The A/t value for this device is
3.6/F. If our additive flow rate is 1% of
the main flow, then the A/t value is 360.
This is more than 100 times the value
that a simple T input for the additive
would provide.
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. |
|