GB2461668A

GB2461668A - Heat pipe and cooling device used in cryotechnology

Info

Publication number: GB2461668A
Application number: GB0919543A
Authority: GB
Inventors: Jens Mueller; Carsten Buehrer; Jan Wiezoreck; Christoph Fuellbier; Ingolf Hahn
Original assignee: Zenergy Power GmbH
Current assignee: Zenergy Power GmbH
Priority date: 2007-06-11
Filing date: 2008-06-05
Publication date: 2010-01-13
Also published as: US20100155034A1; GB0919543D0; WO2008151751A1; DE102007027355A1

Abstract

The invention relates to a heat pipe or a cooling pipe used in cryotechnology, comprising a cladding tube (1) and a chamber (4) which is hermetically enclosed by means of a condensation element (3) on one end of the tube and an evaporation element (2) on the other end of the tube, and filled with a heat transfer medium suitable for cryogenics. The aim of the invention is to be able to cool supraconductive elements or components to the required transition temperature over a short period of cooling time, with high operating safety and in a highly economical manner. To this end, at least one cooling module (20) is built into the chamber (4) between the condensation element (3) and the evaporation element (2). Said cooling module comprises a tubular lateral surface (21) which is partially applied to the inner surface (1') of the cladding tube (1), and is provided with a guiding device (22), at least on the side of the condensation element, for deviating condensed and/or liquid heat transfer media towards the lateral surface (21). The invention also relates to a cooling device comprising a plurality of cooling tubes.

Description

HEAT PIPE AND COOLING DEVICE USED iN CRYOTECHNOLOGY The invention relates to a heat pipe for cryotechnology, with a casing pipe and with a chamber encapsulated hermetically by means of a condensation element at one pipe end and by means of an evaporation element at the other pipe end and filled with heat transfer medium. The invention relates, furthermore, to a cooling device for cryotechnology for the cooling of superconductor components, in particular superconductor coils, such as HIS coils (high-temperature superconductor coils), with at least one heat pipe.

The use of heat pipes, as they are known, is known not only in heat exchanger systems, but, for example, also for the cooling of microprocessors and solar modules or for microelectronics cooling. A heat pipe is a heat exchanger which, using the evaporation heat and condensation heat of a substance, makes it possible to have a high heat flow density. The functioning of a heat pipe is based on causing a heat transfer medium to circulate, preferably solely as a result of gravity, in a hermetically encapsulated pipe, in each case with a heat exchange surface for the heat source and for the heat sink, in order, as a result of the phase transition of the heat transfer medium between liquid and gaseous, to extract heat from the space, material or element to be cooled. For gravity-independent circulation, use can be made in the heat pipe of the capillary action of a shaft. Reference is made, merely by way of an example of the prior art for heat pipes, to EP 483 324 Bi which describes a heat pipe coupled thermally to a solar collector.

When superconductive structural elements, such as, for example, superconductor coils, superconductor generators, linear motors with superconductive coils, superconducting magnets or the like, are employed, it is necessary to cool the superconductive components to a temperature level lying below the transition temperature of the superconductor material. Since a temperature level below about 77 K has to be reached for most superconductive HIS materials, cooling often takes place by means of refrigeration units in the form of cryocoolers with, for example, a closed helium pressure circuit (dry cooling) or in a liquid bath, for example liquid nitrogen (77 K at normal pressure). Conventional low temperature technology, which employs what are known as cryogenic superconductors, even employs for this purpose liquid helium which makes it possible to have an operating temperature of 4.2 K in the liquid bath. Since the aim is to have a temperature level below about - 150°C, numerous different refrigeration units or cryocoolers may be used for cryotechnology, cryogenics or low temperature technology.

Liquid bath cooling, however, has the disadvantage of a high outlay, since a closed and pressure-resistant vessel has to be ensured. If, by contrast, the liquid is allowed to evaporate away, it has to be topped up constantly from a reservoir. The direct contact of a refrigeration unit (cryocooler) with a component to be cooled entails the disadvantage that the discharge of heat takes place via heat conduction in the material, and it is therefore restricted in terms of the distance and the transmittable power or demands the use of a very large amount of additional material which makes practical applications undesirably complicated.

Reference is made, merely as an example of the use of refrigeration units in the form of cryocoolers, combined with a heat conduction pipe, in a superconductive motor, to DE 102 11 363 Al in which, between a secondary part, receiving the superconductive coils, of a motor (rotor) and a refrigeration unit having a cold head, a stationary heat pipe is arranged which projects axially into a lateral cavity co-rotating with the secondary part and which co-operates with a refrigerant (heat transfer medium). The heat transfer medium (refrigerant) consists of a mixture of at least two refrigerant components, the condensed refrigerant being introduced via the heat pipe into the lateral cavity, using a thermosiphon effect, and refrigerant which evaporates in the cavity returning to the condensation unit via the heat pipe. It is known from DE 102 11 363 Al also to employ a heat pipe for cryotechnology.

A conventional heat pipe for heating applications is known from US 2005/02579 18 Al. An installation element is fitted in the chamber of the casing pipe in order to subdivide the casing pipe into an upper and a lower half. The heat transfer medium, which changes its state of aggregation into hot steam at the evaporation element, rises through the installation element up to the condensation element and is precipitated there as condensate at the inner circumference of the casing pipe, the condensed drops which run off downward from the condensation element to the installation element bringing about heat exchange over the entire casing surface of the upper half The installation element serves as a collecting ring, in order to transfer the liquid heat transfer medium into a bridging line which branches off outward and which returns liquid heat transfer medium, along a closed line outside the chamber, to the evaporation element.

The object of the invention is to provide a heat pipe for cryotechnology and a cooling device with corresponding heat pipes, by means of which superconductive elements or components can be cooled to the required transition temperature with high operating reliability and efficiency and in a short cooling time. A further object of the invention is to provide heat pipes, by means of which even superconducting components of greater extent can be cooled.

According to the invention there is provided a heat pipe for cryotechnology, with a casing pipe and with a chamber encapsulated hermetically by means of a condensation element at one pipe end and by means of an evaporation element at the other pipe end and filled with heat transfer medium characterised in that, in the chamber, between the condensation element and the evaporation element, at least one cooling module is installed which partially bears with a tubular surface area against the inner surface of the casing pipe and which is provided at least on the condensation element side with a conducting means in order to guide condensed and/or liquid heat transfer medium to the inside of the surface area of the cooling module.

The liquid or condensed heat transfer medium runs downward along the inside of the surface area of the cooling module, with the result that heat discharge takes place in a directed maimer only in the region of the extent of the surface area. Since the heat pipe according to the invention is to be used for cryotechnology, and since the heat transfer medium employed is a suitable refrigerant for the selected temperature range of cryotechnology, the heat pipe can also be designated as a cold pipe. The cooling module, installed in the heat pipe or cold pipe and bearing only partially in relation to the overall area of the casing pipe against the inner wall of the latter, has the effect that the heat transfer medium or refrigerant causes a cooling of the wall surface solely in specific regions of the casing pipe on account of the direct contact between the surface area of the cooling module and the inner surface of the casing pipe. At the locations where there is contact between the cooling module and casing pipe or at which the cooling module is positioned on the inside, therefore, heat can be discharged in a directed manner, in particular heat from a superconductive component which is connected indirectly or directly to the zone of the casing pipe of the heat pipe or cold pipe. The fl.inctioning of the heat pipe (cold pipe) is based in a way known per se on the fact that the refrigerant which is enclosed hermetically in the cold pipe, and which is preferably a liquefied gas or gas mixture suitable for cryotechnology, evaporates upon the supply of heat and is re-liquefied on the cooled condensation element. The refrigerant which evaporates on warmer regions inside the heat pipe extracts heat from the corresponding zone via the evaporation heat or evaporation enthalpy, with the result that the cooling action is achieved in the region of the cooling modules. In the case of a constant pressure of the refrigerant, the temperature of the refrigerant (boiling temperature) also remains constant during phase transition. It will be appreciated that, in order to operate a heat pipe or cold pipe, the condensation element has to be coupled thermally to a cryocooler, in order to cool the condensation element to a temperature at which gaseous/liquid phase transition takes place for the re-liquefaction of the refrigerant.

In the preferred embodiment, the conducting means in the cooling module is provided with passage slots which open to the inside of the surface area, in order to achieve a directed action upon the surface area by the liquid refrigerant dropping off at the condensation element. In the particularly preferred embodiment, the conducting means is designed as a cone or so as to be funnel-shaped, and it preferably widens from the condensation element in the direction of the surface area. It will be appreciated that each cooling module will normally be at a specific distance from the condensation element.

To order to restrict the cooling action of the casing pipe to a specific zone in a directed manner, it is advantageous, furthermore, if the cooling module is provided on the evaporation element side with a conducting element in order to lead condensed and/or liquid heat transfer medium away from the surface area again. The conducting element may likewise advantageously be designed as a cone or so as to be funnel-shaped. According to an advantageous embodiment, the conducting element may have a sieve-like wall, consist of a perforated plate or be produced from a perforated plate.

The clearances in the sieve or in the perforated plate serve for causing still liquid refrigerant to drop off on the conducting element, in order to supply it to a further cooling module or to the evaporation element at the lower pipe end of the heat pipe.

Alternatively, the conducting element may be provided with run-off slots.

So that a cold pipe according to invention can be manufactured at a relatively low outlay, it is particularly advantageous if the cooling module, together with the conducting means, surface area and conducting element, consists of metal, in particular sheet metal, preferably steel, sheet steel, copper, copper alloy or sheet copper. The cooling module can then be produced by sheet forming, if appropriate without weld seams or the like. To mount a cooling module inside the casing pipe, it is particularly advantageous if the mounting operation is carried out by means of a shrinkage operation, to be precise by the cooling of the cooling module and/or the simultaneous heating of said casing pipe, so that, especially also at the cryogenic temperatures, a reliable positioning of the cooling modules and, at the same time, reliable contacting between the surface area of the cooling module and the inner surface of the casing pipe are ensured.

According to an advantageous embodiment, the cryogenic refrigerant (heat transfer medium) may consist of a mixture of at least two refrigerants having different condensation temperatures, such as, for example, a helium/nitrogen mixture (n-H2) or nitrogen/oxygen mixture suitable for cryotechnology. Alternatively, the refrigerant may consist of a liquefied pure substance gas or an isotope thereof, in particular 4He (liquid helium I), 3He, neon, hydrogen or nitrogen (N2). The advantage of a polyphase refrigerant is that this refrigerant does not have an exact boiling point, but, instead, a boiling range. The thermodynamic equilibrium can then be shifted to the higher-boiling component of the liquid phase, thus bringing about an increase in the boiling point. When a corresponding liquefied heat transfer medium (refrigerant) is heated, phase transition commences when the temperature reaches the boiling temperature of that mixture constituent which has the lower boiling point. Since the particles of this constituent change over to the gas phase to an increased extent, the composition of the mixture changes locally, with the result that the boiling point also changes, until the boiling point of the other component is reached. At the same time, the selected pressure in the heat pipe can be higher or lower in the adaptation to the requirements, so that a fine tuning of the cooling range can thereby also be carried out.

In a particularly preferred embodiment, that side of the condensation element which faces the chamber has a prism-like surface with drop-off tips, the drop-off tips preferably lying in alignment with the passage slots in the cooling module in the S mounted state. This measure, too, serves for the directed supply of the refrigerant liquefied at the condensation element to the conical conducting means of the cooling module and to the passage slots formed there, when the cold pipe is used, standing essentially vertically, and the circulation of the refrigerant takes place as a consequence of gravity. The surfaces of the prisms may also be designed as lamellae in order to enlarge the heat exchange surface. The lamellae in this case stand perpendicularly to the surface, and the tips of the prisms are formed by the lamellae, that is to say the prisms constitute an over-structure.

In order to bring about the circulation of the refrigerant between the cooling modules and the condensation element or between the evaporation element at the lower pipe end and the condensation element at the upper pipe end purely passively by means of gravitational forces, it is particularly advantageous if a shaft is installed which leads from the evaporation element to the condensation element and is preferably laid concentrically to the mid-axis and which, in particular, may be formed by means of a hollow pipe. Gaseous refrigerant can then rise, unimpeded, through the cavity of the shaft or shaft pipe to the condensation element.

A heat pipe according to the invention may have only a single cooling module in the chamber. In the preferred embodiment, however, a plurality of cooling modules are installed in the chamber, so that, by means of one cold pipe, where appropriate, a plurality of superconductive components arranged outside the cold pipe can be cooled to the operating temperature necessary for superconductivity. In the case of a plurality of cooling modules in the chamber, the effect additionally arises whereby each cooling module forms a zone, between which and the condensation element the refrigerant circulates until the zone is cooled to the desired cryogenic temperature level (ideally, for example, about 27 K or 33 K), since only then does liquid refrigerant pass through the perforated plate of the conducting element to the cooling module of the next zone. When a cooling module has reached the temperature level, an approximately constant temperature profile is established between the condensation element and this cooling module, with the result that the condensation zone also increases in size. At the start, the refrigerant will evaporate as far as possible completely in a lower-lying zone, along with a high discharge of heat.

However, on account of the extended condensation zone, this vapor can also condense again, on the cooling module lying above it, into wet vapour or drops, without the vapor having to rise as far as the condensation element. Even in the case of a plurality of cooling modules, it is advantageous to provide a shaft, for which purpose the cooling modules preferably have centrally a leadthrough for a shaft or a hollow shaft pipe. In order to ensure that refrigerant evaporating on the individual cooling modules can rise to the condensation element, the shaft for each cooling module may have at least one radial orifice, above which the conducting means bears sealingly against the hollow pipe.

The central hollow pipe or shaft pipe may be connected to the plurality of cooling modules, in turn, by means of a shrinkage process, in which case, preferably when a heat pipe with a plurality of cooling modules is being manufactured, all the cooling modules are first fastened to the hollow pipe, and then this unit is introduced into the casing pipe, again by means of a shrinkage process. Alternatively, a combination of a shrinkage process with soldering may also be carried out.

According to a further embodiment according to the invention, the casing pipe may be of ring-shaped design and have an inner ring jacket and an outer nng jacket, the cooling module bearing with its surface area against the inner surface of the inner ring jacket or against the inner surface of the outer ring jacket, depending on the positioning of the component to be cooled. The superconductive structural element to be cooled, such as, in particular, a superconductive coil, is expediently positioned on the ring jacket, against the inner surface of which the surface areas of the cooling module or cooling modules come to bear. A ring-shaped heat pipe is suitable especially advantageously for the cooling of large superconductor coils, that is to say coils having large inside diameters. The coils and, correspondingly, the heat pipe may be designed so as to be rotationally symmetrical about a central axis or else may also be of elliptic, oval or racetrack-shaped design. In such embodiments of the heat pipe, a ring-shaped shaft may advantageously be formed between the cooling module or cooling modules and that ring jacket, against the inner surface of which the surface areas of the cooling module or cooling modules do not come to bear. The conducting means and the conducting elements are then correspondingly oriented obliquely in such a way that the conducting means guide condensed heat transfer medium to the surface area on which the coil to be cooled is positioned, and the conducting elements S lead the heat transfer medium away from the surface area again. Preferably, further, if the coil is positioned on the inner jacket of the ring-shaped heat pipe, a thermal insulation may be installed in the centre of the component to be cooled, in order to generate a hot bore at the centre of the coil. So that even long superconductor coils or superconductor elements can be cooled uniformly, a heat distribution element, in particular a copper pipe, may be arranged additionally between the component to be cooled and the ring jacket.

The above-mentioned object is also achieved by means of a cooling device for cryotechnology for the cooling of superconductor components, such as, for example, superconductor coils, in particular HTS coils, which has at least one such heat pipe or cold pipe. The cooling device has a reception pipe, in the inner chamber of which are arranged, according to the invention, a plurality of heat pipes, each with at least one installed cooling module, the condensation elements of which are coupled thermally to a cryocooler and the casing pipes of which are at least partially in contact with the reception pipe. The cooling modules of a plurality of, preferably of all the heat pipes preferably lie in one common plane, and a superconductive component is positioned in the same plane on the outer circumference of the reception pipe. In order to achieve optimal thermal coupling between the cold pipes and the components to be cooled cryogenically, internal thermal coupler elements may be formed in the inner space of the reception pipe at the same installation height as the cooling modules, and/or an external thermal coupler element, such as, for example, a copper ring, may be formed between the superconductive component and the outer jacket of the reception pipe. By means of a cooling device of this type, for example, not only superconductor coils of large inside diameter can be cooled, but at the same time a high cooling capacity can be achieved on account of the multiplicity of heat pipes or cold pipes. Also, by means of such cold pipes, long combinations of coils can be cooled, since a transport of heat over relatively large structural units is ensured.

Where a cooling device is concerned, it is especially advantageous if the heat pipes are anchored with their evaporation elements in a common reception base which is preferably designed to be thermally conductive and which is coupled thermally to a heating device. The heating device then makes it possible to prevent a situation where during cooling, when all the cooling modules have cooled the corresponding portion of the casing pipe to the desired temperature and themselves have the cryogenic temperature, liquid refrigerant collecting at the foot of the heat pipe becomes iced up since the additional supply of heat then evaporates the refrigerant, the vapour rising to the condensation element via the shaft due to convection or to a capillary action.

An advantageous field of use of corresponding cooling devices could be, for example, generators provided with superconductor coils for the conversion of ocean waves or ocean flows into current. Another advantageous application is the cooling of an elongate polysolenoid linear motor or of an elongate and/or large-volume coil of a magnet for current limiters.

Further advantages and embodiments of the invention will be gathered from the following description of advantageous exemplary embodiments shown in the drawing, in which: fig. 1 shows a longitudinal section through a heat pipe according to the invention for cryotechnology, partially cut away; fig. 2 shows a side view of an exemplary embodiment of a cooling module for a heat pipe according to the invention; fig. 3 shows in perspective an exemplary embodiment of a condensation element for a heat pipe according to the invention; fig. 4 shows a cooling device with heat pipes according to the invention in a side view; fig. 5 shows diagrammatically a longitudinal section through the cooling device according to fig. 4, partially cut away;

I

fig. 6 shows a top view of the upper head of the cooling device according to figs. 4 and 5; and fig. 7 shows diagrammatically a longitudinal section through a ring-shaped heat pipe according to a further exemplary embodiment for the cooling of large HTS coils.

The heat pipe or cold pipe for cryotechnology, designated in fig. 1 as a whole by reference symbol 10, has a cylindrical casing pipe 1 as a connecting pipe, which is closed at its lower end by means of an evaporation plate 2, as an evaporation element, and at its upper end by means of a condensation plate 3, as a condensation element or condenser element. The connection between the pipe jacket of the casing pipe 1, the condensation plate 2 and the evaporation plate 3 is made in such a way that a chamber 4 encapsulated hermetically with respect to the surroundings is obtained inside the casing pipe 1. So that the heat pipe or cold pipe 10 shown in fig. 1 can be used for cryotechnology, that is to say for a temperature range below about -150°C, the chamber 4 is filled with a suitable cryogenic refrigerant, not illustrated, as a heat transfer medium, such as, in particular, 4He with a boiling point of about 4.23 K (Kelvin) at 1.013 bar, n-H2 with a boiling point of about 20.4 K or N2 with a boiling point of about 77.35 K. The cryogenic refrigerant may also consist of another liquid pure substance gas or gas mixture. To operate the heat pipe 10, the condensation plate 3 is connected thermally to a suitable cryocooler, not illustrated, by means of which the condensation element 3 can be cooled to a temperature at which gaseous refrigerant enclosed in the chamber 4 changes over to the liquid state of aggregation.

The chamber 4 is preferably filled with the refrigerant at a pressure which is higher than atmospheric pressure, and the heat pipe 10 and all the connections inside the heat pipe 10 can withstand high excess pressure. The heat pipe 10 is preferably designed for standing installation, in which the mid-axis of the jacket pipe 1 stands vertically or assumes a small angle with respect to the perpendicular or vertical of< 30°.

According to the invention, at least one cooling module, designated as a whole by 20, which is illustrated in detail in fig. 2 and which is now first referred to is installed in the chamber 4. The cooling module 20 consisting preferably of metal, such as steel or copper or copper alloy, has a markedly smaller axial length than the casing pipe and has a cylindrical tubular surface area 21 which has adjoining it upward a first cone or conical element 22 which, starting from the transition 23 between the surface area 21 and the conical element 22, tapers upward conically or in a funnel-shaped manner. The conical surface, widening toward the surface area 21, of the cone 22 forms a conducting means in order to guide liquid or liquefied refrigerant, which falls down from above onto the conical element 22 by virtue of the gravitational forces, toward the surface area 21. The conducting action of the conical element 22 is reinforced in that a plurality of, for example four to eight conducting slots 24 are formed, distributed over the circumference of the conical element 22, and extend as far as the margin or transition 23, and make it possible that the liquid refrigerant dropping down from above can pass through the conducting slots 24, designed as orifices, to the inner surface 21' (fig. 1) of the surface area 21, in order to flow off downward there. The conical element 22 issues at the top in a truncated manner into a round dome 25 which forms a circular orifice for a shaft pipe or hollow pipe 5 (fig. 1) which is positioned concentrically to the axis of the casing pipe 1 of the heat pipe 10 and which extends essentially over the entire height of the heat pipe 10.

The surface area 21 has adjoining it downward a second conical element 26 which, in the exemplary embodiment shown, is produced from a sieve plate or the like, has numerous sieve holes 27 and tapers conically from the lower cylindrical margin 28 of the surface area toward the mid-axis. The second conical element 26, too, ends in a truncated manner in a through bore 29 for the passage of the hollow pipe or shaft pipe 5. The clearances or holes 27 in the sieve plate of the conical element 26 serve for conducting still liquid refrigerant away or further on downward, so that liquid refrigerant cannot build up inside an individual cooling module 20. The cone 22 forming the conducting means has essentially the same dimensions as the cone forming the conducting element, but is oriented conversely, in order to achieve an inflow of liquid refrigerant to the casing pipe 1 or a flow away towards the axis and at the same time to guide a stream of gaseous refrigerant inside the cones toward the mid-axis.

In a heat pipe 10 according to the invention, at least one corresponding cooling module 20 is arranged between the evaporation plate 2 closing the lower pipe end of the casing pipe 1 and the condensation plate 3 closing the upper pipe end and is inserted into the chamber 4 in such a way that the surface area 21 bears areally with its outside all around against the inner surface 1' of the jacket pipe 1. Areal bearing contact is preferably brought about by means of a press fit which is achieved as a result of a shrinkage of the cooling module 20 into the jacket pipe 1, in that, for example, for the shrinkage process the jacket pipe 1 is heated and at the same time the cooling module 20 is cooled in order to cause the cooling module 20 and casing pipe ito be joined together as a result of contraction or expansion.

What is achieved by the cooling module 20 installed in the heat pipe 10 is that liquid refrigerant is routed in a directed manner onto the surface area 21 of each cooling module 20, with the result that heat can be discharged at the casing pipe 1 into that region in which the cooling module 20 bears with its surface area 21 against the inner surface 1' of the casing pipe. A superconductive structural element, such as, for example, a superconductive coil, can therefore be positioned on the outer circumference of the jacket pipe 1 of the heat pipe or cold pipe 10, in a region which lies in alignment with the surface area of the cooling module 20, with the result that a liquid refrigerant supplied to this contact zone inside the chamber 4 of the heat pipe can discharge heat in a directed manner and effectively from the superconductor components or superconductive coils, so that these are operated below the transition temperatures of the superconductive material. In this case, for heat discharge, the evaporation enthalpy of the refrigerant is utilised, which the refrigerant requires upon phase transition between the liquid and gaseous states of aggregation. Installing the cooling modules 20 in the cold pipe 10 has the particular effect that the maximum cooling capacity is provided in a limited manner, within the shortest possible time, in that region in which superconductive structural elements are positioned on the outer circumference of the heat pipe.

In order to allow an optimal circulation of the refrigerant inside the chamber 4 in the heat pipe or cold pipe 10, the hollow pipe 5 forming the shaft has, essentially directly below the dome 25 of the upper conical element 22 having the passage slots 24, radial passages 6 of sufficient size, through which refrigerant which has changed over to the gaseous state of aggregation inside a cooling module 20 can flow over into the inner pipe 7 of the shaft pipe 5 and be supplied from there in gaseous form to the condensation plate 3 cooled by means of the cryocooler. This, too, is assisted by the funnel shape or conical shape of the cooling module 20.

Admittedly, fig. 1 shows only one cooling module 20 inside the chamber 4 of the cold pipe 10. However, a plurality of identical cooling modules 20 are preferably arranged, if appropriate distributed uniformly, over the height of the cold pipe 10, liquid refrigerant dropping down from the condensation plate 3 only onto the cooling module 20 uppermost inside the chamber 4 and directly adjacent to the condensation element 3, while liquid refrigerant drops down onto the conducting means or conical elements 22 of the following cooling modules and passes through the holes 27 in the lower conical element 26. The evaporation plate 2 at the lower end of the heat pipe 10 comes into play when the lowest cooling module 20 inside the chamber 4 also allows still liquid refrigerant to pass through downward. In order to prevent an accumulation of liquid refrigerant at the foot or bottom of the cold pipe 10, the evaporation plate 2 may be coupled thermally to a heating device or the like which prevents the liquid refrigerant from icing up at the foot of the cold pipe 10. The refrigerant which has changed over to the gaseous state of aggregation at the evaporation plate 2 can in this case flow over into the shaft inner pipe 7 through radial entrances 8 at the foot of the hollow pipe 5 and flow over from there to the condensation plate 3. For the radial slots 8, it is, where appropriate, sufficient to arrange the foot portion 9 of the shaft pipe 5 at a suitable distance from the evaporation plate 2 or to support it by means of intermediate webs on said evaporation plate or on the casing pipe 1. Before the cooling modules 20 are mounted inside the chamber 4 of the casing pipe 1, preferably all the cooling modules 20 are shrunk onto the hollow pipe 5 by means of a shrinkage process, before the composite structure comprising the shaft pipe 5 and cooling modules 20 is inserted as a unit into the casing pipe 1, making use of thermal expansion/shrinkage.

Fig. 3 shows an advantageous exemplary embodiment of a condensation plate 3 with as large a surface as possible, in order to maximise the contact area for gaseous refrigerant and at the same time to achieve a directed dropping off or falling down of reliquefied or liquefied refrigerant. For this purpose, the condensation plate 3 has on its underside a prism-like surface 13 with a number of drop-off tips 14 which preferably corresponds to the number of passage slots 24 in the uppermost cooling module 20. Each drop-off tip may have, for example, four planar flanks as prism surfaces. The thermal coupling of the condensation plate 3 to the cold head of a cryocooler may take place, for example, via a copper bar or the like as a thermal bus, or the cold head of a cryocooler may be connected directly to the condensation plate 3 of the heat pipe or cold pipe 10.

Figs. 4 to 6 show an example of an application of the use of a plurality of cold pipes within a cooling device designated as a whole by 100. Each cold pipe 10 has in this case a set-up, such as was described with reference to figs. 1 to 3, and each cold pipe 10 has a multiplicity of cooling modules 20 over its height. The individual cold pipes 10 are in this case designed in such a way that, in all the cold pipes 10, the cooling modules 20 are positioned at the same distance from the condensation plate 3 or the evaporation plate of each cold pipe 10.

In the cooling device 100, overall six cold pipes 10 are arranged at an equal angular spacing on a reference circle about a central axis Z of the cooling device 100.

The outer surfaces of the casing pipe 1 of each cold pipe 10 preferably bear directly against a reception pipe 80 which is positioned concentrically to the central axis Z and which encloses all the cold pipes 10 over its entire height. In the inner space of this reception pipe 80, preferably solely in those regions in which the cooling modules 20 are arranged inside the cold pipes 10, on each cooling module plane an inner thermal conductor 81 is positioned as a thermal coupling element which partially brings about direct thermal contact between the entire outer surface of the casing pipe 1 of the individual cooling pipes 10 and the inner surface area 82 of the reception pipe 80, in order to achieve the highest possible heat transmission between the reception pipe 80 and the cooling pipes 10 in that region in which the individual cooling modules 20 are positioned. In the exemplary embodiment shown, outer thermal coupling rings 85 are positioned on those regions of the outer jacket 83 of the reception pipe 80 which lie in alignment with the cooling modules 20 and the inner thermal conductor elements 81, ring-shaped superconductor coils 90 bearing here with their inner ring against said coupling rings.

The superconductor coils 90 can be cooled to below the transition temperature of the superconductive material by means of the respective cooling modules 20 in the cold pipes 10. All the condensation plates 3 of the total of six cold pipes 10 here are connected to one another via a coupling ring 70, to which the cold head 75 of a cryocooler, not illustrated in any more detail, is connected. The reception pipe 80 for the cold pipes 10 is positioned, in turn, inside a tubular jacket 71 which is preferably designed as a cryostatic container. In the cooling device 100, all the cold pipes 10 are arranged with their lower ends closed by means of the evaporation plates in a reception base 72 or are coupled thermally to the latter which is preferably assigned to a heating device, in order to prevent a situation where the refrigerant may freeze inside the individual hermetically encapsulated cold pipes 10.

Fig. 7 shows an exemplary embodiment of a heat pipe 210 for cooling a large and long superconductor coil 290. The heat pipe 210 is designed here to be rotationally symmetric about the central axis Z' and has a ring-shaped casing pipe 201 with an inner ring jacket 261 and with an outer ring jacket 262. A ring-shaped is condensation plate 203 with drop-off tips 214 on its underside is fastened to the upper end of the two ring jackets of the casing pipe 201 and a ring-shaped evaporation plate 202 is fastened at the lower end in such a way as to form in the casing pipe 201 a hermetically encapsulated chamber 204 which is filled with a suitable cryogenic refrigerant. A plurality of cooling modules 220, only one of which is illustrated here, are installed in the ring-shaped chamber 4. Each cooling module 220 bears with a cylindrical surface area 221 against the inner surface 261' of the inner ring jacket 261.

Above each surface area 221 is formed an oblique conducting means 222 which runs in the form of a ring around the inner ring jacket 261 and which guides liquid or condensed refrigerant to the surface area 221. Below each surface area 221, the cooling module 220 has an oblique conducting wall 226 which leads liquid refrigerant away from the surface area 221. The conducting wall 226 is provided with sieve holes 227 so that refrigerant can drop off downward to a further cooling module or to the evaporation plate 204. Between the cooling modules 220 and the outer ring jacket 262 is arranged a ring-shaped intermediate wall 265, by means of which a ring-shaped shaft 207 is formed inside the chamber 4 between the cooling modules 220 and the outer ring jacket 262. The intermediate wall 265 is spaced apart from the condensation plate 203 and the evaporation plate 204, so that liquid and/or gaseous refrigerant can flow over into that part of the chamber 204 in which the cooling modules are arranged. The drop-off tips 214 on the condensation plate 203 lie correspondingly radially within the intermediate wall 265. The intermediate wall 265 is provided with passages 206 directly below the contact point between the conducting ring 222, running obliquely upward here at about 45°, and its contact point with the intermediate wall 265, so that evaporating refrigerant can rise upward inside the cooling modules 220 via the shaft to the condensation plate 203. In the exemplary embodiment shown, the superconductor coil 290 to be cooled is positioned inside the inner pipe jacket 261. In order to achieve good heat conduction between the cooling modules 220 and the coil 290 to be cooled, thermal coupling rings 281 are arranged, opposite the surface areas 221, outside the casing pipe 201. Since the coil 290 extends over almost the entire height of the heat pipe 210, a copper pipe 285 as a heat distribution element bears against the outside of the coil 290 and, in turn, at a plurality of locations is in each case in contact with the coupling rings 281.

A person skilled in the art can gather from the above description numerous is modifications which are to come within the scope of protection of the accompanying claims. The figures show only preferred exemplary embodiments, and, in particular, the number of cooling modules in a cold pipe or heat pipe, the number of cold pipes in a refrigerating device and the thermal coupling between a cryocooler and the condensation elements of the individual cold pipes may vary, without departing from the scope of protection of the accompanying claims. Various pure substance gases, gases or gas mixtures which are suitable for cryotechnology or cryogenics may also be used as refrigerant. The superconductive structural elements and components may be fastened directly to the cold pipes or the reception pipe of the cooling device, or indirectly to these, or may be coupled thermally to these. The pipes may additionally be provided with safety valves for excess pressure, pumping-off valves for generating a vacuum and/or access valves for the introduction of cooling media. In the ring-shaped heat pipe, a thermal insulation could be installed in the centre of the coil, thus giving rise at the centre of the coil to a heat bore. Alternatively, the coil could also bear on the outside of the outer ring jacket. The conducting means and conducting wall of the cooling modules would then be inclined correspondingly obliquely with respect to the outer ring jacket and the surface area would bear against this. The ring-shaped heat pipe could also be of oval or suchlike design. Ducts or gaps could also be formed between the outside of the surface area of the cooling modules and the inner surface in order to allow condensed or liquid heat transfer mediumlrefrigerant to flow through these ducts or gaps in the region of the cooling modules and then to guide it away from the inner surface again by means of suitable devices, such as drop-off rings, and lead it to the inner surface again only in the region of the following cooling module. In this case, the entire heat transfer medium could also flow in each case through only the ducts or gaps.

Claims

CLAIMS: 1. A heat pipe for cryotechnology, with a casing pipe (1; 201) and with a chamber (4; 204) encapsulated hermetically by means of a condensation element (3; 203) at one pipe end and by means of an evaporation element (2; 202) at the other pipe end and filled with heat transfer medium, characterised in that, in the chamber (4; 204), between the condensation element (3; 203) and the evaporation element (2; 202), at least one cooling module (20; 220) is installed which partially bears with a tubular surface area (21; 221) against the inner surface (1'; 261') of the casing pipe (1; 201) and which is provided at least on the condensation element side with a conducting means (22; 222) in order to guide condensed and/or liquid heat transfer medium to the inside (21', 261') of the surface area (21; 221) of the cooling module (20; 220).
2. A heat pipe as claimed in claim 1, characterised in that the conducting means (22) is provided with passage slots (24) which open out to the inside (21') of the surface area (21), and/or that the conducting means (22) is designed as a cone or so as to be funnel-shaped.
3. A heat pipe as claimed in either one of claims 1 and 2, charactensed in that the cooling module (20) is provided on the evaporation element side with a conducting element (26) in order to lead condensed and/or liquid heat transfer medium away from the surface area (21), the conducting element (26) preferably being designed as a cone or being designed funnel-shaped.
4. A heat pipe as claimed in claim 3, characterised in that the conducting element (26) is designed as a sieve or consists of or is formed from a perforated plate.
5. A heat pipe as claimed in claim 3 or 4, characterised in that the conducting element is provided with run-off slots preferably running radially.
6. A heat pipe as claimed in one of claims 2 to 5, characterised in that the cooling module (20), together with the conducting means (22), surface area (21) and conducting element (26), consists of metal, in particular sheet metal, preferably sheet copper or copper alloy or sheet steel.
7. A heat pipe as claimed in one of claims 1 to 8, characterised in that the cooling module (20) is inserted into the casing pipe (1) by means of a shrinkage process by the cooling of the cooling module and/or by the heating of said casing pipe.
8. A heat pipe as claimed in one of claims 1 to 7, characterised in that the heat transfer medium is a mixture of at least two refrigerants having different condensation temperatures, the heat transfer medium preferably being a helium/nitrogen mixture.
9. A heat pipe as claimed in one of claims 1 to 8, characterised in that that side of the condensation element (3) which faces the chamber (4) has a prism-like surface (13) with drop-off tips (14) or a prism-like overstructure with drop-off tips, the drop-off tips (14) preferably lying in alignment or virtually in alignment with the passage slots (24) in the cooling module (20).
10. A heat pipe as claimed in one of claims 1 to 9, charactensed by a shaft (7) which leads from the evaporation element (2) to the condensation element (3) and is preferably laid concentrically to the mid-axis and which, in particular, is formed by means of a hollow pipe (5).
11. A heat pipe as claimed in one of claims ito 10, characterised in that a plurality of cooling modules (20) are installed in the chamber (4).
12. A heat pipe as claimed in claim 11, characterised in that the cooling modules (20) have centrally a leadthrough for a shaft or a hollow pipe (5), the hollow pipe (5) being provided preferably for each cooling module (20) with at least one radial orifice (6), above which the conducting means (22) bears against the hollow pipe (5).
13. A heat pipe as claimed in one of claims 1 to 12, characterised in that a superconductive structural element, such as, in particular, a superconductive coil, is positioned on the outer circumference of the casing pipe (1) in the same installation position as the surface area (21) of the cooling module (20).
14. A heat pipe as claimed in one of claims 1 to 13, characterised in that the casing pipe (201) is of ring-shaped design and has an inner ring jacket (261) and an outer ring jacket (262), the cooling module (220) bearing with its surface area (221) against the inner surface (261') of the inner ring jacket (261) or against the inner surface of the outer ring jacket.
15. A heat pipe as claimed in claim 14, characterised in that the superconductive structural element, such as, in particular, a superconductive coil (290), to be cooled is positioned on the ring jacket (261), against the inner surface of which the surface areas of the cooling module or cooling modules come to bear.
16. A heat pipe as claimed in either one of claims 14 and 15, characterised in that a ring-shaped shaft (207) is formed between the cooling module (220) and that ring jacket (262), against the inner surface of which the surface areas of the cooling module or cooling modules do not come to bear.
17. A heat pipe as claimed in one of claims 1 to 16, characterised in that a thermal insulation for achieving a hot bore is installed in the centre of the component to be cooled, and/or in that a heat distribution element (285), in particular a copper pipe, is arranged between the component (290) to be cooled and the ring jacket (261).
18. A cooling device for cryotechnology for the cooling of superconductor components or superconductor coils, in particular HTS coils, with at least one heat pipe as claimed in one of claims 1 to 17, characterised in that the cooling device has a reception pipe (80), in the inner space (84) of which are arranged a plurality of heat pipes (10), the condensation elements (3) of which are coupled thermally to a cryocooler (75) and the casing pipes (1) of which are at least partially in contact with the reception pipe (80), the cooling modules (20) of a plurality of, preferably of all the heat pipes (10) lying in one common plane, and a superconductive component (90) being positioned in the same plane on the outer circumference (83) of the reception pipe (80).
19. A cooling device as claimed in claim 18, characterised in that internal thermal conducting elements (81) are formed in the inner space (84) of the reception pipe (80) at the same installation height as the cooling modules (20), and/or an external thermal conductor (85) is formed between the superconductive component (90) and the outer jacket (83) of the reception pipe (80).
20. A cooling device as claimed in claim 18 or 19, characterised in that the heat pipes (10) are anchored with their evaporation elements in a common reception base (72) which is preferably designed to be thermally conductive and which is coupled thermally to a heating device.