The aim of this work is to investigate the turbulent hydrodynamic features of a gas-liquid stirred tank by detecting independently and simultaneously the liquid and the bubble phase velocity by means of a two-phase PIV technique. The investigation was carried out in an open, fully-baffled, flat-bottomed cylindrical vessel (diameter, T=23.2 cm) filled of liquid up to a height H=2T. Agitation was provided by a dual turbine – a 6SRGT manufactured by Scaba of diameter D=T/2 placed at the distance C1=T/3 from the vessel base and a down-pumping PBT of diameter D=0.40T placed at the distance C2=T from the bottom impeller. The gas was introduced by a point sparger placed below the bottom impeller. Air was always used as the gas phase, while two liquids of different viscosity were considered: demineralised water and a moderately viscous water-glycerine solution (=5 mPa∙s). The mean flow fields of the gas and the liquid phases, the r.m.s. maps of the two phases and a comparison with the corresponding velocity measurements in single-phase conditions are presented. The typical bubble diameters in the two gas-liquid systems obtained by a digital image processing method are also presented. The effects of liquid viscosity and of the gas flow rate on the hydrodynamic features are discussed.
Turbulent gas-liquid flow and bubble size distribution in multiple impeller stirred vessels
PAGLIANTI, ALESSANDRO;MONTANTE, GIUSEPPINA MARIA ROSA;MAGELLI, FRANCO
2008
Abstract
The aim of this work is to investigate the turbulent hydrodynamic features of a gas-liquid stirred tank by detecting independently and simultaneously the liquid and the bubble phase velocity by means of a two-phase PIV technique. The investigation was carried out in an open, fully-baffled, flat-bottomed cylindrical vessel (diameter, T=23.2 cm) filled of liquid up to a height H=2T. Agitation was provided by a dual turbine – a 6SRGT manufactured by Scaba of diameter D=T/2 placed at the distance C1=T/3 from the vessel base and a down-pumping PBT of diameter D=0.40T placed at the distance C2=T from the bottom impeller. The gas was introduced by a point sparger placed below the bottom impeller. Air was always used as the gas phase, while two liquids of different viscosity were considered: demineralised water and a moderately viscous water-glycerine solution (=5 mPa∙s). The mean flow fields of the gas and the liquid phases, the r.m.s. maps of the two phases and a comparison with the corresponding velocity measurements in single-phase conditions are presented. The typical bubble diameters in the two gas-liquid systems obtained by a digital image processing method are also presented. The effects of liquid viscosity and of the gas flow rate on the hydrodynamic features are discussed.I documenti in IRIS sono protetti da copyright e tutti i diritti sono riservati, salvo diversa indicazione.
