(19)
(11)EP 2 324 307 B1

(12)EUROPEAN PATENT SPECIFICATION

(45)Mention of the grant of the patent:
09.10.2019 Bulletin 2019/41

(21)Application number: 09787035.6

(22)Date of filing:  27.08.2009
(51)International Patent Classification (IPC): 
F25D 19/00(2006.01)
F17C 13/08(2006.01)
G01R 33/3815(2006.01)
F25B 9/14(2006.01)
H01F 6/04(2006.01)
(86)International application number:
PCT/IB2009/053756
(87)International publication number:
WO 2010/029456 (18.03.2010 Gazette  2010/11)

(54)

HORIZONTAL FINNED HEAT EXCHANGER FOR CRYOGENIC RECONDENSING REFRIGERATION

HORIZONTALRIPPENWÄRMETAUSCHER FÜR KÜHLUNG DURCH KRYOGENE RÜCKVERFLÜSSIGUNG

ÉCHANGEUR DE CHALEUR HORIZONTAL NERVURÉ POUR RÉFRIGÉRATION AVEC RECONDENSATION CRYOGÉNIQUE


(84)Designated Contracting States:
AT BE BG CH CY CZ DE DK EE ES FI FR GB GR HR HU IE IS IT LI LT LU LV MC MK MT NL NO PL PT RO SE SI SK SM TR

(30)Priority: 09.09.2008 US 95392

(43)Date of publication of application:
25.05.2011 Bulletin 2011/21

(73)Proprietor: Koninklijke Philips N.V.
5656 AE Eindhoven (NL)

(72)Inventors:
  • PFLEIDERER, Glen, G.
    Cleveland, Ohio 44143 (US)
  • ACKERMANN, Robert, A.
    Cleveland, Ohio 44143 (US)

(74)Representative: van Velzen, Maaike Mathilde 
Philips Intellectual Property & Standards High Tech Campus 5
5656 AE Eindhoven
5656 AE Eindhoven (NL)


(56)References cited: : 
EP-A2- 0 245 057
GB-A- 2 414 538
EP-A2- 1 418 388
US-A- 4 926 646
  
      
    Note: Within nine months from the publication of the mention of the grant of the European patent, any person may give notice to the European Patent Office of opposition to the European patent granted. Notice of opposition shall be filed in a written reasoned statement. It shall not be deemed to have been filed until the opposition fee has been paid. (Art. 99(1) European Patent Convention).


    Description


    [0001] The present application relates to the cryomagnetic arts. It finds particular application in conjunction with magnetic resonance systems employing superconducting magnets and will be described with particular reference thereto. However, it will also find utility in other applications involving the recondensation of helium vapor.

    [0002] Many magnetic resonance systems employ superconducting magnets in order to efficiently attain high magnetic fields, e.g., 1.5 Tesla, 3 Tesla, 7 Tesla, etc. Superconducting magnets are maintained at a temperature that is below the critical temperature for superconductivity of the electric current driving the operating superconducting magnet windings. Because the superconducting temperature is typically below the 77° K temperature at which nitrogen liquefies, liquid helium is commonly used to cool the superconducting magnets.

    [0003] In a closed loop helium cooling system, a vacuum-jacketed helium dewar contains the superconducting magnet immersed in liquid helium. As the liquid helium slowly boils off, it is recondensed into liquid helium to form a closed system. The helium vapor is brought in contact with a cold head, also known as a helium vapor recondenser, which has a recondenser surface cooled to a temperature at which helium recondenses.

    [0004] In some recondensers, the recondensation surface includes a vertically disposed smooth metal structure, e.g., a cylinder, on which smooth metal surface the helium recondenses. The recondensed liquid helium flows down the bottom of the recondenser surface and falls back into the liquid helium reservoir within the dewar. Although the recondensation on the cold surface may occur in film or dropwise condensation, the dominant form is film condensation in which a liquid film covers the entire condensing surface. Under the action of gravity, the film flows continuously from the surface. However, the liquid helium has a sufficiently high surface tension that a relatively thick helium film can be supported on the vertical surface.

    [0005] In some recondensers, the recondensing surface has smooth, longitudinal (vertical) fins extending along the surface in the direction of flow. Although such fins increase the surface area, the fins lead to the formation of a thick film along the fins and restrict the formation of liquid droplets at the end of the recondenser surface.

    [0006] While such cryorecondensers are effective, the present inventors have recognized that the film of liquid helium on the recondenser surface functions as an insulating layer between the recondensation surface and the helium vapor, reducing the efficiency of the regenerative cryogenic refrigerator system. EP 1 418 388 A2 discloses a cryogenic system according to the preamble of claim 1 and a method of maintaining superconductive magnet windings immersed in helium and recondensing helium vapor on a recondenser surface.

    [0007] The present application provides an improved system and method which overcomes the above-referenced problems and others.

    [0008] In accordance with one aspect, a cryogenic system is provided. A liquid helium vessel contains liquid helium. Superconducting magnet windings are immersed in the liquid helium. A helium vapor recondenser has a smooth recondenser surface on which helium vapor recondenses, which recondenser surface is intermittently interrupted by a structure which one or more of causes the liquid helium which condenses to leave the recondenser surface without travelling the full length of the recondenser and/or disrupts a thickness of a film of the liquid helium forming on the recondenser surface.

    [0009] In accordance with another aspect, a method of maintaining superconducting magnets immersed in liquid helium is provided. Helium vapor which boils off from the liquid helium is recondensed on a smooth recondenser surface forming a liquid helium film on the recondenser surface. The liquid helium film is disrupted intermittently along the smooth recondenser surface.

    [0010] In accordance with a further aspect of the method, the liquid helium is caused to leave the smooth recondenser surface without travelling a full vertical length of the recondenser surface.

    [0011] In accordance with another aspect, a recondenser includes a cooled object having a smooth surface configured to be mounted along a vertical axis such that liquids on the surface flow by gravity toward a lower end of the surface. A plurality of fins extend peripherally around the smooth surface with a top edge of each fin being flush with a smooth surface portion immediately above and with a bottom edge of each fin being larger in perimeter than the top edge. A smooth sloping surface is defined between the top edge and the bottom edge of each fin.

    [0012] One advantage resides in improved recondenser efficiency.

    [0013] Another advantage resides in smaller, less energy consumptive recondensing systems.

    [0014] Still further advantages and benefits will become apparent to those of ordinary skill in the art upon reading and understanding the following detailed description.

    [0015] The invention may take form in various components and arrangements of components, and in various steps and arrangements of steps. The drawings are only for purposes of illustrating sample embodiments and are not to be construed as limiting the invention.

    FIGURE 1 is a side sectional view of a diagrammatic illustration of a magnetic resonance system including a helium vessel with a regenerative cryogenic refrigerator;

    FIGURE 2 is a side view of a recondenser with horizontal fins;

    FIGURE 3 is a side view of a second embodiment of the recondenser with spiral grooves; and.

    FIGURE 4 is a side view of the recondenser with spiral grooves of opposite pitch.



    [0016] With reference to FIGURE 1, a magnetic resonance system 10, illustrated as a horizontal-bore type system, includes an annular housing 12 with an inner cylindrical wall 14 surrounding and defining a generally cylindrical horizontally-oriented bore 16. Although a horizontal bore type system is illustrated, it is to be understood that the present concepts are also applicable to superconducting open magnetic resonance systems, C-magnets, and the like.

    [0017] The illustrated magnetic resonance system 10 includes superconducting magnet windings 20 arranged to generate a static (B0) magnetic field oriented coaxially with the bore 16 at least in an examination region located generally at or near an isocenter of the bore 16. In the illustrated system, the superconducting magnet windings 20 have a generally solenoidal configuration in which they are wrapped coaxially around the bore 16. However, other configurations are also contemplated. Additionally, active shim windings, passive steel shims, and additional components (not shown) may also be provided.

    [0018] To keep the superconducting magnet windings 20 below a critical temperature for superconductivity while maintaining an electric current sufficient to generate a desired static magnetic field magnitude, the superconducting magnets are immersed in liquid helium LH that is disposed in a generally annular liquid helium vessel or dewar defined by an outer wall 22, an inner annular wall 24, and side walls 26. To provide thermal isolation, the outer wall 22 is surrounded by a vacuum jacket 28.

    [0019] Although not illustrated in diagrammatic FIGURE 1 for simplicity of illustration, the vacuum jacket is typically provided for the side walls 26 as well. Additional thermal isolation components, such as a surrounding liquid nitrogen jacket or dewar, are also contemplated, but are not illustrated in FIGURE 1. The magnetic resonance system includes additional components such as a set of magnetic field gradient coils which are typically disposed on one or more cylindrical formers disposed coaxially inside the inner cylinder 14; an optional whole-body cylindrical radio frequency coil which again is typically disposed on one or more cylindrical dielectric formers disposed coaxially inside the cylinder wall 14; an optional one or more local radio frequency coils or coil arrays such as a head coil, joint coil, torso coil, surface coil, array of surface coils, or the like, which are typically placed at strategic locations within the bore proximate to a region of interest of a subject; and the like. Other components not illustrated in FIGURE 1 include electronics for operating the magnetic field gradient coils and radio frequency transmit coils and data processing components for reconstructing a magnetic resonance image, performing magnetic resonance spectroscopy, or otherwise processing or analyzing acquired magnetic resonance data.

    [0020] The liquid helium is substantially thermally isolated by walls 22, 24, 26, the surrounding vacuum jacket 28, and other insulation. However, imperfect thermal isolation together with other sources of heating, generally lead to a slow vaporization of the liquid helium LH. This is diagrammatically illustrated in FIGURE 1 by a region of vapor helium VH that collects above the surface of the liquid helium LH. The superconducting magnet windings 20 are immersed in the liquid helium LH.

    [0021] To provide a closed loop regenerative cryogenic refrigeration system, the helium vapor VH is recondensed into liquid helium on a recondenser 30 disposed outside of the liquid helium vessel, but connected to the liquid helium vessel via a neck 32. The recondenser is kept at a temperature sufficiently low to promote the condensation of the helium vapor, for example, kept at a temperature below about 4.2° K, by the cold head 34 driven by a cryocooler motor 36. Because the cryocooler motor 36 has electrically conductive motor windings, it is preferably disposed outside of the magnetic field generated by the superconducting magnet windings 20. To provide vibrational isolation, the cryocooler motor is mounted via a flexible coupling 40.

    [0022] In operation, the vapor helium VH expands into the neck 32 and contacts the recondenser 30 where the vapor liquefies to form condensed liquid helium, particularly a liquid helium film. Because the recondensation surface is positioned above the liquid helium vessel, the recondensed liquid helium drops, under the force of gravity, back into the liquid helium vessel or dewar.

    [0023] With continuing reference to FIGURE 1 and further reference to FIGURE 2, the recondenser 30 includes a smooth, generally cylindrical recondenser surface 50 which surface is interrupted periodically to form a plurality of surface portions or segments by a radially extending fin or structure 52. With a cylindrical recondenser surface 50, the fins 52 are annular. Of course, other cross sections for the recondenser surface 50 and the fin 52 are contemplated. In this manner, the smooth recondenser surface 50 is interrupted periodically with the fins 52 that define a tapered smooth surface 54 which terminates in a sharp edge 56.

    [0024] Condensation of helium vapor on the recondenser 30 may occur in two forms: dropwise condensation or film condensation. The dominant form is film condensation which occurs when a liquid film covers the entire cold surface. Gravity causes this film to flow gradually from the top down towards the bottom, covering the surface with a condensation layer. The thickness of the layer increases towards the lower edge of the recondenser 30. In the illustrated embodiment, a bottom surface of the fin is horizontal to facilitate manufacture by a machining operation. Of course, multiple pieces are also contemplated. In the illustrated embodiment with three finds, the recondenser surface is divided into four shorter portions or segments. The shorter surface segments support a thinner thickness film than would a longer surface.

    [0025] The fins 52 perform two functions. First, they interrupt the film forming on the smooth recondenser surface 50 between each fin which limits the height of the film section, hence its thickness. Second, the sharp edge of the fin 56 forms a drip edge from which recondensed liquid helium drops, hence removing it from the recondenser surface 30 and returning it to the dewar.

    [0026] The rate of cooling by the recondenser 30 is a function of the heat transfer coefficient between the surface and the helium vapor which is represented by the formula: h=K1/δ. Here the rate of cooling h is proportional to the thermal conductivity K1 divided by the film thickness δ. This cooling, of course, decreases when the thermal conductivity K1 decreases and when the thickness δ increases. Thus, the thicker the coating of liquid helium, the slower the rate of cooling and the less efficient the regenerative cryogenic refrigerator becomes. Thinning the liquid helium layer and removing liquid helium from the recondenser 30 both promote more efficient cooling and recondensation of the helium vapor.

    [0027] With reference to FIGURE 3, the recondenser 30 can include a recondenser surface 50' of shapes other than cylindrical, e.g., a tapered, truncated cone. Further, interruptions to the smooth surface can be provided by projecting ribs or inwardly extending grooves 52'. The grooves 52' again have a sharp edge 56' which facilitates removal of the liquid helium at intermediate locations along the recondensation surface before reaching the bottom of the recondenser. Moreover, the interruptions in the liquid helium film again reduce the thickness of the film. The channels 52', like the fins 52 may be a series of annular rings. Alternately, the fins or the groove can be in the form of one or more spirals as illustrated in FIGURE 3. The spiral may include a single groove or fin, or a plurality of parallel grooves or fins.

    [0028] With reference to FIGURE 4, the spiral pattern of grooves or fins may include two or more spiraling grooves 52" with substantially opposite pitch forming a cross-hatched pattern on the recondenser surface 50" such that a short vertical path is created along sections of the recondenser surface between the grooves.

    [0029] The invention has been described with reference to the preferred embodiments. Modifications and alterations may occur to others upon reading and understanding the preceding detailed description. It is intended that the invention be construed as including all such modifications and alterations insofar as they come within the scope of the appended claims.


    Claims

    1. A cryogenic system comprising:

    a liquid helium vessel (22, 24, 26) containing liquid helium (LH);

    superconducting magnet windings (20) immersed in the liquid helium;

    a helium vapor recondenser (30); characterized in that the helium recondenser has a smooth surface recondenser (50, 50', 50") in which helium vapor recondenses which recondenser surface is intermittently interrupted by an interrupting structure (52, 52', 52") which at least one of causes liquid helium which condenses on the smooth surface to leave the recondenser without travelling a full vertical length of the recondenser on the smooth surface and disrupts a thickness of a liquid helium film forming on the recondenser surface.


     
    2. The cryogenic system according to claim 1, wherein the interrupting structure includes at least one of a fin (52) or a groove (52', 52").
     
    3. The cryogenic system according to claim 1, in which a plurality of fins extend peripherally around the smooth surface flush with a smooth surface portion immediately above and with a bottom edge of each fin being larger in perimeter than the top edge and a smooth sloping surface is defined between the top edge and the bottom edge of each fin.
     
    4. The cryogenic system according to claim 2, wherein the smooth surface (50, 50', 50") of the recondenser (30) is generally cylindrical and vertically oriented, and the at least one of the fin (52) or groove (52', 52") extend circumferentially around the generally cylindrical recondenser surface.
     
    5. The cryogenic system according to claim 2, wherein the recondenser surface (50, 50', 50") is generally cylindrical and vertically oriented, and wherein the at least one of the fin (52) or groove (52', 52") extends in a spiral around the generally cylindrical recondenser surface.
     
    6. The cryogenic system according to claim 1, wherein the structure which causes liquid helium to leave the recondenser surface includes a plurality of grooves (52") extending in spirals of substantially opposite pitch around the recondenser surface.
     
    7. The cryogenic system according to claim 1, wherein the interrupting structure includes:
    at least one fin (52) having a sloping upper surface (54) which slopes downward away from an adjacent recondenser surface portion, terminating in a drip edge (56) from which liquid helium droplets leave the recondenser surface without travelling a full length of the recondenser surface.
     
    8. The cryogenic system according to claim 7, wherein the recondenser surface (50) is generally cylindrical and further including a plurality of horizontal fins (52) stacked vertically above each other.
     
    9. The cryogenic system according to claim 1, wherein the interrupting structure includes a groove (52', 52") cut into the recondenser surface, an upper edge of the groove being configured to meet the smooth recondenser surface (52', 52") with a sharp edge (56') that forms a drip edge (56, 56') from which liquid helium drips and returns by gravity to the liquid helium that immerses the superconducting magnet windings (20).
     
    10. The cryogenic system according to claim 9, further including a plurality of grooves (52', 52") arranged in a spiral pattern on the recondenser surface.
     
    11. A method of manufacturing the recondenser (30) of claim 1, the method comprising:
    machining a metal element to define an annular smooth recondenser surface (30) interrupted by a plurality of annular or spiral extending fins (52) projecting from the smooth annular surface or grooves (52', 52") cut into the smooth annular surface.
     
    12. A method of maintaining superconductive magnet windings (20) immersed in liquid helium (LH), the method comprising:

    recondensing helium vapor (VH) which boils off from the liquid helium on a smooth recondenser surface (50, 50', 50") forming a liquid helium (LH) film on the recondenser surface;

    intermittently along the smooth recondenser surface, disrupting the liquid helium film.


     
    13. The method according to claim 12, wherein the step of disrupting the helium film includes:
    causing the liquid helium to leave the smooth recondenser surface without travelling a full vertical length of the recondenser surface.
     
    14. The method according to claim 11, wherein the fins (52) or grooves (52', 52") include a drip edge (56, 56') from which liquid helium drips and returns by gravity to the liquid helium that immerses the superconducting magnet windings (20).
     
    15. A recondenser (30), which is a cryorecondenser, comprising:

    a cooled object having a smooth surface (50) configured to be mounted along a vertical axis such that liquids on the surface flow by gravity toward a lower end of the surface;

    a plurality of fins (52) extending peripherally around the smooth surface with a top edge of each fin being flush with a portion of the smooth surface portion immediately above and a bottom edge of each fin being larger in perimeter than the top edge, a smooth sloping surface (54) being defined between the top edge and bottom edge of each fin (52).


     


    Ansprüche

    1. Kryosystem, umfassend:

    einen Flüssigheliumbehälter (22, 24, 26), der flüssiges Helium (LH) enthält;

    supraleitende Magnetwicklungen (20), die in dem flüssigen Helium eingetaucht sind;

    einen Heliumdampf-Rekondensierer (30); dadurch gekennzeichnet, dass der Helium-Rekondensierer einen glatten Flächenrekondensierer (50, 50', 50") aufweist, in dem Heliumdampf wieder kondensiert, wobei die Rekondensiererfläche intermittierend durch eine Unterbrechungsstruktur (52, 52', 52") unterbrochen ist, wobei wenigstens eine davon flüssiges Helium verursacht, das an der glatten Fläche kondensiert, um den Rekondensierer zu verlassen, ohne eine vollständige vertikale Länge des Rekondensierers an der glatten Fläche zu durchlaufen, und eine Dicke eines flüssigen Heliumfilms, der sich an der Rekondensiererfläche bildet, unterbricht.


     
    2. Kryosystem nach Anspruch 1, wobei die Unterbrechungsstruktur wenigstens eine von einer Finne (52) oder einer Rinne (52', 52") beinhaltet.
     
    3. Kryosystem nach Anspruch 1, in dem sich eine Vielzahl von Finnen peripher um die glatte Fläche bündig mit einem glatten Flächenabschnitt unmittelbar darüber erstreckt und mit einer unteren Kante jeder Finne im Umfang größer als die obere Kante ist, und eine glatte Neigungsfläche zwischen der oberen Kante und der unteren Kante jeder Finne definiert ist.
     
    4. Kryosystem nach Anspruch 2, wobei die glatte Fläche (50, 50', 50") des Rekondensierers (30) im Allgemeinen zylindrisch und vertikal orientiert ist und sich die wenigstens eine von der Finne (52) oder der Rinne (52', 52") am Umfang um die im Allgemeinen zylindrische Rekondensiererfläche erstreckt.
     
    5. Kryosystem nach Anspruch 2, wobei die Rekondensiererfläche (50, 50', 50") im Allgemeinen zylindrisch und vertikal orientiert ist, und wobei sich die wenigstens eine von der Finne (52) oder der Rinne (52', 52") in einer Spirale um die im Allgemeinen zylindrische Rekondensiererfläche erstreckt.
     
    6. Kryosystem nach Anspruch 1, wobei die Struktur, die das flüssige Helium dazu verursacht, die Rekondensiererfläche zu verlassen, eine Vielzahl von Rinnen (52") beinhaltet, die sich in Spiralen mit im Wesentlichen entgegengesetzten Neigungen um die Rekondensiererfläche erstreckt.
     
    7. Kryosystem nach Anspruch 1, wobei die Unterbrechungsstruktur Folgendes beinhaltet:
    wenigstens eine Finne (52), die eine geneigte obere Fläche (54) aufweist, die nach unten, entfernt von einem benachbarten Rekondensiererflächenabschnitt, in eine Abtropfkante (56) mündet, von welcher flüssige Heliumtropfen die Rekondensiererfläche verlassen, ohne eine vollständige Länge der Rekondensiererfläche zu durchlaufen.
     
    8. Kryosystem nach Anspruch 7, wobei die Rekondensiererfläche (50) im Allgemeinen zylindrisch ist und weiter eine Vielzahl von horizontalen Finnen (52) beinhaltet, die vertikal übereinander gestapelt sind.
     
    9. Kryosystem nach Anspruch 1, wobei die Unterbrechungsstruktur eine Rinne (52', 52") beinhaltet, die in die Rekondensiererfläche eingeschnitten ist, wobei eine obere Kante der Rinne konfiguriert ist, um die glatte Rekondensiererfläche (52', 52") auf eine scharfe Kante (56') aufzutreffen, die eine Abtropfkante (56, 56') bildet, von welcher flüssiges Helium abtropft und aufgrund von Schwerkraft zu dem flüssigen Helium zurückgeführt wird, das die supraleitenden Magnetwicklungen (20) eintaucht.
     
    10. Kryosystem nach Anspruch 9, weiter beinhaltend eine Vielzahl von Rinnen (52', 52"), die in einem Spiralenmuster an der Rekondensiererfläche angeordnet ist.
     
    11. Verfahren zum Herstellen des Rekondensierers (30) nach Anspruch 1, wobei das Verfahren Folgendes umfasst:
    maschinelle Bearbeiten eines Metallelements, um eine kreisförmige, glatte Rekondensiererfläche (30) zu definieren, die durch eine Vielzahl von sich kreisförmig oder spiralförmig erstreckenden Finnen (52) unterbrochen ist, die von der glatten, kreisförmigen Fläche oder den Rinnen (52', 52"), die in die glatte, kreisförmige Fläche geschnitten sind, hervorsteht.
     
    12. Verfahren zum Aufrechterhalten von supraleitenden Magnetwicklungen (20), die in flüssigem Helium (LH) eingetaucht sind, wobei das Verfahren Folgendes umfasst:

    erneutes Kondensieren von Heliumdampf (VH), der von dem flüssigen Helium an einer glatten Rekondensiererfläche (50, 50', 50") verdampft, das einen flüssigen Heliumfilm (LH) an der Rekondensiererfläche bildet;

    Unterbrechen des flüssigen Heliumfilms intermittierend entlang der glatten Rekondensiererfläche.


     
    13. Verfahren nach Anspruch 12, wobei der Schritt des Unterbrechens des Heliumfilms Folgendes beinhaltet:
    Verursachen, dass das flüssige Helium die glatte Rekondensiererfläche verlässt, ohne eine vollständig vertikale Länge der Rekondensiererfläche zu durchlaufen.
     
    14. Verfahren nach Anspruch 11, wobei die Finnen (52) oder Rinnen (52', 52") eine Abtropfkante (56, 56') beinhalten, von welcher flüssiges Helium abtropft und aufgrund von Schwerkraft zu dem flüssigen Helium zurückgeführt wird, das die supraleitenden Magnetwicklungen (20) eintaucht.
     
    15. Rekondensierer (30), der ein Kryorekondensierer ist, umfassend:

    ein abgekühltes Produkt, das eine glatte Fläche (50) aufweist, die konfiguriert ist, um entlang einer vertikalen Achse befestigt zu werden, sodass Flüssigkeiten an der Fläche aufgrund von Schwerkraft zu einem unteren Ende der Fläche fließen;

    eine Vielzahl von Finnen (52), die sich peripher um die glatte Fläche erstrecken, wobei eine obere Kante jeder Finne bündig mit einem Abschnitt des glatten Flächenabschnitts unmittelbar darüber ist und eine untere Kante jeder Finne im Umfang größer als die obere Kante ist, wobei eine glatte geneigte Fläche (54) zwischen der oberen Kante und der unteren Kante jeder Finne (52) definiert ist.


     


    Revendications

    1. Système cryogénique comprenant :

    un récipient d'hélium liquide (22, 24, 26) contenant de l'hélium liquide (LH) ;

    des enroulements magnétiques à supraconduction (20) immergés dans l'hélium liquide ;

    un recondenseur de vapeur d'hélium (30) ; caractérisé en ce que le recondenseur d'hélium présente un recondenseur de surface lisse (50, 50', 50") dans lequel de la vapeur d'hélium se recondense, laquelle surface de recondenseur est interrompue par intermittence par une structure d'interruption (52, 52', 52") dont au moins une amène l'hélium liquide qui se condense sur la surface lisse à quitter le recondenseur sans parcourir une longueur verticale entière du recondenseur sur la surface lisse et perturbe une épaisseur d'un film d'hélium liquide se formant sur la surface de recondenseur.


     
    2. Système cryogénique selon la revendication 1, dans lequel la structure d'interruption inclut au moins une parmi une ailette (52) ou une rainure (52', 52").
     
    3. Système cryogénique selon la revendication 1, dans lequel une pluralité d'ailettes s'étend sur la périphérie autour de la surface lisse alignée sur une portion de surface lisse immédiatement au-dessus et avec une arête inférieure de chaque ailette présentant un plus grand périmètre que l'arête supérieure et une surface en pente lisse est définie entre l'arête supérieure et l'arête inférieure de chaque ailette.
     
    4. Système cryogénique selon la revendication 2, dans lequel la surface lisse (50, 50', 50") du recondenseur (30) est généralement cylindrique et orientée verticalement, et l'au moins une parmi l'ailette (52) ou la rainure (52', 52") s'étend sur la circonférence autour de la surface de recondenseur généralement cylindrique.
     
    5. Système cryogénique selon la revendication 2, dans lequel la surface de recondenseur (50, 50', 50") est généralement cylindrique et orientée verticalement, et dans lequel l'au moins une parmi l'ailette (52) ou la rainure (52', 52") s'étend dans une spirale autour de la surface de recondenseur généralement cylindrique.
     
    6. Système cryogénique selon la revendication 1, dans lequel la structure qui amène de l'hélium liquide à quitter la surface de recondenseur inclut une pluralité de rainures (52") s'étendant en spirales de pas sensiblement opposé autour de la surface de recondenseur.
     
    7. Système cryogénique selon la revendication 1, dans lequel la structure d'interruption inclut :
    au moins une ailette (52) présentant une surface supérieure en pente (54) qui s'incline vers le bas loin d'une portion de surface de recondenseur adjacente, se terminant en une arête d'égouttement (56) de laquelle des gouttelettes d'hélium liquide quittent la surface de recondenseur sans parcourir une longueur entière de la surface de recondenseur.
     
    8. Système cryogénique selon la revendication 7, dans lequel la surface de recondenseur (50) est généralement cylindrique et incluant en outre une pluralité d'ailettes horizontales (52) empilées verticalement les unes au-dessus des autres.
     
    9. Système cryogénique selon la revendication 1, dans lequel la structure d'interruption inclut une rainure (52', 52") coupée dans la surface de recondenseur, une arête supérieure de la rainure étant configurée pour rencontrer la surface de recondenseur lisse (52', 52") avec une arête vive (56') qui forme une arête d'égouttement (56, 56') de laquelle de l'hélium liquide s'égoutte et retourne par gravité à l'hélium liquide qui immerge les enroulements magnétiques à supraconduction (20).
     
    10. Système cryogénique selon la revendication 9, incluant en outre une pluralité de rainures (52', 52") agencées dans un motif spiralé sur la surface de recondenseur.
     
    11. Procédé de fabrication du recondenseur (30) selon la revendication 1, le procédé comprenant :
    l'usinage d'un élément métallique pour définir une surface de recondenseur lisse annulaire (30) interrompue par une pluralité d'ailettes (52) s'étendant en anneau ou spirale faisant saillie de la surface annulaire lisse ou des rainures (52', 52") coupées dans la surface annulaire lisse.
     
    12. Procédé de maintien des enroulements magnétiques à supraconduction (20) immergés dans de l'hélium liquide (LH), le procédé comprenant :

    la recondensation de la vapeur d'hélium (VH) qui s'évapore de l'hélium liquide sur une surface de recondenseur lisse (50, 50', 50") formant un film d'hélium liquide (LH) sur la surface de recondenseur ;

    par intermittence le long de la surface de recondenseur lisse, la perturbation du film d'hélium liquide.


     
    13. Procédé selon la revendication 12, dans lequel l'étape de perturbation du film d'hélium inclut :
    l'amenée de l'hélium liquide à quitter la surface de recondenseur lisse sans parcourir une longueur verticale entière de la surface de recondenseur.
     
    14. Procédé selon la revendication 11, dans lequel les ailettes (52) ou les rainures (52', 52") incluent une arête d'égouttement (56, 56') de laquelle de l'hélium liquide s'égoutte et retourne par gravité à l'hélium liquide qui immerge les enroulements magnétiques à supraconduction (20).
     
    15. Recondenseur (30) qui est un cryorecondenseur, comprenant :

    un objet refroidi présentant une surface lisse (50) configurée pour être montée le long d'un axe vertical de sorte que des liquides sur la surface s'écoulent par gravité vers une extrémité inférieure de la surface ;

    une pluralité d'ailettes (52) s'étendant sur la périphérie autour de la surface lisse avec une arête supérieure de chaque ailette étant alignée sur une portion de la portion de surface lisse immédiatement au-dessus et une arête inférieure de chaque ailette présentant un plus grand périmètre que l'arête supérieure, une surface en pente lisse (54) étant définie entre l'arête supérieure et l'arête inférieure de chaque ailette (52).


     




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    Cited references

    REFERENCES CITED IN THE DESCRIPTION



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    Patent documents cited in the description