Liquid flow in the impeller swept region of vessels with a turbine-type agitator was examined for the flow path between the neighboring blades of the rotating impeller. Visualization of the flow and its measurement were done using particle tracking velocimetry with a camera rotating along with the impeller. Internal liquid flow of the impeller differed when the velocity magnitudes were compared in conditions with and without baffles. Larger circumferential and radial velocities were observed without the baffles and with the baffles, respectively, which was considered to result in the difference of impeller power transmission. Efficiencies produced, based on the flow-head concept, reflected the impeller power characteristics. The turbine-type impeller as an actuator was demonstrated to improve in the flow characteristics with viscous losses increased by the baffles. In terms of impeller efficiencies based on the power consumption, the effect of baffles for the energy was as a decreased transmission and an increased transport.

/pdf/liquid-flow-in-impeller-swept-regions-of-baffled-and-3fd6l3rxx4.pdf

Liquid flow in impeller swept regions of baffled and unbaffled vessels with a turbine-type agitator

Abstract For a vessel agitated by the turbine-type impeller, the liquid flow and mixing in the bottom region were studied for comparison between conditions with and without baffles. Visualization of the flow and its measurement were done using particle tracking velocimetry. The flow along the bottom surface of the unbaffled vessel was observed to be more intensified than that of the baffled one. The related local energy dissipation was larger and the effective energy transmission was indicated for the condition without the baffles. For the unbaffled vessel, enhancement of micromixing near the bottom was demonstrated through a mixing experiment in a system involving chemical reactions.

Liquid Flow and Mixing in Bottom Regions of Baffled and Unbaffled Vessels Agitated by Turbine-Type Impeller

In this study, a computational fluid dynamics (CFD) simulation based on an Eulerian-Eulerian approach was used to evaluate the mixing performance of a mud agitator through the distribution of bulk particles. Firstly, the commercial CFD software Star-CCM+ was verified by performing numerical simulations of single-phase water mixing problems in an agitator with various turbulence models, and the simulation results were compared with an experiment. The standard model was selected as an appropriate turbulence model, and a grid convergence test was performed. Then, a simulation of the liquid-solid multi-phase mixing in an agitator was simulated with different multi-phase interaction models, and lift and drag models were selected. In the case of the lift model, the results were not significantly affected, but Syamlal and O’Brien’s drag model showed more reasonable results with respect to the experiment. Finally, with the properly determined simulation conditions, a multi-phase flow simulation of a mud agitator was performed to predict the mixing time and spatial distribution of solid particles. The applicability of the CFD multi-phase simulation for the practical design of a mud agitator was confirmed. Received 1 February 2021, revised 3 March 2021, accepted 11 March 2021 Corresponding author Jong-Chun Park: +82-51-510-2480, jcpark@pnu.edu c 2021, The Korean Society of Ocean Engineers This is an open access article distributed under the terms of the creative commons attribution non-commercial license (http://creativecommons.org/licenses/by-nc/4.0) which permits unrestricted non-commercial use, distribution, and reproduction in any medium, provided the original work is properly cited.

/pdf/cfd-simulation-of-multiphase-flow-by-mud-agitator-in-3nkv9y9i4o.pdf

CFD Simulation of Multiphase Flow by Mud Agitator in Drilling Mud Mixing System

Numerical simulations of flow in an unbaffled mixing tank agitated by a plain disk were performed using the CFD software package Fluent. Pre-processing was done using another software package called Gambit, while post-processing was done using an in-house software based on Matlab code. The circulation and discharge flow rates and their respective non-dimensional numbers were investigated. The locus of the recirculation centre has been found to follow a deformed “C” like path, for a centrally located disk. The circulation flow rate was observed to be linearly dependent on the Re and also on the disk size. The range of clearance values, 0.25 ≤ C ≤ 0.50, has been seen to produce the same discharge and circulation flow rates for a given disk size. A smaller clearance C = 0.15T resulted in reduction of Qc & Nqc and & Nqp. The discharge flow rate was seen to be dependent on both the Re and the disk size. The values of Nqc and Nqp found here are smaller than the ones for radial flow impellers. Both the circulation and discharge flow numbers appear not to be constant over the “entire” range of Re.

Numerical investigations of discharge flow and circulation flow in an unbaffled mixing vessel agitated by a plain disk

Research into the oxygen pressure leaching of zinc sulphide concentrates has identified that oxygen absorption is a rate-controlling process. In this study, the transfer of oxygen from air to aqueous sodium sulphite solutions by gas pumping impellers was studied as a simulation of the gas-liquid mass transfer step. A 200 litre right-cylindrical lucite mixing vessel with near-hemispherical bottom was employed. With this tank design, interference with impeller discharge is minimized and the environment approaches the ideal case of an impeller in the ocean. Four radially mounted baffles could be inserted to induce flow conditions characteristic of industrial mixing vessels. The effects of baffles and impeller type, diameter, immersion depth, and tip speed were evaluated in terms of the oxygen transfer rate, power consumption, and power efficiency of oxygen transfer. It was demonstrated that in the absence of baffling a critical tip speed exists, above which the impeller begins to pump gas at a rate proportional to the impeller tip speed. This critical tip speed is linked directly to the depth of immersion of the impeller on the basis of a theoretical energy balance at the impeller tip. The fit of experimental data to the theoretical was explained in terms of the geometry of the impeller and the shape of the gas vortex it produces. When baffling is introduced, the results obey the critical tip speed relation less accurately, as baffle-impeller interactions significantly alter the flow patterns and change the gas pumping mechanism to bubble capture from surface eddies. In the unbaffled vessel, axial flow impellers pump oxygen at lower rates and energy efficiencies than radial disc impellers, unless placed at shallow immersion. Gas pumping by dual impellers offers no advantage over a single radial disc impeller operating at the

Rates and efficiencies of oxygen transfer by gas pumping agitators in gas-liquid mixing systems

The velocity distribution of liquid in a cylindrical mixing vessel with flat-plate-baffles like those commonly used was measured by the method similar to the one adopted for the agitator without baffles.1)Some of the experimental results are shown in Figs. 3, 4, 5, 6, 7, 8 and 9.Variations of the liquid velocity distributions caused by the baffle-plates inserted in the agitated vessel are shown in Fig. 10. Obviously, the insertion of baffle-plates reduces the circulating flow round the impeller axis (the circumferential component υt of liquid velocity) and promotes the circulation flow in the vertical direction (caused by the discharge flow from the tip of the impeller).The discharging performance of various impellers is represented by the ratio NPB/Nq1, which is a dimensionless factor corresponding to the relative power required for a unit quantity discharge. The ratios for various impellers are listed in Table 3 together with those in the non-baffled condition. It is to be noted that, in spite of a considerable increase in Nq1, the circulation efficiency of agitators is lowered by the insertion of baffle-plates.Furthermore, the power consumption in the neighbourhood of the impeller (NPimp) was calculated and compared with that consumed in the outer region of the vessel (ΔNP) as shown in Table 4.It may be concluded from above that the improvement in the circulating capacity can be accomplished to a certain extent by a proper design of baffle-plates.

https://www.jstage.jst.go.jp/article/kakoronbunshu1953/23/9/23_9_595/_pdf

Yuji Naruse

Papers

Flow Patterns of Liquid in a Cylindrical Mixing Vessel without Baffles