Agitating – Stirrer within stationary mixing chamber – Rotatable stirrer
Reexamination Certificate
2002-09-23
2004-08-03
Cooley, Charles E. (Department: 1723)
Agitating
Stirrer within stationary mixing chamber
Rotatable stirrer
C366S307000
Reexamination Certificate
active
06769800
ABSTRACT:
I. BACKGROUND OF THE INVENTION
A. Field of the Invention
The present invention relates to the field of baffles for use in stirred vessels, such as reaction calorimeters. Specifically, the invention is a set of removable baffles, forming a system, which need not be manufactured with the vessel itself. Due to its construction, the baffle system of this invention is removable and replaceable.
B. Background Discussion
Baffles are well known in the art of fluid mixing and enhance stirred vessel, e.g., stirred tank reactor, performance by preventing segregation of liquid of different densities, retard the formation of vortices which lead to poor mixing, and induce well defined axial flow fields within the vessels to ensure good contacting between liquid phases from the top to the bottom of the vessel and prevent spin-up of the fluid in the vessel, so that there will be a large velocity difference between the impeller tip and a fluid element within the flow field.
Reactors for both laboratories and industry have long been equipped with baffles, designed according to well known arts to effect good mixing. Specifically, it is known that the power to mix (p) is proportional to fluid density (&rgr;), the cube of the impeller rotational speed (N), and the fifth power of the impeller diameter (D), according to the following formula:
&rgr;∝&rgr;N
3
D
5
(I)
Additionally, it is known that power (p) varies proportionally to blade number (B
N
) and blade width (B
W
) in the turbulent regime according to the following formula:
&rgr;∝B
N
B
W
(II)
Baffles are obstructions purposefully placed in the process vessel to redirect flow therein. Baffles, particularly wall baffles, hinder the flow in agitated tanks, to particularly, prevent the fluid from rotating with the impeller. Baffles therefore are generally used to increase the relative velocity between the impeller and the fluid. When the relative difference between impeller speed and baffle speed is maintained high, the result is increased power output, according to Formula I. Accordingly, baffles are used to slow the rotational speed to the fluid without impacting the speed of the impeller. Because the impeller is permitted to rotate unobstructed, and the flow of the fluid is impeded, the rotational speed of the impeller (N) used in Formula I can approximate, if not achieve, its true value. These factors additionally increase and enhance processing capability in the turbulent regime.
Moreover, it is known that baffles prevent the formation of a central vortex which is not effective at mixing. This is due to the fact that when a central vortex is formed, the flow moves in a circular pattern, with little or no axial and/or radial movement, which often leads to separation and classification into small particles. Accordingly, baffles serve as barriers preventing smooth, unobstructed, circular rotation of the fluid in contrast to the movement of the impeller.
Accordingly, stirred vessels, such as reaction calorimeters, have been developed with internal baffles. Specifically, during manufacture, it is possible to form various structures into mixing chamber itself to provide the baffles, as discussed above. However, as many different liquids, having varying densities, are used in the same vessel, and just as many mixing powers are desired with the same vessel, users are forced to acquire varying types of vessels, having different baffle configurations in order to be prepared for the multitude of mixing situations encountered in a typical laboratory or commercial situation.
Although possible, it is not practical to simply insert a set of baffles into a vessel having no baffles manufactured therein. Because many vessels are designed with narrow orifices, only an impeller may be inserted. These vessels are generally designed in a manner, such that they are welded or made with fused glass liners that prevent insertion of rigidly fixed baffles because the rigid baffle system is geometrically too large to pass through the vessel opening or orifice. Therefore, in order to insert a baffle system into an existing vessel, it has been necessary to perform extensive mechanical modifications of expensive vessels that have interior surface finish requirements and jackets for the passage of heat transfer fluids. For example, it is possible to open a sealed vessel, weld or otherwise attached one or more baffle structures to the interior of the opened vessel, and re-seal the vessel. However, the seam created upon re-sealing the vessel may interfere with or otherwise deleteriously effect the internal structure of the vessel. Such seams can provide uneven surfaces or pockets, which prevent complete movement of the fluid. Furthermore, such a procedure requires significant time and expense, and effectively prohibits removal and replacement with a different set of baffles to produce varying turbulent flows.
Therefore, there exists a need in the art for a baffle system which may be added to an existing vessel, without requiring massive mechanical modifications to the vessel structure. Furthermore, the insertable baffle system must fit through the narrow orifice of the vessel which leads to the vessel chamber, without interfering with an impeller or other stirring means.
II. SUMMARY OF THE INVENTION
The invention was developed to solve the problems of the conventional baffle systems. Essentially, the baffle system of the invention includes a pair of rings, attached to a support by a set of linking segments. In order to be easily inserted into a vessel with a narrow orifice, the baffle system has two positions. In the first position, the baffle system is elongated and narrow to pass through the orifice.
Once fully inserted, the baffle system is converted from the first position to a second position. In the second position, the baffle system takes on its operative position, wherein the supports each rest adjacent to the walls of the vessel, and both of the rings are completely inside the chamber.
The present invention, through a unique solution of articulations on baffles, extends the range of many vessels used in the chemical process industry in production facilities, pilot plants and laboratories.
For example, the present invention includes a collapsible baffle system for a stirred vessel having a chamber and an orifice, wherein the orifice is narrower than the chamber, the collapsible baffle system includes a pair of rings; a plurality of supports, connecting the plurality of rings through a plurality of hinged linking segments, wherein at least two, or at least three, sets of at least two, or at least three linked supports are linked in series between the pair of rings. Due to its construction, the baffle system of this invention has a first position, wherein the plurality of linking segments extend axially, with respect to the plurality of rings; and a second position, wherein the plurality of linking segments extend radially with respect to the plurality of rings.
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Biffoni Ulysses John
Cooley Charles E.
The United States of America as represented by the Secretary of
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