A CONVECTIVE HEATSINK
Field of the Invention
This invention relates to convective heatsinks and methods of forming convective heatsinks. Many electronic appliances and devices use heatsinks as a cooling mechanism to ensure that internal components are not damaged by heat build up. In general the heat sensitive components are attached to a suitable base which has air circulated across its surface by means of a fan. Heatsinks are also required for linear photovoltaic solar concentrator systems. The present invention has been particularly developed for this latter application but is equally suitable for incorporation into electronic appliances and devices. Although the invention will be specifically described in relation to its use in the cooling and support of linear photovoltaic solar concentrator systems it should be understood that it is equally applicable to the construction of heatsinks of other applications.
This invention has particular application to the cooling and support of linear photovoltaic solar concentrator systems. In such systems there exists the need to remove excess heat from the photovoltaic solar cells in order to maximise the cell efficiency.
Background Art
In linear photovoltaic solar concentrated systems the solar cells are normally in good thermal contact with a finned metal heatsink which cools cells by means of convection. In the more common arrangements the finned metallic heatsink forms part of the structure which physically supports the solar cells.
In addition to the basic requirement of effective convective dissipation of heat a practical heatsink must have other qualities to ensure its usefulness. Some of these features include:
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(a) it must have sufficient inherent rigidity to ensure that it can support its own weight and attached components without it sagging;
(b) an ability to span long lengths without support;
(c) it must have a high thermal conductivity; (d) it must have a large surface area in proportion to its weight.
There are currently a number of different approaches to the manufacture of suitable heatsinks. In one approach a suitable aluminium composition is extruded to a cross section featuring finned projections and subsequently cut to the desired length. The resulting product has fins that run in the longitudinal direction. Whilst this method of production results in a heatsink that is rigid and can be used in a large span, the geometry of the tool present produces long fins that dissipate heat inefficiently. Additionally, the fins are wide and thick resulting in a heavy heatsink. One example of a heatsink produced in this manner requires a mass of 16.5kg/m2 of sunlight collected when typical solar cells are used.
In another approach aluminium of suitable composition is extruded to produce a cross section again with finned projections. The extrusion is cut to the desired width so that the fins run laterally. In this case the fins are quite short in length in respect to an optimal fin thickness and provide inefficient cooling. The extrusion process requires a base of considerable thickness to allow material to flow, leading to a product that is heavy. A lateral extrusion also has a length limited to the length of the tool. The result is a short device which is unattractive from an economic view point. In practice sections must be joined or otherwise supported to provide a useful length.
In a further approach a sandwich construction is employed in which an array of metal fin plates are mounted on metal rods or the like separated by spacers. The assembly is held together using threaded nuts engaged with correspondingly threaded portions of the rods. Although this construction produces a device that can dissipate heat by convection quite efficiently the geometry makes the device
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heavy if it is to provide a useful span. An example of such a sandwich construction heatsink requires a mass of 8.75kg/m2 of sunlight collected for typical solar cells.
In yet another approach a base is extruded with slotted projections and cut to the desired width so that the projections run laterally. Sheetmetal fins of suitable proportion are pushed into the slot by with an interference fit. Additional length is achieved by joining these pieces end to end. The advantage of the system is that fins are of an appropriate thickness. The limitations are that fin pitch is dictated by the physical limits of extrusion, there is the break between the base and the fin that impedes heat transfer and the continuous length is limited by the need to extrude the base perpendicular to the direction in which the heatsink is used.
Disclosure of the Invention
It is an object of this invention to provide a heatsink convective and a method of forming a convective heatsink which will overcome, or at least ameliorate, one or more of the foregoing disadvantages.
In one aspect this invention provides a method of forming a convective heatsink including the steps of forming one or more protrusions of substantially uniform height in a plurality of generally planar metal fins; arranging the fins on an elongate base in an array with the fins extending substantially transversely to the base and spaced apart by contact of the protrusions on the fins with an adjacent fin; joining the fins to the base; and interconnecting adjacent ones of the fins at a location spaced from the base.
In another aspect this invention provides a convective heatsink including an elongate generally planar base, and a plurality of substantially transversely extending generally planar metal fins attached to said base, said fins including one or more protrusions of substantially uniform height to space the fins apart by
contact of the protrusions with an adjacent fin, adjacent ones of said fins being interconnected at a location spaced from the base.
Preferably, the fins are arranged in a closely spaced mutually parallel configuration. In one form of the invention the interconnection of adjacent ones of the fins is provided by the protrusions. In another form of the invention the interconnection can be achieved by joining the fins to a reinforcing element. Both forms of interconnection can also be used.
Preferably all of the fins are interconnected .
In one form of the invention the protrusions are stamped tabs which extend from the plane of the fin to abut an adjacent fin when the assembly is formed. The protrusions can also, for example, be rounded raised formations or burst holes.
The base is preferably an extruded section and more preferably an aluminium extrusion.
The fins are preferably stamped from a precoated sheet material. The sheet material is preferably aluminium.
The method of this invention can also use metal fins precoated with a low melting point brazing material and include the step of heating the assembled array to a temperature sufficient for the coating to melt and migrate across the region between the fins and the base.
The fins are preferably formed with a folded edge which forms the joint with the base. The edge is preferably a short section of the fin extending perpendicularly to the plane of the fin.
The interconnection of the fins at a location spaced from the connection to the base provides a structure with substantial longitudinal rigidity and strength.
The convective heatsink of this invention provides the following desirable properties:
(i) a structure which results in great rigidity due to the interconnection of fins; (ii) (ii) a means for incorporating thin closely spaced fins which create a superior cooling effect; (iii) each unit can be produced economically using high volume production techniques previously only achievable in relation to longitudinally extruded heatsinks; (iv) assembly costs are low as only a small number of components additional to the heatsink units themselves is required; (v) the width and length of the heatsink can be readily adapted for different applications; (vi) weights as low as 2.5kg/m2 are easily achievable; (vii) the intrinsic geometry of the elongate heatsink adds to the rigidity of the structure allowing a considerable weight saving that in turn offsets production and assembly costs.
The invention will now be described, by way of example only, with reference to the accompanying drawings.
Brief Description of the Drawings
Figure 1 is a perspective view of the convective heatsink according to one embodiment of this invention;
Figure 2 is a perspective view shows the extruded aluminium base forming part of the heatsink of Figure 1 ;
Figure 3 is a perspective view of the fins forming part of the heatsink of Figure 1 ;
Figure 4 is a perspective view similar to Figure 1 showing a second embodiment of the convective heatsink according to this invention;
Figure 5 is a perspective view similar to Figure 1 showing a third embodiment of the convective heatsink according to this invention.
Best Method for Carrying Out the Invention
As shown in the drawings the heatsink of this invention is formed by a plurality of fins 2 that are attached to an elongate base 1. The elongate base 1 is an extruded aluminium section. One side of the base is shaped to accommodate the fitting of photovoltaic photocells (not shown) their protective covers (also not shown) and other components. The side of the base 1 to which the fins 2 are attached includes a generally flat portion 3.
The fins 2 are best shown in Figure 3. The fins are formed by stamping from an aluminium sheet. The stamping produces a generally planar fin with three pressed out tabs 4 that extend outwardly from the surface of the fin 2. Each tab 4 has a bent end 5 to provide for abutment with the surface of an adjacent fin 2. The lower edge of each fin 2 has an edge 6 at substantially right angles to provide a surface area for joining to the flat region 3 of base 1.
The aluminium sheet from which the fins are formed is precoated with a low melting point brazing material (not shown). Aluminium sheeting of this type is commercially available from Sapa Heat Transfer AB, Sweden. The coating on this sheet typically has a melting point 5°C to 10°C less than the melting point of the base material. The fins 2 and elongate base 1 can be assembled as shown in Figure 1 with the fins 2 transverse to a longitudinal extent of base 1. The edge 6 of the fins is in contact with the base 1 and the bent end 5 of tabs 4 is in contact with the opposite surface of the adjacent fin 2. The structure assembled in this manner is clamped is in a suitable jig or the like (not shown) and heated in an inert atmosphere. The brazing material coated on the fins is melted during this process
and migrates into the joints between edge 6 and base 1 as well as the joints between bent ends 5 and the adjacent fins 2. Once the structure is cooled, the fins and base are fused by the brazing material and the clamps or the like can be removed.
Figure 4 shows a second embodiment of the convective heatsink according to this invention. The heatsink is generally the same as that described above in relation to Figures 1 to 3 and the same reference numerals have been used to indentify the same features. In the heatsink of Figure 4 the fins 2 are formed with burst holes 7 instead of the tabs 4. The burst holes 7 are formed by a similar stamping process. In the assembly of the heatsink the burst holes provide spacing between the fins in the same way the tabs 4. Similarly, the edges of the burst holes are brazed to the adjacent fin 2 in the same way as the tabs 5 of the embodiment described with reference to Figure 1. The method of assembly and construction of the heatsink are otherwise the same as described in relation to Figure 1.
In a modification to the second embodiment the burst holes 8 can be replaced with rounded raised formations of a similar size. These rounded formations can also be formed by a similar stamping process.
Figure 5 shows a third embodiment of the convective heatsink according to this invention. The heatsink of the third embodiment is generally the same as the second embodiment described with reference to Figure 4. The same reference numerals have been used to identify the same features. In this embodiment external reinforcing elements 8 are used to interconnect the fins 2 at locations spaced apart from the base 1. The reinforcing elements 8 are aluminium angle sections that extend the full length of the heatsink. In this embodiment it is not essential that the edges of the burst holes 7 are brazed to the adjacent fin 2. The reinforcing elements 8 can be used to join the fins 2 together. If desired both the edges of the burst holes 7 and the reinforcing elements 8 can be used to join the fins together to provide a very rigid structure. The heatsink of the third
embodiment is made using substantially the same method as that for the first and second embodiments except that the reinforcing elements 8 are positioned along the upper edge of the fins 2 prior to the heating step. In some applications it may be desirable to form the reinforcing elements 8 from the same sheet as the fins 2 precoated with low melting point braising material so to ensure a good joint between the fins 2 and the reinforcing element 8.
It will be apparent that the method according to this invention can be readily automated. The protrusions provide a reliable and simple way to space the fins. Additionally the heatsink formed in this way is a rigid structure having a significant useful span length. Photovoltaic solar cells, protective covers and other components can be readily attached and conveniently cooled. In particular, the interconnection of the adjacent fins at a location spaced apart from the elongate base results in a structure of considerable rigidity and strength for its weight.
The foregoing describes only some embodiments of this invention and modifications can be made without departing from the scope of the invention.
The reference to any prior art in this specification is not, and should not be taken as, an acknowledgment or any form of suggestion that that prior art forms part of the common general knowledge in Australia.