EP1842013B1 - Installation for cryogenic cooling for superconductor device - Google Patents

Abstract

The installation has a connection duct between bases of main and auxiliary reservoirs (1, 9). An outlet collector (7a) connected to the reservoir (1) has a restriction unit (11) such that, during overheating of a superconductor device (4), a cryogenic liquid in reservoir (1) flows back, by vaporized liquid pressure, towards the reservoir (9) from where liquid flows again by gravity towards the reservoir (1) when the pressure is reduced.

Description

The present invention relates generally to the field of cryogenic cooling installations of superconducting devices and more particularly to an installation according to the preamble of claim 1. Such an installation is for example known from the document US-A-4,689,439 .

A conventional arrangement of an installation contemplated by the invention is illustrated in FIG. figure 1 of the attached drawing. A reservoir 1 contains a two-phase cryogenic fluid whose liquid phase 2 is surmounted by a vapor phase 3. A superconducting device 4 is immersed in the liquid phase 2. A cryogenic fluid supply conduit 5 is connected to the reservoir 1 and a control valve 6, incorporated in the supply duct 5, makes it possible to control the supply of cryogenic fluid into the tank 1. An outlet manifold 7 is provided for the evacuation of the cryogenic fluid vaporized by the thermal loads of the system. Finally, in the tank 1 is provided a level gauge 8, for example functionally associated with the control valve 6, to detect the level of filling of the tank 1 with cryogenic fluid in the liquid phase and controlling the control valve 6.

The thermal loads of the system are absorbed by partial vaporization of the cryogenic liquid, by acting on the latent heat of vaporization thereof. The vaporized cryogenic fluid is discharged through the outlet manifold 7, while cryogenic fluid in the liquid state is supplied as required under the control of the level gauge 8 and the control valve 6 so that the device superconductor 2 remains permanently immersed.

However, in the presence of a resistive transition of the device or any other thermal disturbance resulting in a strong and rapid increase in the thermal load, the cryogenic fluid in the liquid state in contact with which must be maintained the device disappears quickly and completely to both because of its vaporization due to the increase of the thermal load and due to its turbulent flow at high output in the outlet manifold. The return to a cooling of the device and the recovery of a state of superconductivity requires that cryogenic fluid in the liquid state is fed again into the reservoir. This new supply of liquid cryogenic fluid not only requires time, but above all requires a supply of fluid that is expensive.

The main purpose of the invention is to propose an improved arrangement for an installation of the type in question which makes it possible to ensure its correct and reliable operation in the presence of normal thermal conditions, but which, in the presence of abnormal thermal conditions, allows a re-immersion faster device and faster recovery of the state of superconductivity and also avoids the loss of liquid cryogenic fluid initially present in the tank and therefore allows a substantial saving in cryogenic fluid.

• un réservoir auxiliaire et
• un conduit de raccordement hydrostatique interposé entre les fonds respectifs des réservoirs principal et auxiliaire,
• ledit réservoir auxiliaire étant disposé par rapport au réservoir principal et étant dimensionné de manière à pouvoir recevoir au moins une grande partie du fluide cryogène présent sous forme liquide dans le réservoir principal,
• le susdit conduit d'alimentation en fluide cryogène étant raccordé au réservoir auxiliaire,
• un collecteur de sortie étant raccordé au réservoir auxiliaire,
• des moyens de restriction étant incorporés dans le collecteur de sortie raccordé au réservoir principal.

For these purposes, the invention proposes an installation as mentioned in the preamble which is characterized, being arranged according to the invention, in that it further comprises:

• an auxiliary tank and
• a hydrostatic connection pipe interposed between the respective bottoms of the main and auxiliary tanks,
• said auxiliary reservoir being arranged with respect to the main reservoir and being dimensioned so as to be able to receive at least a large part of the cryogenic fluid present in liquid form in the main reservoir,
• the aforesaid supply duct for cryogenic fluid being connected to the auxiliary reservoir,
• an outlet manifold being connected to the auxiliary tank,
• restriction means being incorporated in the outlet manifold connected to the main tank.

Thanks to these arrangements according to the invention, in the presence of a rapid heating of the superconducting device, certainly liquid cryogenic fluid is vaporized, but its discharge into the outlet manifold of the main tank is strongly braked by the restriction means. As a result, the pressure of the vaporized cryogenic fluid increases in the reservoir and at least a portion of the cryogenic fluid in the liquid state present in the main reservoir is discharged, under the action of this pressure of the vaporized cryogenic fluid, into the auxiliary tank. This liquid cryogenic fluid present in the auxiliary tank flows again by gravity towards the main reservoir when the pressure of the vaporized fluid decreases therein.

Under these conditions, not only is the repressed cryogenic fluid that is reintroduced into the main reservoir, but in addition this filling of the main reservoir occurs without delay as soon as the thermal overload has disappeared and this automatically by gravity. The amount of cryogenic fluid which has passed through the restriction means during this process and which has disappeared remains relatively small and has nothing to compare with the large volume of fluid, both vaporized and liquid, which was evacuated in a conventional installation under the same circumstances.

In order for the auxiliary reservoir to be made in a relatively compact form, it is advantageous for it to be arranged substantially higher than the main reservoir, so that only a small amount of liquid cryogenic fluid is contained therein under conditions normal thermal.

Preferably, means for detecting the level of the liquid cryogenic fluid are arranged in the auxiliary tank.

Depending on the mode of operation required for this installation, it can be provided that, in a simple manner, the restriction means comprise a restriction, or, in a more elaborate embodiment, that they comprise an externally controlled valve.

• la figure 1 est une vue schématique illustrant une installation classique visée par l'invention ;
• la figure 2A est une vue schématique illustrant une installation du type de celle de la figure 1 perfectionnée conformément à l'invention, montrée dans des conditions thermiques normales ;
• la figure 2B est une vue schématique illustrant l'installation de la figure 2A en présence d'une modification notable et rapide des conditions thermiques ; et
• la figure 3 est une vue schématique analogue à celle de la figure 2A montrant une variante intéressante de réalisation de l'installation conforme à l'invention.

The invention will be better understood on reading the following detailed description of a preferred embodiment given solely by way of non-limiting example. In this description, reference is made to the accompanying drawings in which:

• the figure 1 is a schematic view illustrating a conventional installation targeted by the invention;
• the Figure 2A is a schematic view illustrating an installation of the type of figure 1 improved according to the invention, shown under normal thermal conditions;
• the Figure 2B is a schematic view illustrating the installation of the Figure 2A in the presence of a significant and rapid modification of the thermal conditions; and
• the figure 3 is a schematic view similar to that of the Figure 2A showing an interesting variant of embodiment of the installation according to the invention.

Now referring first to the Figure 2A , the installation arranged in accordance with the invention incorporates the elements shown in FIG. figure 1 with further a second tank or auxiliary tank 9.

A hydrostatic connection duct 10 is interposed between the respective bottoms of the main and auxiliary tanks 9. The cryogenic fluid supply duct 5, with its control valve 6, is connected to the auxiliary reservoir 9 and the level gauge 8 is installed in the auxiliary tank 9.

The auxiliary tank 9 is also equipped with an outlet manifold 7b, while the outlet manifold 7a of the main tank 1 is provided with restriction means 11. As illustrated in FIG. Figure 2A , the two collectors 7a and 7b can meet, downstream of the restriction means 11, into a single collector 7.

The auxiliary reservoir 9 is arranged with respect to the main reservoir 1 and is dimensioned so as to receive at least a large part of the cryogenic fluid present in liquid form in the main reservoir 1. The auxiliary reservoir 9 is shifted upwards with respect to the main tank 1.

In normal operation, as shown in Figure 2A the cryogenic fluid in liquid form is received in the auxiliary tank 9 and the transfer gas losses are discharged directly by the collector 7b. Thus, only cryogen in the pure liquid state is delivered by gravity to the main tank 1 through the connecting pipe 10 widely dimensioned, with a negligible pressure drop. The mass flow rate of _normal vaporized cryogen generated in the cryogenic liquid 2 by a thermal load in normal operation is discharged by the collector 7a through the restriction means 11. These are dimensioned so as to allow the normal flow of the gaseous cryogen with low _normal Ap pressure drop which results because of the hydrostatic balance prevailing between the two tanks 1 and 9, a _normal level of .DELTA.h difference between the liquid levels in the respective two auxiliary tanks 9 and main 1 .

The volume of the auxiliary reservoir 9 is such that the liquid 12 that is present there is surmounted by a free volume (that is to say, containing vaporized cryogen) relatively large corresponding at least to the greater part of the liquid cryogen present in the main tank 1.

In the case of a resistive transition of the device 4 or any other thermal disturbance resulting in a large and rapid increase in the thermal load, the cryogenic liquid in the tank 1 vaporizes in a mass flow much higher than it is in normal operation: m _transition >> m _normal . As a result, due to the presence of the restriction means 11 in the outlet manifold 7a which slow the flow of the vaporized cryogen, a significant increase in the pressure drop Δp _transition . Due to the increase in the pressure of the vaporized cryogen in the main tank 1 and the hydrostatic equilibrium between the two tanks, this results in a rapid discharge of the liquid cryogen remaining from the main tank 1 in the auxiliary tank 9, as illustrated. to the Figure 2B . Thus, the hot device 4, which is no longer immersed at least for the most part in the cryogenic liquid, is thermally decoupled therefrom. By its reflux from the main tank to the auxiliary tank, the cryogenic liquid is spared and it is not discharged to the outside and lost as is the case in conventional installations such as that of the figure 1 . When the gas flow in the manifold 7a decreases, the pressure drop in the restriction means 11 also decreases and thus the difference in the liquid levels in the two tanks is reduced until it reaches a point where the transfer of liquid from the auxiliary tank 9 to the main tank 1 can recover. Then the auxiliary tank 9 discharges by gravity into the main tank 1 to return to the normal situation shown in FIG. Figure 2A with the device 4 again completely immersed in the cryogenic liquid.

et donc $${\mathrm{\Delta h}}_{\mathrm{transition}}\mathrm{/}{\mathrm{\Delta h}}_{\mathrm{normal}}\mathrm{=}{\mathrm{\Delta p}}_{\mathrm{transition}}\mathrm{-}{\mathrm{\Delta p}}_{\mathrm{normal}}\mathrm{=}{\left[{\mathrm{m}}_{\mathrm{transition}}\mathrm{/}{\mathrm{m}}_{\mathrm{normal}}\right]}^{\mathrm{2}}$$

Assuming a turbulent gas flow in the outlet manifold 7a and the restriction means 11, one can write: $$\mathrm{.DELTA.h}\mathrm{~}\mathrm{Ap}\mathrm{~}{\mathrm{m}}^{\mathrm{2}}$$

and so $${\mathrm{.DELTA.h}}_{\mathrm{transition}}\mathrm{/}{\mathrm{.DELTA.h}}_{\mathrm{normal}}\mathrm{=}{\mathrm{Ap}}_{\mathrm{transition}}\mathrm{-}{\mathrm{Ap}}_{\mathrm{normal}}\mathrm{=}{\left[{\mathrm{m}}_{\mathrm{transition}}\mathrm{/}{\mathrm{m}}_{\mathrm{normal}}\right]}^{\mathrm{2}}$$

To fix the ideas, assuming a ratio m _transition / _normal m as low as 10, then Δh _transition / Δh _normal is 100, that is to say for example an increase in the difference of the liquid levels of 1 cm to 1 m which easily allows the superconducting device 4 to emerge out of the liquid and the liquid to be backplaced.

It will also be emphasized that the nature and the properties of the cryogenic fluid, whether in the liquid phase or in the vapor phase, do not occur, so that the arrangements according to the invention can be implemented without limitation. It is sufficient only that the outlet manifold 7a and the restriction means 11 are appropriately sized according to the properties of the cryogenic fluid in its liquid and gaseous phases, and also as a function of the thermal loads provided during normal operation.

In the simple embodiment illustrated in Figures 2A and 2B the restriction means 11 comprise a fixed restriction 14 inserted in the conduit 7a. However, other arrangements can be envisaged depending on the mode of operation required for the installation. Thus, the restriction means 11 may comprise, in place of the aforementioned fixed restriction 14, an externally actuated valve 15 as illustrated in FIG. figure 3 . Such an arrangement makes it possible in particular to increase the effectiveness of the liquid cryogen reflux and to control the restart of the transfer of the liquid cryogen to the main tank 1 and the resumption of cooling of the superconducting device 4.

Claims (5)

1. A cryogenic cooling installation for a superconducting device, comprising:

   - a main tank (1) for a two-phase cryogenic fluid in which a superconducting device (4) to be cooled is immersed;

   - a cryogenic fluid supply line (5) operationally associated with the tank (1) in order to supply it with cryogenic fluid;

   - means (6) for controlling the supply of cryogenic fluid, which are placed in said supply line (5); and

   - an auxiliary tank (9);

   - said auxiliary tank (9) being placed relative to the main tank (1) and being dimensioned so as to be able to receive at least most of the cryogenic fluid present in liquid condition (2) in the main tank (1),

   - said cryogenic fluid supply line (5) being connected to the auxiliary tank (9);

   characterized in that it further includes:

   - a hydrostatic connecting line (10) interposed between the respective bottoms of the main and auxiliary tanks (1, 9),

   - an outlet manifold (7a) connected to said main tank (1), and

   - an outlet manifold (7b) connected to the auxiliary tank (9),

   - restrictor means (11) being provided into the outlet manifold (7a) connected to the main tank (1), whereby, in the presence of rapid heating of the superconducting device, cryogenic fluid in the liquid condition which is present in the main tank is discharged, due to the action of the pressure of the vaporized cryogenic fluid, into the auxiliary tank, from which it flows again by gravity into the main tank when the pressure of the vaporized fluid decreases.
2. The installation as claimed in claim 1, characterized in that the auxiliary tank (9) is placed substantially higher than the main tank (1).
3. The installation as claimed in claim 1 or 2,
   characterized in that means (8) for detecting the level of the liquid cryogenic fluid (12) are provided in the auxiliary tank (9).
4. The installation as claimed in any one of claims 1 to 3, characterized in that the restrictor means (11) comprise a restrictor (14).
5. The installation as claimed in any one of claims 1 to 3, characterized in that the restrictor means (11) comprise an externally controlled valve (15).

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