scholarly journals Simulation Study on Gas Holdup of Large and Small Bubbles in a High Pressure Gas–Liquid Bubble Column

Processes ◽  
2019 ◽  
Vol 7 (9) ◽  
pp. 594 ◽  
Author(s):  
Fangfang Tao ◽  
Shanglei Ning ◽  
Bo Zhang ◽  
Haibo Jin ◽  
Guangxiang He
Keyword(s):  
Surface Tension ◽  
High Pressure ◽  
Bubble Column ◽  
Bubble Diameter ◽  
Gas Holdup ◽  
Operating Pressure ◽  
Gas Velocity ◽  
Superficial Gas Velocity ◽  
Critical Bubble ◽  
Small Bubbles

The computational fluid dynamics-population balance model (CFD-PBM) has been presented and used to evaluate the bubble behavior in a large-scale high pressure bubble column with an inner diameter of 300 mm and a height of 6600 mm. In the heterogeneous flow regime, bubbles can be divided into “large bubbles” and “small bubbles” by a critical bubble diameter dc. In this study, large and small bubbles were classified according to different slopes in the experiment only by the method of dynamic gas disengagement, the critical bubble diameter was determined to be 7 mm by the experimental results and the simulation values. In addition, the effects of superficial gas velocity, operating pressure, surface tension and viscosity on gas holdup of large and small bubbles in gas–liquid two-phase flow were investigated using a CFD-PBM coupling model. The results show that the gas holdup of small and large bubbles increases rapidly with the increase of superficial gas velocity. With the increase of pressure, the gas holdup of small bubbles increases significantly, and the gas holdup of large bubbles increase slightly. Under the same superficial gas velocity, the gas holdup of large bubbles increases with the decrease of viscosity and the decrease of surface tension, but the gas holdup of small bubbles increases significantly. The simulated values of the coupled model have a good agreement with the experimental values, which can be applied to the parameter estimation of the high pressure bubble column system.

Bubble Diameter and Effective Interfacial Area in a Novel Hybrid Rotating and Reciprocating Perforated Plate Bubble Column

2012 ◽  
Vol 10 (1) ◽  
Author(s):  
Dhanasekaran S ◽  
Karunanithi T
Keyword(s):  
Liquid Velocity ◽  
Bubble Column ◽  
Bubble Diameter ◽  
Perforated Plate ◽  
Interfacial Area ◽  
Gas Velocity ◽  
The Mean ◽  
Superficial Gas Velocity ◽  
Plate Column

This investigation reports on the experimental and theoretical investigation carried out to evaluate the bubble diameter and effective interfacial area in a novel Hybrid Rotating and Reciprocating Perforated Plate Bubble Column. Air-water system is used in this investigation. Countercurrent mode is employed. The effects of agitation level, superficial gas velocity and superficial liquid velocity on the bubble size distribution are studied. The mean bubble diameter is predicted using photographic technique. A simple correlation is developed for the determination of mean bubble diameter. It is found that the mean bubble diameter values for hybrid column are 1.8 to 2.5 times smaller when compared with conventional reciprocating plate column. The interfacial area is calculated based on the experimental results of the gas holdup and bubble diameter. Effects of agitation level, superficial gas velocity, superficial liquid velocity and plate free area on the interfacial area have been investigated. Correlations are developed for the determination of interfacial area for both mixer-settler and emulsion regions. It could be noted that the interfacial area for the hybrid column is 3 to 6 times higher in both mixer-settler region and emulsion region than that of conventional reciprocating plate column which is quite large.

CFD-PBM simulation of hydrodynamics of microbubble column with shear-thinning fluid

2021 ◽  
Vol 0 (0) ◽  
Author(s):  
Xi Zhang ◽  
Ping Zhu ◽  
Shuaichao Li ◽  
Wenyuan Fan ◽  
Jingyan Lian
Keyword(s):  
Kinetic Energy ◽  
Turbulent Kinetic Energy ◽  
Radial Direction ◽  
Liquid Velocity ◽  
Bubble Column ◽  
Gas Holdup ◽  
Gas Velocity ◽  
Gas Distributor ◽  
Superficial Gas Velocity ◽  
The Right

Abstract A numerical simulation was performed to study the hydrodynamics of micro-bubble swarm in bubble column with polyacrylamide (PAM) aqueous solution by using computational fluid dynamics coupled with population balance models (CFD-PBM). By considering rheological characteristics of fluid, this approach was able to accurately predict the features of bubble swarm, and validated by comparing with the experimental results. The gas holdup, turbulent kinetic energy and liquid velocity of bubble column have been elucidated by considering the influences of superficial gas velocity and gas distributor size respectively. The results show that with the rise of the superficial gas velocity, the gas holdup and its peak width increase significantly. Especially, the curve peak corresponding to high gas velocity tends to drift obviously toward the right side. Except for the occurrence of a smooth holdup peak at the column center under the condition of the moderate distributor size, the gas holdups for the small and large distributor sizes become flat in the radial direction respectively. The distribution of turbulent kinetic energy presents an increasingly asymmetrical feature in the radial direction and also its variation amplitude enhances obviously with the rise of gas velocity. The increase in gas distributor size can enhance markedly turbulent kinetic energy as well as its overall influenced width. At the low and moderate superficial gas velocity, the curves of the liquid velocity in radial direction present the Gaussian distributions, whereas the perfect distribution always is broken in the symmetry for high gas velocity. Both liquid velocities around the bubble column center and the ones near both column walls go up consistently with the gas distributor size, especially near the walls at the large distributor size condition.

Effect of Vibrating Sparger on Mass Transfer, Gas Holdup, and Bubble Size in a Bubble Column Reactor

2013 ◽  
Vol 11 (1) ◽  
pp. 47-56 ◽  
Author(s):  
Laleh Hadavand ◽  
Ali Fadavi
Keyword(s):  
Mass Transfer ◽  
Transfer Coefficient ◽  
Mass Transfer Coefficient ◽  
Vibration Frequency ◽  
Bubble Size ◽  
Bubble Column ◽  
Gas Holdup ◽  
Bubble Column Reactor ◽  
Gas Velocity ◽  
Superficial Gas Velocity

Abstract Bubble size has a key role in gas holdup and mass transfer in bubble column reactors. In order to have small and uniform bubbles, a new structure was designed; the reactor operates in two modes, with vibrating sparger and conventional bubble column in which sparger is fixed. In vibrating mode, the sparger vibrates gently during gas entering. The vibrating sparger performs like a paddle, resulting in a forced recirculation of gas–liquid inside the reactor; moreover, the bubble detachment is accelerated. The superficial gas velocity was between 0.003 and 0.013 ms− 1, and the vibration frequency was changed between 0 and 10.3 Hz. The bubble size was measured at three various positions of the reactor height by photographic method and using MATLAB 7.0.1 software. The mass transfer coefficient was determined by means of the dynamic gassing-out method. The results show that the bubbles were bigger in vibrating mode than those working without vibration. The bubble size decreases with increase in height from sparger. Gas holdup increased with increase in superficial gas velocity and vibration frequency. The effect of vibration increased the gas holdup with an average of 70% for all superficial gas velocities. Volumetric mass transfer coefficient was almost stable as vibration frequency increased.

CFD Simulations for Continuous Flow of Bubbles through Gas-Liquid Columns: Application of VOF Method

2007 ◽  
Vol 2 (1) ◽  
Author(s):  
Abid Akhtar ◽  
Vishnu Pareek ◽  
Moses Tadé
Keyword(s):  
Present Model ◽  
Bubble Column ◽  
Water System ◽  
Design Parameters ◽  
Oscillatory Behaviour ◽  
Gas Velocity ◽  
Cfd Simulations ◽  
Predicted Values ◽  
Superficial Gas Velocity ◽  
Small Bubbles

Hydrodynamics study of a continuous bubble chain rising through liquid column has been performed for laboratory scale bubble column using the volume-of-fluid (VOF) approach. The effect of operating and design parameters on the bubble size distribution and rise trajectory has been investigated for air-water system. For the same distributor, simulation results have indicated the formation of small bubbles at low superficial gas velocity and relatively large bubbles at higher velocities. The increase in the hole-size of distributor has shown similar behaviour. Analysis of bubble trajectories for different superficial gas velocities and distributors has demonstrated an oscillatory behaviour exhibited by small bubbles formed at low superficial gas velocity. A reasonable agreement between the predicted values of gas hold-up with the experimental work has validated the present model.

scholarly journals Hydrodynamics of an airlift reactor for aeration in molten sulfur

2021 ◽  
Author(s):  
Junjie Wang ◽  
Xiao Xu ◽  
Qiang Yang ◽  
Wei Wang ◽  
Yudong Li ◽  
...  
Keyword(s):  
Bubble Diameter ◽  
Gas Holdup ◽  
Airlift Reactor ◽  
Gas Velocity ◽  
Liquid Circulation ◽  
Molten Sulfur ◽  
Circulation Velocity ◽  
Liquid Circulation Velocity ◽  
Superficial Gas Velocity ◽  
Reactor Height

An industrial-scale internal loop airlift reactor is used to remove volatile gas from high-viscosity molten sulfur. The effects of the superficial gas velocity and reactor height on the hydrodynamic characteristics were studied. The gas holdup, average bubble diameter, and liquid circulation velocity in the reactor under different conditions were analyzed using computational fluid dynamics simulation. The superficial gas velocity was varied from 0.0056 m/s to 0.05 m/s at a constant reactor height of 15 m. The total reactor height was varied from 5 m to 25 m at a superficial gas velocity of 0.0389 m/s.Based on the correlation between the gas holdup and liquid circulation velocity proposed by Chisti (1988), an optimized correlation between the gas holdup and liquid circulation velocity was developed by considering the influence of the bubble diameter. The results obtained using the proposed correlation were compared with those obtained using the Chisti correlation and simulation.

scholarly journals The Effect of a Modified Downcomer on the Hydrodynamics in an External Loop Airlift Reactor

2006 ◽  
Author(s):  
Samuel T. Jones ◽  
Theodore J. Heindel
Keyword(s):  
Liquid Velocity ◽  
Bubble Column ◽  
Gas Holdup ◽  
Area Ratio ◽  
Airlift Reactor ◽  
Open Area ◽  
Gas Velocity ◽  
External Loop ◽  
Superficial Gas Velocity ◽  
Superficial Liquid Velocity

Gas holdup and superficial liquid velocity in the downcomer and riser are studied for an external loop airlift reactor with an area ratio of 1:16. Two downcomer configurations are investigated consisting of the downcomer open or closed to the atmosphere. Experiments for these two configurations are carried out over a range of superficial gas velocities from UG = 0.5 to 20 cm/s using three aeration plates with open area ratios of 0.62, 0.99 and 2.22%. These results are compared to a bubble column operated with similar operating conditions. Experimental results show that the gas holdup in the riser does not vary significantly with a change in the downcomer configuration or bubble column operation, while a considerable variation is observed in the downcomer gas holdup. Gas holdup in both the riser and downcomer are found to increase with increasing superficial gas velocity. Test results also show that the maximum gas holdup for the three aerator plates is similar, but the gas holdup trends are different. The superficial liquid velocity is found to vary considerably for the two downcomer configurations. However, for both cases the superficial liquid velocity is a function of the superficial gas velocity and/or the flow condition in the downcomer. These observed variations are independent of the aerator plate open area ratio. When the downcomer vent is open to the atmosphere, the superficial liquid velocity is initially observed to increase with increasing superficial gas velocity until the onset of choking occurs in the downcomer. Increasing the superficial gas velocity beyond the onset of choking increases the effect of choking and decreases the superficial liquid velocity. Once maximum choking is reached, the superficial liquid velocity becomes independent of the superficial gas velocity. When the downcomer vent is closed to the atmosphere, the superficial liquid velocity is initially observed to decrease with increasing superficial gas velocity as choking in the downcomer is immediately present. Once maximum choking occurs, the superficial liquid velocity once again becomes independent of the superficial gas velocity.

scholarly journals Effects of EOR chemicals and superficial gas velocity on bubble size and gas holdup of a bubble column

2019 ◽  
Vol 74 ◽  
pp. 79
Author(s):  
Aloisio E. Orlando ◽  
Luiz F. Barca ◽  
Tania S. Klein ◽  
Ricardo A. Medronho
Keyword(s):  
Sodium Chloride ◽  
Physical Properties ◽  
Bubble Size ◽  
Produced Water ◽  
Bubble Column ◽  
Gas Holdup ◽  
Fluid Viscosity ◽  
Gas Velocity ◽  
Superficial Gas Velocity ◽  
Polymer Surfactant

Chemical Enhanced Oil Recovery (EOR) can boost oil extraction in offshore operations, however one of the main concerns regarding its application is how the efficiency of flotation units for treating produced water is affected. The present work thus focuses on investigating the impact of EOR chemicals on the physical properties of EOR effluents and how this can affect flotation performance parameters such as bubble size and gas holdup. Design of experiments has been used to assess the influence of polymer, surfactant and sodium chloride concentrations on bubble size and gas holdup of a laboratorial bubble column. The influence of superficial gas velocity has also been assessed together with chemicals concentrations, yet at low levels in order to avoid clusters, swarms and foam. The characterization of the synthetic effluent containing polymer, surfactant and sodium chloride has indicated that the fluid behaves as a non-Newtonian fluid, what makes separation processes in flotation cells challenging. Results showed that polymer concentration of 2000 mg/L can lead to significant increases in fluid viscosity, promote a growth of more than 40% in bubble size and only increases gas holdup when surfactant is present at high concentration. Therefore, polymers are expected to be detrimental to produced water treatment. Surfactants decrease both fluid surface tension and bubble size, increasing gas holdup. For the range studied, superficial gas velocity favors gas holdup and sodium chloride concentration seems to weakly influence bubble size and gas holdup. This work highlights the fact that changes in physical properties of produced water do modify bubble size distribution and gas holdup and this must therefore be taken into account when flotation-like systems are designed to deal with EOR effluents.

Effect of L/D Ratio on Phase Holdup and Bubble Dynamics in Slurry Bubble Column using Optical Fiber Probe Measurements

2016 ◽  
Vol 14 (2) ◽  
pp. 653-664 ◽  
Author(s):  
Saba A. Gheni ◽  
Yasser I. Abdulaziz ◽  
Muthanna H. Al-Dahhan
Keyword(s):  
Optical Fiber ◽  
Bubble Dynamics ◽  
Bubble Column ◽  
Gas Holdup ◽  
Solid Loading ◽  
Gas Velocity ◽  
Fiber Probe ◽  
Optical Fiber Probe ◽  
Slurry Bubble Column ◽  
Superficial Gas Velocity

Abstract In this investigation, time average local gas holdup and bubble dynamic data were achieved for three L/D ratios of slurry bubble column. The examined ratios were 3, 4 and 5 in 18″ diameter slurry bubble column. Air-water-glass bead system was used with superficial gas velocity up to 0.24 m/s. The gas holdup was measured using four tips optical fiber probe technique. The results showed that the gas holdup increases almost linearly with the superficial gas velocity in 0.08 m/s and levels off with a further increase of velocity. A comparison of the present data with those reported for other slurry bubble column having diameters greater than 18″ and L/D higher than 5 was made. The results indicated a little effect of diameter on the gas holdup. A local, section-averaged gas holdup increases with increasing superficial gas velocity, while the effect of solid loading are less significant than that of the superficial gas velocity. Chaos analysis was used to analyze the slurry system.

scholarly journals Gas–liquid mass transfer using advanced optical probe in a mimicked FT slurry bubble column

2020 ◽  
Vol 0 (0) ◽  
Author(s):  
Lu Han ◽  
Premkumar Kamalanathan ◽  
Muthanna H. Al-Dahhan
Keyword(s):  
Mass Transfer ◽  
Transfer Coefficient ◽  
Mass Transfer Coefficient ◽  
Bubble Column ◽  
Operating Pressure ◽  
Gas Velocity ◽  
Liquid Phase Mass Transfer ◽  
Solids Loading ◽  
Superficial Gas Velocity ◽  
Reactor Models

AbstractGas-liquid volumetric liquid-phase mass transfer coefficient (kLa) was studied in a slurry bubble column at the conditions mimicking Fischer–Tropsch synthesis. To avoid the hydrodynamic disturbances due to the gas switching, oxygen enriched air dynamic absorption method was used. Influence of reactor models (CSTR, ADM and RCFD) on the volumetric mass transfer coefficient was investigated. Effect of operating pressure, superficial gas velocity and solids loading were investigated. From the reactor models investigated, it is recommended to use ADM model for kLa study. If the CSTR model is used, applicability of the model should be checked. With increase in the superficial gas velocity and operating pressure, volumetric liquid-phase mass transfer coefficient increases, while it decreases with the solids loading corroborating with the literature.

scholarly journals Hydrodynamics of an Airlift Column for Aeration in Molten Sulfur

2021 ◽  
Vol 12 (1) ◽  
pp. 117
Author(s):  
Junjie Wang ◽  
Xiao Xu ◽  
Wei Wang ◽  
Yudong Li ◽  
Shihan Wu ◽  
...  
Keyword(s):  
Bubble Diameter ◽  
Gas Holdup ◽  
Dynamics Simulation ◽  
Column Height ◽  
Gas Velocity ◽  
Liquid Circulation ◽  
Molten Sulfur ◽  
Circulation Velocity ◽  
Liquid Circulation Velocity ◽  
Superficial Gas Velocity

The airlift column is a promising technology for the removal of volatile gas from high-viscosity molten sulfur. However, a detailed analysis is lacking on the hydrodynamic properties inside the column, due to the difficulty in flow behavior detection in the opaque molten sulfur. In this work, we adopted the computational fluid dynamics simulation to understand the hydrodynamic behaviors in an airlift column for molten sulfur aeration. In addition, we analyzed the impacts of the superficial gas velocity (UGr) and column height on the hydrodynamic characteristics, such as gas holdup, average bubble diameter, and liquid circulation velocity (ULr) in the column. The simulation shows that at a constant column height of 15 m, an increase on gas holdup can be obtained with the increase of the superficial gas velocity, while the bubble diameter remains almost constant. Once the superficial gas velocity exceeded 0.333 m/s, the liquid circulation velocity increased slowly. With a variation on the column height from 5 to 25 m, a negligible change on gas holdup, but an obvious increase on liquid circulation velocity and bubble diameter is observed at the given superficial gas velocity of 0.0389 m/s. Furthermore, the simulation shows a similar trend, but with considerably more detailed information, on the relationship between the gas holdup and liquid circulation velocity when compared to the predictions from the Chisti correlation (1988) and an optimized correlation proposed in this work.

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