جستجوی مقالات مرتبط با کلیدواژه "bubble size" در نشریات گروه "مکانیک"

This paper investigates the air bubble size and its transition in a horizontal tube of 700 mm. The tube was assembled with a venturi-nozzle bubble generator. Air and water flow-rates vary in the present study. The data collection mainly used high-speed camera to capture the bubbles at different distances along the horizontal tube at water flow-rates (Qw) of 120-170 litre per min (LPM) and air flow-rates (Qa) of 2-10 LPM. MATLAB was used in image processing for evaluating the bubble size. The data interpretation used YW dimensionless parameter in representing the height of the bubbles’ vertical rise in the horizontal tube. The bubble size along the horizontal tube was characterized by the Weber number as well. The type of two-phase (water-air bubbles) flow along the horizontal tube from the venturi-nozzle bubble generator was determined using flow pattern map and Lockhart-Martinelli parameter. The bubble generator produced bubbles in the range of 0.8-3.1 mm at the inlet of horizontal tube. The bubble diameters increased as the bubbles moved horizontally from inlet to outlet of the horizontal tube and this finding was statistically significant. The vertical rise height of bubbles along the horizontal tube at different water and air flow-rates had been quantified and compared. The vertical rise height of bubbles increased axially from 41 % to 89 % from inlet to outlet of the horizontal tube. The bubbles’ vertical rise height increased when either the air flow-rate or water flow-rate is reduced. The mean Weber number increased along the horizontal tube due to an increase in bubble size. The decrease in water flow-rate caused a decrease in the mean Weber number. The Lockhart-Martinelli parameter of the water-air bubbles flow in the horizontal tube was within 0.58-2.94, indicating that it was a multiphase flow. The findings from this study give fundamental insight into bubble dynamics behaviour in its horizontal transition. This study focuses on the size and transition of air bubbles produced by venturi-nozzle bubble generator along a horizontal tube at different water and air flow-rates, unlike previous studies which only investigate the air bubbles inside or near bubble generator. These findings are very useful for practical industrial applications because the exact air bubble size before being used is known.

To investigate the characteristics of the bubbles trapped in liquid cross flow, air was injected into flowing water circulated in a closed loop. High speed photography was used to record bubble images instantaneously. An image-processing code was specifically developed to identify bubbles in the images and to calculate bubble parameters. Effects of the water velocity and the flow rate of the injected air on bubble patterns were investigated. The results indicate that the inclination of bubble trajectory relative to the nozzle axis is enhanced as the water velocity rises. Meanwhile, bubble size varies inversely with the water velocity. The bubble profile tends to be rounded as the water velocity increases. Fluctuations of the bubble velocity are intensified as the water velocity decreases. As the balance between the external forces exerted on the bubble is reached, an approximately linear relationship between the velocities of the bubble and the water is manifested. For a given equivalent bubble diameter, the bubble terminal velocity is higher than that associated with quiescent water. At small Eötvös number, the consistency of the bubble aspect ratio in the liquid flow and quiescent water is revealed. The range of Eötvös number is extended considerably due to the flowing water. Values of Weber number are accumulated in a range within which high bubble aspect ratio is associated with relatively high water velocity.

Gas holdup and bubble size are important parameters for simulation and designing in bubble column reactors. Because based on these parameters, the available gas-liquid interfacial area is defined for mass transfer. In this paper, the results of applying magnetic fields on the velocity field and volume fraction of gas holdup are reported. Hydrodynamics of the bubble column in the reactors is investigated numerically using Euler-Euler model, standard k-ε turbulence model considering axisymmetric assumption, and the control volume technique. The results show that the magnetic fields have minor effects on increasing the volume fraction of gas holdup, but it causes to change in the flow field and vortex. In addition, effects of other parameters as well as rotation of the fluid, bubble size, and variation of inlet velocity on the volume fraction of gas holdup have been presented