Liquid circulation in a stirred system with an axial flow impeller and a cylindrical draft tube

Abstract This work evaluates the ability of computational fluid dynamics (CFD) to simulate the flow and predict the hydrodynamics of internal gas-lift loop reactor (IGLR)-type anaerobic digester. In addition, it also analyzes if CFD can account for the effects of operating conditions, geometry as well as scale of the reactor. For this purpose, three-dimensional two-phase CFD simulations were performed using CFX for laboratory-scale and pilot-scale IGLR. The CFD predictions were evaluated against experimental data obtained from computer automated radioactive particle tracking (CARPT). The CFD predictions provided good qualitative but only reasonable quantitative comparison. After validation of CFD model, effect of gas flow rate, draft tube diameter, sparger geometry and reactor scale on flow pattern, liquid velocity and dead volume was investigated. Higher gas flow rates did not offer any significant advantage in increasing liquid circulation in the downcomer or decreasing the dead volume. Configuration with draft tube diameter half of tank diameter, equipped with cross sparger showed comparatively better liquid circulation than other configurations. For same superficial gas velocity, increasing the scale increases the magnitude of liquid velocity but fails to match the mixing intensity observed in laboratory scale. Different interphase forces, turbulence models and closures are also evaluated to improve the predictability of CFD models.

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A Theoretical Study of the Performance of an Axial Flow Turbine for a Microhydro Installation

Proceedings of the Institution of Mechanical Engineers Part A Journal of Power and Energy ◽

10.1243/pime_proc_1996_210_019_02 ◽

1996 ◽

Vol 210 (2) ◽

pp. 121-129 ◽

Cited By ~ 4

Author(s):

G J Parker

Keyword(s):

Theoretical Study ◽

Draft Tube ◽

Guide Vane ◽

Turbine Blades ◽

Axial Flow ◽

Prototype System ◽

Blade Angle ◽

Flow Through ◽

Loss Coefficients ◽

Vane Angle

The Bernoulli-with-loss equation, with the losses represented by a constant times the velocity head, has been applied to each section of the flow through a small turbine system consisting of inlet guide vanes, axial flow turbine and draft tube. Using experimental data and the sets of equations, the flow angles around the turbine blades and the loss coefficients in the turbine and in the draft tube were determined. These were used to predict the effect of varying the guide vane angle and the turbine blade angle on performance. They were also used to predict the effects on the performance of a geometrically similar prototype system.

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

10.32920/ryerson.14648676.v1 ◽

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.

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