Guichao Wang

STUDY OF THE TURBULENT FLOW IN AN UNBAFFLED STIRRED TANK BY DETACHED EDDY SIMULATION

Detached eddy simulation (DES) of the liquid-phase turbulent flow in an unbaffled stirred tank agitated by a six-blade, 45°-pitched blade turbine was performed in this study. The tank wall is cylindrical with no baffle and the fluid flow problem was solved in a single reference frame (SRF) rotating with the impeller. For the purpose of comparison, computation based on large eddy simulation (LES) was also carried out. The commercial code Fluent was used for all simulations. Predictions of the phase-averaged turbulent flow quantities and power consumption were conducted. Results obtained by DES were compared with experimental laser Doppler velocimetry (LDV) data from the literature and with the predictions obtained by LES. It was found that numerical results of mean velocity and turbulent kinetic energy profiles as well as the power consumption are in good agreement with the LDV data. When performed on the same computational grid, which is under-resolved in the sense of LES, DES allows better accuracy than LES in that it works better in the boundary layers on the surface of the impeller and the stirred tank walls. It can be concluded that DES has the potential to predict accurately the turbulent flow in stirred tanks and can be used as an effective tool to study the hydrodynamics in stirred tanks.

An experimental study of copper sulfide flotation in a packed cyclonic–static microbubble flotation column

ABSTRACT A method using a cyclonic–static microbubble flotation column packed with fluid guiding media was proposed for improving flotation efficiency of copper sulfide. The installation of packed fluid guiding media in a cyclonic–static microbubble flotation column was for changing flow pattern in 10 the column by avoiding strong cyclonic flow in the upper region of the column, which can cause bubble-particle detachment. Therefore, the attached particles can be more likely to enter the froth zone instead of swirling in the column. The flow rectification contributed to a smaller bubble size in the column and significantly reduced the number of big bubbles with diameter above 1 mm. This scenario was caused by the damping of swirling liquid motion where bubbles tended to 15 concentrate and coalescence in the center of an eddy. The packed fluid guiding media changed the hydrodynamics in the upper column from a cyclonic flow to a gentle flow and as a result improve the column separation. The application of packed fluid guiding media can decrease the bubble-particle detachment and the flotation recovery of copper sulfide could constantly improve with the installation of packed fluid guiding media in the FCSMC column.