Page 369 - APPLIED PROCESS DESIGN FOR CHEMICAL AND PETROCHEMICAL PLANTS, Volume 1, 3rd Edition

Mixing of Liquids 337

Figure 5-47. Luwa BlendrexCTM) motionless mixer. By permission, Luwa Corporation.

Materials of Construction
g. = the lower this value, the more homogeneous the
x mixture. Generally does not need to be lower than
These elements that insert in a pipe or specially fabri- 0. 05, i.e., 5% standard deviation from the arithmetic
cated cylindrical holder can usually be fabricated from mean.
any workable and weldable metal or alloy. In addition,
most plastic that can be fabricated by molding, cutting, cr = standard deviation
heat welding, or even bolting can be used. This wide array x = arithmetic mean
of fabrication materials allows the units to fit an extreme- n = number of samples
ly wide range of corrosive applications.
The results of these calculations depends entirely on
Mixer Design and Solution the manufacturer's design.

For some fluid systems, the motionless mixer may not Pressure Drop
practically achieve total homogeneity. In some situations
of widely diverse fluid densities, the centrifugal motion The energy to drive the fluid through a static mixer
created may "throw" some of the fluid to the outside of comes from the fluid pressure itself, creating a loss in pres-
the flow path when it emerges from the unit. These are sure (usually small) as the fluid flows through the unit.
concepts to examine with the manufacturer, as only the For laminar flow
manufacturer's data can properly predict performance,
and the design engineer should not attempt to actually
physically design a unit. �p 1 = 8.9 X 10-s (N Re ) µM *(L/D') (5- 83)
Mixing fluids with viscosity ratios of over 1,000: 1 is one e D p ( D, )3
of the most difficult applications [39]. Mixing highly vis-
cous fluids is also quite difficult.
Ne = Newton number, depends on unit design. Can range
The statistical measure of homogeneity is expressed as from 0.8 to 1.9, for example.
a function of the element geometry and the length of the M = mass flow rate, lb/hr
unit (i.e., the number of elements in the mixer assembly).
µ = absolute viscosity, Cp
p = density, lb/ cu ft
v. D' = inside pipe diameter, in.
L = mixer length, in.
n
o = �� ( xi - x - � I (5- 82) Re 0 = Reynolds number related to inside diameter of pipe
-)2 and, x =
:':"': --n- Q 8 = flow rate, gal/min
" - I
For Turbulent Fl.ow
xi = temperature, concentration or some other measurable
variable (5-84)