EP2307823A1

EP2307823A1 - Refrigerator, and method for producing very low temperature cold

Info

Publication number: EP2307823A1
Application number: EP09740356A
Authority: EP
Inventors: Alain Benoit; Philippe Camus; Florian Martin; Sébastien TRIQUENEAUX; Gérard VERMEULEN
Original assignee: Centre National dEtudes Spatiales CNES; Centre National de la Recherche Scientifique CNRS; Air Liquide SA; LAir Liquide SA pour lEtude et lExploitation des Procedes Georges Claude
Current assignee: Centre National dEtudes Spatiales CNES; Centre National de la Recherche Scientifique CNRS; Air Liquide SA; LAir Liquide SA pour lEtude et lExploitation des Procedes Georges Claude
Priority date: 2008-07-31
Filing date: 2009-07-22
Publication date: 2011-04-13
Anticipated expiration: 2029-07-22
Also published as: CN102112824A; WO2010012939A1; JP2011529561A; US20110185766A1; JP5313348B2; FR2934674A1; EP2307823B1

Abstract

The invention relates to a method for producing very low temperature cold through a dilution cycle wherein a two-phase mixture of the two isotopes 3He and 4He is created in a mixing chamber (2) from liquid 3He and 4He added separately, wherein said mixture of the 3He from a so-called concentrated phase is extracted so as to pass 3He into a so-called diluted phase, and due to which the frigories generated by passing the 3He into the diluted phase are recovered, the phase separation of the two-phase mixture being carried out by monitoring the flows of pure 3He and 4He, added separately into the mixing chamber (2), and by gravity-independent capillary forces, the dilution cycle operating in a closed loop, the method including a first step of recovering and separating the two isotopes 3He and 4He from the fraction of the mixture extracted through a discharge duct (8) and a second step of adding the two isotopes 3He and 4He, separated during the first step, back into the mixing chamber (2). The invention also relates to a refrigerator.

Description

Refrigerator and method for producing cold at very low temperatures

The present invention relates to a dilution refrigerator and a method for producing cold at a very low temperature. The invention more particularly relates to a dilution refrigerator for obtaining very low temperatures comprising a mixing chamber, a first feed pipe having an upstream end connected to a helium source of isotope 3 ( ³ He) and a downstream end connected to the mixing chamber, a second supply pipe having an upstream end connected to a source of helium isotope 4 ( ⁴ He) and a downstream end connected to the mixing chamber, a conduit of evacuation of the mixture of ³ He- ⁴ He produced in the mixing chamber from ³ He and ⁴ He respectively provided by the first and second conduits, the exhaust pipe comprising an upstream end connected to the mixing chamber and a downstream end connected to a recovery volume of the fraction of the mixture discharged, the downstream ends of the first and second ducts and the upstream end of the evacuation duct fluidly communicating with a common joint so as to form the mixing chamber, the phase separation between the helium ³ He- ⁴ He mixtures being controlled by the 3He and 4He fluxes in the conduits and the capillary forces in the conduits regardless of the gravity .

Among the methods for obtaining very low temperatures, one of the most interesting uses the dilution of the ³ He isotope in ordinary helium ⁴ He.

Below about 0.88K, the ³ He- ⁴ He mixture may have two phases, a so-called concentrated ³ He-rich phase and a so-called diluted ⁴ He-rich phase. When the temperature decreases from 0,88K to OK, the concentration of ³ He from the concentrated phase increases from 67% to approximately 100% while the concentration of ³ He from the dilute phase decreases from 67% to about 6.6%.

A conventional dilution cooler conventionally comprises a box or mixing chamber filled with two liquid helium phases: a dilute phase and a concentrated phase under the thermodynamic conditions described above. The principle of cold production is essentially as follows: a ⁴ He- ³ He mixture is created in the thermodynamically isolated mixing box in such quantities that there are the two phases described above (a dilute phase and a concentrated phase ). Extracting ³ He from the diluted phase, from ³ He from the concentrated phase will dissolve in the dilute phase to maintain the equilibrium concentration. This dilution process leads to the production of cold.

For such a device, or cryostat, to operate continuously, it is sufficient to introduce into the mixing box liquid ³ He, possibly mixed with a little ⁴ He, to compensate the samples.

To enable the operation of these systems it is necessary to locate:

- the concentrated phase (liquid with ³ He majority), - the dilution phase (liquid with ⁴ He majority) and also

- the concentrated vapor phase ( ³ He majority).

This localization of the different phases is carried out conventionally by gravity (the phases separate because of their different densities). On the other hand, when the system is in zero gravity or in certain orientations this localization is not possible.

FR2626658 discloses a dilution cooler system independent of gravity or orientation.

According to this system, three conduits, also called capillaries, are used. The three capillaries are connected together at one end to form a junction (mixing chamber). Two capillaries are used respectively for injecting pure ³ He and ⁴ He mixture to produce a saturated ³ He- ⁴ He (concentrated phase mixture of dilute phase). The helium mixture is extracted by the third capillary and is recovered or discharged into the space which acts as a "free" pump. Phase separation between liquid helium mixtures is controlled only by ³ He and ⁴ He flux and capillary forces, and no longer by gravity.

To overcome gravity constraints, the refrigerator has no distiller. An auxiliary distillation unit may be provided to separate, during a dedicated operation, the two constituents of the ³ He- ⁴ He mixture possibly recovered (for example by means of storage tanks).

The life of this system is however limited by the quantities of helium isotopes expected to feed the mixing box. In addition, when used in spacecraft, the mixture of helium extracted is lost. An object of the present invention is to overcome all or part of the disadvantages of the prior art noted above.

To this end, the refrigerator according to the invention, furthermore in accordance with the generic definition given in the preamble above, is essentially characterized in that it comprises a boiler constituting the recovery volume of the mixture, the boiler ensuring the maintenance of the mixture of ³ He and ⁴ He at the equilibrium liquid-vapor the boiler forming both the source of ³ He and the source of ⁴ He, the first supply duct comprising a selective pumping member of ³ He in the boiler to feed the mixing chamber in ³ He continuously and in a first closed loop, the second supply conduit comprising a selective pumping member ⁴ He in the boiler to feed the mixing chamber in ⁴ He continuously and according to a separate second closed loop.

Furthermore, embodiments of the invention may include one or more of the following features:

the boiler comprises a member for confining the liquid phase with respect to the gaseous phase,

the selective pumping member of the ⁴ He comprises a superficial fluidically connected with the liquid phase confined by the confinement member and a pumping member whose suction is connected to the liquid phase via the superficial,

the first and second ducts and the evacuation duct are assembled to heat exchange between the boiler and the mixing chamber; the pumping member of the first supply duct is a pump for pumping ³ He gas, such as a mechanical pump and / or one or more so-called absorption pumps,

the upstream end of the first supply duct and / or the pumping member of the first supply duct opens into a zone of the boiler collecting mainly ³ He from the ³ He- ⁴ He mixture at the liquid equilibrium -steam,

the pumping member of the second supply duct is a pump for pumping liquid ⁴ He, such as a mechanical pump and / or a so-called fountain pump (thermomechanical pump) or a mechanical pump for ⁴ He,

the upstream end of the second supply duct and / or the pumping member of the second supply duct opens into a zone of the boiler collecting mainly ⁴ He from the ³ He- ⁴ He mixture at the liquid equilibrium -steam,

the pumping member of the second supply duct or the upstream end of the second supply duct opens into an area of the boiler via a selective filtration element of ⁴ He. The invention also relates to a process for producing cold to very low low temperature, especially less than 2K and more preferably less than 1 K by a dilution cycle in which a two-phase mixture of the two isotopes ³ He and ⁴ He is created in a mixing chamber from ³ He and ⁴ He introduced liquid separately via respective supply ducts, in which said mixture is extracted from said mixture, via a discharge duct, with ³ He of a so-called concentrated phase in order to pass ³ He into a so-called diluted phase, and by means of which the frigories generated by the passage of ³ He in dilute phase, the phase separation of the two-phase mixture being achieved by the control of pure 3He and 4He flows introduced separately ns the mixing chamber and capillary forces in the ducts regardless of gravity.

According to an advantageous feature, the dilution cycle operates in a closed loop, the process comprising

a first step of recovering and separating the two isotopes ³ He and ⁴ He from the fraction of the mixture extracted by an evacuation pipe; a second step of re-introducing into the mixing chamber of the two isotopes ³ He and ⁴ He separated in the first step. According to other possible features:

the first step of recovery and separation of the two isotopes is carried out in a boiler designed to maintain the ³ He- ⁴ He mixture at the liquid-vapor equilibrium,

the second step of re-introducing into the mixing chamber the two isotopes ³ He and ⁴ He is carried out via respective pumping members, the mixture of the two isotopes ³ He and ⁴ He is maintained in the mixing chamber at a temperature of between 1 OmK and 30OmK and for example 50 mK and 30OmK,

the pumping pressure of the pumping member of the first conduit is between 0.1 and 50mb, and preferably equal to about 5mbar,

the process comprises, between the first recovery and separation step and the second re-introduction step, a step of cooling respective one or each of the isotopes separated between 1 and 2K and preferably between 1, 4 and 1, 5K - the temperature in the boiler and the concentration of ³ He in the boiler are maintained such that the vapor pressure of ³ He is much higher than that of the ⁴ He,

the delivery pressure of the pump of the first duct is between 50 and 1500 mbar and preferably of the order of 200 mb for liquefaction of the ³ He at a temperature (cooling at the pump outlet) of 1.4-1.5 K ,

the method uses a dilution refrigerator comprising a mixing chamber, a first feed pipe having an upstream end connected to a helium source of isotope 3 ( ³ He) and a downstream end connected to the mixing chamber; a second supply duct having an upstream end connected to a source of helium isotope 4 ( ⁴ He) and a downstream end connected to the mixing chamber, a duct discharging a fraction of the mixture of ³ He - ⁴ He produced in the mixing chamber from the ³ He and ⁴ He supplied by the first and second conduits respectively, the exhaust duct having an upstream end connected to the mixing chamber and a downstream end connected to a volume of recovering the fraction of the mixture discharged, the downstream ends of the first and second conduits and the upstream end of the evacuation conduit fluidly communicating with a common junction so as to form the chamber of mixture, the phase separation between the helium mixtures being controlled by the 3He and 4He fluxes and the capillary forces in the ducts instead of gravity, the refrigerator further comprising a boiler constituting the recovery volume of the mixture, the boiler ensuring the maintenance of the mixture of ³ He and ⁴ He in liquid-vapor equilibrium, the boiler forming both the source of ³ He and the source of ⁴ He, the first supply conduit comprising a selective pumping member of the ³ He in the boiler feeding the mixing chamber in ³ He continuously and in a first closed loop, the second supply duct comprising a selective ⁴ He pumping member in the boiler supplying the mixing chamber ⁴ He continuously and in a second closed loop, - the pressure in the pump of the second conduit (fountain pressure pump) may be several hundred mbar in order to have a turbulent flow in the monophasic capillaries and in the capillary between said fountain pressure pump and the boiler,

in the case where the pump 7 of the second duct 4 is a mechanical pump, the pumping pressure can be negative,

The invention may also relate to any alternative device or method comprising any combination of the above or below features.

Other features and advantages will appear on reading the description below, with reference to the figure which shows schematically and partially the structure and operation of a refrigerator according to a possible embodiment of the invention.

The dilution cooler 1 comprises a mixing chamber 2 formed at the open ends (common junction) of a first ³ He feed 3 conduit, a second ⁴ He feed ⁴ feed and a exhaust duct 8 of the mixture ³ He - ⁴ He.

The exhaust duct 8 comprises, from upstream to downstream, two portions: a first portion (reference zone 13) in which the two phases circulate (concentrated and diluted) and a second portion (reference zone 12) in which the mixture circulates monophasic ³ He - ⁴ He after complete dilution of the concentrated phase in the dilute phase. This evacuation duct 8 thus serves to evacuate the mixture of ³ He- ⁴ He produced in the mixing chamber 2 from ³ He and ⁴ He respectively provided by the first 3 and second 4 ducts.

The phase separation between the helium ³ He- ⁴ He mixtures is controlled by the flows of ³ He and ⁴ He in the conduits 3, 4, 8 and the capillary forces in the conduits 3, 4, 8. that is, the phase separation is not dependent on gravity or orientation (according to the same general principle as in FR2626658). The refrigerator 1 comprises a boiler evaporator 5 in which a diluted ³ He- ⁴ He liquid mixture is found in equilibrium with the ³ He-rich vapor phase.

The boiler 5 ("still" in English) is for example a copper and / or stainless subassembly provided with the required fluid inlets and outlets and constituting a sealed volume of a few cubic centimeters for example. The volume of the boiler 5 is sized so that the liquid-gas interface is established within said volume, depending on the quantities of He circulating in the system. The upstream end of the first duct 3 is connected to the boiler 5 via a pump 6 and the downstream end of the first duct 3 is connected to the mixing chamber 2.

The second supply duct 4 has an upstream end connected to the boiler 5 via a pump 7 and a downstream end connected to the mixing chamber 2.

The exhaust duct 8 is connected to the mixing chamber 2 by its upstream end and is connected to the boiler 5 by its downstream end.

The apparatus 1 thus forms two closed loops between the boiler 5 and the mixing chamber 2. The apparatus 1 is filled with a saturated ³ He and ⁴ He mixture so that there is a vapor-liquid interface in the boiler 5 and a concentrated-diluted interface in the mixing chamber 2.

The first 3 supply duct feeds the mixing chamber 2 into ³ He from the boiler 5 via a pump member 6 such as a pump.

The second supply duct 4 supplies the mixing chamber 2 with ⁴ He from the boiler 5 via a pump member 7 such as a pump.

The pump 6 of the first conduit 3 pumps mainly ³ He (gaseous) because the temperature in the boiler 5 and the concentration of 3He in the boiler 5 are maintained such that the vapor pressure of ³ He is much higher than that of the 4He. This pump 6 may be a mechanical pump or any other equivalent equivalent pumping system placed at room temperature or cryogenic temperature (eg adsorption pump). After being pumped into the boiler, the ³ He is cooled before being introduced into the mixing chamber 2. For example, a cooler 10 provides liquefaction of the pumped ³ He This cooler O can be composed, for example, of a Joule-Thomson expansion system operating with He ( ³ He or ⁴ He) or any cooler making it possible to provide a temperature ideally of the order of 1, 4 to 1, 5 K. After this first cooling 10, the ³ He is cooled by the boiler 5 (heat exchange with the first conduit 3). Then, the ³ He can be cooled via a heat exchange between the first duct 3 and the exhaust duct 8 (this exhaust duct 8 possibly also being in heat exchange with the second duct 4). There is thus a heat exchange zone 12 of the liquid ³ He injected with the monophasic ³ He - ⁴ He mixture and then a heat exchange zone 13 of the liquid ³ He injected with the ³ He - ⁴ He biphasic mixture.

The isotope helium 3 ( ³ He) injected in liquid form into the mixing box 2 typically has a temperature of between 10mK and 30OmK.

The pump 7 of the second duct 4 pumps exclusively liquid ⁴ He. The liquid pump 7 ⁴ He can be connected to the boiler 5 by means for example of a system 9 called superimposed which acts as a semi-permeable membrane allowing only superfluid ⁴ He to be pumped. This superficial 9 has an end 19 immersed in the liquid phase of the boiler 5 and a non-submerged and preferably thermally insulated end 29 of the boiler 5. In addition, a boundary device 14 may be used to allow the ³ He- ⁴ He mixture to be confined. liquid in contact with the submerged end 19 of the superficial. This boundary device 14 can operate by capillarity, for example it can consist of a porous medium with a pore size distribution adapted to the desired application. Other systems, for example by electric field, can be envisaged to obtain this confinement between the liquid phase and the gaseous phase.

Pump 7 may be a fountain effect pump (thermomechanical pump) or a mechanical pump ⁴ He or any other suitable equivalent member disposed if necessary downstream of the superleak 9 at ambient or cryogenic temperature (e.g. pump adsorption or cold turbine ).

The superfluid ⁴ He pumped into the boiler 5 can be cooled by an external cold source 11 which performs the same function as the cooler 10 of the first duct 3 (cooling to a temperature ideally of the order of 1, 4 to 1.5 K ). The two coolers 10 and 11 may moreover constitute only one single and same cooler element. It will be noted that it is thermodynamically feasible to dispense with a cold source (cooler 10 and / or cooler 11 optional (s)), especially if the heat dissipation of the pump 7 of the second duct 4 is sufficiently low. After this first cooling 11, the ⁴ He can be cooled by the boiler 5 (heat exchange with the second duct 4). Then, the ⁴ He is cooled via a heat exchange between the second duct 4 and the exhaust duct 8 (this exhaust duct 8 possibly being also in heat exchange with the first duct 3). There is thus a heat exchange zone 12 of the liquid ³ He injected with the monophasic ³ He - ⁴ He mixture and then a heat exchange zone 13 of the liquid ³ He injected with the ³ He - ⁴ He biphasic mixture.

The isotopic helium 4 ( ⁴ He) injected in liquid form into the mixing chamber 2 typically has a temperature between 1 OmK and 30OmK. Operating temperatures in the mixing chamber 2 are generally in the range of 1 OmK to 30OmK.

In order for the fountain pressure pump 7 of the second duct 4 to operate efficiently, the concentration of ³ He in the liquid phase of the boiler 5 is preferably of the order of 10%, the temperature in the boiler 5 is preferably about 1.05K. As a result, the vapor pressure in the boiler 5 is of the order of 5mb and the concentration of ³ He in the steam close to 95%.

The pumping pressure of the pump 6 of the first duct 3 is therefore typically of the order of 5 mb and the discharge pressure is for example greater or of the order of 200mb, which allows to liquefy the ³ He at the temperature from 1, 4-1, 5K.

The temperature of the fluids after pumping and first cooling 10, 11 is for example between 1 and 2K.

The dilution refrigerator 1 according to the invention therefore uses a containment system 14 for locating the liquid and vapor phases in the boiler 5.

The refrigerator 1 according to the invention thus makes it possible to continuously maintain two distinct streams of isotopes of helium ( ⁴ He and ³ He) according to two closed loops, without the need for external helium supply. The refrigerator 1 or cryostat obtained makes it possible to produce and preserve with unlimited autonomy a stable temperature of the order of, for example, 0.05K in the mixing chamber 2.

The system described above can be mounted on a support that can be rotated in all directions, especially for applications that are not gravity-dependent or subject to a gravity field.

Claims

1. Dilution refrigerator for obtaining very low temperatures comprising a mixing chamber (2), a first feed pipe (3) having an upstream end connected to a helium source of isotope 3 ( ³ He) and a downstream end connected to the mixing chamber (2), a second feed pipe (4) having an upstream end connected to a source of helium isotope 4 ( ⁴ He) and a downstream end connected to the chamber mixture (2), a discharge duct (8) of the mixture of ³ He- ⁴ He produced in the mixing chamber (2) from ³ He and ⁴ He respectively provided by the first (3) and second (4) ducts, the exhaust duct (4) comprising an upstream end connected to the mixing chamber (2) and a downstream end connected to a volume (5) for recovering the fraction of the mixture discharged, the downstream ends of the first (3) and second (4) conduits and the upstream end of the exhaust duct (8) communicating fluidically at a common junction so as to form the mixing chamber (2), the phase separation between the mixtures of helium ³ He- ⁴ He being controlled by the flows of ³ He and ⁴ He in the conduits (3, 4, 8 ) and the capillary forces in the ducts independently of the gravity, characterized in that it comprises a boiler (5) constituting the recovery volume of the mixture, the boiler (5) ensuring the maintenance of the mixture (2) of the ³ He and ⁴ HE at the liquid-vapor equilibrium, the boiler (5) forming both the source of ³ He and the source of ⁴ He, the first feed duct (3) comprising a member (6) for selective pumping of ³ He in the boiler (5) to feed the mixing chamber (2) in ³ He continuously and in a first closed loop, the second conduit (4) supply comprising a member (7, 9) of selective pumping of ⁴ He in the boiler (5) to feed the mixing chamber (2) in ⁴ He continuously and according to a second bou separate closed key.

2. Refrigerator according to claim 1, characterized in that the boiler (5) comprises a member (14) for confining the liquid phase relative to the gas phase.

3. Refrigerator according to claim 2, characterized in that the member (7, 9) for selective pumping of ⁴ He comprises a superfuit (9) in fluidic connection (19) with the liquid phase confined by the containment member (14) and a pumping member (7) whose suction is connected to the liquid phase via (29) the superficial (9).

4. Refrigerator according to any one of claims 1 to 3, characterized in that the first (3) and second (4) ducts and the exhaust duct (8) are assembled to heat exchange between the boiler (5) and the mixing box (2).

5. Refrigerator according to any one of claims 1 to 4, characterized in that the member (6) for pumping the first conduit (3) supply is a pump for pumping ³ He gas, such as a pump mechanical and / or one or more pumps said absorbtion.

6. Refrigerator according to any one of claims 1 to 5, characterized in that the upstream end of the first conduit (3) supply and / or the member (6) pumping the first conduit (3) of feed opens in an area of the boiler (5) collecting mainly ³ He from the mixture ³ He- ⁴ He in equilibrium liquid-vapor.

7. Refrigerator according to any one of claims 1 to 6, characterized in that the member (7) for pumping the second conduit (4) supply is a pump (P) for pumping ⁴ He liquid, such as a mechanical pump and / or a so-called fountain pump (thermomechanical pump) or a mechanical pump for superfluid helium.

8. Refrigerator according to any one of claims 1 to 7, characterized in that the upstream end of the second conduit (4) supply and / or the member (7) for pumping the second conduit (4) of feed opens in an area of the boiler (5) collecting mainly ⁴ He from the mixture ³ He- ⁴ He in liquid-vapor equilibrium.

9. Refrigerator according to any one of claims 7 or 8, characterized in that the member (7) for pumping the second conduit (4) supply or the upstream end of the second conduit (4) feeds in an area of the boiler (5) via a selective filtration element (9) of ⁴ He.

10. Process for producing cold at very low temperature, in particular less than 2K and more preferably less than 1 K by a dilution cycle in which a two-phase mixture of the two is created isotopes ³ He and ⁴ He in a mixing chamber (2) from ³ He and ⁴ He liquid introduced separately via respective supply conduits (3, 4), in which said mixture is extracted via a conduit of evacuation (8), ³ He of a so-called concentrated phase to pass ³ He in a so-called diluted phase, and through which we recover the frigories generated by the passage of ³ He dilute phase; the phase separation of the two-phase mixture is carried out by controlling the flow of pure 3He and 4He introduced separately into the mixing chamber (2) and the capillary forces in the conduits (3, 4) independently of the gravity, characterized in that the dilution cycle operates in a closed loop, the process comprising:

a first step of recovering and separating the two isotopes ³ He and ⁴ He from the fraction of the mixture extracted by an evacuation pipe

(8), a second re-introduction step in the mixing chamber (2) of the two isotopes ³ He and ⁴ He separated during the first step.

11. The method of claim 10, characterized in that the first step of recovery and separation of the two isotopes is carried out in a boiler (5) shaped to maintain the mixture (2) ³ He- ⁴ He in liquid equilibrium. steam.

12. The method of claim 10 or 11, characterized in that the second re-introduction step in the mixing chamber (2) of the two isotopes ³ He and ⁴ He is carried out via respective pumping members (6, 7). .

13. Method according to any one of claims 10 to 12, characterized in that the mixture of the two isotopes ³ He and ⁴ He is held in the chamber (2) mixing at a temperature between 1 OmK and 30OmK.

14. A method according to any one of claims 10 to 13, characterized in that the pumping pressure of the pumping member (6) of the first conduit (3) is between 0.1 and 50mb, and preferably equal to about 5mbar.

15. Method according to any one of claims 10 to 14, characterized in that it comprises, between the first step of recovery and separating and the second re-introducing step, a respective cooling step (10, 11) of one or each of the isotopes separated between 1 and 2K and preferably between 1, 4 and 1, 5K.

16. A method according to any one of claims 10 to 15, characterized in that it uses a dilution refrigerator comprising a mixing chamber (2), a first conduit (3) supply having an upstream end connected to a helium source of isotope 3 ( ³ He) and a downstream end connected to the mixing chamber (2), a second supply pipe (4) having an upstream end connected to a source of helium isotope 4 ( ⁴ He) and a downstream end connected to the mixing chamber (2), a discharge pipe (8) of a fraction of the mixture of ³ He- ⁴ He produced in the mixing chamber (2) from the ³ He and ⁴ He respectively provided by the first (3) and second (4) conduits, the exhaust duct (4) comprising an upstream end connected to the mixing chamber (2) and a downstream end connected to a volume ( 5) recovery of the fraction of the mixture discharged, the downstream ends of the first (3) and second (4) conduits and the upstream end of the evacuation conduit (8) fluidly communicating with a common junction so as to form the mixing chamber (2), the phase separation between the helium mixtures being controlled by the 3He and 4He fluxes and the capillary forces in the ducts instead of gravity, the refrigerator (1) further comprising a boiler (5) constituting the recovery volume of the mixture, the boiler (5) ensuring the maintenance of the mixture (2) of the ³ He and ⁴ He at liquid-vapor equilibrium, the boiler (5) forming both the source of ³ He and the source of ⁴ He, the first conduit (3) of supply comprising a member (6) selective pumping of

³ He in the boiler (5) feeding the mixing box (2) in ³ He continuously and in a first closed loop, the second conduit (4) for supply comprising a member (7) for selective pumping of ⁴ He in the boiler (5) feeding the mixing box (2) in ⁴ He continuously and in a second closed loop.