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Gas-liquid Flow (gas-liquid + flow)

Distribution by Scientific Domains
Chemistry100%

Selected Abstracts

Numerical Study on Bubble Formation of a Gas-Liquid Flow in a T-Junction Microchannel

CHEMICAL ENGINEERING & TECHNOLOGY (CET), Issue 12 2009
L. Dai
Abstract Bubble emergence in a gas-liquid flow in a T-junction microchannel of 100,,m diameter, operated under a squeezing regime, was simulated with the computational fluid dynamics method. In general, bubble formation in channels includes three stages: expansion, collapse and pinching off. After analyzing and comparing quantitatively the three forces of pressure, surface tension and shear stress acting on the gas thread in the whole process, their effects in the different stages were identified. The collapse stage was the most important for bubble formation and was investigated in detail. It was found that the collapse process was mostly influenced by the liquid superficial velocity, and the rate and time of collapse can be correlated with empirical equations including the liquid superficial velocity, the capillary number and the Reynolds number. [source]

Detecting regime transitions in slurry bubble columns using pressure time series

AICHE JOURNAL, Issue 7 2005
Keshav C. Ruthiya
Abstract Changes in the coherent standard deviation and in the average frequency of measured pressure time series with gas velocity, are proposed, as unique and unambiguous criteria to mark flow regime transitions in slurry bubble columns. In a 2-dimensional (2-D) slurry bubble column, pressure time series are measured at different gas velocities simultaneously with high-speed video recording of the gas-liquid flow. The frequency of occurrence and the average diameter of the large bubbles are determined from video image analysis. The gas velocity where the first large bubbles are detected, with an average diameter of 1.5 cm, and with a frequency of occurrence of one bubble per s, is designated as the first regime transition point (transition from the homogeneous regime to the transition regime). At this point, the coherent standard deviation of the measured pressure fluctuations clearly increases from zero. The gas velocity where the average diameter and the frequency of occurrence of the large bubbles become constant, is designated as the second regime transition point (transition from the transition regime to the heterogeneous regime). From this point onward, the slope of the coherent standard deviation of the measured pressure fluctuations clearly decreases with gas velocity, while the average frequency becomes constant. These clear changes with gas velocity in the coherent standard deviation, and in the average frequency are also demonstrated in a 3-D slurry bubble column. © 2005 American Institute of Chemical Engineers AIChE J, 2005 [source]

Pressure buildup in gas-liquid flow through packed beds due to deposition of fine particles

THE CANADIAN JOURNAL OF CHEMICAL ENGINEERING, Issue 3 2002
Murray R. Gray
Abstract In order to understand the increase in pressure drop in hydrotreating reactors due to deposition of fine solids, experiments were conducted with a model suspension of kaolin clay in kerosene. The suspension was circulated through packed beds of catalyst pellets in the trickle-flow and pulse-flow regimes, and the increase in pressure drop measured as a function of particle concentration in the bed. The increase in pressure drop was linear with particle concentrations over the range 0,60 kg.m,3. A consistent approach to modeling the pressure drop behavior was to determine an effective porosity of the packed bed as a function of the concentration of fine particles, then use this porosity in the Ergun equation as a basis for calculating the two-phase pressure drop. Afin de comprendre l'augmentation de perte de charge causée par le dépôt de solides fins dans les réacteurs d'hydrotraitement, des expériences ont été menées avec une suspension modèle d'argile de kaolin dans du kérosène. On a fait circuler la suspension dans des lits garnis de pastilles de catalyseur en régime à écoulement ruisselant et à écoulement pulsé et on a mesuré l'augmentation de perte de charge en fonction de la concentration de particules dans le lit. L'augmentation de la perte de charge est linéaire pour des concentrations de particules se situant dans la gamme de 0,60 kg.m,3. Une façon cohérente de modéliser le comportement de la perte de charge consiste à déterminer une porosité effective du lit garni en fonction de la concentration de fines, puis d'utiliser cette porosité dans l'équation d'Ergun comme base pour calculer la perte de charge diphasique. [source]

Numerical Study on Bubble Formation of a Gas-Liquid Flow in a T-Junction Microchannel

CHEMICAL ENGINEERING & TECHNOLOGY (CET), Issue 12 2009
L. Dai
Abstract Bubble emergence in a gas-liquid flow in a T-junction microchannel of 100,,m diameter, operated under a squeezing regime, was simulated with the computational fluid dynamics method. In general, bubble formation in channels includes three stages: expansion, collapse and pinching off. After analyzing and comparing quantitatively the three forces of pressure, surface tension and shear stress acting on the gas thread in the whole process, their effects in the different stages were identified. The collapse stage was the most important for bubble formation and was investigated in detail. It was found that the collapse process was mostly influenced by the liquid superficial velocity, and the rate and time of collapse can be correlated with empirical equations including the liquid superficial velocity, the capillary number and the Reynolds number. [source]

Liquid-Liquid Stratified Flow through Horizontal Conduits

CHEMICAL ENGINEERING & TECHNOLOGY (CET), Issue 8 2005
T. Sunder Raj
Abstract The stratified configuration is one of the basic and most important distributions during two phase flow through horizontal pipes. A number of studies have been carried out to understand gas-liquid stratified flows. However, not much is known regarding the simultaneous flow of two immiscible liquids. There is no guarantee that the information available for gas-liquid cases can be extended to liquid-liquid flows. Therefore, the present work attempts a detailed investigation of liquid-liquid stratified flow through horizontal conduits. Gas-liquid flow exhibits either smooth or wavy stratified orientations, while liquid-liquid flow exhibits other distinct stratified patterns like three layer flow, oil dispersed in water, and water flow, etc. Due to this, regime maps and transition equations available for predicting the regimes in gas-liquid flow cannot be extended for liquid-liquid cases by merely substituting phase physical properties in the equations. Further efforts have been made to estimate the in-situ liquid holdup from experiments and theory. The analysis considers the pronounced effect of surface tension, and attempts to modify the Taitel-Dukler model to account for the curved interface observed in these cases. The curved interface model of Brauner has been validated with experimental data from the present work and those reported in literature. It gives a better prediction of liquid holdup in oil-water flows and reduces to the Taitel-Dukler model for air-water systems. [source]