US3399691A

US3399691A - Liquid transfer system

Info

Publication number: US3399691A
Authority: US
Inventors: Karl F Schoch; Andrew I Dahl
Original assignee: General Electric Co
Current assignee: General Electric Co
Priority date: 1966-08-15
Filing date: 1966-08-15
Publication date: 1968-09-03
Anticipated expiration: 1985-09-03

Description

Sept. 3, 1968 K. F. scnocm ET AL 3,399,691

LIQUID TRANSFER SYSTEM 2 Sheets-Sheet 1 Filed Aug. 15, 1966 1771/6272202: Kar/ F S'cboc/7. Andrem/ Sept. 3, 1968 K. F. scuocu ET AL 3,399,691

LIQUID TRANSFER SYSTEM 2 Sheets-Sheet 2 F'iled Aug. 15, 1966 United States Patent O 3,399,691 LIQUID TRANSFER SYSTEM Karl F. Schach, Scotia, and Andrew I. Dahl, Schenectady N.Y. assignors t General Electric Company, a cor poration of New York Filed Aug. 15, 1966, Set. N0. 572,526 14 Claims. (Cl. 137-375) ABSTRACT OF THE DISCLOSURE A liquid helium transfer system includes a liquid helium pump for transferring helium through a cooled flexible transfer line into a receiving vessel. A sensor in the vessel controls operation of the umps so that a constant level of helium is maintained in the receiving vessel even though the helium is pumped at variable flow rates.

Our invention relates to a liquid transfer system and in particular to a system for transferring low temperature liquids to operating apparatus.

The invention described herein was made in the performance of work under a NASA contract and is subjeet to the provisions of Section 305 of the National Aeronautics and Space Act of 1958, Public Law 85-568 (72 Stat. 435; 42 U.S.C. 2457).

In former practice, liquid helium has been transferred from liquefiers to storage Dewars and from storage Dewars to cryostats by batch transfer. In some applications such as in a superconducting gyro, batch transfer is not the most desirable system since the use of batch transfer t0 a cryostat results in large thermal gradients and this may cause difliculties with instrumentation and precise angular alignments of the mechanical structure on which the gyro is mounted. One way of remedying these difliculties is to have a continuous flow at a rate suitable to keep the cryogenic liquid in the cryostat at a substantially constant level. In order to maintain liquid in a cryostat at a substantially constant level, the system must continuously pump cryogenic liquid at a regulated rate into the cryostat.

An object of our invention is to provide a system capable of supplying a cryogenic liquid to a container.

Another object of this invention is a system capable of automatic flow control to maintain constant liquid helium level in a cryostat.

Another object of this invention is to provide a transfer system wherein heat transfer into or out of the system is at a minimum.

Another object of this invention is to provide a cryogenie transfer system wherein part of the transfer line is flexible and a rotary joint is also provided.

In brief, our liquid transfer system transfers small increments of liquid from a first container to another with a minimum loss 0r gain of heat to the liquid being transferred. A tube with a pump on its end is inserted into the liquid and the other end of the tube extends out of the first container and into a flexible section. The flexible section has several layers of nonheat conducting material and a transfer line connected to one of its ends. The transfer line has an inner pipe for carrying the liquid and several thicknesses of cooling and nonheat conducting material. At the other end of the insulating line a rotary coupling is attached to the line. The coupling is fashioned of concentrie pipes for insulation and provides a conduit for the liquid t0 pass into a second container. The second container has sensors to eause the pump in the first container to pump more liquid When the level in the second container decreases below a given level and to slow pumping When the level rises above a predetermined point.

Patented Sept. 3, 1968 Although the embodiment described herein shows our invention as applied t0 a cryogenie liquid being transferred to a cryostat, it is understood that our invention will apply to the transfer of any liquid. For example, our invention may be used t0 maintain the level of hydrogen 01' the like in a liquid propellant missile which is in a state of readiness but for some reason one wishes to hold it on standby for a time.

The novel features which are believed to be characteristic of the invention are set forth in the appended claims. The invention itself, however, together with further objects and advantages thereof may best be understood by 'reference to the following description taken in conjunction with the accompanying drawings in which:

FIGURE 1 shows a schematic arrangement of our liquid transfer apparatus.

FIGURE 2 shows the construction details of a flexible section in the transfer line.

FIGURE 3 shows the construction -details of the rotary joint at the point of attachment to the cryostat.

FIGURE 4 shows the structure of a supercond-ucting pump.

The general arrangement of the elements of the liquid helium transfer system in FIGURE 1 shows liquid helium being transferred from a conventional 50 to liter Dewar container to a cryostat. In this embodiment, a cryostat 1 is mounted on a sidereal test table 0f the type actuated by clock work and designed to turn the table top so that it is oriented in space in a constant position, i.e., as the earth moves the table top turns to compensate for the earths motion and to preserve the osition of the table top in relation to the stars.

Test table 2 is rotated at the earths rotational rate about an axis parallel to the axis of a rotary coupling 3 and a transfer line 4. Rotary coupling 3 of this line permits the cryostat to be turned With0ut interruption to the flow of liquid helium through the transfer line. It is contemplated that the rate of flow of liquid helium from the Dewar supply tank to the cryostat Will be on the order of 1 liter per hour. The line is cooled and shielded with liquid nitrogen to prevent excessive evaporation of liquid helium. When the system operates, liquid helium is in the line at all times. A short section of flexible line 6 is provided to isolate the cryostat from mechanical disturbances which might arise. A superconducting pump 7 located at a low level inside the Dewar flask 5 is electrically operated by 60-cycle current and controlled by two thermistors located in cryostat 1 and responsive t0 the liquid level in the cryostat. One thermistor is located above the desired liquid level and one is immersed in the liquid at the desired liquid level. When the lower thermistor is out of the liquid, a control circuit (not shown) actuates a relay valve so that liquid transfer begins, the rate of transfer decreasing When the high level sensor is covered by the liquid. Thermistors are employed because of their characteristics of high temperature coefiicient, small size and low power dissipation. Valves, inlets and outlets are provided at intervals along the cond-uit to allow passage of liquid nitrogen and evacuation of air. A nitrogen fill tube may be used to introduce liquid nitrogen.

In operation of the pump 7 (FIGURE 4), if the liquid level in the cryostat drops somewhat, the amplitude of 60 cycle current supplied to a superconductive coil 40 is increased. When current asses through the coil, pressure is exerted 0n the superconducting piston 41 and bellows 42 of pump 7 to move it upwardly a few thousandths of an inch at each stroke. The upward motion forces liquid through a pump valve 43 into small tube 8 and out into transfer line 4. When current decreases in the coil, the bellows pushes the piston back toward the coil and the bellows refills through inlet port 44 and valve 45 for an other pump stroke.

The pump pistons motion is of small amplitude and the amount of helium moved per stroke is relatively small. The electrically operated helium pump is of small capacity and pumps by small increments per stroke thus assuring continuous flow. While details of the pump illustrated are described in an article by T. A. Buchhold and B Barrel in Cryogenics, April 1965, page 109, any suitable pump may be used and forms no part of this invention.

The transfer line comprises four concentric tubes (FIGURE 2). The innermost tube 9 is made of a material having a low tliermal coefiicient 013 expansion such as, for example, Invar nickel alloy. A second tube 10 made cf similar material to tube 9 surrounds tube 9 and is spaced therefrom by a spacer made 01 a substance, for example, nylon, having a relatively low heat conductance. A third tube 12 surrounds tube 10 and is spaced therefromby similar low heat conducting elements. Surrounding tube 12 and spaced from it is a fourth tube 13 which forms the outer covering for the transfer line. The outer tube 13 is made of a material having the qualities of low heat conductivity and duxability, such as stainless steel nurnber 347. Tube 13 functions to protect the inner parts of the line and to avoid heat transfer through it.

Tubes

9, 10 and 12 preferably are made of a material having a low therrnal coefficient of expansion. These tubes fluctuate in temperature from ambient temperature when empty to a very low temperature when a liquid like helium is passed through the transfer line.

The spaces beween the first and second tubes 9, 10 and the third and

fourth tubes

12, 13 are evacuated to prevent heat loss by convection of air in the spaces. The space between the second and third tubes is filled with a ther-mal radiation shielding material, such as, for example, liquid nitrogen.

FIGURE 2 shows the construction details of the flexible section 6, the innermost element of which is an elongated bellows 14 made of a resilient material such as bronze which does not become brittle at low temperatures. Bellows 14 acts as a conduit for the liquid helium and is in function an extension of the innermost tube 9 of the transfer line which in turn is an extension of tube 8. Several layers of a reflective sheet material 15 such as aluminized Mylar are wrapped about the bellows With the reflective surfaces outward. A cord 16 made of a nonconducting flexible material, for example, nylon, is loosely spiraled about the reflective sheet material and serves as spacing for a

flexible radiation shield

17, 18

made of flexible, reflective and conductive ribbon material such as copper foil. The shield is made of two er more layers of

ribbon

17, 18, spiraled one over the other in opposing directions to give flexibility and maximum radiation protection. The ends 19 of the ribbon axe wrapped onto one end 01 tube 12 Which contains liquid nitrogen supplied through liquid nitrogen input tube 4' (FIG 1). This connection allows conduction cooling of the sh-

ield

17, 18 along its extent. Outside the shield are layers of a thin sheet nonconductive material having a reflective coating such as aluminized Mylar 15'. Surrounding this is an elongated unter bellows element 20 which extends the entire length of the flexible section.

The liquid nitrogen filled annulus tubes 10 and 12 and the helium tube 9 are made of Invar tubing to minimize contraction due to temperature change. The outer bellows 20 is made of a resilient, durable, nonconductive material like type 321 stainless steel.

The rotary coupling 3 shown in FIGURE 3 provides the attachment between helium transfer line 4 and cryostat 1 (FIGURE l). This coupling allows rotation of the cryostat relative to the helium transfer line 4. Of the six concentric tubes in this coupling, the outer three 21, 22, and 23, form an integral element sealed to the cryostat and the inner three 24, 25, and 26, form a male element 27 which is attached to the transfer line and is insertable into the female element 28 and can be fastened to-it.The

male assembly has a gland nut 33 attached to it for forming a leakproof rotatable connection between the male and female assemblies. Liquid helium asses through the center tube 24 of the male assembly and through a bellows 29 and then into the inner tube 30 attached directly to the cryost'at assembly. Tube 21 is made of a durable, nonheat-conducting material like stainless steel number 347 while the other tubes of the male and female fittings can be made of a material having low thermal coeflficient of expansion such as Invar. Preferably

tubes

22 and 25 are made of a heat conducting material such as copper. In order to keep tube 22 cool, a braided heat conductive element 34 conducts heat from tube 22 to the inner wall 0f cryostat 1. The bellows 29 is attached at one end to the inner of the three inner tubes and has upon its other end a slidable coupling 31 which slides on Coupling element 32 attached to the tube 30 leading into the cryostat. Bellows 29 exerts some pressure upon waferlike member 31 and this member rests on element 32. This connection point is substantially closely sealed. Since the bellows keeps a slight pressure upon the connection point, little or no helium is lost between coupling 31 and element 32. The bellows allows for pressure variations and mobility depending upon conditions 0f transfer. If helium leaks by the sliding surface at 31, 32 it will vaporize and build up pressure tendingto equalize the pressure across the joint.

An advantage of this apparatus is that it provides for the virtually continuous but slow filling of a container to a predetermined level. Rather than batch transfer, euch pumping increment is of small displacement and avoids the temperature pumping gradients and discontinuity inherent in batch transfer of liquid helium.

Another advantage is that it provides for transfer 0f low temperature liquid from one container to another With a minimal of heat gain and minimal loss 0f low temperature liquid.

The foregoing is a description of an illustrative embodiment of the invention, and it is applicants intention in the appended claims to cover all forms which fall within the scope of the invention.

What we claim as new and desire to secure by Letters Patent of the United States is:

l. In a liquid supply system for conducting a liquid from a storage point to a container the combination of:

a liqlid conducting tube having a pump attached to one a flexible insulated section for connecting said tube to an insulated transfer line,

an insulated transfer line connected to said flexible insulated section,

an insulated rotary coupling tubular section connected between said insulated line and a container so as to pass liquid from said line to said container.

2. The liquid supply system of claim 1 in which the conducting tube is made of a material having a low thermal coefficient of expansion.

3. The liquid supply system of claim 1 in which the transfer line comprises a plurality of diflerent sized tubes mounted concentrically.

4. The liquid supply system of claim 1 in which the transfer line comprises:

a first inner tube made of a material having very low thermal expansion properties,

a second larger tube coaxial With said first tube and spaced from said first tube,

a third tube coaxial with said second tube and spaced therefrom, and

a fourth outer tube coaxial with said other tubes,

spaced from said third tube and made 01 a durable material.

5. The liquid supply system of claim 4 with the addition oft means for evacuating the spaces between said first und second tubes and said third and fourth tubes.

6. The liquid supply system of claim 4 with the additiom of:

meams for imtroducimg a shieldimg liquid imto the space betweem the secomd and third tubes.

7. A rotary fittimg for a liquid tramsfer system for transferrimg liquid from storage imto a comtaimer comprisimg:

a male assembly adapted to fit snugly imside a female assembly, said male assembly havimg:

an immer tube,

an imtermediate tube spaced from said immer tube and extemding around said immer tube for about half the lemgth of said male assembly,

an exterior tube spaced from said imtermediate tube and extemdimg the lemgth of said immer tube,

an ammular spacer commectimg the emds of said immer tube and said exterior tube,

a glamd mut slidable 0m said male assembly,

a flexible fittimg adapted to form am extemsiom of said immer tube and fastened to said immer tube at said ammular spacer, said female assembly havimg:

am immer tube 0f a size larger tham the exterior tube of said male assembly and havimg at one emd am ammular elememt (32) which slidably emgages said flexible fittimg of said male assembly and havimg a tube attached to the immer edge of said ammular elememt so that liquid may be passed therethrough,

am imtermediate tube larger tham said immer tube and spaced therefrom with one emd mear the middle of said immer tube, the other emd of said imtermediate tube extemdimg imto said comtaimer,

am exterior tube havimg momheat comductimg spacers betweem it and said imtermediate tube mear said other emd of said imtermediate tube,

a cylimdrical fittimg havimg at one emd a partially threaded outer surface and its other emd fastemed betweem said exterior tube and said immer tube, the threads of said cylimdrical fittimg cooperatimg with said glamd mut to allow a rotatable commectiom betweem said male assembly and said female assembly.

a flexible cord of insulatimg material woumd about said reflective imsulatiom,

a shield made of ribbom and reflective imsulatiom and wrapped about said flexible cord,

am outer bellows surroumding said shield and extendimg the lemgth of said flexible sectiom,

fittimgs to commect said bellows to the rest of a liquid tramsfer section.

10. A flexible seetiom for a liquid tramsfer system as set forth im claim 9 whereim said shield is:

a heat comductive ribbom woumd about said flexible cord im a spiral, and

a secomd heat comductive ribbon woumd im a reverse direetiom about said first ribbom whereby the two ribboms form a flexible shield.

11. Am imsulated transfer lime for tramsfer of liquid comprising:

am immer tube extemdimg the lemgth of said lime and made 0f material havimg a low thermal coefliciemt of expamsion,

a secomd tube surroundimg said immer tube, spaced from said immer tube and made of similar material as said immer tube,

a third tube surroundimg said secomd tube, spaced from said secomd tube and made of a similar material as said other tubes,

a fourth tube surroumdimg said other tubes, spaced from said other tubes and made of a durable material havimg low heat comductivity.

12. Am imsulated tramsfer lime as set forth im claim 11 whereim:

spacers made of nomheat comductimg material are used betweem said tubes to maimtaim said tubes apart. 13. Am imsulated transfer lime as set forth im claim 11 im which:

am evacuation tube is conmected to the spaces betweem the first and secomd tubes and the third and fourth tubes to evacuate said spaces. 14. Am imsulated tramsfer lime as set forth in claim 11 in which:

a filler tube is commected to the spaee betweem the secomd and third tubes to allow the imtroductiom of a shield- HENRY T. KLINKSIEK, Primary Examiner.