Fluid sprinkling – spraying – and diffusing – Processes – Including centrifugal force or spattering
Reexamination Certificate
2001-03-26
2003-07-01
Mar, Michael (Department: 3752)
Fluid sprinkling, spraying, and diffusing
Processes
Including centrifugal force or spattering
C239S224000, C239S222130, C239S217000, C239S383000
Reexamination Certificate
active
06585169
ABSTRACT:
TECHNICAL FIELD AND BACKGROUND
The present invention relates to an apparatus and a method for the formation of droplets from a liquid. The apparatus is of the type comprising a feeder, a distributor rotating about an axis at a first angular velocity, and a slinger rotating about the axis at a second angular velocity different from the first angular velocity. At least part of the slinger is radially outside the distributing distributor. The slinger has peripheral droplet-forming cusps on at least two axial levels. The feeder transfers liquid to the distributor which, by its rotation in the circumferential direction distributes the liquid to the levels of the slinger. The slinger, due to its rotation, transfers the liquid to the peripheral droplet-forming cusps, from which the liquid is slung outwardly in the form of droplets.
Such an apparatus is known from U.S. Pat. No. 4,978,069.
The apparatuses disclosed in that patent involve rotating the distributor and the slinger at respective absolute angular velocities which differ from each other in order to provide a relative rotation between the distributor and the slinger. The absolute rotation of the distributor results in the liquid being slung from the distributor towards the slinger. The absolute rotation of the slinger results in each liquid-receiving point of the slinger repeatedly assuming all positions in the circumferential direction. The relative rotation between the slinger and the distributor results in each liquid-receiving point of the slinger receiving liquid from the entire periphery of the distributor. Thus, the liquid from the distributor is distributed uniformly in the circumferential direction on the slinger, whereby droplets of equal size can be formed at the droplet-forming cusps of the slinger.
The above-described prior art is used to form substantially spherical droplets from a liquid. Droplets are slung from the peripheral cusps in a tangentially forward direction in relation to the direction of rotation of the slinger, when the centrifugal force acting on the liquid exceeds the force of adhesion at each cusp. As seen in the direction of the axis of rotation, successively slung droplets will follow diverging paths in a chamber surrounding the apparatus. As the paths are divergent, the droplets are prevented from colliding with each other.
The chamber can be heated so that the slung droplets will dry and form solid particles. Alternatively, if the liquid comprises a melt, then the chamber is preferably cooled, whereby the droplets solidify and form solid particles.
In one embodiment of the apparatus disclosed in connection with FIGS. 1-3 of the above-mentioned U.S. Pat. No. 4,978,069, the distributor comprises a hollow cylinder. The wall of the cylinder has a plurality of radial side openings which are uniformly distributed in the axial and circumferential directions. The cylinder rotates in such manner that the liquid transferred thereto forms a film on the inner wall of the cylinder and is subsequently pressed out of the side openings to be slung onto the slinger.
The slinger comprises a plurality of axially distributed slinger rotors, the number of which corresponds to the number of axially arranged side openings of the distributor and which rotate in unison at an angular velocity different from the angular velocity of the distributor. As a result, a uniform circumferential distribution of the liquid onto the slinger rotors is ensured.
If the side openings of the distributor cylinder are of equal size, the liquid passes therethrough at the same pressure drop. As a result, the same amount of liquid passes through each one of the side openings, and is uniformly divided among the respective slinger rotors.
However, this embodiment of U.S. Pat. 4,978,069 suffers from a number of drawbacks. Firstly, if the liquid tends to form surface coatings, then the side openings of the distributor can become partially clogged. This means that variations may occur in the diameters of the side openings, and the distribution accuracy is lost.
Secondly, an increase or decrease of the total flow in the apparatus, even while the diameters of the side openings remain unchanged, results in an increase or a decrease of the pressure drop. As a result, the total flow, and thus the production volume, can be varied within a narrow range only. For instance, if the total flow is so small as to be insufficient to fill the side openings, the pressure drop disappears, and consequently the distribution accuracy is lost.
In a second embodiment of the apparatus described in connection with FIGS. 4-5 of U.S. Pat. No. 4,978,069, those problems are solved. That embodiment also has a distributor in the form of a rotating hollow cylinder but has a conical inner wall whose narrow end faces the feeder. At this narrow end, a receiving space is defined within the cylinder, the liquid being transferred from the feeding means to said receiving space. A plurality of parallel grooves are formed in an interior wall of the cylinder. The grooves are peripherally uniformly distributed and parallel to the longitudinal direction of the cylinder. Each groove communicates at one end with the receiving space and at the other end with a radial side opening in the cylinder wall. The side openings are uniformly distributed both in the circumferential direction and the axial direction. The slinger comprises a plurality of slinger rotors, which are arranged outside of and concentrically with the distributor. The number of slinger rotors corresponds to the number of axially spaced annular rows of side openings in distribution, the slinger rotors being arranged on the same level as the respective rows of side openings.
The liquid is transferred from the feeder to the receiving space in the distributor, which by its rotation transfers the liquid to the respective grooves of the distribution, which in turn pass the liquid to respective side openings of the distributor. The liquid passes through the side openings without filling them and is then distributed on the slinger rotors in the above-described manner.
Since the side openings in the cylinder are not filled with liquid, this apparatus is not dependent on a pressure drop to distribute the liquid on the slinger rotors, which makes it possible to use a wider production range. Coatings which may be formed by the liquid in the side openings will not throttle the flow through the side openings, since the latter are not filled with the liquid. The negative effects of coatings are thus eliminated.
A disadvantage of this apparatus is, however, that the division of the liquid among the different grooves takes place in an uncontrolled manner. Since the grooves are uniformly distributed in the circumferential direction, an approximately uniform division of liquid is achieved. In spite of this, variations may occur in the division of the liquid, so that some grooves receive a greater amount of liquid than the other grooves. Therefore, some slinger rotors may accidentally receive a greater amount of liquid than other slinger rotors and thus form larger droplets.
Thus, it would be desirable to control in a more reliable way the division of liquid among the different axial levels of the slinger.
A disadvantage which is found in both of the above referenced apparatuses is that problems arise if the apparatus has too great of an axial dimension. This happens if too high a production capacity is desired and use is made of a great number of slinger rotors. The problem is due to the fact that the entire slinger can only be mounted at one of its ends. The reason for this is that the distributor means and the slinger means are normally rotated by means of two respective drive shafts, one of which is arranged within the other. The outer drive shaft operates the distributor means and the inner drive shaft operates the slinger. The feeder is arranged axially above and in direct connection with the distributor, and the slinger is arranged around the distributor. The slinger can thus be connected to the inner drive shaft only in the area below
Burns Doane , Swecker, Mathis LLP
Mar Michael
Nguyen Dinh Q.
Sandvik AB
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