Plate Type Heat Exchangers

Abstract

A heat exchanger is described which is adapted for use with a regenerative type gas turbine engine. The heat exchanger comprises a stack of annular disc plates which are joined in bellows fashion. Inlet and exit plenums extend longitudinally of the stack. The plates define alternate flow paths respectively for radial flow of the hot gas discharge outwardly from the center of the stack and for cross flow of pressurized air from the inlet to exit plenums. Alternate plates are provided with flow path defining corrugations formed both radially, in a general sense, and cross wise, generally concentric of the discs. The remaining plates have generally radially extending, flow paths defining corrugations. The radial corrugations of all plates are curved to be generally concentric of the curved sides of the inlet and exit plenums which are respectively triangular and elliptical in cross section.

Description

The present invention relates broadly to heat exchangers and more particularly to improvements in plate type heat exchangers.

Many different types of heat exchangers are known for transferring heat to or from a fluid, usually transferring heat between two fluid mediums.

In almost all heat exchangers, the rate of heat transfer is of prime concern. This factor is of particular importance where heat exchangers are used in regenerative type gas turbine engines. Briefly, in such engines, waste energy of the hot gas stream exhaust is transferred, through a heat exchanger, to a pressurized air stream as it passes from the engine's compressor to its combustor. Thus the energy level of the hot gas stream generated in the combustor is proportionately increased to give an overall, theoretical, increase in engine cycle efficiency.

Heat exchangers for regenerative type engines not only require a high rate of heat transfer, but also require a minimum impedence or pressure loss to the flow of the pressurized air and the hot gas streams therethrough. Otherwise, excessive pressure drops in either or both of the fluid flow paths could cause losses which more than offset the theoretical gains to be derived from the regenerative cycle. Another factor of concern in such heat exchangers, is the wide range of temperatures encountered in cyclic operation and the resultant stresses that are induced in the component parts of the heat exchanger. Yet, another area of concern in heat exchangers for regenerative type engines, particularly engines utilized for the propulsion of aircraft, is the need for a lightweight construction as well as a configuration having a minimum space envelope.

Plate type heat exchangers, while having other applications, have been found particularly effective in fulfilling the needs described above for regenerative type gas turbine engines. A particularly effective heat exchanger of this type is disclosed in U.S. Pat. No. 3,424,240. In that heat exchanger, a stack of corrugated plates, in the form of annular discs, define a central entrance for the hot gas discharge of the turbine engine. From this central entrance, the hot gasses pass radially outwardly between alternate pairs of plates to a discharge duct. Pressurized air from the engine compressor flows into inlet plenums extending longitudinally of the stack of plates, through cross flow paths between the plates, to exit plenums, also extending longitudinally of the stack of plates and then back to the combustor of the engine.

One object of the invention is to increase the overall effectiveness of stacked plate type heat exchangers of the general configuration referenced above, and in so doing, to particularly combine a high rate of heat transfer with a low impedence to fluid flow in a compact, rugged, lightweight construction.

Another and broader object of the invention is to improve the effectiveness of plate type heat exchangers and particularly to increase the rate of heat transfer capabilities thereof as well as reducing the pressure drops of fluid flows therethrough and further to decrease the induced stresses imposed thereon during operation.

The above ends, in accordance with the broader aspects of the invention, are attained in a heat exchanger which includes a relatively thin plate defining on its opposite sides, opposed portions of flow paths for first and second fluids. This plate is characterized by having first and second series of corrugations with one series being cross corrugations generally at right angles to the other.

The heat exchanger, preferably, further includes a pair of plates disposed on opposite sides of the first plate and respectively defining the opposite bounds of the two fluid flow paths. The second plates also have a series of corrugations which are of the same spacing as and aligned with one of the series of corrugations of the first plate. Further, the corrugations of the second plates are "out of phase" with corrugations of the first plate to define flow paths having longitudinal and cross sections which vary in area. Further, it is advantageous that one of the series of corrugations of the first plate have a lesser height than the other series of cross corrugations thereof and that the corrugations of the second plates are generally aligned with the lower series of corrugations of the first plate.

In a more specific aspect of the invention, a plurality of first and second plates are formed as annular discs and are arranged in stacked relationship to define alternate flow paths for the first and second liquids. Further, longitudinal inlet and exit plenums may be provided through the plates for the introduction and discharge of the first liquid. As specifically adapted for use with a regenerative type gas turbine engine, the inlet plenum would receive pressurized compressor air and the exit plenum would discharge air to the combustor of the engine after the air passes through cross flow, heat exchange flow paths between alternate pairs of plates. The second fluid would be the hot gas discharge of the engine which passes through flow paths radial of the stacked discs.

The second plates, in disc form, have series of corrugations between adjacent plenums which extend, generally, in a radial direction. The first series of corrugations of the first plates also extend radially between adjacent plenums, while the higher, cross corrugations are formed generally concentric of the discs and engage the second plate corrugations on opposite sides.

Further, the first and second plates may have flanges peripherally of their inner and outer diameters. The flanges of the first plates project in one axial direction and the flanges of the second plates project in the opposite direction in matching relationship with flanges of the adjacent plates. These matching flanges are respectively joined to complete the cross flow paths for the pressurized air. Further, the longitudinal plenums may be defined by openings in the first and second plates. The surfaces of the adjacent first and second plates, opposite of the joined plenums thereof, may be joined peripherally of such openings so that the stack of plates becomes a bellows.

Another preferred feature is found in providing radial corrugations adjacent the plenum openings which direct air flow laterally to an entrance chamber for radial flow through a primary heat transfer zone and then to a discharge chamber leading to the exit plenum. Cross corrugations of a lesser height as well as the reduced height radial corrugations are formed in the first plates in the areas of these chambers to facilitate cross flow with a maximum heat transfer.

Another feature of the invention is found in forming each inlet plenum with a generally triangular cross section and each exit plenum with a generally elliptical cross section having its major axis extending in a radial direction. The generally radial corrugations of the first and second plates are then formed generally concentrically of the adjacent sides of the plenums. This feature of the invention may also be utilized in combination with first plates having other forms of corrugations.

The above and other related objects and features of the invention will be apparent from a reading of the following description of a preferred embodiment thereof, in which reference is made to thhe accompanying drawings, and the novelty thereof pointed out in the appended claims.

In the drawings:

FIG. 1 is a longitudinal cross section of a heat exchanger in which the present invention is embodied;

FIG. 2 is an enlarged view of a fragmentary portion of FIG. 1;

FIG. 3 is a perspective view, partially exploded, of a stack of plates comprising the present heat exchanger;

FIG. 4 is a fragmentary perspective view, on a greatly enlarged scale, looking generally in the direction of arrow A in FIG. 3 and illustrating a pair of plates which define an air flow path through the heat exchangers;

FIG. 5 is a fragmentary perspective view, on a greatly enlarged scale, looking generally in the direction of arrow B in FIG. 3 and illustrating a pair of plates defining a portion of the hot gas flow path of the heat exchanger;

FIG. 6 is a section taken on line 6--6 in FIG. 4, on an enlarged scale;

FIG. 7 is a section taken on line 7--7 in FIG. 4, on an enlarged scale;

FIG. 8 is a section taken on line 8--8 in FIG. 4, on an enlarged scale;

FIG. 9 is a section taken on line 9--9 in FIG. 4, on an enlarged scale;

FIG. 10 is a section taken on line 10--10 in FIG. 4, on an enlarged scale; and

FIG. 11 is a section taken on line 11--11 in FIG. 4, on an enlarged scale.

The heat exchanger, illustrated in FIG. 1 and indicated by reference character 10, is adapted for attachment to a gas turbine engine at a point downstream of the final turbine stage of that engine. The engine, itself, may be of conventional construction in accordance with well known designs for regenerative type engines. The hot gas discharge of the engine enters the center of the heat exchanger 10 and then is directed radially outwardly, through a stack of plates 11, to an exhaust system which includes a surrounding duct 12. The heat exchanger 10 comprises an adaptor frame 14, which may be attached to a frame member of the engine. The adaptor frame 14 has a plurality of passageways 16 and 18 which respectively connect with engine passageways (not shown) leading from the engine's compressor and leading to the engine's combustor. The compressor passageways 16 are aligned with a plurality of inlet plenums 20, see also FIG. 3, formed longitudinally through the stack of plates 11. The combustor passageways 18 are aligned with a plurality of exit plenums 22 also extending longitudinally through the stack of plates 11. Cross flow paths between adjacent plenums 20 and 22 provide the primary heat exchange between the radially flowing hot gas discharge and the pressurized compressor air. These cross flow and radial flow paths will presently be described in detail. The heat exchanger 10 further comprises an end frame 24 and an end plate 26, which define the downstream limit of the hot gas discharge flow path so that all of the hot gasses may be turned radially outwardly through the stack of plates 11 and discharged through the exhaust system.

The stack of plates 11, FIG. 3, comprises a series of alternately arranged plates 11a and 11b, which are identical in outline and differ primarily in the flow path defining corrugations formed therein. The plates 11a and 11b are in the form of annular discs having inner and outer flanges 28 and 29. The flanges of the plates 11a project in one axial direction and the flanges of the plates 11b project in the opposite axial direction (FIGS. 2 and 4). Successive pairs of plates 11a and 11b are thus disposed with their flanges 28 and 29 in face-to-face relation. These matching flanges are seam welded or otherwise joined around their full circumferences. The pairs of plates, thus joined, define the bounds of the cross flow paths between plenums 20 and 22.

The plenums 20 and 22 comprise aligned openings 20a, 20b and 22a, 22b, formed in the plates 11a and 11b respectively. The surfaces of plates 11a and 11b facing outwardly of the flange welds are joined, as by welding, peripherally of the openings 22a, 22b, and 20a, 20b, FIGS. 2 and 5. The stack of plates 11 is thus joined in fashion. fashion

The pairs of plates 11a and 11b define alternate flow paths for the pressurized air and the hot gas discharge as well as the plenums 20 and 22. The stack of plates 11 may further be formed as a series of substacks as taught in U.S. Pat. No. 3,385,353. With such an arrangement, and as indicated in FIGS. 1 and 2, a selected number of plates 11a and 11b are joined as just described and their opposite ends are secured to somewhat thicker intermediate plates 30 which have openings corresponding to the openings 20a, 20b, and 22a, 22b, and which further have positioning lugs, that are located by rods 32 extending the full length of the stack 11.

Referencing next FIG. 4, it will be noted that the openings 22a and 22b are generally elliptical and that the openings 20a and 20b are generally triangular and that the adjacent sides of each opening 20 and 22 are similarly curved, or generally concentric. This relationship, maximizes the heat transfer area of the discs and minimizes the overall volume, or space envelope, of the heat exchanger, when coupled with correspondly curved corrugations in the plates 11a and 11b as shown in FIGS. 4 and 5.

More specifically, each of the plates 11a has a series of corrugations 34 between adjacent openings 20a and 22a. The corrugations (see also FIGS. 6-11) are generally sinusoidial or what will herein be referenced as "regular wave-form." The wave form corrugations 34 extend, generally radially, from the inner flange 28 to the outer flange 29 and are further curved, to correspond to the curvature of the sides of the openings 20 a and 22b between which they extend. Each plate 11b is corrugated in a more involved fashion. First, there are flow path defining corrugations 36 and 38 which extend marginally of the openings 22b and 20b respectively. The corrugations 36 and 38 are curved similarly to the wave-form corrugations 34 and are "out of phase" therewith so as to sealingly engage matching corrugations 34 respectively adjacent the openings 22a and 20a. The corrugations 36, on opposite sides of the exit plenum opening 22, extend inwardly from the outer flange 29b and terminate at a point space outwardly of the inner flange 28b. In a similar fashion, the corrugations 38, on opposite sides of each inlet plenum 20a, extend outwardly from the inner flange 28b and terminate in spaced relationship from the outer flange 29b. Between the corrugations 36 and 38, is a series of corrugations 40 of an intermediate height, which have a similar curvature to the curvature of the corrugations 34, are of the same spacing and also "out of phase" therewith. It will also be seen that the series of corrugations 40 extend from the inner flange 28b to the outer flange 29b. Further, there is a series of cross corrugations 42 extending between the co-extensive portions of the corrugations 36 and 38. The corrugations 42, generally at right angles to the corrugations 40, are generally concentric of the axis of the discs 11 and have a spacing generally matching that of the corrugations 40. The heighth of the cross corrugations 42 matches that of the corrugations 36 and 38, so that there is a grid of engagement points between the corrugations 34 and 42 within the boundary defined by the co-extensive portions of the corrugations 36 and 38, herein referenced as a zone of primary heat transfer. In the areas above and below, are inlet and exit chambers, which have a "waffle" type surface formed by the intermediate corrugations 40 and cross corrugations 44 which are of the same intermediate height.

The described configuration of the plates 11a and 11b defines cross flow paths from one inlet plenum 20 to the adjacent exit plenums 22 on either side thereof. The outer grid work of the intermediate height corrugations 40 and 44 form a lateral entranch chamber defined at the left hand end thereof by the linear engagement between the corrugation 36 and its matching corrugation 34. From this lateral entrance chamber, the cross flow path extends radially inwardly between the co-extensive portions of the corrugations 36 and 38, forming a zone of primary heat transfer, and then through a discharge chamber similar to the entry chamber described above except that the opening thereof directs the air towards the plenum 22.

It will be noted that the cross flow path described, provides throughout its length, a varying cross sectional area and longitudinal sectional area which minimizes the boundary layers and thus increases the rate of heat transfer. Further, it will be noted that in the grid of corrugations in the primary heat transfer zone, between the co-extensive areas of corrugations 36 and 38, the variations in the flow path area become more pronounced for greater heat transfer effectiveness. This is opposed to the entry and exit chambers which, while providing flow area variation, also facilitate lateral flow of the air to facilitate its entry and discharge from the primary area.

Using FIG. 4 as a point of reference, the corrugations to the right of the opening 20b between the next adjacent opening 22 would define the same series of an entry chamber, primary exchange zone and discharge chamber as described above. In both instances, the air, from the inlet plenum 20, enters the outer corner of the grid work and flows radially inwardly. This is to say that air passing through the plenum 20 has a split cross flow path to both of the adjacent plenums 22 and similarly both of the plenums 22 receives cross flow from the plenums 20 on either side thereof, as is also indicated in FIG. 3.

Referencing next FIG. 5. Plates 11a and 11b are illustrated as they define a portion of the radial flow path for the hot gas discharge through the stack of plates. As will be seen, the corrugations 34 also form a grid of contact points with the cross corrugations 42, in the plate 11b, to form a flow path for the hot gas discharge (see also FIGS. 6-11) which varies greatly in area from the inner circumference from the plates 11a and 11b to the outer circumference thereof.

It will also be noted that in each instance, the secondary flow of the pressurized air from the passageways 20 to the passageways 22 is counter to the flow of the hot gas stream in the primary area of heat exchange.

All of these factors contribute to a high rate of heat exchange for greater efficiency. Further, the described configuration of both the cross flow paths of the pressurized air and the flow paths of the hot gas discharge have proven to be highly effective in minimizing pressure drops so as to minimize the decrement to overall cycle efficiency which is attributable to such losses.

Yet another factor to be noted is that the described corrugations of the plates 11a and 11b contribute to the overall efficiency of the heat exchanger in that the spring effect, or resilience, of these corrugated plates minimizes induced stresses in the plates which are inherent in any operation in a high temperature environment as described. This is to say that in a cyclic operation of the engine heat exchanger, the plates 11a and 11b will contract and expand exerting compressive forces on the plates themselves which vary in magnitude during operational cycles. The resultant low stresses achieved enable, for a given plate material, use of thinner section material which further contributes to the efficiency of heat transfer. The ability to utilize thinner section material for the plates 11a and 11b also minimizes the overall weight heat exchanger, to the end that its incorporation in a gas turbine engine used for the propulsion of aircraft becomes more efficient in that the overall aircraft system.

While a preferred embodiment has been described, particularly directed towards an application in a gas turbine engine, variations of this embodiment will occur to those skilled in the art for such an application and other variations thereof will be apparent for utilization in other applications of heat exchangers. The broader aspects of the invention, as well as the full spirit and scope thereof, are therefor to be derived solely from the following claims.

Claims

Having thus described the invention, what is claimed is novel and desired to be secured by Letters Patent of the United States is:

1. A heat exchanger comprising

inlet and outlet connections respectively provided for first and second fluids,

a relatively thin, first plate having first and second series of corrugations, one series being disposed, generally, at right angles to the other,

a pair of second plates disposed, respectively, on opposite sides of said first plate, said second plates, in combination with said first plate, defining, on opposite sides thereof, portions of flow paths between the respective inlet and outlet connections for the first and second fluids,

said second plates each having a series of corrugations generally aligned with the first series of corrugations of the first plate and generally at right angles to the second series of corrugations, or cross corrugations, of the first plate,

whereby opposite sides of the first plate define portions of the heat exchange flow paths for both the first and second fluids, which flow paths provide a maximum of turbulence by area variations both longitudinally and transversely of the flow directions, with a minimum impedence to fluid flow.

2. A heat exchanger as in claim 1 wherein

the cross corrugations of the first plate engage the corrugations of the second plates on opposite sides thereof, and

the corrugations of said first series are of a lesser height than that of the cross corrugations, the spacing of the corrugations of said first series matches the spacing of the corrugations of the second plates, the corrugations of said first series are "out of phase" with the corrugations of the second plates.

3. A heat exchanger as in claim 2 particularly adapted for use in combination with a gas turbine engine to increase the energy level of pressurized air (first fluid) by transferring heat thereto from the hot gas (second fluid) discharge of the engine as the pressurized air passes from the engine's compressor to its combustor, said heat exchanger further including

successive first and second plates, the latter also being relatively thin, alternately disposed and defining alternate heat exchange flow paths for the pressurized air and the hot gas,

said first and second plates being in the form of annular discs forming a central entrance connection for the hot gas and an outer outlet connection therefor, said discs also including longitudinal plennums, formed by openings therethrough, providing the inlet and outlet connections for the pressurized air to and from the heat transfer flow paths defined by the first and second plates, and further wherein

the corrugations of the second plates extend generally radially of the discs and open to the inner and outer portions thereof to connect the heat exchange flow paths for the hot gas to the inlet and outlet connections therefor.

4. A heat exchanger as in claim 2 wherein

adjacent first and second plates have inner and outer peripheral flanges respectively joined to form the heat exchange flow path for the pressurized air therebetween as the pressurized air flows from the inlet to the outlet plennums, and

pairs of plates so joined are in turn joined to adjacent pairs by seaming peripherally of the plennum openings therein, whereby the discs are connected in bellows fashion with the several heat exchange flow paths for the pressurized air and the hot gas, respectively, separated from each other.

5. A heat exchanger as in claim 4 wherein

each plate has radial, flow path defining corrugations of the same height as the cross corrugations, said flow path defining corrugations being being disposed on opposite sides of the inlet plennum openings and extending from from the inner peripheral flanges and terminating in radially spaced relation from the outer peripheral flanges, said flow path defining corrgations also being disposed on opposite sides of the outlet plennum openings and extending from the outer peripheral flanges and terminating in radially spaced relation from the inner peripheral flanges,

said flow path defining corrugations engaging corrugations of the second plate with which it is paired, to define the lateral bounds of the pressurized air flow paths between adjacent plennums, said cross corrugations being spaced from the inner and outer flanges, whereby the pressurized air is directed from outer, inlet chambers, radially inwardly through primary zones of heat transfer and then through inner, exit chambers, and further wherein

the first series of corrugations of the first plates extend radially to the inner and outer flanges thereof and cross corrugations of the same intermediate height are formed inwardly and outwardly of the full height corrugations to provide a waffle effect in the portions of the first plates which define the inlet and exit chambers.

6. A heat exchanger as in claim 5 wherein

there are a plurality of inlet and outlet plennums, alternately spaced around said discs,

the disc openings defining the outlet plennums are generally elliptical, and the disc openings defining the inlet plennums are generally triangular and pointed toward the axis of the discs, said triangular inlet openings having concave sides generally concentric of the adjacent convex sides of the outlet plennum openings, and

the generally radially extending corrugations of the first and second plates are curved in generally concentric relation with the sides of the plennum openings between which they extend, and

the cross corrugations of the first plates are generally concentric of the axis of the discs.

7. A heat exchanger comprising

inlet and outlet connections respectively provided for first and second fluids,

a plurality of annular discs, defining alternate heat exchange flow paths for the first and second fluids as the flow between the respective inlet and outlet connections therefor,

the inlet and outlet connections for the first fluid including inlet and outlet plennums extending longitudinally of said discs and defined by openings therein, one of said plennums being generally elliptical in cross section with the major axis thereof generally radial of said discs, the other of said plennums being generally triangular and pointed toward the axis of the discs, the sides of the triangular openings being generally concave and concentric of the adjacent convexly curved sides of the elliptical openings,

the heat exchange flow paths for the first fluid pass between said discs from the inlet plennums to the outlet plennums and the heat exchange flow paths for the second fluid pass between alternate plates from the interior to the exterior of the discs, and

alternate plates comprise series of corrugations, between each adjacent plennum, which corrugations extend generally radially of the discs and are curved generally concentric of the sides of the plennums between which they extend.