Cryogenic Refrigerator

Abstract

A cryogenic refrigerator including cooling means for H.sub.2 before it is expanded in a throttle valve and flows back to one of two containers which are filled with an alloy of A and B in powder form, in which the ratio A : B can vary from 1 : 3 to 2 : 17, wherein A is Ca or one or more of the rare earths, if desired combined with Th and/or Zr and/or Hf, and wherein B is mainly Ni and/or Co, this alloy having the property of readily absorbing H.sub.2 at low temperature and readily desorbing H.sub.2 at high temperature, which gas is again directed to said throttle.

Description

BACKGROUND OF THE INVENTION

The invention relates to a device for producing cold at low temperatures having a system of inlet ducts which comprises one or more counter flow heat exchangers and one or more precoolers in which a high-pressure medium supplied to the system of ducts is cooled to below its inversion temperature associated with said pressure and communicates with a throttle device in which the medium expands; also there is a system of outlet ducts which communicates with the throttle device and along which low-pressure medium can flow away via the counter flow heat exchangers.

Devices of the above-described type are known under the name of Joule-Kelvin systems. In such devices the supply and exhaust of high-pressure medium and low-pressure medium, respectively, is ensured by a compression device communicating with the system of inlet ducts and outlet ducts, respectively. Drawbacks of this is that the compression device produces noise and vibrations as a result of its moving components, and its reliability and lifetime are inadequate to satisfy stringent requirements as regards long reliability and long lifetime. Moreover, in many places where cold has to be produced, for example, in cooled infrared detection systems, the produced noise and vibrations are not tolerable.

Known cooling devices which do not demonstrate the above-described drawbacks are the so-called absorption refrigerators. In these refrigerators a cooling medium of higher pressure is supplied, via an inlet duct which comprises a condenser in which the medium condenses, to a pressure-reducing valve which communicates with an outlet duct having a vaporizer in which the cooling medium evaporates at lower pressure. The inlet duct and outlet duct each communicate with a container in which a substance (liquid or solid) is present which has an absorbing power for the cooling medium, the container with which the outlet duct communicates being cooled and the container with which the inlet duct communicates being heated. Due to this temperature difference, a pressure differential occurs between the two containers, the cooling medium being absorbed in the cold container and desorption of the cooling medium occurring in the warm container. A drawback of these known absorption refrigerators is that, with the known combinations of cooling medium and absorbing substance, the achievable temperature difference is only small so that temperatures much lower than -70.degree. C are substantially unachievable.

SUMMARY OF THE NEW INVENTION

It is the object of the invention to provide a device for producing cold of the type mentioned in the preamble with which temperatures in the order of 25.degree. K can be achieved and which in addition can operate without noise, vibration-free and for a very long period of time in a very reliable manner due to the absence of moving parts.

In order to reach these objectives the device according to the invention is characterized in that the medium is hydrogen and the device furthermore comprises at least one container filled with an alloy of A and B in powder form, in which the ratio A : B can vary from 1 : 3 to 2 : 17, wherein A is Ca or one or more of the elements of the rare earths, if desirable combined with Th and/or Zr and/or Hf, and wherein B is mainly Ni and/or Co, each of the containers being alternately communicable with the system of inlet or outlet ducts, each container furthermore comprising a heating and a cooling device which are alternately switchable. It is to be noted that the element Y is considered among the elements of the rare earths within the scope of the present application.

The operation of the device according to the invention is mainly based on the surprising property of the alloy AB of being capable of absorbing very much hydrogen gas in a short period of time, while it can also rapidly give off again said hydrogen gas.

For each of the alloys belonging to the said group AB, isotherms can be drawn in a diagram in which the hydrogen gas pressure P.sub.H2 is plotted vertically and the absorbed quantity of hydrogen C.sub.H is plotted horizontally. Each isotherm shows at a given pressure a horizontal variation, the so-called "plateau." At the plateau pressure it is possible by means of a small pressure variation to cause much hydrogen gas to be taken up or to be given off in a reversible process. The graph shown in FIG. 1 denotes the variation of the said isotherms for LaNi.sub.5.

Of great advantage in the use of said materials in the device according to the invention, is their power of taking up large quantities of hydrogen gas. For example, 0.80 g of hydrogen gas per centimeter is taken up by LaNi.sub.5 powder having a packing density of 65 percent at a hydrogen gas pressure of 5 atmospheres. The density of the hydrogen gas in these materials may be in the order of magnitude of that of liquid hydrogen and more.

A second advantage is that the hydrogen gas can very rapidly be recovered again from the material. In the graph shown in FIG. 2 it is indicated how for LaNi.sub.5, the quantity of outflowed hydrogen gas depends upon time at different operating temperatures and at an external pressure of 1 atmosphere.

The device according to the invention may comprise two containers filled with the alloy AB of which one is cooled to, for example, 20.degree. C and the other of which is heated to, for example, 80.degree. C. By communicating the heated container with the system of inlet ducts and communicating the cooled container with the system of outlet ducts, desorption of the hydrogen gas at higher pressure (associated with 80.degree. C) will occur in the heated container. This high-pressure hydrogen gas flows through the counter flow heat exchangers and along the precooler and expands in the throttle device while cooling further. The throttled gas then flows along a place to be cooled and thence through the counter flow heat exchanger to the cooled container where it is absorbed. In this manner a refrigerator is obtained without moving components which can supply cold at approximately 25.degree. K, is very reliable, and produces no noise or vibrations.

When only two containers are present, the device according to the invention cannot operate continuously since upon switching the containers, the warm container should be cooled to the temperature of the cold container, while the cold container should be heated to the temperature of the warm container. In a further embodiment of the device according to the invention, at least three containers are therefore present. Two of these containers are always in operation while the third is brought to the desirable temperature in the mean time. If desirable it is also possible to use only one container, the system of outlet ducts comprising a large buffer volume. The desorbing hydrogen gas periodically flows from the container through the system of inlet ducts and via the throttle valve to the buffer volume while after cooling the container, the hydrogen gas flows back from the buffer volume again directly to the container.

In a further preferred embodiment of the device according to the invention the containers comprise one of the alloys LaNi.sub.5 ; La.sub.0.8 Y.sub.0.2 Ni.sub.5 ; La.sub.0.9 Zr.sub.0.1 Ni.sub.5 ; La.sub.x Ce.sub.1.sub.-x Ni.sub.5, where 0.4< x <1; La Ni where La is an alloy containing 85 percent by weight of La, 10 percent by weight of Nd, 4 percent by weight of Pr and 1 percent by weight of Ce. Especially these alloys have proved to have extremely good absorbing and desorbing properties for hydrogen gas. It is to be noted that Ni and/or Co can be partly replaced by some other elements, for example, Fe, Cu, and so on, without the properties as regards the absorption and giving-off of hydrogen gas strongly deteriorating.

The invention furthermore relates to a device for compressing hydrogen gas which is characterized in that it comprises at least one container filled with an alloy of A and B in powder form, in which the ratio A : B can vary from 1 : 3 to 2 : 17, wherein A is Ca or one or more of the elements of the rare earths, if desirable, combined with Th and/or Zr and/or Hf, and wherein B is mainly Ni and/or Co, and which each of the containers can be made to communicate with an outlet for high-pressure hydrogen gas and an inlet for low-pressure hydrogen gas, each of the containers being furthermore provided with a heater and a cooler which are switchable alternately. In this manner an extremely reliable and noiseless operating device for compressing hydrogen gas is obtained.

BRIEF DESCRIPTION OF THE DRAWINGS

In order that the invention may be readily carried into effect, it will now be described in greater detail, by way of example, with reference to FIGS. 3, 4 and 5 of the accompanying drawings.

FIG. 1 shows a graph of isotherms for LaNi.sub.5.

FIG. 2 shows a graph of the H.sub.2 gas outflow from LaNi.sub.5 as a function of time and temperature.

FIG. 3 shows diagrammatically a refrigeration system of the present invention.

FIG. 4 shows diagrammatically another embodiment of the invention of FIG. 3, and

FIG. 5 shows diagrammatically a hydrogen compression device.

DESCRIPTION OF THE PREFERRED EMBODIMENT

Reference numerals 31 and 32 in FIG. 3 denote two containers which are filled with a very fine powder of LaNi.sub.5. Ducts 33 and 34, respectively, communicate with each of the containers and can be made to communicate, via a four-way valve 35, with an inlet duct 36 and an outlet 37, respectively, of a Joule-Kelvin cooling system. The inlet duct 36 comprises a cooler 38, a first counter flow heat exchanger 39, a heat exchanger 40, a second counter flow heat exchanger 41, a throttle valve 42 which communicates with the outlet duct 37 which also comprises the counter flow heat exchangers 39 and 41. In each of the containers 31 and 32, a cooler 44 and 45, respectively and a heating device 46 and 47, respectively, are accommodated which can be actuated alternately.

The operation of this device is as follows. The device is filled with hydrogen in a suitable manner. One container 31 is then cooled by means of cooler 44 by setting valve 48 in the correct position, so that cooling water flows through it, at a temperature of approximately 20.degree. C, while container 32 is heated, by means of the heating device 47, for example, an electric resistance heating, to a temperature of approximately 110.degree. C. It may be seen from the graph shown in FIG. 1 that a pressure of approximately 2 atmospheres will prevail in the container 31, and a pressure of approximately 50 atmospheres will prevail in container 32.

Four-way valve 35 is now set so that container 32 communicates with the inlet duct 36, and container 31 communicates with the outlet duct 37. Desorped hydrogen gas from container 32 will now flow to throttle valve 42 via cooler 38 where it is cooled, counter flow heat exchanger 39, heat exchanger 40, where the hydrogen gas is further cooled by a precooler 50, for example, a vessel containing liquid nitrogen, and via counter flow heat exchanger 41. Here the gas throttles with simultaneous cooling. After the throttle valve, the hydrogen which may then have a temperature of approximately 23.degree. K, is contacted with a place to be cooled and then said medium flows via outlet duct 37 and four-way valve 35 to container 31 where it is absorbed. The desorption in container 32 and the absorption in container 31, respectively, is continued until the pressure in container 32 tends to drop below the plateau pressure associated with 110.degree. C or the pressure in the container 31 tends to rise above the plateau pressure of 20.degree. C. The operation is then switched, that is to say, the cooling water is now conducted through cooler 45 while heating device 47 is switched off and heating device 46 is switched on. The four-way valve is set in a closed position. As soon as the containers 31 and 32 have reached the operating temperatures of 110.degree. and 20.degree. C, respectively, four-way valve 35 is set in the position in which container 31 communicates with the inlet duct and container 32 communicates with the outlet duct.

If desirable, it is possible to avoid this discontinuity in the operation by providing buffer vessels in the inlet and outlet ducts, or by using three or more containers of which always two are coupled to the inlet and outlet ducts, while the non-coupled containers are brought to the desirable operating temperature.

Instead of a four-way valve 35 for controlling the flow of hydrogen gas, each of the containers 31 and 32 may comprise an inlet valve 52 and 54, respectively, and an outlet valve 53 and 55, respectively, as is shown in FIG. 4.

Instead of constructing the pre-cooler 50 as a vessel with liquid nitrogen, it may also be formed by a refrigerator, for example, a cold-gas refrigerator. It is alternatively possible to obtain the precooling by causing the hydrogen gas to expand in an expansion machine while supplying external work.

It may be obvious from the above that the invention provides an extremely reliable cooler for very low temperatures which comprises no moving components and which operates in a noiseless and vibration-free manner.

FIG. 5 show a device for compressing hydrogen gas which consists of two containers 61 and 62, respectively, filled with LaNi.sub.5. Coolers 64 and 65, respectively, and heaters 66 and 67, respectively, are accommodated in each of the said containers. Each of the containers comprises an inlet valve 68 and 69, respectively and outlet valves 70 and 71, respectively. The outlet valves 70 and 71 communicate with an outlet duct 72 for high-pressure hydrogen, while the inlet valves 68, 69 communicate with an inlet duct 73 for low-pressure hydrogen. By alternately actuating the heaters 66, 67 and the coolers 64, 65, one of the containers is brought at a higher temperature and the other is brought at a lower temperature, desorption of hydrogen gas at higher pressure occurring in the higher temperature container and absorption at lower pressure occurring in the lower temperature container. The desorbed high-pressure hydrogen gas is supplied to duct 72, while the hydrogen gas to be absorbed is applied via duct 73. In this manner an extremely simple compression device for hydrogen gas is obtained.

Claims

What is claimed is:

1. A device for producing cold at low temperatures having a system of inlet ducts which comprises one or more counter flow heat exchangers and one or more precoolers in which a high-pressure medium supplied to said system is cooled to below its inversion temperature associated with said pressure and communicates with a throttle device in which the medium expands, as well as a system of outlet ducts which communicates with the throttle device and along which low-pressure medium can flow away via the said counter flow heat exchangers, characterized in that the medium is hydrogen and the device furthermore comprises at least one container which is filled with an alloy of A and B in powder form, in which the ratio A : B can vary from 1 : 3 to 2 : 17, wherein A is Ca or one or more of the elements of the rare earths, if desirable combined with Th and/or Zr and/or Hf, and wherein B is mainly Ni and/or Co, each of the containers being communicable with the system of inlet or outlet ducts, each of the containers furthermore comprising a heater and a cooler which can be switched alternately.

2. A device as claimed in claim 1, characterized in that at least three of the said containers are present.

3. A device as claimed in claim 1, characterized in that each of the containers contains one of the alloys LaNi.sub.5 ; La.sub.0.8 Y.sub.0.2 Ni.sub.5 ; La.sub.0.9 Zr.sub.0.1 Ni.sub.5 ; La.sub.x Ce.sub.1.sub.-x Ni.sub.5 wherein 0.4< x <1; La Ni, wherein La is an alloy containing 85 percent by weight of La, 10 percent by weight of Nd, 4 percent by weight of Pr and 1 percent by weight of Ce.

4. A device for compressing hydrogen gas particularly suitable for use in a device as claimed in claim 1, characterized in that said device comprises at least one container which is filled with an alloy of A and B in powder form, in which the ratio A : B can vary from 1 : 3 to 2 : 17, wherein A IS Ca or one or more of the elements of the rare earths, if desirable, combined with Th and/or Zr and/or Hf, and wherein B is mainly Ni and/or Co, in which each of the containers can be made to communicate with an outlet for high-pressure hydrogen gas and an inlet for low-pressure hydrogen gas, each of the containers furthermore comprising a heater and a cooler which can be switched alternately.

5. A device as claimed in claim 4, characterized in that each of the containers comprises one of the alloys LaNi.sub.5 ; La.sub.0.8 Y.sub.0.2 Ni.sub.5 ; La.sub.0.9 Zr.sub.0.1 Ni.sub.5 ; La.sub.x Ce.sub.1.sub.-x Ni.sub.5 ; wherein 0.4< x <1; La Ni, wherein La is an alloy containing 85 percent by weight of La, 10 percent by weight of Nd, 4 percent by weight of Pr and 1 percent by weight of Ce.

6. Apparatus for producing cold comprising at least one container having therein an alloy of members A and B in powder form in which the ratio of A : B by weight is from 1 : 3 to 2 : 17, and wherein A is a member selected from the group consisting of calcium, the rare earth elements, mixtures of calcium and at least one element selected from the group consisting of Th, Zr, and Hf, and mixtures of a rare earth element and at least one element selected from the group consisting of Th, Zr, and Hf, and where B is a member selected from the group consisting of Ni, Co, and mixtures thereof, a source of high pressure H.sub.2, an inlet duct for flowing said H.sub.2 to said container, an outlet duct for flowing H.sub.2 out of said container, means for cooling H.sub.2 in said outlet duct to below its inversion temperature, throttle means for expanding said cooled H.sub.2 to provide said cold, first means for cooling said container, second means for heating said container, and third means for selectively activating said first and second means.

7. Apparatus according to claim 6 comprising at least two containers as described and switch means for selectively operating said first means for heating one of said containers while operating said second means for cooling the other container.

8. Apparatus according to claim 6 wherein each of said containers contains one of the alloys in the group consisting of LaNi.sub.5, La.sub.0.8 Y.sub.0.2 Ni.sub.5, La.sub.0.9 Zr.sub.0.1 Ni.sub.5, La.sub.x Ce.sub.1.sub.-x Ni.sub.5 wherein 0.4< x <1, and La Ni, wherein La is an alloy containing 85 percent by weight of La, 10 percent by weight of Nd, 4 percent by weight of Pr and 1 percent by weight of Ce.

9. Apparatus according to claim 7 wherein said means for cooling H.sub.2 in the outlet duct comprises at least one counter-flow heat-exchanger cooled by the flow of expanded and cooled H.sub.2 in said inlet duct.

10. Apparatus for compressing H.sub.2 comprising at least one container having therein an alloy of members A and B in powder form in which the ratio of A : B by weight is from 1 : 3 to 2 : 17, and wherein A is a member selected from the group consisting of calcium, the rare earth elements, mixtures of calcium and at least one element selected from the group consisting of Th, Zr, and Hf, and mixtures of a rare earth element and at least one element selected from the group consisting of Th, Zr, and Hf, and where B is a member selected from the group consisting of Ni, Co, and mixtures thereof, a source of low pressure H.sub.2, an inlet duct for flowing said H.sub.2 to said container, an outlet duct for flowing H.sub.2 out of said container, first means for cooling said container, second means for heating said container and third means for selectively activating said first and second means.

11. Apparatus according to claim 10 wherein each of said containers contains one of the alloys in the group consisting of LaNi.sub.5, La.sub.0.8 Y.sub.0.2 Ni.sub.5, La.sub.0.9 Zr.sub.0.1 Ni.sub.5, La.sub.x Ce.sub.1.sub.-x Ni.sub.5 wherein 0.4<x<1, and La Ni, wherein La is an alloy containing 85 percent by weight of La, 10 percent by weight of Nd, 4 percent by weight of Pr and 1 percent by weight of Ce.