František Rieger

Power consumption scale-up in agitating non-newtonian fluids

Abstract A method for the determination of power consumption of industrial agitators in non-Newtonian fluids on the basis of measurements on a model device is presented. The applicability of this method for purely viscous, time dependent and viscoelastic fluids is discussed. The method was tested experimentally using agitators of two different sizes and results of measurements confirmed the applicability of the present method for engineering calculations.

Vortex depth in mixed unbaffled vessels

Abstract An experimental investigation of vortex depth in an unbaffled cylindrical vessel with co-axial agitation was made. Five types of impellers: standard six-blade disc turbine, flat six-blade turbine, pitched six-blade turbine, pitched three-blade turbine and anchor agitator were tested. Turbine impellers were investigated in two positions ( H 2 = d and H 2 = d /3). On the basis of theoretical analysis, the dimensionless vortex depth was statistically correlated as a function of Froude and Galileo numbers and a relative impeller size. Liquid viscosity and impeller size variations were reflected in the value of the Galileo number which was within the range 4 × 10 5 – 5 × 10 10 . The vessel diameters used in the experiments were, D = 0.15, 0.20, 0.30, 0.40 and 0.64 m.

Homogenization efficiency of helical ribbon agitators

Abstract The effects of the main geometrical variables on the homogenization efficiency of helical ribbon agitators in newtonian liquids were investigated. The dependence of mixing time and power consumption on the relative size of the agitator, pitch, width of the ribbon and the number of blades was established. The geometries investigated were compared on the basis of energy consumed for homogenization and suitable geometrical parameters for the mixing process were found.

Homogenization Efficiency of Helical Ribbon and Anchor Agitators

Abstract Power and mixing time measurements were carried out with anchor, pitched blade anchor and helical ribbon agitators. For these types of agitators the relationship of Po = f(Re) and Nθ = f′(Re) were found and compared with the data available. The correlation Pθ/μD3 = f″ (D2ϱ/μθ) was used to compare homogenization efficiency of various types of agitators for mixing of viscous liquids.

Scale-up method for power consumption of agitators in the creeping flow regime

Abstract A method enabling the determination of power consumption of industrial agitators in a non-Newtonian fluid on the basis of measurements on a model device is presented. The applicability of the method is limited to creeping flows in the vessel. The suggested method was experimentally confirmed and is suitable mainly for mixing of highly viscous non-Newtonian fluids.

Power consumption of screw and helical ribbon agitators in highly viscous pseudoplastic fluids

Abstract Power consumption measurement of screw and helical ribbon agitators of efficient geometry which mixed pseudoplastic fluids in the creeping-flow regime, was performed. The values of the Metzner—Otto coefficient k and relations for its calculation were suggested on the basis of experimental results.

Study of the Blending Efficiency of Pitched Blade Impellers

This paper presents an analysis of the blending efficiency of pitched blade impellers under a turbulent regime of flow of an agitated low viscous liquid. The conductivity method is used to determine of the blending (homogenization) time of miscible liquids in pilot plant mixing equipment with standard radial baffles. For the given homogeneity degree (98 %) a three-blade pitched blade impeller is tested with various off-bottom clearances, vessel/ impeller diameter ratios and various impeller pitch angles. The experimental results show in accordance with theoretical data from the literature, that the greatest effect on the dimensionless blending time is exhibited by the vessel/ impeller diameter ratio and the impeller pitch angle. The number of total circulations necessary for reaching the chosen homogeneity degree depends on the impeller pitch angle and amounts more than three. Finally, the energetic efficiency of the blending process is calculated. The results of this study show, that the highest energetic efficiency of the three-blade pitched blade impeller appears for the pitch angle a = 24°, the impeller/vessel diameter ratio T/D = 2 and the impeller off-bottom clearance h/D = 1.

Effect of particle content on agitator speed for off-bottom suspension

This paper deals with the effect of particle content on agitator speed for off-bottom suspension. The measurements were carried out with a pitched six-blade turbine characterized by agitator to vessel diameter ratio d/D=0.3 in dish bottomed vessel equipped with four baffles. The resulting equation for off-bottom suspension was obtained in a wide range of particle sizes for volumetric particle content up to 20%.

Pumping efficiency of screw agitators in a tube

Abstract Most information on pumping efficiency that is available in the literature is limited to the turbulent region (centrifugal pumps). The aim of this paper is to show the effect of the Reynolds number on the pumping efficiency of screw agitators for a wide range of Reynolds number values from creeping to the turbulent flow region. The dependence of the pumping efficiency on the Reynolds number extends our knowledge about the efficiency of classical impeller pumps restricted usually to turbulent region.

Pumping characteristics of a screw agitator in a tube

Most information on pumping characteristics that is available in the literature is limited either to the turbulent region (centrifugal pumps) or to the creeping flow regime (screws). The aim of this paper is to investigate the effect of the Reynolds number on the pumping characteristics of agitators. The results of measurements using the new dynamic method are illustrated for a screw agitator in a tube. The characteristics, in the form of the dependence of the dimensionless specific energy on the dimensionless pumping capacity, were obtained for a wide range of Reynolds number values. The experimental creeping flow characteristic was compared with the theoretical prediction.