This study presents the results of tests on the mixing power and distribution of three velocity components in the mixing tank for an FBT impeller during tank emptying with an operating impeller. A laser PIV system was used to determine speed distributions. It was found that for the relative liquid height in the tank H* = H=H0 approximate to 0.65 and H* approximate to 0.45, the liquid circulation in the impeller zone changed from radial to axial and vice versa. These changes were accompanied by changes in the mixing power which even reached 40%. In the theoretical part, a method of calculating the mixing power using the classical model of the central vortex and distribution of the tangential speed in the impeller zone was proposed. Although the method turned out to be inaccurate, it was useful for determining the relative power.

In this study, the distribution of axial and radial velocities with the use of a PIV laser system was determined and the mixing power in a mixing tank with narrow and wide propeller impellers was measured. The pumping capacity and secondary circulation values in the mixing tank were calculated and on this basis, the energy efficiency of the operation of both types of propeller impellers was determined and compared with the efficiency of turbine impellers with inclined blades. It turned out that propeller impellers with wide blades are most effective as regards the amount of energy that should be supplied to the mixing tank to achieve the required mixing time. It was found that the share of pumping capacity in the total secondary circulation is almost twice as high as the share of induced circulation. Correlation equations for the dependence of the mixing power and dimensionless flow numbers on the pitch of the propeller blade were also formulated. All the results obtained were compared with the works of other authors. The paper also found that propeller impellers with a variable angle of inclination of the blade α depending on the current radius do not meet the theoretical assumption of a constant axial velocity of the liquid flowing out from of the impeller zone. For small radii of the impeller the explanation for this observation is the presence of the hub and shaft in the axis of the mixer and the effect of liquid slip for the steep agitator blades near the hub. For radii close to the radius of the stirrer, the reason is generation of induced circulation as the expense of the kinetic energy of the liquid flowing out of the impeller area.

In this study, the mixing power and the axial and radial velocity distributions were determined for the standard PBT45-6 impeller with inclined blades and for three NACA impellers with airfoil blades. On the basis of the velocity distributions obtained by means of PIV techniques, the pumping efficiency and the size of the secondary circulation for the tested impellers were determined. The next stage was to calculate the efficiency of the impeller operation, in which the comparative criteria were the values of the mixing energy in the form of a dimensional and dimensionless criterion. The lowest mixing energy was obtained for impellers with symmetrical profiled NACA0021 blades, which was 20% lower than the similar mixing energy obtained for the standard PBT45-6 impeller.

The paper presents research on the phenomenon of an increase in mixing power during the emptying of a tank with two 6-PBT45° axial impellers in operation, located on a common shaft, pumping the liquid to the bottom of the mixing tank. A large increase in mixing power took place when the free surface of the liquid was just above the upper edge of one of the impellers (hp/D < 0.1). This increase was even more than 50% compared to the design power for a fully filled mixing vessel. Admittedly, high motor overload, while not very long, may damage it. The study investigated the instantaneous torques acting on the impeller shaft during the emptying of the tank and the velocity distributions in planes r-z. On their basis, the mechanism of the phenomenon observed was determined and correlation relationships were given that permitted the calculation of the numerical values of the power increase factors.

This paper presents an analysis of hydrodynamics in a tank with a 45° and 60° pitched blade turbine impeller operating while emptying the mixer and with an axial agitator working during axial pumping-down of water at different water levels above the impeller. Measurements made with the PIV method confirmed the change in direction of pumping liquid after the level dropped below the critical value, with an almost unchanged liquid stream flowing through the mixer. It was found that an increase in the value of the tangential velocity in the area of the impeller took place and the quantity of this increase depended on the angle of the blade pitch and the rotational frequency of the impeller. Change in this velocity component increased the mixing power.

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An increase of the mixing power was obsd. during emptying tanks with turbine-blade impellers of various blade pitch angles. The decrease of blade pitch angle from 60 degrees down to 15 degrees (occurred primarily for the case when the impeller pumped the liq. to the bottom of the tank) resulted in a relative increase in power consumption. For impellers with blades located perpendicular to the agitating plane, this phenomenon did not occur.

This paper deals with the scale-up of equipment for the mixing of suspensions. The measurement of just-suspended agitator speeds was carried out with standard, pitched, four-blade turbines and folded, four-blade turbines in three vessels (290 mm, 600 mm, and 800 mm in diameter) for several particle sizes and concentrations. The results of measurements confirmed that scale-up based on dimensionless Froude number dependence, on the relative particle size and concentration, can be used. On the basis of the results, a scale-up rule for agitator speeds in a given suspension and equipment geometry was recommended, and various conclusions reported by different investigators were discussed.

Three tanks (diam. D = 200-400 mm) equipped with agitators with diams. related to D in 1:3 ratio were used sep. to measure the torque values of each agitator rotating at various frequencies during emptying tank when level of liq. was lowering close to upper surface of the rotating blades. On the basis, the quantitative increases of power consumption for the frequencies of the rotating agitator were detd. The highest values of mixing power were obsd. for low frequencies of rotating agitators.

The title stirrer and its varieties with addnl. vertical elements as well as with a ring were tested at homogenization of aq. suspensions contg. glass beads (diam. 10 mu m; concn. 5% by vol.). Modifications did not result in any increase of the process efficiency.

The study analyses application possibilities of filtration and thickening models in evaluation of papermaking suspension drainage rate. The authors proposed their own method to estimate the drainage rate on the basis of an existing Ergun capillary model of liquid flow through a granular material. The proposed model was less sensitive to porosity changes than the Ergun model. An empirical verification proved robustness of the proposed approach. Taking into account discrepancies in the published data concerning how the drainage velocity of papermaking suspension is defined, this study examines which of the commonly applied models matches experimental results the best.

Gravity dewatering of fibrous suspension is one of basic technological operations in paper production process. Although there are numerous methods to determine dewatering of such suspensions, none of them can measure undisturbed flow of removed water. In the paper the idea and design of a new apparatus for the determination of drainage rate of fibrous suspensions is presented. The apparatus differs from other known devices by minimisation of filtrate flow resistance in the outlet part of the equipment. In the second part of the paper measurements of the drainage rate have been presented. The flow resistance of the fluid through the bottom wire screen in the device was determined. The calculated flow resistance will be used in the developed model of dynamic drainage of fibrous suspensions, which will be discussed in our following paper (Przybysz et al., 2014).

Glass, poly(vinyl chloride), polyethylene and/or polypropylene beads were suspended in water by mech. stirring under lab. conditions to select the most efficient construction of mixers and shape of mixing blades in the case when both light and heavy beads were suspended. The optimum geometry showed a 2-turbine agitator with inclined blades which allowed for simultaneous down and up motion of suspensions (energy consumption below 200 W/m(3)).

This paper presents a comparison of the blending efficiency of eight high-speed rotary impellers in a fully baffled cylindrical vessel under the turbulent flow regime of agitated charge. Results of carried out experiments (blending time and impeller power input) confirm that the down pumping axial flow impellers exhibit better blending efficiency than the high-speed rotary impellers with prevailing radial discharge flow. It follows from presented results that, especially for large scale industrial realisations, the axial flow impellers with profiled blades bring maximum energy savings in comparison with the standard impellers with inclined flat blades (pitched blade impellers).

This paper deals with the effect of impeller shape on off-bottom particle suspension. On the basis of numerous suspension measurements, correlations are proposed for calculating the just-suspended impeller speed for a standard pitched four-blade turbine and three types of hydrofoil impellers produced by TECHMIX for several particle sizes and for a wide range of particle concentrations. The suspension efficiency of the tested impellers is compared with the efficiency of a standard pitched blade turbine on the basis of the power consumption required for off-bottom suspension of solid particles. It is shown that the standard pitched blade turbine needs highest power consumption, i.e. it exhibits less efficiency for particle suspension than hydrofoil impellers produced by TECHMIX.

Two axial impellers a (std. turbine with 4 inclined blades and a new type impeller with 4 folded blades) were studied for mixing efficiency in two-phase solid-liq. system. The new type impeller was more efficient than the std. one despite of the higher frequency needed because of a lower mixing power demand.

In the study a 3D/2D hybrid model for ribbon mixers, for a laminar range of mixing was verified. Distributions of the experimental and model values of velocity components and the experimental and model values of mixing power for this type of mixers were compared. Further on, based on the model solutions the optimum parameters of ribbon agitators due to the time of homogenization were established.

The aim of paper is to determine just-suspension speed of TX445 impeller produced by TECHMIX and to compare its suspension effects and efficiency necessary for particle suspension with standard pitched six-blade turbine. Suspension measurements were carried out with glass balotine of diameters in range from 0.18 to 0.9 mm and its volumetric concentration changed in the range from 0.025 to 0.4. The just suspension impeller speed was stated visually. The measurements were carried out in dish-bottomed vessel with diameter 300 mm equipped with four standard baffles at the wall. The ratio of vessel to impeller diameter D/d = 3. Turntable with tensometric pick-up of torque was used in power consumption measurements. From the results presented in the paper it follows that TX 445 impeller needs higher just suspension impeller speed but lower power consumption for particle suspension than pitched six-blade turbine.