scholarly journals Numerical study of the hydrodynamics and mass transfer in the external loop airlift reactor

2021 ◽  
pp. 34-34
Author(s):  
Predrag Kojic ◽  
Jovana Kojic ◽  
Milada Pezo ◽  
Jelena Krulj ◽  
Lato Pezo ◽  
...  
Keyword(s):  
Mass Transfer ◽  
Transfer Coefficient ◽  
Mass Transfer Coefficient ◽  
Airlift Reactor ◽  
Volumetric Mass Transfer Coefficient ◽  
Cfd Model ◽  
Gas Velocity ◽  
Liquid Mass ◽  
External Loop ◽  
Liquid Mass Transfer

The objective of this study was to investigate the hydrodynamics and the gas-liquid mass transfer coefficient of an external-loop airlift reactor (ELAR). The ELAR was operated in three cases: different inlet velocities of fluids, different alcohols solutions (water, 0.5% methanol, 0.5% ethanol, 0.5% propanol and 0.5% butanol) and different concentration of methanol in solutions (0%, 0.5%, 1%, 2% and 5%). The influence of superficial gas velocity and various diluted alcohol solutions on hydrodynamics and gas-liquid mass transfer coefficient of the ELAR was studied. Experimentally, the gas hold-up, liquid velocities and volumetric mass transfer coefficient values in the riser and the downcomer were obtained from the literature source. A computational fluid dynamics (CFD) model was developed, based on two-phase flow, investigating different liquids regarding surface tension, assuming the ideal gas flow, applying the finite volume method and Eulerian-Eulerian model. The volumetric mass transfer coefficient was determined using CFD model, as well as artificial neural network model. The effects of liquid parameters and gas velocity on the characteristics of the gas-liquid mass transfer were simulated. These models were compared with appropriate experimental results. CFD model successfully succeed to simulate the influence of different alcohols regarding the number of C-atoms on hydrodynamics and mass transfer.

scholarly journals Volumetric gas-liquid mass transfer coefficient in an external-loop airlift reactor with inserted membrane

2016 ◽  
Vol 22 (3) ◽  
pp. 275-284 ◽  
Author(s):  
Predrag Kojic ◽  
Ivana Sijacki ◽  
Natasa Lukic ◽  
Dragica Jovicevic ◽  
Svetlana Popovic ◽  
...  
Keyword(s):  
Mass Transfer ◽  
Transfer Coefficient ◽  
Mass Transfer Coefficient ◽  
Back Propagation ◽  
Back Propagation Neural Network ◽  
Airlift Reactor ◽  
Liquid Mass ◽  
External Loop ◽  
Feed Forward Back Propagation ◽  
Liquid Mass Transfer

The effects of the inserted membrane in the downcomer of an external-loop airlift reactor, the gas sparger type (single orifice and sinter plate) and added alcohol (ethanol, n-butanol, or n-hexanol) on the volumetric gas-liquid mass transfer coefficient (kLa) were studied. Due to the presence of the membrane in the downcomer, kLa did not change significantly; the differences were smaller than 10%. The highest values of the kLa were obtained using the sinter plate. It was found that the addition of small amounts of alcohol increased the mass transfer. Using our experimental results and the data of other authors, the feed-forward back propagation neural network for prediction of kLa in external-loop airlift reactors with alcohol solutions was proposed.

scholarly journals Packing size effect on the liquid circulation property in an external-loop packed bubble column

2021 ◽  
Author(s):  
Yanling Tang ◽  
Gang Luo ◽  
Zhenmin Cheng
Keyword(s):  
Mass Transfer ◽  
Transfer Coefficient ◽  
Mass Transfer Coefficient ◽  
Bubble Column ◽  
Gas Holdup ◽  
Oxygen Absorption ◽  
Liquid Mass ◽  
External Loop ◽  
Packing Size ◽  
Liquid Mass Transfer

Packing size effects on the fluid dynamics in an external-loop packed bubble column with Raschig rings of three different effective diameters (5, 14 and 41 mm) in the riser were investigated. The overall gas holdup, liquid circulating velocity and gas-liquid mass transfer coefficient were respectively measured by volume expansion method, tracer-response method and dynamic oxygen-absorption technique. CFD simulation with the Euler-Euler two-fluid method was used to predict the liquid circulating velocity by treating the packing as a porous medium. Compared to the empty column, the gas holdup was found to increase with the presence of packing, however, the liquid circulating velocity and gas-liquid mass transfer coefficient may increase or decrease. Specifically, the gas holdup increases with the decrease of packing size, while the liquid circulating velocity is on the contrary, which induces the maximal gas-liquid mass transfer rate at packing diameter of 14 mm.

Research on Mass Transfer Coefficient Measurement Model of External-Loop Airlift Reactor

2012 ◽  
Vol 512-515 ◽  
pp. 2405-2411
Author(s):  
Qian Wu ◽  
Ma Lin Liu ◽  
Tong Wang Zhang
Keyword(s):  
Mathematical Model ◽  
Mass Transfer ◽  
Transfer Coefficient ◽  
Mass Transfer Coefficient ◽  
Measurement Model ◽  
Airlift Reactor ◽  
Continuous Stirred Tank Reactor ◽  
Volumetric Mass Transfer Coefficient ◽  
External Loop ◽  
Coefficient Measurement

A mathematical model considering the inter-phase mass transfer both in the down-comer and the riser of an external-loop airlift reactor was established in this paper. The calculated global volumetric mass transfer coefficient based on the assumption of continuous stirred tank reactor (CSTR) was different from the local volumetric mass transfer coefficients by the newly proposed mathematical model and the difference was discussed. The effects of mass transfer in the down-comer, the hydrodynamic pressure and the experimental time on the mass transfer coefficient measurement model have been studied in detail. And it was also proved that only the global volumetric mass transfer coefficient, but not the local volumetric mass coefficient, can be obtained from a time-concentration curve in the external-loop airlift reactor.

scholarly journals Gas Holdup and Gas-Liquid Mass Transfer Investigations in an Oscillatory Flow in a Baffled Column

2008 ◽  
Vol 2 (1) ◽  
pp. 7
Author(s):  
Taslim Taslim ◽  
Mohd Sobri Takriff
Keyword(s):  
Mass Transfer ◽  
Transfer Coefficient ◽  
Mass Transfer Coefficient ◽  
Power Density ◽  
Volume Fraction ◽  
Gas Holdup ◽  
Gas Velocity ◽  
Liquid Mass ◽  
Liquid Mass Transfer ◽  
Superficial Gas Velocity

Gas holdup and gas-liquid mass transfer were investigated in a vertical baffled column. Pure carbon dioxide (C02) was used as the dispersed phase and tap water was used as the continuous phase. Gas holdup and mass transfer rate of C02 were measured under semi-batch condition, while the liquid phase was measured in batch mode. Gas holdup was estimated as the volume fraction of the gas in the two-phase mixture in the column. Mass transfer was expressed in terms of the liquid-side volumetric mass transfer coefficient (kLa). The effects of oscillation frequency, oscillation amplitude and gas flow rate on gas holdup andmass transfer were also determined. The results showed that a significant increase in gas holdup and mass transfer could be achieved in an oscillatory baffled column compared to a bubble column. Gas holdup and mass transfer were correlated as a function of power density and superficial gas velocity. Keywords: gas holdup, mass transfer coefficient, power density, superficial gas velocity

scholarly journals Ultrasonic Investigation of Hydrodynamics and Mass Transfer in a Gas-Liquid(-Liquid) Stirred Vessel

2005 ◽  
Vol 3 (1) ◽  
Author(s):  
A.H.G. Cents ◽  
D.W.F. Brilman ◽  
G.F. Versteeg
Keyword(s):  
Mass Transfer ◽  
Transfer Coefficient ◽  
Mass Transfer Coefficient ◽  
Water System ◽  
Interfacial Area ◽  
Volumetric Mass Transfer Coefficient ◽  
Volume Fractions ◽  
Liquid Mass ◽  
Liquid Mass Transfer ◽  
Transfer Parameters

The rate of gas-liquid mass transfer is very important in several industrial chemical engineering applications. In many multi-phase reaction systems, however, the mechanism of mass transfer is not well understood. This is for instance the case in Gas-Liquid-Solid (G-L-S) and Gas-Liquid-Liquid (G-L-L) systems. To obtain more knowledge of the mechanism of mass transfer, the mass transfer coefficient, kL, and the interfacial area, a, should be studied separately. In this work an ultrasonic measurement technique is used to study the local interfacial area in a standard sized vessel, equipped with a Rushton type impeller. This is done in combination with experimental determination of the volumetric mass transfer coefficient, kLa, using the dynamic oxygen method, to obtain values for kL. The gas hold-up is determined additionally to obtain values for the Sauter mean bubble diameter at different positions in the vessel. In a coalescing air-water system the bubble size was non-uniform throughout the vessel and increased from small bubbles at the impeller along with the flow pattern to larger sizes in the bulk of the vessel. In a non-coalescing electrolyte system the vessel was much more uniform and the bubbles were smaller when compared to the air-water system. To obtain overall values of the mass transfer parameters the local values were integrated according to their volume fraction in the reactor. In both coalescing and non-coalescing systems the overall values for the mass transfer parameters were in good agreement with literature correlations. The addition of small volume-fractions of toluene to an air-water system caused a strong decrease in both the volumetric mass transfer coefficient and in the gas hold-up. The interfacial area increased, however, but it was shown that this was due to the presence of microbubbles in the solution, which do not take part in the mass transfer process. The enhancing effect on gas-liquid mass transfer due to the addition of larger volume-fractions of toluene could be described reasonably well by a homogeneous model of the shuttle mechanism.

scholarly journals Gas–liquid mass transfer characteristics of aviation fuel scrubbing in an aircraft fuel tank

2021 ◽  
Vol 11 (1) ◽  
Author(s):  
Li Chaoyue ◽  
Feng Shiyu ◽  
Xu Lei ◽  
Peng Xiaotian ◽  
Yan Yan
Keyword(s):  
Mass Transfer ◽  
Dissolved Oxygen ◽  
Transfer Coefficient ◽  
Mass Transfer Coefficient ◽  
Oxygen Concentration ◽  
Gas Holdup ◽  
Aviation Fuel ◽  
Volumetric Mass Transfer Coefficient ◽  
Dissolved Oxygen Concentration ◽  
Liquid Mass Transfer

AbstractDissolved oxygen evolving from aviation fuel leads to an increase in the oxygen concentration in an inert aircraft fuel tank ullage that may increase the flammability of the tank. Aviation fuel scrubbing with nitrogen-enriched air (NEA) can largely reduce the amount of dissolved oxygen and counteract the adverse effect of oxygen evolution. The gas–liquid mass transfer characteristics of aviation fuel scrubbing are investigated using the computational fluid dynamics method, which is verified experimentally. The effects of the NEA bubble diameter, NEA superficial velocity and fuel load on oxygen transfer between NEA and aviation fuel are discussed. Findings from this work indicate that the descent rate of the average dissolved oxygen concentration, gas holdup distribution and volumetric mass transfer coefficient increase with increasing NEA superficial velocity but decrease with increasing bubble diameter and fuel load. When the bubble diameter varies from 1 to 4 mm, the maximum change of descent rate of dissolved oxygen concentration is 18.46%, the gas holdup is 8.73%, the oxygen volumetric mass transfer coefficient is 81.45%. When the NEA superficial velocities varies from 0.04 to 0.10 m/s, the maximum change of descent rate of dissolved oxygen concentration is 146.77%, the gas holdup is 77.14%, the oxygen volumetric mass transfer coefficient is 175.38%. When the fuel load varies from 35 to 80%, the maximum change of descent rate of dissolved oxygen concentration is 21.15%, the gas holdup is 49.54%, the oxygen volumetric mass transfer coefficient is 44.57%. These results provide a better understanding of the gas and liquid mass transfer characteristics of aviation fuel scrubbing in aircraft fuel tanks and can promote the optimal design of fuel scrubbing inerting systems.

Effect of bubble contamination on gas–liquid mass transfer coefficient on CO2 absorption in amine solutions

2008 ◽  
Vol 137 (2) ◽  
pp. 422-427 ◽  
Author(s):  
Rocío Maceiras ◽  
Sebastião S. Alves ◽  
M. Ángeles Cancela ◽  
Estrella Álvarez
Keyword(s):  
Mass Transfer ◽  
Transfer Coefficient ◽  
Mass Transfer Coefficient ◽  
Co2 Absorption ◽  
Liquid Mass ◽  
Liquid Mass Transfer ◽  
Amine Solutions
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