US 3722677 A
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United States Patent 1 Lehnert  DEVICE FOR CAUSING PARTICLES TO MOVE ALONG CURVED PATHS  Inventor: Bo Peter Lehnert, Sommarvagen 1,
8-182 74 Stocksund, Sweden  Filed: June 3, 1971  Appl. No.: 149,732
 Foreign Application Priority Data June 4, 1970 Sweden ..7788/70  U.S. Cl. .209/144, 55/3, 55/100,
209/211, 209/227  Int. Cl ..B04c 3/06  Field of Search ..209/21 1 215, 227,144; 210/222, 223; 55/100, 3
[5 6] References Cited UNITED STATES PATENTS 1,417,189 5/1922 McCarthy ..209/2l5 X I451 Mar. 27, 1973 3,277,631 10/1966 Sunnen ..55/l00 X Primary ExaminerTim R. Miles Assistant ExaminerWilliam Cuchlinski, Jr.
Att0rneyFlynn & Frishauf  ABSTRACT A cylindrical vessel confines a volume therein, the cylindrical vessel being subjected to an axial magnetic field, and a radial electrical field. In order to provide for laminar flow of particles introduced into the vessel and removed therefrom, electrodes establishing the electrical field are formed as rings located at the end surfaces of the cylindrical vessel, and connected to tap points on a voltage divider, to establish an electrical gradient which is substantially parallel to planes passing through the curved paths of movement of the particles.
6 Claims, 1 Drawing Figure DEVICE FOR CAUSING PARTICLES TO MOVE ALONG CURVED PATHS The present invention relates to a device adapted within a confined volume to establish and control movement along curved paths of particles, by example for the purpose of separating those particles from other particles, use being made of a magnetic field and an electric field, the major component of each of said fields being at least substantially perpendicular to each other.
Particles which are present within a confined volume and subjected to the influence of two fields oriented as above will, under that influence, be imparted a movement which is perpendicular to the main direction of the electrical as well as of the magnetic field. By the use of conveniently shaped electrodes defining between themselves the electric field, for example by use of an outer circular electrode which conveniently may also form the outer wall of the confined volume, and an inner centrally located electrode, it is possible to control the movement of the particles in such a way that the corresponding paths will be circumferentially closed and generally circular. Such a device can be looked upon as a centrifuge the radial velocity gradient of the particles being however different from that of the conventional mechanical centrifuge. In a mechanical centrifuging apparatus, the angular velocity of particles at different radial distances is the same. Thus the circumferential velocity increases when the radial distance increases. In contrast thereto, in a device forming the subject of the present invention where the movement of the particles is generated by the influence of electric and magnetic fields the circumferential velocity will remain constant and independent of the radial distance. Stated in other words, this means that those particles which are nearest the center of the device exhibit a very high angular velocity.
In centrifuges it is normal practice continuously to supply particles to be centrifuged and, likewise, continuously to extract separated particles. The corresponding internal particle transport through the centrifuge in combination with the high particle rotation velocities results in soon exceeding the value of Reynolds number, where the laminar flow ceases and is replaced by a turbulent flow pattern. The generation of such a turbulence seriously disturbs the desired radial differences of the locations of the particles as determined by the different mass of the particles. Such disturbances detrimentally affect the overall operation ofthe device.
The object of the invention is to provide a device of such a design that disturbances of the types above referred to are either prevented from arising or so minimized that their negative effect is significantly reduced.
SUBJECT MATTER OF THE INVENTION Electrodes are provided, so located and energized that the gradient of the dominating component of the electrical field is controlled, which component is substantially parallel to curved planes passing through the curved paths of movement of the particles.
In accordance with a concept of the invention the control of the electrical field intensity gradient uses electrodes acting between the common center of rotation of the particles and the outer wall of the confined volume. One feature of the invention which is of special value from structural and operational points of view is that those electrodes may be disposed at the one or both end surfaces of the confined volumes meaning that they do not have to pass axially through the volume.
One embodiment of the invention will now be described in greater detail, reference being made to the accompanying drawing which is an exploded perspective view diagrammatically illustrating the main components of a device adapted to operate as a particle separator.
A cylindrical container confines the volume within which the particle separation is to take place. Container 10 has a lower circular bottom 11 and a top end wall 12. The orifice 13 of a conduit 14 through which the particles to be separated are introduced into the container opens in the center of bottom 11. The separation proper will be described below. At the upper end of the container there are two conduits. The first one is constituted by a pipe 15 connected to the central axis of the container and serving as an outlet for separated light particles whereas the other one, formed by a pipe 16, is connected at the circumference and forms an outlet for heavier particles.
Coils 19, 20 surround a lower and an upper pole face 17, 18 respectively. Direct current is supplied to the coils from external current sources S An axially oriented magnetic field B is generated between pole plates 17 and 18. A plurality of electrodes 21 are concentrically disposed, in relation to the longitudinal central axis of the container, at the bottom 11 of the container. Electrodes 21 are preferably closed in the circumferential direction and each connected to a wire 22 having a slide contact engaging a tap on a voltage divider 23 fed with direct voltage from a source S As is realized, an arrangement as now described will make it possible to let the different annular electrodes 21 assume mutually different electrical potentials.
Operation: Conduit 14 is presumed, via some feeding device such as a pump or the like, to be connected to a vessel containing particles to be separated. The majority of the particles supplied may be electrically neutral but that the total amount of particles must always comprise a certain number of charged particles. The charged particles can be formed by electrical discharge taking place between electrodes 21 inside the container 10. As will appear below, the relative number of charged particles can be low which-is a significant advantage of the invention. Moreover, the total amount of particles may comprise particles of different masses or, stated in other words, the charged particles as well as the neutral ones may comprise relatively light and relatively heavy individual particles.
A positively charged particle inside the container will be subjected to the influence of an electrical field E and a magnetic field B. As is understood, electrical fields will be set up between the annular electrodes and the field intensity lines will pass between those electrodes. This means that in the layer next above bottom 11 those electrical fields will exhibit dominating components which are horizontal and radial. Provided that the potential distribution is generally as has been illustrated on the drawing, i.e. any given electrode has a higher potential than the next adjacent one closer to the central axis of the container, that particle will, under the influence of the just-mentioned electrical field vector, be subjected to a force acting radially inwards. As soon as the particle has started its corresponding inward movement and, in the course thereof, passes across the magnetic field B it will in a manner known per se under the common influence of those two fields assume a resulting average velocity represented by vector V. Due to the circular shape of the electrodes the particle will thus describe a circular path having superimposed on it small radial lateral deflections caused by heat energy movements. Collisions between charged and not charged particles will convey that circular movement to the uncharged particles (the neutral gas) meaning that the crossing magnetic and electric fields and currents will bring all of the gas to rotate around the central longitudinal axis of container 10. As is understood, charged as well as neutral particles of mutually different masses will in response to the corresponding differences in the centrifugal forces acting upon them eventually assume balanced positions at different radial distances from the axis of rotation in the layer close to bottom 11.
The above described rotation of the charged and neutral particles in the bottom layer is propagated upwards throughout all of the confined volume. The physical explanation of that phenomenon is as follows. The particlemixture constitutes an electrically conductive gas which, in the presence of a magnetic filed, has very pronounced direction-dependent properties. In the direction along the magnetic field intensity lines the gas behaves as an electrical conductor of very high specific conductivity. In any direction perpendicular to those field lines the conductivity is likewise great, but only as long as the gas is at rest. As soon as a radial electrical current passes across the magnetic field a rotational movement will be imparted to the gas. This gives rise to a counter-electromotive force, in exactly the same manner as in an ordinary electric motor. As a result thereof the magnetic field intensity lines in the gas may be considered vertical extensions of the electrode rings 21 all the way from the bottom 11 of the container to its top end wall 12. The electrical current density along the field lines will be so high that the rotational movement initiated at the bottom is propagated upwards throughout the entire confined volume until its angular velocity has assumed a substantially constant value along any individual field intensity line. As has been pointed out above, it is a special advantage of the invention that the separation achieved covers neutral particles as well and this so also when the percentage of uncharged particles is low. The reason for this is that rotation of uncharged particles is obtained through collisions between them and the charged ones. Accordingly, the net result will be that charged as well as neutral particles will, along the entire axial extent of the container, be caused to rotate under the influence of forces which, in an initial phase, solely affect charged particles close to the bottom of the container. The neutral particles will naturally during their rotation be affected neither by the magnetic nor by the electrical field. On the other hand, they will be subjected to the centrifugal force C. That force is balanced by a radially inwards acting force, a pressure gradientVP,
the generation of which is due to the fact that the mass density increases with increasing radial distance from the central axis. The higher mass density has two aspects. Firstly, due to the influence of the centrifugal force, the absolute particle concentration will generally tend to be greater in the circumferential regions than at the center. Secondly, the centrifugal force is directly proportional to the particle mass for which reason there will also arise a relative dissimilarity, i.e., the concentration of heavier particles will be greater at greater radial distances.
It should be observed that the effects so far discussed, the separation and the axial propagation of the rotational movement, do not per se call for presence of a plurality of annular electrodes 21. In principle, those effects are attainable by means of a single central electrode and a single outer electrode both disposed at the bottom 11 of the container. In accordance with the invention, presence of the additional electrodes does, however, yield a substantial technical advantage. Potentiometer 22, 23 makes it possible, in response to the actual operational conditions, to adjust and control the potentials of the individual electrodes in such a way that there is created a certain desired radial potential distribution permitting control of the rotational velocities of the particles in different radial layers. As was earlier mentioned one of the major disadvantages of prior art centrifuges of the general type discussed is that, at certain velocity distributions, there will occur turbulence which disturbs all of the flow pattern. In accordance with the present invention the potentiometer and the annular electrodes, permit, in each individual instance to select a velocity distribution which either completely eliminates or strongly reduces such turbulence so that a generally laminar flow pattern can be preserved.
It should be emphasized again that the drawing is diagrammatic and only intended to illustrate the general layout of one practical application of the invention, in a particle separator. The invention may, however, be applied in many other connections, the sole essential condition being that special electrodes are relied upon for control ofthe dominating component of the electrical field thus allowing the control of the velocity distribution above explained. Also as far as the detailed design is concerned many deviations and modifications are possible. By way of example, there is no need for the electrodes to be circular or completely closed in their circumferential direction but, on the other hand, it is obvious that for optimal ease and economy of manufacture, such a configuration is usually used. The electrodes may also be located differently from what has here been shown. Referring directly to the illustrated embodiment it can be said that a second set of annular electrodes may be mounted at the top end wall 12 of the container. In such a case it is possible electrically to connect the electrodes of the lower and upper sets which pairwise correspond to each other, in parallel. The negative terminal of voltage divider 23 is connected to the center of the cylindrical vessel, adjacent orifice 13.
What I claim is:
1. A device to impart movement along curved paths to particles located in a confined volume comprising:
a closed vessel (10, ll, 12) defining therein said confined volume and means providing access to and egress from the confined volumn;
means (17, 19; 18, 20) generating a magnetic field within the vessel;
means (S 21) generating an electrical field within the vessel;
said magnetic field generating means and electrical field generating means being located with respect to each other such that the major components of the magnetic and electrical fields are substantially perpendicular to each other;
wherein the electrical field generating means includes:
a source providing a plurality of tap points (22) to provide electrical potential over an electric gradient;
and a plurality of electrodes (21) located within the vessel and connected to respective tap points and establishing a gradient of the major component of the electrical field in planes substantially parallel to the planes of the paths of the movement of the particles to provide essentially laminar flow during such movement of the particle.
2. A device according to claim 1 wherein the closed vessel (10, 11, 12) is essentially cylindrical;
and said access and egress means comprise means (14) to feed particles into said confined volumn, and means (15,16) to extract particles therefrom;
said extraction means being located at mutually different radial distances from the central axis of the cylindrical vessel.
3. A device according to claim 1 wherein the closed vessel (l0, 11, 12) is essentially cylindrical and has circular end pieces;
and the electrodes comprise a plurality of rings located on at least one of the end pieces and facing the inside of the cylindrical vessel.
4. A device according to claim 3 wherein the electrode rings are closed, concentric rings.
5. A device according to claim 3 wherein the source includes a tapped voltage divider, the rings are concentric, and sequential rings are connected to sequential tap points on the voltage divider to provide said gradient of the electrical field.
6. A device according to claim 1 wherein the mag netic filed extends axially of the cylindrical vessel.