Patent Publication Number: US-2013240193-A1

Title: Method of manufacturing a heat exchanger block, spacer means therefor, and heat exchanger block

Description:
FIELD OF THE INVENTION 
     This invention relates to a method of manufacturing a heat exchanger block, to a spacer means for use in the method, and to a heat exchanger block. 
     BACKGROUND OF THE INVENTION 
     Often it is necessary to cool a working fluid, and it is known for this purpose to use a heat exchanger. Heat exchangers are made in many different sizes, are used with many different working fluids, and utilise many different fluids as the coolant. The present invention is directed primarily at heat exchangers in which the working fluid is a liquid, typically water or oil, and in which the coolant is a gas, typically air. Such heat exchangers are widely used on industrial compressors for example, but the invention is also expected to have utility for other air-cooled heat exchangers. Also, the use of the invention for other heat exchangers, including those for which the coolant is another fluid such as water, is not excluded. 
     Heat exchangers in which the working fluid is a liquid usually comprise a number of tubes suspended between two tube plates, though it is known to use U-shaped tubes with each tube connected at opposite ends to a single tube plate. Typically, the working fluid flows through the tubes, whilst the coolant passes around and between the tubes, the working fluid giving up latent heat (by way of the tubes) to the coolant flowing around the tubes. 
     Each tube will typically carry a number of external fins (mechanically coupled to or integral with the respective tube). The fins increase the available surface area for heat transfer, but also cause an increase in the pressure drop as the coolant passes between and around the tubes. The heat exchanger designer will typically seek to increase the density of the fins so as to increase the heat exchange, without exceeding a maximum permissible pressure drop. 
     Often, each fin will engage more than one tube, with the fins substantially filling the space between the tubes. During the manufacture of a heat exchanger the manufacturer will often make sub-assemblies comprising a chosen number of tubes fitted with a chosen number of fins. These sub-assemblies are referred to herein as heat exchanger blocks, and are sometimes called fin blocks. The heat exchanger is assembled by securing the desired number of heat exchanger blocks to the tube plates. 
     It is a requirement for industrial heat exchangers to minimise the cost of manufacture. The time taken to manufacture the heat exchangers, and in particular the time for which the manufacturing or assembly line is utilised for a particular heat exchanger, is a significant proportion of the cost of manufacture. Most heat exchanger manufacturers therefore wish to reduce the time taken to manufacture their heat exchangers, and also seek alternative materials and methods in order to reduce the manufacturing cost. 
     Another requirement for industrial heat exchangers is to minimise their size and weight without compromising their heat exchange performance. Whilst a larger heat exchanger will typically provide a greater rate of heat exchange from the working fluid to the coolant, heat exchanger designers typically seek to minimise the size and weight of the heat exchanger so as to increase the portability of the heat exchanger, and to make it easier to package the heat exchanger alongside its related componentry. 
     DESCRIPTION OF THE PRIOR ART 
     Heat exchangers are most often constructed from metallic materials, i.e. metallic fins fitted to metallic tubes. Metals are commonly used because of their good thermal transfer properties. To secure a fin to the tube it is known to provide an aperture in the fin and to weld or braze the fin onto the tube. This method of manufacture suffers from several significant disadvantages. Firstly, the materials which can be used for the tubes and the fins are limited to those which can be welded or brazed. Secondly, the grade of the materials used, such as for example the minimum wall thickness of the tube, is determined by the requirement to withstand the welding or brazing operation (so that a relatively thick tube may need to be used, whereas a thinner tube would enhance the heat exchange performance). Thirdly, the welding or brazing operation raises the temperature of the tubes and fins sufficiently to heat treat the materials, the final product being softer than the starting materials—the starting materials must therefore be chosen so that the final product meets the desired material requirements. Fourthly, the requirement for a welding or brazing operation adds time and cost to the manufacture of the heat exchanger. 
     In an alternative known method of manufacture the fins are initially located as a loose fit upon the tubes and the tubes are thereafter mechanically expanded by a specialised expanding machine into thermal engagement with the fins. This method of manufacture also has a number of significant disadvantages. The first disadvantage is shared with the first method stated above, namely that the material of the tube in particular is limited to those which can be mechanically expanded. The second disadvantage is also shared with the first method as stated above, namely that the minimum thickness of the tubes is determined by the requirement for expansion—very thin tubes, which might be particularly suitable for heat exchangers, cannot be used if there is a possibility that they would split during the expansion process, or be sufficiently weakened by the expansion process to fail in service. The third disadvantage is that the fins are sometimes pushed along the tubes during the expansion process, so that the resulting fin spacing or density is not always consistent along the length of the tubes—this can have a significant effect upon both the heat exchanger performance and the pressure drop of the coolant. 
     An alternative and improved method of mounting fins upon heat exchanger tubes (and thereby manufacturing a heat exchanger block) is described in WO96/35093. That document discloses a tube finning machine in which fins can be pressed onto tubes by a linear motor, which has the accuracy required to ensure that the fins are accurately and consistently spaced. Since no welding or brazing is required, and no expansion of the tube is required, the materials of the tubes and/or fins is less limited than the earlier-described methods, and the machine and method can be used with a mixture of different materials for the tubes and/or fins in a single heat exchanger block. 
     The apertures in the fins described in WO96/35093 are closely-sized to match the outside diameter of the tubes. The apertures in many embodiments are formed with collars to enhance the heat exchange performance. Whilst it is primarily intended that the linear motor will determine the position of each of the fins, it is often desired that the collar of one fin engage the collar of the adjacent fin, and it is disclosed that in some heat exchangers the fin spacing can be determined by the engagement of adjacent fins. Since the fin spacing is usually predetermined by the heat exchange and pressure drop required, in such embodiments the length of the collars is designed to provide the desired fin spacing. 
     Another tube finning machine for manufacturing heat exchange blocks is disclosed in WO02/30591. That document discloses the use of a cartridge mechanism into which a large number of fins can be loaded, and which can thereafter be pressed onto the tubes together. This machine and method can provide a considerable reduction in the time taken, and therefore the manufacturing cost of, certain heat exchanger blocks. 
     DISCLOSURE OF THE INVENTION 
     The present invention seeks to provide a method of mounting fins upon heat exchanger tubes which improves further on the efficiencies afforded by the disclosures of WO96/35093 and WO02/30591. The invention also provides a fin and spacer means suitable for use in the method, and a heat exchanger block. 
     According to the invention, there is provided a method of manufacturing a heat exchanger block comprising a number of tubes and a number of fins, the fins having a predetermined spacing, the method including the steps of locating the fins in a carrier and pressing the fins onto the tubes, the method also including the step of providing spacer means for the fins, whereby the spacer means supports a fin during the pressing step and determines the spacing between the fins in the assembled heat exchanger. 
     Accordingly, the present invention shares the benefits of the prior art disclosures of WO96/35093 and WO02/30591 in not requiring a welding, brazing or expansion step, and therefore enables the use of a greater range of materials for the fins and tubes. By providing a spacer means which supports a fin during the pressing step the present invention allows a large number of fins to be pressed onto the tubes together, each fin being supported by a spacer means (and consequently by the other fins) during the pressing step. The spacer means maintains the desired separation between adjacent fins during the pressing step, and also when the pressing step has been completed, i.e. in the assembled heat exchanger block. 
     Accordingly, since the fin spacing or density in the assembled heat exchanger block is determined by the spacer means, there is no requirement to use a linear motor or other machine which can precisely position each fin. Instead, less precise means can be used to press the fins and spacer means onto the tubes. Hydraulic means in particular are suitable for delivering the large forces required to press a large number of fins onto a number of tubes at the same time, whilst being sufficiently accurate in the positioning of those fins. 
     The spacer means may be integral with a fin, or may be provided as a separate spacer component for location between adjacent fins. 
     The spacer means is left in place in the finished heat exchanger block, and can therefore surround the tubes, providing greater support for the fins adjacent to their apertures (and adjacent to the collars surrounding the respective apertures if present) as the fins are slid along the tubes during assembly. 
     Preferably, the spacer means comprises a separate corrugated sheet of metallic material. By making the spacer of a suitable metallic material it can help to transfer heat from the working fluid to the coolant. By making the spacer means corrugated the spacer means can substantially span the area of a fin, and therefore substantially fill the space between adjacent fins, whilst still permitting coolant to flow between the fins and around the tubes. 
     Preferably also, the spacer means has openings corresponding to each tube, the openings being adapted to surround a respective tube. Desirably, the opening is larger than the tube in the direction of the corrugations so that there is an area adjacent to each tube which is free of spacer. This is desirable so that in an assembled heat exchanger the coolant can flow along all of the corrugations, and none of the corrugations are partly or fully closed off by the tube(s) and/or collars of the fins. 
     Desirably, a number of heat exchanger blocks are assembled into a heat exchanger by securing the heat exchanger blocks to respective tube plates. The heat exchanger blocks preferably comprise a single row of tubes interconnected by a number of fins. Making a heat exchanger block from a single row of tubes and their respective fins is particularly cost effective, and heat exchanger blocks can be made in standard dimensions, from standard materials and having standard heat exchange performance, so that a heat exchanger designer can utilise a chosen number of standard heat exchanger blocks to achieve the performance required of the assembled heat exchanger. 
     If the spacer means comprises a number of spacers which are separate from the fins they are preferably designed to substantially match the size and shape of the fins. In the manufacture of a heat exchanger block comprising a single row of tubes the fins and spacers will have a height corresponding to the spacing between adjacent heat exchanger blocks in the assembled heat exchanger, and a length corresponding to the width of the heat exchanger block. Desirably, the axis of the corrugations is substantially perpendicular to the longitudinal axis of the spacer, i.e. parallel to the minor axis of the spacer. It will be understood that during the step of pressing the fins and spacers onto the tubes, the fins will be pressed together and it is necessary to counter the tendency to flatten the corrugations. It can be arranged that the spacer is sufficiently rigid to withstand the forces involved without distortion of the corrugations, and the carrier can be provided with side walls which engage the ends of the spacers and help resist the flattening (and consequential lengthening) of the spacers during the pressing step. 
     The invention places no restriction upon the direction of movement of the fins during the pressing step, i.e. it places no restriction upon the orientation of the pressing machine. The machine may be arranged to move the fins in a substantially horizontal direction during the pressing step, or in a substantially vertical direction, or in any intermediate direction, as desired. 
     There is also provided a heat exchanger block comprising a number of tubes and a number of fins, each fin having a number of apertures which surround the respective tubes, the fins being separated by spacer means, each spacer means having a number of openings which surround the respective tubes, the openings being larger than the apertures. 
     In embodiments utilising a combination spacer means and fin, i.e. in which the spacer means is integral with the fin, the corrugations of the spacer which provide the separation between adjacent fins are added to parts of the fins, the partially corrugated fins being used without separate spacers. 
     As explained in relation to the prior art document WO96/35093, it is known to determine the separation between adjacent fins by way of the collars of the fins, but the present invention uses corrugations (which do not engage the tube) rather than collars (which do engage the tube) to provide the desired fin spacing, and furthermore to provide support for the fins during the pressing step. 
     Preferably, the combination spacer means and fin comprises an alternating series of substantially flat portions and corrugated portions. Ideally, each flat portion has an aperture to receive a tube. Ideally also, each corrugated portion has an opening to receive a tube, the opening being larger than the tube so that the corrugated portion does not engage the tube. 
     There is also provided a forming machine for making a combination spacer means and fin for a heat exchanger, the combination spacer means and fin comprising an alternating sequence of corrugated portions and non-corrugated portions, the machine having cooperating rollers, the rollers having peripheral regions adapted to press a metal sheet into a corrugated form, the rollers having additional regions between the peripheral regions, the additional regions being adapted to maintain a substantially flat form of the sheet. When a flat sheet of metal is passed between the rollers it is formed into a series of corrugated portions (by the complementary forms of the peripheral regions) separated by substantially flat portions (formed by the additional regions). 
     In some manufacturing processes the combination spacer means and fin is passed through the forming machine as the final manufacturing step, i.e. after the formation of the apertures and openings. If the combination spacer means and fin has collars surrounding the apertures the additional regions must include recesses to accommodate the collars. 
     Desirably, the opening in the spacer means is oval rather than circular. Thus, it is necessary that a corrugation does not terminate at a tube, i.e. that there is a flow path along each corrugation, and around the tube, and then along another corrugation. The opening must therefore be larger than the diameter of the tube in the direction parallel with the axis of the corrugations, but can be of a smaller dimension (and perhaps can be of a dimension substantially identical to the diameter of the tube) in the direction perpendicular with the axis of the corrugations. 
     The invention also provides a combination spacer means and fin for a heat exchanger, the combination spacer means and fin having a number of openings and a number of apertures adapted to receive respective tubes in the assembled heat exchanger, the combination spacer means and fin comprising corrugated sections separated by substantially planar sections, a respective aperture being located in a substantially planar portion and being sized to closely fit the tube, a respective opening being located in a corrugated portion, the opening being larger than the aperture. 
     There is also provided an alternative method of assembling the heat exchanger block, in which each of the fins (and each of the spacers, if separate spacers are used) is secured in position relative to the other fins (and spacers) prior to insertion of the tubes, and is supported during the pressing step. In one method, a first mounting plate is located to one side of the fins (and spacers), and a second mounting plate is located to the opposed side of the fins (and spacers), the mounting plates engaging the long sides of the fins (and spacers). The mounting plates have grooves or depressions formed therein, each groove or depression being adapted to locate a long side of a fin (or spacer). The mounting plates therefore serve to maintain the relative position of each of the fins (and spacers) during insertion of the tubes, and provide additional support the fins (and spacers) during that assembly step. 
     In another alternative method, the fins (and spacers) are packed together with a solid material which maintains the relative positions of the fins (and spacers) during insertion of the tubes. The solid material is preferably a flowable material such as a fine silicon sand, or could be a material such as ice for example which can readily be converted to and from a fluid. The solid material could fill the gaps between the adjacent fins (and spacers, if separate spacers are used) so as to maintain the desired separation, and to support the fins (and spacers) whilst the tubes are inserted. The solid material should be flowable (or readily made flowable) so that it can readily be removed from the assembled heat exchanger block. 
     If a solid material is used the fins would preferably be fitted with a series of dowels or the like passing through the aligned apertures and openings before the solid material is introduced, the dowel ensuring that the solid material does not enter the tubes as they are subsequently passed through the apertures and openings as the dowels are removed. 
     Whilst it is a stated advantage of the present invention that a welding or brazing step is avoided, the manufacturer of a heat exchanger block can decide to weld or braze (or solder) the fins to the tubes as an additional manufacturing step if desired for the particular application, or the particular materials being used. The manufacturer may not need to provide an annular joint surrounding the tube, but may instead provide only a spot joint so as to permanently secure the fin(s) to the tube(s). Alternatively, the manufacturer may use a bead of glue upon the tubes so as to secure the fins in position, the glue being chosen for suitability at the temperatures which will be experienced by the heat exchanger. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The invention will be further described, by way of example, with reference to the accompanying drawings, in which: 
         FIG. 1  shows a representation of a heat exchanger block manufactured according to the present invention and components used in the method, the spacer means comprising a set of separate spacers; 
         FIG. 2  shows a plan view of part of an assembled heat exchanger block constructed from the components of  FIG. 1 ; 
         FIG. 3  shows a front view of part of a spacer of  FIG. 1 ; 
         FIG. 4  shows a plan view of the part of the spacer of  FIG. 1 ; 
         FIG. 5  shows a front view of part of a fin of  FIG. 1 ; 
         FIG. 6  shows a plan view of the part of the fin of  FIG. 1 ; 
         FIG. 7  shows a perspective view of a partially-assembled heat exchanger block utilising combination spacer means and fins; 
         FIG. 8  shows a view of an alternative embodiment to that of  FIG. 7 ; 
         FIG. 9  shows a front view of an alternative combination spacer means and fin; 
         FIG. 10  shows a plan view of the fin of  FIG. 9 ; and 
         FIG. 11  shows a side view of a set of corrugating rollers of a forming machine for making a combination spacer means and fin. 
     
    
    
     DESCRIPTION OF THE EXEMPLARY EMBODIMENTS 
       FIG. 1  shows a representation of a heat exchanger block  10  in perspective view.  FIG. 1  is a representation since the heat exchanger block  10  is shown with only one tube  12 , whereas in practice a tube  12  would be located in each of the rows of fin apertures. Mounted upon the tube(s)  12  are a number of fins  14  and spacer means. In this embodiment the spacer means comprises a number of separate spacers  16 . 
     In common with prior art fins as used in the methods of manufacture described in WO96/35093 and WO02/30591, the fins  14  are formed with a row of apertures  20 , each aperture being surrounded by a collar  22  which is a close sliding fit upon the tube  12  (see the separate fin  14  shown in  FIG. 1 ). In this embodiment the tubes are of circular cross-section and the apertures  20  and collars  22  are similarly circular, but it will be understood that other shapes could be used if desired. 
     The spacers  16  have corresponding openings  24 , the openings  24  being aligned with the apertures  20 , but being of greater diameter, as explained in more detail below (see the separate spacer  16  shown in  FIG. 1 ). 
     Prior to assembly into a heat exchanger block such as  10 , the desired number of fins  14  and spacers  16  are loaded into a carrier  26 , only part is shown in  FIG. 1 . The carrier  26  comprises a ledge  30  and a side wall  32 , the carrier  26  being at least as long as the heat exchanger block  10 , and therefore being adapted to carry all of the fins  14  and spacers  16  for the heat exchanger block. Thus, it is desired that the heat exchanger block  10  is manufactured by pressing all of the fins  14  and spacers  16  onto all of the tubes  12  in a single pressing step, although it is recognised that this might not always be possible, and two or more separate pressing steps might be required for a particular heat exchanger block. 
     The fins  14  and spacers  16  are loaded alternately into the carrier  26 , the edge  34  of each spacer being close to, or engaging, the side wall  32  of the carrier  26 . It is also desirable that the corresponding edge of each fin is also close to, or engaging, the side wall  32  of the carrier  26 , so that the carrier  26  acts to locate each of the fins  14  and spacers  16  relative to one another, and can thereby act to locate the fins  14  and spacers  16  as they approach the tubes during the pressing step. 
     Since each of the fins  14  are preferably of identical length and height (even if they are not all of identical materials and thickness), and since each of the spacers  16  are preferably of identical length and height, the positioning of the fins and spacers into the carrier  26  will ensure that the apertures  20  and openings  24  are aligned. Additional alignment could be provided in certain embodiments by a former or guide rod positioned within the apertures  20  and openings  24 . 
     The array of fins  14  and spacers  16  mounted onto the carrier  26  is desirably closely-packed, i.e. each fin engages the adjacent spacers. If desired, the fins and spacers can be secured together by adhesive or other means, prior to mounting onto the tubes  12 . 
     When the desired number of fins  14  and spacers  16  has been loaded onto the carrier  26 , the carrier  26  is moved until the apertures  20  and openings  24  are aligned with the tubes  12 , and a pressing machine (not shown), presses the array of fins and spacers onto the tubes. (It will be understood that whilst the pressing machine can be arranged to move the carrier and fins relative to stationary tubes, an alternative pressing machine could be used in which the carrier and fins are clamped in position and the tubes are driven therethrough, or a machine in which both the carrier and tubes move together during the finning process.) 
       FIG. 1  therefore represents an artificial situation which is presented for the purposes of understanding. As above indicated, it is not intended that the fins and spacers will be pressed onto the single tube  10  shown in  FIG. 1 , but rather all of the tubes which are to be assembled into a heat exchange block are mounted onto the pressing machine and the fins  14  and spacers  16  pressed onto all of the tubes  10  together. Also, the separate fin  14  and the separate spacer  16  are shown for the purposes of understanding, since these components are not pressed separately onto the tubes. 
     It will be understood that the desired array of fins  14  and spacers  16  can be loaded onto the carrier  26  as a separate manufacturing step. Such manufacturing step does not delay the pressing machine, and since it is expected that the loading of the desired number of fins and spacers will be the slowest manufacturing step several loading stations can be operating simultaneously, so that the overall rate of loading the fins and spacers substantially matches the rate of the pressing machine and the manufacturing procedure is optimised. 
     It will also be understood that since each of the collars  20  is in sliding engagement with a respective tube  12 , the force required to press the fins  14  and spacers  16  onto the tubes  10  is considerable. The pressing machine will therefore typically incorporate a hydraulic drive means. A hydraulic drive means will be sufficiently accurate to press the array of fins  14  and spacers  16  to the required position along the tubes  12 . 
     Since the spacers  16  are of substantially identical overall size to the fins  14 , the spacers provide almost complete support for the fins during the pressing step, the spacers  16  maintaining the required separation between the fins  14  both during the pressing step and in the assembled heat exchanger block  10 . 
     In the heat exchanger block  10  of  FIG. 1 , the tube  12  is shown projecting beyond the fins  14 ; this is required so as to permit the heat exchanger block to be mounted into a tube plate during the subsequent manufacturing step of assembling the heat exchanger. 
     The subsequent manufacturing steps are outside the scope of the present invention, and can be identical to the steps of prior art heat exchanger assembly methods. For example, the heat exchanger manufacturer will typically manufacture a desired number of heat exchanger blocks (each block typically comprising a single row of tubes  12  carrying the chosen number of fins  14  and spacers  16 ) and mount the projecting tubes into respective tube plates, the tube plates having openings to accept each of the tubes in each of the heat exchanger blocks. The heat exchanger blocks will typically be stacked together, and one heat exchanger block may rest upon its neighbour, or there may be a small gap between the fins of one heat exchanger block and its neighbours. Typically, the stack of heat exchanger blocks will be arranged so that adjacent blocks are offset so as to form a triangular tube array, i.e. the heat exchanger blocks will be offset by around half of the tube spacing from the neighbouring heat exchanger blocks. 
     It will be observed from  FIG. 1  that the spacer  16  comprises a corrugated sheet, in this embodiment of metallic material so that the spacer contributes also to heat exchange. The axis A-A along the corrugations  36  is substantially perpendicular to the longitudinal axis L-L of the fins  14 . This means that in the assembled heat exchanger the coolant must pass along the corrugations  36  of the spacer  16  of one heat exchanger block  10 , and then along the corrugations  36  of the spacer  16  of a neighbouring heat exchanger block  10 . It is preferable to ensure that the corrugations of neighbouring heat exchanger blocks are substantially aligned so as to minimise the pressure drop, but it will be observed from  FIG. 2  in particular that the area occupied by the fins  14  and spacers  16  is only a small proportion of the total area of the heat exchanger block surrounding the tubes  12 , and the coolant can readily flow from one heat exchanger block to its neighbours, even if the corrugations  36  (and also the fins  14 ) of neighbouring heat exchanger blocks are misaligned. Any misalignment between adjacent heat exchanger blocks will induce turbulence into the working fluid, which turbulence will increase the pressure drop but can also increase the heat exchange. 
     It will be understood from  FIG. 1 , and also from a comparison of the size of the apertures  20  and openings  24  seen in  FIGS. 3 and 5 , that the openings  24  in the spacer  14  are significantly larger than the collars  22 . This allows coolant to flow along all of the corrugations  36 , and in particular to flow along those corrugations which are aligned with the tubes  12 . Thus, if the openings  24  were sized to closely match the tubes  12  then the corrugations  36  which terminate at the openings  24  would become closed off by the tubes  12 . Permitting coolant to flow along the corrugations, around a tube, and then along another corrugation, increases the heat exchange. 
     The form of the corrugations  36  is substantially sinusoidal in this embodiment. It will be understood, however, that the corrugations could have a triangular, square or other form, as desired. The different forms of corrugations will provide different heat exchange and pressure drop performances, and the heat exchanger designer can utilise a corrugation profile which matches the performance characteristics required. 
     As above indicated, the spacers  16  provide support across substantially the full area of the fins  14  during the pressing step. In many heat exchanger blocks it will not be necessary to provide any additional support for the fins  14 . It will also be understood that the spacer  16  must be sufficiently rigid to withstand the loads applied by the pressing machine, which loads can be considerable if a large number of fins  14  and spacers  16  are pressed together onto the tubes  12 . As shown in  FIG. 2 , the material from which the spacers  16  are made can be thicker than the material of the fins  14 . 
     It will also be understood that the tendency of the spacers  16  to elongate under loading will be resisted by the engagement of the ends  34  of the spacers with the side walls  32  of the carriers  26 . 
       FIG. 2  shows the corrugations  36  of the spacers being aligned, i.e. the corrugation peaks of one spacer  16  are aligned with the corrugation peaks of the other spacers. In other embodiments alternate spacers are reversed, so that the peaks of one spacer face the troughs of the adjacent spacers. Such an arrangement will make it less likely that the fins  14  become deformed during the pressing step. 
     It is expected that stainless steel fins  14  and stainless steel spacers  16  would be sufficiently rigid to permit 460 fins (and 459 spacers) to be pressed together onto an array of tubes  12 . A fin spacing of 3 mm would produce a heat exchanger block approximately 1.4 m long which is a standard length used in the heat exchangers of industrial compressors. Other materials and material combinations can, however, be used, for example aluminium fins with copper spacers, the material (or materials) from which the tubes and fins are made ideally being chosen dependent upon the heat exchanger application. 
     The invention is not limited to the manufacture of standard-size heat exchanger blocks, and a heat exchanger block of any practical dimensions can be made according to the present invention. The invention can be utilised to press more (or fewer) than 460 fins and 459 spacers at a time, it being desirable that all of the fins and spacers of a heat exchanger block are pressed together in a single pressing step, regardless of the length of the heat exchanger block. 
     With larger heat exchanger blocks (and in particular longer heat exchanger blocks where a large number of fins and spacers are pressed onto the tubes in a single pressing step), an oscillator can be provided to vibrate the tubes and/or fins, and perhaps to make the tubes and/or fins resonate, it being understood that the force required to press the fins onto the tubes will be reduced if the tubes and/or fins are vibrating as the fins are pressed along the tubes. 
     It will be understood that the separation between the fins  14  is determined by the spacers  16 . The spacers  16  can if desired ensure that the collar  22  of one fin does not engage the collar of the adjacent fin, which engagement is known to increase the force required to press the fins  14  along the tubes  12 . Spacers of different profile can be used at different parts of the heat exchanger block, so that the spacing between chosen fins can differ from the spacing between other fins, dependent upon their position within the heat exchanger block. 
     The heat exchanger block  110  shown in  FIG. 7  comprises a number of tubes  12  and a plurality of combination spacer means and fins  114 . The fins  114  in this embodiment therefore have integral spacers in the form of corrugated portions  116 , each fin  114  comprising an alternating sequence of corrugated portions  116  and substantially flat portions  40 . 
     As shown in  FIG. 7 , the corrugated portions  116  of adjacent fins  114  are offset so that each corrugated portion  116  lies between a substantially flat portion  40  of the adjacent fins, and vice versa. In this way, the adjacent fins  114  are separated by the chosen distance corresponding to the height of the corrugations, as in the earlier embodiments, but without requiring separate spacers. It will be observed that in the embodiment of  FIG. 7  the heat exchanger block has twenty one tubes  12 , so that two types of fin  114  are required. The first type of fin  114   a  has eleven flat portions  40  and ten corrugated portions  116 , and the second type of fin  114   b  has eleven corrugated portions  116  and ten flat portions  40 . In embodiments for heat exchanger blocks having an even number of tubes, the fins  114  could be identical, with an equal number of corrugated portions and flat portions, with alternating fins reversed. 
     In the heat exchanger block  210  of  FIG. 8  the fins  114  having integral spacers are alternated with substantially planar fins  14 . The choice of whether the heat exchanger block comprises solely combination spacer means and fins as in  FIG. 7 , an alternating sequence of combination spacer means and fins with substantially planar fins as in  FIG. 8 , or a mixture of those arrangements, can be made by the heat exchanger designer in accordance with the heat exchange requirements. The heat exchanger designer utilising an embodiment such as that of  FIG. 8  can take advantage of the fact that the fin  14  can be of different material and/or different thickness to the fin  114 , as desired. 
     It will be understood that in accordance with the earlier embodiments, the apertures  120  in the flat portions  40  should preferably closely match the diameter of the tubes  12  (and the apertures  120  can include collars if desired), whereas the openings  124  in the corrugated portions  116  are larger than the diameter of the tubes  12  so that fluid can flow along all of the corrugations and around the tubes. 
     As shown in  FIG. 9 , it is not necessary that the openings in the corrugated portions  216  of the fin  214  be substantially circular, and the openings  224  in this embodiment are oval, having a larger dimension D (in the direction of the axis of the corrugations) which exceeds the diameter of the tube  12  and a smaller dimension d (in the direction perpendicular to the axis of the corrugations) which closely matches the diameter of the tube  12 . Thus, it is only necessary that the corrugated portions  116  do not engage the tube  12  in the direction of the corrugations. Clearly, in heat exchanger blocks having tubes which are not circular, the apertures would be shaped to match the tubes and the openings would be similarly elongated. 
       FIG. 9  shows the first additional feature of a number of raised ribs  42  upon each of the substantially flat portions  240 , and the second additional feature of a raised portion  44 , which ribs  42  and portions  44  act as turbulators to induce turbulence into the coolant as it flows between and around the tubes  12 . 
       FIG. 10  is a plan view of the fin  214 , and shows the (optional) collar  222  which is formed around each of the apertures  220 . 
       FIG. 11  shows a part of the forming machine for making the combination spacer means and fins  114 ,  214 , i.e. the fins with alternating substantially flat portions and corrugated portions. As with known corrugating rollers, the corrugating rollers  46  of this embodiment have peripheral regions  48  with complementary formations, whereby as the rollers  46  rotate the peripheral regions  48  together press a substantially flat metallic sheet  50  into lo the desired corrugated form. To form a combination spacer means and fin (such as the fin  114  or  214 ) with an alternating series of corrugated portions  116 ,  216  and flat portions  40 ,  240  the peripheral regions  48  are discontinuous, and separated by additional regions  52  which have no corrugating formations. As the rollers  46  rotate the additional regions  52  of the respective rollers  46  engage opposed surfaces of the flat metallic sheet  50  and maintain the substantially flat form of the sheet, thereby forming the substantially flat portions  40 ,  240 . 
     In the embodiment of  FIG. 11  each of the additional regions  52  of the upper roller  48  as drawn includes a recess  54  to accommodate the collar  222  and ribs  42  of the fin, so that the corrugated portions  48  can be formed after the aperture and openings have been cut from the sheet  50  and the collar  222  and ribs  42  have been formed therein. In an alternative embodiment the corrugated portions are formed first, so that the recesses  54  are not required. 
     The embodiments of the present application can all be used in preferred methods in which all of the tubes  12  of a heat exchanger block are inserted into the apertures and openings of the fins (and spacers) together, or in less preferred methods in which only one or some of the tubes of the heat exchanger block are inserted at a time. 
     If desired in particular heat exchanger blocks, the fins (and/or spacers if separate) of the embodiments of  FIGS. 1-6 ,  7  and  8  can include vortex generators similar to those of the embodiment of  FIGS. 9 and 10 , i.e. projections which are intended to induce turbulence into the coolant. 
     The resulting form of the heat exchanger block  10  shown in  FIG. 1  resembles to some extent the air-to-air heat exchanger used in a domestic boiler, which comprises sets of corrugated sheets separated by flat sheets, the corrugations of adjacent sheets being perpendicular. Hot air flows in one direction (for example vertically) through certain of the corrugations, and cold air flows in another direction (for example horizontally) through other corrugations. The present invention differs from those arrangements in using tubes to transport the working fluid, as is typical of heat exchangers in which the working fluid is a liquid. 
     If desired, one or both of the end-most fins, i.e. the first and last fins loaded into the carrier  26 , can be of harder material than the remaining fins, for the purpose of reducing the likelihood of damage to the heat exchanger block during subsequent transportation and the assembly procedure.