
Local velocity scaling in upward flow to tooth impeller in a fully turbulent region
Šulc, R. ; Ditl, P. ; Fořt, I. ; Jašíková, D. ; Kotek, M. ; Kopecký, V. ; Kysela, Bohuš
The hydrodynamics and flow field were measured in an agitated vessel using 2D Time Resolved Particle Image Velocimetry (2D TR PIV). The experiments were carried out in a fully baffled cylindrical flat bottom vessel 400 mm in inner diameter agitated by a tooth impeller 133 mm in diameter. Distilled water was used as the agitated liquid. The velocity fields were investigated in the upward flow to the impeller for three impeller rotation speeds – 300 rpm, 500 rpm and 700 rpm, corresponding to a Reynolds number in the range 94 000 < Re < 221 000. This means that fullydeveloped turbulent flow was reached. This Re range secures the fullydeveloped turbulent flow in an agitated liquid. In accordance with the theory of mixing, the dimensionless mean and fluctuation velocities in the measured directions were found to be constant and independent of the impeller Reynolds number. On the basis of the test results the spatial distributions of dimensionless velocities were calculated. The axial turbulence intensity was found to be in the majority in the range from 0.4 to 0.7, which corresponds to the middle level of turbulence intensity.


Dispersion kinetics in mechanically agitated vessel
Bucciarelli, E. ; Formánek, R. ; Kysela, Bohuš ; Fořt, I. ; Šulc, R.
Agitation of two immiscible liquids or solidliquid suspension is a frequent operation in chemical and metallurgical industries. Prediction of mean drop/particle size and drop/particle size distribution (DSD) is vital for emulsification, suspension polymerization, solid particle dispersion or crystallization. Simulation of particulate systems requires the knowledge of DSD and its time evolution. The time evolution of drop size distribution was investigated in baffled vessel mechanically agitated by a Rushton turbine and a highshear tooth impeller. The system water –silicone oil was used as a model liquid. The volume fraction of the dispersed phase was 0.047 %. The drop sizes were determined by image analysis. The time evolution of the drops size dp32 was studied for both impellers tested. The model used involves the first order kinetics. Finally, the following correlations predicted by the KolmogorovHinze theory were evaluated at steady state: dp32/D = C1.We0.6 and dpmax/D = C2.We0.6, where We is the impeller Weber number.

 

The minimum record time for PIV measurement in a vessel agitated by a Rushton turbine
Šulc, R. ; Ditl, P. ; Fořt, I. ; Jašíková, D. ; Kotek, M. ; Kopecký, V. ; Kysela, Bohuš
In PIV studies published in the literature focusing on the investigation of the flow field in an agitated vessel the record time is ranging from the tenths and the units of seconds. The aim of this work was to determine minimum record time for PIV measurement in a vessel agitated by a Rushton turbine that is necessary to obtain relevant results of velocity field. The velocity fields were measured in a fully baffled cylindrical flat bottom vessel 400 mm in inner diameter agitated by a Rushton turbine 133 mm in diameter using 2D Time Resolved Particle Image Velocimetry in the impeller Reynolds number range from 50 000 to 189 000. This Re range secures the fullydeveloped turbulent flow of agitated liquid. Three liquids of different viscosities were used as the agitated liquid. On the basis of the analysis of the radial and axial components of the mean and fluctuation velocities measured outside the impeller region it was found that dimensionless minimum record time is independent of impeller Reynolds number and is equalled N. t(Rmin) = 103 +/ 19.


Local velocity scaling in T400 vessel agitated by Rushton turbine in a fully turbulent region
Šulc, R. ; Ditl, P. ; Fořt, I. ; Jašíková, D. ; Kotek, M. ; Kopecký, V. ; Kysela, Bohuš
The hydrodynamics and flow field were measured in an agitated vessel using 2D Time Resolved Particle Image Velocimetry (2D TR PIV). The experiments were carried out in a fully baffled cylindrical flat bottom vessel 400 mm in inner diameter agitated by a Rushton turbine 133 mm in diameter. The velocity fields were measured in the zone in upward flow to the impeller for impeller rotation speeds from 300 rpm to 850 rpm and three liquids of different viscosities (i.e. (i) distilled water, ii) a 28% vol. aqueous solution of glycol, and iii) a 43% vol. aqueous solution of glycol), corresponding to the impeller Reynolds number in the range 50 000 < Re < 189 000. This Re range secures the fullydeveloped turbulent flow of agitated liquid. In accordance with the theory of mixing, the dimensionless mean and fluctuation velocities in the measured directions were found to be constant and independent of the impeller Reynolds number. On the basis of the test results the spatial distributions of dimensionless velocities were calculated. The axial turbulence intensity was found to be in the majority in the range from 0.388 to 0.540, which corresponds to the high level of turbulence intensity.


Distribution of the turbulent kinetic dissipation rate in an agitated vessel
Kysela, Bohuš ; Sulc, R. ; Konfršt, Jiří ; Chára, Zdeněk ; Fořt, I. ; Ditl, P.
The design of the agitated tanks depends on the proposed operating conditions and processes\nfor that they are used for. Namely dissipation rate of the turbulent kinetic energy is important\nparameter for the scaleup modelling. The dissipation rate is commonly determined as integral\nvalue based on power input of the impeller, but without information about distribution inside\nthe agitated volume. The cumulative distributions of the dissipation rate within an agitated\nvessel are estimated by evaluations of the CFD (Computational Fluid Dynamics) results,\nwhere the data was obtained from RANS (Reynolds Averaged NavierStokes equations) and\nLES (Large Eddy Simulations). The simulations were performed for an agitated vessel\nequipped with four baffles and stirred by a standard Rushton turbine (tank diameter 0.3 m,\nimpeller diameter 0.1 m, offbottom clearance half of tank diameter, impeller speed 200 rpm).\nThe values of the dissipation rate from the LES calculations were approximated by computing\nthe SGS (Sub Grid Scale) dissipation rate.

 
 
 
 