Impeller tank diameter

The pumping number is a function of impeller type, the impeller/tank diameter ratio (D/T), and mixing Reynolds number Re = pND /p.. Figure 3 shows the relationship (2) for a 45° pitched blade turbine (PBT). The total flow in a mixing tank is the sum of the impeller flow and flow entrained by the hquid jet. The entrainment depends on the mixer geometry and impeller diameter. For large-size impellers, enhancement of total flow by entrainment is lower (Fig. 4) compared with small impellers. 

Stirred tank paddles power input suspend solids, 0.2 to 1.6 kW/m UD = 0.7 to 1.05/1. Baffle, four 90° baffle width = 0.08 x tank diameter off-the-wall distance = 0.015 x tank diameter. Minimum level of liquid = 0.15 x tank diameter for impeller tank diameter 0.28 1 and minimum level = 0.25 x tank diameter for impeller tank diameter = 0.4 1. Use a foot bearing plus a single, main axial hydrofoil impeller diameter = 0.28 x tank diameter located 0.2 x tank diameter from the bottom plus a pitched blade impeller diameter = 0.19 x tank diameter located 0.5 x tank diameter from the bottom. Liquid fluidized bed in general, particle diameter 0.5 to 5 mm with density and diameter of the particle dependent on the application. The superficial liquid velocity to fluidize the bed depends on both the diameter and the density difference between the liquid and the particle. Usually, the operation is particulate fluidization. Particle diameter 0.2 to 1 mm reactors superficial liquid velocity 2 to 200 mm/s. Fluidized adsorption bed expands 20 to 30% superficial liquid velocity for usual carbon adsorbent = 8 to 14 mm/s. Fluidized ion exchange bed expands 50 to 200% superficial liquid velocity for usual ion exchange resin = 40 mm/s. Backwash operations fixed-bed adsorption superficial liquid velocity = 8 to 14 mm/s fixed-bed ion exchange superficial backwash velocity = 3 mm/s. 

Figure 4.2. Simulations of oxygen consumption kinetics o/ o,max at different impeller/tank diameter ratios djdj as a function of power consumption P/V, as a typical example of macrokinetics in a 201 vessel. (From Reuss et al., 1982.)...

The flow into the vessel, together with heat and mass transfer, must be considered in emulsion polymerization reactors because all of these mechanisms can have a great influence on polymer properties and reactor behavior. Unfortunately, the mixing and heat-transfer parameters do not scale equally. In Table 6.4 several scale factors are shown for a change from a 50 L pilot-scale vessel to a full-scale vessel of 50 m. The calculated values assume geometric similarity with a constant impeller/tank diameter ratio and a constant height/tank diameter ratio. This table... 

Impellers are usually of the flat-blade turbine type, Fig. 6.36 and c, either centrally located in the vessel or nearer the bottom entry of the liquids. The impeller-tank-diameter ratio d /T is ordinarily in the range 0.25 to 0.33. 

Where Q = volumetric flow of gas, ftVs N = impeller speed, rev/s D = impeller diameter, ft and T = tank diameter, ft. 

AU tbe curves are for axial impeller shafts, witb liquid depth Z equal to tbe tank diameter d,. 

There are three types of mixing flow patterns that are markedly different. The so-called axial-flow turbines (Fig. 18-3) actually give a flow coming off the impeller of approximately 45°, and therefore have a recirculation pattern coming back into the impeller at the hub region of the blades. This flow pattern exists to an approximate Reynolds number of 200 to 600 and then becomes radial as the Reynolds number decreases. Both the RlOO and A200 impellers normally require four baffles for an effective flow pattern. These baffles typically are V12 of the tank diameter and width. 

Suspensions of fine sohds may have pseudoplastic or plastic-flow properties. When they are in laminar flow in a stirred vessel, motion in remote parts of the vessel where shear rates are low may become negligible or cease completely. To compensate for this behavior of slurries, large-diameter impellers or paddles are used, with (D /Df) > 0.6, where Df is the tank diameter. In some cases, for example, with some anchors, > 0.95 Df. Two or more paddles may be used in deep tanks to avoid stagnant regions in slurries. 

D = impeller diameter, m, 6-Llade tiirhine Dt = tank diameter, m E = power input, kW/m ... 

FIG. 23-30a A basic stirred tank design, not to scale, showing a lower radial impeller and an upper axial impeller boused in a draft tube. Four equally spaced baffles are standard. H = beigbt of liquid level, Dj = tank diameter, d = impeller diameter. For radial impellers, 0.3 < d/Dt < 0.6. 

The larger the ratio of impeller diameter to tank diameter, the less mixer power required. Large, slow speed impellers require a low er horsepow er for a given pumping capacity, and solid suspension is governed by the circulation rate in the tank. 

For turbine mixers that the width of a baffle should not exceed more than one-twelfth of the tank diameter and, for propeller mixers, no more than one-eighteenth the tank diameter. With side-entering, inclined or off-center propellers, as shown in Figure 13, baffles are not required. Instead, shrouded impellers and diffuser rings may be used to suppress vortex formation. These devices contribute to flow resistance and reduce circulation by creating intense shear and abnormal turbulence... 

Consider a stirred tank vessel having a Newtonian liquid of density p and viseosity p, is agitated by an impeller of diameter D, rotating at a rotational speed N. Let the tank diameter be D, the impeller width W, and the liquid depth H. The power P required for agitation of a single-phase liquid ean be expressed as ... 

Hicks et al. [8] developed a correlation involving the Pumping number and impeller Reynolds number for several ratios of impeller diameter to tank diameter (D /D ) for pitched-blade turbines. From this coiTclation, Qp can be determined, and thus the bulk fluid velocity from the cross-sectional area of the tank. The procedure for determining the parameters is iterative because the impeller diameter and rotational speed N appear in both dimensionless parameters (i.e., Npe and Nq). 

V3.03. The tank diameter was T = 1 m. Furthermore, Z/T = 1, D/T = 0.33, C/T = 0.32, and rpm = 58. The flow pattern in this tank is shown in Figure 10-9. Experimental data were used as impeller boundary eonditions. Figure 10-10 shows the uniformity of the mixture as a funetion of time. The model predietions are eompared with the results of the experimental blend time eorrelation of Fasano and Penny [6]. This graph shows that for uniformity above 90% there is exeellent agreement between the model predietions and the experimental eorrelation. Figure 10-1 la shows the eoneentration field at t = 0 see. Figures 10-1 lb through 10-1 Id show the eoneentration field at t = 0,... 

Table 5-1 shows that in a cylinder tank, four baffles, each A2 tank diameter above flat bottom, liquid depth is equal to tank diameter, impeller shaft is vertical and at centerline of tank. 

F = fluid force on turbine, perpendicular to shaft, ML./t D = impeller diameter, L Q = volumetric flow, L /t T = tank diameter, L p = fluid density, M/L ty = fluid tdscosity, M/(Lt)... 

Np = power number D = tank diameter d = impeller diameter Z = height of liquid in tank n = revolutions per minute Tm = time... 

For solids W hich float, or which are added from the top, a vortex action helps to draw the material down into the impeller. Often a draft tube is used to serve as a stic-don entrance for the impeller. Uniform suspensions are difficult to maintain when the tank liquid height is much greater than the tank diameter. The impeller is normally placed Vs of liquid depth off the bottom [21]. 

IC = Clearance of impeller off tank bottom, in.. Figure 5-34, equal to impeller (tirrbine) diameter, or IC = D sometimes IC = % D is suggested Absorption coefficient... 

These types of agitator are used in low-viscosity systems (ji < 50 kg m 1 s-1) with high rotational speed. The typical tip speed velocity for turbine and intermig is in the region of 3 m s 1 a propeller rotates faster. These impellers are classified as remote clearance type, having diameters in the range 25-67% of the tank diameter. 

The most common type of agitator is turbine. It consists of several short blades mounted on a central shaft. The diameter of a turbine is normally 35 15% of the tank diameter. There are four to six blades for perfect mixing. Turbines with flat blades give radial flow. This is good for gas dispersion in the media, where the gas is introduced just below the impeller, is drawn up to the blades and broken up into uniform fine bubbles. 

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