CA1038369A - Heat exchanger and heat recovery system - Google Patents
Heat exchanger and heat recovery systemInfo
- Publication number
- CA1038369A CA1038369A CA224,549A CA224549A CA1038369A CA 1038369 A CA1038369 A CA 1038369A CA 224549 A CA224549 A CA 224549A CA 1038369 A CA1038369 A CA 1038369A
- Authority
- CA
- Canada
- Prior art keywords
- fold
- sheet
- heat exchanger
- adjacent
- dimples
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
- Expired
Links
Classifications
-
- F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
- F28—HEAT EXCHANGE IN GENERAL
- F28D—HEAT-EXCHANGE APPARATUS, NOT PROVIDED FOR IN ANOTHER SUBCLASS, IN WHICH THE HEAT-EXCHANGE MEDIA DO NOT COME INTO DIRECT CONTACT
- F28D9/00—Heat-exchange apparatus having stationary plate-like or laminated conduit assemblies for both heat-exchange media, the media being in contact with different sides of a conduit wall
- F28D9/0025—Heat-exchange apparatus having stationary plate-like or laminated conduit assemblies for both heat-exchange media, the media being in contact with different sides of a conduit wall the conduits being formed by zig-zag bend plates
-
- F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
- F28—HEAT EXCHANGE IN GENERAL
- F28F—DETAILS OF HEAT-EXCHANGE AND HEAT-TRANSFER APPARATUS, OF GENERAL APPLICATION
- F28F2275/00—Fastening; Joining
- F28F2275/02—Fastening; Joining by using bonding materials; by embedding elements in particular materials
- F28F2275/025—Fastening; Joining by using bonding materials; by embedding elements in particular materials by using adhesives
Abstract
HEAT EXCHANGER AND HEAT RECOVERY SYSTEM
ABSTRACT OF THE DISCLOSURE
A counterflow or parallel flow heat exchanger includes a housing and a heat transfer sheet for dividing the housing into two fluid-tight chambers. The heat transfer sheet forms the heat transfer surface between two fluids which are forcibly supplied to each of the chambers respectively. The heat trans-fer sheet preferably includes longitudinal undulations or corru-gations for providing additional surface area and for guiding the fluids. A preferred arrangement of the heat transfer sheet includes planar ends which are affixed in fluid-tight manner to planar end members of the housing. Clinching of the corru-gated sheet to create a linear end portion of the sheet is also possible. A heat recovery system employing the heat exchanger is also disclosed.
ABSTRACT OF THE DISCLOSURE
A counterflow or parallel flow heat exchanger includes a housing and a heat transfer sheet for dividing the housing into two fluid-tight chambers. The heat transfer sheet forms the heat transfer surface between two fluids which are forcibly supplied to each of the chambers respectively. The heat trans-fer sheet preferably includes longitudinal undulations or corru-gations for providing additional surface area and for guiding the fluids. A preferred arrangement of the heat transfer sheet includes planar ends which are affixed in fluid-tight manner to planar end members of the housing. Clinching of the corru-gated sheet to create a linear end portion of the sheet is also possible. A heat recovery system employing the heat exchanger is also disclosed.
Description
~o3~369 FIELD OF THE PRESENT lNVENTION
This invention relates to improvements in heat exchangers and, more particularly, to low cost heat exchangers of the liquid-to-liquid or gas-to-gas type.
BACRGROUND OF THE INVENTION
In the design of heat exchangers, an effort is usually made to maximize the surface area exposed to the fluids in a minimum volume. Secondary but important constraints on the design are the requirements of fluid flow and, of course, cost;
--1-- , ~03~369 In situations where the primary and secondary fluids have similar physical properties such as viscosity, conductivity, density, and specific heat (as in most liquid-to-liquid or gas-to-gas heat exchangers)~ extended heat transfer~surfaces are often unnecessary. In such cases, the surface area exposed to each fluid is approximately equal. If the fluids are to be contained (e.g. they are under pressure or must not mix with the ambient atmosphere or each other)~ the inlet and outlet manifolding becomes relatively expensive ant comp}icated. This manifolding problem generally arises from efforts to expose each fluid to as large an area as possible and the potential leaks which con-sequently develop.
Such problem is even more severe in gas-to-gas heat exchangers because of the larger surfaces and manifold areas required for a predetermined heat transfer capacity. This diff-iculty is particularly troublesome in counterflow heat exchangers since these exchangers are most desirable because of their high efficiency.
SUMMARY OF THE INVENTION
It is accordingly an ob~ect of the present invention to provide a low cost, efficient, counterflow or parallel flow heat exchanger which will also be compact and simple to manu-facture.
It is an additional objective of the present invention to provide a counterflow or parallel flow gas-to-gas heat `~
. 1038369 exchanger having an extremely simple manifolding and sealing system.
It is another object of the present invention to pro-vide a counterflow or parallel flow heat exchanger having a heat transfer surface comprising a single sheet.
It is still another object of the present invention to provide a heat exchanger having a heat transfer surface com-posed of low thermal conductivity material.
It is still another object of the present invention to provide a heat exchanger including means to promote turbu-lence in gas streams for increasing heat transfer.
It is also an object of the present invention to pro-vide a heat exchanger adapted for home heating systems and simplified heating systems incorporating such exchangers.
In accordance with the invention, there is provided a heat exchanger for transmitting thermal energy from one mov-ing body of fluid to another comprising a casing of substan-tially constant cross-sectional area and a thermal transfer core within the casing. The core includes a single, integrally formed, substantially continuous sheet of heat conductive material having a plurality of fold sections, separated by fold lines. The individual fold sections of the sheet divides the interior of the casing into adjacent fluid flow passages. Al-ternate ones of these fluid flow passages define first conduit means for conducting relatively warm fluids. The other passages define second conduit means for conducting relatively cool - fluids. The individual fold sections of the sheet have a mul-tiplicity of paris of dimples formed therein. The dimple pairs are aligned longitudinally with respect to each other in at least two longitudinally extending zones. Each pair of dimples comprises a raised dimple and an adjacent depressed dimple wherein the spacing between the raised and depressed dimple in each pair .~,",~ .
is small with respect to the spacing between adjacent, longitu-dinally aligned pairs of dimples. The height of each dimple is substantially equal to one-half the width of the fluid flow passages.
In another preferred embodiment of the present inven-tion, there is provided a heat exchanger for transmitting thermal energy from one moving body of fluid to another comprising a cas-ing of substantially constant cross-section area and a thermal transfer core within the casing. The core includes a sheet of heat conductive material having a plurality of fold sections, separated by fold lines. The individual fold sections of the sheet extends longitudinally of the casing and divides the in-terior of the casing into adjacent fluid flow passages. Alter-nate ones of the fluid flow passages define a first conduit means for conducting relatively warm fluids. The other passages define a second conduit means for conducting relatively cool fluids. The individual fold sections of the sheet have dimples formed therein of a height substantially equal to one-half the width of the fluid flow passages and wherein alternate fold sections have patterns of dimples formed therein which are sub-stantially identical to each other so that upon folding the sheet along alternate fold lines, the dimples of a pair of adja-cent fold sections abut corresponding dimples of the adjacent pair of adjacent fold sections.
;~,,~
Other objects and features of the present invention will become apparent by reference to the following description and drawings while the scope of the invention will be pointed out in the appended claims.
BRIEF DESCRIPTION OF THE DRAWINGS
.
In the drawings, Figure lA illustrates a side view in schematic rep-resentation of a simplified heat exchanger in accordance with the present invention, FIGURE lB is a side view of a heat ex-changer in schematic representation employing a more practicalundulated hea* transfer surface, Figure lC is a partial sec-tional view of the exchanger of Figure lB along lines lC-lC, Figure lD shows a top view of the exchanger of Figure lB.
. Figure 2A illustrates a side view of a modified form of the exchanger in accordance with the invention, Figure 2B
; is an end sectional view taken along the lines 2B-2B of Figure `1 2A, Figure 2C shows a partial sectional view of one type of means for affixing the end plate to the heat transfer sheet, Figure 2D is an isometric representation of the heat exchanger of Figures 2A-2C, Figure 3A represents a partial frontal view of the type of exchanger shown in Figures 2A-2D, Figures 3B and 3C are ~.~ ,,~
~03~369 partial sectional views of the heat transfer sheet of Figure 3A
taken along lines 3B-3B and 3C-3C.
Figure 4A illustrates a side view of another embodi-ment of the present invention; Figure 4B is a partial sectional view of the exchanger shown in Figure 4A along the lines 4B-4B.
Figure 5A is a side view of still another embodiment of the present invention; Figure 5B is still another embodiment of the present invention; Figure 5B ls a sectional view of the exchanger taken along the llne 5B-SB of Figure 5A.
Fig. 6A is a partial frontal view showing a pre-ferret embodiment of an end plate seal; Fig. 6B is a partial side view showing a connection of the ends of th~,heat transfer sheet.
Figure 7A shows a side view of an embodiment of the "i~vention where the corrugations are clinched together at either end of the heat transfer plate;;Fig~ure 7B is an end view of the exchanger shown in Figure 7B; Figure 7C is a modified embodi_ ment of the type of heat exchanger,,shown in Figures 7A and 7B.
Figure ôA is a schematic side view of a heat exchanger of the present invention having entry of the two fluid streams parallel to the heat transfer surface and exit of the streams perpendicular to the surface by appropriate manifolding; Figure 8B is an end view of the exchanger of Figure 8A; Figure 8C is a top view of the heat transfer sheet itself showing the alter-nate closings of corrugation paths.
Figures 9A and 9B are edge views and side views of the heat transfer sheet showing appropriate dimpling to strengthen the sheet; Figures 9C and 9D are edge and side views of the heat transfer sheet showing convDlutions àdded to the sheet to for strength and spacing; Figures 9E and 9F are side views of the heat transfer sheet showing an alternative dimpling technique;
10:~8369 Fig. 9G is a side view of of a preferred embodiment of a single fold of a heat transfer sheet with spacing dimples formed therein; Fig. 9H is a side view of several folds of the heat transfer sheet of Fig. 9G; Fig 9I is a view of Fig. 9H taken along line l-I; Fig. 9J is a schematic vieu of sheet material having the preferred embodiment of spacing dimples and other features formed therein.
:.
~03~369 Figure 10 is an end view of a closed manifolded heat transfer sheet for use with a heat exchanger of the present invention.
Figure 11 is an end view of a cylindrical manifolded heat transfer sheet for use with a hèat exchanger of the pr`esent invention.
Figure 12 is a schematic drawing of a heat exchange system employing a heat exchanger in accordance with the prln-clples of the present invention.
DETAILED DESCRIPTION OF THE PREFERRED
Referring initially to Figure lA, an elementary form of the present invention is shown. There, a heat exchanger 10, which may either be of the counterflow or parallel flow type, has a first fluid stream (Fl) and a second fluid stream~(F2) ~;
which are orcibly supplied to it. A substantially planar heat transfer sheet 11 divides the exchanger 10 into two fluid-tight portions.
First means are connected to one side of the heat trans-fer sheet for confining and guidlng the flow of the first fluid stream Fl are~ shown as top plate 17, the upper portion of end members lS and the upper portion of side members (not shown explicitly). The first means includes an inlet port 20 for entry of the first fluid stream, Fl, and an outlet port 21 for exit of the first f~}uid stream.
~038369 Second means are connected to the other side of the heat transfer sheet for confining and guiding the flow of the second fluid stream, F2, and are shown as bottom plate 18, the lower portion of end members 15 and the lower portion of side members (not explictly shown). The second means includes an inlet port 22 for entry of the second fluid stream, F2, and an outlet port for exit of the second fluid stream.
It may be seen thst as the contained fluids flow on opposite sides of the heat transfer sheet (preferably in counter-flow direction), heat will be transferred from the hotter fluid, through the sheet, to the other and cooler fluid. While the design is casy to construct free of leaks, the Iimited surface area of the plansr heat transfer sheet limits the practical value of this embodiment of the invention.
Referring now to a more practical embodiment shown in Figures lB, lC and lD, (where like numbers refer~ to the same elements), a counterflow or parallle flow heat exchanger 10 has a first fluid stream Fl and a second fluid stream F2 being for-cibly supplied thereto. The exchanger includes a housing 14 which preferably has planar end members 15. A heat transfer sheet 11 internal to the housing 14 has a substantially planar axis shown as 12 in Figure lC. m e sheet includes longitudinal corrugations or undulations shown as 13 in F$gure lC. The corr-ugations extend a predetermined distance above and below the ~03~369 planar axis. The sheet thus divides the houslng into two sep-arate and fluid-tight chambers. The chambers are bounded by ~the end members 15, top and bottom members or baffle plates 17 and 18 and side members 16 shown in Figures lD. The first of the chambers includes an inlet port 20 at one end of the chamber for admitting the first fluid stream Fl and an outlet port 21 at the other end of the chamber for permitting the f$rst fluid stream to exit.
The second of the chambers includes an inlet port 22 st one end of the chamber for admitting the second fluid stream and an outlet port 23 at the other end of the chamber for per-mitting the second fluid stream to exit.
In this design, the heat transfer sheet has vastly greater heat transfer areas than in the Figure lA design. The heat transfer sheet 11, in addition to separating the two fluids, also channels the fluids through the opposite sides of the undul-ations or corrugations. The ma~or portion of the heat will be transferred as the fluids move longitudinally but between the baffle plates 1~ and 18.
The particular arrangement wherein the heat transfer sheet includes planar ends provides a most efficacious and simple fluid sealing arrangement.
The dividlng and directing of fluids into a number of channels, called manifolding, is provided in the present inven-tion by the same folds or undulations which provide the increased surface area. Since the ends of each channel lie in a single, --`` 1038369 heat plane, all of the channels can be simultaneously sealed with no need for special attention for each individual channel.
In Figures 2A and 2B, a particùltr construction of the heat exchanger is shown. In this embodiment, the entry ~nd exit ports 20, 21, 22, 23 are extended at right angles to the heat transfer sheet 11. The height of the heat transfer sheet extends essentially the full dimension between the top and bottom baffle plates 17 and 18. The sides of the heat exchanger sheet are shown affixed to the side plates 16 with resilient gas-kets 25 interposed. Such gaskets may be made of rubber or sim-ilar resilient material.
Figure 2C illustrates one possible closure of the end plate 15 to the heat exchanger sheet. In this case, rods 120 extend the length of the exchanger and compress the end plates 15 with cross bars 123 and nuts 122. A resilient gasket 124 is also included between the end plate and the end plane of the heat transfer sheet.
In Figure 2D, the full perspective of the heat exchanger in Figures 2A-C is shown illustrating the extended rectangular entry and exit ports, 20, 21, 22 and 23.
While the discussion above mentioned the use of a gas-ket to form the seal with the end plate members, other methods of sealing may also be appropriate. For example, the end plate members may be brazed, welded or soldered~ to the planar end of the heat transfer sheet. It is also possible to dip the end of the heat transfer sheet in a hardenable liquid, such as an epoxy resin, which when hard can form the end members themselves (a potted or molded end member) or the hardenable liquid may be used as a form of glue for fastening the planar end of the heat trans-fer sheet to the planar end member or plate.
~' - 10_ -``` 10383~i9 For example, as shown in Flgure 6A, the end plates 500 comprising a boetom 500A and sides 500B ~only one shown) of the heat excXanger may be placed in a horizontal position and filled with a conventional cement 502 such as an epoxy or glue up to a level denoted as 504. Prior to filling the end plate 500 with the cement 502, a reinforcement mesh 506, preferably a wire mesh, is positioned and fastened (such as by welding) to the bottom 500A. The mesh 506 serves to strengthen the structure after the cement hardens with heat transfer sheet set into place. After end plate 500 is filled with cement up to level 504, the ends 508 of heat trans-fer sheet 510 are inserted into the cement (which is still in liquid form). Ends 508 preferably have depressions 512 formed in them (which may or may not comprise the spacing dimples discussed hereinbelow) in order that they become securely fastened within the cement after it hardens. The ends 513 of side panels 514 are also preferably pot~ed within cement 502. This arrangement provides a good seal even though the ends 508 may be exactly even with each other.
Further, this technique of sealing is preferable since the ends 508 usually cannot withstand the forces inherent in a gasket type seal.
Further, a channel 515 may be formed in end plate 500 by leaving a space ad~acent to one of the sides 500B void of cement. This channel serves to collect and direct any condensate which may form to a drain port 516 which may periodically be opened to empty the liquid.
Referring to Fig. 6B, it is important taht a good seal be formed between the edges 518 of the heat transfer sheet 510 and the side panel 514A of the heat exchanger in order to prevent leakage from one gas stream to the other or to ,~ -10~,_ the environment. The edge seal must also ~oin the end seal discussed above so that no significant leakage occurs. As shown in Fig. 6B, the side panel 514A includes an outward-ly extending flange 520 over which heat transfer sheet 510 is laid. The sheet is fastened by clip 522 (or in some other way fastened) to flange 520 and the entire assembly, that is, the core (folded heat transfer sheet), side panel and clip embedded~into the cement 502 in the end plate 500. This forms a continuous seal around the entire edge of the ehat transfer surface.
-lOB-1038~69 Similar methods can be used in fastening the side members. In addition, to the stated use of a resi-lient gasket, gluing, welding, brazing and soldering techniques, the side members may also be produced by extruding them simultaneously with the heat transfer sheet. A preferred metal for such extrusion process is aluminum, however, other materials may also be used effectively, including plastic materials.
The heat transfer sheet itself may be made by extrusion, folding, stamping or any related process well known in the manufacturing art.
A useful variation of the basic folded or corrugated sheet construction shown in Figures lB, C, D and 2A, B, C, is illustrated in Figures 3A, B and C.
Heat transfer sheet llA is a sectional view taken along the central portion of the sheet and is undulated as previously shown and described. At the ends of the sheet, that is, in the region of the entrance and exit ports, the corrugations llB are as shown in Figure 3C. The cor-rugations are seen to diminish to sharp folds at each end to enhance entrance and exit of the fluids.
One of the ma~or features of the present invention is that the heat transfer sheet need not be metal. This feature ste~s from the fact that the heat does not have to be conducted along the heat transfer surface, as with a "finned" design, but only through it (i.e. the "fin efficiency" is IOOZ). This permits the use of low thermal conductivity materials and/or very thin materials where appropriate. Typical materials include plastic, paper, impregnated cloth, cloth, ceramic or glass.
This type of heat exchanger is particularly adapted for use in low velocity systems where exc-ssive stress would not be placed on the heat transfer surface and where the thermal conduction advantage of a metal surface is less important.
, __ ._ _ __ ,, ... , " ~ . . . . .
With the use of thin materials for the heat transfer sheet certain modifications of the basic construction may be beneficial. For example, in the assembly of the exchanger it may be desirable to fasten the tops or outermost peaks of the corrugations or undulations 11 to the top ant bottom baffle plates 17 and 18 as in Flgure 2B. The baffle plates are then forced apart to maintain a tension on the heat transfer sheet.
This tension tends to increase the depth of the corrugations.
the baffle plates are then fastened to the side members while maintaining the tension on the heat transfer sheet. This con-struction helps prevent distortion of the heat transfer surface -\ ~038369 due to differing pressures in the fluid streams.
A related construction, particularly for a thin heat transfer sheet, is to apply longitudinal tension of the sheet.
This may be done, for example, by first potting the planar ends of the heat transfer surface into their respective end plates.
Secondly, the plates are forced apart to put the heat tra~sfer sheet into longitudinal tension. The side plates and baffle plates are affixed while this tension is maintained. This con-struction also enhances the strength of the heat transfer sheet particularly under high differential pressures of the two fluid streams.
Referring now to Figures 4A and 4B, an embodiment is shown which is particularly adapted for use with a thin, flex-ible heat tranafer surface of membrane. This exchanger embodi-ment is most applicable in a system with nearly equal pressures on each side of the surface. Figure 4A illustrates a system of wires 32~ each of which is inserted at the inner side of the end of an undulatlon. Since alternate wires 32 are located at the top or bottom of the consecutive undulations, the heat trans-fer surface 31 will be properly supported by the wire system.
The wires 32 may either be supported by a frame or as shown in Figure 4A, may be affixed to the end plates 33. In any case, the wires should be in tension.
The Figure 4A illustration also shows a variation where the ends of the wire near the plates are first forced further apart. This will tend to stretch the folded or undulated material ~03~369 so as to increase the depth of the undulation. Then, when the wires are~placed in tension, the entire membrane or sheet 31 will be placed~lunder tension. The tension on the transfer'sur-face 31 will be greatest at the entry and exit ports where'it is most needed to assure easy entrance and exit of the fluid streams. I -Since the two fluids would be of nearly equal pressures~
the membrane or sheet would balance when in use. That is, any pressure increase on one side would tend to open those channels further and decrease the resistance to flow of this flui'd stream.
The heat transfer sheet may be made of stretchàble material if desirable.
It is also be possible to design the membrane so that a flutter would be set up in the flat portions of the undulations.
The~flutter acts as a turbulence to the air stream so as to increase the heat transfer between the two fluids.
Figure 5A and 5B illustrate an embodiment of the heat exchanger where the heat transfer surface and the side and baffle plates are simultaneously extruded and for~ a unitary arrangement. The exchanger includes vertical openings 41 and 42 which extend longitudinally in the exchaDger. The material 43 surrounding the openings represents the extruded material. The openings are seen to alternate in their vertical orientation.
Openings 42 are ~uxtaposed closer to the upper surface and open-103~369 ings 41 are juxtaposed closer to the lower surface. The dashed line in Figure 5B represents the essence of the heat transfer surface and is analogous to the undulations in previously des-cribed embodiments. After extruding the entire length of the exchanger, port sections 37 and 38 are created by machining or otherwise removing the outer surfaces to a depth of the internal openings 41 or 42~ End plate 36 is then affixed by any of the methods tescribed earlier.
Referring now to Figures 7A and 7B, an embodiment of the invention is disclosed which is adapted for situations where a low profile is required or where a number of such exchanger units are to be stacked to function as a single larger unit.
Heat exchanger sheet 51, which is provided with undulations, has its ends gradually reduced to approximately a straight line.
Th eline termination may be extended by adding a plate 52. m e manifolding may be reduced by clinching or other graduation process. In this arrangement, the fluid streams enter at the ends of the exchanger in the same direction as the paths of fluid through the exchanger, i.e., paralell to the heat transfer sheet surface. A fluid Fl enters port 53 and its at port 54.
Fluid F2 enters port 55 and exits at port 56. Each port com-prises the inner surface of the outer top or bottom plate 57, side p~lates 50 and the divider 52.
The arrangement shown in Figure 7A illustrates that in `' ~0383~9 some respects thls construction is simpler than the earlier embodiments in that the top and bottom plates extend the length of the exchanger and these plate form the ports with the clinched heat transfer sheet or with a plate affixed to the clinched por-tion.
In the clinching of the undulated sheet, longitudinal passages may be partially blocked for a short distance. This will not significantly affect the performance of the exchanger.
A heat transfer sheet which is graduated to a linear portion becomes more difficult to achieve as the height of the corrugat-ion or folds is increased. When clinching is performed under these circumstance the fluid passages may be significantly blocked. The problem can be overcome by use of the design shown in Figure 7C. The essence of this design is that the fluid portsoopen beyond the point of excessi~e closure due to clinch-in8.
In this case, the end members may be formed in twoparts 61 and 62. Each such part is roughly L-shaped and includes horizontal members 64 and 63. The horizontal members sandwich the linear portion 66 of the heat transfer sheet.
Each port, for example, entry port 5~, allows entry and exit of the fluid beyond the narrowed`closure resulting from clinching of the transfer sheet ends.
Another construction of the heat exchanger in accord~
ance with the present invention is shown in Figures 8A, 8B and 8C. In this arrangement, the sppropriate closure of the ends of specified channels of the undulations, permits floid entry par-allel to the heat transfer surface but fluid exit occurs perpen-dicular to the surface. Figure 8A illustrates this feature. A
first fluid Fl enters a port 70 permitting parallel flow and exits from port 72 which is in a direction perpendicular to the heat transfer surface. Similarly, a second fluid enters port 71 parallel to the surface and exits perpendicular the surface at port 73. Figure 8B shows the cross section of the exchanger and the heat transfer sheet 76.
The guiding of the flow can be understood by reference to Figure 8C. There it is shown that alternating end portions of each undulation are closed off. At the entrance of fluid F2, portions 74 are closed off; at the entrance of fluid Fl, portions 75 are closed off. The fluid at each side enters the available open portions, and travels longitudinally to the end of the undulation channel ~ntil the opposite closed end is reached;
then, the fluid is forced at ri8ht angles to the heat transfer sheet and out the exit port. It should be understood that various combinatlons of side or end manifolding may be used in appropriate applications.
In Figures 9A, 9B and 9C, 9D, embodiments are illus-trated~showing two approaches for making the undulated heat trans-` 1038369 fer ~heet self spacing as well as for supporting and stiff-ening each individual corrugation against differen~ial pressure within the heat exchanger. Figures 9A and 9B
show heat tran.sfer sheet 80 having projecti(~ns or dimples 82 which art~ alternately spaced from one undulation to the next to prevent occurrence too close to one another. These dimples, while spacing the folds, will not significantly interfere with air flow. The dimples also enhance heat transfer for diverging the fluid flow.
Figures 9C and 9D illustrate one of several possible embodiments using convolutions to assure spacing of the folds. Heat transfer sheet 80 includes convolutions 83 on every second fold or undulation. These convolutions span twice the nominal space between folds and are prefer-ably aligrled with one another. This is done in such a way as to insure maximum stiffness of the overall folded sur-face against closure of the fluid passages as a result of pressure or other external force. The convolutions have the advantage of offering greater rigidity of the overall assembly and greater stiffness for each individual fold.
They will however interfere with ~luid flow if extended beyond the baffle plate 17. The convolution can be extended as shown in Figure 9D where the convolutions have curved portions 84 to allow entry and exit of fluid.
Figures 9E and 9F show a variation of the above principles where the high pressure is always on one side of the surface.
~ 18 -~ ~03~369 <~
In those figures, the flat surfaces of the corruga-tions 80 include periodic dimples 81 as sho~n. The dim-ples 81 extend away from the high pressure side and into the low pressure side so that each dimple touches an oppos-ing dimple. This substantially prevents compressionnof the corrugations by the large pressure differential. The use of dimpling can also increase heat transfer by creating turbulence in the fluid stream.
Referring now to Figures 9G to 9J~ a preferred con-figuration of the heat transfer sheet, denoted for pur-poses of this embodiment as 600, is illustrated which en-hances toca surprising degree the ease of fabrication of the core(comprising the undulated or folded heat transfer sheet) as well as the structural rigidity and spacing of the device. As noted above, dimples are formed in the sheet to make the folds self spacing and to maintain the folds under a differential pressure. It has been found that to increase the effectiveness of the dimples, it is desireable to form them such that the raised dimple, denoted as 602R
is as close as possible to the depressed dimple, denoted as 602D, on the same sheet. This is shown in Fig. 9G
where distance (a~ is kept as small as possible, and usu-ally considerably smaller than the spacing of the dimples on the same side of the sheet, for example, distance (b~), between ad~acent raised dimples 602R. The reason for this is readily apparent from Fig. 9~. When a force (denoted F) is transmitted by the dimples it must traverse the minimum distance (a) before encountering the stiffening effect of the adjacent dimple. This feature is desirable in many heat exchangers where a low pressure drop is desirable through the exchanger because an excessive number of dimp-les (required to otherwise prevent buckling of the sheet) will increase the pressure required to force through a given ~ -18A_ flow of fluid. A secondary desirable effect of the mini-mally spaced ad~acent raised and depressed dimples is a réduction of pressure drop through the~heat exchanger caused by the dimples. If the dimples are large, which is often necessary because of the stamping or drawing characteristics of the material, they intermittently block the flow of fluid and would force it to flow in a transverse direction to flow around the dimple. The ad~acent dimple in the oppo-site direction allows the air to flow into this ad~acent r region thus minimizing the flow disturbance and therefore pressure drop.
StiIl reférring to Fig. 9H, when dimples are formed in a sheet of material, the depth to which they can be drawn is a unction of their width and material properties. In most casesit is not practical to draw a dimple to the full depth of the desired spacing between adjacent folds of the core. This problem has been solved by the configuration of the heat transfer sheet 600 shown in Fig. 9H. The sheet is formed so that when it is folded depressed dimples 602D
align with and abut raised dimples 602R. Thus, these dimples need have a height only one half the desired spacing between ad~acent folds of the sheet.
Referring to Fig. 9I, stiffèning channels or forms 604, are formed in each fold in addition to dimples 602 which serve to stiffen each fold. These forms 604 are provided in a manner whereby they nest together as shown upon the heat transfer sheet being folded. This is advantageous since the stiffening forms will not signif-icantly reduce the cross sectional area between the folds available for fluid flow.
Referring now to Fig. 9J, a schematic of an unfolded heat transfer sheet, denoted 700, is shown wherein iden-tical stampins 701 are used to form raised dimples 702R
(solid circles), depressed dimples 702D (open circles) and depressed stiffening channels 704 (lines), so that ~ -18B_ ~038369 the sheet may be folded along primary fold lines 706 only or along primary fold lines 706 and secondary fold lines 708 to form the folded core. In each case, raised dimples will always abut other raised dimples, depressed dimples will always abut other depressed dimples, and stiffening channels will always nest within other stiffening channels. Such a configuration results in all the benefits and advantages discussed above in addition to complete ease and simplicity in manufacture. Each stamping 701 includes two configurations 710A and 710B having the pattern of raised and depressed dimples (and stiffening channels) shown in Fig. 9J.
As seen, the stiffening channels 704 in each configuration 710A
and 710B are intermediate each other and terminate slightly before each primary and secondary fold line 706, 708. This insures nesting and also results in a natural fold line 708 occuring at these intervals. ~his is an important feature in that commercia]
manufacture of a folded heat exchanger core is for the first time made practical. The particular dimple configuration shown in Fig. 9J~ as stated above, permits folding of the core along primary fold lines 706 only (whereby a core is achieved having larger overall dimensions) or along both the primary fold lines 706 and the secondary fold lines 708 (whereby a core is achieved having smaller overall dimenslons). In both cases dimples in adjacent folds align and abut with each other. This advantage results when adjacent configurations 710A and 710B have raised and depressed dimples formed in them respectively in a mirror image pattern with respect to each other as shown in Fig. 9J.
~031~369 While reference has been made to the use of thin or flexible materials, the heat exchanger of the present invention is easily adapted to situations of high pressure differences because of the ease of seal-ing and inherent strength of the corrugated surface to resist beam bending due to the pressure differential.
The problems of bending in the flat surfaces of the corrugations is overcome by the above method.
Another arrangement for high pressure differ-entials is shown in Figure 10. This figure also illus-trates the flexibility of the design of the heat ex-changer of the present invention. The heat transfer sheet 90 is seen to consist of two rows of corrugations or undulations. The two rows are closed and fluid-tight so as to enclose a volume therein. The lower peaks of one row of corrugations are juxtaposed to the upper peaks of the other row. Lowsr pressure fluids are passed through the enclosed volume 92 and higher pressure fluids along the top and bottom outer surfaces of the corrugations. Thus, the heat 10383~9 transfer sheet cannot collapse because of beam bending.
Figure 11 illustrates a heat transfer sheet 95-which has a circular cross section. One fluid is passed longitudinally within the enclosed volume 97, the second fluid along the outer surfaces 96 of the heat transfer sheet, the two fluids being preferably in counter-flow direction:
The heat transfer sheet itself in any of the appli-cations may be made in a single sheet by an extrusion or stamp-lng or msy be made from any number of separate pieces and appro-priately ~oined together.
The simplicity and economy of the present heat exchanger enables it to be used in many applications where an expensive system would not be ordinarily ~ustified. For example, a heat recovery system for home heating systems may utilize the preseht heat exchanger design. Figure 12 illustrates a low cost, com-pact heat exchanger in accordance with the present invention as incorporated in a system to recover heat which would otherwise be lost up the flue or chimney of a gas or oil-fired hot air furnace.
As shown in Figure 12, the system includes a furnace 101 having a flue 102. Heated air from the flue enters heat exchanger 100 which is constructed in accordance with the prin-ciples of the present invention and, in particular, entry port 104. The heated air is drawn by the forced circulation supplied ~0383~9 by fan 113 through the exit port 105 of the exchanger and out the chimney. The heat from the furnace air stream is transferred to a fresh air stream which is drawn through heat exchanger entry port 106 by the forced~?circulation of fan 112. The heated fresh air exchanger exit port 107 and may be re-supplied to the house via air outlet 120.
The system may incorporate a safety damper which permits air to circulate through the exchanger only when the motor 110 drlves the fans 112 and 113. This is a fail-safe feature which insures that failure of the fan would still permit the furnace to operate through the ordinary flueepath 121. Thus, harmful fumes will not escape because of inability of the natural draft to draw through the heat exchanger.
Other features of the system shown in Figure 12 include the use of a single motor 110 to drive both intake fan 112 and exhaust fan 113. The co~nterflow heat exchanger 100 also funct-ions simultaneously as a water condenser. Water will condense on the flue side surfaces of the corrugated heat transfer sheet wetting `exchanger 100 and will rund down the internal surfaces of the exchanger. The flow of air through the exchanger will force the water toward the exit port 105 and toward the drain 116. The water will then drain into the plenum chamber 121 and, finally into the system drain. The system may also include a barometric damper- 114, if necessary.
103~369 While the foregoing specification ant drawings represent the preferred embodlments of the present invention, it will be obvious to those skilled in the art that various changes and modifications may be made therein wlthout departing from the true spirit and scope of the present invention.
This invention relates to improvements in heat exchangers and, more particularly, to low cost heat exchangers of the liquid-to-liquid or gas-to-gas type.
BACRGROUND OF THE INVENTION
In the design of heat exchangers, an effort is usually made to maximize the surface area exposed to the fluids in a minimum volume. Secondary but important constraints on the design are the requirements of fluid flow and, of course, cost;
--1-- , ~03~369 In situations where the primary and secondary fluids have similar physical properties such as viscosity, conductivity, density, and specific heat (as in most liquid-to-liquid or gas-to-gas heat exchangers)~ extended heat transfer~surfaces are often unnecessary. In such cases, the surface area exposed to each fluid is approximately equal. If the fluids are to be contained (e.g. they are under pressure or must not mix with the ambient atmosphere or each other)~ the inlet and outlet manifolding becomes relatively expensive ant comp}icated. This manifolding problem generally arises from efforts to expose each fluid to as large an area as possible and the potential leaks which con-sequently develop.
Such problem is even more severe in gas-to-gas heat exchangers because of the larger surfaces and manifold areas required for a predetermined heat transfer capacity. This diff-iculty is particularly troublesome in counterflow heat exchangers since these exchangers are most desirable because of their high efficiency.
SUMMARY OF THE INVENTION
It is accordingly an ob~ect of the present invention to provide a low cost, efficient, counterflow or parallel flow heat exchanger which will also be compact and simple to manu-facture.
It is an additional objective of the present invention to provide a counterflow or parallel flow gas-to-gas heat `~
. 1038369 exchanger having an extremely simple manifolding and sealing system.
It is another object of the present invention to pro-vide a counterflow or parallel flow heat exchanger having a heat transfer surface comprising a single sheet.
It is still another object of the present invention to provide a heat exchanger having a heat transfer surface com-posed of low thermal conductivity material.
It is still another object of the present invention to provide a heat exchanger including means to promote turbu-lence in gas streams for increasing heat transfer.
It is also an object of the present invention to pro-vide a heat exchanger adapted for home heating systems and simplified heating systems incorporating such exchangers.
In accordance with the invention, there is provided a heat exchanger for transmitting thermal energy from one mov-ing body of fluid to another comprising a casing of substan-tially constant cross-sectional area and a thermal transfer core within the casing. The core includes a single, integrally formed, substantially continuous sheet of heat conductive material having a plurality of fold sections, separated by fold lines. The individual fold sections of the sheet divides the interior of the casing into adjacent fluid flow passages. Al-ternate ones of these fluid flow passages define first conduit means for conducting relatively warm fluids. The other passages define second conduit means for conducting relatively cool - fluids. The individual fold sections of the sheet have a mul-tiplicity of paris of dimples formed therein. The dimple pairs are aligned longitudinally with respect to each other in at least two longitudinally extending zones. Each pair of dimples comprises a raised dimple and an adjacent depressed dimple wherein the spacing between the raised and depressed dimple in each pair .~,",~ .
is small with respect to the spacing between adjacent, longitu-dinally aligned pairs of dimples. The height of each dimple is substantially equal to one-half the width of the fluid flow passages.
In another preferred embodiment of the present inven-tion, there is provided a heat exchanger for transmitting thermal energy from one moving body of fluid to another comprising a cas-ing of substantially constant cross-section area and a thermal transfer core within the casing. The core includes a sheet of heat conductive material having a plurality of fold sections, separated by fold lines. The individual fold sections of the sheet extends longitudinally of the casing and divides the in-terior of the casing into adjacent fluid flow passages. Alter-nate ones of the fluid flow passages define a first conduit means for conducting relatively warm fluids. The other passages define a second conduit means for conducting relatively cool fluids. The individual fold sections of the sheet have dimples formed therein of a height substantially equal to one-half the width of the fluid flow passages and wherein alternate fold sections have patterns of dimples formed therein which are sub-stantially identical to each other so that upon folding the sheet along alternate fold lines, the dimples of a pair of adja-cent fold sections abut corresponding dimples of the adjacent pair of adjacent fold sections.
;~,,~
Other objects and features of the present invention will become apparent by reference to the following description and drawings while the scope of the invention will be pointed out in the appended claims.
BRIEF DESCRIPTION OF THE DRAWINGS
.
In the drawings, Figure lA illustrates a side view in schematic rep-resentation of a simplified heat exchanger in accordance with the present invention, FIGURE lB is a side view of a heat ex-changer in schematic representation employing a more practicalundulated hea* transfer surface, Figure lC is a partial sec-tional view of the exchanger of Figure lB along lines lC-lC, Figure lD shows a top view of the exchanger of Figure lB.
. Figure 2A illustrates a side view of a modified form of the exchanger in accordance with the invention, Figure 2B
; is an end sectional view taken along the lines 2B-2B of Figure `1 2A, Figure 2C shows a partial sectional view of one type of means for affixing the end plate to the heat transfer sheet, Figure 2D is an isometric representation of the heat exchanger of Figures 2A-2C, Figure 3A represents a partial frontal view of the type of exchanger shown in Figures 2A-2D, Figures 3B and 3C are ~.~ ,,~
~03~369 partial sectional views of the heat transfer sheet of Figure 3A
taken along lines 3B-3B and 3C-3C.
Figure 4A illustrates a side view of another embodi-ment of the present invention; Figure 4B is a partial sectional view of the exchanger shown in Figure 4A along the lines 4B-4B.
Figure 5A is a side view of still another embodiment of the present invention; Figure 5B is still another embodiment of the present invention; Figure 5B ls a sectional view of the exchanger taken along the llne 5B-SB of Figure 5A.
Fig. 6A is a partial frontal view showing a pre-ferret embodiment of an end plate seal; Fig. 6B is a partial side view showing a connection of the ends of th~,heat transfer sheet.
Figure 7A shows a side view of an embodiment of the "i~vention where the corrugations are clinched together at either end of the heat transfer plate;;Fig~ure 7B is an end view of the exchanger shown in Figure 7B; Figure 7C is a modified embodi_ ment of the type of heat exchanger,,shown in Figures 7A and 7B.
Figure ôA is a schematic side view of a heat exchanger of the present invention having entry of the two fluid streams parallel to the heat transfer surface and exit of the streams perpendicular to the surface by appropriate manifolding; Figure 8B is an end view of the exchanger of Figure 8A; Figure 8C is a top view of the heat transfer sheet itself showing the alter-nate closings of corrugation paths.
Figures 9A and 9B are edge views and side views of the heat transfer sheet showing appropriate dimpling to strengthen the sheet; Figures 9C and 9D are edge and side views of the heat transfer sheet showing convDlutions àdded to the sheet to for strength and spacing; Figures 9E and 9F are side views of the heat transfer sheet showing an alternative dimpling technique;
10:~8369 Fig. 9G is a side view of of a preferred embodiment of a single fold of a heat transfer sheet with spacing dimples formed therein; Fig. 9H is a side view of several folds of the heat transfer sheet of Fig. 9G; Fig 9I is a view of Fig. 9H taken along line l-I; Fig. 9J is a schematic vieu of sheet material having the preferred embodiment of spacing dimples and other features formed therein.
:.
~03~369 Figure 10 is an end view of a closed manifolded heat transfer sheet for use with a heat exchanger of the present invention.
Figure 11 is an end view of a cylindrical manifolded heat transfer sheet for use with a hèat exchanger of the pr`esent invention.
Figure 12 is a schematic drawing of a heat exchange system employing a heat exchanger in accordance with the prln-clples of the present invention.
DETAILED DESCRIPTION OF THE PREFERRED
Referring initially to Figure lA, an elementary form of the present invention is shown. There, a heat exchanger 10, which may either be of the counterflow or parallel flow type, has a first fluid stream (Fl) and a second fluid stream~(F2) ~;
which are orcibly supplied to it. A substantially planar heat transfer sheet 11 divides the exchanger 10 into two fluid-tight portions.
First means are connected to one side of the heat trans-fer sheet for confining and guidlng the flow of the first fluid stream Fl are~ shown as top plate 17, the upper portion of end members lS and the upper portion of side members (not shown explicitly). The first means includes an inlet port 20 for entry of the first fluid stream, Fl, and an outlet port 21 for exit of the first f~}uid stream.
~038369 Second means are connected to the other side of the heat transfer sheet for confining and guiding the flow of the second fluid stream, F2, and are shown as bottom plate 18, the lower portion of end members 15 and the lower portion of side members (not explictly shown). The second means includes an inlet port 22 for entry of the second fluid stream, F2, and an outlet port for exit of the second fluid stream.
It may be seen thst as the contained fluids flow on opposite sides of the heat transfer sheet (preferably in counter-flow direction), heat will be transferred from the hotter fluid, through the sheet, to the other and cooler fluid. While the design is casy to construct free of leaks, the Iimited surface area of the plansr heat transfer sheet limits the practical value of this embodiment of the invention.
Referring now to a more practical embodiment shown in Figures lB, lC and lD, (where like numbers refer~ to the same elements), a counterflow or parallle flow heat exchanger 10 has a first fluid stream Fl and a second fluid stream F2 being for-cibly supplied thereto. The exchanger includes a housing 14 which preferably has planar end members 15. A heat transfer sheet 11 internal to the housing 14 has a substantially planar axis shown as 12 in Figure lC. m e sheet includes longitudinal corrugations or undulations shown as 13 in F$gure lC. The corr-ugations extend a predetermined distance above and below the ~03~369 planar axis. The sheet thus divides the houslng into two sep-arate and fluid-tight chambers. The chambers are bounded by ~the end members 15, top and bottom members or baffle plates 17 and 18 and side members 16 shown in Figures lD. The first of the chambers includes an inlet port 20 at one end of the chamber for admitting the first fluid stream Fl and an outlet port 21 at the other end of the chamber for permitting the f$rst fluid stream to exit.
The second of the chambers includes an inlet port 22 st one end of the chamber for admitting the second fluid stream and an outlet port 23 at the other end of the chamber for per-mitting the second fluid stream to exit.
In this design, the heat transfer sheet has vastly greater heat transfer areas than in the Figure lA design. The heat transfer sheet 11, in addition to separating the two fluids, also channels the fluids through the opposite sides of the undul-ations or corrugations. The ma~or portion of the heat will be transferred as the fluids move longitudinally but between the baffle plates 1~ and 18.
The particular arrangement wherein the heat transfer sheet includes planar ends provides a most efficacious and simple fluid sealing arrangement.
The dividlng and directing of fluids into a number of channels, called manifolding, is provided in the present inven-tion by the same folds or undulations which provide the increased surface area. Since the ends of each channel lie in a single, --`` 1038369 heat plane, all of the channels can be simultaneously sealed with no need for special attention for each individual channel.
In Figures 2A and 2B, a particùltr construction of the heat exchanger is shown. In this embodiment, the entry ~nd exit ports 20, 21, 22, 23 are extended at right angles to the heat transfer sheet 11. The height of the heat transfer sheet extends essentially the full dimension between the top and bottom baffle plates 17 and 18. The sides of the heat exchanger sheet are shown affixed to the side plates 16 with resilient gas-kets 25 interposed. Such gaskets may be made of rubber or sim-ilar resilient material.
Figure 2C illustrates one possible closure of the end plate 15 to the heat exchanger sheet. In this case, rods 120 extend the length of the exchanger and compress the end plates 15 with cross bars 123 and nuts 122. A resilient gasket 124 is also included between the end plate and the end plane of the heat transfer sheet.
In Figure 2D, the full perspective of the heat exchanger in Figures 2A-C is shown illustrating the extended rectangular entry and exit ports, 20, 21, 22 and 23.
While the discussion above mentioned the use of a gas-ket to form the seal with the end plate members, other methods of sealing may also be appropriate. For example, the end plate members may be brazed, welded or soldered~ to the planar end of the heat transfer sheet. It is also possible to dip the end of the heat transfer sheet in a hardenable liquid, such as an epoxy resin, which when hard can form the end members themselves (a potted or molded end member) or the hardenable liquid may be used as a form of glue for fastening the planar end of the heat trans-fer sheet to the planar end member or plate.
~' - 10_ -``` 10383~i9 For example, as shown in Flgure 6A, the end plates 500 comprising a boetom 500A and sides 500B ~only one shown) of the heat excXanger may be placed in a horizontal position and filled with a conventional cement 502 such as an epoxy or glue up to a level denoted as 504. Prior to filling the end plate 500 with the cement 502, a reinforcement mesh 506, preferably a wire mesh, is positioned and fastened (such as by welding) to the bottom 500A. The mesh 506 serves to strengthen the structure after the cement hardens with heat transfer sheet set into place. After end plate 500 is filled with cement up to level 504, the ends 508 of heat trans-fer sheet 510 are inserted into the cement (which is still in liquid form). Ends 508 preferably have depressions 512 formed in them (which may or may not comprise the spacing dimples discussed hereinbelow) in order that they become securely fastened within the cement after it hardens. The ends 513 of side panels 514 are also preferably pot~ed within cement 502. This arrangement provides a good seal even though the ends 508 may be exactly even with each other.
Further, this technique of sealing is preferable since the ends 508 usually cannot withstand the forces inherent in a gasket type seal.
Further, a channel 515 may be formed in end plate 500 by leaving a space ad~acent to one of the sides 500B void of cement. This channel serves to collect and direct any condensate which may form to a drain port 516 which may periodically be opened to empty the liquid.
Referring to Fig. 6B, it is important taht a good seal be formed between the edges 518 of the heat transfer sheet 510 and the side panel 514A of the heat exchanger in order to prevent leakage from one gas stream to the other or to ,~ -10~,_ the environment. The edge seal must also ~oin the end seal discussed above so that no significant leakage occurs. As shown in Fig. 6B, the side panel 514A includes an outward-ly extending flange 520 over which heat transfer sheet 510 is laid. The sheet is fastened by clip 522 (or in some other way fastened) to flange 520 and the entire assembly, that is, the core (folded heat transfer sheet), side panel and clip embedded~into the cement 502 in the end plate 500. This forms a continuous seal around the entire edge of the ehat transfer surface.
-lOB-1038~69 Similar methods can be used in fastening the side members. In addition, to the stated use of a resi-lient gasket, gluing, welding, brazing and soldering techniques, the side members may also be produced by extruding them simultaneously with the heat transfer sheet. A preferred metal for such extrusion process is aluminum, however, other materials may also be used effectively, including plastic materials.
The heat transfer sheet itself may be made by extrusion, folding, stamping or any related process well known in the manufacturing art.
A useful variation of the basic folded or corrugated sheet construction shown in Figures lB, C, D and 2A, B, C, is illustrated in Figures 3A, B and C.
Heat transfer sheet llA is a sectional view taken along the central portion of the sheet and is undulated as previously shown and described. At the ends of the sheet, that is, in the region of the entrance and exit ports, the corrugations llB are as shown in Figure 3C. The cor-rugations are seen to diminish to sharp folds at each end to enhance entrance and exit of the fluids.
One of the ma~or features of the present invention is that the heat transfer sheet need not be metal. This feature ste~s from the fact that the heat does not have to be conducted along the heat transfer surface, as with a "finned" design, but only through it (i.e. the "fin efficiency" is IOOZ). This permits the use of low thermal conductivity materials and/or very thin materials where appropriate. Typical materials include plastic, paper, impregnated cloth, cloth, ceramic or glass.
This type of heat exchanger is particularly adapted for use in low velocity systems where exc-ssive stress would not be placed on the heat transfer surface and where the thermal conduction advantage of a metal surface is less important.
, __ ._ _ __ ,, ... , " ~ . . . . .
With the use of thin materials for the heat transfer sheet certain modifications of the basic construction may be beneficial. For example, in the assembly of the exchanger it may be desirable to fasten the tops or outermost peaks of the corrugations or undulations 11 to the top ant bottom baffle plates 17 and 18 as in Flgure 2B. The baffle plates are then forced apart to maintain a tension on the heat transfer sheet.
This tension tends to increase the depth of the corrugations.
the baffle plates are then fastened to the side members while maintaining the tension on the heat transfer sheet. This con-struction helps prevent distortion of the heat transfer surface -\ ~038369 due to differing pressures in the fluid streams.
A related construction, particularly for a thin heat transfer sheet, is to apply longitudinal tension of the sheet.
This may be done, for example, by first potting the planar ends of the heat transfer surface into their respective end plates.
Secondly, the plates are forced apart to put the heat tra~sfer sheet into longitudinal tension. The side plates and baffle plates are affixed while this tension is maintained. This con-struction also enhances the strength of the heat transfer sheet particularly under high differential pressures of the two fluid streams.
Referring now to Figures 4A and 4B, an embodiment is shown which is particularly adapted for use with a thin, flex-ible heat tranafer surface of membrane. This exchanger embodi-ment is most applicable in a system with nearly equal pressures on each side of the surface. Figure 4A illustrates a system of wires 32~ each of which is inserted at the inner side of the end of an undulatlon. Since alternate wires 32 are located at the top or bottom of the consecutive undulations, the heat trans-fer surface 31 will be properly supported by the wire system.
The wires 32 may either be supported by a frame or as shown in Figure 4A, may be affixed to the end plates 33. In any case, the wires should be in tension.
The Figure 4A illustration also shows a variation where the ends of the wire near the plates are first forced further apart. This will tend to stretch the folded or undulated material ~03~369 so as to increase the depth of the undulation. Then, when the wires are~placed in tension, the entire membrane or sheet 31 will be placed~lunder tension. The tension on the transfer'sur-face 31 will be greatest at the entry and exit ports where'it is most needed to assure easy entrance and exit of the fluid streams. I -Since the two fluids would be of nearly equal pressures~
the membrane or sheet would balance when in use. That is, any pressure increase on one side would tend to open those channels further and decrease the resistance to flow of this flui'd stream.
The heat transfer sheet may be made of stretchàble material if desirable.
It is also be possible to design the membrane so that a flutter would be set up in the flat portions of the undulations.
The~flutter acts as a turbulence to the air stream so as to increase the heat transfer between the two fluids.
Figure 5A and 5B illustrate an embodiment of the heat exchanger where the heat transfer surface and the side and baffle plates are simultaneously extruded and for~ a unitary arrangement. The exchanger includes vertical openings 41 and 42 which extend longitudinally in the exchaDger. The material 43 surrounding the openings represents the extruded material. The openings are seen to alternate in their vertical orientation.
Openings 42 are ~uxtaposed closer to the upper surface and open-103~369 ings 41 are juxtaposed closer to the lower surface. The dashed line in Figure 5B represents the essence of the heat transfer surface and is analogous to the undulations in previously des-cribed embodiments. After extruding the entire length of the exchanger, port sections 37 and 38 are created by machining or otherwise removing the outer surfaces to a depth of the internal openings 41 or 42~ End plate 36 is then affixed by any of the methods tescribed earlier.
Referring now to Figures 7A and 7B, an embodiment of the invention is disclosed which is adapted for situations where a low profile is required or where a number of such exchanger units are to be stacked to function as a single larger unit.
Heat exchanger sheet 51, which is provided with undulations, has its ends gradually reduced to approximately a straight line.
Th eline termination may be extended by adding a plate 52. m e manifolding may be reduced by clinching or other graduation process. In this arrangement, the fluid streams enter at the ends of the exchanger in the same direction as the paths of fluid through the exchanger, i.e., paralell to the heat transfer sheet surface. A fluid Fl enters port 53 and its at port 54.
Fluid F2 enters port 55 and exits at port 56. Each port com-prises the inner surface of the outer top or bottom plate 57, side p~lates 50 and the divider 52.
The arrangement shown in Figure 7A illustrates that in `' ~0383~9 some respects thls construction is simpler than the earlier embodiments in that the top and bottom plates extend the length of the exchanger and these plate form the ports with the clinched heat transfer sheet or with a plate affixed to the clinched por-tion.
In the clinching of the undulated sheet, longitudinal passages may be partially blocked for a short distance. This will not significantly affect the performance of the exchanger.
A heat transfer sheet which is graduated to a linear portion becomes more difficult to achieve as the height of the corrugat-ion or folds is increased. When clinching is performed under these circumstance the fluid passages may be significantly blocked. The problem can be overcome by use of the design shown in Figure 7C. The essence of this design is that the fluid portsoopen beyond the point of excessi~e closure due to clinch-in8.
In this case, the end members may be formed in twoparts 61 and 62. Each such part is roughly L-shaped and includes horizontal members 64 and 63. The horizontal members sandwich the linear portion 66 of the heat transfer sheet.
Each port, for example, entry port 5~, allows entry and exit of the fluid beyond the narrowed`closure resulting from clinching of the transfer sheet ends.
Another construction of the heat exchanger in accord~
ance with the present invention is shown in Figures 8A, 8B and 8C. In this arrangement, the sppropriate closure of the ends of specified channels of the undulations, permits floid entry par-allel to the heat transfer surface but fluid exit occurs perpen-dicular to the surface. Figure 8A illustrates this feature. A
first fluid Fl enters a port 70 permitting parallel flow and exits from port 72 which is in a direction perpendicular to the heat transfer surface. Similarly, a second fluid enters port 71 parallel to the surface and exits perpendicular the surface at port 73. Figure 8B shows the cross section of the exchanger and the heat transfer sheet 76.
The guiding of the flow can be understood by reference to Figure 8C. There it is shown that alternating end portions of each undulation are closed off. At the entrance of fluid F2, portions 74 are closed off; at the entrance of fluid Fl, portions 75 are closed off. The fluid at each side enters the available open portions, and travels longitudinally to the end of the undulation channel ~ntil the opposite closed end is reached;
then, the fluid is forced at ri8ht angles to the heat transfer sheet and out the exit port. It should be understood that various combinatlons of side or end manifolding may be used in appropriate applications.
In Figures 9A, 9B and 9C, 9D, embodiments are illus-trated~showing two approaches for making the undulated heat trans-` 1038369 fer ~heet self spacing as well as for supporting and stiff-ening each individual corrugation against differen~ial pressure within the heat exchanger. Figures 9A and 9B
show heat tran.sfer sheet 80 having projecti(~ns or dimples 82 which art~ alternately spaced from one undulation to the next to prevent occurrence too close to one another. These dimples, while spacing the folds, will not significantly interfere with air flow. The dimples also enhance heat transfer for diverging the fluid flow.
Figures 9C and 9D illustrate one of several possible embodiments using convolutions to assure spacing of the folds. Heat transfer sheet 80 includes convolutions 83 on every second fold or undulation. These convolutions span twice the nominal space between folds and are prefer-ably aligrled with one another. This is done in such a way as to insure maximum stiffness of the overall folded sur-face against closure of the fluid passages as a result of pressure or other external force. The convolutions have the advantage of offering greater rigidity of the overall assembly and greater stiffness for each individual fold.
They will however interfere with ~luid flow if extended beyond the baffle plate 17. The convolution can be extended as shown in Figure 9D where the convolutions have curved portions 84 to allow entry and exit of fluid.
Figures 9E and 9F show a variation of the above principles where the high pressure is always on one side of the surface.
~ 18 -~ ~03~369 <~
In those figures, the flat surfaces of the corruga-tions 80 include periodic dimples 81 as sho~n. The dim-ples 81 extend away from the high pressure side and into the low pressure side so that each dimple touches an oppos-ing dimple. This substantially prevents compressionnof the corrugations by the large pressure differential. The use of dimpling can also increase heat transfer by creating turbulence in the fluid stream.
Referring now to Figures 9G to 9J~ a preferred con-figuration of the heat transfer sheet, denoted for pur-poses of this embodiment as 600, is illustrated which en-hances toca surprising degree the ease of fabrication of the core(comprising the undulated or folded heat transfer sheet) as well as the structural rigidity and spacing of the device. As noted above, dimples are formed in the sheet to make the folds self spacing and to maintain the folds under a differential pressure. It has been found that to increase the effectiveness of the dimples, it is desireable to form them such that the raised dimple, denoted as 602R
is as close as possible to the depressed dimple, denoted as 602D, on the same sheet. This is shown in Fig. 9G
where distance (a~ is kept as small as possible, and usu-ally considerably smaller than the spacing of the dimples on the same side of the sheet, for example, distance (b~), between ad~acent raised dimples 602R. The reason for this is readily apparent from Fig. 9~. When a force (denoted F) is transmitted by the dimples it must traverse the minimum distance (a) before encountering the stiffening effect of the adjacent dimple. This feature is desirable in many heat exchangers where a low pressure drop is desirable through the exchanger because an excessive number of dimp-les (required to otherwise prevent buckling of the sheet) will increase the pressure required to force through a given ~ -18A_ flow of fluid. A secondary desirable effect of the mini-mally spaced ad~acent raised and depressed dimples is a réduction of pressure drop through the~heat exchanger caused by the dimples. If the dimples are large, which is often necessary because of the stamping or drawing characteristics of the material, they intermittently block the flow of fluid and would force it to flow in a transverse direction to flow around the dimple. The ad~acent dimple in the oppo-site direction allows the air to flow into this ad~acent r region thus minimizing the flow disturbance and therefore pressure drop.
StiIl reférring to Fig. 9H, when dimples are formed in a sheet of material, the depth to which they can be drawn is a unction of their width and material properties. In most casesit is not practical to draw a dimple to the full depth of the desired spacing between adjacent folds of the core. This problem has been solved by the configuration of the heat transfer sheet 600 shown in Fig. 9H. The sheet is formed so that when it is folded depressed dimples 602D
align with and abut raised dimples 602R. Thus, these dimples need have a height only one half the desired spacing between ad~acent folds of the sheet.
Referring to Fig. 9I, stiffèning channels or forms 604, are formed in each fold in addition to dimples 602 which serve to stiffen each fold. These forms 604 are provided in a manner whereby they nest together as shown upon the heat transfer sheet being folded. This is advantageous since the stiffening forms will not signif-icantly reduce the cross sectional area between the folds available for fluid flow.
Referring now to Fig. 9J, a schematic of an unfolded heat transfer sheet, denoted 700, is shown wherein iden-tical stampins 701 are used to form raised dimples 702R
(solid circles), depressed dimples 702D (open circles) and depressed stiffening channels 704 (lines), so that ~ -18B_ ~038369 the sheet may be folded along primary fold lines 706 only or along primary fold lines 706 and secondary fold lines 708 to form the folded core. In each case, raised dimples will always abut other raised dimples, depressed dimples will always abut other depressed dimples, and stiffening channels will always nest within other stiffening channels. Such a configuration results in all the benefits and advantages discussed above in addition to complete ease and simplicity in manufacture. Each stamping 701 includes two configurations 710A and 710B having the pattern of raised and depressed dimples (and stiffening channels) shown in Fig. 9J.
As seen, the stiffening channels 704 in each configuration 710A
and 710B are intermediate each other and terminate slightly before each primary and secondary fold line 706, 708. This insures nesting and also results in a natural fold line 708 occuring at these intervals. ~his is an important feature in that commercia]
manufacture of a folded heat exchanger core is for the first time made practical. The particular dimple configuration shown in Fig. 9J~ as stated above, permits folding of the core along primary fold lines 706 only (whereby a core is achieved having larger overall dimensions) or along both the primary fold lines 706 and the secondary fold lines 708 (whereby a core is achieved having smaller overall dimenslons). In both cases dimples in adjacent folds align and abut with each other. This advantage results when adjacent configurations 710A and 710B have raised and depressed dimples formed in them respectively in a mirror image pattern with respect to each other as shown in Fig. 9J.
~031~369 While reference has been made to the use of thin or flexible materials, the heat exchanger of the present invention is easily adapted to situations of high pressure differences because of the ease of seal-ing and inherent strength of the corrugated surface to resist beam bending due to the pressure differential.
The problems of bending in the flat surfaces of the corrugations is overcome by the above method.
Another arrangement for high pressure differ-entials is shown in Figure 10. This figure also illus-trates the flexibility of the design of the heat ex-changer of the present invention. The heat transfer sheet 90 is seen to consist of two rows of corrugations or undulations. The two rows are closed and fluid-tight so as to enclose a volume therein. The lower peaks of one row of corrugations are juxtaposed to the upper peaks of the other row. Lowsr pressure fluids are passed through the enclosed volume 92 and higher pressure fluids along the top and bottom outer surfaces of the corrugations. Thus, the heat 10383~9 transfer sheet cannot collapse because of beam bending.
Figure 11 illustrates a heat transfer sheet 95-which has a circular cross section. One fluid is passed longitudinally within the enclosed volume 97, the second fluid along the outer surfaces 96 of the heat transfer sheet, the two fluids being preferably in counter-flow direction:
The heat transfer sheet itself in any of the appli-cations may be made in a single sheet by an extrusion or stamp-lng or msy be made from any number of separate pieces and appro-priately ~oined together.
The simplicity and economy of the present heat exchanger enables it to be used in many applications where an expensive system would not be ordinarily ~ustified. For example, a heat recovery system for home heating systems may utilize the preseht heat exchanger design. Figure 12 illustrates a low cost, com-pact heat exchanger in accordance with the present invention as incorporated in a system to recover heat which would otherwise be lost up the flue or chimney of a gas or oil-fired hot air furnace.
As shown in Figure 12, the system includes a furnace 101 having a flue 102. Heated air from the flue enters heat exchanger 100 which is constructed in accordance with the prin-ciples of the present invention and, in particular, entry port 104. The heated air is drawn by the forced circulation supplied ~0383~9 by fan 113 through the exit port 105 of the exchanger and out the chimney. The heat from the furnace air stream is transferred to a fresh air stream which is drawn through heat exchanger entry port 106 by the forced~?circulation of fan 112. The heated fresh air exchanger exit port 107 and may be re-supplied to the house via air outlet 120.
The system may incorporate a safety damper which permits air to circulate through the exchanger only when the motor 110 drlves the fans 112 and 113. This is a fail-safe feature which insures that failure of the fan would still permit the furnace to operate through the ordinary flueepath 121. Thus, harmful fumes will not escape because of inability of the natural draft to draw through the heat exchanger.
Other features of the system shown in Figure 12 include the use of a single motor 110 to drive both intake fan 112 and exhaust fan 113. The co~nterflow heat exchanger 100 also funct-ions simultaneously as a water condenser. Water will condense on the flue side surfaces of the corrugated heat transfer sheet wetting `exchanger 100 and will rund down the internal surfaces of the exchanger. The flow of air through the exchanger will force the water toward the exit port 105 and toward the drain 116. The water will then drain into the plenum chamber 121 and, finally into the system drain. The system may also include a barometric damper- 114, if necessary.
103~369 While the foregoing specification ant drawings represent the preferred embodlments of the present invention, it will be obvious to those skilled in the art that various changes and modifications may be made therein wlthout departing from the true spirit and scope of the present invention.
Claims (8)
1. A heat exchanger for transmitting thermal energy from one moving body of fluid to another comprising a casing of sub-stantially constant cross-sectional area and a thermal transfer core within said casing, said core including a single, integrally formed, substantially continuous sheet of heat conductive mater-ial having a plurality of fold sections, separated by fold lines, the individual fold sections of said sheet dividing the interior of said casing into adjacent fluid flow passages, alternate ones of said passages defining first conduit means for conducting relatively warm fluids, the other passages defining second con-duit means for conducting relatively cool fluids, the indivi-dual fold sections of said sheet having a multiplicity of pairs of dimples formed therein, said dimple pairs being aligned longi-tudinally with respect to each other in at least two longitudinally extending zones, each said pair of dimples comprising a raised dimple and an adjacent depressed dimple wherein the spacing be-tween the raised and depressed dimple in each pair is small with respect to the spacing between adjacent, longitudinally aligned pairs of dimples, the height of each dimple being substantially equal to one-half the width of said fluid flow passages.
2. A heat exchanger as recited in claim 1, further in-cluding longitudinal ridges formed in each fold section inter-mediate each zone extending over the substantial length of said fold section, each ridge terminating before the next adjacent fold section, the terminal ends of said ridges defining a fold line between the adjacent fold sections.
3. A heat exchanger as recited in claim 1, wherein ad-jacent fold sections have patterns of dimples formed therein which are substantially mirror images of each other with respect to the intermediate fold line so that upon folding said sheet along said fold line to bring the adjacent fold sections into confronting relationship, the raised and depressed dimples of each fold section abut corresponding raised and depressed dim-ples respectively of the adjacent fold section.
4. A heat exchanger as recited in claim 3, wherein the adjacent fold sections have a plurality of raised and depressed longitudinally extending ridges respectively formed therein, each such raised ridge in a fold section being colinearly formed with a corresponding depressed ridge in the adjacent fold section so that upon folding said sheet along said fold line to bring the adjacent sections into confronting relationship, corresponding ridges in adjacent fold sections nest within each other.
5. A heat exchanger as recited in claim 1, wherein ridges are defined in the upper and lower edges of each fold section, said casing including top and bottom members, each member being substantially cup-shaped and said upper and lower edges of said fold sections being located within the respective top and bot-tom members, and a cured cement being disposed within top and bottom members encapsulating said ridges thereby fastening said fold sections in place.
6. A heat exchanger as recited in claim 5, wherein said bottom cup-shaped member includes a rim circumferentially extend-ing therearound having a free edge extending beyond the upper surface of the resin defining a trough for condensate forming in said heat exchanger.
7. A heat exchanger as recited in claim 6, wherein a drain port is provided in the portion of said rim which extends above the upper surface of the resin to drain the condensate which may accumulate in the trough.
8. A heat exchanger for transmitting thermal energy from one moving body of fluid to another comprising a casing of sub-stantially constant cross-sectional area and a thermal transfer core within said casing, said core including a sheet of heat con-ductive material having a plurality of fold sections, separated by fold lines, the individual fold sections of said sheet ex-tending longitudinally of said casing and dividing the interior of said casing into adjacent fluid flow passages, alternate ones of said fluid flow passages defining a first conduit means for conducting relatively warm fluids, the other passages defining a second conduit means for conducting relatively cool fluids, the individual fold sections of said sheet having dimples formed there-in of a height substantially equal to one-half the width of said fluid flow passages and wherein alternate fold sections have patterns of dimples formed therein which are substantially iden-tical to each other so that upon folding said sheet along alter-nate fold lines the dimples of a pair of adjacent fold sections abut corresponding dimples of the adjacent pair of adjacent fold sections.
Priority Applications (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| US05/605,654 US4043388A (en) | 1975-04-14 | 1975-08-18 | Thermal transfer care |
Applications Claiming Priority (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| US46606574A | 1974-05-01 | 1974-05-01 |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1038369A true CA1038369A (en) | 1978-09-12 |
Family
ID=23850312
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA224,549A Expired CA1038369A (en) | 1974-05-01 | 1975-04-14 | Heat exchanger and heat recovery system |
Country Status (3)
| Country | Link |
|---|---|
| CA (1) | CA1038369A (en) |
| FR (1) | FR2269694A1 (en) |
| IT (1) | IT1037757B (en) |
Cited By (1)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| ES2631955A1 (en) * | 2016-11-04 | 2017-09-06 | Fundación Para El Fomento De La Innovación Industrial | Fold plate heat exchanger and assembly procedure (Machine-translation by Google Translate, not legally binding) |
Families Citing this family (7)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US4321964A (en) * | 1978-02-11 | 1982-03-30 | Kernforschungsanlage Julich Gesellschaft Mit Berschrankter Haftung, Rosenthal Technik Ag | Recuperative heat exchanger of ceramic material |
| EP0029573A3 (en) * | 1979-11-24 | 1981-12-16 | Uwe Klix | Heat exchangers, their formation and arrangement in an installation for heat recovery by exchange of air, in particular for dwelling houses and comparable lay-outs |
| GB9027994D0 (en) * | 1990-12-22 | 1991-02-13 | Atomic Energy Authority Uk | Heat exchanger |
| JP2627381B2 (en) * | 1992-03-13 | 1997-07-02 | 矢崎総業株式会社 | Absorption refrigerator |
| JPH1194476A (en) * | 1997-09-25 | 1999-04-09 | Konica Corp | Heat exchanger |
| US6244333B1 (en) | 1998-08-27 | 2001-06-12 | Zeks Air Drier Corporation | Corrugated folded plate heat exchanger |
| US6186223B1 (en) | 1998-08-27 | 2001-02-13 | Zeks Air Drier Corporation | Corrugated folded plate heat exchanger |
-
1975
- 1975-04-14 CA CA224,549A patent/CA1038369A/en not_active Expired
- 1975-04-29 FR FR7513366A patent/FR2269694A1/en not_active Withdrawn
- 1975-04-30 IT IT2288475A patent/IT1037757B/en active
Cited By (1)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| ES2631955A1 (en) * | 2016-11-04 | 2017-09-06 | Fundación Para El Fomento De La Innovación Industrial | Fold plate heat exchanger and assembly procedure (Machine-translation by Google Translate, not legally binding) |
Also Published As
| Publication number | Publication date |
|---|---|
| FR2269694A1 (en) | 1975-11-28 |
| IT1037757B (en) | 1979-11-20 |
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