GB2491187A

GB2491187A - Header for a heat exchanger

Info

Publication number: GB2491187A
Application number: GB1108977.8A
Authority: GB
Inventors: Alex Mcdonnell; Keith Wilkins; Richard Armsden; Stephen Joyce; Joel Jennings; Nigel Seeds
Original assignee: Visteon Global Technologies Inc
Current assignee: Visteon Global Technologies Inc
Priority date: 2011-05-27
Filing date: 2011-05-27
Publication date: 2012-11-28
Anticipated expiration: 2031-05-27
Also published as: GB201108977D0; GB2491187B; US20120298344A1

Abstract

A header for a heat exchanger, the header comprises an elongate header plate 234 having two parallel edges 236a, 236b. An elongate slot 238 extends in a first direction across the plate and two ridges 244 extend in a second direction along the plate. The second direction is perpendicular to the first direction. The plate has two edge regions 246a, 246b either side of the two ridges and adjacent the plate edges. The edge regions are orientated in a first plane (248, fig 4b) and crests 250 of the ridges orientated in a second plane (252). The first and second planes are parallel to and offset from each other. The first direction may be perpendicular with the plate edges. The two edge regions may be equal width whereby a first distance between the crest of a first ridge and first plate edge and a second distance between the crest of a second ridge and second plate edge are equal. The plate thickness may be constant. A trough 254 between the two ridges may lie in the first plane or a base 256 of the trough may lie in third plane parallel to and between the first and second planes.

Description

Header for Heat Exchangers

BACKGROUND

a. Field of the Invention

The present invention relates generally to heat exchangers, and more particularly relates to headers for heat exchangers.

b. Related Art Typically, automotive vehicles are provided with an engine cooling system including a heat exchanger, such as a radiator. When the engine is running, heat is transferred from the engine to a coolant that flows through the engine. The coolant then flows from the engine to the heat exchanger through a series of conduits. At the heat exchanger, heat is transferred from the coolant to cooler air that flows over the outside of the heat exchanger. This process repeats itself in a continuous cycle thereby cooling the engine.

A typical heat exchanger includes a series of tubes supported by two chambers or headers positioned at either end of the heat exchanger. One type of conventional header is a flat header. These are so named because, when these flat headers are joined to a respective tube, for example, by brazing, the joint between the header and the tube lies in a flat plane.

During operation of the engine and cooling system, the tubes are subject to thermal cycling (rise and fall of the temperature of the heat exchanger components) which leads to stresses as neighbouring tubes may expand to different degrees such that axial loads are imposed on tubes by their neighbours.

These types of header/tube combinations are, therefore, prone to failure because of the stress concentrations that occur along the header/tube joint. In particular, these designs of header are prone to failure around the nose of the tubes.

A different header, designed to overcome these problems is known from US 7426958. However, when used in heat exchangers including folded tubes, or B-tubes', having a longitudinal seam separating two channels, the failure point is known to have moved from the nose of the tube to the intersection of the seam of the tube with the header.

It is, therefore, an object of the present invention to provide an improved heat exchanger header that overcomes these problems.

SUMMARY OF THE INVENTION

According to the invention there is provided a header for a heat exchanger, the header comprising an elongate header plate having two parallel long edges, the header plate including: -an elongate slot, the slot extending in a first direction across the header plate; and -two ridges extending in a second direction along the header plate, the second direction being perpendicular to the first direction, wherein, two edge regions of the header plate either side of the two ridges adjacent the long edges lie in a first plane and crests of the ridges lie in a second plane, and the first and second planes are parallel to and offset from each other.

Also according to the invention there is provided a heat exchanger comprising a header and at least one tube, the tube including a seam extending along a central region of the tube and the header comprising: -an elongate header plate having two parallel long edges and two edge regions adjacent the long edges; -an elongate slot for receiving an end of said tube, the slot extending in a first direction across the header plate; -two ridges extending in a second direction along the header plate, the second direction being perpendicular to the first direction; and -a trough between the two ridges, wherein, when a tube is received within the slot, the trough is aligned with the central region of the tube, and crests of the ridges intersect the tube further from the end of the tube than both a base of the trough and the edge regions of the header plate.

Typically the header comprises more than one slot and the slots are arranged parallel to each other. Preferably the first direction is perpendicular to the long edges of the header plate, such that when a tube is inserted in the one or more slots the width of the tube extends across the width of the header.

Preferably the header has mirror symmetry along a longitudinal centre line of the header so that the two edge regions are of equal width. In this way, a first distance between the crest of a first ridge and a first long edge of the header plate, and a second distance between the crest of a second ridge and a second long edge of the header plate are equal.

In preferred embodiments the thickness of the header plate is constant over the whole area of the header plate such that the stiffness of the header plate does not vary significantly over its area.

In some designs of heat exchanger it may be desirable if the depth of a trough formed between the two ridges in the header plate is equal to the height of the ridges. As such a base of the trough and the two edge regions of the header all lie in the first plane.

In other designs of heat exchanger it may be desirable if the depth of a trough formed between the two ridges in the header plate is less than the height of the ridges. As such a base of the trough lies in a third plane, parallel to the first and second planes and located between the first and second planes.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will now be further described, by way of example only, and with reference to the accompanying drawings, in which: Figure 1 is a schematic diagram of a heat exchanger, as is known in the

prior art, including a header and tubes;

Figure 2a is a perspective view of a portion of a heat exchanger showing the connection between a tube and a header, the header being of a

geometry known in the prior art;

Figure 2b is a cross-sectional view of a portion of the heat exchanger, along the line Il-Il of Figure 2a; Figure 3a is a perspective view of a portion of a heat exchanger showing the connection between a tube and a header, the header being of a

geometry known in the prior art;

Figure 3b is a cross-sectional view of a portion of the heat exchanger, along the line Ill-Ill of Figure 3a; Figure 4a is a perspective view of a portion of a heat exchanger showing the connection between a tube and a header, the header being according to a first preferred embodiment of the present invention; Figure 4b is a cross-sectional view of a portion of the heat exchanger, along the line IV-IV of Figure 4a; Figure 5 is a cross-sectional view of a portion of a heat exchanger, having a header according to a second preferred embodiment of the present invention; Figure 6 is a cross-sectional view of a portion of a heat exchanger, having a header according to a third preferred embodiment of the present invention; and Figure 7 is a cross-sectional view of a portion of a heat exchanger, having a header according to a fourth preferred embodiment of the present invention.

DETAILED DESCRIPTION

Figure 1 illustrates a known heat exchanger 10, which in this example is part of an automotive radiator assembly. The heat exchanger 10 comprises a plurality of tubes 12 extending between two headers 14, 16 connected to first and second ends 18, 20 of the tubes 12. The tubes 12 extend parallel to each other and are joined at their first or second ends 18, 20 to neighbouring tubes such that a fluid flow path is established through the heat exchanger 10. A number of fins 22 are arranged to span the spaces between neighbouring tubes 12 in an orientation such that, in use, air is able to flow over the surface of the fins 22 and between the tubes 12.

During operation of an engine (not shown) connected to the heat exchanger 10, hot coolant from the engine flows through the tubes 12 and transfers heat energy from the coolant to the walls of the tubes 12. This heat energy is, in turn, transferred to the fins 22 which radiate the heat energy, aided by a flow of cool air over and around the fins 22. Cold coolant then flows back into the engine to complete the cycle.

Figures 2a and 2b show a prior art design of tube 12 and header 14 used in the heat exchanger 10. This design is known as a flat header 14 because a joint 24 between the tube 12 and the header 14 lies in a flat plane 26. Typically the tube 12 and header 14 will be made from an aluminium material and the joint 24 between the tube 12 and the header 14 will be brazed.

As the coolant flows through the heat exchanger 10 and transfers heat energy to the tubes 12 and to the surrounding air, the components of the heat exchanger 10 undergo thermal cycling due to the rise and fall of the temperature. Furthermore, a temperature difference is often created across the width of a tube 12 and between neighbouring tubes 12 because the coolant cools as it flows across the heat exchanger 10. The temperature difference causes neighbouring tubes 12 to expand and contract to different degrees, which in turn leads to axial stresses being imposed on the tubes 12.

These externally induced stresses typically act along the whole of the joint or boundary 24 between the tube 12 and header 14 due to the restriction in the deformation of the tubes 12 in this region caused by the header 14. Furthermore, due to the geometry of the joint 24, stresses are concentrated at the ends 28 of the tube 12, known as the nose 28 of the tube 12. Stress concentration is a physical property and is related to the geometry of the tube/header joint 24.

Stresses are, therefore, concentrated in the nose region 28 due to the change in geometry and small radius of curvature of this part of the tube 12. As such, failure of these heat exchangers 10 usually occurs by radial fracture at or near the intersection of the nose 28 of the tube 12 with the header 14.

One design of header used to overcome this problem is disclosed in US 7426958.

As shown in Figures 3a and 3b this header 114 comprises a raised central portion 102 so that the header 114 has a substantially trapezoidal cross sectional shape.

The raised central portion 102 of the header 114 lies in a second plane 152 parallel to but offset from a plane 126 which includes edge regions 146 of the header 114. This geometry of header 114 distributes stresses more evenly over the tube/header joint 124 thereby increasing the life of the header 114 before failure. In particular, the raised central portion 102 alters the distribution of stress along the joint 124. The greater stresses caused by twisting of the header and bending of the tubes during thermal cycling is now within the central portion 102 of the header, and therefore separated from the regions of greatest stress concentration around the nose 128 of the tube 112.

Reference is now made to Figures 4a and 4b. In newer designs of heat exchanger, it is now increasingly desirable to use folded tubes 212 having a cross-section in the shape of a "B". These "B-tubes" 212 are formed from sheet metal and folded to create a central seam 230 which is then brazed to seal the tube 212.

This design of tube 212 increases the heat transfer surface area of the tube 212 thereby increasing the efficiency of the heat exchanger 210. In addition, these tubes 212 offer increased strength while allowing the use of thinner and lighter materials in their construction.

However, the presence of the seam 230 increases the rigidity of the tube 212 in this central region 232. The tube 212 is, therefore, less able to flex to accommodate stresses caused by thermal cycling. When these tubes 212 are inserted into a flat header 14, as described above, an additional potential point of failure is then created at the intersection of the seam 230 of the B-tube 212 and the header 14. Furthermore, if this type of tube 212 is used in combination with the trapezoidal header 114 described above, the problem is exacerbated as the location of the seam 230 coincides with the region of greatest loading in the central portion 102.

Figures 4a and 4b show a part of a tube 212 and header 214 according to a preferred embodiment of the present invention. The tube 212 is of a folded design, having a central brazed seam 230, as described above. The header 214 comprises a first face or header plate 234, which in this example is an upper face 234, having a substantially rectangular shape and including two opposing longer edges 236a, 236b and two opposing shorter edges (not shown). A series of slots 238 for receiving a first end 218 of each of the tubes 212 is formed in the header plate 234. The slots 238 extend across almost the full width of the header 214 and the length of the slots 238 is perpendicular to a longitudinal axis 240 of the header 214.

The header 214 will also typically comprise a second face (not shown), opposing the first face 234, and in this example forming a base of the header 214. Four side walls, parts of two of which 242a, 242b are shown in the figures, extend between the first 234 and second faces around the periphery of the faces 234, thereby forming an enclosed volume within the header 214.

Typically, the header 214 is made from a suitable metal such as aluminium or steel. The header 214 may be provided with any preferred number of slots 238 for receiving tubes 212, but usually the header 214 will include between six and two hundred slots 238. The spacing between slots 238 will typically be about 4 mm to mm and each slot 238 is about 1 mm to 12 mm wide. The length of the slots 238 can vary from 10 mm to 110 mm, depending on the application. Once a tube 212 has been positioned in a respective slot 238, it is usually fixed in position by brazing or soldering, although mechanical fixings may also be used.

The header plate 234 of the header 214 includes two ridge portions 244 thereby forming a corrugated profile to the header plate 234. The ridges 244 extend longitudinally along the full length of the header plate 234 and the slots 238 cut perpendicularly across the ridges 244 such that the line of intersection between a tube 212 inserted into a slot 238 and the header plate 234 no longer lies in a single plane.

As shown most clearly in Figure 4b, edge regions 246a, 246b of the header plate 234 lie in a first plane 248 and the crests 250 of the ridges 244 lie in a second plane 252, parallel to but offset at a distance from the first plane 248. In this example, the crests 250 of the ridges 244 are raised at a distance from the first plane 248 such that the crests 250 intersect the tube 212 further from the end 218 of the tube 212 which is located within the header 214.

In this embodiment, the dimensions and position of the ridges 244 are such that the crests 250 intersect the tube 212 at points approximately one quarter and three quarters of the way across the width of the tube 212. A trough 254 formed between the two ridges 244 is aligned with the central portion 232 of the tube 212 so that a base 256 of the trough 254 coincides with the seam 230 of the tube 212.

In this example, the depth of the trough 254 between the ridges 244 is such that the base 256 of the trough 254 lies at a point between the first and second planes 248, 252. In other embodiments the base 256 of the trough 254 may lie within the first plane 248.

The ridges 244 are formed from a number of planar sections. In particular the crests 250 of the ridges 244 and the base 256 of the trough 254 are formed by planar sections extending parallel to the first plane 248 and perpendicular to the seam 230 of the tube. The sides of the ridges 244 are also formed from planar sections preferably at an angle of between 20° and 70° to the first plane 248.

Figure 5 shows a second preferred embodiment of the invention. In this example the crests 350 of the ridges 344 and the base 356 of the trough 354 are not formed by planar sections of the header plate 334 but are formed by bends in the header plate 334 so that each of the ridges 344 is shaped like an inverted V'.

Additionally in this embodiment, edge regions 346a, 346b of the header plate 334 are raised to form a rim 360 along the long edges 336a, 336b, and the top of the rim 360 is aligned with the crests 350 of the ridges 144 in the second plane 352.

Figures 6 and 7 show two further embodiments of the invention. In Figure 6, the crests 450 of the ridges 444 are formed from planar or flat sections of the header plate 434 and lie in a second plane 452. The outer side portions 462 of the ridges 444, extending between a long edge 436a, 436b and a crest 450 of a respective ridge 444, are formed from curved sections of the header plate 434. In this example, an upper surface 464 of the header plate 434 has a concave curvature in these regions. A trough 454 between the two ridges 444 is formed from a continuously curved section of the header plate, with the upper surface 464 having a concave curvature in this region.

In Figure 7, edge regions 546a, 546b of the header plate 534 lie in a first plane 548, as in the first embodiment shown in Figure 4b. A base portion 556 of a trough 554 is formed from a flat section of the header plate 534 aligned with a central portion 532 of the tube 512. Ridges 544 in the header plate 534 are formed from continuously curved sections such that the upper surface 564 of the header plate 534 is convex in these regions.

In all of the embodiments according to the invention described above, it is important that the point of intersection of a tube with the header plate is located closer to the end of the tube in regions around the nose of the tube and adjacent to the seam of the tube than in regions between these areas.

Larger stresses, caused by twisting of the header and bending of the tubes due to thermal cycling, are imparted to the joint between the header and the tube at greater distances from the end of the tube. This is because the tube is able to deform to a greater degree due to the temperature differences further from the header. Closer to the header, deformation is restricted due to the fixed joint between the tube and the header plate.

In this way, the ridged profile of the header plate according to the present invention separates regions of higher loading, i.e. regions of intersection further from the end of the tube, from regions of higher stress concentration, i.e. regions of small radius of curvature around the nose of the tube, and regions of increased rigidity adjacent the seam of the tube.

The present invention, therefore, provides an improved header for use in folded-tube heat exchangers that has an increased life span before failure as compared with current designs of header. -11 -

Claims

CLAIMS1. A header for a heat exchanger, the header comprising an elongate header plate having two parallel long edges, the header plate including: -an elongate slot, the slot extending in a first direction across the header plate; and -two ridges extending in a second direction along the header plate, the second direction being perpendicular to the first direction, wherein, two edge regions of the header plate either side of the two ridges adjacent the long edges lie in a first plane and crests of the ridges lie in a second plane, and the first and second planes are parallel to and offset from each other.
2. A header as claimed in Claim 1, in which the first direction is perpendicular to the long edges of the header plate.
3. A header as claimed in Claim I or Claim 2, in which the two edge regions are of equal width, such that a first distance between the crest of a first ridge and a first long edge of the header plate, and a second distance between the crest of a second ridge and a second long edge of the header plate are equal.
4. A header as claimed in any preceding claim, in which the thickness of the header plate is constant over the whole area of the header plate.
5. A header as claimed in any preceding claim, in which the header plate includes a trough between the two ridges, and a base of the trough lies in the first plane.
6. A header as claimed in any of Claims 1 to 4, in which the header plate includes a trough between the two ridges, and a base of the trough lies in a third plane, parallel to the first and second planes, the third plane located between the first and second planes.
7. A heat exchanger comprising a header and at least one tube, the tube including a seam extending along a central region of the tube and the header comprising: -an elongate header plate having two parallel long edges and two edge regions adjacent the long edges; -an elongate slot for receiving an end of said tube, the slot extending in a first direction across the header plate; -two ridges extending in a second direction along the header plate, the second direction being perpendicular to the first direction; and -atrough betweenthetwo ridges, wherein, when a tube is received within the slot, the trough is aligned with the central region of the tube, and crests of the ridges intersect the tube further from the end of the tube than both a base of the trough and the edge regions of the header plate.
8. A heat exchanger as claimed in Claim 7, in which the first direction is perpendicular to the long edges of the header plate.
9. A heat exchanger as claimed in Claim 7 or Claim 8, in which the two edge regions are of equal width, such that a first distance between the crest of a first ridge and a first long edge of the header plate, and a second distance between the crest of a second ridge and a second long edge of the header plate are equal.
10. A heat exchanger as claimed in any of Claims 7 to 9, in which the thickness of the header plate is constant over the whole area of the header plate.
11. A heat exchanger as claimed in any of Claims 7 to 10, in which a base of the trough and the two edge regions lie in a first plane.
12. A header as claimed in any of Claims 7 to 10, in which the two edge regions lie in a first plane, the crests of the ridges lie in a second plane, and a base of the trough lies in a third plane, the third plane being parallel to and located between the first and second planes.
13. A header plate substantially as herein described with reference to or as shown in Figures 4a, 4b or 5 or 6 or 7.
14. A heat exchanger substantialiy as herein described with reference to or as shown in Figures 4a, 4b or 5 or 6 or 7.AMENDMENTS TO THE CLAIMS HAVE BEEN FILED AS FOLLOWSCLAIMS1. A header when used in a heat exchanger, the header comprising an elongate header plate forming a first face of the header and an opposing second face, the header plate being substantially rectangular and having two parallel longer edges and two shorter edges, the header plate including: -an elongate slot having first and second ends, the slot extending in a first direction across the header plate; and -two ridges extending in a second direction along the header plate, the second direction being perpendicular to the first direction, wherein, the slot cuts across both of the two ridges, and two edge regions of the header plate either side of the two ridges adjacent the longer edges and at said ends of the slot lie in a first plane and crests of the ridges lie in a second v plane, the first and second planes being parallel to and offset from each other, and y-15 the second plane being further from the second face of the header than the first plane.2. A header as claimed in Claim 1, in which the first direction is perpendicular to the longer edges of the header plate.3. A header as claimed in Claim I or Claim 2, in which the two edge regions are of equal width, such that a first distance between the crest of a first ridge and a first longer edge of the header plate, and a second distance between the crest of a second ridge and a second longer edge of the header plate are equal.4. A header as claimed in any preceding claim, in which the thickness of the header plate is constant over the whole area of the header plate.5. A header as claimed in any preceding claim, in which the header plate includes a trough between the two ridges, and a base of the trough lies in the first plane.6. A header as claimed in any of Claims I to 4, in which the header plate includes a trough between the two ridges, and a base of the trough lies in a third plane, parallel to the first and second planes, the third plane located between the first and second planes.7. A heat exchanger comprising a header, as claimed in any of claims I to 6, and at least one tube, the tube including a seam extending along a central region of the tube and an end of the tube being received within the slot, wherein, the seam of the tube is aligned with a central region of the header plate between the crests of the two ridges and the crests of the ridges intersect the tube further from the end of the tube than the edge regions of the header plate.8. A heat exchanger as claimed in Claim 7, wherein the header plate includes a trough between the two ridges and the seam of the tube coincides with a base of y-15 the trough.1 9. A header plate substantially as herein described with reference to or as shown in Figures 4a, 4b or 6 or 7. r10. A heat exchanger substantially as herein described with reference to or as shown in Figures 4a, 4b or 6 or 7.