3D CFD Simulation of Gas Hold-up and Mass Transfer in a Modified Airlift Reactor with Net Draft Tube

2019 ◽  
Vol 17 (12) ◽  
Author(s):  
Mehran Nalband ◽  
Elham Jalilnejad
Keyword(s):  
Mass Transfer ◽  
Transfer Coefficient ◽  
Mass Transfer Coefficient ◽  
Cfd Simulation ◽  
Draft Tube ◽  
Axial Flow ◽  
Cfd Modeling ◽  
Reactor Performance ◽  
Simulation Results ◽  
The Impact

Abstract This paper documents CFD simulations of the gas hold-up (ɛg) and volumetric mass transfer coefficient (KLa) for three kinds of airlift reactors (ALRs) namely, conventional ALR, ALR with net draft tube (ALR-ndt), and packed-bed ALR with net draft tube (PBALR-ndt). The 3D two-fluid Eulerian-Eulerian model was adopted to predict the influence of superficial gas velocity on ɛg and KLa. The simulation results were consistent with the trends described previously in the experimental work regarding ɛg and KLa values and a good agreement was obtained (absolute error less than 20 %). Based on the simulation results, axial flow is the dominant flow in the conventional ALR while in ALR-ndt and PBALR-ndt radial flow streamlines are appeared in the reactors due to the presence of concentric net draft tube which improves their performance. The effective role of the net draft tube is proven since consequence of generation of small bubbles by passing through net draft tube is the entrainment of a larger percentage of gas bubbles from the riser into the downcomer which results in improvement of gas holdup and the KLa values. An exponential correlation is used for relating gas hold-up and mass transfer coefficient. Higher power obtained for ALR-ndt and PBALR-ndt (n ≈ 1.22) compared to ALR (n = 0.95) was indicative of high sensitivity of KLa value to gas hold-up in these reactors due to presence of the concentric net draft tube. The CFD modeling is considered to be an invaluable tool allowing us to analyze and visualize the impact of fluidic forces on hydrodynamic properties and consequently, reactor performance.

Modeling phototrophic biofilms in a plug-flow reactor

2014 ◽  
Vol 70 (7) ◽  
pp. 1261-1270 ◽  
Author(s):  
J. D. Muñoz Sierra ◽  
C. Picioreanu ◽  
M. C. M. van Loosdrecht
Keyword(s):  
Mass Transfer ◽  
Transfer Coefficient ◽  
Mass Transfer Coefficient ◽  
Plug Flow ◽  
Microbial Interactions ◽  
Bulk Liquid ◽  
Organic Loading Rate ◽  
Phototrophic Biofilms ◽  
Biofilm Model ◽  
The Impact

The use of phototrophic biofilms in wastewater treatment has been recognized as a potential option for development of new reactor configurations. For better understanding of these systems, a numerical model was developed including relevant microbial processes. As a novelty, this model was implemented in COMSOL Multiphysics, a modern computational environment for complex dynamic models. A two-dimensional biofilm model was used to study the spatial distribution of microbial species within the biofilm and along the length of the reactor. The biofilm model was coupled with a one-dimensional plug-flow bulk liquid model. The impact of different operational conditions on the chemical oxygen demand (COD) and ammonia conversions was assessed. The model was tuned by varying two parameters: the half-saturation coefficient for light use by phototrophs and the oxygen mass transfer coefficient. The mass transfer coefficient was found to be determining for the substrate conversion rate. Simulations indicate that heterotrophs would overgrow nitrifiers and phototrophs within the biofilm until a low biodegradable COD value in the wastewater is reached (organic loading rate <2.32 gCOD/(m2 d)). This limits the proposed positive effect of treating wastewater with a combination of algae and heterotrophs/autotrophs. Mechanistic models like this one are made for understanding the microbial interactions and their influence on the reactor performance.

Sparger Type Influence on the Volumetric Mass Transfer Coefficient in the Draft Tube Airlift Reactor with Diluted Alcohol Solutions

2013 ◽  
Vol 52 (20) ◽  
pp. 6812-6821 ◽  
Author(s):  
Ivana M. Šijački ◽  
Milenko S. Tokić ◽  
Predrag S. Kojić ◽  
Dragan Lj. Petrović ◽  
Miodrag N. Tekić ◽  
...  
Keyword(s):  
Mass Transfer ◽  
Transfer Coefficient ◽  
Mass Transfer Coefficient ◽  
Draft Tube ◽  
Airlift Reactor ◽  
Volumetric Mass Transfer Coefficient

Mass transfer examination in electrodialysis using limiting current measurements

2015 ◽  
Vol 69 (4) ◽  
Author(s):  
Natália Káňavová ◽  
Anna Krejčí ◽  
Martina Benedeková ◽  
Marek Doležel ◽  
Lubomír Machuča
Keyword(s):  
Mass Transfer ◽  
Transfer Coefficient ◽  
Mass Transfer Coefficient ◽  
Limiting Current ◽  
Transfer Coefficients ◽  
Exponential Parameter ◽  
Wide Range ◽  
Spacer Thickness ◽  
Module Geometry ◽  
The Impact

AbstractThe impact of electrodialysis module characteristics on mass transfer was examined using the limiting current method. The current-voltage curves of different electrodialysis modules were measured and limiting currents were determined using the derivative method. The mass transfer coefficients were calculated and the parameters of their dependence on linear flow velocity were estimated. From these the impact of spacer thickness, spacer net type, membrane type, and module geometry were evaluated. It was found that the impact of spacer thickness was almost negligible within the examined range, but a decrease in the mass transfer coefficient could be expected in the case of thicker spacers. By contrast, the spacer net type and type of membrane were found to be very important parameters able to significantly influence the mass transfer. By modifying the module geometry, the mass transfer coefficient could also be altered and, only in this case, the exponential parameter of the dependence was changing. The parameters thus determined may be used to calculate the limiting current in a wide range of operational conditions and may help predict the performance of different electrodialysis module types

scholarly journals The influence of pH on gas-liquid mass transfer in non-Newtonian fluids

2017 ◽  
Vol 23 (3) ◽  
pp. 321-327 ◽  
Author(s):  
Shaobai Li ◽  
Jungeng Fan ◽  
Shuang Xu ◽  
Rundong Li ◽  
Jingde Luan
Keyword(s):  
Mass Transfer ◽  
Transfer Coefficient ◽  
Mass Transfer Coefficient ◽  
Ph Value ◽  
Newtonian Fluids ◽  
Marginal Effect ◽  
Effect Of Ph ◽  
Liquid Mass ◽  
Liquid Mass Transfer ◽  
The Impact

In this study, the effect of pH on the mass transfer of oxygen bubble swarms in non-Newtonian fluids was experimentally studied. The volumetric liquid side mass transfer coefficient (kLa), liquid side mass transfer coefficient (kL), and specific interfacial area (a) were investigated. The pH was regulated by the addition of hydrochloric acid and sodium hydroxide (NaOH). It was found that the kLa increased with the gas flow rate increasing and decreased with the apparent viscosity of the liquid increasing. In the case of pH < 7, a marginal effect of pH on the gas?liquid mass transfer was observed, but when pH value was higher than 7, mass transfer was promoted with the increase of pH value. Via investigating the impact of pH on kL and a, the variation of mass transfer at pH > 7 was attributed to the decomposition of the Xanthan molecular structure by the hydroxyl of NaOH.

scholarly journals The Effect of Various Nanofluids on Absorption Intensification of CO2/SO2 in a Single-Bubble Column

Processes ◽  
2019 ◽  
Vol 7 (7) ◽  
pp. 393 ◽  
Author(s):  
Karamian ◽  
Mowla ◽  
Esmaeilzadeh
Keyword(s):  
Mass Transfer ◽  
Transfer Coefficient ◽  
Mass Transfer Coefficient ◽  
Absorption Rate ◽  
Bubble Column ◽  
Pure Water ◽  
Experimental Studies ◽  
Bubble Liquid ◽  
Acidic Gases ◽  
The Impact

Application of nanoparticles in aqueous base-fluids for intensification of absorption rate is an efficient method for absorption progress within the system incorporating bubble-liquid process. In this research, SO2 and CO2 were separately injected as single raising bubbles containing nanofluids to study the impact of nanoparticle effects on acidic gases absorption. In order to do this, comprehensive experimental studies were done. These works also tried to investigate the effect of different nanofluids such as water/Al2O3 or water/Fe2O3 or water/SiO2 on the absorption rate. The results showed that the absorption of CO2 and SO2 in nanofluids significantly increases up to 77 percent in comparison with base fluid. It was also observed that the type of gas molecules and nanoparticles determine the mechanism of mass transfer enhancement by nanofluids. Additionally, our findings indicated that the values of mass transfer coefficient of SO2 in water/Al2O3, water/Fe2O3 and water/SiO2 nanofluids are, respectively, 50%, 42% and 71% more than those of SO2 in pure water (kLSO2-water=1.45×10-4 m/s). Moreover, the values for CO2 in above nanofluids were, respectively, 117%, 103% and 88% more than those of CO2 in water alone (kLCO2-water=1.03×10-4 m/s). Finally, this study tries to offer a new comprehensive correlation for mass transfer coefficient and absorption rate prediction.

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