US2589262A

US2589262A - Heat exchanger

Info

Publication number: US2589262A
Application number: US676142A
Authority: US
Inventors: Percival C Keith
Original assignee: Hydrocarbon Research Inc
Current assignee: Hydrocarbon Research Inc
Priority date: 1946-06-12
Filing date: 1946-06-12
Publication date: 1952-03-18
Anticipated expiration: 1969-03-18

Description

March 18, 1952 P. c. KEITH HEAT EXCHANGER 4 Sheets-Sheet 1 Filed June 12, 1946 .1 Rw Y ova m m] R E C v T N T l March 18, 1952 P. c. KEITH HEAT EXCHANGER 4 Sheets-Sheet 2 Filed June 12, 1946 BY LC HTTORNEY March 18, 1952 P. c. KEITH HEAT EXCHANGER 4 Sheets-Sheet 3 Filed June 12, 1946 INVENTOR fira'ua/ f. fizz/ BY [I ATTORNEY Patented Mar. 18, 1952 HEAT EXCHAN GER Percival 0. Keith, Peapack, N. J assignor to Hy-- drocarbon Research, Inc., New York, N. Y., acorporation of New Jersey Application June 12, 1946, Serial No. 676,142

9 Claims. (Cl. 257228) The present invention relates to an improved exchanger for recovering the cold content of the outgoing oxygen and nitrogen products of rectification, which may be at a temperature of about 280 F., in the production of oxygen by the liquefaction and rectification of air.

Cold accumulators or regenerators (hereinafter referred to as cold exchangers) of large cold-absorbing capacity are well known. In these cold exchangers, the relatively warm incoming air and the relatively cold outgoing oxygen and nitrogen products of rectification are alternately passed with periodically reversed operation, so that streams of warm air are flowed through the same packing-filled spaces as the cold oxygen and nitrogen traversed during the preceding step in the process, the hi h-boiling impurities deposited in these spaces during the passage of the air therethrough being removed by sublimation during the subsequent flow therethrough of the products of rectification.

An improved form of cold exchanger is described, for example, in copending application Serial No. 641,276, filed January 15, 1946, now Patent No. 2,529,516. The exchanger of said application comprises a cylindrical shell, in which are disposed a large number of tubes divided into two sets. Each tube of both sets has an interior accordion fin of foil-like metal of high heat conductivity disposed to form channels extending longitudinally through the tube and an accordion fin on the exterior thereof also arranged to form longitudinal channels. Oxygen flows through one set of tubes, constituting a minor portion of the tubes, which set of tubes is substantially uniformly distributed through the other set of tubes. Air and nitrogen alternately flow through the interior of the other set of tubes and through the longitudinal channels formed by the fins on the exterior of all of the tubes, the flow of these two media being periodically reversed, so that during one cycle of operation, the air flows through the channels in the interior of these tubes of the second set and the nitrogen through the channels on the exterior of all of the tubes, and during a succeeding cycle of operation the nitrogen flows through the channels in the interior of these tubes of the second set and the air fiows through the channels on the exterior of all of the tubes.

While the construction of said patent application represents a markedadvance over prior known exchangers, it does involve certain objections; for example, for eflicient cold transfer, it is necessary to bondthe exterior fins of one tube to the exteriorfins of contiguous tubes, or at least have them in metal-to-metal contact. Another feature of this exchanger which is somewhat objectionable is that the oxygen tubes must be provided with expansion joints to compensate for differential expansion and contraction taking place between these tubes, which generally are of copper, and the portion of the shell, generally of nickel steel, between the two header plates at each end of the shell through which the oxygen tubes pass and to which they are fastened. Further, it is important to note that in this prior construction, since the set of oxygen tubes is distributed through the other set of tubes and the air stream is to take up the cold content of both the oxygen and nitrogen streams, the pretesting of the individual tubes can only indicate the heat transfer efliciency between air and one product of rectification and not between air and both products of rectification as is desired. Hence, in order to determine whether satisfactory cold exchange will take place in the operation of the exchanger, it is necessary to fabricate and assemble a complete exchanger and then test it by flowing the oxygen and nitrogen products of rectification and air and ascertaining the temperature of the exiting gas streams; it is not possible from a test of an individual tube having the fins on both the interior and exterior thereof to determine whether, when a plurality of such tubes are assembled, satisfactory cold exchange will take place, such that the air will be cooled to the desired low temperature by both the oxygen and nitrogen products of rectification.

Among the objects of this invention is to provide a cold exchanger so constructed and designed that each individual unit can be tested and evaluated to determine whether, in operation, satisfactory cold exchange will take place between the air and the nitrogen and oxygen products of rectification, so that when such unit is assembled with other like units to form an exchanger of any desired capacity, the resultant exchanger will give the desired cold exchange.

Another object is to provide a tubular exchanger, none of the tubes of which need be provided with expansion joints.

Still another object is to provide an exchanger of the type disclosed, for example, in the copending application, Serial No. 641,276, now Patent No. 2,529,516, consisting of a multiplicity of tubular exchanger units having exterior fins in which, however, the exterior fins of one unit do not have to be in bonded or metal-to-metal contact with the exterior fins of adjacent units for satisfactory operation, thereby greatly decreasing the construction cost, and simplifying the assembly of the multiplicity of units constituting the exchanger.

Other objects and advantages of this invention will be apparent from the following detailed description thereof.

In the accompanying drawings forming a part of this specification and showing for purposes of exemplification preferred forms of this invention without limiting the claimed invention to such illustrative instances:

Fig. 1 is a composite view of a cold exchanger embodying this invention, the lower half being a vertical section through the exchanger, and the upper half a front elevation;

Fig. 2 is a fragmentary vertical section through one exchanger unit diagrammatically showing how the pair of concentric tubes constituting this unit. are secured to the header plates at each end of the exchanger;

Fig. 3 is a diagrammatic horizontal section through the cold exchanger of Fig. 1, taken on line 3-3 of Fig. 1;

Fig. 4 is a fragmentary (one-quarter view) horizontal section, on .a greatly enlarged scale, showing one preferred arrangementof fins defining the longitudinal channels associated with the concentric tubes of one exchanger unit;

Fig. 5 is a fragmentary (one-quarter view) horizontal section, on the same scale as Fig. 4, showing a modified form of exchanger unit;

Fig. 6 is a fragmentary (one-quarter) plan view of a disk-type fin which may be employed in a cold exchanger embodying this invention;

Fig. 7 is an enlarged section taken in a plane normal to the disk fin and passing through line 1-1 of Fig. 6;

Fig. 8 is a fragmentary (one quarter) plan view of another form of fin which may be employed-in acold exchanger embodying this invention;

Fig. 9 is an enlarged section taken in a plane normal to thefin and passing through line @-9 of Fig. 8;

Fig. 10 is a horizontal section through still another form of exchanger unit embodying this invention, this unitemploying fins of the type shown inFigs. 6 to 9 Fig. 11 is a vertical section through the exchanger unit of Fig. 10, taken through line i l-l l of Fig. 10; and

Fig. 12 is a composite view of a cold exchanger involving exchanger units of the type shown in Fig. 5; thelower half is a vertical section through the exchanger and the upper half a front elevation.

Referring to the drawings, I5 indicates a cylindrical shell which may be of nickel steel containing approximately 8% nickel, or of other suitable metal. The shell is preferably in the form of a cylinder or drum having concavo-ccnvex ends It provided with centrally disposed openings IT at the opposite ends thereof. Intermediate the ends of the shell I5 are a series of raised and depressed portions or corrugations is extending completely around the shell l5 and forming an expansion joint. This expansion joint accommodates differential expansion and contraction of the shell l5 and the cold exchanger tubes which, as more fully desc ibed hereinafter, preferably are made of a metal, such as copper, of high thermal, conductivity capacity and of different coefficient of expansion than the metal of shell 25. As above indicated, the construction involves a nickel steel shell l5 and copper tubes, in which case the expansion joints l8 are employed; the shell, however, may be of copper, and in view of the increased efficiency of the exchanger units of this invention, both the tubes and shell may be of steel, in which case a shell devoid of expansion joints may be employed.

Since both ends of the shell iii are of the same construction, only one end will be described in detail. A pair of header plates i9 and 213 are suitably welded to the walls of the shell as at 2| to provide a gas-tight seal at each end of the shell. A series of ports 22 are formed in the walls of shell l5 in the area between the header plates l9 and 20, these ports being equally spaced about the periphery of shell l5 and communicate with a manifold 23 extending circumferentially about the shell 15 in the area between the header plates. Manifold 23communicates with a port or opening 24.

A second series of openings 25 are formed in the wall of shell I5 equally spaced about the circumferential surface of the shell just above the header plate 2% viewing the lower end of Fig. 1, this series of openings leading into a manifold 25 extending circumferentially about the shell. A port 2? communicates with this manifold. It will be noted that

manifolds

23 and 26 are formed within a single manifold by means of partition 23a. Thus there are provided at each end of the shell, an oxygen header 28 communicating with the ports 22 which in turn communicate with the manifold 23, a second header 29 communicating with port H, and a third header 30 which,- through ports 25, communicates with the manifold 26 having port 21. The flows of air and nitrogen during one cycle of operation, indicated by full line arrows in Fig. 1, take place through headers 38 and 29, respectively, and, upon reversal during the subsequent cycle of operation, the flows of air anad nitrogen, as indicated by dotted line arrows, take place through the

headers

29 and 39, respectively. Oxygen flows continually through header 28.

In accordance with this invention, each tubular unit disposed within the shell consists of three zones, namely, a first zone for flow of oxygen therethrough, a second zone for flow of nitrogen or air, and a third zone for fiow of air or nitrogen, fiow through the second and third zones being periodically reversed. The cold exchange surface associated with each unit is so proportioned and designed that the desired cold exchange takes place between the three streams flowing through each unit, i. e., the air exits at the desired low temperature. Hence, each unit is self-sufficient from the viewpoint of heat transfer and canbe separately tested and evaluated before assembly in the shell. By assembling a plurality ofsuch units, preferably with a small clearancebetween contiguous units to facilitate the ready assembly thereof, the number thus assembled depending l upon the desired capacity, a cold exchanger results which is eminently satisfactory and efficient in operation.

In the embodiment of the invention shown in Figs. 1 to 4, zone I, the oxygen zone is theannular space 3| between an inner tube 32 and a.concentric outer tube 33, zone2 is disposed in the interior of tube 32, and zone 3 is substantially that outlined by the foil-like metal fin 34 .(Fig s 3 and 4) secured to the exteriorv of the tube 33 which fin in the embodiment of the invention shown in Figs. 3 and 4 has a hexagonal exterior outline. The

tubes

32 and 33 are made of electrolytic copper which is of a high heat transfer capacity, or other metals such as aluminum or alloys of high heat transfer capacity. The tubes are preferably cylindrical; ho ever, a hexagonal tube or even a square tube y be used, if desired; hence, the term tube is used in a broad sense and is intended to include all such polygonal tubular members.

The tube 32 (Fig. 4) is provided with an interior fin 35 and an exterior fin 36, the fins being of a metal of high thermal conductivity, preferably copper, and of foil-like thickness, for example, from .005" to .020" in thickness, preferably a thickness of .008" to .010 Fin 33, it will be noted, functions as an interior fin for tube 33, the latter tube having the exterior fin 34 hereinafter more fully described. The interior fin 35 is constructed and arranged to provide a multiplicity of interrupted contiguous channels extending longitudinally through tube 32. In the preferred embodiment shown in Fig. 4 of the drawings, the interior fin 35 for each section of tube length is produced by folding four strips of foil-like copper, one of which is shown in Fig. 4 in folded position, to form the triangular channels 31 having their bases in contact with the interior wall of tube 32 and their apices disposed remote from this wall, and other triangular channels 38, the apices of which are disposed near the wall of tube 32 and the bases of which are disposed along radii of the tube 32. Each strip of foil-like copper produces triangular channels 31 and 38, completely filling one-fourth of the cross-sectional space of the tube 32, the bases of the triangular channels 38 formed by the adjacent strips being in contact with each other'and the four strips providing triangular longitudinally extending channels completely filling the cross-sectional space within the tube. The longitudinally extending channels are interrupted at spaced intervals by narrow slots like slots 39 (Fig. 1) as hereinafter more fully described.

The use of four strips folded accordion-like to form longitudinally extending channels, triangular in cross-section, as hereinabove described, results in the fin maintaining the position shown in Fig. 3. In other words, where the bases of triangles defining the channels are in contact with each other along the radii of the tube, the channel walls are, in effect, reinforced so as to prevent collapse which might otherwise take place in view of the extreme thinness of the fin. As above indicated, these fins are preferably of a thickness of from .008 to .010". Collapse of the channel walls would be wasteful of heat exchanger surface. When tube 32 is comparatively small or fin 35 is made of comparatively heavy foil, fin 35 may be made by folding accordionlike only two strips of copper so that the bases of the triangular channels 38 of the two adjacent strips are in contact with each other along the diameter of tube 32.

Fin 36 disposed in the annular space between

tubes

32 and 33 is preferably formed by folding, for each section of tube length, a strip of foillike copper into the shape shown in Fig. 4 to provide alternate portions in contact with the inner wall of tube 33 and the outer wall of tube 32 connected by inclined portions, thereby forming two sets of substantially triangular longitudinally extending channels 40 and 4|. Eachstrip of foillike copper so folded may be approximately two inches wide, and adjacent strips are preferably separated by a narrow slot similar to slot 39..

The fin 34 is folded to provide two sets of contiguous triangles 42 and 43, the bases of the triangles 43 being in flat contact with the exterior of the tube 33 and the bases of the triangles 42 being remote from the wall of tube 33 and forming a hexagonal outline, as clearly shown in Fig. 4. Instead of the hexagonal outline of Fig. 4, the triangles may be arranged to produce a substantially square or other polygonal outline; the hexagonal outline is preferred. The exterior fin 34 may be made from one piece of foil-like metal or a larger number of pieces, for example, two pieces each of a length adequate to form onehalf the hexagonal outline, or even six pieces each of a length to form one side of the hexagonal outline.

The accordion-like fins on the interior of tube 32 and exterior of tube 33 are formed by folding strips of foil-like copper 4" to 12" wide, preferably about 6" wide. The triangular channels provided by these fin sections are, therefore, 4" to 12" long along the tube length, there being a multiplicity of these fin sections arranged serially along each tube and separated by a space or slot like slot 39 shown in Fig. 1 between adjacent fin sections 34 attached to the exterior of tube 33. These slots 39 are relatively narrow, say from T 5" to A," wide, preferably about I a" wide. Wider slots may be used but are wasteful of exchanger metal and volume. Such spaces or slots are left between adjacent fin sections on the interior of each of the

tubes

32 and 33, as well as between adjacent fin sections attached to the exterior of tube 33. Also, adjacent fin sections along the length on the interior of tube 32 and, if desired, on the interior of tube 33, may be staggered, i. e., may be positioned out of longitudinal alignment. With the construction herein described, turbulent gas fiow takes place through the channels formed by both the interior and the exterior fins on the tubes. In other words, the spaces or slots 39 occurring at intervals of every 4" to 12" in

fins

34 and 35 and every 2" in the case of fin 3B, induce turbulence in the gas streams which would otherwise have a streamlined or transitional flow. The distance between the slots is such that at about the point where the turbulence induced by one slot disappears, there is another slot to make the stream turbulent again. Furthermore, the staggering of adjacent fin sections augments the turbulence induced by the slots.

The

fins

34, 35 and 36 are desirably bonded to their respective tube walls with which they are associated by coating the interior and exterior surfaces of the

tubes

32 and 33 with solder metal, placing the fin sections, folded as shown in Fig. 4 and spaced to provide the slots between adjacent sections, in contact with the solder coating, then placing the assembly in an oven and heating it to a temperature so that the solder on the tube walls wets the fins and later cooling, thereby obtaining a firm bond between the tube walls and the portions of the fins in flat contact with the tube walls.

From Figs. 1 and 2 it will be noted tube 32 is of somewhat greater length than the concentric larger diameter tube 33, tube 32 being of a length to extend from one header plate l9 to the other header plate ill at the opposite end of shell l5. The space between the end of tube 33 and the end of tube 32 is substantially the same as the distance between the two header plates I9 and 20, as is evidentfrom Fig. 1. Tube 33.. is of a. length to extend between. the two. header plates 20. The fins 34 on the exterior of tubes. 33 do not extend to the ends of these tubes, but the portions of the tubesdisposed within the headers 33 are left free of fins, thereby forming the headers 35' at opposite ends of the shell in the area of the shell containing the ports 25.

The ends of tube 33, as shown in Fig. 2, are. secured to the header plates 20, preferably by disposing the ends within openings 44' in the header plates 2c andbrazing the tubes to the header plates as at 55. to makea gas-tight joint with the header plates. The portions'dfi of the inner tubes 32 near the header plat-es 2b: are flared to: provide an annular space 41 of greater Width than that of space 3|. The larger annular space i! is desirable since more room is thereby provided for inserting tools or other means by which the end of tube 33 is attached to plate 28 as by brazing at 25. This enlarged annular space M can also be obtained by flaring tube 33 outwardly instead of flaring tube 32 inwardly as shown. Theends of tubes 32 are dis posed within openings 48 in the header plates 19 and brazed thereto as at is to form a gas-tight joint with the header, plates 29. It will be'noted that the tubes 32 are'secured to the header plates Is at their ends only; and where they pass through the header plates 29 are not secured thereto. Hence'differential expansion and contraction, if any, between these tubes and the shell is taken up by the expansion joint !8. Tubes 33 are secured at their ends only to the header plate 2%. of this invention eliminates the necessity for employing special tubes having expansion joints.

Each exchanger unit consisting,

tubes

32 and 33 having interior and exterior fins 3d, and 36, as hereinabove described, are assembled in a bundle which, as shown in Figs. 1 and 3, is di posed within shell E5. The individual tubular units may have a small clearance between the bases of the triangular channels 22 associated with one unit and the bases of these channels associated with contiguous u..ts, thereby greatly facilitating the assembly of the units within the shell. The space between the exterior of the bundle of tubes and the interior of the shell is at intervals along the length of the shell is blanked-off by bafiie plates iii: (Fig. 1) which prevent flow through this space and insure that-flow of gas through liltBirfididtB portion of shell it takes place through the channels defined by the exterior fins on the tubes 23. These baflies 58 also act as reiniorcingstays aligning the tube bundle within the shell 55. The spaces between bafiles 56 may be filled with packing 5i, e. g., crumpled aluminum foil or wood blocks. The shell, if desired, may be made closs-fitting relative to the tube bundle, thereby eliminating the bafiles and packing.

In the modification of Fi 5, the oxygen zone is disposed within tube 52 and the air and nitrogen zones, which are periodically reversed as hereinabove described, disposed within tube 53 concentric with tube 52 and the triangular channels formed by fin 54 on the exterior of tube 53. Tubes 52 and 53 are of any metal of high heat conductivity. Fins 54, and 55, associated with these tubes, are of copper or other metal of high heat conductivity.

F111 53 disposed withintube 52 may be produced in. the same manner as fin 35 hereinabove described; and hence'need not be described in Accordingly, the construction 8 further detail. of tube. 53 may be formed in the same manner as fin 34 on the exterior of tube 33. Fin 55 disposed in the annular space between tubes.52' and.

53 is constructed and arranged to provide a multiplicity of interrupted channels extending longitudinally througfi the tube 53. This fin for each section of tube length is produced by folding a strip of foil-like copper or other metal to form two sets of substantially isosceles triangles which completely n11 the space between, tubes 52 and 53. One set of triangles 51 have their base portions in flat contact with the interior wall of the tube 53 and their apices contiguous to the exterior wall of tube 52. The other set of triangles 58 have their bases in flat contact with the exterior wall of tube 52 and their apices contiguous to the interior wall of tube 53.

As in the case of the construction of Figs. 1, 2 and 3, the longitudinally extending channels formed by the fins 5 3, 55 and 55 are separated by narrow slots which may be approximately in width at intervals of from i" to 12', preferably about 6', adjacent sections of fins and 56 alon the length of the interior of tubes and be staggered in order to induce turbulence of the gaseous media flowing through these sections. Als the fins are bonded to the of the tubes 52 and 53 in the same manner as hereinabove described in connection with the bonding of the

fins

36, 35 and to the walls of

tubes

32 and 33, in the modification of E l, 2 and he individual units of the modification of ereinab- 5Q described, arranged with e units a shell to form exchanger of 5165-165. capacity o shown in Fig. 12 in which like those of 1 have been given like reference characters. In the construction of Fig. 12 there is provided at each end of the shell, an oxygen header 2& communicating with the interior of tubes 52 and port El, a header 28 cornx: unicating with the interior of tubes 53 and through ports 22 is and a header 3 communicating with the channels formed by fins 54 on the exterior of tubes 53 and through ports 25 with manifold 26 having port 2?. The flows of air and nitrogen during one cycle of operation, indicated by full line arrows in Fig. 12, take place through headers 3t and r spectively, and upon reversal ng the su. uent cycle of operation, the o s of air and as indicated by dotted place through the headers 28 arrows, take 38 respectively. Oxygen flows-continually 1 ugh header 29 The modification of Figs. 6 to 11 resembles that (iii constitutes the oxygen zone'and and nitrogen Zones are disposed'withintube and in the channels formed by the fins on the exterior of tube 5%, flow through the latter two zones being periodically reversed. In the modification of Figs. 6 to -ll, the channels within tube formed by positioning within this tube in substantially abutting relationship, a multiplicity of disks Si of the type shown in Figs. 6 and 7. These disks may readily be produced by simple stamping operation and with no waste of material from copper or other material of hi rh heat conducting propertiesof foil-like thiclrnes. say from .005 toqOZO inch; Each disk 65 an integral flange 62 on the periphery thereof and has intheface thereof two seriestS and (i of radially-disposed closely- Likewise fin v54 on the. exterior with manifold having port spaced

passages

65 and 66. The two series of passages are separated by a flat portion 6'! of the disk of substantially circular outline. The passages 65 are each formed by cutting the disk along pairs of

radial lines

69 and 69 and then deflecting or twisting the material between each pair of lines so as to move this material out of the plane of the disk about points 19 as pivots and form vanes H. In like manner, the passages 66 are formed by moving the material between each pair of radial cuts 12 and T3 to form the bafiies 14. Thus there are produced baflles or vanes H and 14 acting as the walls of the two series of channels or

openings

63 and 64, respectively, through which the gas flows. The disk 6| is preferably provided with a central hole 15 with a circular flange 16.

These disks are disposed within tube 59, as shown in Fig. 11, so that the flange 62 on one disk substantially abuts the face of a contiguous disk within tube 59. Flow through the

openings

65 and 66 of the disks within the tube 59 is guided by the vanes or bafiles H and. 14, which, in effect, form the longitudinally extending channels, radially disposed within this tube.

The fin 1'! within the annular space between the

tubes

59 and 60 may be of the same construction and design as fin 36 between the

tubes

32 and 33 of the modification of Fig. 4 and may be formed in sections separated by narrow slots 18 comparable to slots 39 in the modification of Fig. 4.

The fin 19 on the exterior of tube 60 in the modification of Figs. and 11 is formed from a series of disks of the type shown in Figs. 8 and 9. These disks may be made of copper of coil-like thickness, say from .005" to .020" thick and produced by a simple stamping operation. Each disk has an interior circular outline 86 adapted to conform to the shape of the tube 60 on which it is mounted, the interior edge 89 having integral therewith a flange 8|. The opposite edge 82 of the disk is preferably of polygonal shape, e. g., a hexagonal shape as shown in Fig. 8. Edge 82 is provided with an integral flange 83. The face of the disk is out along closely-spaced lines 84 and 85 and the material between these lines deflected or rotated about

points

86 and 81 as pivots to produce baffles 88 which guide the gas through the openings 89 thus formed.

As shown in Fig. 11, these disks are assembled on the exterior tube 60 so that the flange 8| of one disk substantially abuts the face of a contiguous disk; the openings 89 which in effect are a multiplicity of longitudinally extending channels formed by baflies 88 are interrupted at closely-spaced intervals, i. e., between each pair of contiguous disks.

The construction hereinabove described, it has been found, provides an exceptionally high area of heat exchanger surface per unit of volume of exchanger and. thereby greatly increases the heat transfer rate. In the fins of the type shown in Figs. 6 to 9, the vanes or baffles are represented as being at right angles to the plane of the disks. However, the vanes may be set at an angle of from 60 to 90 with the plane of the disk. For more complete disclosure of these disk-type fins, reference may be had to copending application of Herman F. Buschow, Serial No. 678,464 filed June 21, 1946, now Patent No. 2,532,288.

The individual exchanger units of Figs. 10 and 11 are arranged with other like units in a shell to form an exchanger of desired capacity, the shell being provided with oxygen, nitrogen and air headers similar to those of Fig. 1.

In the operation of the modification of Figs. 1 to 4, flow of oxygen, as shown by full line arrows, takes place through the port 24 into manifold 23, ports 22, header 28, thence through all the oxygen tubes 33 of the assembly of units within the shell 15 into the header 28 at the opposite end of the shell [5, the oxygen leaving through the ports 22, manifold 23 and port 24 associated with the last-mentioned header 28. This flow is continuous throughout the operation of the exchanger, i. e., no reversal of the oxygen flow takes place. During one period of operation, nitrogen, as shown by the full line arrows, enters through port 11 and header 29 at the same end of the shell at which oxygen enters, flows through tubes 32 into the header 29 at the other end of the shell and exits through the top port l1. At the same time, air enters at the top port 21, flows through manifold 26, ports 25 and then through the channels 42 and 43 formed by fins 34 and exits through the ports 25 into manifold 26, and thence through base port 21. The air, therefore, flows countercurrently to both the nitrogen and oxygen streams. Upon reversal, as indicated by the dotted line arrows, air flows through the port I! into the top header 29, then through the tubes 32, exiting through the header 29 and base port I1. During this reversal period, nitrogen flows through base port 27, manifold 26, ports 25, header 30, then through the channels 42 and 43 formed by the exterior fins 34, and exits through header 30, ports 25, manifold 26 and top port 21. As in the previous cycle of the operation, air flows countercurrently to both the nitrogen and oxygen streams.

In the operation of the modification of Figs. 5 and 12, flow of oxygen, as shown by full line arrows, takes place through base port [1 into the header 29 thence through all of the tubes 52 of the assembly of units in the shell l5 into the top header 29 the oxygen leaving through top port l'i. This flow is continuous throughout the operation of the exchanger, i. e., no reversal of the oxygen flow takes place. During one period of operation nitrogen, as shown by the full line arrows on Fig. 12, enters through base port 24 into manifold 23, flows through ports 22 into the header 28 into and through tubes 53 into the top header 28 and exits through ports 22, manifold 23 and port 24 at the top end of the shell. At the same time, air enters through the top port 21, flows through manifold 26, ports 25 and then through the channels formed by fins 54 and exits through base header 39*, ports 25, manifold 26 and the base port 21. The air therefore flows countercurrently to both the nitrogen and oxygen streams. Upon reversal, as indicated by the dotted line arrows, air flows through top port 24 into the top header 28 then through the tubes 53, exiting through the bottom header 28 and base port 24. During this reversal period nitrogen flows through base port 21, bottom header 39 then through the channels formed by the exterior fins 54 and exits through top header 39 manifold 26 and top port 27. As in the previous cycle of operation, air flows countercurrently to both the nitrogen and oxygen streams.

It will be noted the individual tubular units of the exchanger are each self-suflicient in that each unit is so designed that the oxygen and nitrogen streams flowing therethrough cool the air stream to the desired temperatures. Hence, each unit can be tested and evaluated to determine whether, in operation, satisfactory cold exchange will take place between the air and the nitrogen and oxygen products of rectification, and when such unit, found to be satisfactory upon test, is assembled with other like units to form an exchanger of any desired capacity, the resultant exchanger will invariably be found to be eminently satisfactory and efiicient in operation and to have the desired cold exchange capacity. Furthermore, since each unit is designed independently of the others to give the desired cold exchange, it is not necessary to bond the exterior fins of contiguous units but a small clearance may be left between continguous units of the tube bundle Within the shell, thereby greatly facilitating the introduction of the units within the shell to form an exchanger of desired capacity and the maintenance and repair of the exchanger in operation should it be necessary to replace one or more units. The clearances between contiguous exchanger units should be kept small, say about 1%", so as to prevent a large proportion of gas from flowing through these clearances rather than through channels 42 and 43 of exterior fins 34.

It is well to note that both the accordion-type and the disk-type fins can be used in an exchanger unit of this invention. For instance, in the unit of Fig. 4, the internal accordion fin 35 may be replaced by a stack of disk fins 6| shown in Figs. 6 and 19. Also, in the exchanger unit of Fig. 10, the internal disk fin 6| may be replaced by accordion fin 35 shown in Fig. 4. In the unit of Fig. 5, any one, two or all three accordion-type fins may be replaced by fins of the disk type; it is obvious that where the annular space between the concentric tubes is appreciable, say over about /2, the annular fin may be made by stamping disks of foil-like metal similar to the disk fins 6i and 19 of Figs. 6 and 8, respectively. Such an annular or ring-shaped fin would be provided with flanges along the two edges, one for bonding to the external wall of the inner tubeand the other for bonding to the internal wall of the outer tube. Where the inner tube is comparatively small, the disk fin of the type shown in Fig. 6 may be made with a single series of radially disposed openings.

The tubes and fins assembled to form the exchanger units of this invention may be bonded to each other by using tubes and/or fins which have been precoated with solder, heating the assembly to melt the solder and cooling after the liquid solder has established metal-to-metal contact between the tubes and fins.

The manifolding shown in Fig. 1 for introducing and withdrawing gases to and from the cold exchanger may take any of several forms. An alternative form of means for effecting the introduction and withdrawal of gases is shown with the cold exchanger of the copending application Ser. No. 641,276, now Patent No. 2,529,516.

The cold exchanger has been shown in Fig. 1 in a vertical position with the products of. air rectification entering at the lower end thereof. If desired, air could'instead be introduced at the lower end of the exchanger and the products of rectification introduced at the upper end. Furthermore, particularly in the case of large exchangers, it is advisable to support the cold exchanger in a horizontal position. There is also advantage in making the ports and associated headers at the warmer end of the exchanger larger than the corresponding parts at the colder end to compensate the volume changes occurring in the gaseous fluids flowing therethrough. Also, in some operations, the exchanger may be employed without reversal of fluid streams.

An important advantage of the tubular exchanger units of this invention over the use of two sets of tubes arranged for the flow of cold from one set to the other as disclosed in copending application Ser. No. 641,276, now Patent No. 2,529,516, is that every exchanger unit in a bundle of any number of such units will function as efficiently as any other unit in the bundle. In the arrangement of copending application Ser. No. 641,276, now Patent No. 2,529,516, the tubes along the periphery of the bundle do not exchange as much cold as tubes which are completely surrounded by contiguous tubes. Furthermore, the problem of evenly distributing the set of oxygen tubes in relation to the other set of tubes in the tube bundle of the exchanger of application Ser. No. 641,276, now Patent No. 2,529,516, does not arise in the exchanger of this invention.

It will be noted the cold exchanger has an exceptionally high surface area of cold exchanger surface per unit of volume of exchanger space. With the design of fins herein described employing as the outer tubes circular tubes of from 1 /2 to 4 outside diameter, preferably about 2 /2" outside diameter, having a wall thickness of .035 to .125", preferably about .065", the exchanger may have from 300 to 500 square feet of cold exchanger surface per cubic foot of exchanger volume. The fiat surface contact between portions of the exterior and interior fins on the walls of the tubes results in high fin efficiency. The turbulent flow, caused by the spaced slots in the longitudinally extending channels, further improves the cold transfer efficiency of the exchanger. The exchanger is, therefore, of exceptionally high cold transfer efiiciency. This makes it possible to have the volumetric space through which nitrogen on the one hand and air on the other flows relatively small, thereby minimizing reversal losses. Moreover, the flow through the interior of the tubes and in the channels defined by the fins on the exterior of the tubes takes place in a general longitudinal direction; hence, minimum pressure drop of fluid flowing therethrough occurs.

Furthermore, the expansion joint in the shell accommodates differential expansion and contraction when the tubes and the shell are made of different metals having different coefficients of expansion, since the tubes are fastened to header plates at their ends only and not to any additional header plates intermediate to these end plates. With this construction, therefore, it is not necessary to employ tubes having expansion joints, with consequent saving in construction costs.

Since different embodiments of the invention can be made without departing from the scope of this invention, it is intended that all matter contained in the above description or shown in the accompanying drawings shall be interpreted as illustrative and not in a limiting sense.

What is claimed is:

1. A heat exchanger comprising a cylindrical shell, at least two spaced header plates at each of the opposite ends of the shell defining a first, second and third header at each end of the shell, said first headers being contiguous to the ends of the shell, the said second headers being disposed between the two spaced header plates at each end of the shell contiguous to said first headers, and the said third headers being disposed contiguous to the said second headers, means for supplying oxygen rectification product to one of said headers, means for supplying nitrogen rectification product to another of said headers, means for supplying air to the other of said headers, and a plurality of individual heat exchange units disposed in said shell in spaced relation to each other, each unit comprising a pair of concentric tubes in spaced relation, the inner tube of each pair communicably connecting the said first headers at opposite ends of said shell, the annular space between the two concentric tubes of each unit communicably connecting the said second headers at opposite ends of said shell, each inner tube having therein a large mass of foil-like metal permeated by a multiplicity of closely spaced channels separated from each other by said foil-like metal, the annular space between the two concentric tubes of each unit being filled with a large mass of foil-like metal permeated by a multiplicity of closely spaced channels separated from each other by said foil-like metal, and the outer tube of each unit having thereon a large mass of foil-like metal permeated by a multiplicity of closely spaced channels separated from each other by said foil-like metal, the last-mentioned channels communicably connecting the said third headers at opposite ends of said shell, whereby each unit has fiowing theretfi'ough in indirect heat exchange relation separate streams of air, nitrogen and oxygen rectification products and is therefore self-sufficient from the viewpoint of heat transfer between the air, oxygen and nitrogen, the masses of foil-like metal on all of the outer tubes filling substantially the entire transverse cross-sectional area which surrounds said outer tubes and is within said shell.

2. A heat exchanger comprising a cylindrical shell, at least two spaced header plates at each of the opposite ends of the shell defining a first, second and third header at each end of the shell, said first headers being continguous to the ends of the shell, the said second headers being disposed between the two spaced header plates at each end of the shell contiguous to said first headers, and the said third headers being disposed contiguous to the said second headers, means for supplying oxygen rectification product to one of said headers, means for supplying nitrogen rectification product to another of said headers, means for supplying air to the other of said headers, and a plurality of individual units disposed in said shell in spaced relation to each other, each unit comprising a pair of concentric tubes in spaced relation, the inner tube of each pair communicably connecting the said first headers at opposite ends of said shell, the annular space between the two concentric tubes of each unit communicably connecting the said second headers at opposite ends of said shell, each inner tube of each unit having therein an accordion fin formed by folding sections of thin metal of high heat conductivity to produce a multiplicity of short closely spaced, longitudinally extending passages completely filling the cross sectional area of said inner tube, a plurality of such sections being employed for each unit length of the tube and contiguous sections being separated by a narrow space, the annular space between two concentric tubes of each unit having therein an accordion fin folded to form two sets of triangular shaped passages with the bases of one set in contact with the inner wall of the outer tube and the bases of the other set in contact with the outer wall of the inner tube, the outer tube of each unit having thereon a third accordion fin folded to form two sets of triangular closely spaced channels with the bases of one set in contact with the outer wall of the tube and the bases of the other set disposed to produce a polygonal outline surrounding said tube, said closely spaced channels communicably connecting said third headers at the opposite ends of said shell, whereby each unit has flowing therethrough in indirect heat exchange relation separate streams of air, nitrogen and oxygen rectification products and is therefore self-sufiicient from the viewpoint of heat transfer between the air, oxygen and nitrogen.

3. A heat exchanger as defined in claim 2 in which each of the tubes of each unit is of copper and the fins are also of copper and have a thickness of from .005" to .020".

4. A heat exchanger as defined in claim 1,

having at .each end of said shell a pair of mamfolds on the outside of said shell, one of said manifolds of each pair communicating only with the third header through a series of openings spaced about the periphery of said shell, and the other of said manifolds of said pair communicating only with the second header through a series of openings spaced about the periphery of said shell.

5. A heater exchanger as defined in claim 2, having at each end of said shell a pair of cylindrical manifolds surrounding said shell and concentric therewith, one of said manifolds of each pair communicating only with the third header through a series of openings spaced about the periphery of said shell, and the other of said manifolds of said pair communicating only with the second header through a series of openings spaced about the periphery of said shell.

6. A heat exchanger as defined in claim 2 in which the polygonal outline of the third accordion fin is an equilateral hexagon.

'7. A heat exchanger comprising a cylindrical shell, two spaced header plates at each of the opposite ends of the shell defining a first, second and third header at each end of the shell, said first headers being contiguous to the ends of the shell, the said second headers being disposed between the two spaced header plates at each end of the shell contiguous to said first headers, and the said third headers being disposed contiguous to the said second headers, a plurality of individual heat exchange units disposed in said shell in spaced relation to each other, each unit comprising a pair of concentric tubes in spaced relation, the inner tube of each pair communicably connecting the said first headers at opposite ends of said shell, the annular space between the two concentric tubes of each unit communicably connecting the said second headers at opposite ends of said shell, and the space surrounding the outer tube of each unit communicably connecting the said third headers at opposite ends of said shell, whereby each unit has flowing there through in indirect heat exchange relation three separate fiuid streams and is therefore self-sufficient from the viewpoint of heat transfer between the three fiuid streams, a pair of manifolds surrounding said shell at each end of said shell, one of said manifolds of each pair communicating only with the third header through a series of openings spaced about the periphery of said shell and the other of said manifolds of said pair communicating only with the second header through a series of openings spaced about the periphery of said shell, means for supplying one fluid stream to one of said first headers, means for supplying two other fluid streams to the pair of manifolds at one end of said shell, means for withdrawing the one fluid stream from the other of said first headers, and means for withdrawing the two other fluid streams from the pair of manifolds at the other end of said shell.

8. A heat exchanger as defined in claim 7 in which the pair of manifolds at each end of the shell has a common wall separating the manifolds of said pair.

9. A heat exchanger comprising a cylindrical shell, at least two spaced header plates at each of the opposite ends of the shell defining a first, second and third header at each end of the shell, said first headers being contiguous to the ends of the shell, the said second headers being disposed between the two spaced header plates at each end of the shell contiguous to said first headers, and the said third headers being disposed contiguous to the said second headers, a plurality of individual heat exchange units disposed in said shell in spaced relation to each other, each unit comprising a pair of concentric tubes in spaced relation, the inner tube of each pair communicably connecting the said first headers at opposite ends of said shell, the annular space between the two concentric tubes of each unit communicably connecting the said second headers at opposite ends of said shell, each tube of each unit having therein a large mass of thin high heat conducting material, which mass of high heat conducting material is permeated by a, multiplicity of closely spaced channels separated from each other by said thin high heat conducting material, the outer tube of each unit having thereon a large mass of thin high heat conducting material, which mass of high heat conducting material is permeated by a multiplicity of closely spaced channels separated from each other by said thin high heat conducting material and communicably connecting the said third headers at opposite ends of said shell,

whereby each unit has flowing therethrough in indirect heat exchange relation three separate fluid streams and is therefore self-sufficient from the viewpoint of heat transfer between the three fluid streams, a pair of manifolds surrounding said shell at each end of said shell, one of said manifolds of each pair communicating only with the third header through a series of openings spaced about the periphery of said shell and the other of said manifolds of said pair communicating only with the second header through a series of openings spaced about the periphery of said shell, means for supplying one fluid stream to one of said first headers, means for supplying two other fluid streams to the pair of manifolds at one end of said shell, means for withdrawing the one fluid stream from the other of said first headers, and means for withdrawing the two other fluid streams from the pair of manifolds at the other end of said shell.

PERCIVAL C. KEITH.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 164,757 North June 22, 1875 516,349 Hall Mar. 13, 1894 745,312 Baragwanath Dec. 1, 1903 1,854,619 Mortensen Apr. 19, ,2

1,920,800 McCausland Aug. 1, 1 33 1,980,791 Duggan et a1 Nov. 13, 1934 2,059,992 Gould Nov. 3, 1936 2,075,511 De Baufre Mar. 30, 1937 2,336,879 Mekler Dec. 14, 1943 2,439,208 Gloyer Apr. 6, 1948 2,460,859 Trumpler Feb. 8, 1949 FOREIGN PATENTS Number Country Date 371,608 Great Britain Apr. 28, 1932 881,258 France Jan. 22, 1943 44,339 Switzerland May 30, 1908