Note: Descriptions are shown in the official language in which they were submitted.
`-~ 1126;Z56
TITLE
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Thermoplastic Heat-Exchanger
Background of the Invention
Heat exchangers have long been known, and
historically were made of metal components. More
recently, heat exchangers have been fabricated of
plastics, including thermoplastics. Although, for a
given use, a thermoplastic heat exchanger must have a
larger heat exchange area than the area of a metal one,
it has the advantages of being lighter in weight and
significantly less expensive than a metal one. For
example, in U.S. 4,069,807 there is a description of a
thermoplastic heat exchanger which comprises individual
heat exchanger elements wherein the interior of each
element is divided into many long narrow ducts. There
are problems with such heat exchangers when they are
used for carrying a liquid or for a condensing system
within the elements, especially at low flow rates and
for the thinner elements, as gas blinding in the case
of a circulating liquid, or fluid droplet blinding in
the case of a condensing system, frequently blocks flow
through the narrow ducts and interferes with the heat
transfer. Even when the fluid within such elements is
a gas, condensation of droplets of liquid can blind
the ducts and interfere with efficient heat transfer.
Further, the control of flow to and from the ducts in
such elements must be through the use of headers at the
ends of the ducts, which necessitates complex forming
and sealing to assure the proper flow of the fluid.
Accordingly, there has been a need for an improved
thermoplastic heat exchanger.
Summary of the Invention
The invention relates to an improved thermo-
plastic heat exchanger. Briefly, the heat exchanger
comprises individual heat exchange elements, made of
two sheets of thermoplastic film and havingprotuberanceswhich
1126256
extend from one of the sheets toward the other sheet,
the element having openings for conducting a fluid into
and out of the element. Said opellings can eit.ler be in
the sheets of film, in which case the elements are
sealed together at thc edges of the shcets, or thcy
can be in the edges of the elements, e.g., in the septa
around the edges of the elements.
More specifically, one embodimentof the invention
comprises a thermoplastic heat exchanger element com-
prising first and second thermoplastic sheets spaced
apart from one another by a plurality of protuberanceswhich project from one of said sheets and which extend
toward the other of said sheets, a seal between said
sheets near the edges thereof, one of said sheets
having a first opening therein to permit introduction
of a first fluid therethrough, and one of said sheets
having a second opening therein remote from said first
opening to permit removal of said first fluid there-
through, said element being adapted to exchange heat
between said first fluid and a second fluid in contact
with the exterior faces of said sheets.
The invention further comprises a thermoplastic
heat exchanger comprising a plurality of such elements
which are spaced apart to permit passage of the second
fluid between adjacent exterior faces of the elements.
Brief Description of the Drawings
Fig. 1 is a prospective view of a p~l~tion of a
heat exchanger fabricated of a thermoplastic resin.
Fig. 2 is a sectional view of one of the elements
of the heat exchanger of Fig. 1.
Fig. 3 is an enlarged perspective view, partially
in section, of a portion of an element of the heat
exchanger of Fig. 5.
Fig. 4 is an elevation cr another heat
exchanger of the invention.
Fig. 5 is a sectional view of one of the types
of elements of the heat exchanger of Fig. 4.
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Fig. 6 is a sectional view of the other of the
types of elements of the heat exchanger of Fig. 4.
Figs.7 and 8 are partial sectional views of
layouts for elements which can be used in place of those
S shown in Figs. 5 and 6.
Detailed Description
Fi~ures 1, 2 and 3 depict one illustrative em~x~ent
of the heat exchanger of the invention.
Referring first to the specific heat exchanger
element of Fig. 3, sheets 151 and 152 of thermoplastic
film, which serve as the heat exchange surfaces, are
spaced apart from one another. Proximate faces of the
two sheets are joined to one another near the edges
thereof, in this embodiment by edge septa, only one of
which, edge septum 153, is shown in this partial view.
Throughout the space defined by the two sheets and the
edge septa, there is a plurality of protuberances 168
which project from sheet 152 and extend toward sheet 151.
Protuberances 168 serve to maintain sheets 151 and 152
in a spaced-apart relationship to one another, thus
pre~venting collapse of the two sheets against one another,
which would restrict or stop the flow of fluid between
the sheets. Channel septum 165 extends between and is
joined to proximate faces of sheets 151 and 152, and
serves as a barrier between channels to direct the flow
of a first fluid in a defined path between the two sheets.
It should be understood that both edge septa
and channel septa are optional but preferred features of
the heat exchanger element. The edge portions of sheets
151 and 152, being flexible, can be joined directly
to one another without intervening edge septum 153.
Also, when a heat transfer element having only one fluid
channel is desired, there will be no channel septa.
The use of protuberances to maintain the channels
in a spaced-apart relationship makes it feasible to
use wide channels, i.e., channels which are wide enough
~hat blinding of the channel by gas bubbles or liquid
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droplets will not occur, and which might otherwise
collapse if there were no protuberances. Although gas
bubbles or liquid droplets can still form within the
heat exchange element, they only locally block heat
transfer and flow, and do not completely stop the flow
of fluid in that channel.
As depicted at junction 171 of edge septum 153
with sheet 152, at junction 172 of channel septum 165
with sheet 152, and at junction 173 of protuberance 168
with sheet 152,theadg~septa, protuberances and channel
septa are preferably formed integrally with sheet 152.
Sheet 152 with protuberances 168 can conveniently be
made by extrusion of a thermoplastic resin from a
suitable c'ie on.o a --atternec- c.rul~ with the technique
15 s:r.o~n in a.ry ^f ~.S. Patents ~o. 3, 509, 005; 3, 515, 778 '
or 3,635,63i, an .ne edge and channel se?ta, if present,
are made at the same time. In some cases, sheet 152 and
the protuberances and septa can also be made by injection
molding. Sheet 151 is then joined to sheet 152 at the
20 edges thereof, for example, by heat sealing or with a
suitable adhesive, preferably by heat sealing, either
directly as noted above, or by sealing to the top 174 of
edge septum 153 and the tops of other edge septa not
shown, and to the top 175 of channel septum 165 and the
25 tops of all other channel septa,if such septa are present.
A suitable technique for sealing sheet 152 to the tops o~
the edge and channel septa and is disclosed
in U.S. 3,821,051.
While protuberances 168 can be shorter than the
heightof ~e septa,it is preferred that they extend to and
are joined to sheet 151. When protuberances 168 are
joined to sheet 151, this can also suitably be done by
joining the top 176 of each protuberance 168 to sheet
151 by heat sealing or with a suitable adhesive,
preferably heat sealing. It is preferred that protu-
berances 168 be joined to both sheets 151 and 152, as
this prevents ballooning of sheets 151 and 152 away
from one another when the pressure of the first fluid
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within the heat transfer element exceeds the pressure
of the second fluid in contact with the exterior faces
of the element. If such ballooning were not prevented,
the flow of the second fluid in contact with the exterior
faces of the element could be restricted or stopped.
Fig. 2 depicts a sectional view of one heat
exchanger element. Sheet 152 of thermoplastic film
carries edge septa 153, 154, 155 and 156 joined to the
sheet at its edges. The space within the element is
divided into channels 157, 158, 159, 160, 161 and 162
by channel septa 163, 164, 165, 166 and 167 which are
joined to sheet 152 as described above. Protuberances
168, of which only three groups are shown in Fig. 2,
project from sheet 152 throughout all of the channels.
Sheet 152 contains two openings, a first opening 169
through which the first fluid enters the interior Ot-
the element, and a second opening 170 through which the
first fluid is removed from the element. The flow of
the first fluid through the channels is in the direction
of the arrows shown.
The number of channels 157 etc. can vary from
as few as one channel up to any number as may be desired
or needed for a particular heat exchange.
The six-channel element depicted in Fig. 2 is merely
typical, and is suitable for many uses where six heat
exchange stages are desirable. The heat exchange elements
can have either an even or odd number of channels, and
the location of opening 170, through which the first
fluid is removed, will vary, and it will be placed at
the downstream end of the last channel through which the
first fluid flows.
In Fig. 1 a portion of a typical heat exchanger
of the invention is shown in perspective. The arrows
associated with numerals 2,2 refer to the direction of
the sectional view shown in Fig. 2. ~hown are five
individual heat exchange elements 101, 102, 103, 104 and
105. In this view sheets 151 and 152 and edge septa
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153 and 154 can be seen. Each of sheets 151 and 152,
and the corresponding sheets of all the other elements
102 etc. except the last element (not shown), contain
both first and second openings which are not seen in this
view, such as first opening 169 and second opening 170
seen in Fig. 2. All of the first openings are in line,
and all of the second openings are in line. The final
element (not shown) contains first and second openings
in only the first sheet, i.e., the sheet w:lich faces
toward the adjacent element, there being no openings in
the second sheet, i.e., the sheet of the last element
which is farthest away from the penultimate element.
A first series of coaxial rings 106, 107, 108, 109 and
110 is situated such that each ring lies between and
is joined to adjacent elements and is disposed to
surround the first openings in the sheets they contact.
For example, ring 106 joins onto sheet 152 to surround
first opening 169, and joins onto sheet 150 to surround
the corresponding first opening in that sheet. Similarly,
a second series of coaxial rings 111, 112, 113, 114 and
115 is situated such that each ring lies between and is
joined to adjacent elements and is disposed to surround
the second openings in the sheets they contact. For
example, ring 111 joins onto sheet 152 to surround second
opening 170, and joins onto sheet 150 to surround the
corresponding second opening in that sheet. Spacer
bars 116, 117, 118, 119 and 120 are positioned between
adjacent pairs of heat transfer elements to aid in
maintaining the elements in a spacec~ apart relationship.
The spacer bars should be secured in place to prevent
them from shifting out of place; this can be done, for
example, by joining them to the heat exchanger elements
by heat sealing or with a suitable adhesive. The spacer
bars need not be sealed along their entire length to
the elements; it is adequate to secure them merely with
seals near each end of the bar. Passages 131, 132, 133,
134 etc., and similar passages adjacent the opposite
262S6
side of the spacer bars, carry the second fluid which ls
to exchange heat with the first fluld. The spacer bars
are disposed in a direction substantially perpendicular
to the direction in which the first fluid flows in the
5 channels within the elements, thus serving to guide the
flow of the second fluid in a direction substantially
perpendicular to the direction of flow of the first
fluid. Two hollow cylindrical fittings are joined to
sheet 151, a first fitting 121 surrounding the first
10 opening in sheet 151 and a second fitting 122 surrounding
the second opening in sheet 151. The fittings serve as
means for connecting pipes, tubes, hoses or other ducts
to the heat exchanger, so as to permit introduction and
removal of the first fluid into and from the heat
exchanger elements.
Taken together fitting 121 and rings 106, 107,
108 etc. constitute a discontinuous duct and serve as
means to distribute the first fluid into the space
inside of all the heat exchange elements lOl, 102, 103
etc. Similarly, taken together, fitting 122 and rings
111, 112, 113 etc. constitute a discontinuous duct and
serve as means to collect the first fluid from the space
inside of all heat exchange elements 101, 102, 103 etc.
The fittings can be located differently, but in a
manner functionally equivalent to that described above.
It is necessary only that the first and last sheets of
the heat exchanger taken together i.e., the first sheet
of the first element and the second sheet of the last
element, which sheets face away from the adjacent
3~ elements, have a total of two openings. Both openings
can be on either the first sheet or the last sheet, or
each sheet can have one opening; in either case, the
discontinuous ducts will properly distribute and collect
the first fluid.
It should be understood that a heat exchanger
may comprise as few as one heat exchange element to as
many such elements as may be desired for a particular
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use, which may number in the hundreds.
~ ings 106-110 and 111-115 are suitably circular
in shape. They can be joined to sheets 152, 150 and
other like sheets by heat sealing or with a suitable
adhesive, preferably by heat sealing. A preferred method
of joining the members is by a technique variously termed
as electromagnetic bonding or magnetic heat-sealing,
wherein a composition comprising a sui.table thermoplastic
resin such as polyethylene and a magnetic material such
13 as iron, steel, iron oxide or a ferrite in the form of
micron or submicron particles is applied at all places
where a sealed joint is to be -ormed, and then the
assembly is placed in a high frequency magnetic field of
an electric induction generator, whereby said composition
1~ heats and forms a secure bond to the thermoplastic
members which it contacts. Such sealing compositions
are known in the art and are commercially available in
numerous forms including molded and extruded shapes such
as films and gaskets, liquid or paste compositions in
aqueous or solvent binder systems, and hot melts.Informa-
tion concerning the technique can be found in the Mbdern Plastics
Encyclopedia, 1977-78 Edition, McGraw-Hill, N.Y., octo~er 1977, pages
420-21, "Electr~magnetic 8Onding~, and pages 424-25, "Magnetic
Heat-Sealing". ~;ore information concerning the techniquQ
and typical compositions suitable for making such bonds
are found, for example, in U.S. Patents No. 3,620,875;
3,620,876; 3,461,014, and 3,779,564.
One method, which is a preferred method, of
formlng the distribution and collectlon systerns for tne
first fluid to and from the inside of the heat exchange
elements is to seal the rings 106, 107 etc. and 111, 112etc.
to sheets 152, 150, etc. before the first and second
openings typified by openings 169 and 170 have been
formed. That is, each heat exchange element is first
fabricated without any first or second openings in it;
rings 106 etc. and 111 etc. are then sealed at sites
where openings 169 and 170 and corresponding openings
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in the remaining sheets are to be formed. Fittings 121
and 122 are also sealed to sheet 151 at sites where the
openings in sheet 151 are to be formed. The openings
are then cut by inseLting a tubular cutter through the
S assembly inside of each series of coaxial rings. The
openings can be cut through all the sheets except the
second sheet of the last heat exchange element;
alternatively the openings can be cut through both sheets
of all the elements including the last element, following
which the two openings in the second sheet of the last
element are sealed shut with a thermoplastic film, disk,
or cup-shaped member. If cup-shaped members are employed,
they can be sealed in place before the openings are cut,
i.e., at the same time that the rings and fittings are
sealed in place.
It is possible to entirely eliminate the use
of rings 106, 107 etc. and 111, 112 etc., in which case
adjacent pairs of elements are directly joined to one
another in ring-shaped areas surrounding the first
and second openings. The direct joint can be made by
heat sealing or with the use of an inductively-heatable
adhesive composition as described above. For example,
ring-shaped areas surrounding openings169 and 170 in
sheet 152 can be sealed directly to like ring-shaped
areas surrounding corresponding first and second openings
in sheet 150. One method to effect this construction
is to seal appropriate circular areas before the openings
have been made, and then to cut through the assembly
with a tubular cutter of diameter less than the diameter
of the sealed circular areas. Of course, fittings 121
and 122, and seals cver any openings cut in the second
sheet of the last heat exchange element as explained
above, are still needed. Joining the individual heat
exchange elements in this way is possible as the sheets
35 150, 151, 152 and like sheets are of flexible thermo-
plastic film, and thus elements 101, 102 etc. are not
completely rigid. When the heat exchange elements are
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joined in this way without rings 106 etc and lll etc.,
it may be convenient to assemble the heat exchanger and
make the seals around the first and second openingsbe.ore
the;pacer bars 116, 117 etc. have been put in place;
a~ter t~eseals around the first and second openings
ha~rebeen made, the heat exchange elements are carefully
spreadapart sufficiently to permit insertion of the
~spacerbars which are then sealed in place.
The spacer bars 116, 117 etc. are per se an
10 optionalfeature, as other means can serve to maintain
theheat exchange elements in spaced-apart relationship-
~~orexample, individual heat exchange elements could be
-thermoformed to have protrusions, and generally a
plurality of protrusions, which project toward an adja-
cent element. In one such arrangement the heat exchangeelements from the second element to the penultimate
element couldbe so thermoformed; the first and last
elementscould also be so thermoformed but such is not
required. In another such arrangement, alternate
; 20 elements (i.e., every second element) could be thermo-
formed with protrusions extending from both sheets; for
example, even-numbered elements could be so thermoformed
and odd-numb~red elements need not be so thermoformed.
It is necessary only that there be protrusions on
. 25 sufficient sheets to maintain the elements spaced apart.
- Protuberances 168 suitably can be of circular
cross-section, or they can be any other shape desired,
the cross-section being, for example, triangular, oval,
streamlined, rectangular, etc. The protuberances need
not be of uniform cross-section, and can be tapered,
provided with chamfer, etr, ~ as decired.
The arrangement of protuberances can be
staggered or in line, and can be ordered on triangular
centers, on rectangluar or square centers or in any
pattern desired, or it can be random.
If desired, some protuberances can also be
connected by partial septa, which could be useful for
~1%625~
' 1
example in directing or controlling fluid flow. The
height of such partial septa would ordinarily be less
than half the distance between the two sheets of the
heat exchange element.
Sheets 151 and 152 can vary in thickness from
as thin as 1 mil to as much as 25 mils. Although heat
will move more quickly through the thinner sheets, they
are more difficult to make and are less rugged than
thicker sheets. Sheets thicker than 25 mils transmit heat
too slowly and are seldom necessary to provide for
operation at high pressures. The sheets are kept as thin
as possible consistent with the pressures to be employed
and the geometry of the protuberances and septa. For
most uses sheets 2 to 5 mils thick are preferred.
The spacing between the two sheets of a heat
transfer element can vary from about 10 mils up to about
0.5 inch. The spacing will be determined in part by
the type and flow rate of first fluid to be carried within
the element, and the amount of heat to be transferred.
For a liquid at a high rate a larger spacing would be
used. For low flow rates, thinner spacing is appropriate.
For most purposes, spacing of 20 mils to 0.1 inch is
suitable.
The protuberances can vary in size, and if
circular in cross-section, can have diameters from about
5 mils to about 0.2 inch. The smaller diameters are
generally used with thin sheets and the larger diameters
with thicker sheets. Protuberances of other cross-sec-
tional shape will be of similar size. Protuberances
other than circular in cross section will ordinarlly have
the largest cross-sectional dimension lyinq gener~llv i n
the direction of fluid flow, and can have a long
dimension of an inch or more. The spacing of protu-
berances can vary from about 15 mils to about 2 inches,
center to center. The closer spacing is suitable for
thinner elements and thin protuberances, and wider
spacing for thick elements and thick protuberances.
11
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12
For most purposes, circular protuberances 20 mils to 0.1
inch in diameter, on centers spaced 0.1 to 0.3 inch, are
preferred.
The edge septa have a thickness equal to the
spacing between the sheets as described above, and a
width varying from about O.OS inch to about 0.2 inch.
Edge septa 0.1 inch wide are suitable for most purposes.
The channel septa also have a thickness equal
to the spacing between the sheets, and a width varying
from about 4 mils to about 0.05 inch. The narrower
septa are suitable for thin elements, and thicker septa
for thick elements. Channel septa are spaced at least
0.5 inch apart to prevent blinding of the channels.
Typical channel widths range from 1 to 5 inches. A
channel septum will ab~ one edge septum, and will
ordinarily terminate a distance from the opposite edge
septum about equal to the width of the channels.
The spacer bars are suitably square or rectan-
gular in cross-section. The thickness of the bar will
determine the spacing between adjacent elements, and can
vary from about 50 mils to about 1 inch, preferably
from 70 mils to 0.5 inch. The width of the bar will
usually be equal to, or slightly greater than, the
thickness. The length of the bar will be approximate
the height of the elements to be separated.
Rings 106 etc. and 111 etc. usually have a
thickness equal to the thickness of the spacer bars, and
thus range ir~ thickness from about 50 mils to about 1
inch, preferably 70 mils to 0 5 inch. The diameter will
vary, depending on the amount of fluid to be carried
and the width of the channel it serves. ~ical outside;l J~eters
range from 0.35 inch to 2 inches, and typical wall
thicknesses from about 0.05 to 0.15 inch.
Fittings 121 and 122 ordinarily will have an
outside diameter and wall thickness equal to those of
the rings used. The fittings can vary in length,
usually at least 0.5 inch, and most often from about
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13 ~262S6
l inch to 2 inches long.
The invention is applicable to all plastic
sheet exchangers made from melt processible polymers.
The most preferred polymers are polyolefins such as
polyethylene and polypropylene. Other preferred
polymers include polyfluorocarbons such as copolymers
of tetrafluoroethylene, e.g., tetrafluoroethylene/hexa-
fluoropropylene copolymers, and polychlorofluorocarbons,
e.g., polychlorotrifluoroethylene. In special situations,
other polymers such as acrylonitrile/butadiene/styrene
polymers, polymethyl methacrylate, polyphenylene oxide,
polysulfones, polyamides, polyesters, polychlorocarbons,
nitrile polymers, and polymer blends, e.g., a blend of
polyphenylene oxide and polystyrene, can be used.
If desired, the sheets of film can be reinforced
by adding reinforcing fillers such as oriental polymer
fibers or glass fibers. Also the sheets can be
biaxially oriented to increase strength and decrease
film thickness. Oriented film, or woven or non-woven
fabrics can also be combined with or incorporated into
the two sheets of the element.
The amount of heat exchange area in a heat
exchanger of the invention, and its overall dimensions,
will vary greatly depending on the type and flow rate
of the fluids between which heat is to be exchanged, the
heat transfer coefficient of the particular system,
and the amount of heat to be exchanged. The active
heat exchange area may be only a few square feet, or
as much as thousands or tens of thousands of square
feet. The two long dimensions of individual heat
exchange elements can range from a few inches to manyfeet;
and one long dimension can be 100 feet or more. Spacer
bars, when used, will ordinarily be placed at distances
of 2 to 6 inches from one another. The heat exchanger
35 may have only a few heat exchange elements or as many
as hundreds of elements.
An example of a heat exchanger of the invention
is a heat exchanger made of high density polyethylene,
13
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~126256
L4
suitable for a gas-liquid heat exchange wherein heat
from water at 120 to 185F is transferred to air at a
rate of up to 60,000 Btu per hour. The elements are 2
feet long by 1 foot high, and have a layout as shown in
Fig. 2. Sheets 151 and 152 are 3 mils thick. The
spacing between the sheets is 34 mils. The edge septa
are 34 mils thick and 0.1 inch wide. The channel septa
are 34 mils thick, 8 mils wide, and traverse 22 inches
of the sheets starting alternately from opposite ends of
the sheets, so that the channels are connected end to
end to provide a serpentine flow path for the first
fluid which i.s water. The protuberances 168 are
circular in cross-section with a 35 mil diameter, are
34 mils long, are joined to both sheets 151 and 152,
15 having been formed upon extrusionofone sheet and
subsequently heat-sealed~o the second sheet, and are
arranged triangularly on 0.125 inch centers. The overall
thickness of the element is 40 mils. The six channels
are each approximately 2 inches wide.
The heat exchanger has 125 such heat exchange
elements. The elements are joined together by two
series of polyethylene rings 106, 107 etc. and 111, 112
etc., each ring being 0.1 inch thick and having an
outside diameter of 0.75 inch and an inside diameter of
25 0.5 inch, the two series being placed at adjacent corners
of the elements, one coaxial series at the beginning of
the first flow channel and the other coaxial series ~t
the end of the last flow channel. Two fittings 121 and
122,each fittin being 1.5 inches iong and having an
30 outside diameter of 0.75 inch and an inside diameter Oc
0.5 inch, are joined to the first sheet of the first
element, one fitting being placed coaxially with each
series of rings. The rings and fittings are joined to
the elements by sealing with the aid of an inductively
35 heated compositi.on comprising polyethylene and magnetic
iron oxide. The first openings typified by opening 169
and second openings typified by opening 170 are then
14
~26256
cut by inserting a tubular cutter 0.5 inch in~i~meter
through the whole assembly, once within the first series
of coaxial rings and once within the second series of
coaxial rings. The first and second openings cut
through the second sheet of the last (125th) heat
exchange element are then closed by sealing over each
opening a polyethylene disk 0.1 inch thick and 0.75 inch
in diameter, using the same sealing technique described
akove. Spacer bars 12 inches long, 0.1 with thick and
0.1 inch wide are inserted between adjacent elements
disposed parallel to edge septa 153 and 155, i.e., in a
direction generally perpendicular to the channel septa
and the direction of fluid flow in the channels, and
are joined to both adjacent elements near each end of
each bar by the sealing technique described above.
Five bars are placed between each adjacent pair of sheets,
on centers approximately 4.8 inches apart, one bar being
placed near the edges of the elements adjacent edge
septum 155 and corresponding edge septa of the
remaining elemen~. Thus passages between adjacent
elements are formeJ for the second fluid, which is air,
to flow in said passages in a direction parallel to the
spacer bars. As noted above the pla~ar dimensions of
the elements are 1 foot by 2 feet. The thickness of
the heat exchanger through the 125 elements and 124
passages which separate the elements is approximately
17.4 inches.
In use, the heat exchanger will ordinarily be
mounted in a housing which fits closely around four
sides of the heat exchanger and which provides plenums
for distributing the second fluid into the passages
between the elements and for collecting the second
fluid as it exits from the passages. The four sides
around which the housing fits closely are (1) the side
35 adjacent edge septum 153 and corresponding edge septa
of the remaining elements, (2) the side adjacent edge
septum 155 and corresponding edge septa of the remaining
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L126256
16
elements, (3) the side adjacent the flrst sheet of the
first element, i.e., sheet 151, and (4) the side adjacent
the second sheet of the last element, the second sheet
beil~g the sheet facing away from the penultimate element.
Optionally, a flat sheet of thermoplastic film
can be sealed over the side of the heat exchanger
adjacent edge septum 153 and corresponding edge septa
of the remaining elements, and a second such sheet can be
sealed over the side adjacent edge septum 155 and
corresponding edge septa of the remaining elements.
Such sheets effect a more positive retention of the
second fluid in those passages between the elements which
are adjacent the sides of the elements. To the same
end, it is also possible to fabricate the individual
heat exchange elements with two narrow strips of excess
film adjacent edge septa 153 and 155, as extensions of
either sheet 151 or 152; after the heat exchanger has
been assembled as described above, the narrow strips
of excess film of one element can be bent over and
sealed to the adjacent edges of the next element.
The hea exchanger of the invention will operate
efficiently when the direction of flow within the elements
is such that the channel first fed with the first
fluid is adjacent the downstream end of the passages
which carry the second fluid.
Another embodiment of the invention is a heat
exchanger comprising at least three parallel substantially
flat sheets of thermoplastic film; edge septa which
join each pair of adjacent said sheets near the edge
portions thereof, said sheets and edge septa defining
passages for fluids, alternate passages beginning with
the first such passage being first passages for a first
fluid, and alternate passages beginning with the second
such passage being second passages for a second fluid;
protuberances in at least each alternate passage joined
to one sheet defining that passage and extending toward
the second sheet defining that passage; each sheet except
16
~1;262~6
17
the first sheet and the last sheet having four openings,
the first and last sheets taken together having a total
of four openings; said openings being in four sets, all
the openings in each set being in line, a set of first
openings and a set of second openings being adjacent,a
set of third openings and a set of fourth openings being
adjacent, and said sets of ihird and fourth openings
being remote from said sets of first and second openings;
series of first coaxial rings disposed in said first
passages, one first ring in each first passage, each
ring joined to proximate sides of said sheets defining
said first passage and surrounding said first openings
in those sheets; a series of second coaxial rings
disposed in said second passages, one second ring in
each second passage, each ring joined to proximate
sides of said sheets defining said second passage and
surrounding said second openings in those sheets;
a series of third coaxial rings disposed in said first
passages, one third ring in each first passage, each
ring joined to proximate sides of said sheets defining
said first passage and surrounding said third openings
in those sheets; a series of fourth coaxial rings
disposed in said second passages, one fourth ring in
each second passage, each ring joined to proximate
sides of said sheets defining said second passage and
surrounding said fourth openings in those sheets; and
four hollow cylindrical fittings, there being a fitting
disposed coaxially with each of the four series of rings,
each fitting joined to either said first or said last
sheet and surrounding one of said four openings in said
first and last sheets.
In this embodiment, each of the first and
~econd fluids is confined within first passages and
second passages, respectively, every passage being
defined by two adjacent sheets of film and edge septa
which join them. Access to the passages is again
accomplished by a discontinuous duct similar to that
17
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126256
18
described above, but in this case the rings are fabrica-
ted as an integral part of the component elements of the
heat exchanger when the flat sheets with edge septa are
fabricated.
Such an embodiment is shown in elevation in
Fig. 4. Heat exchanger 201 comprises a plurality of
elements 202 and a plurality of elements 203 arranged
alternately and joined to one another. The heat
exchanger shown in Fis. 4 has five elements 202, and
four elements 203. It should be understood that the
number of elements 202 can be even or odd, the number of
elements 203 can be even or odd, and the total number of
both elements can be even or odd, but the two types of
elements will always be arranged alternately; the heat
exchanger could have as few as one element of each
type, will preferably have a plurality of each type,
and could have as many as hundreds of elements. In the
embodiment of Fig. 4, elements 203 have a thickness
yreater than that of elements 202. The arrows associa-
ted with the numerals 5,5 and 6,6 in Fig. 4 refer to
the direction of the sectional views of Figs. 5 and 6.
Element 202 is shown in cross-section in Fig. 5.
It comprises a flat sheet of thermoplastic film 221,
generally rectangular in shape, having edge septa 204,
205, 206 and 207 joined to sheet 221 near the edge
portions thereof. The interior portion constitutes a
passage which is divided into channels, in this example
six channels, by channel septa 208, also joined to sheet
221. Rings 209 and 210 are also joined to sheet 221,
and are at sites remote from one another. One ring i3
disposed at the upstream end of the first channel to
receive the first fluid in that passage, and the other
ring is disposed at the downstream end of the last
channel to carry the first fluid in that passage. All
of the edge septa, channel septa and rings which are
part of element 202 are of the same height from sheet 221.
In the channels of element 202 there are protuberances
18
:~1262~
19
268, of which only three groups are shown, which project
from sheet 221. Protuberances 268 can be shorter than
the septa end rings, but prefera~ly are of the same
height as the septa and rings. The edge septa, channel
septa, rings and protuberances all project from the same
side of sheet 221. The flow pattern of the first fluid
in the channels is shown by arrows.
Element 203 is shown in cross-section in Fig. 6.
It is similar to element 202, but with some differences.
Flat sheet of film 222 is bounded by edge septa 211, 212,
213 and 214. The interior portion constitutes a passage
divided into channels by channel septa 215. Rings 216
and 217 are disposed remote from one another, with one
ring at the upstream end of the first channel to receive
the second fluid in that passage, and the other ring is
disposed at the downstream end of the last channel to
carry the second fluid in that passage. All the edge
septa, channel septa and rings of element 203 are the
same height, which, in this example, is greater than the
height of the septa and rings of element 202. In the
channels of element 203 there are protuberances 269
which project from sheet 222. Again they may be shorter
than the septa and rings but preferably are of the same
height. The edge septa, channel septa, rings and
protuberances all project from the same side of sheet 222.
me flow pattern of the second fluid in the channels is sho~n by arrows.
In heat exchanger 201, each of the sheets of
film 221 and 222 (except for the two exposed sheets 223
and 228, as will be explained below) has four openings
in it. Sheet 202 has openings 301, 302, 303 and 304,
and sheet 203 has openings 311, 312, 313 and 314.
Openings 301 and 303 lie within and are surrounded by
rings 209 and 210, and openings 312 and 314 lie within
rings 216 and 217. The rings and openings are so
35 disposed that all openings 301 and 311 are superimposed
in line in heat exchanger 201; similarly, openlngs 302
and 312 are in line, openings 303 and 313 are in line,
and openings 304 and 314 are in line. As explained above
19
~ 1 26256
in relation to the heat exchanger of Fig. 1, the openings
are ordinarily cut after the individual elements 202 and
203 have been assembled and joined to one another.
Heat exchanger 201 is assembled by stacking
elements 202 and 203 alternately in the desired number.
They can be joined by heat sealing or with an adhesive,
and preferably with an inductively heatable composition,
as explained above. The open side of the first element
202 is closed to form a first passage by sealing a flat
sheet of film 223 over it. During assembly, it is
necessary to join the tops of only the edge septa and
rings of each element to the back side of the adjacent
element. Although it is not necessary to join the tops
of the channel septa and protuberances to the back side
of the adjacent element, it is preferred to do so. In
the end view of Fig. 4, edge septa 204 and 211 are seen.
Dotted lines indicate the positions of rings 209, 210,
216 and 217 within heat exchanger 201. After assembling
and joining the elements, the four sets of openings are
cut by inserting appropriately sized tubular cutt~rs
through the assembly, coaxially within each series of
rings.
Hollow cylindrical fittings 224, 225, 226 and
227 are joined to exterior sheets 223 and 228 of heat
exchanger 201, such as with the inductively heatable
composition. The fittings can be joined to the exterior
sheets either before or after the openings 301 etc. and
311 etc. have been cut in sheets 221 and 222. In the
embodiment shown, fittings 224 and 225 are joined to
exterior sheet 228 surrounding openings 301 and 303, and
fittings 226 and 227 are joined to exterio~ sheet 223
surrounding openings 312 and 314. As explained above in
relation to Fig. 1, when the openings are cut, the cutting
can be stopped short of cutting the unneeded holes in
sheets 223 and 228, or, if cut through, the unneeded holes
can be sealed over with pieces of film, plastic dis~s or
plastic cup-shaped members. In the embodiment shown,
sheet 223 needs only two holes, one in line with 302 and
21 11~6256
312, the other in line wlth 304 and 314, and sheet 228
(which is a sheet 221 of an element 202) needs only two
holes, one in line with 301 and 311, and the other in
line with 303 and 313.
Four discontinuous ducts are thus formed.
Fitting 226, rings 216 and openings 302 and 312 constitute
a duct to distribute the first fluid into the first
passages in elements 202. Fitting 227, rings 217 and
openings 304 and 314 constitute a duct to collect the
first fluid from the first passages. Fitting 225, rings
210 and openings 303 and 313 constitute a duct to
distribute the second fluid into the second passages in
elements 203. Fitting 224, rings 209 and openings 310
and 311 constitute a duct to collect the second fluid
from the second passages.
It should be understood that the fittings can
be located in different ways functionally equivalent to
that described above. It is necessary only that the
first and last sheets of the heat exchanger, e.g., sheets
223 and 228 of heat exchanger 201, taken together, have
a total of four openings. The four openings can be two
in each exterior sheet as above, or they can be three in
one sheet and one in the other sheet, or all four can be
in one sheet; in any of these cases the discontinuous
ducts will properly distribute and collect the fluids.
Furthermore, the two fittings for the first fluid can
both be on the same exterior sheet, or one on each
exterior sheet; the same holds for the two fittings for
the second fluid. Connections of pipes , hoses or tubing
3~ to the fittings are most easily made if the fittings are
distributed two on the first sheet and two on the last
sheet, e.g., as in Fig. 4.
The layout of the channels in elements 202
and elements 203 are substantially identical. With
channels so arranged, the heat exchanger is adapted for
countercurrent flow of the first and second fluids in
the first and second passages. In this arrangement,
the channels first fed with the first fluid are adjacent
~' .
-` ~126256
~ 2
the final channels for the second fluid, and the final
channels for the first fluid are adjacent the channels
first fed with the sec~nd fluid~ As above, the number
of channels and channel septa is optional, and each
element can have as few as one channel, or as many as
desired.
The protuberances 268 and 269 can be circular
in cross-section or other shapes as described above.
In heat exchangers of the type exemplified in
Fig. 4, protuberances are needed only in alternate
passages. Thus, either protuberances 268 or protuberances
269 can be omitted in heat exchanger 201. Nevertheless,
it is preferred that there be protuberances in all first
passages and all second passages, as this will most
effectively prevent collapse of the sheets into any
passage. When there are protuberances only in alternate
passages, it ls preferred that they extend to and are
joined to the adjacent sheet, as this also serves to
prevent collapse into the passages without protuberances.
It is most preferred that there be protuberances in all
passages, and that they extend to and are joined to the
adjacent sheet.
In a device like that of Fig. 4 wherein the
elements are of different thickness, protuberances 268
and 269 need not be of the same cross-sectional area.
Protuberances 269, for example, could be of larger
cross-sectional area than that of protuberances 268.
The elements and passages of such a device
need not be of different thicknesses. A similar heat
exchanger could be built up from elements 231 and 241,
parts of which are shown in Figs. 7 and 8. Thus, element
231 having sheet 232, edge septa 233, channel septa 234
and protuberances 270 is substantially identical dimen-
sionally to element 241 having sheet 242, edge septa 243,
channel septa 244 and protuberances 271; they have four
identical superimposable openings, and differ only in
the location of identical rings 235 and 236 in element
22
',..
6Z56
23
231 and rings 245 and 246 in element 241. Heatexchangers
of this kind having first and second passages of equal or
similar thickness are best adapted for liquid-liquid
and gas-gas heat exchanges, where the volumes flow rates
and heat capacities of the two fluids are the same or
similar. In the absence of such similarity between the
two fluids, such as a gas-liquid heat exchange, one set
of elements and passages will generally be thicker than
the other set; in such cases, the thin element will
usually have rings of larger diameter and the thick
element will have rings of smaller diame~er, so as to
accomodate the higher volume flow rate to the thicker
elements and passages.
In general, the heat exchanger of Fig. 1 is
preferred for gas-liquid heat exchange. Especially
when the gas is conducted at a high flow rate, for example,
a stream of air in a forced air residential heating
system, a heat exchanger having open linear passages for
the air such as passages 131, 132 etc., e.g., the embcdiment
of Fig. L is desirable.
The heat exchanger of Fig. 4 can be a preferred
embodiment for some heat exchanges, as the flows of the
first and second fluids in this embodiment are
countercurrent. Additionally, assembly of the Fig. 4
embodiment is simpler as far fewer individual components
are handled, inasmuch as there are no spacer bars, and
the rings are not separate but are an integral part of
the elements. As the rings are not separate elements
in this embodiment, the alignment of the rings so that
each series of rings is in register coaxially is easier.
In the present disclosure, the word "remote",
when used in describing the relative placement of openings
in the sheets and elements, is in reference to the flow
path of the fluid within the given element, and not to
- 35 the mere physical locaton of the opening. Thus, two
openings are remote when they are disposed such that one
opening is at the upstream end of the first channel to
23
- ` ~126256
24
carry the fluid in an element and the other opening is
at the downstream end of the last channel to carry the
fluid in that element.
In further embodiments of the invention, the
first fluid can be introduced to the space within a heat
exchanger element through an edge of the element, e.g.
through an edge septum, and also withdrawn from the
element in the same manner. Such can be accomplished
through two opposing ends or edges of an element, said
edges being either entirely open, i.e., having no septa
on those edges, or said edges being sealed along only a
portion thereof as for example by having only partial
septa, in which cases headers will be used to introduce
the fluid into the element or into a plurality of
elements. When such element or elements have a plurality
of channels in a serpentine path, the fluid in the element
can be transferred from one channel to the next with a
header which receives it from one channel through the
edge of the element and feeds it to the next channel
also through the edge of the element.
The heat exchanger of the invention is adapted
; for use in all type of fluid-fluid heat exchange. Both
the first fluid and the second fluid can be either gas
or liquid, i.e., the channels for the first fluid
within the elements can carry either gas or liquid, and
the passages for the second fluid between the elements
can carry either gas or liquid. In the case of a gas-
liquid exchange, the liquid will ordinarily be within
the elements and the gas in the passages between the
elements. Either the first fluid or the second fluid
; can be the fluid which accepts heat. The heat exchanger
is also adapted for use with condensing systems and
with evaporating systems. Typical gases include air
andwastegaseous combustion products. Typical liquids
include wàter, glycol-water mixtures such as those in a
solar heating system, and chemical baths such as dye
baths.
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