FR2750481A1 - Dual element cryogenic pulsed gas cooler used for cooling miniature elements - Google Patents

Abstract

Items to be cooled are placed at the tubes (1,1') cold point heat-exchangers (2,2'). Heat extracted is transferred out at the warm point exchangers (3,3'). Cold points are connected via regenerators (4,4') to gas pressure pulse generators (7,7'), operating in mutual antiphase. The warm points are connected to reservoirs (5,5'), and the regenerators are thermally coupled. This basic layout is developed into a more compact configuration, with piezo-electrically controlled membranes, dividing a single pulse generator cavity, delivering alternate pulses in phase opposition. The two cold points adjoin each other, forming a single cooling area, and the reservoirs are eliminated, the warm points being directly interconnected.

Description

PULSED GAS COOLER
The invention relates to a pulsed gas cooler and more particularly to a tube micro-cooler.

The most used refrigeration devices are based on "Stirling" machines, liquid nitrogen cryostats, expansion ports
Joule-Thomson, condensing machines and Peitier elements.

 Among the machines operating continuously, only Stirling and Peltier elements are suitable for miniaturization.

 The Stirling ("Bat") refrigerator has a cooling power of 150 mW at 80 K, an input power of 6 W and a weight of 0.4 kg. On the other hand, the principle of the Stirling cycle generates vibrations, and limits the lifespan to 2000 hours (due to cold moving parts).

Cooling systems exploiting the cyclic thermodynamic transformations of a gas (eg Carnot cycle) are widely used today for their energy yields. The cycle of
Carnot is conceptually the simplest, but its implementation quickly leads to very high pressures.

The other cycles (Gifford Mac Mahon, Stirling, Brayton,
Vuillemier ...) have solved this problem by deformation of the Carnot cycle, but therefore require a heat storage and restitution element during the cycle using a regenerator.

 Figures la to show as an example the Stirling cycle, and defines the successive phases (figures la to I d) of compression (pI), transfer of heat from the gas to the regenerator (p2), expansion (p3) and transfer of heat from the regenerator to the gas (p4). The diagram in the figure illustrates the Stirling diagram in comparison to the Carnot and Ericson diagrams.

 The regenerator must have a calorific capacity sized in relation to the volume of gas which will pass through it, as well as a very large exchange surface for good transfer efficiency. This element often appears as a limitation, especially in systems where it is inserted as a cold moving part.

 The invention solves this problem.

 The invention therefore relates to a pulsed gas cooler comprising two elementary coolers each comprising a hollow tube, a first end of which is equipped with a first heat exchanger intended to be coupled to an element to be cooled (charge) and of which a second end is equipped with a second heat exchanger intended to evacuate the heat; the first end of the tube of each elementary cooler being hydraulically coupled to an alternating pressure generator via a heat regeneration system which causes the circulation of a coolant from the first end of a tube to through the first exchanger to the second exchanger and vice versa; the second end of the tube of each cooler being coupled to a reservoir; and the two elementary coolers being coupled together by their heat regeneration systems and / or their tanks.

The various objects and characteristics of the invention will appear more clearly in the description which follows and in the appended figures which represent:
- Figures la to le, a cooling system with cycle of
Stirling described above;
- Figure 2, a pulsed gas cooler system known in the
technical;
- Figure 3, a system with two pulsed gas coolers
coupled by heat exchange means (between them).

- Figure 4, a system with two pulsed gas coolers
coupled by the outputs of the cooling exchangers;
- Figure 5, a combination of the systems of Figures 3 and 4;
- Figure 6, an embodiment of a generator
compact pressure applicable to the invention;
- Figures 7 and 8, examples of embodiments of
coolers according to the invention;
- Figures 9a to 9n, a detailed example of embodiment of a
chiller according to the diagram in figure 7.

 Referring to Figure 2, we will first describe a pulsed gas cooler known in the art such as that which is the subject of French patent application No. 94 03185 filed ie March 18, 1994.

The system of Figure 2 includes:
- a tube 1 at the ends of which are arranged exchangers
heat 2 and 3, is in communication with a space
regenerator 4 on the one hand, and on the other hand with a reservoir 5
through an orifice 6;
- a pressure oscillator 7 maintains a pressure wave
in the tube 1 by acting through the regenerator 4;
- a radiator 8 allows the heat transmitted by
the exchanger 3.

 Under these conditions, the exchanger 2 located on the side of the regenerator 4 gives off heat to the gas which cools down upon expansion, before being thermalized by the regenerator 4: it therefore constitutes the cold point of the cooling system.

 Such a cooler can be produced in miniature form and can be intended to cool an element of small dimensions. The use of microelectronics techniques makes it possible to maintain a low production cost, a reduction in "dead" volumes (thermodynamically, and even from the standpoint of space) and technological compatibility with the majority of electronic circuits (infrared detectors, sensor magnetic field or low noise amplifier).

 FIG. 3 represents a first embodiment of a cooler according to the invention. This cooler comprises elementary coolers each similar to the cooler in FIG. 2.

 Each elementary cooler comprises a pulsed gas tube (1, 1 '), a tank (5, 5'), a coil (4, 4 ') and a pressure generator (7, 7'). The coils (4, 4 ') are thermally coupled together, which allows a heat exchange between the two elementary coolers.

This is shown diagrammatically in FIG. 3 by element 14.

 The system is thus divided into two subsystems operating in phase opposition, when one of the subsystems is in phase (2) (heat transfer from the gas to the regenerator), the other is then in the phase (4) (heat transfer from the regenerator to the gas). Since a heat exchange system is used between the two subsystems, the phase described above can be summarized as a transfer of heat from the gas of the first subsystem to that of the second. The role of heat storage is then filled by the gases themselves, and the heat capacity of the system is no longer essential: its only role being to allow the exchange of heat between the gases of the two subsystems, this element becomes an exchanger.

 Such a system has the advantage of having performances subject to the efficiency of heat exchange between the two circuits of the exchanger as well as to the quantity of gas passing through it. The calorific capacity of the component (regenerator) is no longer necessary and can be reduced to the maximum, thus gaining on the weight and volume of the whole. In addition, microfabrication techniques currently make it possible to make exchangers at low cost, which is less easy for regenerators.

 FIG. 4 represents another embodiment of the invention in which the two elementary coolers are coupled by the outputs of the exchangers 3 and 3 '.

 In some systems, for example pulsed gas tubes, the need to close the circuit to avoid contamination requires placing a tank at the end of the tube. This stores the gas after passing through the "hot" exchanger, and its volume, depending on the cooling power required, is generally greater than 10 times the volume of the tube.

 In the embodiment of FIG. 4, the reservoirs have been eliminated and the outlets of the tubes 1 and 1 ′ on the side of the exchangers 3 and 3 ′ have been connected to each other by a pipe 15. With respect to the system of FIG. 2, this amounts to having two volume tubes half in communication with the same tank but in phase opposition, the pressure in the tank remains constant and in this case, the volume of the tank no longer intervenes, because the storage role of the gas is filled by one of the two pulsed tubes.

 The tanks can therefore be removed. Such a system has the advantage of obtaining a very significant reduction in volume of the system. In addition, the reduction of the constituent elements leads to the reduction of the dead volumes of communication between them.

 The systems of Figures 3 and 4 are controlled by pressure generators 7, 7 'operating in phase opposition. They can also be controlled by a common generator supplying two suction / compression cycles in phase opposition on two outputs as shown in FIG. 5.

 The system of Figure 5 is a combination of the systems of Figures 3 and 4. It has two pulsed gas tubes 1 and 1 'whose outputs to the exchangers 3, 3' are coupled by a pipe 15 and whose regenerators are replaced by counter-current heat exchange coils.

 The two coils can be coupled by a wall (Si) playing the role of thermal bridge.

 The pressure generator 17 of FIG. 5 can be produced as shown in FIG. 6. It comprises an enclosure 20 containing two membranes 21, 22 determining in the enclosure a volume 23 and one or more volumes 24, 24 '.

 An outlet 25 is connected to volume 23 and an outlet 26 is connected to volumes 24, 24 '. The membranes 21, 22 are with piezoelectric control for example and their movements induce complementary effects on the volume 23 on the one hand and on the volumes 24, 24 'on the other hand. It follows that the pressure phases at the outputs 25, 26 are in opposition.

 FIG. 7 represents a simplified diagram of an embodiment of the invention constructed around a pressure generator such as that of FIG. 6.

 This pressure generator 17 of FIG. 6 is found in this figure. The outputs 25 and 26 of the pressure generator are respectively connected to the heat exchange coils 4 and 4 ′. These coils connect the outputs 25, 26 to the tubes 1 and 1 '. To have a compactness of the system, the tubes 1 and 1 ′ are arranged parallel to one face of the pressure generator. Similarly, the coils are arranged in planes parallel to the plane of this face. The heat exchangers 3 and 4 are attached to one face of the pressure generator.

 One such embodiment corresponds to the system of FIG. 5.

 The advantage of the double membrane system is that the displaced volumes are greater and that the vibrations generated by the system are less because there is a compensation effect because the controls are in phase opposition.

 FIG. 8 represents a variant of FIG. 7 in which the pressure generator comprises only one membrane defining two volumes 23, 24.

 Referring to Figures 9a to 9n, we will now describe a detailed embodiment of the device of Figure 7. This device comprises a stack of plates or layers as shown in Figures 9a to 9k.

 The upper part of the device in FIG. 8 is represented by FIG. 9a and the lower part by FIG. 9k. The device is produced by stacking the various plates pa to pk represented by FIGS. 9a to 9k according to the order of numbering in the figures.

 We will describe the roles of the various plates of the device.

As far as possible, the same references are found in these figures as those in FIG. 7 to designate the same elements.

 The plate pa of FIG. 9a is a sealed closure plate of the device and is very good conductor of heat.

 The plate pb in FIG. 9b comprises ribs 3, 3 'delimiting spaces for circulation of the fluid and constituting the heat exchangers 3, 3'. This plate is made of a material which is a good conductor of heat.

Provision may be made to produce this plate by etching the ribs on one face of the plate pa of FIG. 9a. This plate has areas cl and c'l for communication of the fluid located at the ends of the ribs.

 The pc plate of Figure 9c is attached to the pb plate of Figure 9b. It is made of thermally insulating material and has two holes c2, c'2 for the passage of fluid which communicate with the zones cl, c'l.

 The stack of plates in FIGS. 9a to 9c is shown in FIG. 91.

 The three plates pd to pf of FIGS. 9d to 9f are produced in the form of crowns and determine the cavities 23, 24 and 24 'of the device of FIG. 7. Between the plates pd and pe on the one hand and between the plates pe and pf on the other hand are provided the membranes 21 and 22 of Figure 7 (not shown in Figures 9a to 9k). The membranes are made of piezoelectric material in such a way that they can be deformed under the control of an electrical signal or, in general, they are designed so as to be deformable. The plates pd to pf of FIGS. 9d to 9f have holes c3, c4, c5, c'3, c'4, c'5 communicating with the holes c2 and c'2. Similarly, openings dl, d2, d3 and el, e2 make it possible to communicate with the cavities 23, 24, 24 'through the thicknesses of the plates pd to pf. These plates are made of thermally insulating material.

 The stack of plates in Figures 9d to 9f is shown in Figure 9m.

 The plate pg of FIG. 99, made of thermal insulating material, has a smooth face which makes it possible to close the cavity 24 '. The face opposite this smooth face has a groove 4 'in the form of a helix and communicating through a hole e3 and through the holes el, e2, with the cavity 23.

 The plate Si of FIG. 9h is a thin plate which is a good conductor of heat. It corresponds to the plate Si in FIG. 7 and is for example made of silicon.

 The plate pi of FIG. 9i, in thermal insulation, has on its face in contact with the plate Si, a groove 4 in the form of a helix. This groove communicates, through the openings d5, d4, d3, d2, dl of the preceding plates, with the cavities 24 and 24 '. The grooves 4, 4 ′ of the plates pg and pi coincide with each other when the plates are stacked.

 The plate pj in FIG. 9j, made of a material which is a good thermal conductor, comprises engravings of elongated shapes making the tubes 1 and 1 '. At one end of each tube are provided ribs acting as a filter or heat exchangers 2, 2 '. These ribs are located under openings of the preceding plates communicating with the grooves 4, 4 '. Thus the ribs of the exchanger 2 communicate through the opening fl with the groove 4 and the ribs of the exchanger 2 'communicate through the openings f' 2, f '1 with the groove 4'.

 The engravings constituting the tubes 1 and 1 ′ are closed by the plate pk in FIG. 9k which is preferably made of a material which is a good conductor of heat. The plates pj and pk of FIGS. 9j and 9k can be manufactured in the same plate by etching a plate made of a material which is a good conductor of heat.

 The engravings of the tubes 1 and 1 'communicate through the various plates through the holes c1 to c8 and c'l to c'8 with the exchangers 3 and 3' of FIG. 9b.

 The plates of Figures 9g to 9k are stacked as shown in Figure 9n.

 By stacking the different plates according to the order of numbering in the figures, a cooler such as that of FIG. 7 is thus produced and a compact structure is obtained.

 As an example, the diameter of the plates can be from 1 to 3 cm (2 cm for example). The height of the stack can be 0.5 to 2 cm (1 cm for example). One can then produce tubes 1, 1 ′ with a section of 30 mm 2 and a length of 30 mm.

 For the use of such a cooler, one or more radiators are provided on the upper face of the plate of FIG. 9a and the component or components to be cooled will be pressed against the plate of FIG. 9k in the area of the exchangers 2, 2 '.

Claims (10)

 1. Pulsed gas cooler comprising two elementary coolers each comprising a hollow tube (1, 1 '), a first end of which is equipped with a first heat exchanger (2, 2') intended to be coupled to an element to be cooled ( charge) and a second end of which is equipped with a second heat exchanger (3, 3 ') intended to dissipate the heat; the first end of the tube of each elementary cooler being hydraulically coupled to an alternating pressure generator via a heat regeneration system (4, 4 ', 14), which causes the circulation of a cooling fluid from the first end of a tube through the first exchanger to the second exchanger and vice versa; the second end of the tube of each cooler being coupled to a reservoir; and the two elementary coolers being coupled together by their heat regeneration systems and / or by their tanks.  2. Cooler according to claim 1, characterized in that the second ends (3, 3 ') of the two tubes of the two elementary coolers being directly coupled by a pipe (15), the first ends being supplied by two alternating pressure generators, the operations are phase shifted by 1,800 one with respect to the other or being supplied by a common generator having two pressure supply ports phase shifted by 1,800 each connected at a first end.  3. Cooler according to claim 1, characterized in that each first end (2, respectively 2 ') of the two tubes is connected to a coil (4, respectively 4'), the two coils being thermally coupled together, these first ends being supplied by two alternating pressure generators whose operations are phase shifted by 1800 to each other or being supplied by a common generator having two 180 ° phase shifted pressure supply ports each connected at a first end.  4. Cooler according to claim 2, characterized in that each first end (2, respectively 2 ') of the two tubes is connected to a coil, the two coils being thermally coupled together, said coils connecting the first ends to the two generators ( or the common generator).  5. Cooler according to claim 1, characterized in that the second exchangers of the two elementary coolers each have at least one communication hole towards the tank, the section of this hole being of the order of 10 000 to 50 000 pm2, the first exchangers each having at least one hole with a cross section greater than that of the holes of the second exchangers.  6. Cooler according to claim 5, characterized in that the exchangers have several holes whose overall impedance is equivalent to that corresponding to a single hole of section less than 50,000 pm2 (or 0.05 mm2).  7. Cooler according to claim 5, characterized in that the tubes (1), the reservoirs (5) are made of material with low thermal conduction and in that the exchangers (2, 2 ', 3, 3') are strong thermal conduction.  8. Cooler according to claim 1, characterized in that each exchanger comprises a plate made of a good thermal conductor material, an area of which is structured so as to improve the heat exchange between the two faces of the plate and serves as a heat exchanger, the rest of the plate being at least partially thermally coupled either to the load to be cooled or to the radiator depending on whether the corresponding exchanger of the plate is the first or the second exchanger.  9. Cooler according to claim 8, characterized in that it comprises the stacking of the following plates or layers:  - a plate (bp) made of a material which is a good thermal conductor,  having two hollow zones (cl, c'l) communicating between  them by one or more grooves or holes (3, 3 ');  - at least two plates (pd, pe, pf) made of insulating material  separated by at least one deformable membrane  on order and defining at least two volumes of fluid  (23, 24), these three plates producing the pressure generator;  - two plates (pg, pi) made of thermal insulating material  each comprising a groove (4s, 4) constituting a  heat exchange coil, these two plates being  separated by a heat exchange plate (Si) in  good heat conductive material, first end  of each groove communicating with one of said volumes of  fluid;  - a plate (pj) made of a material which is a good conductor of heat  comprising two engravings of elongated shapes and constituting  each one of said tubes (1, 1 '), each etching comprising at  one end of the grooves or holes constituting a  heat exchanger (2, 2 '), communicating with a  second end of one of said grooves constituting a  serpentine, and at another end, a communicating area  each with one of said hollow zones (cl, c'l) through  holes (c2 to c8 and c'2 to c'8) provided in the different  plates.  10. Cooler according to claim 9, characterized in that the plates have a size less than 3 cm, the stack of plates having a thickness of between 0.5 and 2 cm.