TUBE DIAMETER

VERTICAL TUBES

Multiphase flow

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IIT Madras

Theoretical investigation of the diameter effect on flooding in countercurrent flow

International Journal of Multiphase Flow

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

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.

Effect of tube diameter on flooding

Turbulence Models and Their Application in Hydraulics

1996 NRC annual report. Volume 13

Flooding and churn flow in vertical pipes

Experimental Thermal and Fluid Science

Air/water countercurrent flow limitation experiments with full-scale fuel bundle structures

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

Journal	Data powered by TypesetInternational Journal of Multiphase Flow
Publisher	Data powered by TypesetElsevier Ltd
ISSN	03019322
Open Access	No