Method of forming a heat exchanger and a spacer therefor

Abstract

 A method of forming a heat exchanger comprising:-
providing a plurality of extruded tubes 1 having parallel micro-bores 2 extending therethrough;
closing the ends 3 of the micro-bores 2;
forming an aperture 4 adjacent each end of each tube 1 normal to the micro-bores 2, piercing the micro-bores;
forming a plurality of spacers 15 by forming apertures 12 in a strip 10 of sheet metal and folding the strip 10 about one or more transverse fold lines 13 such that the apertures 12 are aligned to form a continuous flow path;
assembling the heat exchanger by locating a spacer 15 between each end region of adjacent tubes 1 to locate the tubes 1 in spaced parallel relationship and bonding the spacers 15 to the tubes 1 such that the aperture 4 formed in each end of each tube is in fluid communication the corresponding aperture in an adjacent tube via the aperture 12 in the spacer 15.

Description

[0001] The present invention relates to a heat exchanger and more specifically to a spacer for a heat exchanger as well as to a method of forming a spacer and a method of forming a heat exchanger using the spacer.

[0002] Due to the environmental impact of the release of R134a refrigerant from refrigeration devices, carbon dioxide is becoming popular as an alternative refrigerant, particularly for vehicle air conditioning systems. However, the use of CO₂ as a refrigerant has the disadvantage of requiring significantly higher operating pressures than required for R134a refrigerant. Such higher pressures place higher demands on the construction of the heat exchanger which must be designed to withstand such higher pressures.

[0003] A typical heat exchanger comprises a plurality of spaced parallel tubes having internal passageways for the flow of a refrigerant, the tubes being separated by ribs or gaps through which air or another fluid to be heated or cooled can pass. The ends of the tubes are usually connected to a header to provide a common inlet or outlet for the tubes.

[0004] A particular problem area for high pressure heat exchangers required for use with CO₂ refrigerant is the manifolding of the heat exchanger tubes and the sealing of the ends of the heat exchanger tubes to the headers.

[0005] According to a first aspect of the present invention there is provided a spacer for spacing, and providing a flow path between, adjacent tubes of a heat exchanger, said spacer comprising a folded strip of deformable material, said spacer having at least one aperture extending therethrough.

[0006] According to a second aspect of the present invention there is provided a heat exchanger comprising a plurality of parallel spaced apart tubes, each tube having a plurality of elongate passages extending therethrough to provide coolant flowpaths, apertures being formed adjacent the ends of each tube in a direction normal to said elongate passages to form flow passages into and out of the plurality of passages, at least one spacer as defined above being provided between respective end regions of adjacent tubes, the at least one aperture in the spacer being aligned with or substantially aligned with one or more apertures in the tubes to provide a flow path between adjacent tubes.

[0007] According to a third aspect of the present invention there is provided a method of forming a spacer for spacing and providing a flow path between adjacent ends of parallel tubes of a heat exchanger comprising providing an elongate strip of deformable material, forming a plurality of apertures in said strip, and folding the strip about one or more transverse fold lines such that the apertures are aligned or substantially aligned to form a continuous flow path.

[0008] According to a fourth aspect of the present invention there is provided a method of forming a heat exchanger comprising:-

providing a plurality of elongate tubes, each tube having a plurality of elongate passages extending therethrough;

closing the ends of the passages in each tube;

forming at least one aperture adjacent each end of each tube in a direction normal to said elongate passages, said aperture piercing at least some of said plurality of passages;

forming a plurality of spacers in accordance the third aspect of the present invention;

assembling the heat exchanger by locating at least one spacer between each end region of adjacent tubes to locate said plurality of extruded tubes in spaced parallel relationship and bonding the spacers to the tubes such that the one or more apertures formed in each end of each tube are in fluid communication the one or more apertures in each end of an adjacent tube via said one or more apertures in said spacer.

[0009] Embodiments of the present invention will now be described with reference to the accompanying drawings, in which:-

Figure 1 is a perspective view of an end of a heat exchanger tube according to an embodiment of the present invention;

Figure 2 is a perspective view of an end of the heat exchanger tube of Fig. 1 showing an end closure cap;

Figure 3 is a plan view of a blank of sheet material used to form a spacer according to an embodiment of the present invention;

Figure 4 is a perspective view of a spacer formed from the blank of Fig. 3;

Figure 5 is a plan view of a blank of sheet material used to form a spacer according to a further embodiment of the present invention; and

Figure 6 is a perspective view of a spacer formed from the blank of Fig. 5.

[0010] A heat exchanger according to an embodiment of the present invention is formed from a plurality of elongate extruded tubes having a plurality of micro-bores defining flow paths for a coolant, such as CO₂. Each tube 1, as shown in Fig. 1, is provided with a plurality of parallel micro-bores 2 extending therethrough from one end of the tube to the other. As such, the tube is rigid and provides a high burst strength and the micro-bores can withstand high pressures without requiring large wall thicknesses or other reinforcement. The tubes 1 are longer than the required operating length of the heat exchanger to enable the ends of the tubes to form part of the inlet and outlet headers as will be explained below.

[0011] An oval aperture 4 (although other shapes are envisaged) is formed adjacent each end of the tube in a direction normal to the micro-bores 2, cutting through the micro-bores to define a manifold distributing flow between the micro-bores, as can be seen in Fig. 1.

[0012] The ends 3 of the micro-bores 2 may be closed by a closure cap 5, as shown in Fig. 2, or may be closed by brazing, welding or by crushing the ends of the tube. Alternatively, the ends of the tube 1 may be folded into a serpentine bend to close off the ends of the micro-bores 2.

[0013] A heat exchanger can formed by bonding the ends of the tubes 1 to intermediate spacers located between the ends of adjacent tubes 1 to form a stacked array of parallel, spaced apart tubes 1, such spacers having apertures which are aligned with the apertures 4 in the tubes 1, such that the tubes 1 are located in spaced apart parallel relationship with gaps therebetween to permit the flow of air or another fluid therethrough. The apertures 4 in the ends of the tubes 1 and the apertures in the spacers define inlet and outlet headers by means of which a refrigerant can be supplied to the heat exchanger, as will be explained in more detail below. The ends of the thus formed headers can be closed by bonding caps thereto or by omitting apertures 4 from the outermost tubes 1.

[0014] In one embodiment, shown in Figs. 3 and 4, each spacer is formed from a strip of sheet metal 10, such as steel or more usually aluminium (although it is envisaged that other deformable materials may be used). Apertures 11, 12, corresponding in size to the apertures 4 formed in the tubes 1, are punched or otherwise formed in the strip on either side of a central fold line 13, about which fold line the strip is folded to bring the apertures 11 and 12 into alignment and to form the spacer 15, as shown in Fig. 4. Thus the spacer 15 can be built up to the desired thickness by increasing the number of fold lines and apertures to form a spacer having two, three or more times the thickness of the sheet material from which it is formed.

[0015] If required, the abutting faces of the strip may be bonded together by welding, brazing or adhesive.

[0016] In the embodiment shown in Fig. 1, all of the micro-bores in the tube 1 are linked via a single aperture 4 to form a single flow path such that the flow of fluid, such as refrigerant, through the tubes 1 is transverse to the flow of air through the heat exchanger (known as crossflow). The efficiency of the heat exchanger can be improved if the flow of fluid through the tubes has at least a component in a direction opposed to the flow of air through the heat exchanger (known as counterflow).

[0017] This can be achieved by providing multiple passes through the micro-bores of the tubes in alternating direction such that the fluid effectively travels across the width of each tube 1 in a direction opposed to the flow of air through the heat exchanger.

[0018] To achieve such alternating flow pattern, the headers must transfer fluid from one micro-bore, or a group of micro-bores, into an adjacent micro-bore, or group of micro-bores. This can be achieved by providing a plurality of spaced apertures extending through the ends of the tube 1 normal to the micro-bores and arranged along a line transverse to the tube and providing means for transferring the fluid from one aperture to an adjacent aperture. To achieve the required return flow between adjacent apertures in the ends of the tube 1, the spacer shown in Figs. 5 and 6 can be used.

[0019] As with the embodiment shown in Figs. 4 and 5, the spacer 30 is formed from a flat strip 20 of sheet metal. Two transverse fold lines 21,22 are defined at equally spaced location on the strip 20. Pairs of spaced apertures 23,24,25,26 are formed in the strip, by piercing or other methods, between each fold line 21,22 and each end of the strip, such apertures 23,24,25,26 corresponding in size and spacing to apertures provided in the ends of the tube 1 (not shown). A single elongated aperture 27 is formed in a central region of the strip 20 between the fold lines 21,22. The strip 20 is folded in serpentine manner about fold lines 21 and 22 such that the apertures 23 and 24 are brought into alignment with apertures 25 and 26, aperture 27 providing a connecting passage between apertures 23,24,25 and 26.

Claims

1. A spacer for spacing and providing a flow path between adjacent tubes of a heat exchanger, said spacer comprising a folded strip of deformable material, said spacer having at least one aperture extending therethrough.

2. A spacer as claimed in claim 1, wherein the deformable material is a metal.

3. A heat exchanger comprising a plurality of parallel spaced apart elongate tubes, each tube having a plurality of elongate passages extending therethrough to provide coolant flowpaths, apertures being formed adjacent the ends of each tube in a direction normal to said elongate passages to form flow passages into and out of the plurality of passages, at least one spacer as defined above being provided between respective end regions of adjacent tubes, the at least one aperture in the spacer being aligned with or substantially aligned with one or more apertures the tubes to provide a flow path between adjacent tubes.

4. A heat exchanger as claimed in claim 3, wherein said plurality of passages comprise micro-bore passages.

5. A method of forming a spacer for spacing and providing a flow path between adjacent ends of parallel tubes of a heat exchanger comprising providing an elongate strip of deformable material, forming a plurality of apertures in said strip, and folding the strip about one or more transverse fold lines such that the apertures are aligned or substantially aligned to form a continuous flow path.

6. A method as claimed in claim 5, wherein the folding step comprises folding the strip about two spaced parallel transverse fold lines to form a spacer having a thickness three times that of the unfolded strip.

7. A method as claimed in claim 6, wherein two or more apertures are formed in each end region of the strip between each transverse fold line and each end of the strip, a single, preferably elongated, aperture being formed in a central region of the strip between the fold lines, the strip being folded about the transverse fold lines such that each of the apertures provided in said end regions of the strip are in fluid communication with the elongated aperture formed in the central region of the strip such that the spacer can be used to form a return bend of a counterflow heat exchanger.

8. A method as claimed in any of claims 5 to 7, including the further step of bonding abutting faces of the strip to one another, preferably by adhesive, welding or brazing.

9. A method of forming a heat exchanger comprising:-

providing a plurality of elongate tubes, each tube having a plurality of elongate passages extending therethrough;

closing the ends of the passages in each tube;

forming at least one aperture adjacent each end of each tube in a direction normal to said elongate passages, said aperture piercing at least some of said plurality of passages;

forming a plurality of spacers in accordance with any of claims 5 to 8;

assembling the heat exchanger by locating at least one spacer between each end region of adjacent tubes to locate said plurality of extruded tubes in spaced parallel relationship and bonding the spacers to the tubes such that the one or more apertures formed in each end of each tube are in fluid communication the one or more apertures in each end of an adjacent tube via said one or more apertures in said spacer.

10. A method as claimed in claim 9, wherein said step of closing the ends of the passages comprises one of:-

i) welding or brazing the ends of the passages to close said ends;

ii) bonding a closure member or cap over the ends of the passages;

iii) crushing the tube walls adjacent the ends of the passages;

iv} folding each end region of each tube into a serpentine bend.

Drawing