CFD simulation of single-phase flow in flotation cells: Effect of impeller blade shape, clearance, and Reynolds number
|نوع نگارش مقاله||
scopus – master journals – JCR
۴٫۲۷۶ در سال ۲۰۲۰
۲۶ در سال ۲۰۲۱
۰٫۹۰۱ در سال ۲۰۲۰
|شاخص Quartile (چارک)||
Q1 در سال ۲۰۲۰
خرید محصول توسط کلیه کارت های شتاب امکان پذیر است و بلافاصله پس از خرید، لینک دانلود محصول در اختیار شما قرار خواهد گرفت و هر گونه فروش در سایت های دیگر قابل پیگیری خواهد بود.
فهرست مطالب مقاله:
A series of numerical simulations of turbulent single-phase flows are performed to understand the flow and mixing characteristics in a laboratory scale flotation tank. Four impeller blade shapes covering a wide range of surface areas and lip lengths are considered to highlight and contrast the flow behavior predicted in the impeller stream. The mean flow close to the impeller is fully characterized by considering velocity components along the axial direction at different radial locations. Normalized results suggest the devel- opment of a comparatively stronger axial velocity component for a blade design with the smallest lip length, called big-tip impeller here. Normalized turbulent kinetic energy profiles close to the impeller reveal the existence of an asymmetric trailing vortex pair. The highest turbulence kinetic energy dissipa- tion rates are observed close to the impeller blades and stator walls where the radial jet strikes the stator walls periodically. Furthermore, liquid phase mixing in the flotation cell is studied using transient scalar tracing simulations providing mixing time data. Finally, pumping capacity and efficiency of different impeller designs are calculated based on which the impeller blade design with a rectangular blade design is found to perform most efficiently.
|بخشی از متن مقاله:|
Mechanical flotation cells are commonly used in the mineral processing industry to concentrate valuable minerals from the accompanying gangue material. The flow inside the flotation cell is typically very turbulent in nature due to high agitation rates. Moreover, the presence of dispersed phases makes the flow highly non-uniform and complex [1–۴]. The length and time scales of pro- cesses occurring inside flotation cells span many orders of magni- tude [2,5]. In the remainder of this section, past studies using computational fluid dynamics (CFD) for flotation research with a focus on hydrodynamics are briefly reviewed and the motivation for current work is presented.
The earliest application of CFD to understand flotation micro- processes was performed by Koh et al. , who studied bubble- particle collisions in mineral flotation cells. Closely following their pioneering work, Koh and co-workers published a number of papers in which they developed flotation kinetic rate model for lab scale flotation cells [۵,۷–۹]. Evans et al.  studied mixing
and gas dispersion in lab scale flotation cells using Eulerian multi- phase CFD simulations. Liu and Schwarz  used numerical sim- ulations to study isolated bubble-particle collisions in the presence of turbulent flow. Recently, Karimi et al. [۲,۱۱] developed and implemented a CFD model for prediction of flotation rate constant and compared their predictions against experimental measure- ments of Newell . However, both experimental measurements of Newell  and CFD simulations of Karimi et al. [2,11] were per- formed in a stirred tank using a Rushton turbine.
Local flow measurements in flotation cells, especially in the impeller region are not widely reported and the data reported is generally limited to regions outside the rotor-stator region. In recent years, more focus has been given to vessel hydrodynamics due to the increasing size and complexity of flotation machines. For instance, Shi et al.  used particle image velocimetry (PIV) measurements and CFD simulations to study the effect of the impeller blade angle on mean flow characteristics in a lab-scale
0.2 m3 KYF flotation cell. Based on their analysis of power draw
behavior, Shi et al.  recommend backward impeller design for efficient operation. Comparison of CFD predictions and PIV mea- surements were made for the WEMCO flotation machine by Kuang et al. . More recently, Jaszczur et al.  reported detailed velocity measurements for a lab-scale flotation cell using detailed
PIV measurements in critical regions of the cell, for both aerated and unaerated flow conditions. Xia et al.  performed numerical simulations of single-phase flow in an Outotec tank cell. They com-
pared three turbulence models namely, standard k-e, realizable k-e
and Reynolds stress model (RSM) and reported two re-circulation zones in the cell which is typical of radial impellers at intermediate clearance. Trailing vortices characterized by high velocity close to the impeller were also observed, and the stator is found to weaken the tangential component of the flow to very low levels in bulk of the tank. More recently, Basavarajappa et al. , performed PIV measurements and CFD simulation of flows developed by flotation impeller in a cylindrical mixing tank. They reported important dif- ferences in mean local flow behavior created by different impeller
blade designs and suggested similar exercise for flotation cells. A brief overview of past studies using CFD to study single phase hydrodynamics in flotation cells is given in Table ۱٫
The impeller blade shape is known to critically affect dispersion, mixing and turbulence level in mixing vessels . In multiphase flows, especially in gas-liquid flows, breakage of gas bubbles occurs in the region of high turbulence kinetic energy dissipation rates [4,8,24]; usually in the impeller stream. Also, particles have been shown to preferentially concentrate in regions of high or low vor- ticity based on their size .
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