CFD simulation of a venturi gas bubbles generator in a water-air system
Keywords:
Fluid dynamic simulation, gas bubbles, ANSYS Fluent, venturi, VOF modelAbstract
The efficiency of the flotation process strongly depends on the characteristics of the gas dispersion: bubble diameter, gas holdup, and bubble surface area flux. Bubble size is important since it is responsible of colliding, attaching, and carrying the valuable species out of the column as concentrate; therefore, it is important to design spargers to control the gas dispersion characteristics and to increase the metallurgical performance of flotation. n this research work the Computational Fluid Dynamics (CFD) simulation method was applied to design and study the hydraulic phenomena that occur inside the sparger type venturi, when bubbles are generated. This sparger was simulated to be externally attached to a flotation column, and for a water-air system.
The CFD was solved through the software ANSYS Fluent R16.2®, and the preprocessor Gambit 2.4.6Ò. During the solution two turbulence models were assumed: k-e, and LES; and the multiphase model: VOF.
The simulated venturi has the inlet and outlet diameter of 0.0381 m, whereas in the center the diameter is 0.0127 m (contracted vein). The convergent and divergent angles are of 15 degrees. Eight holes were radially distributed around the vein contract or throat of the venturi, to supply compressed air to the sparger.
Experimental results show that the bubble size and distribution of the bubbles swarm is more homogeneous when the gas is supplied through the eight orifices. The simulation results indicate that with the models VOF/k-ε both the dynamic pressure and phases velocity are not homogeneous inside the venturi, and when the bubbles swarm goes into the flotation column, a severe mixing is observed, caused by the appearance of zones with different density in the column. On the other hand, with the models VOF/LES the dynamic pressure and phases velocity are more uniform inside the sparger, ensuring an even bubble swarm distribution in the column.
References
Clayton R, Jameson GJ, Manlapig EV, The development and application of the Jameson cell. Minerals Engineering, 4(7): p. 925-933. 1991.
Madrid RG, Evaluación por modelación CFD del proceso de flotación en una celda de agitación mecánica y del efecto de la granulometría en la recuperación de mineral, in Facultad de Ciencias Físicas y Matemáticas. 2012, Universidad de Chile: Santiago, Chile.
Liu TY, Schwarz M, CFD-based modelling of bubble-particle collision efficiency with mobile bubble surface in a turbulent environment. International Journal of Mineral Processing, 90(1): p. 45-55. 2009.
Launder BE, Spalding DB, Lectures in mathematical models of turbulence. 1972.
Blazek J, Computational fluid dynamics: principles and applications. Butterworth-Heinemann. 2015.
FLUENT 14.5 Theory Guide. Chapter 6, 143-173. Canonsburg, PA, USA: ANSYS Inc, 2012.
Capote J, et al., Influencia del Modelo de Turbulencia y del Refinamiento de la Discretización Espacial en la Exactitud de las Simulaciones Computacionales de Incendios. Revista internacional de métodos numéricos para cálculo y diseño en ingeniería, 24(3): p. 227-245. 2008.
Wilcox D, Turbulence modeling for CFD. La Canada, California: DCW Industries. Inc, 5354: p. 124-128. 1998.
Launder BE, Spalding D, The numerical computation of turbulent flows. Computer methods in applied mechanics and engineering, 3(2): p. 269-289. 1974.
Ponasse M, et al., Bubble formation by water release in nozzle---II. Influence of various parameters on bubble size. Water Research, 32(8): p. 2498-2506. 1998.
Paladino, EE, Maliska CR, Computational modeling of bubbly flows in differential pressure flow meters. Flow Measurement and Instrumentation, 22(4): p. 309-318. 2011.
Sundararaj S, Selladurai V; Flow and Mixing Pattern of Transverse Turbulent Jet in Venturi-Jet Mixer. Springer Science & Business Media B.V., 38(12), p. 3563-3573. 2013.
Grau RA, Laskowski JS, Role of frothers in bubble generation and coalescence in a mechanical flotation cell. The Canadian Journal of Chemical Engineering, 84(2), 170-182. 2006.
Diaz PP, Dobby G. Kinetic studies in flotation columns: bubble size effect. Minerals Engineering, 7(4), 465-478. 1994.
Olmo-Velázquez A, et al., Estudio y modelación del flujo bifásico líquido-gas para bajos valores de Reynolds. Ingeniería Mecánica, 18(1): p. 1-11. 2015.
Kim MI, et al., Numerical and experimental investigations of gas–liquid dispersion in an ejector. Chemical Engineering Science, 62(24): p. 7133-7139. 2007.
