Static mixer for two or more fluids

Distribution of a fluid additive through multiple passages across the cross section of a pipe carrying molten/fluid polymer wherein the polymer flow is distributed across the cross section of the pipe provides uniform distribution of the fluid additive when the passages are directed in the downstream direction of flow and substantially parallel to the longitudinal axis of the pipe carrying the polymer. This device is advantageous for mixing of two or more fluids independent of the viscosity differences.

The present invention relates to a mixer for two or more fluids and more 
particularly it relates to a static mixer for distributing additive fluids 
at locations over the cross section of a pipe carrying another fluid of 
different viscosity. 
The uniform distribution and dispersion of an additive into a polymer 
stream flowing through a pipe under laminar flow conditions is a difficult 
task. A variety of approaches have been disclosed for this task such as: 
(a) distributing/dispersing of the additive into polymer under laminar flow 
conditions (due to high viscosity and low velocity of the polymer) by 
injecting the additive at the wall of the pipe and using inline static 
mixers to mix the additive into the molten polymer stream; 
(b) injecting the additive directly at the center of the pipe and mixing 
with polymer using inline static mixers; 
(c) using a flow inverter downstream of the injection point to bring the 
wall injected additive to the center and then mixing with the polymer 
using inline static mixers. 
The commercially available inline static mixers can disperse and distribute 
the additive only at the cost of a very high pressure drop. This pressure 
drop, which is energy dissipated into the polymer, results in temperature 
increase of the polymer, causing degradation and poor quality of the final 
product. 
The present invention deals with a flow distributor that provides a 
positive distribution of the additive in multiple streams/droplets, across 
the cross section of a pipe carrying molten/liquid polymers. Using the 
exiting stream from this distributor as the feed stream to commercially 
available inline static mixers, the mixing of low viscosity/high viscosity 
additives to polymer streams can be accomplished at a much lower combined 
pressure drop compared to the processes described above. 
SUMMARY OF THE INVENTION 
A mixer for two or more fluids that includes an elongated substantially 
hollow tubular member having a longitudinal axis in which multiple flow 
passages are made available for the main polymer flow as well as for the 
additive streams. The mixing zone has at least two orifices for carrying 
the additive fluid and two or more orifices for the flow of the main 
polymer. The orifices have substantially circular cross sections and 
longitudinal axes which are substantially parallel to the longitudinal 
axis of the substantially hollow tubular member. A fluid entry port is 
provided for discharging a second fluid in the mixing zone. An array of 
passages are connected to the fluid entry port. The passages are 
distributed within said mixing zone, and have one end connected to the 
fluid entry port and their other end directed substantially parallel to 
the longitudinal axis of the substantially hollow tubular member.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
Referring now to FIG. 1 the mixer 10 includes a pipe 12 which is 
constricted by a mixing zone i.e., static mixer designated 14. The mixing 
zone 14 is a plate 14a having substantially circular orifices 16, 18 and 
20 for the passage of molten polymer. Orifices 16, 18 and 20 have 
longitudinal axes which are substantially parallel to the longitudinal 
axis of the pipe 12. A fluid entry port 22 extends radially through the 
wall of pipe 12. An array of passages 30, 32, 34, and 36 are distributed 
within the mixing zone and connected to fluid entry port 22 at one end 
while the other ends of these passages are directed substantially parallel 
to the longitudinal axis of pipe 12 in the downstream direction of the 
polymer flow in pipe 12. 
FIGS. 4 and 5 depict a preferred embodiment with six additive passages 31, 
33, 35, 37, 39 and 40 and three polymer orifices 16, 18 and 20. 
FIGS. 6-11 show alternative embodiments of polymer orifice and fluid 
additive passage arrangements that may be used. In each case, the fluid 
additive passages are smaller than the polymer orifices. More 
particularly, FIG. 6 shows a two polymer hole-6 additive hole arrangement. 
FIG. 7 shows a two polymer hole-2 additive hole arrangement. FIG. 8 shows 
a three polymer hole-3 additive hole arrangement. FIG. 9 shows a four 
polymer hole-8 additive hole arrangement. FIG. 10 shows a four polymer 
hole-12 additive hole arrangement. FIG. 11 shows a nine polymer hole-16 
additive hole arrangement. 
FIG. 12 shows an arrangement with a center polymer orifice 50 and an 
annular polymer orifice 51 along with 8 additive holes 52-59 arranged in 
an array concentric with and between the orifices. 
These patterns of orifices and passages are only indicative of the 
possibilities using this concept (multiple holes for the additive, 
multiple holes for the polymer and symmetric distribution of the additive 
and polymer holes across the cross section in each quadrant). As an 
extension of this concept, one can also propose a very random pattern of 
numerous polymer holes and additive holes so that in each quadrant, there 
are equal flow rates of polymer and additive. 
Since the additive is added in quantities of 0.5% to 10%, the additive 
passages are much smaller in diameter than polymer orifices. The 
distribution and size of the additive passages and that of the polymer 
orifices is such that flow rates through cross sections of the additive 
passages and polymer orifices are approximately the same in at least each 
quadrant. The size of the polymer orifices will depend on the pressure 
drop that can be allowed, the flow rate of the polymer etc., and will be 
based on standard design procedures. The design will also ensure there is 
no stagnation of the polymer as it enters or exits the mixing zone 14. The 
size of the additive passages away from the center will be larger than 
those close to the center, if the main feed passage for the additive is 
feeding the various additive holes from the center. This is to make sure 
that the flow rate of the additive through each additive passage is 
approximately the same. Standard design equations, well known in the art, 
can be used to size these holes. 
The viscosity ratio is not important in this case as the additive will be 
forced out across the cross section of the pipe in multiple streams 
independent of viscosity. By providing very small diameter additive 
passages, we can help break up the additive droplets into much finer 
droplets, thereby improving dispersion. This device enhances dispersion 
and distribution of the additive in the polymer. This device should 
perform well if additive viscosity is higher or lower than the polymer 
viscosity or even identical to the polymer viscosity. We can also 
contemplate increasing the number of additives by increasing the number of 
individual passages dedicated to individual additives and substantially 
maintaining equal distribution of each additive in each quadrant of the 
pipe.