Classifications

• • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
  • F28—HEAT EXCHANGE IN GENERAL
  • F28F—DETAILS OF HEAT-EXCHANGE AND HEAT-TRANSFER APPARATUS, OF GENERAL APPLICATION
  • F28F13/00—Arrangements for modifying heat-transfer, e.g. increasing, decreasing
• • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
  • F25—REFRIGERATION OR COOLING; COMBINED HEATING AND REFRIGERATION SYSTEMS; HEAT PUMP SYSTEMS; MANUFACTURE OR STORAGE OF ICE; LIQUEFACTION SOLIDIFICATION OF GASES
  • F25D—REFRIGERATORS; COLD ROOMS; ICE-BOXES; COOLING OR FREEZING APPARATUS NOT OTHERWISE PROVIDED FOR
  • F25D19/00—Arrangement or mounting of refrigeration units with respect to devices or objects to be refrigerated, e.g. infrared detectors
  • F25D19/006—Thermal coupling structure or interface
• • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
  • F28—HEAT EXCHANGE IN GENERAL
  • F28F—DETAILS OF HEAT-EXCHANGE AND HEAT-TRANSFER APPARATUS, OF GENERAL APPLICATION
  • F28F13/00—Arrangements for modifying heat-transfer, e.g. increasing, decreasing
  • F28F2013/005—Thermal joints
  • F28F2013/008—Variable conductance materials; Thermal switches

Definitions

• the present invention relates to a gas thermal switch of the type comprising:
• the invention is used, for example but not exclusively, to establish thermal connections between components which are placed at cryogenic temperatures, for example, for an application in the field of space.
• cryogenic temperatures are temperatures of less than 120 K.
• thermal switches allow a thermal connection between a first component and a second component to be established or disengaged as desired.
• the first component and the second component can be components of a coolant system, for example, an evaporator and a cold source.
• thermal switch including in particular mechanical switches and gas type switches.
• Mechanical switches comprise two terminals which are each intended to be connected to one of the components between which the switch is arranged.
• the switch further comprises a movable element in order to establish mechanical contact, and therefore a thermal connection, between the two terminals. If it is desirable to reach high levels of thermal conductance, these switches are generally large and heavy and therefore unsuitable for use in the field of space.
• the first heat-exchange element is a rod which is fixedly joined to the first terminal and the second heat-exchange element is a tube which is fixedly joined to the second terminal and which receives the rod, with a space being provided around it.
• This space is very thin, generally in the order of from one to a few times the mean free path of the gas used. For example, this thickness may be in the order of 100 ⁇ m when helium is used at a pressure of a few millibars at the operating temperature.
• the chamber of the switch is delimited by the terminals, which are generally in the form of discs, and by an outer casing which is generally cylindrical and which surrounds the second heat-exchange element and whose ends are fixed to the two terminals.
• This outer casing forms a cross-member between the two terminals and it is therefore generally produced from a material which is a very poor conductor of heat, for example, from titanium, with a small thickness.
• the switch also comprises a device for introducing and removing heat-exchange gas to/from the chamber.
• This device may be, for example, an adsorption pump.
• the gas When the gas is introduced into the chamber, the gas fills the space between the two heat-exchange elements and a heat exchange takes place between the two elements by means of conduction, owing to the particles of gas which will preferably collide with the elements and/or with each other.
• the heat exchange between the two elements is proportional to the pressure of the gas, which allows this exchange to be modulated by controlling the pressure.
• the switch is used in an “all or nothing” manner, and, for this reason, the thickness of the space is selected to be slightly greater than the mean free path of the particles of gas, in order to maximise the heat exchange and render it independent of any fluctuations in the pressure of the exchange gas.
• the heat exchange between the two elements will be substantially inversely proportional to the thickness of the space between the heat-exchange elements.
• the switch thus allows a thermal connection to be provided between the two components to which the terminals thereof are connected.
• the switch can therefore be said to be in a closed configuration.
• the switch When the gas has been removed from the chamber, the only thermal connection existing between the two terminals is provided by the outer casing. Owing to its small thickness and the material selected, the thermal flux thus established is very small and acceptable. The switch can therefore be said to be in an open configuration.
• one of the terminals of the switch is fixed directly to the corresponding component, for example, by means of screwing, and the other terminal is connected to the corresponding component by means of a flexible strand which allows mechanical decoupling to be provided.
• the terminals of the switch may be subject to mechanical loads, in particular during a relative movement between the first component and the second component.
• An object of the invention is to overcome this problem by providing a switch of the above-mentioned type whose operation is less sensitive to the mechanical forces which are capable of being applied to these terminals.
• the invention relates to a switch of the above-mentioned type, characterised in that at least one of the heat-exchange elements can be moved relative to its respective terminal.
• This mobility is intended to be understood in its most general form, that is to say, in terms of translation and/or in terms of rotation.
• the invention may comprise one or more of the following features, taken in isolation or according to any technically possible combination:
• FIGURE is a schematic perspective view of a gas switch according to the invention, one half of the switch being broken-away by a section taken along a longitudinal centre plane.
• the FIGURE illustrates a gas thermal switch 1 which is intended to operate in a temperature range of between 0 and 10K and which uses helium as a heat-exchange gas.
• This switch 1 is intended, for example, for an application in space, for example, to thermally connect a first component and a second component which may be components of a coolant system.
• the switch 1 principally comprises a body 3 , a device 5 for moving a heat-exchange element inside the body 3 , a device 7 for introducing and removing the heat-exchange gas and a system 8 for controlling the devices 5 and 7 in order to carry out the operation described below.
• the body 3 has a generally cylindrical shape about a longitudinal axis L.
• the body 3 is substantially rotationally symmetrical about the axis L but, as mentioned below, other forms may be envisaged.
• the body 3 principally comprises:
• the terminals 9 and 11 are generally of disc-like form and are each arranged at a longitudinal end of the body 3 .
• the terminals 9 and 11 are extended longitudinally by lugs 19 and 21 , respectively, for mechanical and thermal connection to the first and second component, for example, by means of screwing directly to these components or by means, for example, of flexible strands of copper wires.
• the lugs 19 and 21 may be provided with orifices 23 .
• this mechanical connection of the lugs 19 and 21 to the first component and the second component allows a thermal connection to be provided between the terminals 9 and 11 and these two components.
• a channel 25 which is connected to the introduction and removal device 7 extends through the first terminal 9 (at the left-hand side in the Figure).
• Another channel also extends through the terminal 9 and is intended to allow a first filling operation with heat-exchange gas, as will be described below.
• the casing 17 is constituted, in the example illustrated, by a narrow tube having a circular base which is produced from a material with a low level of thermal conductivity and which may be non-magnetic in accordance with the type of movement device 5 used.
• this tube is produced from titanium which is a non-magnetic material.
• the casing 17 is fixed, with the two longitudinal ends thereof, to the terminals 9 and 11 , for example, by means of fitting to protrusions 29 and 31 of the terminals 9 and 11 and generally soldering thereto, although adhesive-bonding may also be used.
• the outer casing 17 forms a cross-member and it delimits internally, with the terminals 9 and 11 , a sealed chamber 33 which is intended to contain the heat-exchange gas.
• the first heat-exchange element 13 is a cylindrical rod having a circular base which is centred on the axis L.
• the rod 13 extends the first terminal 9 towards the second terminal 11 and extends over the main part of the length of the chamber 33 .
• the rod 13 is integral with the first terminal 9 and in particular with the protrusion 29 , and is therefore constructed in one piece therewith. In this example, the rod 13 is therefore fixedly joined to the first terminal 9 .
• the second heat-exchange element 15 is a tube having a circular cross-section which is also centred on the axis L. In the example illustrated, it is a blind tube, one end of which, in this instance, the one facing the second terminal 11 , is closed by a base 35 .
• the inner diameter of the heat-exchange tube 15 is slightly greater than the outer diameter of the heat-exchange rod 13 and the rod 13 is arranged inside the tube 15 .
• the rod 13 and the tube 15 together delimit a space 37 which has a small thickness e and which is slightly greater than the mean free path of the heat-exchange gas.
• This space 37 is intended to be filled by the heat-exchange gas, as will be seen below.
• the tube 15 covers the rod 13 over a significant portion of the length of the chamber 33 , the rod 13 and the tube 15 have facing surfaces 39 and 41 with large surface-areas so that, when the heat-exchange gas is present in the space 37 , significant heat-exchange is provided by conduction between the rod 13 and the tube 15 .
• Passages 43 for circulation of the heat-exchange gas are provided in the tube 15 in the region of the base 35 . In some variants, passages are also provided in the base 35 .
• passages 43 allow the filling of the space 37 with heat-exchange gas to be accelerated, as will be described below.
• the surface 45 of the base 35 positioned opposite the second terminal 11 is preferably in the form of a spherical cap centred on the axis L.
• the surface 47 of the terminal 11 positioned opposite has a complementary shape. These two surfaces 45 and 47 have the same radius of curvature. These two surfaces 45 and 47 therefore converge towards the axis L, in the direction from the first terminal 9 towards the second terminal 11 .
• the heat-exchange tube 15 can be moved in the chamber 33 , relative to the second terminal 11 , between a first position of lesser heat transfer with the second terminal 11 and a position of greater heat transfer with the second terminal 11 . These two positions are extreme positions, that is to say, at the end of the path.
• the first position of lesser heat transfer is illustrated in the Figure.
• the base 35 is longitudinally spaced from the second terminal 11 and is supported longitudinally, in the direction towards the first terminal 9 , against the end of the rod 13 remote from the first terminal 9 .
• the base 35 In the second position of greater heat transfer (not illustrated), the base 35 is longitudinally spaced from the rod 13 and is supported longitudinally against the terminal 11 .
• the surfaces 45 and 47 are then fitted one inside the other thus centering the tube 15 with respect to the terminal 11 .
• the device 5 comprises a ferromagnetic core 49 which is, for example, a ring of soft iron, and means 51 for creating a magnetic field in the chamber 33 , in this instance with field lines which are directed longitudinally.
• the core 49 is fixed to the end of the tube 15 opposite the base 35 . More precisely, the core 49 extends the tube 15 towards the first terminal 9 and surrounds the rod 13 .
• the means 51 for creating a magnetic field comprise a first coil 53 and a second coil 55 which are arranged longitudinally beside each other.
• the first coil 53 is adjacent to the first terminal 9 and the second coil 55 is adjacent to the first coil 53 .
• the means 51 for creating a magnetic field are mounted on the body 3 at the outer side of the casing 17 and are, for example, fixed to the terminal 9 by means of screwing.
• the means 51 for creating a magnetic field extend practically over only the left half (in the FIGURE) of the body 3 .
• the means 51 comprise a partition wall 59 .
• the core 49 remains radially opposite, or in any case close, to the wall 59 , and therefore the intermediate region 57 between the two coils 53 and 55 , during the movement of the tube 15 .
• the core 49 of soft magnetic material is substantially centred on the partition wall 59 .
• the core 49 When, for example, voltage is applied to only the first coil 53 , the core 49 is positioned in the direction towards the first coil 53 in order to maximise the magnetic flux which passes through the core 49 , that is to say, to move the tube 15 to its first position. That is to say, as in variable reluctance motors, the core 49 will move so that a maximum induction flux can pass through it and thus reduce the reluctance.
• the switch 1 may comprise a sensor 60 for detecting the position of the tube 15 connected to the control system 8 . It should be noted that the polarisation of the coils 53 and 55 has no influence on the movement of the tube 15 since the core is of soft magnetic material.
• the force required to move the tube 15 may be very small, for example, in the order of 0.4 N and each coil may be a coil of 1500 ampere turns. Again in applications on the ground, the force required for the movement may also be reduced in arrangements where the switch 1 is placed in a horizontal position. Also in this instance, in the same manner as in applications in space, the coil 53 or the coil 55 may be supplied with electrical power only intermittently simply to move the tube 15 into the desired position, the electrical power supply being stopped after the tube 15 has reached the required position.
• the coils 53 and 55 may be produced from superconductive wire.
• the device 7 for introducing and removing the heat-exchange gas 7 may be, for example, a miniature adsorption pump.
• a pump conventionally comprises an adsorbant block 61 and a heating resistor 63 .
• the block 61 When the block 61 is not heated by the resistor 63 , it adsorbs the molecules of the heat-exchange gas which has been introduced beforehand into the chamber 33 via the first filling channel (not illustrated). The device 7 then removes the gas from the chamber 33 .
• the block 61 which desorbs the molecules which have been adsorbed previously is heated via the resistor 63 .
• the switch 1 has an open configuration and a closed configuration.
• the heat-exchange gas has been removed from the chamber 33 by the device 7 and the tube 15 is in the first position thereof.
• the only heat exchange between the terminals 9 and 11 is provided by thermal conduction via the outer casing 17 .
• the casing has been sized and the material thereof selected in such a manner that the corresponding thermal flux is very weak and acceptable.
• the terminals 9 and 11 therefore establish practically no thermal connection between the first and the second components.
• the heat-exchange gas has been introduced into the chamber 33 via the device 7 and fills in particular the space 37 between the tube 15 and the rod 13 .
• the molecules of gas thus collide with the surfaces 39 and 41 of the tube 15 and the rod 13 , thereby providing significant heat exchange by means of conduction between the rod 13 and the tube 15 .
• the tube 15 is in the second position thereof.
• the surface 45 of the tube 15 is therefore in contact with the surface 47 of the terminal 11 and thus provides heat transfer between the terminal 11 and the tube 15 .
• a significant thermal flux can be transmitted from the terminal 9 to the terminal 11 and therefore between the two components to which the two terminals 9 and 11 are connected.
• the thermal conductance is also increased compared with that of conventional mechanical switches, whilst retaining a reduced mass and spatial requirement and reliable operation.
• the time for moving between the closed configuration and the open configuration may be reduced compared with the conventional operation of a gas thermal switch.
• the passages 43 also allow the heat-exchange gas to rapidly fill and leave the space 37 and therefore allow the time to be reduced for moving from the open configuration to the closed configuration, and vice-versa.
• the switch 1 thus provides a plurality of intermediate configurations between the open configuration and the closed configuration, these configurations corresponding to increasing levels of thermal conductance. It should be noted that controlling the switch 1 to reach these intermediate configurations is much more straightforward owing to the fact that it can be carried out by moving the tube 15 rather than controlling the pressure of the exchange gas in the chamber 33 .
• the two heat-exchange elements 13 and 15 are arranged in the chamber 33 , it is possible to obtain facing heat-exchange surfaces with large surface-areas, which allows significant heat exchange to be achieved whilst preserving small dimensions for a thermal switch.
• the movement device 5 does not use a permanent magnet and is therefore less sensitive with respect to the high temperatures which may be reached, in particular during the soldering of the outer casing 17 to the terminals 9 and 11 .
• movement devices 5 may be envisaged, for example, devices comprising permanent magnets in place of the core 49 .
• the core 49 may be of hard magnetic material, which is magnetised in the same direction as the magnetic field produced by the means 51 , the casing 17 still being of non-magnetic material.
• This may be carried out, for example, by adhesively-bonding the casing 17 to the terminals 9 and 11 at the two ends thereof.
• the coils 53 and 55 may advantageously be replaced with the same coil, for example, located at a central position between the positions of the coils 53 and 55 of the preceding embodiment.
• the configuration of the switch 1 is determined by the direction of the current which passes through the single coil which replaces the coils 53 and 55 .
• the complementary surfaces 45 and 47 allow the tube 15 to be centred relative to the terminal 11 and therefore the axis L.
• a space may be provided between the surfaces 45 and 47 , for example, having a thickness which is equal to e and which is more generally less than the mean free path of the heat-exchange gas selected, that is to say, a few ⁇ m or some tens of ⁇ m.
• the heat transfer between the tube 15 and the terminal 11 is provided by means of conduction between the surfaces 45 and 47 .
• one of the heat-exchange elements 13 and 15 will be a male element and the other heat-exchange element a female element which receives the male element.
• Their shapes may be varied. For example, they may be cylinders having bases which have shapes other than circular, for example, triangular, square . . . .
• the female element is not necessarily blind as described above, but instead may be open at both ends thereof.
• the elements 13 and 15 are not necessarily male and female elements. They may, for example, be combs whose teeth are intended to engage with each other.
• the tube 15 it is also possible for the tube 15 to be able to be moved relative to the terminal 11 in order to provide the mechanical decoupling, but without this mobility constituting positions corresponding to substantially different heat transfers between the terminal 11 and the tube 15 . That is to say, the thermal conductivity of the switch 1 remains substantially constant relative to the terminal 11 , regardless of the position of the tube 15 .
• the movable element is not necessarily the element 15 described above, but instead may be the element 13 which is intended to be thermally connected to the first terminal 9 .
• the two elements 13 and 15 can be moved relative to the terminals 9 and 11 .
• the switch 1 may not comprise a device 7 for introducing and removing heat-exchange gas.
• the heat-exchange gas therefore permanently remains in the chamber 33 even when the switch is in an open configuration.
• the gas thermal switch 1 described above and the different variants thereof may be used in a number of applications and are by no means limited to cryogenic temperatures and the field of space.

Landscapes

• Engineering & Computer Science (AREA)
• Physics & Mathematics (AREA)
• Mechanical Engineering (AREA)
• Thermal Sciences (AREA)
• General Engineering & Computer Science (AREA)
• Chemical & Material Sciences (AREA)
• Combustion & Propulsion (AREA)
• Thermally Actuated Switches (AREA)

Applications Claiming Priority (3)

Publications (1)

Family

ID=37776535

Family Applications (1)

Country Status (4)

Cited By (1)

Families Citing this family (2)

Citations (6)

Family Cites Families (2)

• 2006
  • 2006-06-23 FR FR0605686A patent/FR2902868B1/fr not_active Expired - Fee Related
• 2007
  • 2007-06-22 EP EP07788919A patent/EP2032933A1/fr not_active Withdrawn
  • 2007-06-22 US US12/306,326 patent/US20120152492A1/en not_active Abandoned
  • 2007-06-22 WO PCT/FR2007/001040 patent/WO2007147981A1/fr active Application Filing

Patent Citations (6)

Also Published As

Similar Documents

Legal Events