AND HEAT EXCHANGER BLOCK FIELD OF THE INVENTION

This invention relates to a method and machine for manufacturing a heat exchanger block, to fins for manufacturing a heat exchanger block, and to a heat exchanger block. The invention describes certain improvements over the method and apparatus of our copending application PCT/GB201 1/052054.

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, sometimes called "extended surface members", which are 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. One arrangement using this method utilises fins with integral spacer means. The integral spacer means avoids the third disadvantage, but the first and second disadvantages present a significant concern to heat exchanger manufacturers who might wish to use this method.

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 which engage the tubes in use and 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 exchanger 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 to manufacture, and therefore the manufacturing cost of, certain heat exchanger blocks.

DISCLOSURE OF THE INVENTION

The present invention seeks to provide a method and machine for 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 for use in manufacturing a heat exchanger block, 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, neighbouring fins being separated by a predetermined spacing by way of spacer means, the method including the steps of locating a number of fins and fitting the fins onto the tubes, the method including the step of vibrating the tubes and/or the fins during the step of locating the fins upon the tubes.

In preferred embodiments of the method, the tubes are oriented with their longitudinal axes substantially vertical whereby gravity acts to move the fins along the tubes to their required position. The mechanical engagement between the fins and the tubes is sufficiently large to provide the required heat transfer between the tubes and the fins, and yet permits the vibration to move the fins along the tubes under the force of gravity alone.

The invention can, however, alternatively be utilised with the tubes at another angle, including substantially horizontal, with the vibration acting to assist the force provided by a pressing machine. In these alternative embodiments, the fins can be moved by the pressing machine relative to the stationary tubes, or the tubes can be moved relative to the stationary fins, or both the fins and tubes can be moved, as desired, the vibration reducing the force which is required to be provided by the pressing machine, or increasing the number of fins which can be pressed by the pressing machine. 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. Nevertheless, the present invention does not exclude the use of a brazing or welding step, or otherwise securing adjacent fins together, if that is desired in a particular heat exchanger block. In one example, a chosen number of fins can be secured together by brazing or gluing prior to their location upon the tubes. The invention also provides a fin for a heat exchanger block, the fin having integral spacer means whereby the spacer means of one fin can engage the neighbouring fin and determine the spacing therebetween, the fin having a number of apertures to receive a number of tubes, the spacer means being located at a distance from the apertures.

Accordingly, the fins of the present invention differ from the fins of WO96/35093 in providing the spacer means away from the tubes, and in particular separate from any collar which surrounds an aperture and engages the tube. Thus, it is known that in embodiments in which the collars act to space the fins, the collar of one fin can interlock with the collar of an adjacent fin, increasing the force required to press the fins onto the tubes. The present invention avoids the possibility of the collars interlocking by providing spacer means remote from the apertures, which therefore do not engage the tubes. The integral spacer means allows a number of fins to be located upon the tubes together, each fin being supported by a spacer means (and consequently by the other fins). The spacer means maintains the desired separation between adjacent fins as the fins are moved onto the tubes, and also 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. 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 may comprise a single row of tubes interconnected by a number of fins, or may comprise an array of tubes. If desired, the heat exchanger block may comprise all of the tubes of a complete heat exchanger core (such as the finned core of a compressor cooler for example).

Alternatively, making a heat exchanger from a number of heat exchanger blocks which comprise a single row of tubes and their respective fins is particularly cost effective, as the heat exchanger blocks can be made in standard dimensions, from standard materials and having standard heat exchange performance. A heat exchanger designer can utilise a chosen number of standard heat exchanger blocks to achieve the performance required of the assembled heat exchanger.

There is also provided a heat exchanger block comprising a number of tubes and a number of fins, each fin having integral spacer means located at a distance from the tubes. Each fin has a number of apertures which surround the respective tubes, the fins being separated by the integral spacer means.

Preferably, the spacer means comprises a plurality of spacing elements carried by the respective fins. Desirably the spacing elements are deformations in the fin, usefully raised ribs, dimples or tongues of the fin material. The fins are ideally arranged in an alternating sequence with a series of first fins interspersed with a series of second fins, the spacing elements of the first fins being out of alignment with the spacing elements of the second fins.

Preferably, the spacing elements each have a contact part which is out of alignment with the plane of the fin, and at least one support wall connected to the contact part. Ideally the support wall is substantially perpendicular to the plane of the fin. The provision of substantially perpendicular support walls enables the spacing elements to provide good support for the adjacent fins as the fins are moved along the tubes. The support walls can be aligned substantially parallel to the flow direction of the coolant in use, whereby the support walls do not present a significant barrier to the passage of the coolant, and therefore do not significantly increase the pressure drop across the heat exchanger. Alternatively, the support walls may be aligned across the flow direction whereby to induce turbulence into the coolant. The size and position of the spacing elements, and in particular their support walls, can be chosen by the heat exchanger designer to satisfy the heat exchange and pressure drop requirements.

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 perspective view of a first embodiment of machine for manufacturing a heat exchanger block according to the present invention; Fig.2 shows a perspective view of a second embodiment of machine for manufacturing a heat exchanger block according to the present invention;

Fig.3 shows a front view of a fin and integral spacer means of the present invention;

Fig.4 shows a front view of a fin and integral spacer means which is complementary to that of Fig.3;

Fig.5 shows a front view of another fin and integral spacer means of the present invention;

Fig.6 shows a front view of a fin and integral spacer means which is complementary to that of Fig.5; Fig.7 shows an enlarged view of some of the fins of Figs. 5 and 6;

Fig.8 shows a plan view of a stack of fins of Figs. 5 and 6 prior to assembly into a heat exchanger block; and

Fig.9 shows an enlarged view of a part of the machine of Fig .1 .

DESCRIPTION OF THE EXEMPLARY EMBODIMENTS

Fig.1 shows a machine 10 for making a heat exchanger block, part of which heat exchanger block is represented by the numeral 12. In known fashion, the heat exchanger block 12 comprises a number of fins 14 and a number of tubes 16, the fins being in thermal engagement with the tubes.

In the embodiments of Figs. 1 and 2, the heat exchanger block 12 comprises an array of tubes 16 arranged in multiple rows, whereas the heat exchanger block created from the fins of Figs. 3-8 comprises a single row of fins. The number of rows of tubes in the heat exchanger block, as well as the number of tubes 16, and the number and spacing of the fins 14, can vary according to the heat exchange requirements.

The machine 10 of Fig.1 and the machine 1 10 of Fig.2 both comprise a base plate 20 which can rest upon, or be secured to, the floor. The base plate 20 carries four substantially vertical support posts 22, which are connected together at their tops by a top frame 24. The base plate 20, the support posts 22 and the top frame 24 together comprise a rigid structure. Mounted upon the base plate 20 is a tube-mounting plate 26. The tube-mounting plate 26 is mounted upon resilient bushes 28 (Fig.9) which are designed to mechanically isolate the tube-mounting plate 26 from the base plate 20, for the purpose described below.

The tube-mounting plate 26 has a carrier 30 which has an array of recesses or openings (not shown), each of which can accommodate the end of a respective tube 16. The desired array of tubes 16 can therefore be mounted upon the carrier 30, with their longitudinal axes substantially parallel and vertical.

A movable top plate 32 is mounted upon the posts 22 by way of respective sets of cam follower bearings 34, which permit the top plate to be moved up and down along the posts 22.

A pair of vibrators 36 is mounted upon the tube-mounting plate 26 in the embodiment of Fig.1 . In the alternative embodiment of Fig.2 a similar pair of vibrators 136 is mounted upon the top plate 132. Apart from the different location of the vibrators 36, 136, the embodiments of Figs. 1 and 2 are substantially identical.

The vibrators 36 and 136 each contain an electric motor which is connected to an eccentric weight (not seen). As the electric motor is rotated the eccentric weight is caused to rotate and the eccentricity causes the vibrator to vibrate with the frequency of the motor. It is arranged that the rate of rotation of the motor is variable whereby the frequency of the induced oscillations can be varied to match the requirements of the particular heat exchanger block 12. In one embodiment, the motor rotates at 3,000 rpm, providing vibrations with a frequency of 50 Hz.

The tube-mounting plate 26 is mechanically isolated from the base plate 20 so as to reduce, and ideally minimise, the vibrations which pass to the base plate 20 and to the underlying floor.

In order to assemble a heat exchanger block 12 the desired array of tubes 16 is mounted onto the carrier 30. A stack of fins 14, comprising a chosen number of fins which can be mounted together onto the tubes 16, is located adjacent to the top ends of the tubes. As shown in the alternative embodiments of Figs.3-8, each of the fins has an array of apertures 40 which are positioned to match the array of tubes 16 in the particular heat exchanger block, each aperture 40 being an interference fit upon a respective tube.

The top end of each tube 16 is fitted with a tapered member (not seen) which is smaller than the aperture 40 in the fins 14, whereby the stack of fins can be placed over the tapered members prior to movement along the tubes. It can be arranged that the "stack" of fins comprises a single fin, i.e. a single fin is moved along (down) the tubes at a time, but preferably the stack comprises a plurality of fins which are moved along the tubes together. The stack of fins can be initially secured together by a preliminary brazing, welding, or gluing step and can be presented to the tubes as a single unitary block such as that shown in Fig.8. Alternatively, the stack of fins can be mounted in a cartridge and loaded together onto the tubes, notwithstanding that the fins 14 remain separable at that stage.

Once the stack of fins 14 has been located at the uppermost ends of the tubes 16, the top plate 32, 132 is lowered into engagement with the top-most fin 14. As shown in Figs. 1 and 2, the top plate 32, 132 has an opening 42 which is of a size and shape to surround the array of tubes 16. However, it is arranged that the fins 14 project beyond the array of tubes, and the opening 42 is smaller than the fins, whereby the top plate 32, 132 engages the periphery of the top-most fin 14.

The motors of the vibrators 36, 136 are actuated whereupon a vibration is induced into the fins 14 and tubes 16, the vibration effectively reducing the frictional engagement between the tubes 16 and fins 14 sufficiently to cause the stack of fins 14 to move down the tubes 16 under the influence of gravity.

In the embodiment of Fig.1 the top plate 32 carries a pair of weights 44 which increase the downwards force upon the fins 14, whereas in the embodiment of Fig.2 the vibrators 136 provide the desired weight upon the top plate 132. It will be understood that in common with many prior art fins, the fins 14 have a collar 46 (see the alternative embodiment of Figs.7 and 8) surrounding each aperture 40, the collars 46 being designed for mechanical and thermal engagement with the tubes 16 in the assembled heat exchanger block 12. It is arranged that the mechanical engagement is not sufficient to prevent the stack of fins 14 being driven downwardly by the vibration-assisted force of the top plate 32, 132, and yet is sufficient to provide a good thermal engagement required for heat transfer in the assembled heat exchanger block.

It will be understood that Figs. 1 and 2 show one or more stacks of fins 14 which have already been driven down the tubes 16 into engagement with the carrier 30, and another stack of fins 14 adjacent to the top of the tubes 16 ready to be moved down the tubes. The fins 14 in each stack are very closely spaced and appear as solid in Figs. 1 and 2, but as seen in the enlarged view of Fig.9 comprise a number of discrete (but interengaging) fins (see also the interengaging fins in the alternative embodiment of Fig.8). It will also be understood that only some of the tubes 16 are shown in Figs. 1 and 2, so that the form of the fins 14 can be better understood. Clearly, when the machine 10, 1 10 is in use a respective tube 16 would occupy each of the openings 40 of the fins 14.

The fins 14 which are used in the present invention are fins with integral spacer means such as those of Figs. 3-8. A first pair of fins and integral spacer means which can be used with the machine and method of the present invention are shown in Figs. 3 and 4, and a second pair is shown in Figs. 5-8. In other uses of the method the fins do not have integral spacer means, and neighbouring fins are separated by a discrete spacer, such as the corrugated spacer of our copending application PCT/GB201 1/052054. The fins 214a, 214b of Figs. 3 and 4 each comprise a substantially flat sheet 50 carrying a number of spacing elements 52a, b. In this embodiment the spacing elements 52a, b are deformations created by cutting the flat sheet and pressing out a tab or tongue of the material (the sheet being cut and pressed to form spacing elements similar to that shown in the embodiment of Fig.8). In other embodiments the spacing elements comprise wells, dimples, deformations or the like pressed from the fin material. It is arranged that two distinct arrays of spacing elements are provided on the respective fins 214a, 214b, the arrays forming complementary spacing elements 52a and 52b with the spacing elements 52a of one array being out of alignment with the spacing elements 52b of the other array. The fins 214a and 214b are arranged in an alternating sequence whereby the spacing elements 52a each engage a substantially flat (or undeformed) part of the fin 214b, and vice versa. In this way, the spacing elements 52a and 52b will act to separate the adjacent fins 214a,b by a predetermined distance corresponding to the height h of the spacing elements (Fig.8). The form of the fins 314a, 314b in the alternative embodiment of Figs. 5-8 differ slightly from the fins 214a,b. Specifically, there are fewer of the respective spacing elements 52. It will be observed that the fins 314a and 314b are identically formed and that the fin 314b has simply been rotated through 180° so as to misalign the respective spacing elements 52.

The spacing elements 52, 52a and 52b each comprise a tab or tongue of material which has been cut and pressed from the material of the fin. The tab is pressed in such a way that the spacing elements have a contact part 56 (see Fig.7) which engages the neighbouring fin in use. In this embodiment the contact part is a continuous wall which lies in a plane which is substantially parallel to the plane of the fins. The contact wall is connected to two support walls 58 which serve to space the contact wall from the plane of the fin.

The support walls 58 and the contact wall 56 are of U-shape, and are cut and pressed from the fin material 50. In one method of making a spacing element 52, a pair of parallel slits is formed through the fin material and a pressing machine presses the material between the slits out of alignment with the remainder of the fin and into the U-shape. It will be seen that the support walls 58 in this embodiment are not perpendicular to the plane of the fin, but instead lie at a small angle to the perpendicular. The closer the support walls are to being perpendicular the greater they will resist deformation of the spacing element 52 during assembly of the heat exchanger block.

When the chosen number of fins are placed together with the spacing element of one fin engaging the adjacent fin, the fact that the support walls 58 are substantially perpendicular to the plane of the fins provides maximum support for the fins, i.e. the likelihood of the spacing elements being deformed whereby to reduce the fin spacing is reduced.

It will also be observed that the spacing elements 52, 52a, 52b are arranged substantially across the full area of the fins 214, 314, whereby they provide full support across the fins, both as the fins are moved along the tubes, and also during use of the assembled heat exchanger.

However, it will also be understood that the presence of the support walls 58 between the adjacent fins reduces the area through which the coolant may pass, and therefore increases the pressure drop across the heat exchanger block. The pressure drop can be minimised by arranging the spacing elements to that the contact walls 56 are substantially perpendicular with the intended direction of coolant flow C represented in Figs. 6-8. Alternatively, as in the embodiments shown in Figs. 3-8, the contact walls are substantially aligned with the coolant flow direction C, and therefore induce turbulence in the coolant.

The heat exchanger designer will be able to arrange the spacing elements so that their number and orientation provides the desired amount of turbulence whilst avoiding an unacceptable pressure drop.

As above indicated, the apertures 40 are surrounded by a respective collar 46. Whilst the provision of collars is not necessary for the present invention, they generally increase the thermal engagement between a fin and a tube and are therefore usually preferable. As shown in Fig.8, the height of each collar is significantly less than the height h of each spacer element 52, so that the collars of adjacent fins do not interengage or nest together, which is known to increase the force required to move the fins along the tubes. Alternatively stated, in the present invention the separation of adjacent fins is determined entirely by the spacer means which are located at a distance from the tubes.

It will be understood that the vibration-induced movement of the fins 14 (or more properly the stack of fins 14 which are located together) along the tubes will terminate when the fins engage either the carrier 30, or the top-most fin of a previously fitted stack of fins such as that shown in Figs 1 and 2. The spacing between each fin in each stack, and between the fins of adjacent stacks of fins, is determined entirely by the spacer means, and not by any part of the machine 10, 1 10 itself.

When a stack of fins 14 has been moved into engagement (either with the carrier 30 or with a previously fitted stack of fins), the vibrators 36, 136 are switched off and the top plate is lifted to clear the top of the tubes for the insertion of the next stack of fins, whereupon the procedure is repeated.

Importantly, in the embodiments of Figs. 1 and 2 there is no requirement for the top plate to be driven along the posts 22, in either the upwards or downwards direction, and the downwards movement of the top plate is preferably dependent only upon the force of gravity, and the upwards movement by a separate crane or lifting device (not shown). The invention does not, however, exclude the possibility of a pressing machine to move the fins, in conjunction with the vibration provided by vibrators such as 36, 136. Thus, the invention can be performed with the tubes substantially horizontal, with the force to move the fins being provided by a pressing machine (which may be hydraulically, pneumatically or electrically actuated, as desired). The vibration of the tubes and fins will nevertheless assist the pressing machine by reducing the force required to move the fins along the tubes. It will be understood that the invention could also be performed with the fins being held stationary and the tubes being moved therethrough, and also with both of the fins and tubes being movable.

The frequency of the oscillations of the vibrators 36, 136 can be varied (during movement of the fins if desired) so as to facilitate movement of the fins along the tubes. Thus, it is expected that a particular form of heat exchanger block (comprising a particular number and array of tubes, and a particular form of fins), may require a unique vibration frequency to achieve the desired manufacturing efficiency.

If desired, one or both of the end-most fins (i.e. the bottom and top-most fins of a vertically-aligned heat exchanger block), 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.