US3627040A - Simplified heat exchanger for paper mills and the like - Google Patents

Abstract

A high-capacity, simplified heat exchanger for a paper mill or the like in which alternate pairs of adjacent plates of a multiplicity of flat, generally rectangular metal plates have lines of interlocking open spacers along a first pair of opposite edges and lines of interlocking closed spacers along a second pair of opposite edges while the other pairs of adjacent plates have lines of interlocking closed spacers along their first opposite edges and lines of interlocking open spacers along their second opposite edges so that each pair of adjacent plates have interlocking spacers extending continuously around their peripheries with the plates and spacers assembled by means of elongated bolts extending through the plates and the interlocking portions of the spacers thus to provide respective paths for the flow of fluid at right angles to each other through the spaces between the plates of adjacent pairs. Additional open and closed spacers may be bolted in position between adjacent plates within the peripheries thereof for rigidity, to reduce vibration of the structure, and to generate turbulence in the fluid to enhance the heat exchange provided by the structure.

Description

United States Patent [72] Inventor Joseph A.V1l1alobos Rlmsey,N.J. [21] AppLNo. 879,489 [22] Filed Nov.24, 1969 [45] Patented Dec.14,197l [73] Assignee Aer Corporation RamIey.N-J.

[54] SIMPLIFIED HEAT EXCHANGER FOR PAPER MILLS AND THE LIKE 14 Claims, 12 Drawing Figs.

[52] U.S.Cl 165/166, 165/180 [51] lnt.Cl F28l3/00 [50] FieldofSeal'ch 165/165, 166,180

[5 6] References Cited UNITED STATES PATENTS 2,634,958 4/1953 Simpelaar l65/l66 x 2,997,280 8/1961 Keast 165/166 3,289,757 12/1966 Rutledge 165/166 3,435,893 4/1969 Withers l65/l65x 3,517,733 6/1970 Taskeretal.

Primary Examiner- Frederick L. Matteson Assistant ExaminerTheophil W. Streule Attorney-Shenier and OConnor ABSTRACT: A high-capacity, simplified heat exchanger for a paper mill or the like in which alternate pairs of adjacent plates of a multiplicity of flat, generally rectangular metal plates have lines of interlocking open spacers along a first pair of opposite edges and lines of interlocking closed spacers along a second pair of opposite edges while the other pairs of adjacent plates have lines of interlocking closed spacers along their first opposite edges and lines of interlocking open spacers along their second opposite edges so that each pair of adjacent plates have interlocking spacers extending continu ously around their peripheries with the plates and spacers assembled by means of elongated bollts extending through the plates and the interlocking portions of the spacers thus to provide respective paths for the flow of fluid at right angles to each other through the spaces between the plates of adjacent pairs. Additional open and closed spacers may be bolted in position between adjacent plates within the peripheries thereof for rigidity, to reduce vibration of the structure, and to generate turbulence in the fluid to enhance the heat exchange provided by the structure.

Patented Dec. 14, 1971 3,627,040

5 Shook-Shoot 1 $4M KM RTTORNEYS BACKGROUND OF THE INVENTION There are installations such as those in paper mills wherein tremendous quantities of air are employed and wherein there are many opportunities for the recovery of heat generated in the process. In the prior art in the manufacture of paper there is known an air-to-air heat exchanger which is fabricated from corrugated sheet steel plates which are welded together at points of contact of the corrugations of adjacent plates to form the exchanger. In order that the corrugated plates be able to withstand the welding operation the sheet metal used must be of at least 22 gauge. This material is expensive and it results in a structure which is relatively heavy for the purpose intended. Not only is the cost of the material of this heat exchanger extremely high, but a large amount of very expensive labor is required to fabricate the exchanger. This will readily be ap preciated from a consideration of the extensive welding required in manufacture.

I have invented a simplified heat exchanger which is especially adapted for air-to-air heat exchange in a papermill or the like. My heat exchanger overcomes the disadvantages of the heat exchanger of the prior art discussed hereinabove. My exchanger does not require heavy gauge material. My exchanger can readily be assembled by relatively unskilled labor. It is inexpensive to manufacture. My simplified heat exchanger performs in a manner which is at least as satisfactory as that of the heavy and expensive heat exchanger of the prior art.

SUMMARY OF THE INVENTION One object of my invention is to provide a simplified heat exchanger especially adapted for high volume air-to-air heat exchange in a papermill or the like.

Another object of my invention is to provide a simplified heat exchanger for a papermill which overcomes the defects of the heat exchanger heretofore employed.

A further object of my invention is to provide a heat exchanger for a papermill or the like which does not require the use of heavy sheet material.

Yet another object of my invention is to provide a simplified heat exchanger which incorporates relatively few parts.

A still further object of my invention is to provide a simplificd heat exchanger which can be assembled by relatively unskilled labor;

Still another object of my invention is to provide a simplified heat exchanger which is less expensive to manufacture than are heat exchangers of the prior art.

A still further object of my invention is to provide a simplified and inexpensive heat exchanger which functions in a manner at least as well as do expensive heat exchangers of the prior art.

Other and further objects of my invention will appear from the following description.

In general my invention contemplates the provision of simplified heat exchanger in which I assemble a multiplicity of flat, generally rectangular metal plates with interlocking open spacers along a first pair of opposite edges and interlocking closed spacers along second opposite edges of alternate pairs of adjacent plates together with interlocking closed spacers along first opposite edges and interlocking open spacers along second opposite edges of the other pairs of adjacent plates by means of rods extending through the plates and through the interlocking portions of the spacers. Additional spacers may be arranged within the peripheries and between adjacent plates for rigidity and to generate turbulence in the fluid streams passing through the exchanger.

BRIEF DESCRIPTION OF THE DRAWINGS In the accompanying drawings which form part of the instant specification and which are to be read in conjunction therewith and in which like reference numerals are used to indicate like parts in the various views:

FIG. I is a front elevation of one form of my simplified heat exchanger.

FIG. 2 is a side elevation of the form of my simplified heat exchanger illustrated in FIG. I, taken along the line 2-2 of FIG. 1.

FIG. 3 is a sectional view of my simplified heat exchanger 7 taken along the line 3-3 of FIG. 2 and drawn on an enlarged scale.

FIG. 4 is a sectional view of my simplified heat exchanger taken along the line 4-4 of FIG. 2 and drawn on an enlarged scale.

FIG. 5 is a top plan view of one of the open spacers employed in my simplified heat exchanger.

FIG. 6 is a sectional view of the spacer illustrated in FIG. 5 taken along the line 6-6 ofFIG. 5.

FIG. 7 is a sectional view of the spacer shown in FIG. 5 taken along the line 7-7 of FIG. 5.

FIG. 8 is a sectional view of one of the closed spacers which l employ in my simplified heat exchanger.

FIG. 9 is a sectional view of the spacer shown in FIG. 8 taken along the line 9-9 of FIG. 8. I

FIG. I0 is an end elevation of the spacer shown in FIG. 8 taken along the line 10-40 of FIG. 8.

FIG. 11 is a fragmentary perspective view of my simplified heat exchanger.

FIG. 12 is a fragmentary view of my simplified heat exchanger with a part broken away illustrating the manner in which the spacers of my heat exchanger are interconnected.

DESCRIPTION OF THE PREFERRED EMBODIMENT Referring now to the drawings my simplified heat exchanger indicated generally by the reference character I0 includes a plurality of flat generally rectangular plates l2, l4, l6, I8, 20, 22, 24, 26 and 28. While I have shown nine plates in the particular embodiment illustrated in the drawings it will readily be appreciated from the description hereinafter that I may employ a greater or lesser number of plates to make up my exchanger. These plates may for example be formed of stainless steel. While the gauge of the plates is in no way critical, owing to my construction I may employ plates which are much thinner than the 22 gauge plates required in the welded structure of the prior art. Not only does the thinner plate reduce the cost of my exchanger, but heat exchange between fluids on opposite sides of the plate is enhanced. In addition, since my construction does not require a welding operation I may use coated materials such for example as galvanized, aluminized and galvaneal sheet metal the properties of which, such as cor rosion resistance, are not deleteriously affected by my assembly operation as they would be by a welding process.

For purposes of clarity in exposition, I will consider the plates of my heat exchanger as being; made up of alternate pairs of adjacent plates I2 and 14, I6 and 18, 20 and 22 and 24 and 26 and other pairs of adjacent plates 14 and I6, 18 and 20, 22 and 24 and 26 and 28. As will be apparent from the description hereinbelow the alternate pairs of adjacent plates provide fluid paths extending in one direction through my exchanger while the other pairs provide fluid paths extending through the heat exchanger in a direction transverse to that of the first paths.

Referring now to FIGS. 5 to 7 one of the elements of my simplified heat exchanger is an open spacer indicated generally by the reference character 30 comprising spaced sidewalls 32 and 34 connected at points along their length by spaced struts including a left-hand strut 36, intermediate struts 38 and a right-hand strut 40 as viewed in the drawings. We form the spacer 30 with a connecting lug,42 extending outwardly from the left hand strut 36. We provide the right-hand of spacer 30 with a pair of extensions 44l and 46 of the sides 32 and 34 extending outwardly from the right-hand strut 40. I so dimension the lug 42 and the extensions 44 and 46 that the extensions fonn a socket for receiving the lug 42 along a line or at a corner. Specifically the length of the lug 42 is equal to the depth of the socket formed by extensions 44 and 46. The lug length moreover, is equal to the width of the sides 32 and 34 less the thickness of a side. 1 provide the lug 42 with a bore 48 adapted to register with aligned holes 50 in the extensions 44 and 46 when the lug 42 is inserted in the socket either from the end of an adjacent spacer 30 or from the side of the spacer. I streamline all of the leading edges 52 of the struts 36, 38 and 40 while providing the trailing edges 54 with sharp corners so as to provide a sharp discontinuity in airflow to create turbulence thus to improve the heat transfer characteristics of the exchanger. Similarly the leading edges 55 of the sides 32 and 34 are streamlined.

Referring now to FIGS. 8 to my heat exchanger includes a plurality of closed spacers indicated generally by the reference character 56 comprising sides 58 and 60 and an end wall 62. l form the closed spacers 56 with a plurality of struts including a left-hand strut 64, spaced intermediate struts 66 and a right-hand strut 68 extending between sides 58 and 60. Owing to the presence of the end wall 62 it is not necessary to provide as many intermediate struts 66 in the closed spacers 56 as are present in the open spacers 30. 1 form the left end of the closed spacer 56 with a lug 70 extending outwardly beyond the end strut 64. l form respective extensions 72 on sides 58 and 60 and an extension 74 on wall 62 to provide a socket for the reception of a lug 70 of an adjacent closed spacer 56 or a lug 42 of an adjacent open spacer 30. The dimensions of the lugs 70 are similar to those of the lugs 42 so that a lug 70 fits closely within the socket formed by extensions 44 and 46 and strut 40 or within the socket formed by extensions 72 and 74 and strut 68 whether the lug be inserted in the socket from the end of an adjacent spacer or from the side of an adjacent spacer. Particularly, the length of a lug 70 is equal to the length of the extensions 44, 46 and 72 and its thickness is equal to the spacing between walls 32 and 34 and the spacing between sides 58 and 60. The length of the lug 70 moreover, is equal to the width ofa side 58 from its lower edge to the inner surface of wall 62. I provide each lug 70 with a bore76 which registers with aligned bores 78 in extensions 72 or with the aligned bores 50 in extensions 44 and 46 when the lug 70 is inserted in a socket.

1 form the open spacers 30 and the closed spacers 56 from any suitable material which is tough and which has good high temperature resistant properties. I have discovered that the parts molded from nylon reinforced with asbestos fibers are eminently suited for my use. The part may also be made of other materials such for example as polycarbonate, polypropoline or urethane resins any of which can be reinforced with asbestos, glass or metal fibers. Alternatively, the spacers might be molded from metals such as zinc or aluminum or any soft alloy. The parts might also be cast from a wide range of metals.

Referring now to FIGS. 2, 3, 11 and 12 and considering by way of example one of the other pairs of adjacent plates 14 and 16 along the upper edges of these plates l dispose a line, indicated generally by the reference character 80, of closed spacers 56 extending from the upper left-hand corner to the upper right-hand comer of the plate with the lugs 70 of one of a pair of adjacent spacers 56 inserted in the socket formed by the extensions 72 and 74 of the other spacer of the pair. I locate a similar line, indicated generally by the reference character 82, of spacers 56 extending along the lower edges of the two plates 14 and 16 from the lower left-hand corner to the lower right-hand comer as viewed in FIG. 3.

Along the respective leftand right-hand edges between the plates 14 and 16 I arrange lines, indicated generally respectively by the reference characters 84 and 86, of open spacers 30 with the lug 42 of one of a pair of adjacent spacers 30 in the socket formed by the extensions 44 and 46 of the other spacer of the pair. At the upper left-hand comers and at the lower right-hand corners of the pair of plates 14 and 16 a lug 70 of a closed spacer 56 is disposed in the socket of an open spacer 30. At the lower left corners and at the upper right corners of the plates 14 and 16 a lug 42 of an open spacer 30 is disposed in the socket formed by the extensions 72 and 74 of a closed spacer.

It will be appreciated that between the plates 14 and 16 interengaging spacers extend continuously around the peripheries of the plates in the space therebetween. Moreover at each of the interlocking points the lug holes are aligned with the socket holes. The plates 14 and 16 are previously provided with holes in such a pattern that the plate holes are aligned with the holes in the spacers at the interlocking points. The lines 84 and 86 of open spacers 30 at the left and right hand edges as viewed in FIG. 3 and the lines and 82 of closed spacers 56 at the upper and lower edges provide a path for the flow of air from left to right as viewed in FIGS through the space between plates 14 and 16. I arrange peripheral spacers between the remaining other pairs of adjacent plates 18 and 20, 22 and 24 and-26 and 28 in the manner described in connection plates 14 and 16. 1

Preferably I provide additional groups of spacers between the other pairs of adjacent plates such as 14 and 16 for the purposes of increasing the rigidity of the structure, reducing vibration and to increase turbulence for better heat transfer. By way of example I may provide respective pairs of vertically extending lines indicated generally by the reference characters 88 and 90, and 92 and 94, of open spacers 30. In the particular arrangement shown single closed spacers 56 connect the ends of lines 88 and 90 and connect the ends of lines 92 and 94. All of these inner spacers are interconnected in the same manner as are the peripheral spacers and the plates 14 and 16 are preformed with holes at the interlocking points of the spacers. Moreover, all of the open spacers are arranged with the leading edges 52 of their struts upstream of the flow of air indicated by the arrows in FIG. 3.

Referring to FlGS. 2, 4, l1 and 12 and considering by way of example an alternate pair 20 and 22 of adjacent plates, 1 dispose respective lines, indicated generally by the reference characters 96 and 98, of open spacers extending along the edges of the plate from corner to comer thereof. Similarly, I arrange respective lines, indicated generally by the reference characters 100 and 102, of closed spacers along the leftand right-hand edges of the plates as viewed in FIG. 4 from top to bottom thereof. The spacers of these lines are interconnected around the entire periphery in a manner similar to those associated with the pair of adjacent plates 14 and 16. Between the plates of these alternate pairs of adjacent plates I may also arrange fourvertically extending lines indicated generally by the respective reference characters 104, 106, 108 and of closed spacers 56. Single spacers 30 connect the ends of the two pairs of lines 104 and 106 and 108 and 110. The arrangement is such that the registering lug and socket holes of the spacers between these alternate pairs of adjacent plates are aligned with holes previously formed in the plates and with the holes of all other pairs of plates.

It will be appreciated that the alternate pairs of adjacent plates 12 and 14, 16 and 18, 20 and 22 and 24 and 26 and the lines of spacers applied thereto in the manner described in connection with the pair of plates 20 and 22 provide a plurality of fluid paths extending generally transversely of the paths provided by the other pairs of adjacent plates and with each alternate pairs path except one being disposed between a pair of other adjacent plate pair paths.

In order to join all of the plates and spacers to complete the assembly I insert a plurality of elongated bolts or rods 112 through the registering sets of holes in the plates, lugs and sockets until their heads 114 engage one of the outer plates such for example as the plate 12. Nuts 116 are applied to the other ends of the rods or bolts 112 and are turned down until the assembly is secured. In the course of the assembly operation I may apply a high temperature sealing agent of any suitable type known to the art over the contact surfaces between the plates and the spacers to insure that the assembly is absolutely air and watertight.

The mode of assembly of my heat exchanger will be apparent from the description given hereinabove. In applying the spacers 30 care is taken to insure that the streamline leading edges 52 of the struts 38 and the edges 55 of the spacer sides 32 and 34 face the air stream and that the sharp trailing edges are downstream. This arrangement increases turbulence in the air stream thus to enhance the heat exchange between the two streams. By way of example l have illustrated a heat exchanger in which the alternate plate pairs provide generally vertically extending paths as viewed in HO. 1 through which cool dry air may be passed from top to bottom of the exchanger 10. The other pairs of adjacent plates provide horizontally directed paths through which hot moist air may, for example, pass.

it will be seen that l have accomplished the objects of my invention. l have provided a simplified heat exchanger which overcomes the defects of heat exchangers of the prior art. My heat exchanger requires no welding for its assembly so that relatively lighter gauge sheet material may be employed in making the exchanger. My exchanger can be assembled by relatively unskilled labor. It is appreciably less expensive to construct than are heat exchangers of the prior art. lts operation is at least equal to that of the relatively expensive heat exchangers of the prior art.

It will be understood that certain features and subcombinations are of utility and may be employed without reference to other features and subcombinations. This is contemplated by and is within the scope of my claims. it is further obvious that various changes may be made in details within the scope of my claims without departing from the spirit of my invention. it is, therefore, to be understood that my invention is not to be limited to the specific details shown and described.

Having thus described my invention, what i claim is:

l. In a heat exchanger an assembly including in combination, a pair of flat plates of thermally conductive material, respective first groups of closed spacers disposed between and extending over spaced first portions of the peripheries of said pair of adjacent plates, respective second groups of open spacers disposed between and extending over the remainder of the peripheries of said pair of adjacent plates to define a path for the flow of fluid through the space between the plates of said pair, each of said spacers having a length which is appreciably less than that of the peripheral portion of the plates with which it is associated, each of said closed spacers having a sidewall and having spaced respective top and bottom walls for engaging the surfaces of the upper and lower plates with which it is associated, each of said open spacers having spaced respective top and bottom walls for engaging the surfaces of the upper and lower plates with which it is associated, each of said spacers having a male connector at one end thereof and having a female connector at the other end thereof for receiving the male connector of an adjacent spacer, said groups of spacers forming a continuous extent between and around the periphery of said pair of adjacent plates, and means for holding said plates and said spacers in assembled relationship.

2. A heat exchanger including in combination, a plurality of flat plates of thermally conductive material, respective first groups of closed spacers disposed between and extending over spaced portions of the peripheries of a first pair of adjacent plates of said plurality to define a first path for the flow of fluid through the space between the plates of the first pair, respective second groups of closed spacers disposed between and extending over spaced portions of the peripheries of a second pair of adjacent plates of said plurality to define a second path generally transverse to said first path for the flow of fluid through the space between the plates of the second pair, each of said closed spacers having a length which is appreciably less than that of the peripheral portion of the plates with which it is associated, each of said closed spacers having a sidewall and having spaced respective top and bottom walls for engaging the surfaces of the upper and lower plates with which it is associated, each of said closed spacers having a male connector at one end and a female connector at the other end for receiving the male connector of an adjacent spacer, and means for holding said plates and said spacers in assembled relationship.

3. A heat exchanger as in claim 2 in which said pairs of plates comprise a common plate.

4. A heat exchanger as in claim 2 including groups of open spacers extending over the remainder of the peripheries of the plates of said first pair and second groups of open spacers extending over the remainder of the peripheries of the plates of the second pair, each of said open spacers having a length appreciably less than that of the peripheral portion with which it is associated, each of said open spacers having spaced respective top and bottom walls for engaging the surfaces of the upper and lower plates with which it is associated, each of said open spacers having a male connector at one end and having a female connector at the other end for receiving the male connector of an adjacent spacer, the groups of open and closed spacers associated with a pair of adjacent plates forming a continuous extent therearound.

5. A heat exchanger as in claim 2 in which each of said spacers is formed from synthetic resin reinforced with heat-re sistant fibers.

6. A heat exchanger as in claim 4 in which said assembling means comprise rods extending through said plates and through said interlocking elements.

7. A heat exchanger as in claim 6 in which said connectors comprise a lug on each of said spacers and means forming a socket on each spacer for receiving a lug of an adjacent spacer.

8. A heat exchanger including in combination, a plurality of generally rectangular flat plates comprising alternate pairs of adjacent plates and other pairs of adjacent plates, said plates having corresponding pairs of side edges and corresponding top and bottom edges, respective first lines of closed spacers between the plates of said alternate pairs, said first lines of closed spacers being disposed along pairs of side edges of said plates of said alternate pairs, respective first lines of open spacers between the plates of said alternate pairs, said first lines of open spacers being disposed along said top and bottom edges of said plates of said alternate pairs to form continuous extents of said spacers around the peripheries of the plates of said alternate pairs, respective second lines of closed spacers between the plates of said other pairs, said second lines of closed spacers being disposed along the top and bottom edges of said plates of said other pairs, respective second lines of open spacers between the plates of said other pairs, said second lines of open spacers being disposed along pairs of said side edges of said plates of said other pairs to form continuous extents of said spacers around the peripheries of said other pairs, the arrangement being such that said alternate pairs of plates and their associated spacers forming first fluid paths and said other pairs of plates and their associated spacers forming second fluid paths extending generally transversely of said first paths, each of said spacers having a length which is appreciably less than that of the edges with which it is associated, each of said closed spacers having a sidewall and having spaced respective top and bottom walls for engaging the surfaces of the upper and lower plates with which it is associated adjacent the edges thereof, each of said open spacers having spaced respective top and bottom walls for engaging the surfaces of the upper and lower plates with which it is associated adjacent the edges thereof, and means for holding said spacers and plates in assembled relationship.

9. A heat exchanger as in claim 8 in which said connectors comprise a lug formed at one end thereof and means forming a socket at the other end thereof, and in which each of said closed spacers comprises a lug formed at one end thereof and means forming a socket at the other end thereof, the lugs of each of said open and closed spacers adapted to fit the sockets of said open and closed spacers.

10. A heat exchanger as in claim 8 including other lines of spacers within the peripheries of adjacent pairs of plates.

Ill. A heat exchanger as in claim 8 in which each of said open spacers comprises spaced struts connecting the top and bottom walls thereof, the edge of each strut leading with respect to the path with which it is associated being streamlined.

ll2. A heat exchanger as in claim 8 in which said male connectors comprise generally rectangular lugs and in which said female connectors comprise extensions of said top and bottom walls forming sockets for receiving said lugs.

13. A heat exchanger as in claim 8 in which said connecting means comprise means forming aligned holes in said male and female connectors and rods extending through said holes.

14. A heat exchanger as in claim 8 in which said plates are metal and in which said spacers are molded synthetic resin.

i I i 4 i

Claims (14)

1. In a heat exchanger an assembly including in combination, a pair of flat plates of thermally conductive material, respective first groups of closed spacers dispOsed between and extending over spaced first portions of the peripheries of said pair of adjacent plates, respective second groups of open spacers disposed between and extending over the remainder of the peripheries of said pair of adjacent plates to define a path for the flow of fluid through the space between the plates of said pair, each of said spacers having a length which is appreciably less than that of the peripheral portion of the plates with which it is associated, each of said closed spacers having a sidewall and having spaced respective top and bottom walls for engaging the surfaces of the upper and lower plates with which it is associated, each of said open spacers having spaced respective top and bottom walls for engaging the surfaces of the upper and lower plates with which it is associated, each of said spacers having a male connector at one end thereof and having a female connector at the other end thereof for receiving the male connector of an adjacent spacer, said groups of spacers forming a continuous extent between and around the periphery of said pair of adjacent plates, and means for holding said plates and said spacers in assembled relationship.

2. A heat exchanger including in combination, a plurality of flat plates of thermally conductive material, respective first groups of closed spacers disposed between and extending over spaced portions of the peripheries of a first pair of adjacent plates of said plurality to define a first path for the flow of fluid through the space between the plates of the first pair, respective second groups of closed spacers disposed between and extending over spaced portions of the peripheries of a second pair of adjacent plates of said plurality to define a second path generally transverse to said first path for the flow of fluid through the space between the plates of the second pair, each of said closed spacers having a length which is appreciably less than that of the peripheral portion of the plates with which it is associated, each of said closed spacers having a sidewall and having spaced respective top and bottom walls for engaging the surfaces of the upper and lower plates with which it is associated, each of said closed spacers having a male connector at one end and a female connector at the other end for receiving the male connector of an adjacent spacer, and means for holding said plates and said spacers in assembled relationship.

3. A heat exchanger as in claim 2 in which said pairs of plates comprise a common plate.

4. A heat exchanger as in claim 2 including groups of open spacers extending over the remainder of the peripheries of the plates of said first pair and second groups of open spacers extending over the remainder of the peripheries of the plates of the second pair, each of said open spacers having a length appreciably less than that of the peripheral portion with which it is associated, each of said open spacers having spaced respective top and bottom walls for engaging the surfaces of the upper and lower plates with which it is associated, each of said open spacers having a male connector at one end and having a female connector at the other end for receiving the male connector of an adjacent spacer, the groups of open and closed spacers associated with a pair of adjacent plates forming a continuous extent therearound.

5. A heat exchanger as in claim 2 in which each of said spacers is formed from synthetic resin reinforced with heat-resistant fibers.

6. A heat exchanger as in claim 4 in which said assembling means comprise rods extending through said plates and through said interlocking elements.

7. A heat exchanger as in claim 6 in which said connectors comprise a lug on each of said spacers and means forming a socket on each spacer for receiving a lug of an adjacent spacer.

8. A heat exchanger including in combination, a plurality of generally rectangular flat plates comprising alternate pairs of adjacent plates and other pairs of adjacent plates, said plates having Corresponding pairs of side edges and corresponding top and bottom edges, respective first lines of closed spacers between the plates of said alternate pairs, said first lines of closed spacers being disposed along pairs of side edges of said plates of said alternate pairs, respective first lines of open spacers between the plates of said alternate pairs, said first lines of open spacers being disposed along said top and bottom edges of said plates of said alternate pairs to form continuous extents of said spacers around the peripheries of the plates of said alternate pairs, respective second lines of closed spacers between the plates of said other pairs, said second lines of closed spacers being disposed along the top and bottom edges of said plates of said other pairs, respective second lines of open spacers between the plates of said other pairs, said second lines of open spacers being disposed along pairs of said side edges of said plates of said other pairs to form continuous extents of said spacers around the peripheries of said other pairs, the arrangement being such that said alternate pairs of plates and their associated spacers forming first fluid paths and said other pairs of plates and their associated spacers forming second fluid paths extending generally transversely of said first paths, each of said spacers having a length which is appreciably less than that of the edges with which it is associated, each of said closed spacers having a sidewall and having spaced respective top and bottom walls for engaging the surfaces of the upper and lower plates with which it is associated adjacent the edges thereof, each of said open spacers having spaced respective top and bottom walls for engaging the surfaces of the upper and lower plates with which it is associated adjacent the edges thereof, and means for holding said spacers and plates in assembled relationship.

9. A heat exchanger as in claim 8 in which said connectors comprise a lug formed at one end thereof and means forming a socket at the other end thereof, and in which each of said closed spacers comprises a lug formed at one end thereof and means forming a socket at the other end thereof, the lugs of each of said open and closed spacers adapted to fit the sockets of said open and closed spacers.

10. A heat exchanger as in claim 8 including other lines of spacers within the peripheries of adjacent pairs of plates.

11. A heat exchanger as in claim 8 in which each of said open spacers comprises spaced struts connecting the top and bottom walls thereof, the edge of each strut leading with respect to the path with which it is associated being streamlined.

12. A heat exchanger as in claim 8 in which said male connectors comprise generally rectangular lugs and in which said female connectors comprise extensions of said top and bottom walls forming sockets for receiving said lugs.

13. A heat exchanger as in claim 8 in which said connecting means comprise means forming aligned holes in said male and female connectors and rods extending through said holes.

14. A heat exchanger as in claim 8 in which said plates are metal and in which said spacers are molded synthetic resin.

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