US3568758A

US3568758A - Regenerative heat exchangers

Info

Publication number: US3568758A
Application number: US840275A
Authority: US
Inventors: Oliver K Kelley
Original assignee: Motors Liquidation Co
Current assignee: Motors Liquidation Co
Priority date: 1969-07-09
Filing date: 1969-07-09
Publication date: 1971-03-09
Anticipated expiration: 1988-03-09

Abstract

A regenerative heat exchanger has a heat exchange mass in the form of a multilayer band of thin metal sheet, preferably many turns of a single strip or sheet of metal. Sealing of the band is effected by rollers between which it passes in traversing from one fluid path to the other. The band is driven by a bevel gear engaging the margin of the band, which is formed with gear teeth. The layers of the band are compressed together where they pass through the rollers, to minimize fluid carryover from one path to the other. Elsewhere, the layers are spread apart by spring tabs struck from the metal and bearing against adjacent layers so that a free path for flow of fluid is provided between the layers.

Description

United States Patent [72] Inventor Oliver K. Kelley Bloomfield Hills, Mich. [21] Appl. No. 840,275 [22] Filed July 9, 1969 [45] Patented Mar. 9, 1971 [73] Assignee General Motors Corporation Detroit, Mich.

[54] REGENERATIVE HEAT EXCHANGERS 21 Claims, 5 Drawing Figs.

[52] US. Cl 165/6, 165/10 [51] Int. Cl F28d 19/00 [50] Field ofSearch 165/6, 10, 8, 9

[56] References Cited UNITED STATES PATENTS 2,866,624 12/1958 l-lolmquist 165/6 2,915,297 12/1959 Lange 165/9 M l L Primary Examiner-Albert W. Davis, Jr. Attorneys-Paul Fitzpatrick and Jean L. Carpenter ABSTRACT: A regenerative heat exchanger has a heat exchange mass in the form of a multilayer band of thin metal sheet, preferably many turns of a single strip or sheet of metal. Sealing of the band is effected by rollers between which it passes in traversing from one fluid path to the other. The band is driven by a bevel gear engaging the margin of the band, which is formed with gear teeth. The layers of the band are compressed together where they pass through the rollers, to minimize fluid carryover from one path to the other. Elsewhere, the layers are spread apart by spring tabs struck from the metal and bearing against adjacent layers so that a free path for flow of fluid is provided between the layers.

PATENTEDFAR 9 |97| sum 1 or 2 INVENTUR.

A M m REGENERATIVE HEAT EXCHANGERS My invention is directed to regenerative heat exchangers, particularly to an improved heat exchange matrix and driving and sealing means for such a matrix.

g A regenerative heat exchanger, as the term is used here, is a device providing discrete passages for two streams of fluid, usually gases, and including a matrix which moves in a closed course so as to be exposed alternately to the fluids. The matrix absorbs heat from a hot fluid and delivers heat to a colder fluid.

Such regenerators have received much consideration as elements of gas turbine engines because of the great contribution the regenerator may make to the efficiency of the power plant, particularly under light load conditions. In a gas turbine, the regenerator transfers heat frornthe exhaust gases leaving the turbine to compressed air delivered by the compressor of the engine. Since the pressure ratio of such an engine is ordinarily at least 2 /zto 1, there is ordinarily some or more pounds per square inch pressure difference between the two gases.

This present serious problems in the sealing of the matrix where it passes through seals from one gas flow path to the other to prevent or minimize loss of compressed air. Another serious problem with respect to scaling is carryover losses. Since thematrix must be of a generally porous or openwork nature to provide passages for flow of the fluids, a considerable amount of the compressed air is carried through in. the pores or voids of the matrix at the point where it moves from the compressed air path to the exhaust path and is wasted in the turbine exhaust.

While it has long been known thatminimizing carryover losses and other leakage losses in a regenerator is of great importance in increasing the efficiency of a gas turbine employing the regenerator, so far as I am aware there have been no schemes for minimizing carryover loss in the matrix which have proved sufficiently practical for commercial adoption. Examples of prior art proposals along this line embodied in U.S. Pat. Nos. 2,915,297 to Lange for Regenerative Heat Exchanger with Movable Matrix, Dec. 1, 1959; No. 2,938,713 to Collman for Regenerative Heat Exchanger, May 31, 1960; and No. 3,155,151 to Pouit for Heat Exchangers, Nov. 3, 1964.

My invention is directed to providing a regenerative heat exchanger having improved structure and improved operating characteristics over previously known devices.

The principal object of my invention is to provide regenerators having improved characteristics so far as heat transfer efficiency, minimization of leakage and carryover of fluid, and durability and economy of manufacture are concerned. A further object is to provide improved driving means for a multilayer regenerator band which effectively maintains synchronism and provides for separation of the layers of the band. A further object is to provide a multilayer heat exchange matrix having inherently self-separating layers which may be pressed together to expel fluid at the point where the matrix passes through a seal from one fluid path to another. An ultimate object of my invention is to improve the efficiency, economy, and commercial feasibility of regenerative gas turbine engines.

My invention is primarily concerned with a heat exchanger matrix composed preferably of a single continuous thin sheet metal band formed into a number of nesting or coiled layers, with each layer from the innermost outward being progressively longer to allow for uniform clearance between all the layers. The matrix may, however, be made up of two or more thin sheet metal bands coiled in alternating relationship.

My invention also is concerned with driving means to drive each layer of the matrix at a linear speed proportional to its length so as to achieve equal heating and cooling of all layers of the matrix and also to achieve substantially equal angular movement of all layers around a central point in an arc of movement so as to minimize relative sliding movement between the layers.

My invention also is concerned with sealing means which minimize the clearance between the matrix and the bulkhead which separates the high-pressure and low-pressure fluids. This is preferably achieved with seals in rolling contact with the matrix at the bulkhead.

It is an important concern of my invention to minimize both direct leakage through the seals from high pressure to low pressure and carryover losses which result from the transportation of gas entrapped in the voids of the matrix from one fluid path to the other, regardless of the pressure differential. The carryover loss is the more difficult problem of the two, so far as sealing is concerned. According to my invention, such carryover loss is substantially eliminated, thus making possible many advantages including a higher rate of movement of the matrix without accompanying penalties or higher compression ratios of the engine without higher penalties from carryover losses. l I

A very important concern of my invention is layer separating means built into the layers of the matrix which achieve and assure maintenance of substantially uniform desired spacing between adjacent layers of the matrix. It will be understood that, with a regenerator embodying thin sheets of metal, the effectiveness of the heat exchanger decreases as the spacing between the sheets or layers increases; however, with too close spacing, proper flow is impeded. With sheets approximately 0.002 inch thick, the optimum spacing is something like 0.015 inches. Thus, it is desirable that the layers of the matrix maintain a small constant spacing from near the main seals all the way around as closely as possible to the point at which they reenter the main seals.

Also, with the thin sheets in a current of rapidly flowing gas, it is important to eliminate flutter of the sheets. Both these ends are achieved, according to my invention, by the provision of integral spring tabs extending outward from each layer or from alternate layers so as to create an inherent tendency of the layers to separate to a desired extent and to damp incipient flutter while permitting the layers to be closed together while passing through the seal to eliminate the carryover.

According to a feature of the invention, the spring tabs which actuate the spacing of the sheets and control any tendency to flutter also serve to create a'desired degree of turbulence in the flow thus speeding the transfer of heat between the matrix and the gas. As a result, a smaller area of heat transfer sheets may be employed in the matrix.

The nature of my invention and its advantages will be apparent to those skilled in the art from the succeeding detailed description of preferred embodiments of the invention and the accompanying drawings thereof.

FIG. 1 is a somewhat schematic sectional view of a regenerator.

FIG. 2 is a sectional view of the heat exchanger, with parts cut away, taken on broken planes indicated generally by the line 2-2 in FIG. 1.

FIG. 3 is a fragmentary enlarged view of a portion of the matrix as viewed in FIG. 1.

FIG. 4 is a view similar to FIG. 3' illustrating a different form of matrix.

FIG. 5 is a fragmentary plan view of a matrix sheet or layer.

Referring first to FIG. 1, the regenerator 10 includes an outer case 11 and an inner case 12 of roughly figure eight shape which defines between them an arcuate cool air path 14 and an arcuate hot gas path 15 or, in general, paths for two fluids at 14 andlS, the two fluids flowing in a direction perpendicular to the plane of the figure and preferably in opposite directions. The outer case 11 and inner case 12 define between them a track or path for a heat exchange matrix 16 which is an endless flexible structure made up of thin sheet metal in the form of a multilayer band which slowly traverses the track between the outer and inner walls. The track could be circular or any desired closed curve but the preferred form is generally as illustrated. In a typical application of the regenerator, the cool air path conducts air from the compressor of a gas turbine engine to the combustion apparatus of the engine and the hot gas path conducts exhaust gas from the turbine to the engine exhaust. The matrix continually circulates in the closed path defined between the inner and outer walls, any portion of the matrix thus passing successively through the hot gas and the cool air and serving to transfer heat from the hot gas to the cool air. The two gas paths may be of unequal size, as illustrated.

The air and gas paths are separated from each other and the matrix is driven by the matrix sealing and driving assembly 18 disposed between the two fluid paths. Referring also to FIG. 2, the sealing and driving assembly 18 is mounted in the outer case 11 which at this point includes a rear wall 19 disposed between the air and gas paths and which also includes a cover plate 20 likewise disposed between the air and gas paths, the ends of which are indicated by the dotted lines at 22 in FIG. 1. The sealing and driving assembly includes a main or driving roll 23 and preferably four sealing rolls 24. The matrix is fed between the driving roll and two of the sealing rolls as it passes from each of the two fluid paths to the other. Before proceeding'further to describe the sealing and driving assembly, it may be best to consider more fully the nature of the matrix itself.

The structure of the matrix will be more clearly apparent from FIGS. 3, 4, and 5. It is made up of many layers of thin sheet metal preferably made by coiling a single continuous band. For example, in a particular case, the matrix might comprise 250 layers of metal, each of 0.002-inch stock. While conceivably each layer could be a closed band, it is highly advantageous to have the matrix made of a single multiturn strip, or a few such strips, so as to avoid numerous joints, one for each layer of the matrix, in the endless band.

Referring first to FIG. 3 which shows several layers of the matrix identified as the outermost layer 26 and intermediate layers 27, all of the layers except the outermost layer are formed with spring tabs 28 struck out from the sheet extending from the sheet in the direction away from the direction of motion of the matrix indicated by the arrow 30.

The tabs 28 may take any suitable form such as that indicated in FIG. 5. The arrangement of the tabs is largely a matter of choice and sound design. They may be in echelon as illustrated or in a rectangular pattern.

When there is no force pressing the layers of the matrix together, these tabs extend slightly from each surface of the sheet 27 and serve to separate the layers of the matrix to provide for flow of gas between the layers. When the matrix is passed between rollers 23 and 24, the tabs are flattened into the plane of the tabbed sheets and the matrix is compacted so as to expel substantially all of the air or gas which otherwise might be carried through the seal in the voids of the matrix.

An alternative form of the matrix is shown in FIG. 4 in which the matrix is made up by wrapping two alternating sheets, one being a plain sheet 31 and the other being a tabbed sheet 32. In this case, the tabbed sheet has tabs 33 extending from both surfaces of the sheet so as to bear against both of the adjacent plain sheets 31. In this case the direction of motion is to the right as illustrated, the same as in FIG. 3. The leading edges of the two outer layers are attached by welding as indicated at 35 so that they will track the other layers through the rolls. In all cases the leading end of the sheet, whether at the inside or the outside of the matrix, should be somehow secured so that it cannot double back and is pulled along by the sheet next to it.

At this point it may also be mentioned that the tabs 28 or 33 are further useful in creating turbulence in the fiow of gas through the matrix which is obstructed by the tabs in the path of flow. By breaking up laminar boundary layer flow, heat transfer to or from the matrix is improved. The tabs may be inclined to the direction of flow or skewed so as not to be exactly edge-on to the gas flow so as to increase the turbulence created by the tabs.

A suitable material for the matrix is a high temperature stainless steel which retains its elastic properties at the high temperature level encountered in a regenerator.

Returning now to consideration of the matrix sealing and driving arrangement with reference primarily to FIG. 2, roll 23 is on the inner side of the matrix band and rolls 24 are on the outer side. The rolls cause the matrix to be convex outwardly at the point where it passes through the seal in an arcuate path. This arcuate path is needed to cause the matrix to mesh properly with two driving bevel pinions 41. One edge, as shown, of the matrix 16 bears gear teeth 42 which are progressively larger, or at least of progressively greater spacing, from the inner side of the matrix at roll 23 to the outer side of the matrix at rolls 24. This progressive increase in spacing of the teeth causes them to mate properly with the tapered teeth 43 of the bevel pinions 41 when the matrix is curved around roll 23 to cause the teeth to define a segment of a bevel gear at the driving point.

Because of the separation of the layers of the matrix as it moves through the heat exchange path, it is necessary for the outer layers of the matrix to move farther than the inner layers, and it is extremely desirable that all layers make the circuit in the same time; therefore, the outer layers should move faster than the inner. By proportioning the increase in pitch of the matrix teeth and of the mating bevel gear teeth from the inner side to the outer side of the matrix to the difference in length of path of each layer, the entire matrix moves together in synchronism without significant slip between the layers or any tendency to wind up or unwind the matrix c9i coil. Thus, the rolls 24 are so placed as to cause the matrix to follow the arc of the teeth of the bevel gears which, of course, enter into and leave the teeth in the margin of the matrix as the matrix passes the gear. All of rolls 23 and 24 are rotatably mounted by stub shafts journaled in the case wall 19 and cover 20 except that one end of roll 23 is supported by an input shaft 61 journaled in the cover and splined at 62 to the main roll. Shaft 61, which provides the drive for the matrix, also is journaled in a nonrotating block or flow-blocking member 63 one face of which abuts an end of driving roll 23. Two bevel pinions 41 disposed normal to the axis of shaft 61 and roll 23 are mounted on stub shafts, the inner ends of which are journaled in the block 63 and the outer ends of which are journaled in the cover 20. A driving bevel gear 66 on the end of roll 23 engages teeth of the bevel pinions 41 which extend outwardly beyond the roll and are in driving engagement with teeth 42 of the matrix. Thrust washers 67 at the outer ends of the bevel pinions and 68 at the inner ends of the pinions engage the cover 20 and the block 63, respectively, and serve to block fluid flow past the seal. The outer washers 67 engage the ends of rolls 24.

An idler bevel gear 70, freely rotatable on shaft 61, meshes with the bevel pinions 41 and thus serves to block off leakage or carrythrough by the teeth of the bevel gears. As will be seen, the structure including block 63 closes any bypass around that edge of the matrix. At the other edge of the matrix a conical-faced disc 71 defined by a flange on the roll 23 engages the other edge of the matrix to resist the bevel gear side thrust and to seal against leakage at that edge. Slight clearances may be provided between the parts to allow for differentials of expansion when the apparatus heats and cools but, as will be seen, there is no significant leakage clearance and the apparatus may be designed so that the leakage clearances are minimized at operating temperatures of the structure.

The matrix 16 as it loops through the cool air and hot gas sections of the regenerator is guided in arcuate paths and allowed to open up due to the spring action of the tabs on sheets 35 to a desired degree to provide passages for flow of gas between the sheets. The degree of opening up of the matrix is controlled preferably by engagement of the outermost and innermost sheets with the walls 11 and 12 of the track, respectively. Since these sheets may be in frictional engagement with the walls, they preferably are plain or untabbed.

While there may be variations in the dimensions and constants of the structure to suit desired conditions, it may be informative to set out some dimensional values with respect to a preferred embodiment. In this example, the tabs are 0.37 inches long and extend from the surface in the unstressed condition a distance of 0.03 inches. Insuch case, they may run with the sheets at the nominal spacing of 0.015 inch and, in such case, the tabs can exert a sufficient separating force per inch of strip length to bias the matrix against the inner and outer guiding structures and to stabilize the strips with substantially evenspacing between the guiding walls. With such a structure, in a 6 inch-wide strip, a separating force of approximately 0.14 pounds per inch of strip length could be provided. As the strips emerge from the rolls, the tabs would exert an initial force of twice the value to open the matrix early after its emergence from the roll. I

It should be apparent to those skilled in the art from the foregoing description of preferred embodiments of my invention that it is indeed adapted to provide better regenerators and thus improve performance of gas turbine engines incorporating regenerators. The structure results in better sealing between the gases at two different pressures and in substantially complete elimination of carryover through the main seals in the matrix. It also eliminates many of the structural problems of rigid matrix discs and drums.

Furthermore, the structure is relatively inexpensive, since the matrix itself is merely lanc'ed out. sheets, plus flat sheets if desired. The formation of the gear teeth in the matrix may e be accomplished by any suitable machining or punching technique, gradually increasing the spacing-of the teeth from the inner side to theouter side of the matrix in accordance with the changes in length of the loops of the matrix and the accompanying change in spacing of the driving bevel gear teeth.

The detailed description of preferred embodiments of the vancing means includes rolls engaging opposite faces of the invention for the purpose of explainingthe principles thereof is not to be considered as limiting or restricting the invention, since many modifications may be made by the exercise of skill in the are without departing from the scope of the invention.

lclaim:

'1. A heat exchanger comprising, in combination, a housing defining a closed track for aheat transfer matrix and defining distinct paths for two fluids across the track, a continuous heat exchange matrix extending around the track through the said paths, and means disposed between the'paths for progressively advancing the matrix around the track,.- thematrix being formed by a large number of layers, each layer being a thin sheet of elastic material, at least someof the layers, bearing spring tabs normally biasing the layers apart for flow of fluid between the layers, and the advancing means including means for pressing the layers together at the advancing means.

2. A heat exchanger as defined in claim 1 in which the advancing means includes a tapered driving gear and the band has gear teeth engaging the gear, the number of such gear teeth being the same on each layer of the matrix.

1 3. A heat exchanger as defined in claim 2 in which the advancing means includes means for guiding the matrix in an arcuate path so that the said gear teeth define a segment of a bevel gear at the area of engagement with the driving gear.

4. A heat exchanger asdefined in claim 1 in which a single sheet of elastic material makes a plural number of turns to define a plural number of layers of the matrix.

5. A heat exchanger as defined in claim 1 in which the matrix has alternating plain and tab-bearing layers, each matrix for pressing the layers together.

9. A regenerative heat exchanger comprising, in combination, a housing, means defining a first path through the housing for a first fluid, means defining a second path through the housing for a second fluid, a multilayer continuous heat exchange band having a portion disposed in each path, and means disposed in the housing between the paths for traversing the band through the paths and for providing a seal between the paths comprising a roll engaging each face of the band, sealing means engaging one edge of the band, and a banddriving bevel gear engaging the other edge of the band,

. the said other edge having teeth to engage the bevel gear.

10. A heat exchanger as defined in claim 9 in which the heat exchange band comprises two alternating sheets, one including resilient means to separate the sheets, and in which each sheet continues through a multiplicity of turns to define a multiplicity of layers of the band.

11. A heat exchanger as defined in claim 9 in which the heat exchange band comprises a multiplicity of abutting turns of single sheet including resilient means to separate the turns.

12. A heat exchanger as defined in claim 9 in which one said roll includes means coupling it to the said bevel gear to drive the bevel gear.

13. A regenerative heat exchanger matrix comprising a continuous flexible multilayer band formed by a plurality of turns of thin flexible metal sheet with successive layers of the band in face-to-face abutting unbonded relation and with spring means within the band yieldably biasing the layers apart.

14. A matrix as defined in claim 1'3 defined by abutting turns of a single sheet bearing leaf springs extending from the sheet to bear against an adjacent .turnof the sheet. 15. A matrix as defined in claim 13 defined by alternate turns of a plain sheet and of a sheet bearing leaf springs engaging the plain sheet.

16. A matrix as defined in claim 13 in which the band has gear teeth in at least one edge.

17. A matrix as defined in claim 16 in which the number of gear teeth is the same in all layers and the spacing of the gear teeth varies progressively from inside to outside of the edge of the band.

18. A regenerative heat exchanger matrix comprising a continuous multilayer band formed by a plurality of layers of a single thin metal sheet with successive layers of the sheet in face-to-face relation, the sheet bearing spring tabs unitary with the sheet projecting from the sheet to bias abutting layers apart for fluid flow between the layers, the tabs being elastically deformable substantially into the plane of the layer by exertion of compressive force on the band.

19. A matrix as defined in claim 18 in which the band is formed with gear teeth at one edge.

20. A matrix as defined in claim 19 in which the pitch of the gear teeth varies progressively from face to face of the band.

21. A regenerative heat exchanger comprising, in combination, a continuous multilayer heat exchange band formed by a plurality of layers of thin sheet, and sealing and driving means for the band comprising a driving roll; two idler rolls disposed adjacent to and spaced circumferentially aroundthe driving roll, a disc at one end of the driving roll engaging the idler rolls, a driving bevel gear on the other end of the driving roll, two bevel pinions rotatable on axes intersecting the axis of the driving roll and driven by the driving bevel gear, an idler bevel gear coaxial with the driving roll meshing with the bevel pinions, a flow blocking member closing the space outlined by the bevel gears and bevel pinions, the band being disposed between the driving roll and each of the idler rolls, the disc engaging one edge of the band and the bevel pinions engaging the other edge of the band.

Claims

1. A heat exchanger comprising, in combination, a housing defining a closed track for a heat transfer matrix and defining distinct paths for two fluids across the track, a continuous heat exchange matrix extending around the track through the said paths, and means disposed between the paths for progressively advancing the matrix around the track, the matrix being formed by a large number of layers, each layer being a thin sheet of elastic material, at least some of the layers bearing spring tabs normally biasing the layers apart for flow of fluid between the layers, and the advancing means including means for pressing the layers together at the advancing means.

3. A heat exchanger as defined in claim 2 in which the advancing means includes means for guiding the matrix in an arcuate path so that the said gear teeth define a segment of a bevel gear at the area of engagement with the driving gear.

4. A heat exchanger as defined in claim 1 in which a single sheet of elastic material makes a plural number of turns to define a plural number of layers of the matrix.

5. A heat exchanger as defined in claim 1 in which the matrix has alternating plain and tab-bearing layers, each defined by a plural number of turns of a single sheet.

6. A heat exchanger as defined in claim 1 in which the matrix is made up by abutting coils of a single tab-bearing layer.

7. A heat exchanger as defined in claim 1 in which the track includes means limiting the extent of such biasing.

8. A heat exchanger as defined in claim 1 in which the advancing means includes rolls engaging opposite faces of the matrix for pressing the layers together.

9. A regenerative heat exchanger comprising, in combination, a housing, means defining a first path through the housing for a first fluid, means defining a second path through the housing for a second fluid, a multilayer continuous heat exchange band having a portion disposed in each path, and means disposed in the housing between the paths for traversing the band through the paths and for providing a seal between the paths comprising a roll engaging each face of the band, sealing means engaging one edge of the band, and a band driving bevel gear engaging the other edge of the band, the said other edge having teeth to engage the bevel gear.

14. A matrix as defined in claim 13 defined by abutting turns of a single sheet bearing leaf springs extending from the sheet to bear against an adjacent turn of the sheet.

15. A matrix aS defined in claim 13 defined by alternate turns of a plain sheet and of a sheet bearing leaf springs engaging the plain sheet.

21. A regenerative heat exchanger comprising, in combination, a continuous multilayer heat exchange band formed by a plurality of layers of thin sheet, and sealing and driving means for the band comprising a driving roll, two idler rolls disposed adjacent to and spaced circumferentially around the driving roll, a disc at one end of the driving roll engaging the idler rolls, a driving bevel gear on the other end of the driving roll, two bevel pinions rotatable on axes intersecting the axis of the driving roll and driven by the driving bevel gear, an idler bevel gear coaxial with the driving roll meshing with the bevel pinions, a flow blocking member closing the space outlined by the bevel gears and bevel pinions, the band being disposed between the driving roll and each of the idler rolls, the disc engaging one edge of the band and the bevel pinions engaging the other edge of the band.