US2321110A - Heat exchanger - Google Patents

Description

I June 8, 19 3- B. c. SHIPMAN HEAT EXCHANGER 4' Sheets-Sheet 1 I INVENTOR.

A; ATTORNEY.

11m 8, 1943'. B, c. SHIPMAN mm EXCHANGER Filed Aug. 25, 193

4 Sheets-Sheet 2 INVENTOR. 3M M MW ATTORNE.

June 8, 1943. s. c. SHIPMAN HEAT EXCHANGER 7 Filed Aug. 25, 1936 4 Sheets-Sheet 3 'VIIIIIIIIAZII 1N VENTOR.

ATTORNEY.

June 8, 1943. B. C. 'SHIPMAN aEA'r Excmuzenn Filed Aug. 25. 1936 4 SheetsQ-Sheet 4 v IN ENTOR.

M. ATTORNEY.

Patented June 8, 1943 HEAT 'EXCHANGER Bennet Carroll Shipman', Evansville, Ind., 'assig niir to Servel, Inc., New York, N. Y., a corporation of Delaware Application August 25, 1936, Serial No. 97,146

17 Claims.

My invention relates to heat exchangers, and more particularly to heat exchangers of the type having a plurality of plates arranged to provide a number of closely adjacent passages for effecting heat transfer between fluids flowing through the passages. I

The objects of my invention are to provide an improved heat exchanger utilizing a plurality of closely adjacent plates to obtain a relatively large amount of heat transfer surface in a minimum amount of spacegto provide such a heat exchanger in which only a few different parts are required; to form the parts in such a manner that they can be quickly and easily assembled and at the same time insure an accurate spacing of the heat transfer plates; and to provide such a heat exchanger in which only a relatively small amount of welding or soldering is required to unite the parts.

The above and further objects and advantages of my invention will become apparent from the following description, taken in conjunction with the accompanying drawings forming a part of this specification, and of which Fig. 1 is a side sectional view of a heat exchanger embodying my invention taken on line of Fig. 2; Figs. 2 and 3 are sectional views taken on lines 22 and 3-3, respectively, of Fig. 1; Fig. 4 is an enlarged fragmentary sectional view illustrating more clearly parts of the heat exchanger shown in Fig. 2; Fig. 5.is an enlarged fragmentary perspective view of a part of the heat exchanger shown in Figs. 2 and 4; Fig. 6 is an enlarged sectional view illustrating more clearly one end of the heat exchanger shown in Fig. 1; Fig. 7 is a fragmentary sectional view taken on line '|-'l of Figs. 3 and 8; Fig. 8-is a fragmentary sectional view taken on line 8 8 of Figs. 6 and '7; Fig. 9 is a fragmentary end view, with parts thereof in difierent sections; of the heat exchanger shown in Fig. 1; Figs. 10 and 11 are fragmentary se'ctional views taken on lines ||l||l and I, respectively, of Figs. 6 and 9; Fig. 12 is an enlarged fragmentary side elevat on of parts of the heat exchanger shown in Figs. 1 and 6; Fig. 13 is a sectional view similar to Fig. 2 illustrating a modiflcation of the invention; Fig. 14 is a side sectional view similar to Fig. 1 illustrating a further modification of the invention; Fig. 15 is a sec tional view taken on line |5-|5 of Fig-l4; Fig. 16 is an enlarged fragmentary sectional view taken on line |6--|6 of Fig. 14; and Figs. 1'7 and 18 are fragmentary sectional views taken on lines I and l8-|8, respectively, of Fig. 16.

Referring to Figs. 1 to 3 inclusive, the heat exchanger embodying my invention comprises a casing l0 having inlet and outlet openings II and I2 fo'r fluid flowing through one group of passages l3, and inlet and outlet openings and I5 for. fluid flowing through another group of passages [6 in the casing. The casing I0 is rectangular in section and formed of side members l1 and a plurality of individual closure strips I8 having raised U-shaped bends |9 and 20 along their longitudinal edges.

The side members l1 and closure strips l8 support and maintain in properly spaced relation a plurality of" heat transfer plates 2| disposed alongside each otherand extending between the opposite side walls of the casing having the inlet .and outlet openings. The plates 2| and strips l8 are so constructed and arranged that they form a zigzag structure which extends acrossthe casing to provide the passages l3 and I6; The plates 2| are of the general shapeof the heat exchanger shown in Fig. 1 with parallel top and bottom edges intermediate the ends, and inwardly sloping edges at the ends adjacent the inlet and outlet openings of the casing. The top and bottom edges of the plates 2| throughout their length are offset laterally in opposite directions with the extreme edge portions substantially parallel to the main body portions of the plates. Thus, when several plates 2| are arrangedalongside each other in the manner shown in Figs. 2 and 4, one edge of each plate except an outside plate abuts an edge of an adjacent plate and is spaced from the'edge of an adjacent plate by a distance which is four times the amount of ofiset effected by the sloping parts 22 of the plates.

The closure strips l8 extend along the intermediate portion of the plates 2| and terminate at the inner edges of the openings H, l2, l4, and l5. The closure strips I8 are four times the width of offset effected by the sloping parts 22 of the plates 2|, and the U-shaped bends 20 are slightly larger than the U-shaped bends I9. The U-shaped bends IQ of the closure strips l8 receive and hold the abutting edges of two adjacent plates 2|, and each of the U-shaped bends 20 receives and hold the u-shaped bend IQ of an 7 ceives and holds an edge of an outside plate 2|.

The U-shaped bends 24 are ofiset inwardly with respect to the U-shaped bends 23 and receive and jections 29.

hold a bend of an outside closure strip which is the same size as the U-shaped bends l9 and in turn receives and holds the abutting edges of two adjacent plates 2| of which one is an outside plate.

The sloping abutting edges at the ends of the plates 2| are secured and held together by U- shaped strip members 25, as shown most clearly in Figs. 3 and 8. The abutting ends of closure strips l8 and strip members are cut oil at the proper angle and soldered or welded together, as indicated at 25' in Fig. 7.

In order to cover the triangular-shaped .openings of the passages I3 and I6 at the extreme ends of the plates 2|, the ends of the plates are provided with triangular-shaped projections 26, as shown in Fig. 12, the projections on alternate plates having the apex of the triangle pointed upward and the projections on the remaining plates having the apex of the triangle pointed downward. These triangular-shaped projections 26 are bent at 28 at the ends of the plates to cover similar shaped triangular openings formed at the ends of the passages l3 and I6, as shown in Figs. 9 and 11.

Adjacent the top and bottom sloping edges at the ends of the plates 2| are provided projections 29. With the top and bottom sloping edges of adjacent plates abutting each other, the projections 29 are arranged in pairs and in staggered relation. Gaskets 30 formed of suitable material, such as rubber, for example, fit over the bent triangular-shaped projections 26 and are provided with slots that coincide with the staggered pro- Cover plates 3| forming the end walls of casing Ill fit over the gaskets 38 with the projections 29 extending through slots in the cover plates. After the gaskets 30 and cover plates 3| are placed over the bent triangularshaped projections 26, the projections 29 are bent in opposite directions to secure the gaskets and cover plates in position to seal the extreme ends of the passages 3 and IS.

The cover plates 3| project beyond the sloping edges of the plates 2| and extend between the side members II to form the outer walls 32 of duct sockets at the inlet and outlet openings l2, l4, and IS. The ends of the side members project or extend above the sloping edges of the plates 2| to form two side walls 33 of the duct sockets. Plates or members 34 extend across the casing at the inner edges of the openings to form the inside walls of the duct sockets. The mem bers 34 are notched to straddle the raised U- shaped bends 20 of the closure strips l8 and are welded or soldered thereto, as indicated at 35 in Figs. '7 and 8. Tabs 36 which project or extend from the ends of the closure strips I 8 between the U-shaped bends l9 and 20 are bent upward and secured, as by -welding indicated at 3'! in Fig. 7, to the inner surfaces of the members 34.

It will now be understood that the passages l3 and I6 extend the entire length. of the heat exchanger between the inlet and outlet openings ll, l2, l4, and IS. The passages l3 are open at the inlet and outlet II and I2 and closed at the inlet and outlet I4 and I5, so that fluid will flow through the passages l3 in the manner indicated by the solid arrows in Fig. 1; and conversely, the passages -l6 between the passages l3 are open at the inlet and outlet l4 and I5 and closed at the inlet and outlet and I2, so that fluid will flow through the passages IS in the manner indicated by the dotted arrows in Fig. 1, the inlets I surfaces of the plates 2|.

and outlets being arbitrarily chosen for counterflow of fluids in the passages l3 and I6.

In order to maintain an accurate spacing between the heat transfer plates 2l, particularly when the plates are relatively wide or thin, the plates may be indented or provided with longitudinal grooves 38 and 39. The grooves 38 and 39 of adjacent plates are close to each other, as shown in Fig.2, so that the plates are rigidly spaced apart. To space one of the outside plates 2| from a side member ll of the casing, longitudinal rods 40 are secured to the inner surface of the side member.

In addition to rigidly spacing the plates 2| the grooves 33 and 39 may also be utilized to insure a more uniform distribution of fluids over the For this reason the grooves 38 extend along the entire length of the plates 2| and are curved at their ends toward the inlet and outlet openings, the spacing grooves in the passages I3 being curved upward at inlet and outlet openings and |2,and the spacing grooves in the passages l6 being curved downward at the inlet and outlet openings l4 and I5.

In the heat exchanger just described only a relatively few difierent parts are required. All of the heat transfer plates 2| may be exact duplicates formed in one or more stamping operations to provide the laterally ofi'set top and bottom edges, to form the grooves 38 and 39, and to provide the projections 29 and triangular-shaped projections 26. This is possible because in arranging the plates 2| alongside each other, alternate plates may be reversed longitudinally or turned 180 with respect to the remaining plates.

strip members 25, it is onlynecessary to apply pressure to the U-shaped bends l9 and 20 of the closure strips l8 and U-shaped bend of the strip members 25, as'by a suitable knurling device, for example, to obtain a, firm and intimate contactat the abutting edges of the plates which will effectively seal the heat exchanger against interof welding or soldering is required at 25' at the abutting ends of closure strips l8 and strip members 25, at 35 to secure the inner walls 34 of the duct sockets to the closure strips l8, and at 31 to secure the tabs 36 to the inner surfaces of the members 34.

In Fig. 13 I have shown a modification which is similar to the embodiment just described and differs therefrom in that, in place of forming grooves 38 and 39 in the heat transfer plates 2|, spaced angle members 4| are secured to the plates in a lengthwise direction to maintain the plates in rigid spaced relation as well as to insure a more uniform distributiton of fluids flowing over their surfaces. The angle members 4| may be secured in any suitable manner to the plates 2|, as by welding or brazing, for example, with all of the plates built up in the same manner whereby the versed longitudinally or turned 180 with respect to the remaining plates, as shown in Fig. 13, so

that the angle members on each plate will contact a portion of an adjacent plate strengthened by an angle member. To space one of theoutside heat transfer plates 2| from a side member H e of the casing, spaced angle members 42 are secured to the inner surface of the side member.

In order to develop more turbulence of the fluids flowing through the passages of the heat exchanger to increase the rate of heat transfer, the heat transfer plates may be waved or corrugated. Such a modification is shown in Figs. 14 and 15 in which the portions of the heat transfer plates between the grooves 38 and 39' and the grooves and the top and bottom edges of the plates are corrugated or waved. The corrugations extend approximately between the inlet and outlet openings of the ends of the casing and deflect and change the direction of flow of the fluids in the passages to increase the rate of heat transfer between the fluids.

Although the inlets and outlets for the two groups of passages l3 and I6 ar shown adjacent to the same side walls of the casing in the embodiment shown in Fig. 1, it may be desirable in certain instances to construct the heat exchanger in such a mannerthat the inlet and outlet for each group of passages are located at pposite side walls of the casing. In the modification shown in Fig. 14, for example, the inlet and outlet openings H and I2 for fluid flowing through one group of passages l3 and the inlet and outlet openings l4 and i5 for fluid flowing through the other group of passages l6 are located at the opposite side walls of the casing. To provide the inlet and outlet openings at opposite side walls of the casing it is only necessary to modify the construction at one end of the heat exchanger. The heat exchanger shown in Fig. 14 similar to that described above and shown in seen above the member 34; and wherein in Fig.

18 a view in elevation of a strip member 25 is seen below the cross member 34' and a sectional view of the U-shaped bends l9 and 20 of adjacent enclosure strips I8 is seen above the member 34'.

' The tabs 36' at the ends of the closure strips I8 Figs. 1 to 12 inclusive and differs therefrom only in the manner in which the sloping edges at the left hand portion of the plates 2| are secured together. Referring more particularly to Fig. 16, the top portion of the zig-zag structure formed by the plates 2| and enclosure strips l8 intermediate the inlet and outlet openings is indicated. in dotted lines. Instead of securing together the same edges of the plates 2| at the sloping end portions at the inlet II and outlet I5 to provide a structure similar to that shown in Fig. 1, the heat transfer plates 2| are slotted inwardly from the top and bottom edges at the ends of the enclosure strips IS. The plates 34' forming the inside walls of the duct sockets at the inlet II and the outlet I5 are of greater depth than the plates 34 at the outlet l2 and inlet I4 and extend into the slots formed in the plates 2|. The slop ng ends of the plates 2|, extending from the cross plates 34' to the extreme end of the casing, are offset at 43 in the opposite direction from the 01T- set portions 44 of the intermediate portions to 'which the enclosure strips l8 are secured.

It will now be apparent that between the inlets and outlets at the ends of the casing the plates 2| are ofiset in one direction and secured to an adjacent plate, whereas at the inlet II and outlet I5 the plates 2| are offset in the other direction and secured to an opposite adjacent plate by the U-shaped strip members 25. This is clearly shown in Figs. 17 and 18 wherein in Fig. 1'7 a sectional view of a strip member 25 is seen below the member 34' and a view in elevation of a U-shaped bend 20 of an enclosure strip I8 is may be secured to the outer surfaces of the members 34' and the latter secured to the plates 2| at the slotted portions thereof by welding or soldering to effectively seal the passages l3 and I6 at the inlet and outlet II and I5, respectively.

It will now be understood that the passages in- .dicated by the reference numerals l3 in Fig. 16,

casing, are in the present modification open atthe outlet l5 at the top wall of the casing and closed at the inlet II at the bottom wall of the casing.

In order to insure a'uniform distribution of fluids flowing over the surfaces of the plates 2|, the grooves 38 and 39' are So formed in the plates that the grooved portions of the plates extending into the passages l3 are curved downward at the inlet II' and curved upward at the outlet I2; and that the grooved portions of the plates extending into the passages l6 are curved downward at the inlet I4 and curved upward at the outlet 15. g 7

By providing the heat transfer plates 2| with side edges that are offset laterally in opposite directions the groups of openings of the passages I3 and H5 at the inlets and outlets grad ually taper in widthfrom twice the width of the spacing of the main body portions of the plates to the width of the spacing, as shown most clearly in Fig. 3, thereby providing an,

easy transition and smooth path of flow of fluids through the passages l3 and Hi from and to ducts connected to the duct sockets. Further, the particular construction of the heat exchanger provides inlets and outlets which are at such angles that, an abrupt change in direc tion of the flow of fluids is avoided. The inlets and outlets may be formed at-any desired angle and are preferably at such an angle that the static lossis reduced to a minimum.

Although I have shown and described several embodiments of my invention it-will be apparent to those skilled in the art that various changes and modifications may be made without departing from the spirit and scope of my invention.

What is claimed is:

1. A heat exchanger including a casing having end walls and openings adjacent both ends of two opposite side walls, and heat transfer plates disposed alongside each other within said casing and extending between the side walls having the openings, said plates being so constructed and arranged that they form a zigzag edge portion connected to an edge portion of an vadjacent plate and the other edge portion connected to the edge portion of an opposite adjacent plate, two of the openings adjacent opposite ends of the casing serving as an inlet and outlet for fluid flowing through alternate passages and the other two openings adjacent opposite ends of the casing serving as an inlet and outlet for fluid flowing through the other passages.

2. A heat exchanger including a casing having end walls and openings adjacent both ends of two opposite side walls, and a plurality of heat transfer plates disposed alongside each other within said casing and extending between the side walls having the openings, said plates having inwardly sloping edges at the openings, said plates being so constructed and arranged that they form a zigzag structure extending across the casing to provide a plurality of closely adjacent passages between said plates, said casing including closure members having U-shaped bends to receive the edges of said plates.intermediate the openings to close the passages, strips at the openings provided with U-shaped bends to receive said sloping edges so that said plates have one sloping edge secured to a sloping edge of an adjacent plate and the other sloping edge sccured to the sloping edge of an opposite adjacent plate, two of the openings adjacent opposite ends of the casing serving as an inlet and outlet for fluid flowing through alternate passages and the other two openings adjacent opposite ends of the casing serving as an inlet and outlet for fluid flowing through the other passages. V

3. A heat exchanger including a casing having end walls and openings adjacent both ends of two opposite side walls, and a plurality of heat transfer plates disposed alongside each other within said casing and extending between the side walls having the openings, each plate having the longitudinal edges thereof offset laterally in opposite directions with the extreme edge portions substantially parallel to the main body portions of said plates, said plates being so constructed and arranged that they form a zigzag structure extending across the casing to provide a plurality of closely adjacent passages between said plates, said casing including enclosure members having U-shaped bendsrto receive the edge portions of said plates to close the passages, said plates at the openings having one edge portion connected to an edge of an adjacent plate and the other edge portion connected to the edge por tion of an opposite adjacent plate, two of the openings adjacent opposite ends of the casing serving as an inlet and outlet for fluid flowing through alternate passages and the other two openings adjacent the opposite ends of the casing serving as an inlet and outlet for fluid flowing through the other passages.

4. A heat exchanger including a casing having end walls and openings adjacent both ends of two opposite side walls, and a plurality of form a zigzag structure extending across the casing to provide a plurality of closely adjacent passages between said plates, said casing including enclosure members having U-shaped bends to receive the edge portions of said plates to close the passages, strips at the openings Provided,

with U-shaped bends to receive said sloping edges so that said plates have one sloping edge secured to a sloping edge of an adjacent plate and the other sloping edge secured to the sloping edge of an opposite adjacent plate, two of the openings adjacent opposite ends of the casing serving as an inlet and outlet for fluid flowing through alternate passages and the other two openings adjacent the opposite ends-of the casing serving as an inlet and outlet for fluid flowing through the other passages.

5. A heat exchanger including a plurality of heat transfer plates arranged alongside each other with each plate having substantially parallel opposed edges intermediate the ends and inwardly sloping edges at the ends, said plates having one edge abutting an edge of an adjacent plate and the other edge abutting an edge of an opposite adjacent plate to form a zigzag structure having a plurality of closely adjacent passages, structure for closing said passages at the extreme end of said plates, a plurality of closure strips for closing the passages between the edges of adjacent plates along the intermediate portions having opposed parallel edges, the sloping abutting edges at the ends of said plates being secured to each other to provide a plurality of openings, two groups of the openings at opposite ends of said plates serving as an inlet and outlet for fluid flowing thro'ugh' alternate passages and the other two groups of openings at the opposite ends of said plates serving as an inlet and outlet for fluid flowin through the other passages. I

6. A heat exchanger including a plurality of heat transfer plates arranged alongside each other with each plate having substantially parallel opposed edges intermediate the ends and inwardly sloping edges at the ends, said plates having one edge abutting an edge of an adjacent plate and the other edge abutting an edge of an opposite adjacent plate to form a zigzag structure having a plurality of closely adjacent passages, structure for closing said passages at the extreme ends of said plates, a plurality of individual closure strips having U- shaped bends along their longitudinal edges for closing the passages between the edges of adjacent plates along the intermediate portions having opposed parallel edges, said strips having one bend adapted to receive and hold the abutting edges of two plates and the other bend adapted to receive and hold the adjacent abutting edges of two plates and a U-shaped bend of an adjacent closure strip, the sloping abutting edges at the ends of said plates being secured to each other to provide a plurality of openings, two groups of openings at opposite ends of said plates serving as an inlet and outlet for fluid flowing through alternate passages and -the other two groups of openings at opposite ends of said plates serving as an inlet and out let for fluid flowing through the other passages.

7. A heat exchanger including heat transfer plates arranged alongside each other to iorm a zigzag structure having a plurality of closely adjacent passages, said plates having one edge portion abutting an edge portion of an adjacent plate and the other edge abutting an edge portion of an opposite adjacent plate, structure for closing said passages at the extreme ends of said plat :s, a plurality ofclosure strips extending intermediate the ends or said plates for closing the passages between the edge portions of adjacent plates and maintaining the latter in spaced relation, the abutting edge portions of said plates extending between the ends of said closure strips and the extreme ends of said plates being connected to provide a plurality of openings, two groups of the openings at opposite ends of said plates serving as an inlet and outlet for fluid flowing through alternate passages and the other two groups of openings at opposite ends of said plates serving as an inlet and outlet for fluid flowing through the other passages.

8. A heat exchanger including heat transfer plates arranged alongside each other to form a zigzag structure having a plurality of closely adjacent passages, said plates having one edge portion abutting an edge portion of an adjacent plate and the other edge abutting an edge portion of an opposite adjacent plate, structure for closing said passages at the extreme ends of said plates, a plurality of individual closure strips extending intermediate the ends of said plates for closing the passages between the edge portions of adjacent plates and maintaining the latter in spaced relation, said strips having U- shaped bends at their longitudinal edge portions, said strips having one bend adapted to receive and hold the abutting edge portions of two plates and the other bend adapted to receive and hold the adjacent abutting edge portions of two plates and a bend of an adjacent closure strip, the abutting edge portions of said plates extending between the ends of said closure strips and the extremeends of said plates being connected together to provide a plurality of openings, two groups of the openings at opposite ends of said plates serving as an inlet and outlet for fluid flowing through alternate passages and the other two groups of openings at opposite ends of said plates serving as an inlet and outlet for fluid flowing through the other passages.

9. A heatexchanger including a plurality of heat transferplates arranged alongside each other with each plate having substantially parallel opposed edges intermediate the ends and'inwardly sloping edges at the ends, said plates being arranged to form a zigzag structure having a plurality of closely adjacent passages with said plates having one edge abutting an edge of an adjacent plate and the other edge abutting an edge of an opposite adjacent plate, a plurality of individual closure strips having U- shaped bends along their longitudinal edges for closing the passages between the edges of adjacent plates, along the intermediate portions having opposed parallel edges, said strips having one U-shaped bend adapted to receive and hold the the abutting, edges of two plates and the other bend adapted to receive and hold the adjacent abutting edges of two plates and a U- shaped bend of an adjacent closure strip, structure for closing the passages at the extreme ends of said plate, the abutting sloping edges of said plates being secured together to provide a plurality of openings, two groups of the opening at opposite ends of said plates serving as an inlet and outlet for fluid flowing through alternate passages and the other two groups of openings at the opposite ends of said plates serving as an inlet and outlet for fluid flowing through the other passages.

10. A heat exchanger including a plurality of heat transfer plates arranged alongside each other to form a zigzag structure having a pinrality of closely adjacent passages, said plates having one edge abuttingan edge of an adjacent plate andthe other edge abutting an edge of an opposite adjacent plate, structure for closing the passages at the extreme ends of said plates, a plurality' of individual closure strips extending intermediate the ends of said plates for closing the passages between the longitudinal edges of adjacent plates, said strips having U- shaped bends along their longitudinal edges, said strips having one bend adapted to receive and hold the abutting edges of two plates and the other bend adapted to receive and hold the adjacent abutting edges of two plates and' a bend of an adjacent closure strip, and U-shaped strip members for securing the abutting edges of said plates extending from said closure strips to the ends of said plates to provide a plurality of openings, two groups of the openings at opposite ends of said plates serving as an inlet and outlet for fluid flowing through alternate passages and the other two groups of opening at the opposite ends of said plates serving as an inlet and outlet for fluid flowing through the other passages.

11. A heat exchanger including a plurality of heat transfer plates arranged alongside each other with each plate having substantially parallel opposed edges intermediate the ends and inwardly sloping edges at theends, said plates being arranged to form a zigzag structure having a plurality of closely adjacent passages with said plates having one edge abutting an edge of an adjacent plate and the other edge. abutting an edge of an opposite adjacent plate, structure for closing said passages at the extreme ends of said plates, a plurality of individual closure strips for closing the passages between the longitudinal edges of adjacent plates along the intermediate portion having opposed parallel edges, said strips having U-shaped bends along their longitudinal edges, said strips having one bend adapted to receive and hold the abutting edges of two plates and the other bend adapted to receive and hold the adjacent abutting edges of two plates and a bend of an adjacent closure strip, and U-shaped strip members for securing the abutting sloping edges at the ends of said plates to provide a plurality of openings, two groups of the openings at opposite ends of said plates serving as an inlet and outlet for fluid flowing through alternate passages and the other 4 two groups of openings at opposite ends of said plates serving as an inlet and outlet for fluid flowing through the other passages.

12. A heat exchanger including a plurality of heat transfer plates arranged alongside each other with each plate having substantially parallel opposed edges intermediate the ends and inwardly sloping edges at the ends, said plates having the edges thereof offset laterally extreme ends of said plates, a plurality of closure strips for closing the passages between the edges of adjacent plates along the intermediate portions having opposed parallel edges, the abutting sloping edges of said plates being secured together to provide a plurality of openings, two

groups of the openings at opposite ends of said plates serving as an inlet and outlet for fluid flowing through alternate passages and the other two groups of openings at the opposite ends of said plates serving as an inlet and outlet for fluid flowing through the other passages.

13. A heat exchanger including a plurality of heat transfer plates arranged alongside each other with each plate having substantially parallel opposed edges intermediate the ends and inwardly sloping edges at the ends, said plates having the edges thereof ofiset laterally in opposite directions with the extreme edge portions substantially parallel to the main body portions of said plates, said plates being arranged to form a zigzag structure having a plurality of passages between adjacent plates with said plates having one ofiset edge abutting an edge of an adjacent plate and theother ofiset edge abutting an edge of an opposite adjacent plate, structure for closing the passages at the extreme ends of said plates, a plurality of individual closure strips-having U-shaped bends along their longitudinal edges for closing the passages between the edges of adjacent plates along the intermediate portions having opposed parallel edges, said strips having one bend adapted to receive and hold the abutting edges of two plates and the other bend adapted to receive and hold the adjacent abutting edges of two plates and a bend of an adjacent closure strip, the abutting sloping edges of said plates being secured together to provide a plurality of openings, two groups of the openings at opposite ends of said plates serving as an inlet and outlet for fluid flowing through alternate passages and the other two groups of openings at opposite ends of said plates serving as an inlet and outlet for fluid flowing through the other passages.

14. A heat exchanger as defined in claim 12 in which alternate plates are provided with longitudinal grooves which extend into alternate passages and are curved at their ends toward two groups of openings at opposite ends of said plates, and the other plates are provided with longitudinal grooves which extend into the other passages and are curved at their outer ends toward the other two groups of openings at opposite ends of said plates.

15. A heat exchanger as defined in claim '7, in which alternate plates are provided with longitudinal grooves which extend into alternate passages and are curved at their ends toward two groups of openings at opposite ends of said plates, and the other plates are provided with longitudinal grooves which extend into the other passages and are curved at their outer ends toward the other two groups-of openings at opposite ends of said plates,

16. A heat exchanger including a casing of rectangular cross section, said casing being open at the ends thereof and having openings adjacent both ends of two opposite side walls, a baflle of zig-zag cross section comprising heat transfer plates arranged alongside each other within said casing to provide a plurality of closely adjacent passages, said casing including closure members having U-shaped bends to receive the edge portions of said plates to close the passages at the two opposite side walls of the casing having the openings, and means including a closure plate and a sheet of packing material for sealing the ends of the passages formed by said baflle and for dividing said casing into two ducts, one of said ducts communicating with two openings adjacent the ends of said casing and the other of said ducts communicating with the other openings adjacent the ends of said casing.

17. A heat exchanger including a casing having end walls and openings adjacent both ends of two opposite side walls, and heat transfer plates disposed alongside each other within said casing and extending between the side walls having the openings, said plates being arranged so that they form a zig-zag structure extending across the casing to provide a plurality of closely adjacent passages between said plates, said casing including enclosure members having U- shaped bends to receive the edge portions of said plates to close the passages, said plates at the openings having one edge connected to an edge of an adjacent plate and the other edge connected to the edge of an opposite adjacent plate, two of the openings adjacent opposite ends of the casing serving as an inlet and an outlet for fluid flowing through alternate passages and the other two openings adjacent opposite ends of the casing. erving as an inlet and an outlet for fluid flowing through the other passages,

and said plates being of wave form having alternating connected curves, whereby turbulence of fluids in the passages is effected without substantially impeding the flow of the fluids.

BENNET CARROLL SHIPMAN.

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