Thermoplastic heat exchanger

Abstract

 A thermoplastic heat exchanger which comprises individual elements made of two sheets of thermoplastic film sealed together at the edges of the sheets, either directly or with edge septa, there being protuberances extending from one of the sheets toward the second sheet and which may join to the second sheet. Optionally, the interior of the element may be divided into a plurality of channels by channel septa joined to both sheets. Two openings in the element provide access to the interior of the element for introduction and removal of a first fluid to and from the inside of the element. The device is adapted to exchange heat between the firstfluid conducted within the sheets and a second fluid in contact with the exterior faces of the sheets.

Description

Background of the Invention

[0001] 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

[0002] The invention relates to an improved thermoplastic heat exchanger. Briefly, the heat exchanger comprises individual heat exchange elements, made of two sheets of thermoplastic film and having protuberances which 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 openings can either be in the sheets of film, in which case the elements are sealed together at the edges of the sheets, or they can be in the edges of the elements, e.g., in the septa around the edges of the elements.

[0003] More specifically, one embodiment of the invention comprises a thermoplastic heat exchanger element comprising first and second thermoplastic sheets spaced apart from one another by a plurality of protuberances which 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 therethrough, said element being adapted to exchange heat between said first fluid and a second fluid in contact with the exterior faces of said sheets.

[0004] 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

[0005] 

Fig. 1 is a prospective view of a portion 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. ₁.

Fig. 4 is an elevation of 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.

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 shown in Figs. 5 and 6.

Detailed Description

[0006] Figures 1, 2 and 3 depict one illustrative embodiment of the heat exchanger of the invention.

[0007] 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 preventing 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.

[0008] 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.

[0009] 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 that blinding of the channel by gas bubbles or liquid 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.

[0010] 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, the edge 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 die onto a patterned drum with the technique shown in any of U.S. Patents No. 3,509,005; 3,515,778; or 3,635,631, and the edge and channel septa, 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 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 tops of all other channel septa,if such septa are present. A suitable technique for sealing sheet 152 to the tops of the edge and channel septa and is disclosed in U.S. 3,821,051.

[0011] While protuberances 168 can be shorter than the height of the 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 protuberances 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 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.

[0012] 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 cf 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.

[0013] 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.

[0014] 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. Shown are five individual heat exchange elements 101, 102, 103, 104 and 105. In this view sheets 151 and 152 and edge septa 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 which 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 spaced 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 side of the stater here, carry the seccod fluid which is to exchange heat with the first sluid. The ipaoer bars are disposed in a direction substantially perpendicuiar to the direction in which the first fluid flows in the 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 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.

[0015] 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 ^_nside of all the heat exchange elements 101, 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 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 flurd.

[0016] It should be understood that a heat exananger may comprise as few as one heat exchange element to as many such elements as may be desired for a partioular use, which may number in the hundreds.

[0017] Rings 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 suitable thermoplastic resin such as polyethylene and a magnetic material such 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 formed, and then the assembly is placed in a high frequency magnetic field of an electric induction generator, whereby said composition 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. Information concerning the technique can be found in the Modern Plastics Encyclopedia, 1977-78 Edition, McGraw-Hill, N.Y., October 1977, pages 420-21, "Electromagnetic Bonding", and pages 424-25, "Magnetic Heat-Sealing". More information concerning the technique 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.

[0018] One method, which is a preferred method, of
forming the distribution and collection systems for the first fluid to and from the inside of the heat exchange elements is to seal the rings 106, 107 etc. and 111, 112 etc. 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 in the remaining sheets are to be formed. Fittings 121 and 122 are also sealed to sheet 151 at series where the openings in sheet 151 are to be formed. The openings are then cut by inserting a tubular cutter through the assembly inside of each series of coaxial vings. 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.

[0019] 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 openings 169 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 150, 151, 152 and like sheets are of flexible thermoplastic film, and thus elements 101, 102 ets. are not completely rigid. When the heat exchange elements are joined in this way without rings 106 etc and 111 etc., it may be convenient to assemble the heat exchanger and make the seals around the first and second openings before th pacer bars 116, 117 etc. have been put in place; after the seals around the first and second openings have been made, the heat exchange elements are carefully spread apart sufficiently to permit insertion of the spacerbars which are then sealed in place.

[0020] The spacer bars 116, 117 etc. are per se an optional feature, as other means can serve to maintain the heat exchange elements in spaced-apart relationship. For example, individual heat exchange elements could be thermoformed to have protrusions, and generally a plurality of protrusions, which project toward an adjacent element. In one such arrangement the heat exchange elements from the second element to the penultimate element could be so thermoformed; the first and last elements could also be so thermoformed but such is not required. In another such arrangement, alternate elements (i.e., every second element) could be thermoformed with protrusions extending from both sheets; for example, even-numbered elements could be so thermoformed and odd-numbered elements need not be so thermoformed. It is necessary only that there be protrusions on sufficient sheets to maintain the elements spaced apart.

[0021] 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, etc., as desired.

[0022] 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.

[0023] If desired, some protuberances can also be connected by partial septa, which could be useful for 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 the heat exchange element.

[0024] 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.

[0025] 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.

[0026] 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-sectional shape will be of similar size. Protuberances other than circular in cross section will ordinarily have the largest cross-sectional dimension lying generally in the direction of fluid flow, and can have a long dimension of an inch or more. The spacing of protuberances 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. For most purposes, circular protuberances 20 mils to 0.1 inch in diameter, on centers spaced 0.1 to 0.3 inch, are preferred.

[0027] The edge septa have a thickness equal to the spacing between the sheets as described above, and a width varying from about 0.05 inch to about 0.2 inch. Edge septa 0.1 inch wide are suitable for most purposes.

[0028] 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 abut one edge septum, and will ordinarily terminate a distance from the opposite edge septum about equal to the width of the channels.

[0029] The spacer bars are suitably square or rectangular 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.

[0030] Rings 106 etc. and 111 etc. usually have a thickness equal to the thickness of the spacer bars, and thus range in 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. Typical outside dimeter range from 0.35 inch to 2 inches, and typical wall thicknesses from about 0.05 to 0.15 inch.

[0031] 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 inch to 2 inches long.

[0032] The invention is applicable to all olastic 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.

[0033] 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.

[0034] 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 many feet; 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 may have only a few heat exchange elements or as many as hundreds of elements.

[0035] An example of a heat exchanger of the invention is a heat exchanger made of high density polyethylene, suitable for a gas-liquid heat exchange wherein heat from water at 120 to 185°F 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 is 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, having been formed upon extrusion of one sheet and subsequently heat-sealed to 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.

[0036] 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 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 at the end of the last flow channel. Two fittings 121 and 122, each fitting being 1.5 inches long and having an outside diameter cf 0.75 inch and an inside diameter of 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 heated composition comprising polyethylene and magnetic iron oxide. The first openings typified by opening 169 and second openings typified by opening 170 are then cut by inserting a tubular cutter 0.3 inch indrareter through the whole assembly, once within the ficst 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 above. 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 elements. Thus passages between adjacent elements are fromed for the second fluid, which is air, to flow in said passages in a direction parallel to the spacer bars. As noted above the planar 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.

[0037] 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 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 elements, (3) the side adjacent the first sheet of the first element, i.e., sheet 151, and (4) the side adjacent the second sheet of the last element, the second sheet being the sheet facing away from the penultimate element.

[0038] 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.

[0039] The hean 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.

[0040] 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 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 third 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.

[0041] In this embodiment, each of the first and second 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 described above, but in this case the rings are fabricated as an integral part of the component elements of the heat when the flat sheets with edge septa are fabricated.

[0042] 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 Fig. 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 greater than that of elements 202. The arrows associated with the numerals 5,5 and 6,6 in Fig. 4 refer to the direction of the sectional views of Figs. 5 and 6.

[0043] 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 is 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 268, of which only three groups are shown, which projact from sheet 221. Protuberances 268 can be shorter than the septa end rings, but preferably 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.

[0044] 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. The flow pattern of the second fluid in the channels is shown by arrows.

[0045] 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 30l 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 disposed that all openings 301 and 311 are superimposed in line in heat exchanger 201; similarly, openings 302 and 312 are in line, openings 303 and 313 are in line, and openings 304 and 314 are in line. As explained above 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.

[0046] 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 cutters through the assembly, coaxially within each series of rings.

[0047] 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 exterior 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 disks or plastic cup-shaped members. In the embodiment shown, sheet 223 needs only two holes, one in line with 302 and 312, the other in line with 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.

[0048] 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.

[0049] 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 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.

[0050] 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 the final channels for the second fluid, and the final channels for the first fluid are adjacent the channels first fed with the second 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.

[0051] The protuberances 268 and 269 can be circular in cross-section or other shapes as described above.

[0052] 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 is 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.

[0053] 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.

[0054] 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 dimensionally 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 23i and rings 245 and 246 in element 241. Heat exchangers 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 diameter, so as to accomodate the higher volume flow rate to the thicker elements and passages.

[0055] In general, the heat exchanger of Fig. 1 is t 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 embodiment of Fig. 1, is desirable.

[0056] 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.

[0057] 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 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 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.

[0058] 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.

[0059] 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. Euither the first fluid or the second fluid can be the fluid which accepts heat. The heat exchanger is also adapted for use wich condensing systems and with evaporating systems. Typical gases include air and waste gaseous combustion products. Typical liquids include water, glycol-water mixtures such as those in a solar heating system, and chemical baths such as dve

Claims

1. A thermoplastic heat exchanger element comprising first and second thermoplastic sheets spaced apart from one another by a plurality of protuberances which project from one of said sheets and which extend toward the other of said sheets, a seal between said sheets along at least portions of the edges thereof, said element having at least one first opening therein to permit introduction of a first fluid therethrough and at least one second opening therein remote from said first opening to permit removal of said first fluid therethrough, said element being adapted to exchange heat between said first fluid and a second fluid in contact with the exterior faces of said sheets.

2. A thermoplastic heat exchanger element comprising first and second thermoplastic sheets spaced apart from one another by a plurality of protuberances which 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 therethrough, said element being adapted to exchange heat between said first fluid and a second fluid in contact with the exterior faces of said sheets.

3. The heat exchanger element of Claim 1 or Claim 2 wherein there are edge septa which form said seal near the edges of said sheets, two opposite faces of the edge septa being joined to proximate faces of said sheets.

4. The heat exchanger element of Claim 1 or Claim 2 wherein said sheets are sealed directly to one another.

5. The heat exchanger element of Claim 3 wherein the space defined by said sheets and said edge septa is divided into a plurality of channels by at least one channel septum, two opposite faces of each such channel septum being joined to proximate faces of said sheets

6. The heat exchanger element of any one of Claims 1 to 5 wherein said protuberances extend to and are joined to said second sheet.

7. A thermoplastic heat exchanger comprising a plurality of said elements of any one of Claims 1 to 6, said elements being spaced apart to permit passage of said second fluid between adjacent exterior faces of said elements.

8. The heat exchanger of Claim wherein

there is a first series of coaxial rings, and, remote from said first series, a second series of coaxial rings, each said series containing one less ring than the number of said elements;

each said sheet of each said element except the first sheet of the first element and the second sheet of the last element containing both first and second openings, the first sheet of said last element and the second sheet of said first element facing toward adjacent elements, all of said first openings being in line and all of said second openings being in line, said first sheet of said first element and said second sheet of said last element taken together having a total of one first opening and one second opening;

each ring of said first series lying between and being joined to two adjacent elements and disposed to surrounc the first opening in the second sheet of one element and the first opening in the first sheet of the next element;

each ring of said second series lying between and being joined to two adjacent elements and disposed to surround the second opening in the second sheet of one element and the first opening in the first sheet of the next element;

and two hollow cylindrical fittings joined to either the first sheet of the first element or the secondsheet of the last element, a first such fitting surrounding said first opening and a second such fitting surrounding said second opening in those sheets.

9. The heat exchanger of Claim 7 wherein each said sheet of each said element except the first sheet of the first element and the second sheet of the last element contains both first and second openings, the first sheet of said last element and the second sheet of said first element facing toward adjacent elements, all of said first openings being in line and all of said second openings being in line, said first sheet of said first element and said second sheet of said last element taken together having a total of one first opening and one second opening;
an area surrounding the first hole in the second sheet of each element except the last element being sealed directly to an area surrounding the first hole in the first sheet of the next element,
an area surrounding the second hole in the second sheet of each element except the last element being sealed directly to an area surrounding the second hole in the first sheet of the next element,
and two hollow cylindrical fittings joined to either the first sheet of the first element or the second sheet of the last element, a first such fitting surrounding said first opening and a second such fitting surrounding said second opening in those sheets.

10 . The heat exchanger of Claim 8 or Claim 9 wherein each adjacent pair of said elements is spaced apart by at least one spacer bar, each such spacer bar being disposed in a direction substantially perpendicular to the direction in which said first fluid flows in said channels.

11. The heat exchanger of any one of Claims 7. to 10 wherein at least each second element is thermoformed to have a plurality of protrusions which project toward an adjacent element.

12. The heat exchanger of Claim 10 wherein adjacent first edges of said elements, said first edges being parallel to said spacer bars, are joined together by thermoplastic film sealed to said first edges, and wherein adjacent second edges of said elements, said second edges being parallel to said spacer bars, are joined together by thermoplastic film sealed to said second edges.

13. 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 cefining that passage and extending toward the second sheet defining that passage:

each sheet except 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 third 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.

14. The heat exchanger of Claim 13 wherein said protuberances extend to and are joined to said second sheet defining that passage.

15. The heat exchanger of Claim 13 or Claim 14 wherein said protuberances are in all of said first and second passages.

16. The heat exchanger of any one of Claims 13 to 15 wherein there is a plurality of said first passages and a plurality of said second passages.

17. The heat exchanger of Claim 16 wherein each passage is divided into a plurality of channels by one or more channel septa, the number and layout of said channels in said first passages and in said second passages being identical, said first and second openings being disposed at the upstream end of the first channel, and said third and fourth openings being disposed at the downstream end of the last channel.

Drawing