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Kinds of Impellers

A rotating impeller in a fluid imparts flow and shear to it, the shear resulting from the flow of one portion of the fluid past another. Limiting cases of flow are in the axial or radial directions so that impellers are classified conveniently according to which of these flows is dominant. By reason of reflections from vessel surfaces and obstruction by baffles and other internals, however, flow patterns in most cases are mixed. When a close approach to axial flow is particularly desirable, as for suspension of the solids of a slurry, the impeller may be housed in a draft tube and when radial flow is needed, a shrouded turbine consisting of a rotor and a stator may be employed. [Pg.288]

Shrouded turbines consisting of a rotor and a stator ensure a high degree of radial flow and shearing action, and are well adapted to emulsification and dispersion. [Pg.288]

Flat plate impellers with sawtooth edges are suited to emulsification and dispersion. Since the shearing action is localized, baffles are not required. Propellers and turbines also are sometimes provided with sawtooth edges to improve shear. [Pg.288]

Cage beaters impart a cutting and beating action. Usually they are mounted on the same shaft with a standard propeller. More violent action may be obtained with spined blades. [Pg.288]


Some of the many kinds of impellers are shown in Figure 7.10. For clear liquids, some form of closed impeller [Figure 7.10(c)] is favored. They may differ in width and number and curvature of the vanes, and of course in the primary dimension, the diameter. Various extents of openness of impellers, [Figs. 7.10(a) and (b)] are desirable when there is a possibility of clogging as with slurries or pulps. The impeller of Figure 7.10(e) has both axial propeller and... [Pg.137]

Figure 7.25. Efficiency and head coefficient qad as functions of specific speeds and specific diameters of various kinds of impellers (Evans, 1979). Example An axial propeller has an efficiency of 70% at A, = 200 and Ds = 1.5 and 85% at Ns = 400 and Ds = 0.8. See Table 7.4 for definitions of qad, Ns, and Ds. Figure 7.25. Efficiency and head coefficient qad as functions of specific speeds and specific diameters of various kinds of impellers (Evans, 1979). Example An axial propeller has an efficiency of 70% at A, = 200 and Ds = 1.5 and 85% at Ns = 400 and Ds = 0.8. See Table 7.4 for definitions of qad, Ns, and Ds.
This depends on the kind of impeller and operating conditions described by the Reynolds, Froude, and Power numbers as well as individual characteristics whose effects have been correlated. For the popular turbine impeller, the ratio of diameters of impeller and vessel falls in the range, d/D, = 0.3-0.6, the lower values at high rpm, in gas dispersion, for example. [Pg.287]

Figure 10.2. Representative kinds of impellers (descriptions in the text). Figure 10.2. Representative kinds of impellers (descriptions in the text).
Figure 10.5. Power number, Np = PgJN3Dsp, against Reynolds number, NR = ND2p/p, for several kinds of impellers (a) helical shape (Oldshue, 1983) (b) anchor shape Oldshue, 1983) (c) several shapes (1) propeller, pitch equalling diameter, without baffles (2) propeller, s = d, four baffles (3) propeller, s = 2d, without baffles (4) propeller, s = 2d, four baffles (5) turbine impeller, six straight blades, without baffles (6) turbine impeller, six blades, four baffles (7) turbine impeller, six curved blades, four baffles (8) arrowhead turbine, four baffles (9) turbine impeller, inclined curved blades, four baffles (10) two-blade paddle, four baffles (11) turbine impeller, six blades, four baffles (12) turbine impeller with stator ring (13) paddle without baffles (data of Miller and Mann) (14) paddle without baffles (data of White and Summerford). All baffles are of width 0.1D [after Rushton, Costich, and Everett, Chem. Eng. Prog. 46(9), 467 (1950)]. Figure 10.5. Power number, Np = PgJN3Dsp, against Reynolds number, NR = ND2p/p, for several kinds of impellers (a) helical shape (Oldshue, 1983) (b) anchor shape Oldshue, 1983) (c) several shapes (1) propeller, pitch equalling diameter, without baffles (2) propeller, s = d, four baffles (3) propeller, s = 2d, without baffles (4) propeller, s = 2d, four baffles (5) turbine impeller, six straight blades, without baffles (6) turbine impeller, six blades, four baffles (7) turbine impeller, six curved blades, four baffles (8) arrowhead turbine, four baffles (9) turbine impeller, inclined curved blades, four baffles (10) two-blade paddle, four baffles (11) turbine impeller, six blades, four baffles (12) turbine impeller with stator ring (13) paddle without baffles (data of Miller and Mann) (14) paddle without baffles (data of White and Summerford). All baffles are of width 0.1D [after Rushton, Costich, and Everett, Chem. Eng. Prog. 46(9), 467 (1950)].
FIG. 23-30 Basic stirred tank design and selected kinds of Impellers, (fc) Propeller, (c) Turbine, (d) Hollow, (e) Anchor. [Pg.1870]


See other pages where Kinds of Impellers is mentioned: [Pg.288]    [Pg.288]    [Pg.291]    [Pg.586]    [Pg.288]    [Pg.288]    [Pg.291]    [Pg.586]    [Pg.615]    [Pg.288]    [Pg.288]    [Pg.291]    [Pg.586]    [Pg.288]    [Pg.288]    [Pg.291]    [Pg.586]    [Pg.769]    [Pg.244]    [Pg.244]    [Pg.247]   


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