US3845639A

US3845639A - Relatively rotatable cryogenic transfer system

Info

Publication number: US3845639A
Application number: US00257640A
Authority: US
Inventors: J Smith; P Thullen
Original assignee: Massachusetts Institute of Technology
Current assignee: Massachusetts Institute of Technology
Priority date: 1972-05-30
Filing date: 1972-05-30
Publication date: 1974-11-05
Anticipated expiration: 1991-11-05
Also published as: CA988983A

Abstract

A relatively rotatable cryogenic transfer apparatus for transferring fluid between two relatively rotatable devices which are rotatable relative to each other at significant speeds; said apparatus including a housing, a first unit fixed to the housing and including a first relatively long, stiff, thin, low thermal conductivity conduit; a second unit including a second relatively long, stiff, thin, low thermal conductivity conduit surrounding and spaced from the first unit to provide a first relatively long, narrow relative motion gap that provides a relatively stagnant environment in which convection currents are minimized and vapor from the fluid acts as an insulator; first means for relatively rotatably interconnecting the housing and the second unit for maintaining the housing and second unit in uniform spaced alignment and having its heat producing relative motion parts disposed in a first ambient temperature portion of the apparatus proximate the area where the first unit is fixed to the housing remote from the supercooled portions of the apparatus; second means for relatively rotatably interconnecting the housing and the second unit disposed in a second ambient temperature portion of the apparatus spaced from the first ambient temperature portion and remote from the cooler portions of the apparatus; first port means in the housing between the first and second ambient temperature portions; the second unit including a third relatively long, stiff, thin, low thermal conductivity conduit surrounding the second conduit, the third conduit being spaced from the housing to provide a second relatively long, narrow relative motion gap extending from the first port means to the first ambient temperature portion and a third relatively long, narrow relative motion gap extending from the first port means to the second ambient temperature portion; each of the second and third relative motion gaps provide a relatively stagnant environment in which convection currents are minimized and vapor from the fluid acts as an insulator; the first sealing means between the housing and the second unit in the first ambient temperature portion sealing the ambient temperature end of the first relative motion gap and of the second relative motion gap; and second sealing means between the housing and the second unit and the second ambient temperature portion for sealing the ambient temperature end of the third relative motion gap.

Description

United States Patent 1191 Smith, Jr. et al.

[451 Nov. 5, 1974 1 RELATIVELY ROTATABLE CRYOGENIC TRANSFER SYSTEM [75] Inventors: Joseph L. Smith, Jr., Concord;

' Philip Thullen, Dover, both of Mass.

[73] Assignee: Massachusetts Institute of Technology, Cambridge, Mass.

[22] Filed: May 30, 1972 [21] Appl. No.: 257,640

[52] U.S. Cl 62/505, 62/55, 310/54,

310/61 [51] Int. Cl. F25!) 31/12 [58] Field of Search 62/55, 505; 310/54, 61

[56] References Cited UNITED STATES PATENTS 12/1971 Lorch 62/505 Primary ExaminerMeyer Perlin Assistant Examiner--Ronald C. Capossela Attorney, Agent, or Firm-Arthur A. Smith, Jr.; Joseph S. landiorio; Robert Shaw [5 7 ABSTRACT currents are minimized and vapor from the fluid acts as an insulator; first means for relatively rotatably interconnecting the housing and the second unit for maintaining the housing and second unit in uniform spaced alignment and having its heat producing relative motion parts disposed in a first ambient temperature portion of the apparatus proximate the area where the first unit is fixed to the housing remote from the supercooled portions of the apparatus; second means for relatively rotatably interconnecting the housing and the second unit disposed in a second ambient temperature portion of the apparatus spaced from the first ambient temperature portion and remote from the cooler portions of the apparatus; first port means in the housing between the first and second ambient temperature portions; the second unit including a third relatively long, stiff, thin, low thermal conductivity conduit surrounding the second conduit, the third conduit being spaced from the housing to provide a second relatively long, narrow relative motion gap extending from the first port means to the first ambient temperature portion and a third relatively long, narrow relative motion gap extending from the first port means to the second ambient temperature portion; each of the second and third relative motion gaps provide a relatively stagnant environment in which convection currents are minimized and vapor from the fluid acts as an insulator; the first sealing means between the housing and the second unit in the first ambient temperature portion sealing the ambient temperature end of the first relative motion gap and of the second relative motion gap; and second sealing means between the housing and the second unit and the second ambient temperature portion for sealing the ambient temperature end of the third relative motion gap.

4 Claims, 4 Drawing Figures PAIENTEmv sum sum 1 4 3.845.639

l RELATIVELY ROTATABLE CRYOGENIC TRANSFER SYSTEM FIELD OF INVENTION This invention relates to an apparatus for transferring cryogenic fluid between a source of the fluid and a device which uses the fluid, and more particularly such a transfer apparatus wherein the source and device are rotatable relative to each other at a significant speed.

BACKGROUND or INVENTION Recently the development of a superconducting alternator was undertaken. In the course of this development it was determined that it was desirable to include in the rotor the superconducting winding which produced the magnetic field. It therefore became necessary to supply the supercooled fluid, typically liquid Helium, to a rotary vessel. Previously, the cryogenic systems were used in stationary environments i.e. the part of the system supplying the coolant and the part to be cooled were not normally rotating or moving relative to each other during operation. In initial attempts to cool the generator rotor, the rotor was immersed in an open top Dewar vessel which was rotated about its central vertical axis but the resulting cooling was extremely inefficient and the heating up of the fluid was more pronounced than expected. This more pronounced effect was discovered to be due to the centrifugal convection currents which drew warm, ambient temperature helium gas down about the stationary pipe which fed the fluid to the Dewar and forced the cooled helium gas against the outer wall of the Dewar and up and over the top of that wall. One attempt to stifle the convection current resulted in a cover being placed in the Dewar at the surface of the liquid but the required mechanical interconnections of the cover produced frictional heat from the contact of the parts which seriously detracted from the cooling efficiency of the system. A further attempt which placed the cover a substantial distance above the surface was similarly unsuccessful because the closed-loop centrifugal convection currents which occurred in the enclosed space also seriously reduced the efficiency of the system. More detailed discussion of these considerations is contained in a thesis, a copy of which is enclosed for deposit in the Patent Office Library, by W. David Lee, entitled Con- Iinuous Transfer of Liquid Helium to a Rotating Dewar,

submitted in partial fulfillment of the requirements for the degrees of Bachelor of Science and Master of Science, Mechanical Engineering Department, Massachusetts Institute of Technology in June, 1970 and deposited in the Institutes library Sept. 10, 1970.

SUMMARY OF INVENTION It is therefore an object of this invention to provide a relatively rotatable transfer system for transferring supercooled fluid between a stationary member and rotating member.

It is a further object of this invention to provide such a transfer system inwhich the seals are located in an area of the system remote from the supercooled fluid. 7

It is a further object of this invention to provide such a transfer system in which the coolant stream is protected by an insulation medium.

It is a further object of this invention to provide such a transfer system in which destructive mechanical vibration and mechanical rubbing between parts in the supercooled area are eliminated.

It is a further object of this invention to provide such a transfer system which is capable of recovering the spent coolant and of transferring the fluid in and out in separate streams at different temperatures.

This invention results from the discovery that despite the many physical limitations on a relatively, rotatable cryogenic transfer system an efficient, even an extremely efficient system, can be constructed by utilizing a long narrow relative motion gap between the rotating parts which suppresses centrifugal convection and permits a relatively stagnant column of vapor to reside there as an insulator. The use of a long narrow relative motion'gap also reduces the convection of heat to the supercooled region by the small centrifugal convection flow; cold gas moves toward the warm region near the outer wall of the relative motion gap and warm gas moves toward the cold end near the inner wall of the relative motion gap. As the gap becomes small these two counter currents come close together and heat may flow readily from the warm to the cold current. Thus the warm gas is precooled by the cold gas before the warm gas reaches the supercooled region thus further reducing the energy carried into the supercooled region. The long length of the gap further enables the necessary contacting parts, producers of frictional heat, to be confined in an area remote from the cooled area. Finally there is the realization, that such a long, narrow gap could be constructed using concentric and relatively rotatable conduits whose length would tend to reduce heat conduction especially if they are made with thin walls and low thermal conductivity material, and which could be designed with sufficient rigidity to be free from vibration at the speed of rotation of the machines to be cooled.

The invention features a relatively rotatable cryogenic transfer apparatus for transferring fluid between two relatively rotatable devices which are rotatable relative to each other at significant speeds. The apparatus includes a housing and a first unit fixed to the housing and including a first relatively long, stiff, thin, low thermal conductivity conduit. There is a second unit including a second relatively long, stiff, thin, low thermal conductivity conduit surrounding and spaced from the first unit to provide a first relatively long, narrow relative motion gap that provides a relatively stagnant environment in which convection currents are minimized and vapor from the fluid acts as an insulator. First means for relatively rotatably interconnecting the housing and second unit for maintaining the housing and in uniform spaced alignment is disposed proximate the area where the first unit is fixed to the housing so that its heat producing relative motion contacting parts are remote from the supercooled portion of the apparatus. Second means for relatively rotatably interconnecting the housing and second unit is disposed in a second ambient temperature portion of the apparatus spaced from the first ambient temperature portion and remote from the cooler portions of the apparatus. First port means are located in the housing between the first and second ambient temperature portions. The second unit includes a third relatively long, stiff, thin, low thermal conductivity conduit surrounding the second conduit. The third conduit is spaced from the housing to provide a second relatively long, narrow, relative motion gap extending from the first port means to the first ambient temperature portion and a third relatively long, narrow relative motion gap extending from the first port means to the second ambient temperature portion. Each of the second and third relative motion gaps provides a relatively stagnant environment in which convection currents are minimized and vapor from the fluid acts as an insulator. There are first sealing means between the housing and the second unit in the first ambient temperature portion for sealing the ambient temperature end of the first relative motion gap and of the second relative motion gap; and there are second sealing means between the housing and second unit in the second ambient temperature end of the third relative motion gap.

DISCLOSURE OF PREFERRED EMBODIMENT Other objects, features and advantages will occur from the following description of a preferred embodiment and the accompanying drawings, in which:

FIG. 1 is a schematic cross-sectional diagram of the coupling portion of a cryogenic transfer system.

FIGS. 2a and 2b taken together form a schematic cross-sectional diagram of a preferred embodiment of a cryogenic transfer system according to this invention with portions of the conduits broken away to show internal structure.

FIG. 3 is a schematic, diagrammatic, axonometric view of a portion of a cryogenic generator which may use the cryogenic transfer system of this invention.

There is shown in FIG. 1 a portion of a cryogenic transfer system 8 including a stationary section 10 and a rotating section 12.

Sections

10 and 12 are relatively rotatably interconnected by an alignment bearing 14 having an outer race 16 carried by stationary section 10 and an inner race 18 carried on sleeve 20 mounted on rotating section 12. Two rows of

ball bearings

22 and 24 are disposed between inner race 18 and outer race 16. Transfer of the supercooled fluid, typically liquid Helium, is accomplished by means of two units relatively rotatable with respect to one another. In FIG. 1 the relative rotation is accomplished by one unit including stationary section 10 and another unit including rotating section 12. The first unit also includes a Helium inlet/outlet tube 30 which is connected at its lower end 32 to a second larger tube 34 which is coaxial with and spaced about tube 30. The volume between outer tube 34 and inner tube 30 constitutes a vacuum conpartment 36 for insulating the inner tube 30 that carries the liquid Helium. In FIG. 1 and the other figures of the drawing wherever tubes are shown their walls are indicated by a single, heavy line, even though the view is actually in cross-section, in order to clarify the drawings and to eliminate confusion which might occur when a great number of parallel lines appear close together in a drawing.

The second unit in addition to section 12 includes a first tube 40 concentric with, surrounding and spaced from tube 34 and a second tube 42 surrounding, spaced from and concentric with tube 40. The space between

tubes

40 and 42 is sealed at the upper end 44 and the lower end, not shown, to form a vacuum compartment 46 which surrounds the liquid Helium as it leaves the lower end of tube 30, arrow 48, and descends in tube 40. The space between

tubes

40 and 34 is the relative motion gap 50.

The upper end of relative motion gap 50 communicates with an annular volume 52 which contains a graphite seal 54 that bears on the hardened Stellite face of seat ring 56, attached to sleeve 20; graphite seal 54 is urged downward in sliding contact with seat ring 56 by means of a spring 58. A second annular seal 60 engages the side of annular, carbon face seal 54 and bears on section 10.

In operation the supercooled fluid e.g. liquid Helium at 4.2K enters through the top of tube 30 and descends downwardly to the end of tube 30 wherefrom it descends farther within tube 40. At this point the cryogenic fluid has been transferred from the fixed to the moving body and may be directed within the moving body to accomplish the cooling as desired, vapor at approximately 4.2K rising from the supercooled fluid moves upward through tube 40 and then through the relative motion gap 50 to fill space 52 where it encounters seals 54 and 60. Ducts or other vent means are provided in the apparatus to be cooled associated with section 10 to remove the Helium gas but neither the vents nor the apparatus is shown. A temperature gradient from 4.2K at the lower end of gap 50 to room temperature at the upper end of gap 50 and in annular volume 52 occurs in the vapor. Thus the sealing apparatus, i.e. seals 54 and 60, since they are located in a room temperature environment remote from the supercooled fluid, are prevented from contributing any substantial amount of their frictional heat to the supercooled fluid. Similarly, the alignment bearing 14 is also located remote from the supercooled fluid area at the room temperature end of the system so that it, too, is prevented from passing any substantial amount of heat to the supercooled fluid. Significantly, the path of the liquid Helium during its entire journey through tube 30 and within tube 40 and beyond is surrounded by one or more vacuum compartments. Initially as it moves through tube 30 to the portion of tube 30 located within section 10 there is provided the vacuum compartment 36. Then slightly below the top section 12 at end 44, the second vacuum compartment 46 envelops

tube

30, 34 and tube 40 so that as the liquid Helium leaves the end 32 of tube 30 jacketed by vacuum compartment 36 it is still surrounded by vacuum compartment 46.

In order to minimize heat transfer by centrifugal convection in the relative motion gap 50, a primary source of heat transfer, the relative motion gap 50 is made as narrow as possible. The heat transfer by centrifugal convection may be expressed as:

where:

q is the heat transfer rate P, is the prandtl number of helium C,, is the specific heat at constant pressure of helium p, is the density at 32 of helium a, is the viscosity at 32 of helium w is the frequency of rotation of the rotating parts T is the temperature at 32 r is the mean radius of the relative motion gap 50 h is the width of the relative motion gap 50 L is the length of tube 34 from section to end 32 and of relative motion gap 50 T is the temperature at 52 For the coupling shown in FIG. 1:

C 5.2 Joules/gram Kelvin p 0.0l67 gram/cubic centimeter p. 12.7 X 10 gram/centimeter second to 377 radians/second T 4.2 Kelvin r 0. 128 inches h 0.0075 inches L 2 inches T 300 Kelvin q 0.07 X 10' watts The

tubes

34 and 40 are at room temperature at end 44 and at 42 K at end 32. Any heat conducted along the metal walls of the tubes adversely affects the thermal insulating properties of the apparatus. Tubes are made as small in thickness and as long as possible consistent with vibrational requirements in order to minimize heat conduction along the tubes. The heat transferred from the warm region 52 to the cold region 32 by conduction is given by:

q FA (AT/l) where q is the heat transfer rate F is the means thermal conductivity between 52 and AT is the difference in temperature between 52 and I is the distance between 52 and 32 A is the cross-section-area for heat conduction between 52 and 32 Th us in FIG. 1:

k 0.25 Watts/inch Kelvin AT 300K I 2 inches A 0.01144 square inch q 0.429 watts Vibrational requirements are important because any substantial vibration of the

tubes

34 and 40 causes them to violate the space of relative motion gap and disturb the relatively stagnant column of Helium vapor which acts as an insulator against heat transfer. In extreme cases tube 34 might be caused to contact tube 40 thereby generating heat, and causing mechanical interference.

Tubes

30 and 34 can execute lateral vibrations as a cantilevered beam. The lowest frequency for free or natural vibrations of a thin walled, cylindrical, cantilevered beam is:

r 0.046 inch 1 2 inches w 910 l/seconds This is sufficiently higher than the typical operating speed of the machine, which is 377 l/seconds thus the machine frequency is always lower than the lowest vibration frequency and a resonant condition is avoided during normal operation. Although all three factors of conduction, vibration and convection are treated, the apparatus is designed most conservatively for centrifugal convection.

Preferably, as is the case in FIG. 1, the inner unit in

cluding tubes

30 and 34 is kept stationary and the outer

unit including tubes

40 and 42 is rotated but this is not a limitation. However, this arrangement is preferred because vortices which adversely affect stability in the vapor columns may be produced when the inner unit is rotated and the outer unit remains stationary. When the outer unit rotates greater stability is possible because centrifugal force generated by the rotation tends to move the gas towards the surface of tube 40. Relative motion gap 50 is maintained as small as possible within the limitations of mechanical alignment in order to minimize centrifugal convection currents in the gap which might adversely affect the insulating temperature gradient capability of the relatively stagnant vapor column in the gap. With

tubes

30 and 34 having O.D.s of 0.065" and 0.120" and wall thicknesses of 0.009 and 0.013", respectively, and

tubes

40 and 42 having O.D.s of 0.250 and 0.165" and wall thicknesses of 0.015" and 0.015", respectively, a gap of0.008 inches for relative motion gap is workable.

A preferred embodiment of a relatively rotatable I transfer system having multiple inlet/outlet connections which may be used in conjunction with a closed refrigeration loop or to maintain more than one stream of supercooled fluid flowing through the system, is shown in FIGS. 2a and 2b. System 70 includes a housing 72 which includes

solid portions

74, 76, 78 typically formed in two parts joined together at

flanges

74, 76, 78' with bolts and suitable sealing means, not shown, and vacuum jackets.

Jacket 80 is formed of an inner tube 84 surrounded by a concentric, spaced outer tube 86 between which the vaccum compartment 88 is formed. Vacuum jacket 80 also includes an inlet/outlet connection 90 which communicates with the interior of the vacuum jacket 80 and includes a tube 92 surrounded by a second tube 94 between which is formed vacuum area 96, an extension of vacuum compartment 88. Similarly vacuum jacket 82 includes an inner cylindrical tube 98 and an outer tube 100 surrounding, concentric with, and spaced from the inner tube 98 to form a vacuum compartment 102 therebetween. Vacuum jacket 82 also includes an inlet/outlet connection 104 which communicates with the interior of the vacuum jacket 82 and includes an inner tube 106 and an outer tube 108 which is concentric with and spaced from the inner tube 106 between which is formed vacuum area 110, an extension of vacuum compartment 102.

Within housing 72 is a first tube 112 through which liquid Helium may be introduced into the system and a second tube 114 concentric with and spaced from tube 112 which is sealingly joined to tube 112 at their lower ends 116. The space between

tubes

112 and 114 functions as a vacuum compartment 118 and tube 114 is typically fixed in aperture 120 of housing 72. Surrounding tube 114 and spaced therefrom by relative motion gap 122 is a tube 124 and surrounding and spaced therefrom, tube 126; the space between

tubes

124 and 126 creates a vacuum compartment 128.

Tubes

124 and 126 are sealingly joined together at the upper end of rotatable section 132 which is fixed to one portion of bearing 134 while the other portion of bearing 134 is fixed to the stationary housing section 74. Annular carbon face seal 136 is kept in sliding contact with a seat ring 138 by springs 140; the seat ring 138 is attached and sealed to section 132. An annular static seal 142 mounted in a groove in seal 136 completes the seal between the rotating section 132 and stationary section 74 of housing 72 so that the volume 144 which communicates with the relative motion gap 122 is sealed from the volume 146; volume 146 is between the

seals

136 and 142 and bearing 134 is at room temperature.

There is an inner tube 150 spaced from, surrounding,

and concentric with

tubes

124 and 126 and an outer tube 152 surrounding, spaced from and concentric with tube 150; the space between

tubes

150 and 152 creates a vacuum compartment 154 which is sealed at the upper end where

tubes

150 and 152 are joined to tube 126 at junction 156. A low thermal conductivity support spacer 158 may be used in fluid space 153 to maintain more rigid alignment between tube 126 and tube 150; low thermal conductivity spacers such as spacers 125 may also be used in the various vacuum compartments. Tube 126' is effectively a continuation of tube 126 insofar as the cryogenic system is concerned even though, physically, tube 126 is a separate tube interconnected with tube 126 by junction 156. Ports 157 in junction 156 permit fluid in space 153 to enter annular channel 159 in collar 161 having a port 163 to which tube 92 is mounted; annular channel 159 also communicates with relative motion gap 164.

Rotating section 160 is fastened to outer tube 152 which is fixed tolone portion of alignment bearing 162 the other portion of which is fixed to stationary section 76 of housing 72. The space between outer tube 152 and the vacuum jacket 80 and section 76 of housing 72 forms a relative motion gap 164. Relative motion gap 164 extends around tube 152 from volume 166 above junction 156 to volume 168 between tube 152 and vacuum jacket 80. Volume 166 communicates with volume 146 since bearing 134 is not gas tight. Volume 168 is sealed by annular carbon face seal 170 which is held in sliding engagement with a seat ring 172, attached to rotating section 160 fixed to outer tube 152, by springs 174 and by an annular static seal 176 mounted in an annular groove in seal 170 and bearing on the inner surface of section 76.

Inner tube 180 and outer tube 188 are surrounding and spaced from tube 152 to form space 187 and are spaced from each other to form vacuum compartment 190 between them.

Tubes

180 and 188 may be joined to seal the upper end of space 190 and may be fixed to tube 152 at junction 192. The space to the right of bearing 203, between outer tube 188, and vacuum jacket 82 and fixed section 78 of housing 72 forms a relative motion gap 194 which communicates with volume 196 and volume 198 which is sealed by means of an annular carbon face seal 200 which is held in sliding contact with the seat ring 202, attached and sealed to generator shaft 204 by springs 206 and by means of an annular static seal 208 mounted in a groove in seal 200;

generator shaft 204 is fixed to outer tube 188. Ports 193 in junction 192 permit fluid in space 187 to enter annular channel 189 in collar 19] having port 195 to which tube 106 is mounted. Annular channel 189 also communicates with relative motion gap 194. A spacer 158 similar to spacer 158 may be used in space 187. The transfer system shown in FIG. 2 may be extended to any additional number of sections by adding on units in a manner similar to that described.

Typical dimensions for the parts and structure of FIGS. 2a and 2b are listed as follows: tube 112 has a Vs outer diameter and a wall thickness of 0.02l vacuum compartment 118 has a width of 0.01625; tube 114 has an outer diameter of 3/16 of an inch and a wall thickness of 0.015" and a length of 3%"; relative motion gap 122 has a width of 0.0125"; tube 124 has an outer diameter of 4 of an inch and a wall thickness of 0.020; tube 126 has an outer diameter of l3/ l6 of an inch and a wall thickness of 0.028; tube 152 has an outer diameter of 13/ l 6 of an inch and a wall thickness of 0.028"; relative motion gap 164 has a width of 0.01125"; tube 84 has an outer diameter of /3 of an inch and a wall thickness of 0.020"; the distance from bearing 134 to bearing 162 is 13 inches; tube 188 has an outer diameter of 1%" and a wall thickness of 0.028"; relative motion gap 194 has a width of 0.01125; tube 182 has an outer diameter of 1 9/16 and a wall thickness of 0.020"; tube 98 has an outer diameter of 1 9/16 and a wall thickness of 0.020"; and the distance from bearing 162 to bearing 203 is 13 inches.

In operation the supercooled fluid, such as liquid Helium, may be introduced through and recovered from any one of the three inlet/

outlet tubes

112, 92 and 106. Further,

tubes

112, 92 and 106 may be used to transfer more than one fluid into or out of the rotor or the same fluid in separate streams in or out of the rotor. For example. liquid Helium may be introduced through tube 112; as it descends it clears the end 116 of tube 112 and continues downwardly within tube 124 to the area where it is to be utilized. The liquid Helium in the collection area is at approximately 4.2K. The vapor at 4.2K rises to fill the various relative motion gaps in the system to provide various temperature gradients in the range from 4.2K to room temperature. Thus vapor rising with tube 124 rises to the end 116 of tube 112 and then moves upwardly in the relative motion gap 122 and fills volume 144.

Seals

136 and 142 are at approximately room temperature. Similarly vapor moves upwardly in space 153 and is moved out by centrifugal force through a number of ports 157 in junction 156 to fill relative motion gap 164 and

volumes

166 and 168 and to leave the system through tube 92 for recovery.

Similarly vapor rising in space 187 is moved outwardly through ports 193 in junction 192 to fill relative motion gap 194 and

volumes

196 and 198 and enter tube 106 for recovery. Typically, with liquid Helium at 4.2K supplied through tube 112, Helium gas at to 200K is recovered from connection 104 and Helium vapor at 20K is recovered from connection 92.

In certain areas of the device illustrated in FIGS. 1 and 2a and 2b compensating bellows may be used to accommodate the shrinkage of the inner tube of the double walled transfer tube when it is subject to the supercooled temperature at the level of liquid Helium or another supercooled fluid. Without such accommodation,

especially in the longer transfer tubes the thermal contraction of the inner tube would stress the smaller tube beyond its yield point. Such compensating bellows 250 are shown in FIG. 1. Bellows 250 is formed of a number of e.g. six stainless steel disks with holes in the center and which are welded to adjacent disks at their inner and outer perimeters; the end disks are welded to the corresponding portions of outer tube 34. Thus when liquid Helium at approximately 4.2K is present within tube 30 and that tube begins to contract, outer tube 34 which at its upper end proximate volume 52 is at approximately room temperature, will be able to effectively contract also by means of thecompression of bellows 250. Bellows may be included at various points in system 70 such as, for example, bellows 250', FIG. 2a, attached to tube 86 and bellows 250", FIG. 2b, attached to tube 100.

The transfer system of this invention as illustrated in FIGS. 1 and 2a and 2b may be used to cool the superconducting field windings in the rotor of a superconducting generator 219 as shown in FIG. 3. In FIG. 3 transfer system 70 serviced by a refrigeration unit 220 functions to cool the superconducting field winding 222 mounted on rotor 224 which is driven through drive shaft 226 to rotate within armature winding 228. Transfer system 70 includes an inlet tube 112 surrounded by tube 113, an outlet 90 including tube 92 surrounded by tube 94, and outlet 104 including tube 106 surrounded by tube 108. Tube 188 is fixed to section 204 of rotor 224 and tube 188 and

other tubes

150 and 152, and 124 and 126' are brought into the cooling area 240 within rotor 224 where they are connected to internal piping which effects the cooling of the superconducting winding 222 and the mechanical support portions at either end of rotor 224. Generator 219 also includes an image shield 244, removable from shield 246, end flange 248 and many more parts which have been omitted for clarity as generator 219 forms no part of this invention but is included only to show one typical application ofthe cryogenic transfer device.

In FIGS. 2a and 2b the liquid Helium stream is always surrounded by a vacuum insulation space or compartment as the Helium moves through the system by virture of the fact that each of the overlapping sections includes in it a vacuum space or compartment. All mechanical rubbing, contact, sealing devices and alignment bearings are positioned at the room temperature portions of the system so that none of the frictional heat generated thereby will be dissipated in the supercooled portions of the system. All tubes are made of thin wall low conductivity material and are as long as possible consonant with vibrational considerations. Further the relative motion gaps are as long and narrow as possible consonant with mechanical and vibrational considerations. There is thus provided an extremely efficient and workable transfer system which provides great flexibility in controlling the flow of the cryogenic fluid and the temperature gradients maintained thereby.

Other embodiments will occur to those skilled in the art and are within the following claims:

What is claimed is:

.1. A relatively rotatable cryogenic transfer apparatus for transferring fluid between two relatively rotatable devices which are rotatable relative to each other at significant speeds said apparatus comprising:

a housing;

a first unit fixed to said housing and including a first relatively long, stiff, thin, low thermal conductivity conduit and a second relatively long, stiff, thin, low

thermal conductivity conduit spaced from and surrounding said first conduit to form a vacuum insulating space therebetween;

second unit including a third relatively long, stiff,

thin, low thermal conductivity conduit surrounding and spaced from said first unit to provide a first relatively long, narrow relative motion gap that provides a relatively stagnant environment in which convection currents are minimized and vapor from the fluid acts as an insulator, said second unit further including a fourth relatively long, stiff, thin,

low thermal conductivity conduit surrounding and spaced from said third conduit to provide a vacuum insulating space therebetween;

first means for relatively rotatably interconnecting said housing and said second unit for maintaining said housing and second unit in uniform spaced alignment and having its heat-producing relative motion contacting parts disposed in a first ambient temperature portion of said apparatus proximate the area where said first unit is fixed to said housing remote from the supercooled portions of the apparatus, including an alignment bearing with two relatively rotatable parts one fastened to said housing the other to said second unit;

second means for relatively rotatably interconnecting said housing and said second unit disposed in a second ambient temperature portion of said apparatus spaced from said first ambient temperature portion and remote from the cooler portions of said apparatus, including an alignment bearing with two relatively rotatable parts one fastened to said housing the other to said second unit;

first port means in said housing between said first and second ambient temperature portions;

said fourth conduit being spaced from'said housing to provide a second relatively long, narrow, relative motion gap extending from said first port means to said first ambient temperature portion and a third relatively long, narrow, relative motion gap extending from said first port means to said second ambient temperature portion. each of said second and third relative motion gaps providing a relatively stagnant environment in which convection currents are minimized and vapor from the fluid acts as an insulator;

first sealing means between said housing and second unit in said first ambient temperature portion for sealing the ambient temperature end of said first relative motion gap and of said second relative motion gap including a first sliding seal engaging one of said housing and said second unit and a second seal engaging the first seal and the other of said housing and said second unit; and

second sealing means between said housing and said second unit in said second ambient temperature portion for sealing the ambient temperature end of said third relative motion gap, including a first sliding seal engaging one of said housing and said second unit and a second seal engaging the first seal and the other of said housing and said second unit.

2. The apparatus of claim 1 further including a third unit fixed to said second unit and including a fifth relatively long, stiff, thin, low thermal conductivity conduit surrounding and spaced from said fourth conduit and forming a vacuum insulated space therebetween;

third means for relatively rotatably interconnecting said housing and said third unit in a third ambient temperature portion of said apparatus spaced from said second ambient temperature portion and fan ther spaced from said first ambient temperature portion and remote from the cooler portions of said apparatus, including an alignment bearing with two relatively rotatable parts one fastened to said housing the other to said third unit;

second port means in said housing between said second and third ambient temperature portions;

said fifth conduit being spaced from said housing to provide a fourth relatively, long, narrow, relative motion gap extending from said second port means to said second ambient temperature portion and a fifth relatively long, narrow, relative motion gap extending from said second port means to said third ambient temperature portion, each of said fourth and fifth relative motion gaps providing a relatively stagnant environment in which convection currents are minimized and vapor from the fluid acts as an insulator;

third sealing means between said housing and third unit in said third ambient temperature portion for sealing the ambient end of said fifth relative motion gap, the ambient temperature end of said fourth relative motion gap being sealed by said second sealing means, including a first sliding seal engaging one of said housing and said third unit and a second seal engaging the first seal and the other of said housing and said third unit.

3. The apparatus of claim 1 further including third port means in said fourth conduit and cooperating with said first port means in said housing, and a first chamber between said third and fourth conduits extending from the supercooled portions of said apparatus to said third port means, for transporting fluid from the supercooled portion to said second and third relative motion gaps and said first port means.

4. The apparatus of claim 1 further including fourth port means in said fifth conduit cooperating with said second port means in said housing, and a second chamber between said fifth and fourth conduits extending from the supercooled portion of said apparatus to said cooled portion to said fourth and fifth relative motion gaps and said second port means.

Claims

1. A relatively rotatable cryogenic transfer apparatus for transferring fluid between two relatively rotatable devices which are rotatable relative to each other at significant speeds said apparatus comprising: a housing; a first unit fixed to said housing and including a first relatively long, stiff, thin, low thermal conductivity conduit and a second relatively long, stiff, thin, low thermal conductivity conduit spaced from and surrounding said first conduit to form a vacuum insulating space therebetween; a second unit including a third relatively long, stiff, thin, low thermal conductivity conduit surrounding and spaced from said first unit to provide a first relatively long, narrow relative motion gap that provides a relatively stagnant environment in which convection currents are minimized and vapor from the fluid acts as an insulator, said second unit further including a fourth relatively long, stiff, thin, low thermal conductivity conduit surrounding and spaced from said third conduit to provide a vacuum insulating space therebetween; first means for relatively rotatably interconnecting said housing and said second unit for maintaining said housing and second unit in uniform spaced alignment and having its heatproducing relative motion contacting parts disposed in a first ambient temperature portion of said apparatus proximate the area where said first unit is fixed to said housing remote from the supercooled portions of the apparatus, including an alignment bearing with two relatively rotatable parts one fastened to said housing the other to said second unit; second means for relatively rotatably interconnecting said housing and said second unit disposed in a second ambient temperature portion of said apparatus spaced from said first ambient temperature portion and remote from the cooler portions of said apparatus, including an alignment bearing with two relatively rotatable parts one fastened to said housing the other to said second unit; first port means in said housing between said first and second ambient temperature portions; said fourth conduit being spaced from said housing to provide a second relatively long, narrow, relative motion gap extending from said first port means to said first ambient temperature portion and a third relatively long, narrow, relative motion gap extending from said first port means to said second ambient temperature portion, each of said second and third relative motion gaps providing a relatively stagnant environment in wHich convection currents are minimized and vapor from the fluid acts as an insulator; first sealing means between said housing and second unit in said first ambient temperature portion for sealing the ambient temperature end of said first relative motion gap and of said second relative motion gap including a first sliding seal engaging one of said housing and said second unit and a second seal engaging the first seal and the other of said housing and said second unit; and second sealing means between said housing and said second unit in said second ambient temperature portion for sealing the ambient temperature end of said third relative motion gap, including a first sliding seal engaging one of said housing and said second unit and a second seal engaging the first seal and the other of said housing and said second unit.

2. The apparatus of claim 1 further including a third unit fixed to said second unit and including a fifth relatively long, stiff, thin, low thermal conductivity conduit surrounding and spaced from said fourth conduit and forming a vacuum insulated space therebetween; third means for relatively rotatably interconnecting said housing and said third unit in a third ambient temperature portion of said apparatus spaced from said second ambient temperature portion and farther spaced from said first ambient temperature portion and remote from the cooler portions of said apparatus, including an alignment bearing with two relatively rotatable parts one fastened to said housing the other to said third unit; second port means in said housing between said second and third ambient temperature portions; said fifth conduit being spaced from said housing to provide a fourth relatively, long, narrow, relative motion gap extending from said second port means to said second ambient temperature portion and a fifth relatively long, narrow, relative motion gap extending from said second port means to said third ambient temperature portion, each of said fourth and fifth relative motion gaps providing a relatively stagnant environment in which convection currents are minimized and vapor from the fluid acts as an insulator; third sealing means between said housing and third unit in said third ambient temperature portion for sealing the ambient end of said fifth relative motion gap, the ambient temperature end of said fourth relative motion gap being sealed by said second sealing means, including a first sliding seal engaging one of said housing and said third unit and a second seal engaging the first seal and the other of said housing and said third unit.

4. The apparatus of claim 1 further including fourth port means in said fifth conduit cooperating with said second port means in said housing, and a second chamber between said fifth and fourth conduits extending from the supercooled portion of said apparatus to said fourth port means for transporting fluid from the supercooled portion to said fourth and fifth relative motion gaps and said second port means.