GB2334778A

GB2334778A - Heat exchanger

Info

Publication number: GB2334778A
Application number: GB9901538A
Authority: GB
Inventors: Keith Thomas Symonds
Original assignee: Chart Marston Ltd
Current assignee: Chart Heat Exchangers Ltd
Priority date: 1998-02-28
Filing date: 1999-01-26
Publication date: 1999-09-01
Also published as: CA2330930A1; GB9901538D0; AU2292499A; WO1999044004A1

Abstract

A heat exchanger which may be used either as a heat sink to remove heat from an article or to heat a fluid, comprising a base (12) to which an article to be cooled can be attached and a plurality of fins (13) the fins being formed by a plurality of individual components stacked together.

Description

DESCRIPTION HEAT EXCHANGER This invention relates to a heat exchanger having a structure that can be used as a heat sink for the cooling of one or more articles which generate heat or as a means of heating a fluid which is passed across the heat exchanger.

Heat sinks are well known and usually provide cooling by natural convection of a fluid, usually air, or by forced convection wherein the cooling medium is passed over and/or through the heat sink by means of a fan or blower.

A heat sink normally has a base to which the item(s) to be cooled can be fixed and integral fins extending from the base. The base may have a number of fixing and location holes whereby the item(s) to be cooled can be attached to it to provide a good thermal contact. Alternatively, an item to be cooled may fit into a correspondingly sized recess in the base, which may be surrounded by fins whereby it may dissipate its heat by conduction into the portion of the base with which is it is in direct contact. Thus heat from the item(s) is conducted via the base, which acts as the heat "sink", to the finned region where it is dissipated to the atmosphere.

Conventionally, one general type of heat sink, which is usually of cuboid structure with fins forming one or more faces of the cuboid, is manufactured as an extruded section, the section having a base portion and an integral fins portion extending from the base. The extrusion method to achieve this product necessarily limits the choice of materials from which the heat sink can be made, particularly where designs with closely pitched thin fins are required. In practice aluminium is usually the only suitable choice.

It has excellent thermal conductivity, low density and is relatively inexpensive. Even so, it is not ideal as it is difficult to extrude successfully into very fine sections and as a consequence some regions of a product may be starved of metal. Hence optimum designs in terms of thermal efficiency may not be achievable in practice. Moreover, the tooling costs for the extrusion process can be very expensive and post-extrusion operations are required to provide the necessary location/fixing holes, which again adds to the cost of the product.

Another type of heat sink is of generally cylindrical structure with fins extending as an outer annular portion of the cylinder. This type of heat sink may also be made by extrusion but is usually made by a casting process followed by machining to defme locations for the fins. Again this is an expensive process and it is difficult to achieve very fine finning or complex fin patterns.

It is an object of the invention to provide an improved structure in which the aforesaid problems of heat sinks are eliminated or at least ameliorated and which structure can also be used with advantage to heat a fluid passing across it. In other words the structure of the invention may be used for the primary purpose of removing heat from an article needing to be cooled or for the primary purpose of heating a fluid from a source of heat.

Accordingly, the invention comprises a heat exchanger, the heat exchanger having a base against which an article to be cooled can be attached and a plurality of fins, the fins being formed by a plurality of individual components stacked together.

The base may be a solid, one-piece unit but preferably is also formed as a stack of individual components.

In one embodiment individual components are formed to comprise both a base portion and a fin portion. Thus the base and fin components may be integral, i.e. each component is formed in one piece and has a base portion and a fin portion. The stack, in one embodiment, may be made of a plurality of identical components.

In a first general embodiment, the heat exchanger of the invention may be generally cuboid in structure with fins forming one or more faces of the cuboid. The passageways for fluid, which may be a cooling fluid to remove heat from a heat source or a fluid to be heated, e.g. to cause a reaction, are defined between adjacent fins and in this embodiment extend transversely to the longitudinal extent of the base, i.e. transversely to the direction of stacking of the components. It will be appreciated, therefore, that a similar fin and base arrangement providing this transverse extent of the passageways can be obtained for any other desired geometrical shape of heat exchanger. It can be provided, for example, in a heat exchanger of generally cylindrical shape with individual fins and passageways extending transversely to the longitudinal, i.e. axial, direction of the cylinder.

In a second general embodiment the passageways defined in the fin portions extend in the longitudinal direction of the heat exchanger.

Preferably in this embodiment the heat exchanger is generally cylindrical in shape but it could, equally, be cuboidal or of other desired shape. In this embodiment, the passageways are defined by the alignment of holes or slots through each fin component (or through the fin portion of each combined fin and base component), i.e. the passageways pass through the fin components rather than being defined between adjacent fins.

For convenience, the invention will be described more specifically below with reference to heat sinks to remove heat from a hot article but it will be appreciated that any structure of the invention may equally be used to heat a fluid passing across the structure. In this latter useage the fluid stream may comprise, e.g. a mixture of gases which it is desired to react. The reaction may also be catalytically enhanced, e.g. by the deposition of catalyst on the fins of the heat exchanger.

In the preferred cuboid form of the first general embodiment referred to above, the individual components may be rectangular plates in plan whereas, in the preferred cylindrical form of the second general embodiment, they are circular plates or discs in plan, assuming that the cylinder is a right cylinder.

To form a cuboid heat sink according to the first general embodiment of the invention, each component may conveniently be formed with a base portion of greater thickness than its fin portion, whereby adjacent fm portions will be spaced apart in a stack of the components.

In a preferred form of the second general embodiment, the passageways are provided by apertures through planar plates and the plates are stacked directly in contact with adjacent plates, i.e. without spacing, so that the passageways provided by the apertures are completely enclosed by the walls defining the apertures.

To form a cylindrical heat sink according to the second general embodiment of the invention, if it is desired to provide a recess in the cylinder to receive an article to be cooled, it will be necessary to have at least first and second different disc-like components. Both components may have an outer annular region perforated to provide the desired fins. A first component will have a central hole defined by the inner perimeter of the perforated annular region. A stack of these first components provides the desired recess surrounded by fins, the recess being formed by the central holes, wherein an article to be cooled can be fitted into the recess. A second component will have a solid central region surrounded by the perforated annular region. A stack of these second components provides a solid base surrounded by fins and the two stacks can be mounted together so that an article in the recess of the first stack sits on the base of the second stack.

If a recess in the cylindrical component is not required, a single type of component only is needed. This may have a solid central region surrounded by a perforated annular region, thereby providing in a stack of identical components a solid core to which an article to be cooled can be attached.

In a further embodiment, a cylindrical (or other shaped) stack could be formed having a recess at each end of the cylinder with a solid central core between the two recesses.

In a yet further embodiment the disc-like components may have an outer solid unperforated annular region and a central region containing the desired pattern of slots.

The individual components may be manufactured by any suitable method, e.g. by machining from a larger piece of material, by blanking and forming or, preferably, by chemical etching. Thus a heat sink can be assembled from a series of components of pre-determined profiles. By choice of starting material thicknesses a wide variety of combinations of fin thickness, spacing and height can be achieved by selective removal of material by the chosen method of manufacture. Moreover, combinations of fin thickness, height and pitch may be chosen which could not be satisfactorily achieved using a conventional heat sink manufacturing technique.

The stacked components may be joined together by any suitable means.

For example, they may be clamped together. However, it is preferred that they be permanently bonded together. The bonding may be achieved, for example, by adhesive bonding, brazing or diffusion bonding. Where brazing is used the material from which the components are formed may conveniently be pre-coated with a suitable brazing medium or the medium may be introduced in foil or powder form between adjacent components and the assembly then brazed by well known techniques.

It will be appreciated that the components must be designed to withstand any pressure associated with the bonding technique, e.g. they must withstand the typical loading pressure exerted by a brazing or diffusion bonding jig. The skilled man of the art will readily be able to determine the requirement for his particular processes.

The number of components used will, of course, depend on their thickness and the length of heat sink required and the invention provides a most convenient means whereby a plurality of identical components or a plurality of each of a small number of different components can be utilised and assembled to form heat sinks of different length.

As indicated above, it is not essential that all the components be identical and two or more different types may be assembled to form the desired stack. However, it may be preferred to use no more than two different components to reduce manufacturing and assembly costs.

The invention enables a much wider choice of materials to be made than for the conventional methods of manufacture. Thus, for example, the components for use in the invention may be made of aluminium, copper, stainless steel (especially nickel alloys) and titanium.

In another embodiment of the invention a number of components may be formed in a single sheet of material. For example only, six disc-shaped components may be formed in a single sheet. The single sheet may be of, say, rectangular form and provides a multi-component sheet. A plurality of the sheets may then be stacked together to form a multi-heat exchanger assembly. It will be appreciated that the number of components in each sheet may be varied to suit individual requirements and that the plan shape of the sheet may be changed to, e.g. circular, square, etc., to fit a particular assembly requirement.

Embodiments of the invention will now be described by way of example only with reference to the accompanying drawings in which: Figure 1 is a cross-section through a first form of heat sink of the invention; Figure 2 is a view in the direction of arrow A of Figure 1; Figure 3 is a plan view of one plate component used to form a second form of heat sink of the invention; Figure 4 is a cross-section on line IV-IV of Figure 3; Figure 5 is a cross-section on line V-V of Figure 3; Figure 6 is an elevation in side view of a heat sink made from a plurality of components similar to those of Figure 3; Figure 7 is an end view in the direction of arrow C of Figure 6; Figure 8 is a plan view of a disc component for use in a third form of heat sink of the invention; Figure 9 is a plan view of another disc component for use in the third form of heat sink of the invention; Figure 10 is an elevation in side view of the heat sink made from a plurality of each of the disc components of Figures 8 and 9; Figure 11 is a plan view of a further disc component for use in a heat sink of the invention; Figures 12 and 13 are plan views of two discs, the one of Figure 12 to be used stacked alternately with a disc as shown in Figure 8 and the one of Figure 13 to be used stacked alternately with a disc as shown in Figure 9 to provide a further heat sink ofthe invention.

Figure 14 is a plan view of a yet further disc component for use in another heat sink of the invention; Figure 14A is an enlarged view of a portion of the surface of the disc component of Figure 14; and Figure 15 is a section on line XV-XV of Figure 14.

In Figures 1 and 2 a generally cuboid heat sink 10 is made in the form of a stack of bonded identical components 11. Each component 11 is of rectangular plate-like configuration having in transverse cross-section a thicker base portion 12 from which extends a thinner fin portion 13. When the components are stacked together with their adjacent base portions in contact and bonded together, the fins 13 are spaced from each other by gaps 14 corresponding to the difference in thickness between the base and fm portions. The gaps provide transverse passages for air and the heat sink is particularly suitable for natural convection away from the base of heat conducted through the base from an article in contact with base surface 12A.

Each component 11 has been etched, machined or otherwise formed from plate of uniform thickness and a pair of holes 15 is provided in the base portion of each component. These holes are aligned in the stack to form integral continuous passages 16, 17 through which coolant may be passed.

Alternatively the holes may be used for fixing or location purposes.

In Figures 3, 4 and 5 is shown another form of combined base and fin component 30 which can be stacked with a plurality of identical components and, which can then be bonded together to form a heat sink. Component 30 is of rectangular plate-like configuration and has a base portion 31 and a thinner fin portion 32. Fin portion 32 has been formed with three holes 33, 34 and 35 through its thickness, each hole being surrounded by an annular raised collar 36, 37, 38 respectively on one face of the fin portion. Hole 32 with its collar 36 is positioned centrally of the component 30 and lies just above the base portion 31. Holes 34 and 35 with their respective collars 37 and 38 lie one towards each upper corner of fin portion 32.

When the plate components are stacked and bonded together with their collars facing in the same direction, the collars act as bosses or spacers which compensate for the lesser thickness of the fin portions and butt against and are bonded to the uncollared face of the respective adjacent component. This provides not only the air gaps and transverse passageways between the fins as described above but also three longitudinal passageways through the stacked heat sink.

A heat sink 40 made in a manner similar to that described with reference to Figures 3, 4 and 5 is shown in Figures 6 and 7. This is made from a plurality of identical base and fin components, each having a base portion 41 and fin portion 42 and similarly positioned holes 43, 44, 45 with collars 46, 47, 48 respectively. When stacked as described above, transverse air passages 49 are formed between adjacent fin portions 42 and the holes 43, 44 and 45 align with their respective holes in adjacent components to form longitudinal passageways through the heat sink. Thus for example, coolant fluid can be passed in the direction of arrow D and/or arrow E through the heat sink (or the directions may be reversed or in the same direction) to provide additional cooling and to encourage heat dissipation from an article attached to face 40A of the heat sink. This is particularly useful when high ambient air temperature is encountered.

In Figures 8 and 9 are shown two heat sink components 50 and 70 respectively. As will be described in more detail below, a plurality of components 50 is stacked together, a plurality of components 70 is stacked together and the two stacks are abutted together and the components of the combined stack bonded to form the heat sink. The components 50 and 70 are circular disc-like plates and are stacked together to form a cylindrical heat sink.

In Figure 8 component 50 has a central hole 51 of circular plan form concentric with the outer perimeter 52 of the disc. The perimeter 53 of hole 51 and the perimeter 52 define between them an annular region 54. Region 54 is provided with a series of slots 55 in rows which define fins 56 and ligaments 57 which extend between adjacent slots to join adjacent fms.

(Although only one half of annular region 54 has, for convenience, been shown provided with slots, fms and ligaments, it will be appreciated that the whole of that region is so provided.).

As shown in Figure 8, the fins extend across the annular region 54 in parallel rows each row being, effectively, a cord across the circle parallel to a diameter of the circle. (One row 58 of fins extends effectively as a diameter across the circle.). The rows of slots end just short of perimeters 52 and 53 to form unperforated rims 59 and 60 at the outer and inner edges of annulus 54.

When a plurality of plates 50 is stacked concentrically together, their fins and ligaments will be aligned through the stack and will be able to withstand pressure exerted through the stack during, for example, the process of diffusion bonding. The stack will have a hollow cylindrical central region and an annular finned outer region. Slots 55 of adjacent discs are aligned to provide axially-extending passageways for cooling fluid. The stack 61 is shown in Figure 10 with a recess 62 formed by the hollow cylindrical central region and a finned outer annulus 63.

In Figure 9 component 70 is a disc of circular plan having a solid central region 71 also of circular plan and concentric with outer perimeter 72 of the disc. Discs 50 and 70 have the same overall diameter. Between the solid central region 71 and perimeter 72 is defined an annular region 74. As with disc 50, region 74 of disc 70 is provided with a series of slots 75 in rows defining fins 76 and ligaments 77 which extend between adjacent slots to join adjacent fins. (Again only one half of annular region 74 has been shown with slots, fins and ligaments for convenience.). Again the fins extend in parallel rows across the disc as in disc 50 and end just short of the outer perimeter and a notional inner perimeter corresponding to perimeter 53 of Figure 8.

A plurality of plates 70 can be stacked concentrically together with their fms and ligaments aligned through the stack so as to be able to withstand bonding pressure and their slots aligned to provide axial passageways. The stack will have a solid cylindrical central region, and will be surrounded by an annular finned outer region. The stack 81 and finned annular outer region 83 are shown in Figure 10, the solid cylindrical central region not being visible in that view.

It will be appreciated that by arranging that the slots, fins and ligaments of discs 50 are the same size and in the same positions as their counterparts on discs 70, the two stacks 61 and 81 can be stacked together and bonded in a single bonding operation to form the heat sink of combined stacks 61 and 81 shown in Figure 10. The stack has axial passageways to provide a throughway for cooling fluid in the direction of arrows F.

In Figure 11 a circular disc 90 is one of a plurality of identical components that can be stacked together to form part of yet another heat sink of the invention. Disc 90 comprises four concentric rings 91, 92, 93, 94, adjacent rings being joined together by a series of radial fins. The fins are defined by corresponding series of slots formed through the discs. (As before, not all the fins and slots are shown.).

As shown in one region of the disc, slots 95 define radial fins 96 between outer ring 91 and adjacent ring 92, slots 97 define radial fins 98 between rings 92 and 93 and slots 99 define radial fins 100 between ring 93 and inner ring 94.

As shown for convenience in another region of the disc is a different arrangement 101 of slots and fins between rings 91, 92, 93 and 94, although it will be appreciated that a single disc would normally only be provided with one or other of these two arrangements.

The fins are pitched to maintain a similar cross-section of conducting disc material for heat flow radially while the slots in a stack of the discs provide axial passages for cooling fluid, e.g. air, flow. This may be preferentially directed according to the prevailing pressure drop characteristics.

Central region 102 of disc 90, i.e. defined inside ring 94, may be hollow or solid. Thus two stacks of discs as described with reference to Figures 8, 9 and 10 may be formed and bonded together to form the heat sink.

In Figures 12 and 13 are shown two discs 50A and 70A respectively.

A first stack is formed of alternating discs 50A with discs 50 of Figure 8 and a second stack is formed of alternating discs 70A with discs 70 of Figure 9.

As can be seen on comparing disc 50 with disc 50A (and similarly disc 70 with disc 70A), the slots 55A and 75A and ligaments 57A and 77A, which are defined between rows 56A and between rows 76A respectively, are offset along their rows relative to slots 55 and 75 and to ligaments 57 and 77. In all other respects discs 50 and 50A and 70 and 70A are identical. Thus when the discs are stacked 50, 50A, 50, 50A and so on and 70, 70A, 70, 70A and so on, air flow forced through the passageways defined by the slots will take a more tortuous path on passing from each disc 50 or 70 to each disc 50A or 70A and so on because of the offset effect, i.e. the ligaments act as splitter bars and the slots of one disc overlap with those of adjacent discs. Heat transfer will, thereby, be improved.

As with the Figures 8 and 9 embodiment, a stack of alternating discs 50, 50A will have a central recess and annular finned outer region and a stack of alternating discs 70, 70A will have a solid central region and an annular finned outer region. When the two stacks are paced together the central recess of the one stack will be coaxial with and of substantially the same diameter as the solid central region of the other.

In Figures 14, 14A and 15 is shown a stack of three discs 150A, 150B, 150C, only one of which, 150A, is seen in the plan view of Figure 14.

As shown in Figure 14, the disc has essentially the same structure as disc 50 of Figure 8, but with like parts being numbered with the addition of 100. Thus disc 1 50A has an annular region 154 containing rows of slots 155 defined between fins 156 and ligaments 157. One row of fins 158 extends as a diameter across the disc. The rows of slots end just short of perimeters 152 and 153 to form unperforated rims 159 and 160 at the outer and inner edges of annulus 154.

As shown in Figure 15 each disc has channels 161 in its faces, the channels extending through its fins 156 to link adjacent slots across the fins.

Thus mixing passageways from one slot to a neighbouring slot are formed for fluid passing through the stack. This is advantageous particularly if a slot becomes blocked as fluid can then bypass the blockage by flowing through a channel 161 from that slot to an adjacent slot.

As shown, the channels 161 are etched or otherwise formed through a portion only of the thickness of each disc in its fin region so that the integrity and strength of the stack can be maintained during the bonding process. The channels may be, for example, of depth about half the thickness of the disc.

It is also possible that similar channels can be formed in the ligaments 157 (shown dotted in Figure 15) to provide alternative or additional mixing passageways between adjacent slots.

As stated above, all the structures described with reference to the drawings can be used either for the primary purpose of cooling a hot article, e.g. a printed circuit board or a lamp, or for the primary purpose of heating a fluid stream.

Claims

CLAIMS 1. A heat exchanger having a base against which an article to be cooled can be attached and a plurality of fins, the fins being formed by a plurality of individual components stacked together.
2. A heat exchanger according to Claim 1, in which the base is formed as a stack of individual base components.
3. A heat exchanger according to Claim 2, in which a base component and a fin component are formed as an integral, one-piece component.
4. A heat exchanger according to Claim 1, 2 or 3, in which passageways for cooling fluid are defined between adjacent fins, the fins extending transversely to the longitudinal direction of the stack.
5. A heat exchanger according to Claim 4, which comprises a cuboid stack having integral base and fin components.
6. A heat exchanger according to Claim 5, in which the base portion of each integral component is of greater thickness than the fin portion.
7. A heat exchanger according to Claim 6, in which the fin portion has holes through its thickness each hole being surrounded by an annular collar, the collars in the stack acting as spacers which butt against the fin portion of an adjacent component, the holes and collars providing passageways through the stack.
8. A heat exchanger according to Claim 1, 2 or 3, in which passageways for cooling fluid are defined by the alignment of holes or slots through the fin portions of each of the stacked components, whereby the passageways extend longitudinally of the heat sink.
9. A heat exchanger according to Claim 8, which comprises a cylindrical stack of disc-like components.
10. A heat exchanger according to Claim 8 or 9, having a recess to receive the article to be cooled, in which the stack is formed of two different components, the first components having a central hole surrounded by a perforated outer region and providing thereby a portion of the stack with a central recess and the second components having a solid central region and providing thereby a portion of the stack with a solid base.
11. A heat exchanger according to Claim 10, in which a recess is provided at each end of the stack.
12. A heat exchanger according to any one of Claims 8 to 11, in which the components have an unperforated outer region and a central region containing the holes or slots.
13. A heat exchanger according to any one of Claim 8 to 12, in which the components in the stack have their holes or slots overlapping with the holes or slots of the immediately adjacent components whereby the passageways defined by the holes or slots take a tortuous path.
14. A heat exchanger according to any preceding claim, in which the components have been formed to the desired configuration by chemical etching.
15. A heat exchanger according to any one of Claims 9 to 13, in which each disc-like component comprises a plurality of concentric rings, adjacent rings being joined by a series of radial fins, the fins defining slots through the discs.
16. A heat exchanger according to Claim 15, in which a solid central region is defined inside the innermost ring.
17. A heat exchanger according to Claim 15 or 16, in which the fins are pitched to maintain a similar cross-section of conducting material for radial heat flow.
18. A heat exchanger according to any preceding claim, which is formed of a stack of sheets, each sheet containing a plurality of the individual components whereby the stack provides a multi-heat exchanger assembly.
19. A heat exchanger according to any one of Claims 8 to 18, in which solid fin areas between adjacent holes or slots in the fin portion of a stacked component have channels etched parkway through the thickness of the fin portion, the channels providing communication between said adjacent holes or slots.
20. A heat exchanger according to Claim 1, substantially as hereinbefore described with reference to and as shown in Figures 1 and 2 or 3 to 7 of the accompanying drawings.
21. A heat exchanger according to Claim 1, substantially as hereinbefore described with reference to and as shown in Figures 8 to 10; 11; 12 and 13; or 14 and 15 of the accompanying drawings.