GB2367885A

GB2367885A - Heat exchanger with improved header system

Info

Publication number: GB2367885A
Application number: GB0024942A
Authority: GB
Inventors: Richard Henry Howard Barr
Original assignee: Centrax Ltd
Current assignee: Centrax Ltd
Priority date: 2000-10-11
Filing date: 2000-10-11
Publication date: 2002-04-17
Also published as: GB2367886A; GB0124311D0; AU2001293986A1; WO2002031425A1; GB2367886B; GB0024942D0

Abstract

A heat exchanger, for donating heat from one fluid stream to another fluid stream, having a plurality of heat exchanger plates which are corrugated in cross section and are stacked together to form a heat exchanger matrix (2), respective pairs of plates being sealed to one another at their edges to define respective heat exchanger cells (4), respective cells (4) being joined together by holes cut into the plates and sealed around their edges, such holes also providing fluid inlets (6) and outlets (8) to each cell (4) and means being provided in the region of the holes so that the said fluid stream which flows within the cells (4) can flow transversely across corrugations of the corrugated plates to occupy substantially the full extent of the cells (4). The said means may comprise a local reduction in height of the corrugations of at least one of the corrugated plates of each cell (4) in a region (W1, W2) adjacent one of the holes of the cell (4). Alternatively or in addition, the said means may comprise the criss-crossing of the wave pattern of the corrugations of the plates in adjacent cells (4) so that gases entering and leaving the cells (4) via the holes, traverse sideways across the crests of the corrugations to occupy substantially the full extent of the cells (4).

Description

HEAT EXCHANGER WITH IMPROVED HEADER SYSTEM TECHNICAL FIELD This invention relates to a heat exchanger with an improved header system BACKGROUND Heat exchangers are used in gas turbine engines as a means of increasing efficiency by extracting heat from the exhaust gas and donating this heat to the compressed air leaving the compressor prior to its entering the combustion chamber. Such exchangers are of two general types, firstly the rotating disc type, commonly known as a regenerator and secondly, the static plate type commonly known as a recuperator, with which this invention is concerned.

Such heat exchangers have to withstand the considerable temperature experienced in the exhaust gases, which might be up to 700OC, and the high pressure of the compressed air which might be up to eight times atmospheric.

The present invention seeks to provide a heat exchanger which is compact, cheap to manufacture and technically reliable.

STATEMENT OF INVENTION According to a first aspect of the present invention there is provided a heat exchanger, for donating heat from one fluid stream to another fluid stream, having a plurality of plates which are corrugated in cross section and are stacked together to form a heat exchanger matrix, respective pairs of plates being sealed to one another at their edges to define respective heat exchanger cells, respective cells being joined together by holes cut into the plates and sealed around their edges, such holes also providing fluid inlets and outlets to each cell and means being provided in the region of the holes so that the said fluid stream which flows within the cells can flow transversely across corrugations of the corrugated plates to occupy substantially the full extent of the cells.

According to a second aspect of the present invention there is provided a heat

exchanger having a plurality of heat exchanger plates which are corrugated in cross-section and are stacked together to form a heat exchanger matrix, respective pairs of heat exchanger plates being sealed to one another at their edges to define respective heat exchanger cells, a fluid inlet being provided into each cell and a fluid outlet being provided out of each cell, corrugations of the corrugated plates being reduced in height locally in the region adjacent the said fluid outlets and/or the said fluid inlets, so that fluid entering or leaving a respective cell can transverse the corrugations, to occupy substantially the full extent of the cell.

In accordance with a preferred embodiment of the invention, the heat exchanger operates to extract heat from a first gas stream at a first temperature and to donate the heat to a second gas stream at a second temperature lower than the first temperature by heat conduction through stationary metallic plates.

Preferably, the plates are pressed around the perimeter, respective pairs of plates being welded or otherwise fixed around their perimeters in the pressed region to form cells which are sealed around their perimeters as a result of the welding. A matrix is formed by stacking cells together on top of one another so that one stream of gas can flow along the corrugations in between adjacent cells and a second stream of gas can be made to flow along the corrugations on the insides of the cells, preferably in a counter direction to the first stream by admitting it to the corrugations on the insides of the cells through holes cut In the corrugations.

The holes are preferably elongated in shape in the direction of the corrugations.

The two gas streams are sealed from one another by connecting holes of adjacent cells to one another by welding or otherwise fixing around the perimeters of the holes.

The holes in the cells at the extremity of the matrix so formed may be welded or otherwise fixed to a support structure within which the two streams of gases are separated and directed.

Preferably, the heat exchanger comprises a heat exchanger matrix of rectangular cross-section.

A particular advantage of the present invention is that gas is distributed evenly from the elongated holes so that it occupies the whole of the matrix. This is best

achieved in a preferred embodiment by reducing the height of the corrugations in a localised area transversely in line with the elongated holes. This may be achieved in two ways.

Firstly, if the corrugations of the corrugated plates follow an oscillating path so that the corrugations define a wave pattern when viewed in a direction normal to the surface of the heat exchanger and if the plates are arranged so that the wave patterns of adjacent plates criss-cross, then space is provided at the crests of the corrugations as a result of the criss-crossing. This enables gas emerging from the holes to traverse sideways across the corrugations and thereby to occupy substantially the whole volume of the cells of the matrix. The additional advantages of criss-crossing of the wave pattern of the plates are that it avoids interlocking of the plates and gives better support against pressure forces.

Secondly, as an alternative, or in addition to, the above method of distributing the gas from the holes transversely to the direction of the corrugations, the heights of the corrugations may be reduced at their crests in an area transversely in line with the elongated holes, so that the stream of gas flowing through the holes can flow transversely through the space within the cells provided by the reduced height or corrugations, thereby entering the whole width of matrix from which it can proceed in a uniform manner longitudinally in the axial direction of the corrugations. The heights of the corrugations are preferably reduced at their crests only on the one side of the corrugations identified with flow from the holes so that in the preferred arrangement where the gas stream flowing through the holes is the high pressure compressed air flowing from the compressor of a gas turbine the matrix will still continue to be well supported against pressure forces in this area of reduced corrugation height because the corrugations of adjacent cells will still contact each other in this area. A further advantage of the invention is that the whole matrix can be manufactured from cells comprising two corrugated sheets without the need for additional support means in the header region. This second method of distribution does not necessarily require the corrugations to be of a wavy form or to criss-cross, but if the corrugations are of this form heat transfer is improved considerably as compared with straight corrugations.

Preferably, the ends of the elongated holes are V shaped to assist in the spreading of the gas stream flowing between cells to occupy the whole of the

matrix comprised by the cells.

Preferably, the corrugations of the corrugated plates will follow an oscillating path so that the corrugations define a wave pattern when viewed in a direction normal to the surface of the heat exchanger.

Preferably the holes at one end of the matrix should be staggered relative to the holes at the other end of the matrix in order to equalise further the flow distribution.

Whilst the above invention has been described in relation to a heat exchanger matrix of rectangular cross-section it could equally be applied to matrices comprised of curved cells such as might be appropriate for an annular heat exchanger or to the area surrounding the holes of a heat exchanger matrix made from a single spirally wound cell.

According to a third aspect of the present invention there is provided a heat exchanger in which heat is extracted from a first gas stream at a first temperature and donated to a second gas stream at a second temperature lower than the first temperature by heat conduction through stationary metallic plates, In which heat exchanger the plates are corrugated in cross-section and are pressed around the perimeter, respective pairs of plates being welded or otherwise fixed around their perimeters in the pressed region to form heat exchanger cells which when stacked together form a heat exchanger matrix, in which heat exchanger: (a) holes are provided near each end of the plates, the holes being welded around their perimeters to join together adjacent cells ; (b) the height of the corrugations of the heat exchanger plates is reduced locally around the holes, such reduction in height being at the crest of only one side of a corrugated plate ; (c) the surfaces of adjacent cells contact each other on the unreduced crests of corrugations over the whole area of the cell ; and (d) the matrix of cells is supported in a structure such that the second

stream of gas enters and leaves through the elongated holes and the first stream of gas passes in between adjacent cells in a counter flow direction.

BRIEF DESCRIPTION OF THE DRAWINGS For a better understanding of the present invention and to show how the same may be carried into effect reference will now be made, by way of example, to the accompanying drawings, in which: Figure 1 is a perspective view of a heat exchanger matrix in accordance with the present invention; Figure 2 is a part section A-A through the heat exchanger matrix of Figure 1; and Figure 3 is a part section B-B through the heat exchanger matrix and inlet ports of Figure 1.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS Referring to the drawings, Figure 1 shows a heat exchanger matrix 2 comprising a plurality of heat exchanger cells 4 which are stacked one on top of the other.

Each cell comprises a pair of corrugated heat exchanger plates which are welded or otherwise fixed together around their edges 5. Aligned holes are provided through each plate of each cell 4 and the respective heat exchanger cells are welded or otherwise fixed together around the perimeter 7 of each hole. Each aligned set of welded together holes comprises an inlet port 6 or an outlet port 8 which is in fluid communication with the interior of each of the cells 4.

In the illustrated embodiment, the heat exchanger matrix 2 comprises a recuperator for use in a gas turbine engine. Cold high pressure air C from the compressor of the gas turbine engine is directed into the inlet port 6 by means of a manifold (not shown). From the inlet ports, the cold high pressure air C is directed between the corrugated heat exchanger plates of each heat exchanger cell 4 and makes its way along the heat exchanger matrix 2 into the outlet ports 8, which are themselves connected to an outlet manifold (not shown). Hot low pressure exhaust gas E from the gas turbine engine is directed into an end of the

heat exchanger matrix 2 and is forced between the cells 4 of the heat exchanger matrix 2. As the exhaust gas E is forced between the heat exchanger cells 4 and the colder high pressure air C is forced through the interior of the heat exchanger cells 4, heat is donated from the exhaust gas E to the colder high pressure air C.

Preferably, the plates of the heat exchanger cells are corrugated, so the air C has to follow a tortuous path. Consequently, heat transfer occurs over a greater surface area and over a greater time than if the corrugations are straight, and the overall heat transfer is improved.

A problem that can occur in a heat exchanger of the above-mentioned type is that In order to make the heat exchanger matrix rigid, It is preferable that the crests of the corrugations of the corrugated plates of the heat exchanger cells abut. It will be appreciated that, if the corrugations of the corrugated plates forming each cell abut within the cell, the corrugations form barriers to the flow of air C in a direction perpendicular to the corrugations. This problem is addressed in the following two ways.

According to a first embodiment of the present invention, the crests of the corrugations of at least one of the heat exchanger plates forming a respective heat exchanger cell 4 are reduced in height (for example by pressing the heat exchanger plate in a press) in discrete regions W1, W2 adjacent the inlet ports and the outlet ports 8. This arrangement is best shown in Figures 2 and 3.

Figure 2 is a partial section A-A through the heat exchanger matrix 2. The partial section comprises two complete heat exchanger cells 4a, 4b and a heat exchanger plate representing half a heat exchanger cell 4c. Thus, in Figure 2 the ends of five heat exchanger plates are shown. For simplicity, the corrugations of the heat exchanger plates are not shown. Instead, they are represented by two imaginary lines. For each heat exchanger plate one of the lines joins the peaks of the corrugations and the other line joins the troughs of the corrugations. As shown in Figure 2, the corrugations of adjacent heat exchanger plates have an unreduced amplitude of h1 and abut for substantially the full width of the heat exchanger plates at a central section A-A of the heat exchanger matrix 2.

Figure 3 shows a section B-B through the heat exchanger matrix in the region of the inlet ports 6. In this region, the height of the corrugations on one side of each

heat exchanger plate has been reduced locally, to an amplitude h2, for example by pressing of the corrugations prior to assembly of each cell 4. As a result, each pair of heat exchanger plates which form a heat exchanger cell 4 do not abut in the region adjacent the inlet ports 6. Consequently, cold high pressure air C which is forced into the inlet ports 6 is able to enter the gaps between the heat exchanger plates of each heat exchanger cell 4 and thereby spread out into the corrugations of the heat exchanger plates across substantially the full extent of the heat exchanger matrix 2. Although the region (s) of heat exchanger corrugations which are reduced in height may be varied depending on the particular application of the heat exchanger matrix 2, in the illustrated embodiment the corrugations are reduced in height only in the areas W1 and W2, illustrated in Figure 1.

In addition or instead of reducing the height of the corrugations locally in the regions adjacent the inlet ports and outlet ports, the corrugations of the heat exchanger plates forming a heat exchanger cell may criss-cross, such that the corrugations of one heat exchanger plate are out of phase with the corrugations of the other heat exchanger plate. Preferably, the corrugations are 1800 out of phase. An additional advantage of this arrangement is that where a heat exchanger plate abuts the next heat exchanger plate in the matrix 2, it cannot intermesh with it, so that the matrix as a whole is rigid and stable.

Claims

1. A heat exchanger, for donating heat from one fluid stream to another fluid stream, having a plurality of heat exchanger plates which are corrugated in cross section and are stacked together to form a heat exchanger matrix, respective pairs of plates being sealed to one another at their edges to define respective heat exchanger cells, respective cells being joined together by holes cut into the plates and sealed around their edges, such holes also providing fluid inlets and outlets to each cell and means being provided in the region of the holes so that the said fluid stream which flows within the cells can flow transversely across corrugations of the corrugated plates to occupy substantially the full extent of the cells.

2 A heat exchanger as claimed in claim 1, in which the said means comprises a local reduction in height of the corrugations of at least one of the corrugated plates of each cell in a region adjacent one of the holes of the cell

3. A heat exchanger as claimed in claim 2, in which the said means comprises a local reduction In height of the said corrugations in regions adjacent both holes in each cell.

4. A heat exchanger as claimed in claims 2 or 3, in which the height of the corrugations is reduced In a region which is wider In a direction transverse to the corrugations than in a direction parallel to the corrugations.

5. A heat exchanger as claimed in any one of claims 2 to 4, In which the height of the corrugations is reduced at the crests of the corrugations on one side only of at least one of each pair of heat exchanger plates of a respective cell.

6 A heat exchanger as claimed in any one of the preceding claims, in which the surfaces of adjacent cells contact each other on the unreduced crests of the corrugations over the whole area of the cells.

7. A heat exchanger as claimed in any one of the preceding claims, in which

the corrugations are pressed around the perimeter of the plates, and respective pairs of plates are welded or otherwise fixed around their perimeters in the pressed region to form the said matrix of heat exchanger cells.

8. A heat exchanger as claimed in any one of the preceding claims, in which the fluid inlet hole into a respective cell is provided at one end of the matrix and the fluid outlet hole into the said cell is provided at the opposite end of the matrix.

9. A heat exchanger as claimed in claim 8, in which the holes in the cells are staggered at one end of the matrix relative to the holes in the cells at the other end of the matrix.

10. A heat exchanger as claimed in any one of the preceding claims, in which the holes are elongated in a direction parallel to the corrugations.

11. A heat exchanger as claimed in claims 3,4 or 5, in which the inlet holes are welded or otherwise fixed around their perimeters and/or the outlet holes are welded or otherwise fixed around their perimeters to join together adjacent cells.

12. A heat exchanger as claimed in any one of the preceding claims, in which heat is extracted from a first gas stream at a first temperature and donated to a second gas stream at a second temperature lower than the first temperature by heat conduction through the said heat exchanger plates.

13. A heat exchanger as claimed in claim 12, in which the two gas streams flow in a substantially counter direction along the corrugations of the matrix.

14. A heat exchanger as claimed in claim 13, in which the second gas stream enters through the fluid inlets and leaves through the fluid outlets respectively and the first gas stream passes in between adjacent cells in a counter flow direction.

15. A heat exchanger as claimed in any one of claims 12 to 14, in which the first gas stream comprises the exhaust gases of a gas turbine and the second gas stream comprises the compressed air of the said gas turbine prior to its entering the combustion chamber of said turbine.

16. A heat exchanger as claimed in any one of the preceding claims, in which the cells are substantially flat.

17. A heat exchanger as claimed in any one of claims 1 to 15, in which the cells are curved.'

18. A heat exchanger as claimed in any one of the preceding claims, In which the matrix is made from a single spirally wound cell.

19. A heat exchanger as claimed in any one of the preceding claims, in which corrugations of the corrugated plates follow an oscillating path, so that the corrugations define a wave pattern when viewed in a direction normal to the surface of the plate.

20. A heat exchanger as claimed in claim 19, in which the said means comprises the criss-crossing of the wave pattern of plates in adjacent cells so that gases entering and leaving the cells via the holes traverse sideways across the crests of the corrugations to occupy substantially the full extent of the cells.

21. A heat exchanger as claimed in any one of the preceding claims, in which the plates of a respective cell are spaced apart by means of spacer bars.

22. A heat exchanger as claimed in claim 21, in which the spacer bars are welded or otherwise fixed to the plates.

23. A heat exchanger as claimed in any one of claims 1 to 20, in which the pates of a respective cell are spaced apart by a bent over pressed portion of one of the plates.

24. A heat exchanger as claimed in claim 23, in which the bent over pressed

portion is welded or otherwise fixed to the other plate of the cell.

25. A heat exchanger as claimed in any one of claims 1 to 20, in which the pates of a respective cell are spaced apart by bent over pressed portions of both plates.

26. A heat exchanger as claimed in claim 25, in which the bent over portions are welded or otherwise fixed together.

27. A heat exchanger substantially as described herein, with reference to, and as shown in the accompanying drawings.