Note: Descriptions are shown in the official language in which they were submitted.
~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;
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~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
.~,",~ .
1038369
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.
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1038369
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
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~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.
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~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.
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~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
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1038369
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
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1038369
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
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\ ~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
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~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-
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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~
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1038369
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_
103B369
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.
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~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
-- 19 --
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
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~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.
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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.
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