Page 334 - Applied Process Design for Chemical and Petrochemical Plants Volume I

Mixing of Liquids 305

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0 2 Flat Paddles ~ ~ ~ W = ~ ~
I
Propeller Pitch -

Figwe 5-48. Laminar flow mixing. For known impeller type, diameter, speed, and viscosity, this nomograph will give power consumption. Con-
and diameter, also viscosity and impeller scale. The intersection of these two separate lines with alpha and beta respectively is
then connected to give horsepower on the HP scale. By permission, Quillen, C. S., Chern. fngr., June 1954, p. 7 77 1151.

NQ = flow number, dimensionless, Then Q/P = (NQ/Np) (l/p N'D') (5-37)

NQ z Q'/ (N,D3) (5-2) When comparing flow (or pumping) per power, we
determine that it is dependent QII the impeller type,
NRe = Reynolds number, dimensionless speed, diameter, and geometry of the installation. The
mixer is not fully specified until torque, 2, and lateral
loads (fluid force, F) are included in the analysis [29].

NF = force number, NF 3 F/(PN'D") (5-34) z = N, p N2D5/ (2~) (5-38)

when M = mass F = NF p N2D4 (5-39)
L = length
T = temperature Table 5-2 presents the effects of expected performance
t = time on various parameters or relationships for mixing. To
F = force, ML/~~ actually calculate a numerical result of comparing
impeller performances, the dimensionless numbers for
flow power and force are needed. Note that in Table 5-2
Bldshue [ 291 expresses pumping effectiveness as
pumping per power and recognizes it as a key function for the constant basis is across the horizontal top of the chart
processes that are flow controlled or need more flow than and the function to be examined or compared is along
head or shear. the vertical left side. The functions in the body of the
table are used as ratios for condition (1) and condition
(2), holding the basis constant.
Q = NQND3 (535)
For example, referring to Table 5-2, if power input (P)
P = Np p N3 D5 (5-36) and impeller diameter, D, are kept constant, then speed,