GB2119071A

GB2119071A - Joule-Thomson cooling apparatus

Info

Publication number: GB2119071A
Application number: GB08310583A
Authority: GB
Inventors: John Thornton; Frank Morecroft
Original assignee: British Aerospace PLC
Current assignee: BAE Systems PLC
Priority date: 1982-04-19
Filing date: 1983-04-19
Publication date: 1983-11-09
Also published as: GB2119071B

Abstract

A core element 14/17 for a cooler operating on the Joule-Thomson principle and having a low thermal mass is formed by activating the surface of a substrate 20 of thermally insulating material to render it electrically conductive and then plating a thin layer of metal over the surface. The core element may take the form of the former around which the heat exchanger 16 is coiled or it may take the form of a frusto-conical mounting member 14 which carries a detector substrate 12. <IMAGE>

Description

SPECIFICATION Cooling arrangements This invention relates to cooling arrangements operating on the Joule-Thomson effect and in particular to detector devices employing such cooling arrangements.

In a known form of cooling arrangement, a coil of metal tubing serving as a heat exchanger is wound on a conical core and has one end connected to a source of pressurized fluid and an orifice at its other end through which the fluid exhausts to provide a cooling effect. In operation fluid exhausts to provide cooling for a component located near the orifice, the exhausted, cooled fluid then is caused to flow over the coils of the tubing thereby to cool the pressurized fluid upstream of the orifice and hence to provide a regenerative effect which markedly reduces the temperature of the exhausted fluid. In some applications, a gas such as Argon or Air is employed on the working fluid and after only a short period of operation the cooling and regenerative effects of the arrangement cause the gas upstream of the orifice to liquify.

The requirements of the former in the above cooling arrangement are: (1) The core should be sufficiently strong to support the coil of tubing both when it is wound during manufacture and during subsequent operation, (2) The core should allow both ends of the tubing to be secured to the core, for example by soldering to enable a bond to be formed which is sufficiently strong to withstand the large range of operating temperatures, (3) The core should have minimal thermal mass to allow rapid cooling and hence a reduction in response time of the cooling arrangement, (4) The core should conduct as little heat as possible from its warm end (that end nearest the pressurized source) to its cold end (that end nearest the orifice).

In the past, the core has been made by pressing or spinning sheet metal into the desired form, but this type of core has a relatively high thermal mass even when using the thinnest sheet metal considered to be practicable. Problems such as buckling of the sheet during forming and uneven wall thickness of the core, especially in corner regions have been present.

According to one aspect of this invention, there is provided a cooling arrangement operating on the Joule-Thomson effect, said arrangement including a length of tubing having one end for connection to a source of pressurized fluid and an orifice at its other end through which the pressurised fluid may ex haunt to provide a cooling effect, a core element adapted to support said tubing, said core element being formed by electroplating a relatively thin layer of metal onto a major portion of a substrate.

Preferably, the substrate is formed of a thermally insulating material - such as expanded polyurethane - having a surface rendered electrically conducting by depositing thereon a metal. The substrate may be left in place after forming of the core element to reduce heat transfer within the element by convection and/or radiation.

Alternatively, the substrate may be removed.

Preferably, said tubing is secured to the core element by soldering portions thereof to metallic plated surface portions of the core element.

The thickness of the plated layer preferably lies in the range of from 30 to 50 microns.

Preferably, substantially the whole of the surface region of the substrate is electroplated to form the core element.

According to another aspect of this invention, there is provided a detector device which includes the cooling arrangement previously defined.

The device conveniently includes mounting means for mounting a detector element within the device, said mounting including a plate-like element of rigid thermally conductive and electrically insulating material such as sapphire or alumina which carries said detector element and a relatively thin mounting member secured to said plate-like element, the mounting member being formed by electroplating a relatively thin layer of metal on to a substrate and subsequently removing said substrate.

In either of the above aspects, the metal is preferably nickel or a nickel alloy.

By way of example only, a detector arrangement will now be described in detail, reference being made to the accompanying drawings, in which Figure lisa cross-sectional view of the detector arrangement; and Figure 2 is a cross-sectional view of the core element of the arrangement of Figure 1.

The arrangement comprises a housing 10 of generally frusto-conical form and having a window 11 through which signals may pass to a detector 12.

The detector 12 is mounted on a disc 13 of rigid but thermally conductive and electrically insulating material such as, for example, sapphire or alumina, the disc 13 being carried by a relatively thin frustoconical mounting member 14. The inner periphery of the mounting member is attached to the periphery of disc 13 and its outer periphery is embedded in a frusto-conical portion 15 of insulating material such as expanded polyurethane which acts as a thermal insulator.

The detector 12 is cooled by means of a cooling arrangement operating on the Joule-Thomson effect. The cooling arrangement comprises a heat exchanger 16 in the form of a coil of finned metalic capillary tubing which is wrapped around a core element 17. The heat exchanger 16 has one end 18 for attachment to a source of pressurized fluid for example Argon or Air and is provided at its other end with a small orifice 19 through which the pressurized fluid exhausts to provide a cooling effect.

The core element is manufactured by moulding an expanded polyurethane cone 20 around a metal mounting boss 21, activating the surface of the cone to render it electrically conducting, for example, by depositing a very thin layer of silver onto the surface from an aqueous solution of silver nitrate and then electroplating the core 20 with a metal such as nickel or a nickel alloy to form a layer 23 of thickness of between 30 and 50 microns. The heat exchanger 16 is then wrapped around the formed core element 17 and secured to it by soldering.

The heat exchanger 16 and core element 17 are mounted within the housing 10 and urged against the inner surface of frusto-conical portion 15 by means of a coil spring 22. The frusto-conical portion 15 serves to insulate the cooling arrangement and also provides a gas seal for the heat exchanger 16 so that cooled fluid issuing from orifice 19 is caused to flow past the heat exchanger, thereby to absorb heat from the fluid therein.

In use, pressurized fluid issues through orifice 19 produce a cooling effect for the detector 12, the exhausted fluid then passes back over the heat exchanger 16to cool the pressurized fluid therein and hence to produce a regenerative effect.

The core element may be of shapes other than that illustrated; for example, it may be of tapered form having an included angle of 30 , or it may be cylindrical.

The expanded polyurethane cone 20 could be removed after formation of the core element, but it is preferred to keep it in place to reduce heat transfer by convection and radiation within the element. The cone 20 also provides a useful supportforthe plated metal layer.

The metal boss 21 serves to receive an end of the heat exchanger 16 which may be secured thereto by soldering.

The relatively thin frusto-conical member 14 may be formed in a similar manner as the core element 17, or by plating on a suitable reusable substrate which is removed after forming of the member. The detector 12 may be mounted on a substrate of different shape to the disc 13 in which case the shape of the mounting member 14 should be altered accordingly.

The above arrangement allows the thickness of the metal and thus the termal mass of the core element 17 and the frusto-conical mounting member 14to be kept to both uniform and ata minimum, hence reducing the amount of wasteful heat transfer, yet still providing a core of sufficient rigidity to support the beat exchange both during manufacture and again the thermal strains imposed during subse quent operation.

Claims

1. A cooling arrangement operating on the Joule-Thomson effect, said arrangement including a length of tubing having one end for connection to a source of pressurized fluid and an orifice at its outer end through which the pressurized fluid may ex haustto provide a cooling effect, a core element adapted to support said tubing, said core element being formed by electroplating a relatively thin layer of metal on to a major portion of a substrate.

2. A cooling arrangement according to Claim 1 wherein the substrate is formed of a thermally insulating material.

3. A cooling arrangement according to Claim 1 or Claim 2 wherein said tubing is secured to the core element by soldering a portion of the tubing to electropated portions thereof.

4. A cooling arrangement according to any of the preceding Claims wherein the thickness of the electroplated layer lies in the range of from 30 to 50 microns.

5. A cooling arrangement according to any of the preceding Claims wherein substantially the whole of the exposed surface region of the substrate is electroplated to form the core element.

6. A detector device including a cooling arrangement as claimed in any of the preceding Claims including mounting means for mounting a detector element within the device, said mounting means including a plate-like element of rigid thermally conductive and electrically insulating material supported by means of a relatively thin mounting member said mounting member having been formed by electroplating a relatively thin layer of metal on to a substrate and subsequently removing said substrate.

7. A method of forming a core element for a cooling arrangement as claimed in Claim 1 which comprises rendering a surface region of a substrate of thermally insulating material electrically conducting, and electroplating a thin layer of metal onto said surface region.

8. A cooling arrangement substantially as hereinbefore described with reference to and as illustrated in any of the accompanying drawings.

9. A detector device substantially as hereinbefore described with reference to and as illustrated in any of the accompanying drawings.

10. A method of forming a core elementfor a cooling arrangement substantially as hereinbefore described with reference to and as illustrated in any of the accompanying drawings.