Two-blade impellers

The ethylene polymerization was carried out using a 12 OZ glass reactor equipped with a two blade impeller under a constant ethylene pressure of 20 psi. A predetermined amount of solvent (n-heptane), monomer, MAO and embedded catalyst were charged in series into the reactor. Polymerization was carried out at 70"C with agitation speed of 800 rpm. The polymer obtained was washed with excess amount of methanol containing hydrochloric acid solution and dried in vacuo for 24 hrs. The polymerization rate was determined from the amount of consumed ethylene, measured using a mass flow meter. DSC analyses (Dupont V4.0B) was carried out at a rate of 10 C /min, and the results were obtained in the second scan. 

Two-bath, two-stage dyeing process, 9 198 Two-bladed impellers, 16 672-673 Two-color thermometers, 24 457 Two-component epoxy—amine coatings, 10 443... 

Mechanical stirrer with two blade impellers (IKAWerke RW, Germany)... 

MODELING OF THE HYDRODYNAMIC BEHAVIOR OF HIGHLY VISCOUS FLUIDS IN STIRRED TANKS EQUIPPED WITH TWO-BLADE IMPELLERS... 

CLASSICAL TWO-BLADE IMPELLER, 471 Flow in Horizontal Planes, 471 Flow in Vertical Planes, 471 Stresses, 471... 

Large blade impellers generally are used for laminar mixing of highly viscous fluids. One of the commonly used impellers is the two-blade impeller (Figure 1). The ratio (D/T), impeller diameter to tank diameter, can be varied from 0.5 to 0.9. In this case of large diameter impellers, these last ones can be used for heat transfer and can successfully replace anchor impellers. 

The ratio (W/T), impeller height to tank diameter, can vary from 1/12 to 0.95 (Figure 2). The case 1/12 corresponds to the case of the classical paddle impellers. These often are used for the mixing of miscible fluids of low viscosity [1-3]. These two-blade impellers are classified as turbines, and the flow is essentially radial in the discharge flow of the impeller if the impeller speed is sufficient. They generally are used for smooth mixing with the tip speed varying from 1.2 to 2.3 m/s. 

In the literature, blade impellers have been experimentally and theoretically studied. Several experimental pieces of equipment have been used to study the flow structure generated by two-blade impellers [5-9]. Most studies show that, for a low impeller speed, the flow is essentially tangential. Hiraoka et al. [10] and Bertrand and Couderc [11] studied the 2D flow of viscous Newtonian and non-Newtonian fluids generated by two-blade impellers and paddle agitators, using computation fluid dynamics (CFD). For some years, some new CFD studies concerning the flows... 

In this section, a large two-blade impeller, the height of which is equal to the liquid level, is considered. This impeller scrapes the tank bottom without any friction it is this kind of impeller that was frequently studied in the previous works, assuming 2D flows. In the following, more precise results are presented. 

In this section, the flow produced by a classical two-blade impeller is considered. The ratio between the blade height and the impeller diameter is lower for this impeller than in the case of a paddle agitator (W/T = 0.25). The ratio between the impeller diameter and the tank diameter is D/T = 0.7. The impeller is located near mid-height of the tank (C/T = 0.4). 

The flows generated by two-blade impellers with a small W/T ratio are mainly characterized by an increase of the radial and axial components of the velocity in the vicinity of (he impeller. The flow generated for Re = 10 at two different heights in the tank is presented in Figure 14. In the plane under the impeller (Z = 0.24), the flows are directed to the axis in a spiral. The formation of an axial eddy in the lower part of the tank tends to generate a suction motion of the fluid to the axis of the two-blade impeller. In the volume defined by the impeller, the flow remains tangential with a low part of recirculation near the second blade. 

Figure 14. Tangential and radial velocity components for a classical two-blade impeller. Re = 10.

The influence of the position of the impeller in the tank is studied in the case of a two-blade impeller with W/T = 0.10 and C/T = 0.17. The vicinity of the tank bottom leads to a small decrease in the intensity of the flows for the recirculation loop (Figure 17). 

Thus, the flows generated by the two-blade impeller are mainly tangential for low values of the Reynolds number and become more and more radial when the Reynolds number increases. The profile of the radial velocity component for Re = 61 is parabolic. 

The power consumption constitutes a global parameter very easy to measure. Several experimental works have been devoted to the analysis of this two-blade impeller... 

A comparison of the two previous studied geometries, the paddle agitator and the two-blade impeller, shows a rather good agreement, except in the case of the two-blade impeller, for Re = 61. It seems that in this case, the observed physical flow... 

The operation consisting of mixing two miscible fluids of high viscosity remains difficult with two-blade impellers. Correlations obtained from experimental data to estimate the time necessary to get a good homogeneity cannot be found in the literature. 

In this paper, results obtained by numerical simulations of hydrodynamics generated by two-blade impellers are presented for the laminar flow range. 

Bertrand, J. and J.P. Couderc, Agitation of Pseudoplastic Fluids by Two-Blade Impellers, Anchors and Gate-Agitators , Can. J. Chem. Eng. 60, 738-744 (1982). 

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