Gas levitator having fixed levitation node for containerless processing

A method and apparatus is disclosed for levitating a specimen of material in a containerless environment at a stable nodal position independent of gravity which includes providing an elongated levitation tube 10 having contoured interior in the form of convergent section 12, constriction 15 and divergent section 14 wherein the levitation node 16 is created. Gas flow control means 30, 54 controls flow to prevent separation of flow from the interior walls in the region of specimen 18. Apparatus 64, 66, provides for levitating and heating the specimen 18 simultaneously by combustion of a suitable gas mixture combined with an inert gas 74.

BACKGROUND OF THE INVENTION 
This disclosure describes apparatus for performing containerless material 
processing of both conducting and nonconducting materials on earth and in 
the low gravity of space. The apparatus maintains the material at a fixed 
levitation node, in a stable manner, without physical or electromagnetic 
support, in a gas filled volume. This disclosure describes the method of 
levitating materials by aerodynamic forces created by gas flowing through 
an enclosed volume. The enclosed volume contains a convergent-divergent 
section. The duct cross-section is either circular or rectangular. Spheres 
and right circular cylinders can be levitated by a conduit having circular 
cross-section while cylinders can be levitated in a stable manner by a 
conduit having a rectangular cross-section. 
Heretofore, a column of gas has been utilized to support objects during 
scientific research for example, the growth of a drop of water supported 
by the upward flow of a cloud has been studied in a vertical tapered tube. 
The water drop was held stationary in the tube by varying the upward 
velocity of the air flow until the drag forces on the sphere equalled the 
drop weight. Airplane spin characteristics have been studied using free 
falling scale models in a vertical air column. Very small uranium spheres 
have been levitated in argon/flourine gas, above 1400K, using a vertical 
jet comprised of a central jet tube surrounded by multiple equally spaced 
jets of the same diameter All jets exhausted into a funnel shaped nozzle 
and an electromagnetic field was used to maintain stability. 
These examples of single, vertical jets, become unstable when the jet axis 
is tilted so that the object center of gravity is no longer colinear with 
the jet axis. 
Other attempts to provide containerless processing of materials using air 
jets has included several individual jets placed at equal spherical angles 
impinging on a central material object. 
On earth, metal samples for metallurgical anaylsis are melted without a 
container while suspended and heated by a high frequency electric field. 
This technique is being extended to space processing because it is not 
gravity dependent. 
Apparatus for shaping and enhancing acoustical levitation forces is 
illustrated in U.S. Pat. No. 4,218,921. High power acoustic fields provide 
levitation forces adequate to position small spheres of material in space. 
Interest in acoustic levitation has been stimulated by potential space 
applications but does not have a history of wide usage in earth 
laboratories. 
Acoustic levitation in liquids can be accomplished on earth by establishing 
standing waves in a column of liquid. A droplet of another liquid, 
immiscible in the column liquid will position itself in a stable manner 
near a pressure node, when an acoustic transducer establishes a high 
intensity sound field. However, levitation of fluids in an immiscible 
fluid is not a technique useful in containerless processing. 
The prior art for earth applications, utilizing a single jet, are gravity 
dependent for positioning and are not applicable to low gravity operation. 
This disclosure describes a gas levitator which will support the material 
as the levitator axis is rotated from vertical to horizontal, to inverted, 
to vertical. This levitator can be used on earth at any angle of 
inclination with respect to an earth reference and in space. 
In addition, none of the prior levitation devices have demonstrated the 
capability of containerlessly processing non-conducting material at high 
temperature (i.e., .gtoreq.800.degree. C.). The materials which have been 
successfully processed were conductors only. Electromagnetic coil 
assemblies have been required to provide stable levitation of the melt. 
Accordingly, an important object of the present invention is to provide an 
apparatus for positioning a material specimen in a containerless 
environment for processing on earth and in low gravity environments. 
Another important object of the present invention is to provide a simple 
apparatus for levitating a specimen by means of a gas which will operate 
in any orientation and is not gravity dependent. 
Still another important object of the present invention is to provide a gas 
levitator device which will operate in any orientation and provides a 
stable positioning of the specimen. 
Another important object of the present invention is to provide a gas 
levitator device which will operate over a broad temperature range. 
Another important object of the invention is to provide apparatus for 
levitating a specimen in a gas which will operate for conductors and 
non-conductors as well. 
SUMMARY OF THE INVENTION 
The above objectives are accomplished according to the present invention by 
means of an elongated gas levitator tube having a convergent/divergent 
section wherein the material is levitated at a node in the divergent 
section. The tube may be oriented in any direction and the specimen 
remains stable in its levitated position. Numerous arrangements for 
developing a sufficient gas flow through the tube to levitate the specimen 
are illustrated.

DESCRIPTION OF A PREFERRED EMBODIMENT 
The disclosure relates to an apparatus of performing containerless 
processing of materials on earth and in the low gravity environment of 
space. This disclosure describes apparatus to maintain the position of 
material objects in a gas without support or suspension by electromagnetic 
means. Levitation forces are achieved by gas flowing through a 
convergent-divergent portion of a conduit having circular or rectangular 
cross-section. Objects placed in the downstream (divergent) volume of the 
conduit constriction are positioned centrally in the conduit and at a 
particular levitation point or node on the longitudinal axis of the 
conduit. 
Material processing is accomplished when materials are altered to produce a 
desired, controlled change in its composition, properties, size or shape. 
Basic material processing events include heating-melting, 
mixing-separation and cooling as a continuing fluid or to form a solid. 
Containerless processing requires that between injection, and the storage 
of the processed materials, no solid or liquid will touch the material. 
The system described herein has successfully processed small (up to 5 mm 
dia.) spheres of glasses and metals on earth at temperatures up to 
1200.degree. C. 
The apparatus can position material specimens of useful size and can be 
adapted to a method to inject or add raw material, translate if necessary 
and then eject, capture and store the containerless processed material. In 
the processing of alloys, the method and apparatus include insertion means 
for adding a raw material to the region of the nodal point for combination 
with the specimen. 
Referring now to the drawings, apparatus for levitating a specimen of 
material in a containerless environment is illustrated as including 
elongated tubular means A having a hollow interior defined by interior 
contoured wall means and having inlet and outlet ends. A narrow throat is 
formed in the hollow interior and convergent means within the hollow 
interior is defined by the interior wall means converging to the narrow 
throat. Divergent means within the hollow interior is defined by the 
interior wall means diverging away from the narrow throat toward the 
outlet end. The divergent means creates a levitation node at a point along 
a longitudinal axis of the divergent means at which the specimen is 
levitated. The inlet end of the tubular means is adapted for connection to 
a source of pressurized gas so that a flow is established through the 
divergent means suspending the specimen generally out of contact with the 
interior wall means whereby the specimen may be processed in a 
containerless environment. 
Referring now in more detail to FIG. 1, elongated tubular means A is 
illustrated in the form of gas levitation tube 10 which is circular in 
cross-section having convergent-divergent means in the form of a 
convergent section 12 and a divergent section 14 defined before and after 
a minimum throat constriction diameter 15. The levitation node is in the 
area of the divergent section 14 along its longitudinal axis such as 
illustrated at 16 wherein a spherical specimen 18 is levitated by a gas 
flow entering inlet end 20 of the tube and exiting outlet end 20a which 
may be in the form of an expansion device. Inlet 20 may be adapted by 
means of flexible hosing 20b for connection to a source of gas. 
Any suitable divergent-convergent nozzle design may be utilized in 
accordance with the present invention such as one designed in accordance 
with conventional nozzle theory. 
The interior tube shape between the convergent and divergent areas is 
shaped to provide non-turbulent flow through the upstream, constricted and 
downstream volumes. The interior tube surface must be smooth enough to 
prevent vortices which would cause flow separation from the tube wall. The 
constriction shape should prevent flow separation in the upstream 
(convergent) and downstream (divergent) volumes. Experience has shown that 
satisfactory levitation is achieved with an interior having identical, as 
possible, up and downstream shapes, unlike some venturi tubes. The 
interior volume 22 is filled with a gas such as air or hydrogen. The gas 
flow rate and pressure are regulated to provide the aerodynamic forces 
that position the materials 18 which as placed in the divergent volume. 
FIG. 1 shows a cylindrical shaped material 24 levitated in circular 
cross-section gas levitator A. 
FIG. 2 is a longitudinal cross-section of an arrangement for levitating an 
elongated cylindrical rod 30 in a levitator tube 32 having inlet and 
outlet ends 32a and 32b and an interior duct 32c of rectangular 
cross-section as seen in FIG. 2A. Longitudinally, the interior duct 30a 
resembles that of the cylindrical tube of FIG. 1 as including a convergent 
portion 34 throat constriction 36, and divergent portion 38 in which rod 
30 is levitated at a levitation node by gas flowing therein. The design of 
interior duct 32c may be done with the same criteria as discussed above 
for tube 10. Inlet 32a may include an inlet plenum 37 which may include 
anti-vortex screens 38a carried within a stilling chamber for stabilizing 
the incoming gas flow. Gas deflectors 38b may be utilized to direct gas to 
enhance levitational forces. 
FIG. 3 illustrates, schematically, orientation of the levitator apparatus 
in three different attitudes at earth gravity. A vertical attitude is 
shown at 28a, a horizontal attitude at 28b, and an inverted vertical 
attitude at 28c. The specimen 18 remains stable in all three attitudes as 
being levitated at the nodal point, thus operating of the device 
independent of the force of gravity. 
Referring now to FIG. 4, an enlarged view of the gas levitator tube is 
illustrated wherein a specimen 18 is levitated with the tube A shown in a 
vertical orientation and which includes air flow control means for 
controlling the air flow around a specimen 18 to prevent flow separation 
and provide stability. The means is illustrated as including a tube 39 
through which a suction may be applied to control the air flow in the area 
behind the specimen 18. Alternately, a pressurized flow of gas, such as 
hydrogen, may be introduced in the tube 39 that will cool the specimen 
and/or provide material insertion means by which to distribute material in 
the area of the specimen when it is desirable in the processing of certain 
alloys. For example, tube 39 may be used to transfer powders, or 
granulated material into proximity to specimen 18 where processing of 
alloys or mixtures can be accomplished or multilayers of immiscible 
materials could be formed on an initially levitated fluid sphere. 
FIG. 5 illustrates apparatus utilizing suction to avoid or delay 
separation. The gas levitconcentric housing tube 40 which is positioned to 
enclose the convergent-divergent section and a gas levitator support tube 
14. Housing tube 40 includes an inlet end 42 and an outlet end 44 which 
are closed around tube A to provide a pressure tight sliding seal. A 
suction port 46 is carried by the housing to provide a connection to a 
continuous variable, controllable pressure source (not shown) less than 
the gas pressure in tube A and includes a valve 48 by which the connection 
may be cut off and on. Tube A is cut through at a point downstream of the 
location of levitated material 18 and separated into sections 50 and 52. 
The alignment of the separated sections is maintained by a separation 
control gas nozzle 54 as best seen in FIG. 5 which includes an annular 
passage 56 inclined about 30.degree. to the axis of the tube so that 
entering or leaving gas is deflected along or removed from the volume 
adjacent to tube interior wall. Tube section 50 is sealingly fitted within 
a top portion of valve 54 and section 52 within a bottom portion of valve 
54 as illustrated. Alignment of tube A with the nozzle is accomplished by 
making the mating surfaces 54a and 54b concentric with the counterbore 
which locates them on tube A. Gas flows through the inclined nozzle 
passage through a series of holes 60 concentric with tube A in part 54b. 
In this manner, control of the flow behind specimen 18 is controlled to 
prevent separation of the flow from the tube interior walls and thus 
provide stable levitation. 
The location of control nozzle 54 may be determined by a series of tests 
conducted on the gas levitator tube sized for the particular intended 
application and bench tested to give acceptable stable positioning during 
the processing sequence. Tube A is cut at a point downstream from the 
location of material 18. After assessing the position stability with 
varying suction, a small additional amount of upstream tube A is removed 
and nozzle 54 reinstalled for another test-evaluation of material 
stability. Throttling valve 48 is placed in the exterior suction line to 
adjust/maintain suction during testing and processing. 
FIG. 6 discloses apparatus for heating a material levitated in the gas 
levitator which may include a conventional spark igniter 62 and burner 64 
carried within a housing 66. Levitator tube 10 is carried within port 
opening 68 in a sealed manner. Oxygen is supplied from a source 70 which 
is fed to burner 64 for combustion with the hydrogen supplied from source 
72. A supply of inert gas 74 is illustrated which flows into housing 66 
via inlet port 76 and around the burner 64 and enters the levitator tube 
10. Both the inert gas and the hydrogen-oxygen gas mixture being combusted 
in burner 64 mix and levitate the article. The inert gas provides bulk to 
the levitation gas mixture. After the specimen has reached a desired 
temperature, the burner 64 may be cut off and the inert gas continues to 
levitate and cool the specimen. Nitrogen may be utilized in most cases. 
When processing glass specimens, an inert gas such as oxygen is 
preferable. 
While a preferred embodiment of the invention has been described using 
specific terms, such description is for illustrative purposes only, and it 
is to be understood that changes and variations may be made without 
departing from the spirit or scope of the following claims.