The
A/t value generated may be shown to be
288/p 2F.
For a 1% additive flow rate this gives us
an A/t value of 2921. In addition we have
been able to obtain a significant
improvement in the distribution and
dispersion of the additive. The SIDD can
be applied to situations where the
additive viscosity value is much lower or
the same as the main product.
These three devices all
possess an intriguing property. As the
additive fraction size goes down, the A/t
value goes up. This is the reverse of
experience with most conventional designs
of static mixer systems.
VISCOSITY
AND PRESSURE DROP CONSIDERATIONS
| Most
polymeric materials are shear
sensitive. That is to say, their
viscosity is dependent on the
shear rate to which they are
exposed. Usually an increased
shear rate produces a lowering of
viscosity and is referred to as
shear thinning. Viscosity versus
shear rate data is usually
provided by the polymer
manufacturer in the form of a
graph on log/log paper. We list
below the shear rate and pressure
drop formula for each of the
devices we have described and
others together with the units
involved. Main pipe inside
diameter = D inches
Main product flow rate = Q gpm
Shear rate = g
sec-1
Viscosity = m cP
Pressure drop = dP psi
Axial length = L inches
Additive fraction = F
Number of mixing elements = n
|

|
| Device |
A/t
Value |
Shear
rate |
Pressure
drop |
Comments |
| Open
pipe |
---------- |
39.2Q/D3 |
22.73x10-6Qm L/D4 |
Hagen-Poiseuille
Equation |
| Helix |
np |
96.0Q/D3 |
205x10-6Qm n/D3 |
Helix
L/D ratio = 1.5:1 |
| L/H
unit |
8/p2
F |
215Q/D3 |
5.9x10-4Qm /D3 |
Each
hole dia. = 0.45D |
| H/L
unit |
3.6/F |
81.7Q/Dt2 |
22.1Qm L/Dt3 |
Where
annulus dia.= 2D/3 |
| SIDD |
288/p2 F |
593Q/D3 |
12.6x10-4
Qm
/D3 |
Each
hole dia. = 0.3D |
| PARAFLO |
8pN/F |
Contact factory for
shear rate and pressure drop
calculations. |
|