US3713305A

US3713305A - DEVICE FOR PRODUCING COLD AT TEMPERATURE LOWER THAN THAT OF lambda -POINT OF HELIUM

Info

Publication number: US3713305A
Application number: US00885542A
Authority: US
Inventors: F Staas; A Severijns
Original assignee: US Philips Corp
Current assignee: US Philips Corp
Priority date: 1968-06-05
Filing date: 1969-12-16
Publication date: 1973-01-30
Anticipated expiration: 1990-01-30
Also published as: NL6807903A

Abstract

A device for cooling to temperatures lower than that of the lambda -point of helium, in which some high-pressure helium, after being cooled, expands to low-pressure and flows back to the compression device, and the remainder of the He is cooled to below its lambda -temperature forming superfluid He4 that flows through a superleak, and normal He4, and a vortex tube for communicating.

Description

United States Patent 1 I11 3,713,305 Staas et al. [4 1 Jan. 30, 1973 U4] DEVICE FOR PRODUCING COLD AT 3,427,817 2/l969 Rietdijk ..62/so0 TEMPERATURE LOWER THAN THAT 3,447,339 6/1969 Rietdikj OF A-POINT 0E HELIUM 3,464,230 9/1969 Rietdijk .;....62/5l4 [75] Inventors: Frans Adrianus Staas; Adrianus Petrus Severijns, both of Emmasinprimary Examine, Meyer m, gel, Eindhoven, Netherlands Aomey Frank Trifari [73] Assignee: U.S. Philips Corporation, New

York, N.Y. 221 Filed: Dec. 16, 1969 [57] ABSTRACT A device for coolin to tern eratures lower than that l 8 42 8 P [2 1 App] No of the A-point of helium, in which some high-pressure helium, after being cooled, expands to low-pressure [52] :J.S.C|l "62/5292, 62/1514 and flows back to the compression device and the remainder of the- He is cooled to below its A-temperae 0 ea c ture forming superfluid He that flows through a su- [56] Reerences Cited perleak, and normal He, and a vortex tube for communlcatmg.

UNITED STATES PATENTS V M is H .6 3,360,955 l/l968 Witter ..62/5 l4 15 Claims, 4 Drawing Figures mm 30 m;

SHEETIOFZ 'FRANS ANT mm m 3.713.305

, sum 2 0r 2 'INVENTORS FRANS A. sTAAs ADRIANUS P. savsmms MKW DEVICE FOR PRODUCING COLD AT TEMPERATURE LOWER THAN TI-IAT OF k-POINT OF IIELIUM BACKGROUND OF THE INVENTION The invention relates to a device for producing cold at temperatures lower than that of the A -point of helium. The device comprises a source for high pressure helium which communicates with a supply system including a pre-cooler a counter-current heat exchanger in which the high-pressure helium is cooled to below its inversion temperature associated with said pressure, and a throttle device in which the high-pressure helium expands; the expanded helium then flows via an outlet system and the said counter-current heat exchanger, to a suction place for low-pressure helium.

Devices of the above-mentioned type are known as Joule-Thompson cooling systems. In these devices, high-pressure helium is cooled by pre-coolers and in counter-current heat exchangers to below the inversion temperature associated with the said pressure, and is then expanded in a throttle valve, in which a temperature decrease occurs. The expanded helium is then returned, via the said counter-current heat exchangers, to a compression plant. The temperature at which the cold is produced depends upon the pressure which prevails after the throttle valve. In order to reach very low temperatures it is necessary to expand to very low pressures. A pressure of 1 atm. after the throttle valve is necessary for reaching a temperature of 4.2K; for 3.6"K a pressure of k atmosphere after the throttle valve is required, while for reaching a temperature of 1.9K a pressure of 17 mm Hg after the throttle valve is required. For reaching even lower temperatures, even much lower pressures after the throttle valve are necessary. For reaching said extremely low pressures after the throttle valve, it is necessary for the compressor to have a suction pressure which, as a result of the resistance to flow in the counter-current heat exchangers, will have to be even lower, which means that the compressors become extremely bulky. In practice it is therefore substantially impossible to produce cold at temperatures lower than l.9K.

SUMMARY OF THE NEW INVENTION municates on its one side, via one or more heat exchangers in which the helium cools to below the )t-t'emperature of helium and at least one controllable throttle valve, with a first place of the system of supply or outlet ducts, and communicates on its other side with a cold space, said space further communicating, via a vortex tube, with a second place of the device, where a lower pressure prevails than at the said first place. A superleak should be understood to mean within the scope of the present invention, a mass of a material having the property that normal helium cannot pass said mass, and superfluid helium can pass said mass without moving vortices occurring during the flow.

A vortex tube is to be understood to mean within the scope of the present invention, a duct having dimensions such that, in the prevailing operating conditions, moving vortices occur in the superfluid when liquid helium flows through said duct.

By communicating the superl'eak with the system at a place of higher pressure and communicating the vortex tube with a place of a lower pressure, a differential pressure occurs across the series arrangement of superleak, cold store and vortex tube. In the first instance the overall differential pressure will occur across the vortex tube, because no temperature difference prevails across the superleak yet, and consequently no differential pressure either. Due to this differential pres-v sure across the vortex tube, medium therein will start flowing to the second place, the superfluid helium exceeding its critical velocity, and vortices occurring, as a result of which normal helium is also transported to the second place. This means a thermal transport from the cold store to the said second place, so that the temperature in the cold store will decrease and a temperature difference will occur across the superleak. This temperature difference corresponds to a differential pressure adjusting across the superleak. An equilibrium condition will be adjusted in which the overall differential pressure is distributed between the superleak and the vortex tube. So in this manner it is reached that without any extra precautions of the Joule-Kelvin cooling system, cold is nevertheless supplied at a temperature which is lower than corresponds to the pressure which prevails after the throttle device; The device according to the invention enables the production of cold at temperatures which are lK or lower, without it being necessary for the compressors of the Joule-Kelvin system to be excessively large.

In order to obtain a suitable differential pressure across the series arrangement of superleak, cold space andvortex tube, in a favorable embodiment of the device according to the invention at least one of the said throttle devices is arranged between the said first and the said second place. This means that the differential pressure which prevails across the relative throttle device also prevails across the series arrangement of superleak, cold space and vortex tube.

It is known from prior art of a Joule-Kelvin system in which cold is produced at temperatures which are lower than the temperature which corresponds to' the pressure after the throttle device. This is achieved in' that the throttle device is constructed as a throttle ejector, the outlet side of which communicates on the one side, via the said counter-current heat exchangers, with the suction side of the compression device, said outlet side communicating on the other hand, via a throttle valve, with a cold space the vapor space of which communicates with the suction side of the ejector. The suction pressure of the ejector will prevail in the cold space, so that the cold is supplied at a temperature which is lower than the temperature at the outlet side of said ejector. Such a device operates excellently for temperatures lying above that of the lt-point of helium, but when the temperature at the outlet side of the ejector or in the cold space falls considerably below that of the lt-point of helium, the fact presents .itself that in the duct communicating the cold space with the ejector, pressure gradients occur which cause thermal flows from the outlet side of the ejector to the cold space, which is just not the intention in a refrigerator, and

consequently is disturbing to the operation of the refrigerator. A further embodiment of the device ac cording to the invention provides a solution to the said problem and is characterized in that at least one of the said throttle devices is formed by a throttle ejector, the

outlet of said ejector communicating on the one side with the system of outlet ducts and communicating on the other hand, if desirable through a counter-current heat exchanger and a throttle valve, with a heatexchanging space the vapor space of.which communicates, via the said counter-current heat exchanger, with the suction side of the ejector, the superleak communicating with its one side, via a heat exchanger in which the helium exchanges heat with the heatexchanging space, a throttle value and, if desirable, a further heat exchanger, with afirst place of the system of supply ducts situated in the direction of the flow in front of the throttle ejector, the vortex tube communicating with the heat-exchanging space.

In a further embodiment in which one of the throttle devices is also formed by a throttle ejector the outlet of said ejector communicates, beside with the heatexchanging space, also via a further throttle valve and a further heat exchanger in which the helium exchanges heat with the heat'exchanging store, with the one side.

of the superleak, the vortex tube furthermore communicating again with the heat-exchanging space. In both latter casesv again a differential pressure prevails across the series arrangement of superleak, cold space and vortex tube, as a result of which cold is produced in the cold space at temperatures which are lower than those which prevail in the heat-exchanging space.

The cold produced in the cold space may be used for cooling articles. In such cases it is frequently not possible, for all kinds of structural reasons, to contact said articles directly with said space, so that the cold has to be supplied at some distance from the space. In order to realize this efficiency, a further embodiment is characterized in that at least oneduct communicates with the cold space and with its other side can be brought in thermal contact with the place to be cooled, if desirable via a further space, said duct comprising a sintered superleak which extends throughout the length of the duct and covers a part of the cross-section thereof. In this manner it is possible in a very efficient manner to supply the produced cold at a distance from the cold store.

In connection with the checking of heat leak it is furthermore of advantage, according to the invention, to arrange the superleak against the inner wall of the duct.

BRIEF DESCRIPTION OF THE DRAWINGS In order that the invention may be readily carried into effect, a few examples ofdevices as described above will now be described in greater detail with reference to the accompanying drawings.

FIGS. 1, 2, 3 and 4 diagrammatically show not to scale four different embodiments of devices for producing cold at temperatures lower than that of the A-point ofhelium. I a

DESCRIPTION OF THE PREFERRED EMBODIMENT Reference numeral 1 in FIG, 1 denotes a'compression device the outlet side 2 of which, for compressed helium, communicates with a system of supply ducts 3, in which a water cooler 4 for removing the heat of compression, a number of counter-current heat exchangers 5, and two pre-coolers 6 and 7' are arranged. The system of supply ducts 3 communicates with the inlet 8 of an ejector 9. The outlet side of said ejector communicates at 10 on the one hand with the system of outlet ducts 11 in which the counter-current heat exchangers 5 are also incorporated, and on the other hand with a duct 12which communicates, via a counter-current heat exchanger 13 having a low resistance to flow, on the one hand with a throttle valve 14 and on the other hand with a throttle valve 15. Throttle valve 14 opens into a heat-exchanging space 16 which communicates with the suction side 17 of the ejector 9. The throttle valve 15 communicates with a heat exchanger 18 which is in thermal contact with the space 16 and in turn communicates with a superleak 19 which communicates with its other side with a cold space 20. This cold space communicates, through a vortex tube 21, with the heat exchanging space 16.

The operation of this device is as follows: the compressor l compresses helium to a pressure of approximately 30 atm. which compressed helium leaves the compression device via the outlet 2 and delivers its heat of compression to' cooling water in the heat exchanger 4. The compressed helium then flows through the first counter-current heat exchanger 5 and then along the precooler 6, then through the second heat exchanger 5, and then along the second pre-cooler 7, and then through the last counter-current heat exchanger Sin which the high-pressure helium will then have a temperature which lies below the inversion'temperature associated with the pressure of 30 atm.

The'high-pressure helium'then expands in the ejector 9 to a pressure of, for example, I atm. and a temperature of 4.2K. A part of the expanded helium flows via the outlet duct 11 to the inlet side 22 of the compression device 1. Another part of the expanded helium flows via duct 12 and heat exchanger 13 to the throttle valves .14 and 15. Since the heat-exchanging space 16 communicates with the suction side 17 of the ejector 9, a low pressure of approximately 12 mm Hg will adjust in the space 16, with which a temperature of [.8 "K is associated, so a temperature lower than that of the itpoint of helium. This means that the helium in the heatexchanger 18 will also assume this low temperature. Since a differential pressure prevails across the series arrangement of superfluid will start flowing through the superleak 19 to the space 20 while superfluid and normal helium flow to the space 16 through the vortex tube I 21 in which the superfluid exceeds its critical velocity. Since with the superfluid no thermal energy is transported through the superleak to.the space 20, while with the flow of normalfluid through the vortex tube thermal energy is indeed removed from the space 20, the space 20 will show alower temperature, for example, in the order of K, than the heat exchanging space 16. In this manner a device is obtained with which cold is produced at very low temperatures, while the suction pressure of the compression device 1 nevertheless need be only 1 atmosphere.

The cold produced in the space can be used for cooling articles, for example, electric components, infrared cells superconductive resonant cavities, and so on. These articles may be, for example, in direct contact with the space 20. However, for all kinds of structural reasons a certain distance will usually exist between the space 20 and the article to be cooled, certainly when cooling of several articles which are arranged at a distance from each other have to be cooled with one space 20. This cooling at a distance can very efflciently be carried out by communicating a duct 23 at its one side with the space 20 and bringing its other side in thermal contact with an article 27 to be cooled. So helium at a temperature below that of the )t-point of helium will also be present in the duct 23. It is known that this helium at the said temperatures has an extremely good thermally conductive power which may be up to l,000 times higher than that of solid substances. This property can be explained by the fact that at said temperatures the helium consists partly of normal fluid, with viscosity and entropy, and partly of superfluid which shows no viscosity and entropy. When a temperature difference is applied between two places in the said helium, the superfluid will flow to the place with the higher temperature without transporting thermal energy, while normal fluid flows in the opposite direction in such manner that the overall mass flow is zero. With this normal fluid thermal energy is transported indeed. It has been found that the mutual friction between normal and superfluid by moving vortices in the superfluid adversely influences the thermal conductivity of Hell.

In the device shown in FIG. 1 this disadvantageous effect has been counteracted by covering the inner wall of the duct 23 with a superleak 24 of, for example, aluminum oxide particles of silicon carbide particles of very small dimensions which are sintered together. Such a superleak has the property that normal fluid cannot pass it while superfluid flows through it without moving vortices occurring. When thermal energy is supplied to the end 28 of the duct 23 by the article to be cooled, said end 28 will assume a slightly higher temperature than that prevailing in the space 20. A differential pressure corresponds to this temperature difference across the duct 23, so that normal and superfluid flows through the core of the duct 23 to the space 15, while an equally large mass flow of superfluid flows through the superleak 24 to the article 27 to be cooled. With the flow of normal fluid thermal energy of the article to be cooled is transported to the space 20, the transported heat flow being proportional to the rate of flow of the normal fluid. Since no mutual friction is present between the flow of normal fluid and the flow of superfluid in the direction of the end 28 of the duct (superfluid flows through the superleak), the temperature gradient across the duct is not adversely influenced thereby so that a large heat flow from the article to be cooled to the space 20 is obtained with a small temperature difference between the article to be cooled and the space 20.

It is not necessary for the superleak 24 to be arranged against the inner wall, although this does provide the advantage that heat leak from without is counteracted; however, it is alternatively readily possible to arrange the superleak 24 detached from the wall of the tube, for example, as a core in the duct.

Instead of contacting the end 28 of the duct with an article 27, the duct 23 may communicate with its end 28 with a further space which serves either as a cold buffer for the article to be cooled, or as a space from which liquid can be drained.

FIG. 2 shows a device which in general is equal to the device shown in FIG. 1, but in which the superleak l9 communicates with the place 30 of the system of supply ducts, via the heat exchanger 18 and throttle valve 15 a further heat exchanger 13. A throttle valve 31, in which the high-pressure helium expands from 30 atm. to, for example, 5 atm, is accommodated in the system of supply ducts. It is to be noted that such a throttle valve is not strictly necessary and may be dispensed with in circumstances. In the device shown in FIG. 1, said throttle valve 31 may also be present. The operation of this device is the same as that shown in FIG. 1. High-pressure helium is supplied both to the ejector 9 and to the throttle valve 15. In the heat exchanger 18, again a temperature will prevail which is lower than that of the k-point of helium, so that in combination with the differential pressure across the series arrangement of superleak 19, cold space 20 and vortex tube 21, cold will again be produced in the space 20 at a very low temperature.

It is shown in FIG. 3 how the heat-exchanging store 16 can have the form of a real heat-exchanger. For the rest, this device is quite similar to that shown in FIG. 2.

FIG. 4 shows a device for producing cold at very low temperatures which in general also corresponds to the device which is shown in the preceding Figures, but in which the high-pressure helium is first expanded in the throttle valve 31 to, for example, a pressure of 5 atmosphere, after which this expanded helium is further expanded in a second throttle valve 32 to, for example, a pressure of 17 mm Hg, which pressure therefore also prevails in the heat exchanging space 33. The inlet side of the superleak l9 communicates with a place 34 which, viewed in the direction of flow, is situated in front of this throttle valve 32, while the vortex tube 21 communicates with the store 33, Between the place 34 and the superleak a throttle valve 15 is again provided and a heat exchanger 18 in which a temperature prevails which lies below that of the )t-point of helium, while the pressure there is higher than in the space 33, so that again superfluid helium will start flowing through the superleak 19 without moving vortices occurring and from the store 20 helium will flow through the vortex tube 21, in which the superfluid helium exceeds its critical velocity, to the space 33 and then through the system of outlet ducts 11 to the inlet side of the compression device 1. In this device also the production of cold in the space 20 will occur at a temperature which is lower than that in the space 33, in which the compression device 1 needs sucking only at a pressure which corresponds to the pressure in the space 33.

It will be obvious from the above that the invention provides an extremely simple extension of a Joule-Kelvin system with which it is possible, without the introduction of moving components and without the presence of an extremely bulky compression device, to produce cold at temperatures in the proximity of lK and lower. Devices or the type to which the present invention relates are therefore suitable for use as precoolers for He-l-le mixture refrigerators, with which it is possible to produce cold continuously at temperatures in the proximity of 20 millidegrees K.

What is claimed is:

l. A device for producing cold at temperatures lower than that of the )t-point of helium, which device in cludes a source for high-pressure helium with a low pressure suction inlet, and a high pressure outlet which communicates with a supply duct system including at least one pre-cooler and at least one counter-current heat exchanger in which the high-pressure helium is cooled to below its inversion temperature associated with the said pressure, the counter-current heat exchanger communicating with at least one throttle device in which the high-pressure helium expands to a second lower pressure, the expanded helium then flowing, via an outlet duct system and said counter-current heat exchanger to said suction side of said source, characterized in that the device furthermore comprises a further heat exchanger, a cold space, a throttle valve, a vortex tube, and at least one superleak which communicates on its one side via said further heat exchanger in which the helium cools to below the x-temperature of helium and said throttle valve with said outlet duct system, and communicates on its other side with said cold space, said cold space furthermore communicating via said vortex tube, with said He at said second lower pressure which is a lower pressure than prevails at said cold space.

2. A device as claimed in claim 1, characterized in that said throttle device is formed by a throttle ejector, the outlet of said ejector communicating on one side with the system of outlet ducts and on the other side via a counter-current heat exchanger and a throttle valve, with a heat exchanging space the vapor space of which communicates, via said counter-current heat exchanger, with the suction side of the ejector, the superleak communicating with its one side via a heatexchanger, in which the helium exchanges heat with the heat exchanging space, a throttle valve and a further heat exchanger, with a first place of the system of supply ducts situated before the throttle ejector in the direction of flow, the vortex tube communicating with the heat exchanging space.

3. A device as claimed in claim 1, characterized in thatat least one of the said throttle devices is formed by a throttle ejector, the outlet of said ejector communicating on the one side with the system of outlet ducts and communicating on the other side, via a countercurrent heat exchanger and a first throttle valve, with a heatexchanging space the vapor space of which communicates, via the counter current heat-exchanger, with the suction side of the ejector, the superleak communicating with its one side, via a heat-exchanger in which the helium exchanges heat with the heatexc hanging space, and a second throttle valve, with a place between the first throttle valve and the heatexchanger, the vortex tube furthermore communicating with the heat-exchanging space.

4. A device as claimed in claim 1, further comprising a further space, and further duct means having one end communicating with said cold space, and a remote end thermally contactable with said further space, said further duct means comprising a sintered superleak.

which extends throughout the length of the duct and covers a part ofthe cross-section thereof.

5. A device as claimed in claim 4, characterized in that the superleak covers the entire inner wall of the further duct.

6. A cryogenic refrigerator apparatus for producing cold at a temperature lower than the )t-point of helium, comprising a source of He gas with a first high pressure and a first high temperature, a supply duct means for transporting He from said source, first meansfor cooling He in said supply duct means to a second tempera-. ture below the inversion temperature associated with said first pressure, second means for expanding the cooled He from said first means to a second lower pressure, further duct means for dividing said expanded He from said second means into first and second portions, third means for further expanding and cooling said second portion of He to a third temperature below the )t-point thereof and for forming at least some of said second portion He into superfluid He and the remainder of said second portion into normal liquid He, a cold space container, a superleak communicating between said third means and said cold space container, a vortex tube communicating between said cold space container and said third means, whereby the superleak permits passage of only superfluid He from said third means to said cold space container, and a turbulent flow of normal and superfluid He occurs in the vortex tube from said container to said third means.

7. Apparatus according to claim 6 wherein said first means for cooling He comprises heat exchangers, said second means comprises an ejector, said third means comprises a Joule-Thompson throttle expander and further heat exchanger, and said vortex tube has an aperture with a cross-section corresponding to the pressure differential across said aperture such that the flow of normal He therethrough is turbulent.

8. Apparatus according to claim 6 wherein said second means comprises a throttle-device for expanding said He.

9. Apparatus according to claim 6 further comprising a second container for containing liquid He formed by said third means, and means for applying low pressure suction on said second container from said second means.

10. Apparatus according to claim 6 wherein said third means comprises a throttle device.

11. Apparatus according to claim 6 wherein said second means is an ejector including an inlet, an outlet, and a suction side, the apparatus further comprising a heat exchange container having space for liquid and vapor He from said third means,,return duct means communicating said vapor to the suction side of said ejector, said return duct means being a counter-flow portion of a heat exchanger for cooling said second portion of said He before it is expanded by said third means.

12. Apparatus according to claim 11 furthercomprising final heat exchange means being cooled by said liquid He in said heat exchange container, the apparatus further comprising fourth means for further expanding He from said ejector and communicating this expanded He to said final heat exchanger with the superfluid He thereformed communicated to said superleak.

13. Apparatus according to claim 11 further comprising final heat exchange means being cooled by said liquid He in said, heat exchange container, the apparatus further comprising fourth means for further expanding some of the He from said first means, and communicating this expanded He to said final heat exchanger with the superfluid He thereformed communicated to said super-leak.

14. Apparatus according to claim 11 wherein said second means is a throttle device, said third means comprises a throttle device receiving He from said further duct means and expanding said He and communicating same to be cooled in a counterflow heat exchanger with the superfluid He thereformed then communicated to said superleak, said counterflow heat exchanger cooled by He from said vortex tube which is then communicated to said suction side of the ejector.

15. Refrigeration apparatus comprising a source of He at a first high pressure and an inlet for receiving He at a second lower pressure, supply duct means for transporting said high pressure He from said source,

return duct means for transporting He to said source inlet, first means for cooling He in said supply duct means to below the inversion temperature associated with said first pressure, second means for expanding and further cooling He from said supply duct means and dividing same into first and second portions, third means for further expanding said first portion and for further cooling same to below the )t-point thereof to form a mixture of normal and superfluid He, a cold space container, a superleak which permits passage of only superfluid He from said third means to said cold space container, a vortex tube through which flows both normal and superfluid He from said container to said second means, and means for communicating said second portion of expanded He to said return duct means. I

i l l t! t

Claims

1. A device for producing cold at temperatures lower than that of the lambda -point of helium, which device includes a source for high-pressure helium with a low pressure suction inlet, and a high pressure outlet which communicates with a supply duct system including at least one pre-cooler and at least one counter-current heat exchanger in which the high-pressure helium is cooled to below its inversion temperature associated with the said pressure, the counter-current heat exchanger communicating with at least one throttle device in which the high-pressure helium expands to a second lower pressure, the expanded helium then flowing, via an outlet duct system and said counter-current heat exchanger to said suction side of said source, characterized in that the device furthermore comprises a further heat exchanger, a cold space, a throttle valve, a vortex tube, and at least one superleak which communicates on its one side via said further heat exchanger in which the helium cools to below the lambda -temperature of helium and said throttle valve with said outlet duct system, and communicates on its other side with said cold space, said cold space furthermore communicating via said vortex tube, with said He at said second lower pressure which is a lower pressure than prevails at said cold space.

2. A device as claimed in claim 1, characterized in that said throttle device is formed by a throttle ejector, the outlet of said ejector communicating on one side with the system of outlet ducts and on the other side via a counter-current heat exchanger and a throttle valve, with a heat exchanging space the vapor space of which communicates, via said counter-current heat exchanger, with the suction side of the ejector, the superleak communicating with its one side via a heat-exchanger, in which the helium exchanges heat with the heat exchanging space, a throttle valve and a further heat exchanger, with a first place of the system of supply ducts situated before the throttle ejector in the direction of flow, the vortex tube communicating with the heat exchanging space.

3. A device as claimed in claim 1, characterized in that at least one of the said throttle devices is formed by a throttle ejector, the outlet of said ejector communicating on the one side with the system of outlet ducts and communicating on the other side, via a counter-current heat exchanger and a first throttle valve, with a heat exchanging space the vapor space of which communicates, via the counter curRent heat-exchanger, with the suction side of the ejector, the superleak communicating with its one side, via a heat-exchanger in which the helium exchanges heat with the heat-exchanging space, and a second throttle valve, with a place between the first throttle valve and the heat-exchanger, the vortex tube furthermore communicating with the heat-exchanging space.

4. A device as claimed in claim 1, further comprising a further space, and further duct means having one end communicating with said cold space, and a remote end thermally contactable with said further space, said further duct means comprising a sintered superleak which extends throughout the length of the duct and covers a part of the cross-section thereof.

6. A cryogenic refrigerator apparatus for producing cold at a temperature lower than the lambda -point of helium, comprising a source of He gas with a first high pressure and a first high temperature, a supply duct means for transporting He from said source, first means for cooling He in said supply duct means to a second temperature below the inversion temperature associated with said first pressure, second means for expanding the cooled He from said first means to a second lower pressure, further duct means for dividing said expanded He from said second means into first and second portions, third means for further expanding and cooling said second portion of He to a third temperature below the lambda -point thereof and for forming at least some of said second portion He into superfluid He4 and the remainder of said second portion into normal liquid He4, a cold space container, a superleak communicating between said third means and said cold space container, a vortex tube communicating between said cold space container and said third means, whereby the superleak permits passage of only superfluid He4 from said third means to said cold space container, and a turbulent flow of normal and superfluid He4 occurs in the vortex tube from said container to said third means.

7. Apparatus according to claim 6 wherein said first means for cooling He comprises heat exchangers, said second means comprises an ejector, said third means comprises a Joule-Thompson throttle expander and further heat exchanger, and said vortex tube has an aperture with a cross-section corresponding to the pressure differential across said aperture such that the flow of normal He4 therethrough is turbulent.

8. Apparatus according to claim 6 wherein said second means comprises a throttle device for expanding said He.

11. Apparatus according to claim 6 wherein said second means is an ejector including an inlet, an outlet, and a suction side, the apparatus further comprising a heat exchange container having space for liquid and vapor He from said third means, return duct means communicating said vapor to the suction side of said ejector, said return duct means being a counter-flow portion of a heat exchanger for cooling said second portion of said He before it is expanded by said third means.

12. Apparatus according to claim 11 further comprising final heat exchange means being cooled by said liquid He in said heat exchange container, the apparatus further comprising fourth means for further expanding He from said ejector and communicating this expanded He to said final heat exchanger with the superfluid He4 thereformed communicated to said superleak.

13. Apparatus according to claim 11 further comprising final heat exchange means being cooled by said liquid He in saiD heat exchange container, the apparatus further comprising fourth means for further expanding some of the He from said first means, and communicating this expanded He to said final heat exchanger with the superfluid He4 thereformed communicated to said superleak.

14. Apparatus according to claim 11 wherein said second means is a throttle device, said third means comprises a throttle device receiving He from said further duct means and expanding said He and communicating same to be cooled in a counterflow heat exchanger with the superfluid He4 thereformed then communicated to said superleak, said counterflow heat exchanger cooled by He from said vortex tube which is then communicated to said suction side of the ejector.