Gas holdup, liquid circulation velocity and shear rate in an external loop airlift containing non-Newtonian polymer solutions

1998 ◽  
Vol 19 (5) ◽  
pp. 399 ◽  
Author(s):  
P. Ayazi Shamlou ◽  
J. Rajarajan ◽  
A. P. Ison
Keyword(s):  
Shear Rate ◽  
Polymer Solutions ◽  
Gas Holdup ◽  
Liquid Circulation ◽  
External Loop ◽  
Circulation Velocity ◽  
Liquid Circulation Velocity

scholarly journals Mixing characteristics of draft tube airlift bioreactor using the electrical resistance tomography

2021 ◽  
Author(s):  
Farouzatu Yakubu-Gumery
Keyword(s):  
Shear Rate ◽  
Xanthan Gum ◽  
Draft Tube ◽  
Mixing Time ◽  
Airlift Bioreactor ◽  
Liquid Circulation ◽  
Mixing Characteristics ◽  
Circulation Velocity ◽  
Liquid Circulation Velocity ◽  
The Cross

In this work, mixing characteristics in terms of mixing time, hydrodynamics (liquid circulation velocity and gas hold up) and shear rate were performed in the downcomer of a draft tube airlift bioreactor with different geometries (i.e., Ad/Ar between 0.38 – 2.31 and bottom clearances between 0.003-0.00 m). Newtonian (water and 34.5% coalescing sugar solution) and on Newtonian (0.2% and 0.5% xanthan gum solutions) with different viscosities were used as the liquid phase. Compressed air was used as the gas phase which was introduced through cross and circular shaped sparger configurations at superficial velocities Ugr = 0.00165-0.00807 m/s. The combined effects of geometric parameters (Ad/Ar, bottom clearances), sparger configuration, and liquid viscosity on mixing characteristics have been presented. Results showed that the increase in superficial gas velocity (Ugr) corresponds to an increase in energy generated, and thus decreases in mixing time. However, the increase in Ugr corresponds to the increase in liquid circulation velocity, gas holdup and shear rate values. Moreover, bottom clearances and draft tube diameters show effects on flow resistance frictional losses which affect results of mixing parameters investigated. The influence of sparger configurations on mixing time and liquid circulation velocity is significant due to their effect on gas distribution. Mixing time decreased to about 40% in air-water media using the cross shaped sparger. Results obtained with cross shaped sparger showed even and uniform distribution of gas, which provided better mixing as compared to the circular shaped sparger configuration. However, the sparger configuration effect on shear rate is not as significant (about 20% reduction in shear rate values using the cross shaped sparger). The effect of fluid viscosity had a significant influence on both mixing times and circulation velocity, especially in the coalescing media of sugar and xanthan gum solutions. Results from this work will help to develop a clear pattern for operation and mixing that can help improving [sic] several industrial processes, especially the ones related to emerging fields of technology such as the biotechnology industry.

scholarly journals Effect of Superficial Gas Velocity on Continuous Hydrogen Production by Anabaena sp. in an Internal-loop Airlift Bioreactor

2021 ◽  
Author(s):  
Zahra Zarei ◽  
Peyman Malekshahi ◽  
Mohammad Hossein Morowvat ◽  
Rahbar Rahimi ◽  
Seyyed Vahid Niknezhad
Keyword(s):  
Mass Transfer ◽  
Hydrogen Production ◽  
Light Intensity ◽  
Gas Flow ◽  
Biomass Concentration ◽  
Gas Holdup ◽  
Liquid Circulation ◽  
Airlift Photobioreactor ◽  
Circulation Velocity ◽  
Liquid Circulation Velocity

Abstract Global warming and rising air pollution which has been caused by using too much fossil fuel has led to look for a new clean source, sustainable and eco-friendly of energy like H2, which can be produced by cyanobacteria and microalgae. In this study, Anabaena sp. was used in a continuous operation to achieve biohydrogen production. To this end, an airlift photobioreactor (20 L) was considered. The effects of the gas holdup, liquid circulation velocity, and the amount of dissolved oxygen on hydrogen production were investigated. Gas holdup, liquid circulation velocity, and KLa (mass transfer coefficient) showed an upward trend by increasing the velocity of the inlet gas. Maximum biomass concentration of and maximal H2 production were observed 1.2 g L-1 d-1 and 371 mL h-1 PBR-1, respectively under light intensity of 3500 lux/m2 applying a light-dark cycle in 7 days, at Ad/Ar of 1.25 and 0.185 and 0.542 cm/s. pH, temperature (30+2 °C), light intensity, and inlet gas flow to the bioreactor (containing 98% air and 2% carbon dioxide) were remained steady. Using the airlift photobioreactor with a good mass transfer and light availability to cyanobacteria growth can be a cost-effective and environmentally technology for biological H2 production.

scholarly journals Mixing characteristics of draft tube airlift bioreactor using the electrical resistance tomography

2021 ◽  
Author(s):  
Farouzatu Yakubu-Gumery
Keyword(s):  
Shear Rate ◽  
Xanthan Gum ◽  
Draft Tube ◽  
Mixing Time ◽  
Airlift Bioreactor ◽  
Liquid Circulation ◽  
Mixing Characteristics ◽  
Circulation Velocity ◽  
Liquid Circulation Velocity ◽  
The Cross

In this work, mixing characteristics in terms of mixing time, hydrodynamics (liquid circulation velocity and gas hold up) and shear rate were performed in the downcomer of a draft tube airlift bioreactor with different geometries (i.e., Ad/Ar between 0.38 – 2.31 and bottom clearances between 0.003-0.00 m). Newtonian (water and 34.5% coalescing sugar solution) and on Newtonian (0.2% and 0.5% xanthan gum solutions) with different viscosities were used as the liquid phase. Compressed air was used as the gas phase which was introduced through cross and circular shaped sparger configurations at superficial velocities Ugr = 0.00165-0.00807 m/s. The combined effects of geometric parameters (Ad/Ar, bottom clearances), sparger configuration, and liquid viscosity on mixing characteristics have been presented. Results showed that the increase in superficial gas velocity (Ugr) corresponds to an increase in energy generated, and thus decreases in mixing time. However, the increase in Ugr corresponds to the increase in liquid circulation velocity, gas holdup and shear rate values. Moreover, bottom clearances and draft tube diameters show effects on flow resistance frictional losses which affect results of mixing parameters investigated. The influence of sparger configurations on mixing time and liquid circulation velocity is significant due to their effect on gas distribution. Mixing time decreased to about 40% in air-water media using the cross shaped sparger. Results obtained with cross shaped sparger showed even and uniform distribution of gas, which provided better mixing as compared to the circular shaped sparger configuration. However, the sparger configuration effect on shear rate is not as significant (about 20% reduction in shear rate values using the cross shaped sparger). The effect of fluid viscosity had a significant influence on both mixing times and circulation velocity, especially in the coalescing media of sugar and xanthan gum solutions. Results from this work will help to develop a clear pattern for operation and mixing that can help improving [sic] several industrial processes, especially the ones related to emerging fields of technology such as the biotechnology industry.

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 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.

Gas holdup and liquid circulation velocity in a draft tube gas-liquid spouted vessel.

1988 ◽  
Vol 14 (5) ◽  
pp. 593-600 ◽  
Author(s):  
Masayuki Toda ◽  
Naoki Mogi ◽  
Shinobu Yoshikawa ◽  
Fumiko Sugano ◽  
Hirotaka Konno
Keyword(s):  
Draft Tube ◽  
Gas Holdup ◽  
Liquid Circulation ◽  
Circulation Velocity ◽  
Liquid Circulation Velocity
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