GB2312737A - Heat exchanger and method of making a heat exchanger - Google Patents

Abstract

A heat exchanger comprises a plurality of layers of tubes. A first layer of tubes (13) is laid onto a base plate (10) so that the tubes lie parallel to side walls (12A, 12B). A similar layer running at right angles to the first and sitting on an intermediate plate (20), is laid on top of the first layer. The packing is arranged such that when heat and loading is applied to the composite structure in a vacuum, the tubes (13) are deformed and are bonded to the plates with the sidewalls ( 12A, 12B ) being bonded to the plate above.

Description

HEAT EXCHANGER This invention relates to a heat exchanger and, particularly, to a heat exchanger formed from a plurality of tubes.

It has been proposed to manufacture a heat exchanger in which fluid passageways are created, for example, in two adjacent metal sheets by forming bonds between the sheets along spaced parallel weld or diffusion bonded lines and then super-plastically deforming the material of the bonded sheets to form a passageway between each adjacent pair of bond lines.

The present invention aims to provide a simpler method of making a heat exchanger from seamless or welded and drawn tubes.

Accordingly, in one aspect the invention provides a method of making a heat exchanger comprising at least two layers of tubes in which a first layer of substantially parallel tubes is laid on a base plate, two sidewalls are positioned on the base plate with the tubes lying between and substantially parallel to the sidewalls, at least one further layer of substantially parallel tubes is positioned above the first layer, each further layer resting on an intermediate plate and between two parallel sidewalls of the intermediate plate, the distance between the sidewalls of each plate being greater than the sum of the measured outside diameters of the tubes of its respective layer by an amount predetermined by calculation from the sum of such diameters, and the height of the sidewalls being such that the tubes of each layer extend above their respective sidewalls whereby each intermediate plate rests on the tubes of the layer immediately below, a top plate being positioned on the uppermost layer of tubes. Heat and loading are applied to the composite structure so formed whilst in a vacuum to deform the tubes thereby reducing the height of the tubes, whereby tubes adjacent plates are bonded to said plates, and the tops of the sidewalls bond to the plate above. The tubes may also be bonded to each other.

The tubes will normally be of circular cross-section initially and will deform to slightly oval shape.

The two sidewalls may be integrally-formed with their respective plate. Alternatively, separate side walls may be fitted to a plate with adequate means, e.g. jigs, to resist side loading pressure from the deforming tubes. The sidewalls extend upwardly to a predetermined height above the tubes, typically by an amount calculated with reference to the measured outside diameters of the tubes.

Preferably, the sidewalls are spaced from their adjacent tubes and each tube is spaced from its neighbours in the layer and the spacings or gaps may all be substantially equal. However, this is not essential and each sidewall may, for example, contact its adjacent tube in the composite structure before pressure is applied provided that the overall spacings are sufficient to close the gaps and bond the product effectively without undue distortion.

The invention is particularly applicable for use with plates and tubes of metals, such as titanium and its alloys, stainless steel or other nickel-based alloys. Other tubes that can be provided in the desired sizes and of sufficiently closely controlled tolerances may be used. Where metal tubes are used, the bonding is preferably carried out under conditions of temperature and loading and in a vacuum chamber to effect diffusion bonding.

In another aspect the invention provides a heat exchanger comprising a plurality of layers of parallel tubes, a top plate, a base plate, an intermediate plate between each layer of tubes and a pair of sidewalls extending parallel to and confining each layer of tubes, the tubes adjacent plates being bonded to said plates, the sidewalls and plates being bonded together, and the tubes having been deformed to reduced height, e.g. from circular to slightly oval configuration.

It will be appreciated that the temperature and pressure required to provide adequate bonding of the various components of the composite structure will depend on the materials from which the tubes and plates are made and on the dimensions used, i.e. tube diameters and wall thickness and plate thickness. However, the skilled man of the art will readily be able to determine appropriate conditions for his particular circumstances.

Moreover, it will also be appreciated that the spacings of the tubes and the relative heights of the tubes and sidewalls must be carefully determined for a particular composite structure. Again the skilled man can readily determine the appropriate requirements. The bore of the tubes is determined by the heat transfer and pressure drop requirements of the heat exchanger, the wall thickness of the tubes is determined by the ruling pressure in use and the required tolerances can then be readily determined and appropriate tubing obtained to meet those requirements.

For example, with stainless steel tubes of 6mm outside diameter, calculations suggest that the spacings between adjacent parallel tubes and between outer tubes and their respective sidewalls are around 0.2mm so that the total spacing across an array of n tubes in a layer will be (n +1) x 0.2mm. For such tubes, the sidewalls may be about 0. lmm less in height than the outside diameter of the tubes.

The plates may be flat plates or some of them may be contoured, e.g. corrugated. Thus, for example, the base plate and intermediate plates may have corrugations defined to provide the pre-determined spacings between individual tubes positioned to lie in the valleys of the corrugations. Alternatively, where flat plates are use, the tubes may be positioned as required on the flat surface to provide the necessary gaps.

As indicated above, it may be preferred to provide substantially equal gaps between the tubes and between the outermost tubes and the sidewalls. However, this is not essential and irregular spacings may be used provided that the application of pressure to the composite structure causes movement of the tubes to completely fill the gap between the sidewalls with deformed, substantially equi-spaced tubes.

It is preferred that alternate layers of parallel tubes extend transversely to each other (and hence, that the sidewalls of one layer extend transversely to the sidewalls of each immediate adjacent layer.).

However, this is not essential and, if desired, adjacent layers of tubes may extend parallel to each other or a mixture of adjacent parallel and adjacent transverse tubes may be utilised depending on the desired final configuration.

The invention is not restricted to tube and plate configurations which provide a simple cross-flow heat exchanger in which one fluid passes in a single direction from one side of the heat exchanger to the other, whilst a second fluid in an adjacent layer passes in a single direction at right angles to that of the first fluid. With the present invention the tubes for one fluid may change direction towards one or both sides of the heat exchanger, typically through a right angle, so as to provide configurations e.g. in which one fluid enters and leaves the heat exchanger on the same side. In such instances the tubes are preformed with their right angles adjacent one or both ends before being assembled together such that they are parallel to one another along both of their respective directions. In this way configurations such as those known as "cross contra" etc. can be formed. In these cases, there are more than two sidewalls.

The required loading may be applied, for example, by a hydraulic ram in a heated vacuum chamber so that pressure can be progressively applied to the composite structure to achieve the desired diffusion bonding. Thus the load applied is initially confined to the protruding tubes which will deform sufficiently for the gaps to close. The plates will then come in contact with the sidewalls below and a further increase in load will increase pressure at the contact points between the tubes and the plates, the tubes and the sidewalls and the sidewalls and the plates sufficiently to achieve the minimum required bonding pressures throughout. This condition is held until the diffusion bonding is complete.

The top and base plates should be of sufficient thickness to allow subsequent welding of header tanks and/or auxiliary equipment needing to be attached to the bonded structure.

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 diagrammatic representation in end elevation of a composite structure of the invention prior to bonding; Figure 2 is a plan view of one plate for use in the invention loaded with tubes; and Figure 3 is a perspective view of a bonded product of the invention.

In Figure 1, a composite structure for a heat exchanger having three layers of tubes is shown. A base plate 10 is a tray having a rectangular base 11 and sidewalls 1 2A and 1 2B running the length of its longer sides. A first layer of eight tubes 13 is positioned on base 11.

The tubes are of outside diameter, e.g., 6mm and are positioned to run parallel to sidewalls 1 2A and 1 2B with gaps 14 of about 0.2mm between adjacent tubes and a gap 15 of about 0.2mm between outer tube 1 3A and is adjacent sidewall 12A and between outer tube 13B and its adjacent sidewall 12B.

Sidewalls 12A and 12B are about 0. lmm less in height than the outside diameter of the tubes so that the tubes protrude above the sidewalls. An intermediate plate 20 is positioned to rest on the tops of tubes 13. This plate is similar to plate 10 (although it need not be so thick) and has two sidewalls, only one of which 22A is shown and a base (not shown). Plate 20 is positioned so that its sidewalls are transverse to those of base plate 10. A row of eight tubes (not shown) is similarly positioned on the base of intermediate plate 20 with similar spacings to the tubes 13 but with the tubes parallel to sidewall 22A and hence at right angles to the first layer of tubes 13.

Because tubes 13 are taller than sidewalls 12A, 12B, a gap 17A, 1 7B is provided between the top of sidewalls 12A, 1 2B respectively and the underside of plate 20.

A further similar intermediate plate 30 with a base 31 and a pair of sidewalls 32A, 32B is positioned on the tops of the tubes on plate 20.

These sidewalls are positioned to be parallel to sidewalls 12A, 12B of the base plate 10. A further eight tubes 33 are positioned on base 31 with the same spacing as for the previous layers. Thus there are gaps 34 between adjacent tubes and gaps 35 between outer tube 33A and sidewall 32A and between outer tube 33B and sidewall 32B.

As can be seen, a gap 27A is formed between sidewall 22A and the underside of plate 30. A similar gap (not shown) is, of course, formed between the other sidewall of plate 20 and the underside of plate 30.

A top plate 40 is placed on the tops of tubes 33 whereby a gap 37A, 37B is formed between the tops of sidewalls 32A and 32B respectively and the underside of plate 40.

The composite structure so formed is now ready for pressing, the arrows A in Figure 1 indicating the direction of pressing.

Figure 2 shows a plan view of a single plate, base plate 10 with sidewalls 12A, 1 2B and eight tubes 13 positioned on the plate with gaps 14 and 15 shown as described in Figure 1. The sidewalls are each provided with two vertical through holes 18A, 1 9A and 18B, 19B respectively, one adjacent each end of its sidewall, whereby the assembly of plates and tubes may be accurately assembled in a jig having vertical guide bars to pass through the holes.

Thus it can be appreciated that successive layers of trays and tube can be built up with alternate layers of tubes having their longitudinal axes at right angles to each other until the total desired layer height is achieved. Once assembled, the structure may be placed under a ram system in a heated vacuum chamber and heat and pressure progressively applied.

As indicated above, the load applied is initially confined to the protruding tubes causing them to deform to slightly oval configuration.

This process continues until all the tubes have deformed sufficiently for all the gaps (14, 34, etc.) to close and the tubes to come into contact with adjacent parallel tubes of their respective layer. The pressure loading then increases between the tubes and their contacts with the plates. Also at this point in the process, the correct clearances having been allowed for the specific circumstances, the undersides of plates 20, 30 and 40 will have closed gaps 17A, 17B; 27A, 27B and 37A, 37B and will have come into contact with the tops of the sidewalls 12A, 12B; 32, 32B, etc. The loading is then further increased to ensure bonding throughout the product.

Again, as indicated above, the pressure is held in this stable condition to allow the diffusion bonding process to be completed.

A finished product is shown in Figure 3. The heat exchanger unit 50 has a base plate 51, a top plate 52 and four intermediate plate layers 53, 54, 55 and 56. Base plate 51 and intermediate plates 53, 54, 55, 56 are tray-shaped plates, each having a pair of sidewalls 5 lA, 53A, 54A, 55A and 56A respectively.

Alternate plates 51, 53, 54, 55, 56 are positioned at right angles to each other and each plate carries eight parallel tubes 61, 63, 64, 65 and 66 respectively.

The unit is completely bonded together, i.e. the tubes of each layer are bonded to adjacent tubes ofthat layer and to the plate immediately above and below. The outer tubes of each layer are bonded to their respective sidewalls. The tops of the sidewalls are bonded to the peripheries of their respective plate above.

As can be seen, the ends of the tubes are visible and accessible in the side faces of the unit and may be connected by conventional means, as required, to receive their respective fluid flow. Header tanks and other fitments may be welded to the exposed surfaces of base plate 51 and top plate 52. The tubes are now slightly oval in cross-section.

The trays may be machined from solid plate to have sidewalls which are slightly less in height than the outside diameters of the tubes or, as mentioned above, flat plates may be used and separate side plates, e.g. accurately machined side bars, may be jigged to the plates to form the desired trays with adequate resistance to the side pressure from the distorted tubes.

It will be appreciated that the number of layers of tubes and the number of tubes in each layer may be varied considerably and the above examples are for illustration only.

Claims (5)

1. A method of making a heat exchanger comprising at least two layers of tubes in which a first layer of substantially parallel tubes is laid on a base plate, the base plate having two sidewalls with the tubes lying between and substantially parallel to the sidewalls, at least one further layer of substantially parallel tubes is positioned above the first layer, each further layer resting on an intermediate plate and between two parallel sidewalls of the intermediate plate, the distance between the sidewalls of each plate being greater by an amount predetermined by calculation than the sum of the measured outside diameters of the tubes of its respective layer, and the height of the sidewalls being such that the tubes of each layer extend above their respective sidewalls whereby each intermediate plate rests on the tubes of the layer immediately below, a top plate is positioned on the uppermost layer of tubes, and heat and loading are applied to the composite structure so formed to deform the tubes thereby reducing the height of the tubes, whereby the tubes are bonded to said plates and the tops of the sidewalls bond to the plate above.

2. A method according to Claim 1, in which the tubes are initially of circular cross-section and are deformed to slightly oval cross-section.

3. A method according to Claim 1 or 2, in which the sidewalls are integrally-formed with their respective plates.

4. A method according to Claim 1,2 or 3, in which the tubes and plates are of metal and the bonding is diffusion bonding.

5. A heat exchanger comprising a plurality of layers of parallel tubes, a top plate, a base plate, an intermediate plate between each layer of tubes and a pair of sidewalls extending parallel to and confining each layer of tubes, the tubes being bonded to said plates, the sidewalls and plates being bonded together, and the tubes having been deformed to reduced height from circular to slightly oval configuration.