WO2007012803A1

WO2007012803A1 - Apparatus for use in a refrigeration unit

Info

Publication number: WO2007012803A1
Application number: PCT/GB2006/002563
Authority: WO
Inventors: Bengt Ake Viklund; Niels Liengard; Leo Ostergaard Mogensen
Original assignee: T I Group Automotive Systems Limited
Priority date: 2005-07-29
Filing date: 2006-07-11
Publication date: 2007-02-01
Also published as: GB0515615D0; GB2428774A

Abstract

Apparatus for use in a refrigeration unit (101) comprising: a first tube (207) of a first metal and having a first end (301) and a second end (304); and a capillary tube (209) formed from a different second metal. The capillary tube is joined to the first tube (207) at a braze joint (307) where the capillary tube (209) enters the first tube (207). The capillary tube has a middle portion (302) extending through the bore of the first tube and end portions (211 , 303) projecting out from the first tube at the braze joint and at the second end (304). The capillary tube has a bore for transporting liquid refrigerant and an outside diameter sufficiently small to allow a passageway through the first tube for refrigerant vapour. The first tube has a deformed portion (306) at its second end (304) such that its bore is configured to receive an end of an inlet tube (208) positioned over the capillary tube (209) as well as an end of an outlet tube (206) positioned alongside the inlet tube (208). By this arrangement the capillary tube (209) remains unexposed at the second end of the first tube in a refrigeration unit.

Description

Apparatus For Use In A Refrigeration Unit Background of the Invention

The present invention relates to apparatus for use in a refrigeration unit and a method of manufacturing apparatus for use in a refrigeration unit. In domestic refrigerators and freezers, it is usual to have a copper capillary tube which transports liquid refrigerant to an aluminium evaporator, and a copper suction tube which transports gaseous refrigerant from the evaporator. It is also known to locate a portion of the length of the capillary tube within the bore of the suction tube to form a heat exchanger. Consequently, refrigerant fluid transmitted from the evaporator by the suction tube is warmed by the fluid transmitted to the evaporator in the capillary tube, and similarly fluid transmitted to the evaporator is cooled by the fluid returned from the evaporator.

A problem with such an arrangement is that the copper capillary tube must be coated to prevent chemical reactions taking place between it and the water which inevitably exists on and around the evaporator and reaction between the resulting aqueous solution and the aluminium of the evaporator.

A second problem is the high cost of the copper used to form the suction tube.

Brief Summary of the Invention

According to a first aspect of the present invention, there is provided apparatus for use in a refrigeration unit, said apparatus comprising: a first tube of a first metal and having a first end and a second end; a capillary tube formed from a different second metal and joined to said first tube at a braze joint where said capillary tube enters said first tube, said capillary tube having a middle portion extending through the bore of said first tube and end portions projecting out from said first tube at said braze joint and at said second end, said capillary tube having a bore for transporting liquid refrigerant and an outside diameter sufficiently small to allow a passageway through said first tube for refrigerant vapour; and wherein said first tube has a deformed portion at its second end such that its bore is configured to receive an end of an inlet tube positioned over said capillary tube and an end of an evaporator outlet tube positioned alongside said inlet tube, whereby said capillary tube remains unexposed at said second end of said first tube in a refrigeration unit.

According to a second aspect of the present invention, there is provided a method of manufacturing apparatus for use in a refrigeration unit, said method comprising: obtaining a first tube of a first metal and having a first end and a second end; obtaining a capillary tube formed from a different second metal, said capillary tube having a bore for transporting liquid refrigerant and an outside diameter sufficiently small to allow a passageway through said first tube for refrigerant vapour when said capillary tube is located within the bore of said first tube; locating the capillary tube within said first tube such that said capillary tube extends through the bore of said first tube and end portions of said capillary tube project out from said first tube at a first position and at said second end; and brazing said capillary tube to said first tube at said first position, wherein said method also comprises the step of deforming the first tube at its second end to produce a deformed portion having a bore configured to receive an end of an inlet tube positioned over said capillary tube and an end of an evaporator outlet tube positioned alongside said inlet tube, whereby said capillary tube remains unexposed at said second end of said first tube.

According to a third aspect of the present invention, there is provided a pair of tubes connected together by a braze joint, comprising: a first tube having a wall defining a bore and a hole extending through said wall, said hole being spaced from a first end of said first tube; a second tube having a portion located within the bore of said first tube such that said second tube extends into said first end of said first tube and past said hole; and braze material located between the outer surface of the second tube and the inner surface of the first tube adjacent to said hole to form a braze joint between said tubes, and such that said first end of said first tube is spaced from said braze material.

According to a fourth aspect of the present invention, there is provided a method of brazing two tubes together comprising the steps of; obtaining a first tube and a second tube such that the first tube is locatable within the bore of the second tube; producing a hole through the wall of the second tube at a distance from one end of the second tube; introducing a portion of said first tube into the bore of said second tube such that said first tube extends past said hole; heating said first tube and said second tube in the vicinity of said hole; and introducing braze material into said hole such that said braze material melts and enters a gap between the outer surface of said first tube and the inner surface of said second tube to form a leak-tight seal between said tubes.

Brief Description of the Several Views of the Drawings

Figure 1 shows a perspective view of a domestic refrigeration unit 101 ;

Figure 2 shows a schematic representation of the domestic refrigeration unit 101 ;

Figure 3 shows a cross-sectional view of the suction tube 207 connected to the inlet 208 and outlet 206 of the evaporator and to the compressor connecting tube 210;

Figures 4A and 4B respectively show the evaporator tube 204 prior to its assembly to the evaporator plate 205, and a cross-sectional view of the inlet and outlet ends of the tube 204 (circled in Figure 4A);

Figure 5 shows a perspective view of the complete evaporator 104; Figure 6 shows the capillary tube 209, the suction tube 207 and the compressor connecting tube 210 prior to assembly;

Figures 7A and 7B respectively show the method of deforming the end 303 of the suction tube and the resulting deformed portion 306;

Figure 8 shows the process of brazing together the capillary tube 209, the suction tube 207 and the compressor connecting tube 210;

Figure 9 shows the brazed heat exchanger 901 ;

Figure 10 shows the portion 303 of capillary tube 209, which extends from the second end 304 of suction tube 207, being inserted into the open end of inlet tube 208; Figure 11 shows the inlet 206 and outlet 208 of the evaporator 104 being brazed to the end 304 of the suction tube 207;

Figure 12 shows a cross-sectional view of the braze material 1201 between the inlet tube 208, the outlet tube 206 and the suction tube 207;

Figure 13 shows a cross-sectional view of the braze material 1301 between the outside surface of the capillary tube 209 and the inner surface of the cylindrical portion 402 adjacent to the notch 405;

Figure 14 shows the complete evaporator and heat exchanger assembly 1401 after brazing of the suction tube 207 to the inlet 208 and outlet 206 of the evaporator 104; and Figures 15A and 15B respectively show an alternative heat exchanger 1501, and a cross-sectional view of a portion circled in Figure 15A.

Written Description of the Best Mode for Carrying out the Invention Figure 1

A perspective view of a domestic refrigeration unit 101 is shown in

Figure 1. In the present example, the refrigeration unit is a refrigerator having a door 102 at its front to allow access to a refrigeration cavity 103.

The cavity is configured to provide cold storage for perishable goods such as food, drinks, etc. The refrigerator 101 has a heat transfer system which pumps heat from the refrigeration cavity 103 to the air surrounding the refrigerator. The heat transfer system includes an evaporator 104 located within the cavity 103 and a condenser 105 mounted on the back of the unit 101. In operation, the evaporator 104 becomes relatively very cold and moisture from the air in the cavity 103 condenses on the evaporator to form ice.

In alternative embodiments the refrigeration units are freezers, and in one of these embodiments the evaporator is a type known as a Nofrost evaporator which has a heating element arranged to periodically heat the evaporator to prevent build-up of ice. Consequently, the evaporator is frequently subjected to liquid water as the ice is melted.

Figure 2 A schematic representation of the domestic refrigeration unit 101 is shown in Figure 2. The heat transfer system of the unit 101 includes an electrically powered compressor 201 located within a lower rear compartment 202 of the refrigerator, the condenser 105, a drying and filtering unit 203, and the evaporator 104 mounted within the refrigeration cavity 103.

The condenser 105 comprises a meandering tube attached to a panel mounted on the rear of the unit which assists transportation of heat from the tube to the surrounding air during operation.

The evaporator 104 comprises a continuous meandering tube 204 attached to a plate 205 which assists transportation of heat to the tube 204 from the air in the cavity 103. (In alternative embodiments, the evaporator comprises a plurality of fins in place of the single plate 204. For example, in the freezer with the Nofrost evaporator, the evaporator tube passes through many fins arranged perpendicular to the straight portions of the tube.) The evaporator tube 204 has an outlet 206 connected to a suction tube 207 and an inlet 208 in which is located one end of a capillary tube 209. The opposite end of the capillary tube 209 is connected to the outlet of the condenser 105 via the filtering and drying unit 203; the condenser itself being connected to the outlet of the compressor 201. As mentioned above, one end of the suction tube 207 is connected to the outlet of the evaporator. The other end of the suction tube 207 is connected to the inlet of the compressor via a compressor connection tube 210.

The heat transfer system contains a refrigerant fluid that is a gas at ambient pressure and temperature but is capable of being liquefied under pressure. During operation, the compressor 201 pumps the refrigerant around the circuit comprising the condenser 105, the drying and filtering unit 203, the capillary tube 209, the evaporator 104, the suction tube 207, and the compressor connecting tube 210, in that order. The capillary tube 108 has an internal diameter of typically of 0.7 millimetres, which is small when compared with the internal diameters of the tubes of the condenser

105 and the evaporator 104. Consequently, the capillary tube acts as a resistance to flow of refrigerant and, during operation of the compressor, it allows pressure to build up in the condenser 105.

During operation, the compressor 201 pumps very warm gaseous refrigerant (typically at 70 degrees centigrade) into the condenser 105. As the refrigerant travels through the condenser 105 it loses heat to the surrounding air until its temperature becomes so low that it condenses to form a liquid. (Typically at around 35 degrees centigrade.) Thus, by the time the refrigerant reaches the capillary tube 209 it is in the form of a warm liquid.

The capillary tube 209 transports liquid refrigerant into the evaporator where the pressure is comparatively low. Due to the relatively low pressure, the refrigerant evaporates into a gas again. The process of evaporation requires the absorption of the latent heat of evaporation of the refrigerant and thus it has a cooling effect on the evaporator 104 and the refrigeration cavity 103.

The gaseous refrigerant then passes through the suction tube 207 back to the compressor 201.

A middle portion of the length of the capillary tube 209 is located within the bore of the suction tube 207. Consequently, heat is conducted from the liquid refrigerant in the capillary tube to the fluid in the suction tube. This has two beneficial effects. Firstly, the heat from the capillary tube received by the suction tube ensures that any residual liquid leaving the evaporator 104 is evaporated before it reaches the compressor 201. Secondly, the loss of heat from the liquid refrigerant in the capillary tube means that it's temperature is reduced during its passage to the evaporator.

Consequently, the low temperature of the liquid entering the evaporator ensures that the evaporation of liquid takes place along much of the length of the evaporator. Thus, the suction tube 207 in combination with the capillary tube 209 form a heat exchanger which has beneficial effects on the operation of the refrigeration unit 101.

As illustrated in Figure 2, one end portion 211 of the capillary tube

209 extends from one end of the suction tube 207 to the drying and filtering unit. The end portion 211 is located in the compressor compartment 202 which contains relatively warm and dry air, and consequently the tubing it contains generally does not suffer from condensation and corrosion.

The other end of the capillary tube 209 is connected to the inlet of the evaporator 104 which, due to its relatively cold temperature, is subjected to condensation from the air in the refrigeration cavity. However, as described now with reference to Figure 3, the capillary tube is shielded from the atmosphere of the refrigeration cavity 103.

Figure 3 A cross-sectional view of the suction tube 207 connected to the inlet 208 and outlet 206 of the evaporator and to the compressor connecting tube 210 is shown in Figure 3. The suction tube 207 is typically between one and two metres in length but only eight millimetres (8mm) in diameter, and therefore the central section of the suction tube (and capillary tube) have been omitted to simplify the illustration.

The capillary tube 209 enters the suction tube 207 at its first end 301 , has a middle portion 302 which extends along the bore of the suction tube and an end portion 303 which extends from the second end 304 of the suction tube. The first end 301 of the suction tube 207 has a deformed portion 305 into which are fixed the capillary tube 209 and the compressor connecting tube 210 by a braze joint 307.

The second end 304 has a deformed portion 306 into which are brazed the inlet 208 and outlet 206 of the evaporator 104. The end portion 303 of the capillary tube 209 extends from the suction tube 207 directly into the inlet 208 of the evaporator and consequently remains shielded from the surrounding atmosphere.

The evaporator tube 204 and the suction tube 207 are formed from aluminium, while the capillary tube 209 is formed from copper. Therefore, if the capillary tube were exposed to the damp conditions surrounding the evaporator, then adverse chemical reactions could take place between the copper of the capillary tube, condensed water and the aluminium of the suction tube and/or evaporator tube. However, because the copper capillary tube 209 remains unexposed at the second end of the suction tube 207 such reactions are avoided.

It should be noted that the suction tube and/or the evaporator tube may be manufactured from aluminium or an aluminium alloy. Therefore both aluminium and aluminium alloys are herein referred to as aluminium. Figures 4A and AB

The manufacture of the aluminium evaporator 104 is illustrated by

Figures 4A, 4B and 5. The evaporator tube 204 is shown in Figure 4A prior to its assembly to the evaporator plate 205, while the inlet and outlet ends of the tube 204 (circled in Figure 4A) are shown in cross-section in Figure

4B.

The tube 204 is manufactured by straightening and cutting to length cylindrical aluminium tubing. The ends of the tube are then processed to produce the form shown in Figure 4B. Firstly the diameter of end portions of the tube 204 are reduced by a rotary swaging process. In this process, a set of small dies make radial oscillations against the outer wall of the tube. Machines capable of performing such a process are produced by Felss GmbH, Germany.

Due to the rotary swaging process, the inlet end 208 of the tube 204 is provided with a conical portion 401 which tapers down to a cylindrical end portion 402, and the outlet end 206 is provided with a conical portion 403 tapering down to a cylindrical portion 404. By this means, the cylindrical portion 402 of the inlet end 208 is provided with an internal diameter that is approximately 0.2mm greater than the outside diameter of the capillary tube 209. This allows the capillary tube to be brazed within the cylindrical portion

402 in a subsequent process step.

The cylindrical portion 404 is then bent such that the ends of the tube 204 are sufficiently close together and parallel for subsequent assembly to the suction tube. A notch 405 is then milled into the side of the cylindrical portion 402 to produce a hole through the tube wall. This hole is used in the subsequent capillary tube brazing process described below with respect to Figure 11. After milling, the internal bore of the cylindrical portion 402 is de- burred to avoid the possibility of damaging the capillary tube when it is inserted. The tube is then bent into a planar serpentine form shown in Figure 4A.

Figure 5 The complete evaporator 104 is shown in the perspective view of

Figure 5.

After forming into its serpentine shape, the majority of the tube 204 is hydraulically pressed such that it is provided with two substantially flat and parallel faces 501. The previously formed portions at the ends of the tube 204 are left cylindrical and undisturbed by the hydraulic press.

One face of the flatted tube 204 is then welded against one face of a pre-cut aluminium plate 205 to form the completed evaporator 104. In the present example, the welding is performed by laser spot welding along each side of the tube (for example at spot welds 502). To produce the laser spot welds, a laser welding head is provided with associated rollers which act on the sides and upper surface of the part of the tube 204 currently being welded. Thus, the rollers ensure that the tube is correctly positioned against the plate 205 during welding. The laser welding head and associated rollers are moved along the tube by a robotic arm and welds are produced at regular intervals along the flattened portion of the tube.

In alternative embodiments the tube is attached to the plate by electrical spot welding, brazing or clipping.

Figure 6 The manufacture of the heat exchanger formed by the capillary tube

209 and suction tube 207 is illustrated by Figure 6 to 9.

The capillary tube 209, the suction tube 207 and the compressor connecting tube 210 are shown prior to assembly in Figure 6.

The compressor connecting tube 210 is formed by straightening and cutting to length a piece of copper tubing. In the present example, six millimetre diameter tubing is used, but the use of other diameters is envisaged.

The capillary tube 209 is also formed by straightening and cutting to length a piece of copper tubing, but as illustrated in Figure 6 this is then provided with several coils 601 near to its end that is to be connected to the condenser.

The suction tube 207 is manufactured by straightening and cutting to length a piece of tubing, which typically has a diameter of eight millimetres (8mm), and then deforming the ends as described now with respect to Figure 7 A.

In alternative embodiments, the suction tube has a diameter other than the typical value of eight millimetres.

Figures 7 A and 7B The method of deforming the end 303 of the suction tube 207 is illustrated by Figure 7A and the resulting deformed portion 306 is shown in Figure 7B.

The end 304 of suction tube 207 is deformed by forcing a mandrel 701 into it. The mandrel 701 comprises a cylindrical shaped member 702 which has a diameter similar to that of the cylindrical portion 404 of the evaporator tube 204. The cylindrical member 702 has a domed front end 703 and a deforming part 704 extending in parallel along its side. The deforming part 704 generally has a uniform section but it is provided with a tapered front end 705 which follows a line up from the domed end 703. In use, the domed front end of the mandrel 701 is forced into the open end 304 of the tube 207, and the tapered front end of the deforming part 704 acts like a wedge against the inner surface of the tube 207. As the tube 207 rides up over the tapered front end 705 of the mandrel, the adjacent tube material is pulled hard against the cylindrical member 702 whereby the deformed portion 306 is produced. By this method, the deformed portion 306 is provided with a keyhole- like shape 706 defined by a substantially cylindrical wall 707 which blends into a wall 708 with a smaller radius of curvature.

Due to the dimensioning of the mandrel 701 , the cylindrical wall 707 is configured to allow the cylindrical portion 404 of evaporator tube 204 to be received, while the wall 708 is configured to allow the smaller cylindrical portion 402 to be received.

Although, the deformation process has been described in respect of deformed portion 306, it will be understood that the deformed portion 305 at the first end of the suction tube is produced by a similar method in which a similar mandrel is used to produce a keyhole-shaped bore. Thus, the deformed portion 305 is configured to receive compressor connecting tube 210 and capillary tube 209.

Figure 8

After production of the components shown in Figure 6, the capillary tube is inserted into the first end 301 and along the bore of the suction tube 207 until a portion 303 of the capillary tube extends from the second end 304 of the suction tube. Brazing flux is then applied to one end of the compressor connecting tube 210 and the relevant section of capillary tube before the connecting tube is inserted into the deformed portion 305 of the suction tube 207. The three components are then fixed together by brazing.

The process of brazing together the capillary tube 209, the suction tube 207 and the compressor connecting tube 210 is shown in Figure 8. These three components are heated by gas torches in the vicinity of the first end 301 of the suction tube 207. When they are sufficiently hot, wire 801 of braze material is applied to each side of the gap between the capillary tube 209 and connecting tube 210 adjacent the suction tube 207. Braze material flows between the capillary tube 209 and connecting tube 210 and between the outside of these tubes and the inner surface of the deformed portion 305 of the suction tube. Consequently, the three components are fixed together and the bore of the suction tube 207 is connected to that of the connecting tube 210 by a leak-tight braze joint.

In the present case, the wire 801 is Brazing Wire Zn Al 2, and the flux is Al-Flux 028 Cs/D as supplied by Flux Schweiss-und Lόtstoffe GmbH.

Figure 9

The brazed heat exchanger 901 is shown in Figure 9. In the present case, the capillary tube 209 and connecting tube 210 are brazed side by side into the first end 301 of the suction tube 207. However, in an alternative embodiment, the first end is not deformed as described with respect to Figure 7A but is left cylindrical, and a small hole is drilled through the wall of the suction tube a few centimetres from the first end. In this embodiment, the capillary tube enters the small drilled hole, extends along the bore of the suction tube and out from the second end 304. The capillary tube is fixed into the suction tube by a leak-tight braze joint at the small drilled hole, and the connecting tube 210 is brazed separately into the first end of the suction tube. However, both the heat exchanger 901 and the alternative heat exchanger have the deformed portion 306 at the second end 304 to allow it to receive the inlet and outlet of the evaporator 104.

Figure 10

The assembly of the heat exchanger 901 and the evaporator 104 are described with reference to Figure 10 to 14. Flux is applied to the surfaces to be brazed on the inlet tube 208 and outlet tube 206 of the evaporator and to the capillary tube 209. The portion 303 of capillary tube 209 that extends from the second end 304 of suction tube 207 is then inserted into the open end of inlet tube 208 as shown in Figure 10. The end of the capillary tube 209 is pushed along the cylindrical portion 402 past the notch 405 while the ends of the cylindrical portions 402 and 404 are pushed inside the deformed portion 306 of suction tube 207. The evaporator is then brazed to the suction tube as described with reference to Figure 11.

Figure 11

The inlet 206 and outlet 208 of the evaporator 104 are shown being brazed to the end 304 of the suction tube 207 in Figure 11. At the. same time as brazing the evaporator to the suction tube, the capillary tube is brazed into the cylindrical portion 402 of the evaporator inlet tube 208. To effect the braze, the components are heated by gas torches in the vicinity of the end 304 of the suction tube and in the vicinity of the notch 405. It should be noted that the notch is sufficiently large such that flames from the gas torches are able to access the capillary tube and ensure that it reaches braze temperatures rapidly. When the components are at sufficiently high temperature braze wire 801 is applied to each side of the gap between the two cylindrical portions 402 and 404 adjacent to the suction tube 207 to cause braze material to melt and flow between said portions and between said portions and the inner surface of the suction tube 207. Braze wire is also applied through the notch 405, and said wire melts and flows to form a braze joint between the outer surface of the capillary tube and the inner surface of the inlet tube 208.

Figures 12 A cross-sectional view of the braze material 1201 between the inlet tube 208, the outlet tube 206 and the suction tube 207 is shown in Figure 12. It should be understood that the braze material 1201 provides a leak- tight joint between the suction tube 207 and the outlet tube 206 while allowing the capillary tube 209 to enter the inlet tube 208 from the suction tube. Figure 13

A cross-sectional view showing the braze material 1301 between the outside surface of the capillary tube 209 and the inner surface of the cylindrical portion 402 adjacent to the notch 405 is shown in Figure 13. The braze material 1301 provides a seal such that in use refrigerant injected from the end of the capillary tube cannot pass backwards along the cylindrical portion 402 and into the suction tube 207. Instead, the refrigerant must flow from the capillary tube 209 along the full length of the evaporator and out through the outlet 206 to the suction tube 207.

It should be understood that the purpose of the notch 405, in this instance, is to allow braze material to be supplied to the gap between the two tubes 402 and 209. This is important, because due to the presence of the suction tube, braze material cannot be applied to the end of the tube 402.

Another potential benefit of applying brazing material through the notch 405 relates to the temperature of the capillary tube during brazing. In some refrigeration units, a free copper capillary tube is brazed into an inlet tube of the evaporator. Conventionally, the braze joint is made at a position where the capillary tube enters the inlet tube. It is known for the temperatures attained by the capillary tube during the brazing process to cause annealing, which in turn causes the capillary tube to weaken and break at the position where it enters the inlet tube. The notch 405 is displaced from the end of the inlet tube 208 such that the brazed portion of the capillary tube is also spaced from the end of the inlet tube.

Consequently, the portion of the capillary tube 209 that is annealed by the brazing process is surrounded and supported by the cylindrical portion 402 of the inlet tube 208, while the portion of the capillary tube at the end of the inlet tube 208 is left in its non-annealed state. Thus, the method of brazing the capillary tube into the larger diameter inlet tube by applying braze material through a hole in the wall of the inlet tube maintains the strength of the capillary tube at the position where the two tubes meet.

Figure 14

The complete evaporator and heat exchanger assembly 1401 is shown in Figure 14 after brazing of the suction tube 207 to the inlet 208 and outlet 206 of the evaporator 104.

Before installation of the assembly 1401 into a refrigeration unit, the suction tube and capillary tube may be pre-bent to simplify the installation process. After installation, the capillary tube 209 is connected to the condenser 105 and the compressor connecting tube 210 is connected to the compressor 201 in a conventional manner.

Figures 15A and 15B

An alternative heat exchanger 1501 is shown in Figure 15A, and a cross-sectional view of a portion circled in Figure 15A is shown in Figure 15B.

Like the assembly 1401 shown in Figure 14, the heat exchanger 1501 comprises a capillary tube 209 and a compressor connecting tube

210 located within a suction tube 207. These three components are manufactured and brazed together as described with reference to heat exchanger 901 of Figure 9. However, instead of connecting the suction tube directly to an evaporator, the suction tube is provided with a pair of aluminium connecting tubes 1502 and 1503.

Connecting tubes 1502 and 1503 are formed from lengths of cylindrical aluminium tubing which are shaped by the hammering process used to shape the ends of the evaporator tube 204. Thus the tube 1502 is provided with a cylindrical connecting portion 1504 which tapers down by means of a conical portion 1505 to a small cylindrical portion 1506. By this means, the small cylindrical portion 1506 is provided with a bore that is dimensioned to receive the capillary tube 209. The tube 1503 is also provided with a connecting portion 1507, a conical portion 1508 and a small cylindrical portion 1509. The small cylindrical portion 1509 is bent such that the complete heat exchanger is configured to connect to the inlet and outlet of an evaporator. The small cylindrical portion 1506 is provided with a milled notch 1510 similar to notch 405.

The small cylindrical portion 1506 of connecting tube 1502 is then slid over the end of the capillary tube 209 and inserted into the deformed portion 306 at the end of the suction tube 207. The connecting tube 1503 is also inserted into the end of the suction tube 207 and the connecting tubes 1502, 1503 are brazed into place in the manner described for the assembly 1401. The connecting portions 1504 and 1507 of tubes 1502 and 1503 have diameters that are chosen to allow connection and brazing to the inlet and outlet of an evaporator.

Claims

1. Apparatus for use in a refrigeration unit, said apparatus comprising: a first tube of a first metal and having a first end and a second end; a capillary tube formed from a different second metal and joined to said first tube at a braze joint where said capillary tube enters said first tube, said capillary tube having a middle portion extending through the bore of said first tube and end portions projecting out from said first tube at said braze joint and at said second end, said capillary tube having a bore for transporting liquid refrigerant and an outside diameter sufficiently small to allow a passageway through said first tube for refrigerant vapour; and wherein said first tube has a deformed portion at its second end such that its bore is configured to receive an end of an inlet tube positioned over said capillary tube and an end of an evaporator outlet tube positioned alongside said inlet tube, whereby said capillary tube remains unexposed at said second end of said first tube in a refrigeration unit.

2. Apparatus for use in a refrigeration unit according to claim 1 , wherein said apparatus comprises a connecting tube brazed to said first end of said first tube for connecting the bore of said first tube to a compressor.

3. Apparatus for use in a refrigeration unit according to claim 2, wherein said braze joint joining said capillary tube to said first tube is located at the first end of said first tube and said capillary tube enters said first tube alongside said connecting tube.

4. Apparatus for use in a refrigeration unit according to any of claims 1 to 3, further comprising an inlet tube positioned over said capillary tube and an outlet tube positioned alongside said inlet tube, and said inlet and outlet tubes are brazed into the deformed portion of said first tube such that said outlet tube provides a passageway to the bore of the first tube.

5. Apparatus for use in a refrigeration unit according to any of claims 1 to 4, wherein said inlet and outlet tubes comprise of substantially the same material as the first tube.

6. Apparatus for use in a refrigeration unit according to claim 5, wherein said first tube is formed from aluminium and said inlet and outlet tubes are formed from aluminium.

7. Apparatus for use in a refrigeration unit according to any of claims 1 to 6, wherein said first tube is formed from aluminium and said capillary tube is formed from copper.

8. Apparatus for use in a refrigeration unit according to any of claims 4 to 7, wherein said inlet and outlet tubes each have an open end for connection to the inlet and outlet respectively of an evaporator in a refrigeration unit.

9. Apparatus for use in a refrigeration unit according to any of claims 4 to 7, wherein said inlet and outlet tubes are the end portions of a tube forming an evaporator in a refrigeration unit.

10. Apparatus for use in a refrigeration unit according to claim 9, wherein said tube forming said evaporator is extruded aluminium.

11. Apparatus for use in a refrigeration unit according to claim 9 or claim 10, wherein said evaporator comprises a meandering tube and one or more plates or fins attached to said meandering tube.

12. Apparatus for use in a refrigeration unit according to any of claims 4 to 11 , wherein said capillary tube is fixed within said inlet tube by a brazed joint.

13. Apparatus for use in a refrigeration unit according to any of claims 4 to 12, wherein said inlet tube has a wall defining a hole spaced from the end of the inlet tube, and braze material is located between the outer surface of the capillary tube and the inner surface of the inlet tube adjacent to said hole.

14. Apparatus for use in a refrigeration unit according to any of claims 1 to 13, wherein said deformed portion at the second end of said first tube has a bore having a keyhole shape in which a substantially cylindrical wall blends into a wall with a smaller radius of curvature.

15. A refrigeration unit comprising: apparatus according to any of claims 1 to 14; and an evaporator; wherein said capillary tube is configured to transport refrigerant to said evaporator, and said first tube is configured to transport refrigerant from said evaporator.

16. A method of manufacturing apparatus for use in a refrigeration unit, said method comprising: obtaining a first tube of a first metal and having a first end and a second end; obtaining a capillary tube formed from a different second metal, said capillary tube having a bore for transporting liquid refrigerant and an outside diameter sufficiently small to allow a passageway through said first tube for refrigerant vapour when said capillary tube is located within the bore of said first tube; locating the capillary tube within said first tube such that said capillary tube extends through the bore of said first tube and end portions of said capillary tube project out from said first tube at a first position and at said second end; and brazing said capillary tube to said first tube at said first position, wherein said method also comprises the step of deforming the first tube at its second end to produce a deformed portion having a bore configured to receive an end of an inlet tube positioned over said capillary tube and an end of an evaporator outlet tube positioned alongside said inlet tube, whereby said capillary tube remains unexposed at said second end of said first tube.

17. A method of manufacturing apparatus for use in a refrigeration unit according to claim 16, wherein a connecting tube is brazed to said first end of said first tube for connecting the bore of said first tube to a compressor.

18. A method of manufacturing apparatus for use in a refrigeration unit according to claim 16, wherein said capillary tube is brazed to said first tube at the first end of the first tube and the capillary ^' tube enters the first tube alongside said connecting tube.

19. A method of manufacturing apparatus for use in a refrigeration unit according to any of claims 16 to 18, further comprising the steps of: positioning an inlet tube over said capillary tube; positioning an outlet tube alongside said inlet tube; and brazing said inlet and outlet tubes into the deformed portion of said first tube such that said outlet tube provides a passageway to the bore of the first tube.

20. A pair of tubes connected together by a braze joint, comprising: a first tube having a wall defining a bore and a hole extending through said wall, said hole being spaced from a first end of said first tube; a second tube having a portion located within the bore of said first tube such that said second tube extends into said first end of said first tube and past said hole; and braze material located between the outer surface of the second tube and the inner surface of the first tube adjacent to said hole to form a braze joint between said tubes, and such that said first end of said first tube is spaced from said braze material.

21. A pair of tubes connected together by a braze joint according to claim 20, wherein said second tube is a capillary tube.

22. A pair of tubes connected together by a braze joint according to claim 20 or claim 21 , wherein said second tube is formed from copper.

23. A pair of tubes connected together by a braze joint according to any of claims 20 to 22, wherein said tubes are configured to carry refrigerant in a refrigeration unit.

24. A pair of tubes connected together by a braze joint according to any of claims 20 to 23, wherein said first tube is an inlet tube of an evaporator.

25. A pair of tubes connected together by a braze joint according to any of claims 20 to 22, wherein said hole is formed as a notch.

26. A method of brazing two tubes together comprising the steps of; obtaining a first tube and a second tube such that the first tube is locatable within the bore of the second tube; producing a hole through the wall of the second tube at a distance from one end of the second tube; introducing a portion of said first tube into the bore of said second tube such that said first tube extends past said hole; heating said first tube and said second tube in the vicinity of said hole; and introducing braze material into said hole such that said braze material melts and enters a gap between the outer surface of said first tube and the inner surface of said second tube to form a leak-tight seal between said tubes.

27. A method of brazing two tubes together according to claim 26, wherein said second tube is a capillary tube.

28. A method of brazing two tubes together according to claim 26 or claim 27, wherein said second tube is formed from copper.

29. A pair of tubes connected together by a braze joint according to any of claims 26 to 28, wherein said hole is formed by milling a notch into said first tube.

30. A method of manufacturing apparatus for transporting refrigerant in a refrigeration unit comprising the method of brazing two tubes together according to any of claims 26 to 29.

31. A method of manufacturing apparatus for transporting refrigerant in a refrigeration unit according to claim 30, wherein said first tube is an inlet tube of an evaporator.