WO1997004215A1

WO1997004215A1 - Scroll decompression device for cryogenic temperatures

Info

Publication number: WO1997004215A1
Application number: PCT/FR1996/001102
Authority: WO
Inventors: Gérard Claudet
Original assignee: Commissariat A L'energie Atomique
Priority date: 1995-07-17
Filing date: 1996-07-16
Publication date: 1997-02-06
Also published as: EP1251278A3; FR2736999B1; EP0839258A1; FR2736999A1; JPH11509597A; EP1251278A2

Abstract

A temperature reduction device using scrolls for cryogenic expansion is disclosed. The device for expansion of a gaseous, liquid or two-phase fluid, comprising an expansion compartment which includes a first scroll (72), a second scroll (70) inside said first scroll, and means for enabling circular translation but not actual rotation of the second scroll inside the first scroll for fluid expansion.

Description

SPIRAL RELAXATION DEVICE FOR CRYOGENIC TEMPERATURES

DESCRIPTION Technical field and prior art

The invention relates to the field of cryogenic expansion machines.

The cryogenic refrigeration gas cycles can be classified into two categories according to whether the process considered implements either a periodic circulation back and forth, or a permanent circulation in a defined direction of the gas.

In alternating circulation cycles, the gas exchanges heat with a thermal accumulator or a heat regenerator which retains heat when the gas circulates in one direction, and releases it when returning in the opposite direction.

The best known alternative circulation cycles are the Stirling, Gifford Mac Manon, or the pulsation tube cycle. The latter is generally reserved for the production of low cooling powers of the order of a fraction of a watt around 4 Kelvin, around ten watts around 15 Kelvin, and around a hundred watts around 80 Kelvin.

A schematic description of corresponding devices is given in Figures IA to 1C.

Figure IA shows a Stirling machine. A compressor 1 or pressure oscillator consists of a piston actuated mechanically by a crankshaft 2.

The Gifford and Mac Mahon machine, illustrated in FIG. 1B, is characterized by a gas compressor 3 with an inlet 4 at low pressure and an outlet 5 at high pressure, permanent and connected to the machine refrigeration proper 10 by an inlet valve 6 and an outlet valve 7 respectively, which are opened in turn to generate the necessary pressure cycles. The refrigerating machine 10, which is connected to these compressors 1 and 3 is the same in both cases. It consists of a tube 9 in which slides a displacement piston 11 which divides the contents of the tube 9 into two chambers with variable volume, connected together by a bypass 12, on which a heat regenerator 13 is installed. The chamber connected to compressor 1 or 3 is at temperature T2 (corresponding to the hot source), and the other chamber is at temperature T3 from the cold source. The displacer piston 11 passes the compressed gas from the chamber at temperature T2 to the chamber at temperature T3, by exchanging its heat with the heat regenerator 13 in response to the pressure increases in the compressor. The expansion of the gas is produced when it mainly occupies the room at temperature T3, then the gas is reheated by passing through the heat regenerator 13 towards the room at temperature T2 before undergoing a new cycle. The heat regenerator 13 has the property of restoring to the gas flowing there in one direction the heat which it previously took from the gas flowing in the opposite direction. In the embodiment of FIG. 1B, the temperature chamber T2 communicates with the compressor 3 by the inlet 4 and the outlet 5; in the embodiments of FIG. IA, the connection of the compressor 1 to the compressor chamber at the temperature T2 is carried out by a single pressure tapping pipe 15.

From the illustration of FIG. 1A, it can be seen that the machines thus alternative are the seat of two periodic waves in the volume of trigger 15, one of pressure and the other of flow. It is possible to control the phase shift of these two waves by mechanical means which control the movements of the compressor piston 1 or of the valves 6 and 7, generally at ambient temperature, and of the displacing piston 11 which can, for applications in cryogenics, have to operate at very low temperatures. We then effectively arrive at the desired situation where the maximum expansion, that is to say the maximum heat absorption, is simultaneous with the maximum gas flow rate in the cold source T3.

Figure 1C illustrates a pulse tube machine. It comprises a pressure oscillator 16, symbolized by a mechanical compressor, a heat regenerator 17 connected to the compressor 16 by a pressure tapping pipe 18 and a pulsation tube 19 which branches at the end of the heat regenerator 17 opposite to the pressure oscillator 16. The pulsation tube 19 is closed at the end opposite to the heat regenerator 17. By the combined effect of the different volumes and throttles, the phase shift necessary for the cooling effect of the flow waves and pressure is obtained by completely static means in the pulsation tube 19, which is therefore free or devoid of any moving object such as a displacer piston. More specifically, the pulsation tube 19 is throttled near the heat regenerator 17, where the cold source SF is located, while the hot source SC is located at the opposite end of the pulsation tube 19, at the end of a portion enlarged and for example cylindrical thereof. The gas column is set in sustained oscillations, and the dimensions and the shape of the various elements of the apparatus make it possible to choose the operating frequency to obtain the phase shift of the flow waves and of pressure which effectively extracts heat from the cold source, to transfer it to the hot source.

Continuous circulation cycles are better suited to the production of high powers.

Such machines, operating on the principle of the Brayton cycle and the Claude cycle are respectively illustrated in FIGS. 2A and 2B.

They consist of different arrangements of the following three main components:

a compressor 20 recycles the gas from the low pressure level (BP), usually close to atmospheric pressure, to the high pressure level, generally between approximately 15 and 30 bars, one or more heat exchangers 22 against -current ensure the precooling of the compressed gas by exchange with the gas at low pressure,

- one or more expansion machines 23 are the real source (s) of refrigeration production. We use either machines 23 in which the gas provides mechanical work, or simple throttles or expansion valves 24 where the gas undergoes a pressure drop.

The Brayton cycle (Figure 2A) can operate with nitrogen if the desired cold source

25 is at a temperature above 80 Kelvin. For lower temperatures, the cycle gas will generally be helium.

The Claude cycle of FIG. 2A rather corresponds to a helium cycle, the cold source 26 of which is a bath of liquid helium.

The expansion machines capable of producing work apply the first principle of thermodynamics according to which the sum of the quantities of heat Q and of work W brought into play in a cycle of reversible transformations is zero:

W + Q = 0 Relaxation with work will therefore always absorb heat, but it requires the use of machines with cold parts in motion.

An expansion without work or at constant enthalpy does not absorb heat, but it is generally used in the immediate vicinity of the saturation curve of the fluid to effect the phase change by expansion of the gas which is partially liquefied.

The expansion with work is carried out, either in turbines when the flow is sufficient, or in piston machines a little better adapted to low flows.

In both cases, the gas during expansion practically cannot exchange heat with the cold source and the expansion obtained is said to be adiabatic or isentropic.

For certain applications, it could be preferable to obtain the conditions of an isothermal expansion allowing to extract more heat on condition of ensuring a permanent heat exchange with a small temperature difference between the cold source and the gas in progress. of relaxation.

Both for turbines and for piston machines, expansion with phase change is to be avoided to avoid mechanical destruction, either of the turbine unbalanced by droplets, or of the piston subjected to the "blows" of the liquid which risks s' accumulate there.

Even by limiting their use outside of the presence of liquid thanks to temperatures or Sufficiently high pressures, the currently used expansion machines induce many difficulties of design or use.

The expansion turbines must rotate at high speeds, of several tens or hundreds of thousands of revolutions per minute, and are generally supported by non-contact bearings, most often gas.

To handle low flow rates, turbines are ill-suited to miniaturization.

In fact, when the diameter decreases down to centimeter sizes, the clearance between the mobile and fixed parts of the turbine takes on increasing relative importance, and the relaxed leakage rate without work lowers efficiency. When the injection nozzles where the gas flows at sonic speed must be reduced to diameters of one tenth of a millimeter, the flow conditions quickly become disturbed and sources of irreversibility, or simply subject to impurities.

The piston regulators are, a priori, better adapted than the turbines to treat reduced flows, but their reliability is strongly conditioned by the achievement of the friction sealing between piston and cylinder, and by the existence of cold valves with the mechanisms associated command.

Statement of the invention

The object of the invention relates to an original solution making it possible to produce machines for cooling fluid by expansion, in particular cryogenic (either isentropic or, if necessary, isothermal) better suited than turbines and piston machines for treating small flows with good efficiency, and good reliability, while being insensitive to the presence of liquid or fluid in double phase.

The subject of the invention is a device for lowering the temperature of a fluid by expansion of the fluid, in the gaseous or liquid state or in double phase, characterized in that it comprises an expansion compartment comprising:

- a first spiral,

- a second spiral arranged inside this first spiral,

- Means for allowing a circular translational movement, without proper rotation, of the second spiral inside the first, during the expansion of a fluid. This device makes it possible to reduce the temperature of the fluid thanks to the expansion carried out in the expansion compartment. There is therefore cooling of the fluid as soon as it leaves this compartment.

The invention uses moving parts without contact and without the use of valves. This device is compatible with miniaturization to treat low flow rates. In addition, it can accept, without any problem, the formation of two-phase fluid during expansion. It can, moreover, include in one of the spirals at least one heat exchange circuit making it possible to tend towards isothermal conditions.

The means allowing circular translational movement, without proper rotation, can take various forms. They can for example include:

- two eccentric shafts, each one connected to the movable spiral by one end in rotation about an axis fixed relative to the device, - or at least one deformable part linked by one of its ends to a fixed part of the device and the other end of which is linked to the movable spiral,

- Or magnetic means exerting on the movable spiral or on a fixed part with respect to the movable spiral, forces such that translation can take place by preventing any rotation.

In addition, means can be provided to control the speed of rotation of the movable spiral during its movement.

Thus, in the case of a movement with two eccentrics, one of them can carry the rotor of an electric brake, the stator being fixed relative to the device. In the case of a movement with deformable parts, the movable spiral can be linked to a part around which an eccentric sleeve is rotating, a part linked to the eccentric sleeve being able to support the rotor of an electric brake. The rotation of this socket can be done with, on at least one of its two faces, a contactless bearing, of the magnetic or gas type.

A means of controlling the axial play between the two spirals can be provided. The spirals can be, for example, Archimedes' spirals where defined by a succession of arcs of a circle.

A fluid expansion system can comprise at least two expansion stages, each comprising a device according to one of the forms described above. A common shaft may possibly allow a phase movement of the movable spirals of the various expansion devices.

A cryogenic expansion machine can therefore include a compressor, an exchanger and an expansion device or system as described above. Brief description of the figures ^•

In any case, the characteristics and advantages of the invention will appear better in the light of the description which follows. This description relates to the exemplary embodiments, given by way of explanation and without limitation, with reference to the appended drawings in which:

FIG. 1A to 1C respectively illustrate Stirling, Gifford and pulsation tube machines,

FIGS. 2A and 2B illustrate machines of Brayton and Claude,

FIGS. 3A to 3D illustrate the operating principle of an expansion compartment of a device according to the invention,

FIG. 3E represents an embodiment with 4 spirals,

FIGS. 4A to 4C represent a sectional view of an expansion compartment of an either adiabatic or isothermal device according to the invention,

FIG. 5 represents a first embodiment of the invention,

FIGS. 6 to 9 show other embodiments of the invention,

- Figure 10 shows a three-stage regulator according to the invention.

Detailed description of embodiments The principle of the invention is based on the use of an expansion compartment comprising, as illustrated in FIGS. 3A to 3D and 4A, a first fixed spiral 28 and a second spiral 30 arranged movable at the inside the first. Each spiral rests or is linked to a flat bottom 32, 34.

The gas to be expanded is introduced through an intake tube 36. An exhaust can be provided. Thus, reduced clearances 40, 42, provided between the upper part of the partitions 28, 30 of the spirals and the flat bottoms 32, 34 allow the fluid to escape outside the movable spiral, then the fixed spiral ( arrow referenced 44 in Figure 4). The gas can only circulate by increasing volume (expansion) and by exerting a force on the movable wall 30 (work), subjected to a circular translational movement. As a result of this movement, each point of the spiral 30 describes a circle, the movable part remaining permanently parallel to itself.

FIGS. 3A to 3D illustrate the progress of the expansion of the gas in different stages, by which it is possible to follow the evolution of a fraction of the gas, from quarter to quarter to quarter of a turn. This gas passes through the continuously increasing volumes 46, 48, 50, 52, then finally 54, before exhaust.

The volume of the gas during expansion is at all times limited by a partition of the fixed spiral and a partition of the movable spiral, which become tangent every 180 degrees, following their development.

These tangent points provide a total or partial seal depending on whether the parts are in contact or preferably separated by a reduced clearance 40, 42.

The circular translational movement amounts to sliding the points of tangency along the profile of the fixed spiral, thus allowing the gas considered to move from the center towards the outside of the spiral while increasing in volume. A very wide range is offered for the realization of the spiral pieces concerned:

- the spiral profiles may be Archimedes' spirals (the radius R of such a spiral varies linearly with the angle from the same center (R≈aθ)),

the profiles can be defined by a succession of arcs of a circle, of different centers and of different radii, either for example at each half-turn, or again at each quarter-turn.

Depending on the flow rates to be treated and the expansion rates to be obtained, the geometry can be optimized either by using a single spiral or by several nested spirals in any number. An exemplary embodiment with several spirals is illustrated in FIG. 3E. Two fixed spirals 27 and 29 are arranged symmetrical, at 180 ° relative to an axis of symmetry Δ. Two mobile spirals 31 and 33 become tangent alternately on one side with the spiral 27 and on the other side with the spiral 29.

The thicknesses of the partitions of the spirals can be chosen constant or variable to optimize their mechanical strength and their size. The materials that can be used will preferably satisfy the condition that the two parts (fixed and mobile) are compatible, from the point of view of their expansion, so that the reduced clearances are obtained at nominal operating conditions at low temperature. To reduce deformations, preference will be given to materials with low expansion, such as composites, for example carbon fiber, or metallic alloys (such as Invar). To tend towards isothermal conditions copper or aluminum will be more favorable. For the moving part we can use low density materials, such as titanium or light alloys, strong enough to limit the inertial forces and associated deformations. Plastic materials can also be used. They can come in massive form. They can also be locally added (in the form of segments or surface deposits), either to limit the effects of possible friction, or to obtain, by progressive wear, a running-in effect causing the parts to adapt their shape to each other. 'other. We will preferably try to reach the best compromise between low contact and low leakage. The essential advantages of the invention reside in the possibility offered to achieve an expansion, with gas working, by using moving parts without contact, and without recourse to valves. The flow rate of the device can be adjusted by adjusting its speed of rotation. To this end, means for adjusting the speed of rotation can be provided. Examples will be given later.

A device according to the invention can work at slow speed. For a fixed flow, a slow speed will lead to the use of larger rooms, therefore less sensitive to miniaturization to treat low flows.

A decisive advantage of the invention results from its ability to accept without any contraindication the formation, by expansion, of two-phase fluid, the liquid phase of which can possibly be evacuated towards the exhaust without difficulty.

Variants of the device of Figure 4A are given in Figures 4B and 4C. On the face 4B, a cold coil source 35 is fixed against the flat bottom 34 of the fixed spiral. In FIG. 4C, a cold source 37 is integrated in the walls of the fixed spiral: a fluid can therefore circulate in these walls.

FIG. 5 represents a cryogenic expansion valve whose fixed parts are supported by a structure 50 which carries two eccentric shafts 52, 63. The shaft 52 centered on the bearings 53 includes an electric brake composed of a rotor 54 and a stator 55 making it possible to control the speed of rotation and to extract the expansion work towards an adaptable load receiver 56. The shaft 52 is provided with two eccentric axes 57 and 58 which allow, by means of the bearings 59 and 60 and an arm 62, a mechanical connection with a movable plate 61. The arm 62 allowing a very stable positioning and specific. The mass of this arm can, moreover, be chosen to bring the center of gravity of the mobile assembly to the desired level.

The movable plate 61 is linked by the second eccentric shaft 63 mounted on the ball bearings 64 and 65. The movement of this shaft 63 is in phase with that of the shaft 52, so that the movement of the plate 61 is a translation circular, without rotation.

All the mechanical parts described above operate at ordinary temperature in a housing 66 and a plate 67, which contain the cycle fluid 68. The latter can be, for example, helium at the exhaust pressure of the regulator. , close to atmospheric pressure. The compressed gas 69 exerts a work by setting in motion the movable spiral 70 and the plate 61, both fixed to at least one connecting element 71. The plate and the fixed spiral 72, carried by a tube 73, are protected from inputs external heat by an enclosure 74, which also makes it possible to evacuate the volume 75 by conventional means, not shown.

The connecting elements 71 and the tube 73 have a hot end and a cold end. They are preferably dimensioned to be mechanically rigid, while causing minimal thermal leakage to the gas circuit to be expanded.

An auxiliary cooling circuit 76, for example supplied with liquid nitrogen around 80 K, makes it possible to reduce thermal leaks towards the plates 70 and 72.

In a Claude cycle helium liquefier, such as that illustrated in FIG. 2B, regulators of the type of that of FIG. 5 can be used with gas 69 and the plates 70 and 72 working, on the first stage, around 50 at 60 Kelvin or, on the second floor, around 15 to 20 Kelvin.

For its part, the last expansion stage, where the partial liquefaction takes place, operates at around 5 to 7 Kelvin and, in this case, the auxiliary circuit 76 will preferably be supplied by the preceding stages at 50 K or 20 K.

Under the effect of the expansion of the gas 69 in the spiral compartment 70, 72, the movable spiral is driven in movement. The latter is transmitted, by the connecting elements 71, to the plate 61. The eccentric shafts 52, 63, in phase, make it possible to block the component of proper rotation of the movement of the movable spiral. There remains the translational movement rotary of the latter, therefore of the plate 61 and of the arm 62. Thanks to the eccentric axes 57, 58, the shaft 52 is rotated. The electric brake (stator 55 and rotor 54) makes it possible to control the speed of this rotation, therefore of the rotation of the axes 57, 58 and therefore the speed of the rotary translation movement of the movable spiral 70.

Other solutions can be found to prohibit the rotation of the movable spiral. One can use, for example, deformable elements such as a network of fibers or springs, one end of each fiber or spring being fixed to the movable spiral or to its flat bottom, while the other end is linked to the fixed part of the device. A solution, using a deformable element, is illustrated in FIG. 6. The movable spiral 77 is linked, by connecting elements 78, to a movable plate 79 whose own rotation is blocked by a bellows 83. The latter is fixed , at its lower part, to the plate 79, and at its upper part, to a fixed part 84 of the device. The bellows also makes it possible to separate the atmosphere from part 86 of the enclosure, where lubricant vapors may exist, from part 87 of the enclosure reserved for high purity cycle gas. An eccentric shaft 80 85 fixes the circular translational travel of the plate 79. This shaft 80 is in rotation about its axis 88 ", fixed relative to the device. The axis 85 is in rotation around the fixed axis 88. The shaft 80 can also support the rotor 81 of an electric brake, the stator of which is designated by the reference 82. The device is, moreover, identical or similar to that described above in connection with FIG. 5.

Another solution uses magnetic means, exerting forces such as translation can take place by prohibiting rotation.

The principle of this solution is illustrated in FIG. 7. The movable part 88 or rather the flat bottom, or from above, of the movable spiral is integral with a bar 89, either ferromagnetic, or with permanent magnetization. Both are placed in the magnetic field of an external dipole 90 whose parallel field lines fix the orientation of the part. The moving part 88 and its bar 89 are shown in three different positions. These parts can be linked to a plate such as the plate 79 in FIG. 6, the latter itself being guided by a single eccentric, as described above in connection with this same FIG. 6.

Another variant capable of ensuring the mechanical transmission of the circular translation movement will preferably be used for its greater compactness and the greater ease of dynamic balancing. This variant is illustrated in FIG. 8.

The fixed base 91 supports the stator of the electric brake 92 and the hot end of a bellows 93. The latter is intended for locking in rotation of the movable spiral 94.

The mobile part is composed of the central plate 95 connected to the mobile spiral 94 by the connecting elements 96.

An eccentric sleeve 97, free to rotate, is centered in the base 91 by the bearing 99 and supports the central plate 95 by means of the bearing 98.

The circular translation of the movable spiral 94 is transformed into rotation of the sleeve 97 whose speed is controlled by the electric brake 92. Dynamic balancing is obtained, on the one hand by a shim 100 which makes it possible to bring the center of gravity of the mobile assembly 94, 96, 95, 100 into the plane of the bearings 98 and 99 and, on the other hand, by shims 101 and 102, which make it possible to balance all the inertias applied horizontally inside the bearing 99.

All the solutions described above use different mechanical variants but remain essentially designed to operate at ordinary temperature.

The use of non-contact cryogenic bearings (for example magnetic bearings or gas bearings) can also give rise to a second family of solutions. This solution has the advantage of greater mechanical rigidity to allow better control of the respective position of the fixed and mobile spirals intended for the implementation of one invention. An example, illustrated in FIG. 9, uses in combination radial gas bearings and an axial magnetic stop. We could just as easily have used the opposite, or any other combination imaginable between these two known technologies. The example in FIG. 9 represents a helium regulator at 7 K and about 15 bars which, by expansion, will come out of the spiral towards 4.5 K, under 1 bar, in double phase, with a high proportion of liquid . The same solution may, let alone be used for relaxation of helium at any ^other temperature, such as 20 K or 60 K, or any other pressure.

The same solution could, similarly, be used for the expansion of any other gas as for for example hydrogen, neon or nitrogen, at suitable temperature and pressure levels.

The gas to be expanded enters via line 111 at 7 Kelvin, it performs its work between the fixed spiral 112 and the movable spiral 113, before leaving as a liquid-vapor mixture via line 134.

The mobile assembly, actuated by the spiral 113, is connected by the connecting elements 115 to the plate 116 which rotates the eccentric bush 117, held in axial position by the connection 118 to the ball bearing 119 located in the hot part, at 300 K, which is braked and speed controlled by the electric brake 120.

The plate 116 is blocked in rotation by the bellows 121, itself fixed to the hot casing 122.

The rotation of the sleeve 117 makes it possible to maintain, on its two faces, two hydrodynamic gas bearings 123 and 124, which ensure the contactless movement inside the cryostat 125. This cryostat is protected from the entry of parasitic heat by the auxiliary cooling circuits 126, which hold the plate 116 of the socket 117, and the bearings 123 and 124 as well as a thermal screen 127, around 20 Kelvin and by the circuit 128, supplied around 80 K with liquid nitrogen, which is connected on screen 129.

All the cold parts are installed in a vacuum enclosure 130, the pumping means of which are not shown.

The axial play between the two spirals 112 and 113 is preferably strictly controlled to remain close to a few hundredths of a millimeter.

This play, measured by a cold position sensor 131, is controlled by a regulator 132 which acts on the electromagnet 133, by controlled attraction of a ferromagnetic plate 134. To avoid having to generate excessive forces in one electromagnet 133, it is possible either to puncture the wall of the bellows 121 to put it under pressure, or to control the internal pressure of the bellows 121 at a value close to the expansion pressure of the mixture obtained in the outlet line 134.

A regulator according to one of the embodiments described above can be used to perform a Brayton cycle, as described in the introduction to the present application, in connection with FIG. 2A.

The invention is not limited to the production of single-stage regulators using only one pair of spirals, one being fixed and the other mobile.

In particular, it can be implemented in such a way that the same mechanical equipment and the same suspension set can be used for the operation of several regulators. For example, to make a Claude cycle refrigerator as illustrated in FIG. 2B, the same mechanical equipment can be used to operate a three-stage regulator shown in FIG. 10, where several of the variants described have been deliberately combined in combination previously.

On the first stage, helium enters under 15 bars and 80 Kelvin via line 141, and it comes out relaxed at 1.1 bar and 50 Kelvin in 142.

The second stage works between 15 bars, 25 Kelvin (at point 143) and 1.2 bar, 15 Kelvin (at point 144).

The third stage receives (at 145) gas at 15 bars at 7 Kelvin, which emerges (at 146) at 4.4 K as a liquid-gas mixture at 1.3 bars. A possible variant to make the expansion on the third stage more isothermal could be to coat the plate of the fixed spiral 171 with a condenser 180 where liquid helium could be condensed directly supplying the cold source.

The three mobile spirals 147, 148, 149 are linked to the same shaft 150, the sections of which decrease with the temperature level.

The shaft 150 is integral with a plate 151, at room temperature, and a plate 152, at a temperature equal to about 30 Kelvin.

The plate 151 rotates the eccentric ring 153 mounted on the ball bearings ^' 154 and 155. This ring is speed controlled by the brake 156.

At the cold plate 152, another technology is used, which is the rotation of an eccentric ring 157. It could also be braked but, in Figure 10, it is shown free.

The eccentric ring 157 is held in position by a vertical magnetic stop 158. It is centered radially by two hydrodynamic gas bearings 159 and 160 which could just as easily be replaced by magnetic bearings, either with permanent magnets or with superconductors, d '' a nature to be defined according to the temperature level.

The fixed spirals 171, 172 and 173 are integral with a casing 174 which will be isolated by a vacuum enclosure (of which the primer 175 has only been sketched without representing the pumping means).

The gas circuits are separated from each other by bellows 176 and 177. Another bellows

178 separates the cryogenic circuit from the casing 179 which can either operate at a different pressure, or contain lubricant vapors if bearings 154 and 155 are greased.

The bellows 176, 177 and 178 also contribute to fixing in rotation the movable assembly integral with the plates 151 and 152 and the shaft 150 to control the desired movement of circular translation.

The example was given of a three-stage regulator for carrying out a Claude cycle. It is possible to make a regulator with a different number of stages (either two, or a number N> 3). Likewise, it is possible to use any combination of the various embodiments set out above.

In all the examples described above, the respective position of the fixed and mobile spirals must preferably be able to be adjusted precisely, in order to limit the clearances both in the axial direction and in the radial direction. The adjustment means used remain entirely conventional and have not been shown to avoid weighing down the illustrations. One can, for example, use shims of suitable thickness for axial adjustments and provide means for adjusting the distance between the eccentric shafts to adjust the strokes. We can also consider lapping operations in position to eliminate any surface or geometry defects.

Claims

CLAIMS.

1. Device for lowering the temperature by expansion of the fluid in the gaseous or liquid state or in double phase, characterized in that it comprises an expansion compartment comprising:

- a first spiral (28, 72, 112, 171, 172, 173),

- a second spiral (30, 70, 77, 94, 113, 147, 148, 149) disposed inside this first spiral, - means (52, 63; 80, 83, 85; 93, 95, 97 ; 116,

117, 121) to allow a circular translational movement, without proper rotation, of the second spiral inside the first, during the expansion of a fluid.

2. Device according to claim 1, the means allowing a circular translational movement, without proper rotation, comprising two eccentric shafts (52, 63), each being linked to the movable spiral (170) by one end in rotation around an axis fixed relative to the device.

3. Device according to claim 1, the means allowing a circular translational movement, without proper rotation, comprising at least one deformable part (83, 93, 121) connected by one of its ends to a fixed part (84, 122) of the device, and the other end of which is linked to the movable spiral (77, 94, 113).

4. Device according to claim 3, the deformable part or parts comprising a bellows (83, 93, 121, 176-178), a network of fibers or springs.

5. Device according to claim 1, the means allowing a circular translational movement, without proper rotation, being magnetic means (90) exerting on the movable spiral or on a fixed part (88) relative to the movable spiral, forces such that translation can take place by preventing any rotation.

6. Device according to claim 5, the movable part (88) being integral with at least one ferromagnetic or permanently magnetized element (89), means being provided for generating a magnetization whose field lines fix the orientation of the moving part.

7. Device according to one of claims 3 to 6, further comprising an eccentric shaft (80) connected to the movable spiral (77) by one end in rotation about a fixed axis relative to the device.

8. Device according to one of claims 3 to 6, the movable spiral being linked to a part around which an eccentric sleeve is in rotation.

9. Device according to one of claims 1 to 8, further comprising means (55, 82, 92, 120, 156) for controlling the speed of rotation of the movable spiral during its movement.

10. Device according to claims 2 and 9, one of the eccentrics (52) carrying the rotor (54) of an electric brake, the stator (55) being fixed relative to the device.

11. Device according to claims 7 and 9, the eccentric shaft (80) supporting the rotor (81) of an electric brake, whose stator (82) is fixed relative to the device.

12. Device according to claims 8 and 9, a part linked to the eccentric sleeve (97) supporting the rotor of an electric brake, the stator (92) of which is fixed relative to the device.

13. Device according to one of claims 8 or 12, the rotation of the sleeve being on at least one of its two faces by a bearing (123, 124, 159, 160) without contact.

14. Device according to claim 13, the bearing being of the magnetic type.

15. Device according to claim 13, the bearing being of the gas type.

16. Device according to one of claims 13 to 15, further comprising means for controlling the axial play between the two spirals.

17. Device according to one of claims

12 to 16, the rotation of the sleeve taking place in a cryostat.

18. Device according to one of claims 1 to 17, the spirals being Archimedes' spirals.

19. Device according to one of claims 1 to 17, the spirals being defined by a succession of arcs of a circle.

20. Device according to one of claims 1 to 19, the partitions of the spirals being of variable height.

21. Device according to one of claims 1 to 20, each spiral being linked to a flat bottom (32, 34).

22. Device according to claim 21, a reduced clearance being ensured, at least at the operating temperature of the device, between the upper part of the partition of a spiral and the flat bottom of the other spiral.

23. Device according to one of claims 1 to 22, the materials from which the two spirals are made having a low coefficient of thermal expansion.

24. Device according to claim 23, the spirals comprising a carbon fiber composite material or a metal alloy.

25. Device according to one of claims 1 to 24, plastic materials being used, at least locally, at least in the part of one of the two spirals located opposite the bottom (32, 34) of the other spiral.

26. Device according to one of claims 1 to 25 using in at least one of a spiral heat exchange circuit in conjunction ^'with the cold source to make the isothermal expansion.

27 Fluid expansion system, comprising at least two expansion stages, each stage comprising a device according to one of claims 1 to 26.

28. The system of claim 27, a common shaft (150) allowing a movement in phase of the movable spirals (147, 148, 149) of the various expansion devices.

29. Cryogenic expansion machine comprising a compressor (20), a heat exchanger (22) and an expansion device according to one of claims 1 to 26.

30. Cryogenic expansion machine comprising a compressor (20), heat exchangers (22) and an expansion system according to one of claims 27 or 28.