DE202021102764U1 - Assembly for forming a device for heat exchange between two solids - Google Patents

Abstract

Assembly for forming a device for heat exchange between two solid bodies, at least comprising a first solid body for thermal connection (18) and a component (17) to be cooled as a second solid body, the component (17) to be cooled having a threaded pin (1) with an external thread ( 6) or is formed as a threaded pin (6) and can be screwed to a further solid body which has a complementary internal thread (7) and wherein the further solid body either corresponds to the first solid body (18) or a third solid body which is a ring (3) which can be screwed separately to the first solid body (18).

Description

The invention relates to an assembly for forming a device for heat exchange between two solid bodies, as is often used in all areas of technology in which a connection for transferring or dissipating heat is provided between different components, in particular in cryostats .

description

The invention is used in particular in cryostats, although it can also be used in other devices. Cryostats are devices in which defined, spatially limited areas or components are cooled to a predetermined, relatively low temperature, i.e. there is a heat exchange between these areas / components with the environment, which is implemented with selected means. Contrary to the usual practices in the field of heat transport, terms such as "cold transport" and the like are used in the field of cryostat technology and refrigeration technology. In the following, the terms of heat transport or heat exchange or also heat conduction and heat are used in this description, which always include (according to the laws of thermodynamics) that there is heating in one direction and cooling in the opposite direction at the same time , up to equilibrium.

The means with which the heat exchange in cryostats takes place in order to achieve the relatively low temperatures in the intended areas / components are varied. Relevant means and methods are presented in the review article by B. Baudouy (Heat Transfer and Cooling Techniques at Low Temperature, CERN Yellow Report; CERN-2014-005, pp. 329-352). A cryostat with indirect heat exchange is particularly relevant for the present invention, i.e. the heat exchange takes place on the component to be cooled via a thermal link and not directly via a coolant. The thermal connection is generally provided at one end with an end piece as a connecting piece which is associated with the thermal connection and is connected to a component to be cooled.

A thermal connection in cryostats is usually formed from twisted (braided) strands of copper wires (threads), also called copper braid, or aluminum wires or foils, at the ends of which connecting pieces made of copper or copper alloys or other materials are arranged.

In particular, high-purity copper, so-called OFHC copper (from English Oxygen-Free High-Conductivity Cupper) with a purity> 99.95%, which has particularly good thermal conductivity, is used in cryostats. For more effective cooling below 20 K, a purity of> 99.999% is indicated.

The components to be cooled in the mentioned cryostats are mostly so-called sample holders, in which selected materials arranged there are examined for their physical properties at low temperatures (<200 K, in particular <77 K and especially <4 K) in the cryostat.

The sample holders are also made of copper, for example. Other materials, e.g. sapphire, are also used.

The connection between the sample holder (component to be cooled) and the end piece of the thermal connection is decisive for the heat exchange between the two solids. The main parameters here are the size of the contact area between the solid bodies, the intimacy of the contact and the thermal conductivity of the materials used. The connection should withstand thermal and mechanical stress, in particular at the low temperatures advised by the cryostat.

In the U.S. 3,807,188 the heat exchange takes place via a bellows filled with liquid metal between an end piece (here the so-called "cold finger") and a component to be cooled, in which the metal solidifies during cooling, thus creating an intimate connection between the parts.

In the U.S. 3,999,403 the connection is made via an elastic bellows made of metal, whereby a paste with high thermal conductivity is applied in addition to improve the heat transfer.

Another example of a device for exchanging heat in cryostats is shown in FIG U.S. 4,450,693 given, in which a plug connection for heat exchange is pressed with a spring for better contact. Here, too, the heat exchange is optimized with a paste with high thermal conductivity.

In article 1 by G. Authelet et al. (Conceptual design of a cryogen-free µMRI device, IOP Conference Series: Material Science and Engineering 278, 2017, 012122 - 2-7) corresponds to the generic connection of the device for heat exchange of claim 1. This is by a simple contact between a copper plate with flange as the end of the thermal Connection and a sample carrier, realized as a component to be cooled, made of sapphire.

Object of the invention

The object of the invention is to provide a device for heat exchange between two solid bodies with which an improved heat exchange is achieved compared to the prior art and at the same time it is suitable for vacuum and improved stability and flexibility.

The object is achieved by the subject matter of claim 1. Advantageous refinements are the subject matter of the subclaims.

The subject matter of claim 1 relates to an assembly which, when assembled, forms a device for heat exchange between two solid bodies. The assembly comprises at least one end piece of a thermal connection as a first solid body and a component to be cooled as a second solid body, which together form the assembly, which consists of the two or more individual pieces and is intended to form a unit or, when assembled, forms a unit . The fact that it is an assembly forms an advantage of the invention, since it can be mounted reversibly. The heat exchange takes place at least between the end piece of the thermal connection and the component to be cooled.

und O_Gew.= Oberfläche des Gewindes, n = Anzahl der Gewindegänge; A_aussen = Fläche des Querschnitts der gesamten Schraube; A_Kern = Fläche des Kerndurchmessers der Schraube. Die Multiplikation mit 2 resultiert aus dem Umstand, dass jeder Gewindegang eine Ober- und Unterseite hat. Die Beziehung gilt für zylindrische Schrauben. Der Einfluss der Neigungen auf den Oberflächen des Gewindes ist vernachlässigbar und bleibt unberücksichtigt. Falls die Schrauben kegelig (konisch) ausgebildet sind, muss die Gleichung angepasst werden. Ein komplementäres Innengewinde weist entsprechend die gleiche Fläche auf.The component to be cooled has at least one threaded pin with an external thread. The threaded pin can also be addressed as the shaft of a screw. The thread can be designed as a partial or full thread. On the one hand, the threaded pin can be designed as protruding from the component to be cooled and, on the other hand, the entire component itself can form a threaded pin. For use in a cryostat, in particular along the thread axis, the component to be cooled has an end which is provided for receiving a sample or has a sample receptacle and can be specially shaped for this purpose. The component to be cooled with the threaded pin or as a threaded pin with an external thread is advantageously made from one piece. It is also advantageous to design the thread with a deep thread cut and a large number of threads. The deeper the thread cuts and the more threads, the higher the area F _Gew. , Which is formed by the thread, according to: $${\mathrm{F.}}_{Gew.}=2\cdot O_{Gew}\text{with}{O}_{Gew}=n\cdot \left({\mathrm{A.}}_{aussen}-{\mathrm{A.}}_{Kern}\right)$$

and O _Gew. = surface of the thread, n = number of threads; A _outside = area of the cross section of the entire screw; A _core = area of the core diameter of the screw. The multiplication by 2 results from the fact that every thread turn has a top and a bottom. The relationship applies to cylindrical screws. The influence of the inclinations on the surface of the thread is negligible and is not taken into account. If the screws are tapered (conical), the equation must be adapted. A complementary internal thread accordingly has the same area.

The component to be cooled (second solid body) can be screwed to a further solid body which has an internal thread complementary to the external thread of the threaded pin of the component to be cooled. This further solid body corresponds either to the first solid body, ie a screw connection takes place with the end piece of the thermal connection, or the component to be cooled can be screwed to a third solid body as a further component of the assembly, which corresponds to a ring. According to one embodiment, the ring is advantageously designed as a clamping ring. The ability to generate increased contact pressure via the clamping ring in addition to the screw connection increases the stability of the connection and the intimacy of the contact. The ring / clamping ring, in turn, can be screwed to the end piece of the thermal connection (first solid body). The ring or clamping ring can also correspond to a sleeve or be elongated as a cylinder. It is advantageous for the invention if the individual parts of the assembly are designed to be flat and smooth on their smooth contact surfaces and have the lowest possible roughness. The counterpart, ring / clamping ring or end piece of the thermal connection to the threaded pin of the component to be cooled is equipped with an internal thread complementary to the thread of the threaded pin, which is able to accommodate the threaded pin in a form-fitting manner, i.e. in particular the depth of the internal thread is equal to the length of the threaded pin adapted so that the threaded pin can be screwed into the internal thread up to the end of the internal thread, resulting in a complete form fit. In particular, the internal thread in the ring or clamping ring is designed as a through hole, so that the threaded pin can be screwed into the through hole in such a way that the end of the threaded pin is flush with a base of the ring or clamping ring, as corresponds to an embodiment. The surface formed in this way from a base of the ring or clamping ring and the end of the threaded pin or the base of the ring or clamping ring opposite the internal thread forms the end face of the connection, which is connected to the end piece of the thermal connection to form of the thermal contact can be connected, in particular screwed.

It should be noted that the clamping ring in particular is advantageous for the device, since it forms a lateral, additional thermal contact with the threaded pin that is more effective than the simple ring due to the contact pressure via the clamping and the fixation is improved. The latter reduces possible rotation and unscrewing of the clamping ring from the threaded pin, which is caused by torques that act on the device, e.g. the spring effects of a tight copper braid.

The design of the component to be cooled with a threaded pin or as a threaded pin and the complementary counterpart or internal thread in a further component (further or first or third solid body) of the assembly results in the advantage of the invention over the prior art. The connection via the thread means a more intimate contact compared to a flat contact surface, in which the depth of the thread cut and the distance between the threads results in a significantly larger contact surface, which also ensures high stability and at the same time contact pressure via the form-fitting screw connection. The invention is also advantageous with regard to the fact that the contact surface available through the component to be cooled can be enlarged as desired. It should be noted here, however, that increasing the contact area beyond a certain level is not beneficial. This is due to the fact that the maximum heat conduction of the thermal connection is limited by the heat conduction of the threaded pin and / or the copper braid (i.e. by their cross-sections / diameter). This degree of heat transfer can be calculated if necessary. The enlarged contact surface is formed, on the one hand, by the thread and, on the other hand, when screwed into the ring, additionally by the contact surface added by the ring on the end face. The screw connection also increases the stability. Screwing the components together in the manner according to the invention also allows the component to be cooled and the thermal connection to be connected coaxially even with relatively small, in particular thin, components to be cooled in relation to the end piece of the thermal connection. The coaxial connection brings about an improved resistance to torsion around the connection point. The proportionality relates to the area available through the end piece of the thermal connection for the formation of a thermal contact.

The creation of the connection between the solid bodies via the screw connection also makes the additional use of contact means superfluous and thus creates better suitability for vacuum.

In the event that the assembly comprises a ring or clamping ring, this is attached to the end face, i.e. with the thread axis of the component to be cooled, perpendicular to the contact surface of the end piece of the thermal connection. The connection can advantageously be implemented as a screw connection, since high contact pressures can be achieved by screwing. Other connections, such as those via terminals, are not excluded.

All materials are to be selected according to the type of application, preferably those that have a high thermal conductivity and can be processed, such as metals, in particular copper, OFHC copper, silver, copper alloys and here in particular those with tin, zinc, nickel or lead as a component , as well as aluminum and aluminum alloys or gold.

1. 1. durch die Stirnfläche des Gewindestifts und
2. 2. seitlich in den Gewindestift, durch das Gewinde des Klemmrings bzw. Rings,

und somit erhöht ist.Another advantage of the invention is, in particular, a heat transfer or heat exchange, which takes place via two channels from the component to be cooled with the thermal connection:

1. 1. through the face of the threaded pin and
2. 2. laterally into the threaded pin, through the thread of the clamping ring or ring,

and thus is increased.

Embodiments

The invention is explained in more detail below in two figures and an exemplary embodiment.

• 1 Schematische Ansicht der Bauteile einer erfindungsgemäßen Baugruppe zur Bildung einer Vorrichtung zum Wärmeaustausch zwischen zwei Festkörpern gemäß einem Ausführungsbeispiel in einzelnen Bauteilen.
• 2 Die Bauteile der Baugruppe des Ausführungsbeispiels gemäß 1 zusammengesetzt.

The figure shows:

• 1 Schematic view of the components of an assembly according to the invention for forming a device for heat exchange between two solid bodies according to an exemplary embodiment in individual components.
• 2 The components of the assembly of the embodiment according to 1 composed.

An exemplary embodiment of an assembly according to the invention for forming a device for exchanging heat between two solids is shown in FIG 1 schematically for the assembly in components and assembled in the 2 shown. In the exemplary embodiment, the assembly is formed from a component to be cooled 17th (second solid body), which has a threaded pin 1 with a thread 6th has at one end and a sample holder 16 at the other end. Furthermore, a ring, which in the embodiment as a clamping ring 3 (in the Embodiment of further and third solid bodies) is executed. The clamping ring 3 instructs on the thread 6th of the threaded pin 1 complementary internal thread 7th on. The clamping ring is by closing an axial slot 15th by screwing the screws 11 with their complementary drill holes 10 to tension. The screw connection of the threaded pin 1 with the clamping ring 3 should be in a not fully closed position of the clamping ring 3 respectively. The clamping ring also has four drill holes 8th for a screw connection with the thermal connection 18th on their front side 13th on. The thermal connection 18th (first solid body) is formed from a copper braid 4th (only shown schematically), an end piece 2 and the cold finger 5 (English cold finger) of the cryostat. The thermal connection between stranded copper 4th and tail 2 is realized in an advantageous manner as a press connection or alternatively as a welded or soldered connection. In the end piece 2 are four holes with screws 9 provided to this with the clamping ring 3 and the threaded pin that may be screwed in 1 connect to. The contact between the clamping ring 3 and the end of the thermal connection 2 takes place over the face of the clamping ring 13th and the contact area 14th of the end piece 2 the thermal connection 18th as well as the front 12th of the threaded pin instead. The end-face contact surfaces are advantageously to be polished, in particular to a roughness value of 0.01 R _a . There is also the lateral, lateral thermal contact of the threaded pin 1 with the clamping ring 3 . The front side 12th of the threaded pin and the face 13th of the clamping ring 3 should be on one level. The threaded pin can do this 1 in the clamping ring 3 screwed in if this is with the end piece 2 the thermal connection 18th connected is. the 2 shows the identical components of the assembly of the 1 only put together here. In the exemplary embodiment, all parts are made from OFHC copper. The threaded pin 1 has a diameter of 6.2 mm. The thread 6th is characterized by n = 14 (number of threads); A _outside = 30.191 mm ² (area of the cross section of the entire screw); A _core = 26.878 mm ² (area of the core diameter of the screw), which results in an area of
F _weight = 46.382 mm ² results.

QUOTES INCLUDED IN THE DESCRIPTION

This list of the documents listed by the applicant was generated automatically and is included solely for the better information of the reader. The list is not part of the German patent or utility model application. The DPMA assumes no liability for any errors or omissions.

Patent literature cited

• US 3807188 [0009]
• US 3999403 [0010]
• US 4450693 [0011]

Non-patent literature cited

• In article 1 by G. Authelet et al. (Conceptual design of a cryogen-free µMRI device, IOP Conference Series: Material Science and Engineering 278, 2017, 012122-2-7) [0012]

Claims (2)

Assembly for forming a device for heat exchange between two solid bodies, at least comprising a first solid body for thermal connection (18) and a component (17) to be cooled as a second solid body, the component (17) to be cooled having a threaded pin (1) with an external thread ( 6) or is formed as a threaded pin (6) and can be screwed to a further solid body which has a complementary internal thread (7) and wherein the further solid body either corresponds to the first solid body (18) or a third solid body which is a ring (3) which can be screwed separately to the first solid body (18). Assembly according to Claim 1 , characterized in that the ring is a clamping ring (3).

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