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(11) | EP 0 442 698 A2 |
| (12) | EUROPEAN PATENT APPLICATION |
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| (54) | Plate fin heat exchanger with self-locating ribbon fins |
| (57) Typical plate fin heat exchangers 1 use inherently difficult to manufacture square
and sine wave fin plates 12, 13, 14 and thus, the range of materials with which plate
fin heat exchangers can be manufactured is curtailed a plate fin heat exchanger in
which fins (25) are separately formed of self-standing or supporting strips. The fins
(25) being constructed to have step or side projectioons (26, 27; 45, 46, 47, 48;
51, 52, 53) to ensure a self supporting nature whilst allowing the fins to be secured
to parallel plates (2, 3, 4, 5) of the heat exchanger. These projections (26, 27;
45, 46, 47, 48; 51, 52, 53) also being arranged additionally to space the parallel
plates (2, 3, 4, 5) or additional projections being provided solely for this function. |
[0001] This invention relates to heat exchangers and has particular relevance to plate fin heat exchangers. Plate fin type heat exchangers are well known. Essentially they comprise a series of parallel spaced plates which are combined with edge strips to form a plurality of flow paths for fluids to be placed in heat exchange relationship.
[0002] To space the plates accurately and to enhance heat exchange within the flow paths, corrugated fins are used to separate the plates. The fins may be either sinusoidal in form or, more frequently, may be of top hat type section. To manufacture a plate fin heat exchanger, an assembly is made commencing with a bottom plate applying suitable edge strips and laying the corrugations between the edge strips. A second plate is then applied over the first plate. Further edge strips are laid on. Further corrugated fins are laid on the second plate and then a third plate is laid on top. This assembly is continued until the entire heat exchanger is formed. In some cases the heat exchanger will be relatively simple in that the layers will be substantially identical, one to the other. In many cases however, the core of the heat exchanger is a complex structure adapted to accommodate more than two fluids with some fluids being in countercurrent, some in cross current and some in a mixture of currents. The core once assembled is bonded together for example by vacuum brazing or french brazing or salt dip brazing in manners well known per se. Tanks are then welded onto the core to complete the structure.
[0004] By the present invention there is provided a plate fin heat exchanger including a plurality of spaced parallel plates defining, in conjunction with edge strips, a plurality of flow paths for the flow of fluids in heat exchange relationship one with the other through one or more of the flow paths, a plurality of fins between adjacent plates to space said plates and to enhance heat transfer, characterised in that the fins are in the form of ribbons having a width equal to the spacing between the plates, the ribbons being on edge between the plates and being provided with means to make each ribbon self-supporting.
[0006] The ribbons may be formed of strips having been deformed at portions along their length to space each ribbon one from the other and to permit each ribbon to be self-supporting. The functions of self-supporting and spacing may be combined in a single deformed portion of the ribbon or separate portions may be deformed so as on the one hand to self-support the ribbons and in other positions to space the ribbons.
[0007] The fins may be provided at each end with a portion bent along an axis at right angles to the longitudinal axis of the ribbon and being provided with an aperture to permit fluid to flow therethrough in the flow path. The aperture may lie in a portion at right angles to the plane of the major portion of the ribbon. The ribbon may be further deformed beyond the aperture to have a portion lying parallel to the major portion of the ribbon. The further deformed portion may be parallel to and adjacent to the major portion or may be parallel to and beyond the major portion.
[0008] The major portion may be flat and straight or may be zigzagged or otherwise bent from flat whilst still extending substantially perpendicularly between the plates.
[0009] The further portion may be connected to the major portion by one ligand so that the aperture extends through one side of the ribbon.
Alternatively, the further deformed portion may be connected to the major portion by two ligands, one on each side of the aperture.
[0010] The aperture may be formed by slitting the ribbon from one side, at right angles to the major axis, to extend close to the other side, the slit then being continued parallel to the major axis, so that on deforming the ribbon in the plane of the ribbon at substantially right angles to the major axis along the first portion of the slit and then further deforming the strip at the distal end of the second portion of the slit, an aperture is formed and a projection is produced which can locate the ribbon to its next adjacent ribbon.
[0011] The deformed portion may have a length substantially equal to the major portion and may have a further deformed portion attached to it.
[0012] The ribbon may be of substantially 'I', 'L' or inverted 'V' or inverted 'T' section so as to be self-supporting. The ends of the ribbon may incorporate side projections to locate the ribbon.
[0014] The ribbons and the plates may be formed of any suitable material such as aluminium, aluminium alloys, stainless steel, titanium, or titanium alloys.
[0016] By way of example embodiments of the present invention will now be described with reference to the accompanying drawings of which
FIGURE 1 is a schematic perspective view of a simple plate fin heat exchanger,
FIGURE 2 is a sectional enlarged view of a prior art corrugation fin and plate flow path,
FIGURE 3 is a schematic perspective view of an assembly of fins in accordance with the invention,
FIGURE 4 is an enlarged view of a part of a fin shown in Figure 3,
FIGURES 5 and 6 are side views of a fin prior to deformation,
FIGURE 7 is a plan view of fins in accordance with the invention,
FIGURE 8 is a plan view of an alternative form of fins in accordance with the present invention, and
FIGURE 9 is a schematic perspective view of two ends of a further form of fins in accordance with the present invention.
[0017] Referring to Figure 1, this shows a heat exchanger core generally indicated by 1 comprising four spaced parallel plates 2, 3, 4, 5 which are separated by edge strips 6, 7, 8, 9, 10 and 11. Between the plates 2 and 3 is a corrugated fin 12, between plates 3 and 4 is a corrugated fin 13 and between plates 4 and 5 is a corrugated fin 14.
[0018] The heat exchanger core would typically be provided with tanks welded to the ends of the flow paths to control the flow of fluids through the heat exchanger. The flow path between plates 2 and 3 would typically confine a fluid in the direction of arrow 15, whereas the flow path between plates 3 and 4 would typically confine fluid flowing in the direction of arrow 16. The flow path between plates 4 and 5 could also confine a fluid again flowing in the direction of arrow 17.
[0019] It can be seen therefore that the fluid flowing in the direction of arrow 16 would be in heat exchange relationship with the fluids flowing in the direction of arrows 15 and 17.
[0020] Normally, the corrugations 12, 13 and 14 would be bonded to plates 2, 3, 4 and 5 serving the dual function of spacing the plates and holding the heat exchanger core assembly together so that it can more readily resist the effect of high internal pressures. A typical material for the heat exchanger core would be aluminium or an aluminium alloy.
[0021] The corrugations shown in Figure 1 are sliced in that they appear to form a sine wave. In practice however, the corrugations tend to be more rectangular in cross-section as is shown clearly in Figure 2. In Figure 2 the corrugation 18 located between and bonded to the plates 19 and 20 is generally of square wave form or of top hat section. The spacing 21 between the legs of the corrugation is substantially equal to the spacing 22 between the plate 20 and the underside of the corrugated member 18.
[0022] It can be seen that the horizontal portion 23 of the corrugated fin member 18 is useful only in locating the fins in correct alignment and in holding portion 24 of the fins in vertical alignment. It would be appreciated that a series of upright fins with no interconnection would have both a tendency to fall over, the height of the fin being large with the thickness, and would be difficult to locate in correct alignment and distance from each other.
[0023] There are advantages however in removing the horizontal portion 23 of the fin. Firstly, the cross sectional area for fluid flow would be increased by the thickness of the fin. Secondly, the metal reduction would lead to savings in final weight and material cost. Thirdly, the radius cast by the present forming process at the point where the upright portion 24 meets the plate 19 would be eliminated, giving better pressure carrying structures. Finally, elimination of the horizontal connection 23 would enhance heat transfer between the plate 19 and the fluid in the flow path, in that heat would not have to travel through the thickness of the portion 23 of the fin.
[0024] The remaining figures show fins in accordance with the present invention and it will be appreciated that these would be laid up between plates in the conventional manner.
[0025] Referring to Figure 3, this shows a fin in the form of a ribbon 25 which is deformed at locations 26, 27 to be self-standing. It may be seen that the major portion of the ribbon 25 sits in an upright manner between the plates and can therefore be bonded along its edges to the plates. In order that the ribbon can be self-supporting and can space the adjacent ribbon, it is slit transversely from one edge and then bent as shown in figure 4. The slit extends from the edge 28 to a position 29 adjacent the other edge 30. The slit then runs parallel to the major axis of the ribbon 25 along the line 31. The ribbon is then bent at right angles perpendicularly to the major axis of the ribbon 25 so as to produce the bent portion 32. The ribbon is then bent again so that the portion 32 forms a ligand between the portion 33 and the portion 34 with the portion 35 of the ribbon forming a spacer.
[0026] By so bending or deforming the ribbon, an aperture 36 is formed and fluid can pass through the aperture. It will be appreciated that the ribbon deformed in the manner shown in Figure 4 will be self-supporting and a series of ribbons can be assembled as is shown clearly in Figure 3.
[0027] If no spacer portion 35 is required then a slot can be cut as at 37 in the ribbon 38 and by bending the ribbon twice an aperture can be formed connected by the ligand 39. Alternatively, the slot 37 may be replaced by an aperture 40 which will interconnect portions 41, 42 by ligands 43 and 44.
[0028] Rather than using stepped ribbons as is shown in Figure 3, ribbons may be formed with their ends deformed inwardly as shown in Figure 7 so that the ribbon 44 is bent inwardly at 45, 46 and again bent inwardly at 47, 48 to form an elongate 'C' shaped member which may be spaced from adjacent ribbon 49.
[0029] It will be appreciated that the ribbon forming the fin could be zigzag in shape as at 50 (Figure 8). Rather than using thin ribbons as is shown in Figures 3 to 8, the ribbons could be of generally 'I' shaped cross-section as is shown in Figure 9.
Adjacent 'I' beams 51, 52 may be located and spaced by side projections 53.
[0030] The 'I' beams may be 'T' shaped in cross-section being used in the inverted 'T' condition. Alternatively, the 'I' beams could be 'L' shaped or inverted 'V' shaped.
[0032] The material of the heat exchanger can be any suitable material such as aluminium or an aluminium alloy. Alternatively, the material may be stainless steel or titanium or a titanium alloy or formed of niobium, zirconium, hafnium, tantalum or an alloy based thereon.
[0033] Titanium and titanium alloys may be used to form heat exchangers of the bonded structure in which the titanium plates are bonded to the titanium ribbons by a suitable means and such a structure would be strongly resistant to both internal pressures and corrosion.
[0034] Because titanium is a difficult metal to manipulate, it would be difficult to produce a square wave cross-sectional heat exchanger fin as shown in Figure 2 from a titanium strip. By comparison however, the strips of the invention can be made in manageable production processes from titanium. This is particularly true of the strips illustrated in Figures 3 to 8.
1. A plate fin heat exchanger including a plurality of spaced parallel plates 2, 3, 4,
5 defining, in conjunction with edge strips 6, 7, 8, 9, 10, 11 a plurality of flow
paths for the flow of fluids in heat exchange relationship one with the other through
one or more of the flow paths, a plurality of fins between adjacent plates to space
said plates and to enhance heat transfer, characterised in that the fins are in the
form of ribbons 25 having a width equal to the spacing between the plates 2, 3, 4,
5, the ribbons 25 being on edge between the plates 2, 3, 4, 5 and being provided with
means 26, 27; 45, 46, 47, 48; 51, 52, 53 to make each ribbon self-supporting.
2. A plate fin heat exchanger according to Claim 1 wherein the ribbons and parallel plates
are bonded to each other.
3. A plate fin heat exchanger according to Claim 1 or 2 wherein the means to make each
ribbon self-supporting comprises a deformed portion of each ribbon.
4. A plate fin heat exchanger according to Claim 3 wherein either each deformed portion
ensures spacing between the parallel plates or additional deformed portions ensure
spacing between the parallel plates.
5. A plate fin heat exchanger as claimed in proceeding claim wherein an aperture 36 to
permit fluid flow is formed in a further deformed portion of the ribbon.
6. A plate fin heat exchanger as claimed in Claim 5 or 6 wherein the aperture is arranged
at a right angle to the major portion of the ribbon.
7. A plate fin heat exchanger as claimed in Claim 5 or 6 wherein the further deformed
portion is in a step section between two major portions of the ribbon that lie in
two parallel planes.
8. A plate fin heat exchanger as claimed in Claim 5, 6 or 7 wherein the further deformed
portion includes a ligand whereby the aperture extends through one side of the ribbon.
9. A plate fin heat exchanger as claimed in Claim 5, 6 or 7 wherein the further deformed
portion includes two ligands, one on each side of the aperture.
10. A plate fin heat exchanger as claimed in Claim 1 or 2 wherein each ribbon has an inter-engaging
cross-section to allow each ribbon to be located with respect to other ribbons.
11. A plate fin heat exchanger as Claim 10 wherein ribbons have a substantially "I" shaped
or "L" shaped or "V" shaped or "T" shaped section so as to be self-supporting.
12. A plate fin heat exchanger as claimed in Claim 10 or 11 wherein the ribbon incorporates
side projections to locate the ribbon.
13. A plate fin heat exchanger as claimed in any proceeding claim wherein a substantial
portion of the ribbon is flat and straight or zigzagged or bent whilst maintaining
a substantially perpendicular arientation between the plates.
14. A method of forming fins for a plate fin heat exchanger from a ribbon, by slitting
the ribbon 25 from one side, at right angles to the major axis, to extend close to
the other side, the slit then being continued parallel to the major axis, so that
on deforming the ribbon in the plane of the ribbon at substantially right angles to
the major axis along the first portion of the slit and then further deforming the
strip at the distal end of the second portion of the slit, an aperture is formed and
a projection is produced which can locate the ribbon to a next adjacent ribbon.
15. A ribbon fin element for a plate fin heat exchanger comprising a length of deformable
material including a step or side portion arranged to allow the ribbon fin to be self-supporting
within plate members of a heat exchanger and allow spaced inter-arrangement with other
ribbon fin elements.
16. A ribbon fin element as claimed in Claim 15 wherein the step or side portion has an
aperture to facilitate fluid flow there through.