Shell and tube heat exchanger

Abstract

 A heat exchanger comprising a generally tubular shell (12), a pair of end assemblies (14, 16) coupled to the axially opposed ends of the shell (12) and a plurality of multi-­walled tubes (75) having inner and outer walls (57, 96) and extending axially between the end assemblies (14, 16). Each end assembly (14, 16) comprising a tube sheet (40, 42) for receiving an outer wall (96) of a tube (75) and a center flange (32, 34) for receiving an inner wall (57) of the tube (75). At least in one end assembly (14) the outer wall (96) and the inner wall (57) of each multi-walled tube (75) are supported by the tube sheet (40) and the center flange (32) with an axially movable relationship, respectively, the center flange (32, 34) is disposed in an axially spaced relationship to the tube sheet (40, 42), and sealing means are provided between the tube sheet (40, 42) and the center flange (32, 34) for sealing the outer wall (96) of each tube (75) in an axially movable relationship to the tube sheet (40, 42) and for sealing the inner wall (57) of each tube (75) in an axially movable relationship to the center flange (32, 34).

Description

[0001] The present invention relates to a heat exchanger as de­fined in the precharacterizing portion of claim 1.

[0002] A heat exchanger of this kind is already known from EP-A-66 425. Said heat exchanger comprising:

a) a generally tubular shell (12) extending between axially opposed ends and having first inlet means (54) and first outlet means (62) for respectively permitting the in­gress and egress of a first heat exchange fluid and a second inlet means (18) and a second outlet means (20) for respectively permitting the ingress and egress of a second heat exchange fluid,

b) a pair of end assemblies (14, 16) coupled to the axially opposed ends of the shell (12) to define an internal chamber (22) therein, and

c) a plurality of multi-walled tubes (75) having inner and outer walls (57, 96) and extending axially within the internal chamber (22) between the end assemblies (14, 16) at each end, said end assemblies (14, 16) comprising each

d) a tube sheet (40, 42) having a plurality of axially ex­tending apertures therethrough, each receiving an outer wall (96) of a different multi-walled tube (75), said tube sheet (40, 42) is provided together with further means (210) for establishing a flow path of the second fluid through the internal chamber (22),

e) a center flange (32,34) disposed on a side of the tube sheet (40, 42) opposite the internal chamber (22), said center flange (32, 34) is provided with a plurality of axially extending apertures (95) therethrough, each re­ceiving an inner wall (57) of a different multi-walled tube (75), and

f) means (24, 28; 26, 30) for coupling the first heat ex­changer fluid into the inner walls (57) of at least a plurality of the tube members (75).

[0003] With respect to this heat exchanger, however, the risk of temperature-induced stresses in the connecting parts between the tube sheet, the center flange and the multi-walled tube members or in other parts of the heat exchanger is rela­tively high so that problems may occur in case of a large difference between the temperature of the first and second fluids.

[0004] It is therefore an object of the invention to provide a heat exchanger having an enhanced reliability also in a high temperature difference area.

[0005] According to the invention, at least in one end assembly, the outer wall and the inner wall of each multi-walled tube are supported by the tube sheet and the center flange with an axially movable relationship, respectively, the center flange is disposed in an axially spaced relationship to the tube sheet, and sealing means are provided between the tube sheet and the center flange for sealing the outer wall of each tube in an axially movable relationship to the tube sheet and for sealing the inner wall of each tube in an ax­ially movable relationship to the center flange.

[0006] In a preferred embodiment, the means for sealing includes for each multi-walled tube a bushing disposed between the tube sheet and center flange with an internal bore there­through having a diameter at an end adjacent the tube sheet selected to movably receive the outer wall of the tube in a sealing relationship, the bushing internal bore having a diameter at an end adjacent the center flange that is smal­ler than the diameter at the end adjacent the tube sheet and selected to movably receive the inner wall of the tube in a sealing relationship.

[0007] In another preferred embodiment the means for sealing in­cludes for each bushing a first seal slideably sealing the smaller diameter bore to an inner tube wall passing there­through and a second seal slideably sealing the larger dia­meter bore to an outer tube wall extending partway there­through.

[0008] In a still further embodiment the heat exchanger is charac­terized by a vent chamber defined between the tube sheet and center flange, means for providing a fluid flow path between the vent chamber and the exterior of the heat ex­changer, and a radial bore extending through each bushing at a location axially positioned between a transition from the larger diameter bore to the smaller diameter bore and the end of the outer tube wall extending partway through the larger diameter bore.

[0009] Each tube member may include an inner tube having a wall of uniform thickness and a spiral groove formed therein and an outer tube disposed concentrically about the inner tube and having a uniformly thick wall with a spiral groove formed therein which mates with the spiral groove of the inner tube such that an inner surface of the outer tube wall en­gages an outer surface of the inner tube wall along the ma­ting grooves of the inner and outer tubes.

[0010] The foregoing and additional features of the invention will become apparent from the detailed description which follows.

[0011] In the drawing,

Fig. 1 is a side elevation view partially broken of a heat exchanger in accordance with the invention;

Fig. 2A is an exploded perspective view of the fluid #1 inlet end assembly, the opposed or outlet end assembly being substantially the same;

Fig. 2B is a fragmentary view in perspective of the fluid #1 inlet end of the heat exchanger with the end assembly and fluid-conducting tubes omitted;

Fig. 3 is a cross-section of the heat exchanger taken at 3-3 of Fig. 1;

Fig. 4 is an enlarged longitudinal cross-section of the fluid #1 inlet end assembly illustrating in part the heat exchange tube sealing and venting mechanisms;

Fig. 5 is an enlarged cross-sectional view of a portion of enhanced surface tubing taken about the indi­cated section line 5 of Fig. 4;

Fig. 6 is a cross-sectional view of the fluid #1 inlet end assembly of the invention taken at 6-6 of Fig. 1;

Fig. 7 is a cross-sectional view of the fluid #1 out­let end assembly of the invention taken at 7-7 of Fig. 1;

Fig. 8 is partial longitudinal cross-section of the fluid #1 outlet end assembly, illustrating in part the heat exchanger tube expanded bush and means of venting in case of gasket failure.

[0012] Fig. 1 is a side elevation view of a heat exchanger 10 in accordance with the invention. The heat exchanger 10 generally comprises an elongated cylindrical outer shell 12 that terminates in end assemblies 14 and 16, the former assembly being denoted the inlet end assembly and the latter the outlet end assembly in recognition of the fact that the invention contemplates that a first thermal ex­change fluid, such as relatively cold potable water, is to enter the heat exchanger 10 through an inlet port 54 in the end assembly 14 and exit through an outlet port 62 in the end assembly 16.

[0013] A second thermal exchange fluid, such as a superheated refrigerant (i.e., ammonia), is applied through an inlet 18, comprising an aperture in a neck flange 46. The second fluid thereafter exits the heat exchanger through an out­let 20 in the neck flange 44.

[0014] The outer shell 12 is shown partially broken in Fig. 1, exposing a substantially cylindrical inner chamber 22. The device as shown in Fig. 1 is not a complete assembly; as will be described in greater detail, and as illustrated in Figs. 2A and 2B, a plurality of heat exchange tubes 75 and a chamber-partitioning longitudinally extending baffle assembly 74 are positioned within the chamber 22 to effect a multi-pass, contraflow thermal exchange process, during operation, between the first and second fluids within the chamber 22 and the inner tubes 75 thereby facilitating the transfer of heat therebetween. The additional assemblies for such purpose are illustrated in subsequent drawing figures.

[0015] As shown in Fig. 1, neck flanges 44 and 46 are affixed to axially opposed ends of the shell 12 as by welding or an equivalent process. For reasons which will become apparent, the neck flanges 44, 46 are conveniently identical in structure, each including a port 20, 18 respectively and so forth, but are rotally offset 72° from each other prior to affixation to the shell.

[0016] The assemblies 14, 16 respectively comprise a sandwich-­like arrangement of elements joined to neck flanges 44 and 46 by a plurality of bolts 48 peripherally arranged about the assemblies 14 and 16 and threadedly engaged to nuts 50. As shown in Figs. 1 and 2A, the inlet end assembly 14 in­cludes an end cap 24, a center pressure flange 32 and an inner tube sheet 40. A similar outlet end assembly arrange­ment comprises end cap 26, center pressure flange 34, and inner tube sheet 42.

[0017] The neck flange 44 conveniently includes exit port 20, through which the second heat transfer fluid exits, as well as a port 85 for pressure relief valve 86. Both ports com­municate with interior chamber 22 as subsequently described in greater detail. By including both ports as part of the neck flange, the ports may be formed as part of a molding process by which the flange is conveniently made, provi­ding a less expensive alternative to drilling the ports in the shell and welding to the shell threaded fittings.

[0018] An axially-extending chamber-partitioning baffle assembly 74, located within the chamber 22, partitions the chamber into five axially-extending parts or sub-chambers. Each of the five partitioned regions encloses a defined nest of heat exchange tubes 75. The baffle assembly 74 and tubes 75 are described more clearly by reference to Fig. 3.

[0019] Fig. 3 is a cross-section of the heat exchanger 10 taken along line 3-3 in Fig. 1. The baffle assembly 74 is seen to be formed from five interlocking baffle members 76, 78, 80, 82 and 84 which may be simply and economically formed from, for example, aluminum via an extrusion process. Re­ferring in detail to the baffle member 76, it is seen to comprise a radial arm 134 and a circumferential arm 132 that corresponds generally to the inner circumference of the shell 12.

[0020] The circumferential arm 132 and radial arm 134 extend axially through the chamber 22. As shown in Fig. 3, the circumferential arm 132 extends generally circumferentially away from the radial arm 134 and terminates in a hook-like leg portion 140. The junction of the radial and circum­ferential arms includes a socket 136 having a complimenta­ry shape to leg 140 so that it captures a similar leg 138 of adjacent baffle member 84. The leg 140 similarly cap­tured by the socket of neighboring baffle member 78.

[0021] In baffle assembly 74, baffle member 76 lies interjacent baffle members 84 and 78, member 84 being adjacent in a clockwise direction and member 78 being adjacent counter-­clockwise. The radially inner portion of the radial arm 134 terminates in a hook-shape adapted to interlock with the corresponding appendage of the counter-clockwise ad­jacent baffle member 78. Similarly, the appendage 137 is adapted to interlock with the terminus of the clockwise adjacent radial arm of baffle member 84. As shown in Fig. 3, each radial arm butts against its adjacent neigh­bors and interlocks.

[0022] Construction is particularly inexpensive. To assemble baffle assembly 74, a first baffle member 84 is placed in the shell 12. The distal end of the leg (e.g. 138) of the first baffle member is inserted into the proximal end of the socket (e.g., 136) of the second member while simul­taneously inserting the hooked appendage 137 of the second member into the appendage of the first. The second member is slid relatively axially into the chamber so that there is full engagement between the terminus/appendage and socket/leg, which are shaped such that the members cannot separate unless slid axially. Each of the third through fifth members is thereafter slid axially into place, and the resulting baffle assembly is slid into the chamber 22 as hereinafter described in detail. The radially exten­ding arms are slightly oversized to provide a radially directed compression of the assembly, effecting a seal where the radial arms abutt.

[0023] The circumferential arms of the baffle members include radially outward extending legs 76a, 78a, 80a, 82a and 84a which maintain a clearance of approximately 1 mm bet­ween the radially outer surface of the baffle assembly and the inner wall of the shell 12.

[0024] Fig. 3 additionally illustrates a cross-section of the in­let 18 for the second heat exchange fluid and tubes 75 for conducting the first heat exchange fluid. The second heat exchange fluid enters the baffle Sector I defined by baffle member 84 and radial arm 134, and flows axially out of the drawing. The inlet 18 includes an aluminum sleeve 71 which is passed through the aperture in the shell 12 into inlet 18 and has been expanded into position. Accor­dingly, the incoming second fluid cannot pass into the space between the baffle and the inside wall of the shell 12. For reasons which will be explained subsequently, no corresponding expanded sleeve is associated with the out­ let 20 or pressure relief port 85 (Fig. 1), thereby enabling a portion of egressing second fluid to fill the space 145 in operation.

[0025] As an alternative to the expanded sleeve 71, a "sleeve" may be drawn out of the baffle assembly wall: specifically, out of circumferential arm 147. In essence, the inlet hole is punched through the arm 147 and the material drawn out­ward to form a funnel-like conduit integral with the baffle member. In assembling the heat exchanger, the punched baffle member is placed within the chamber 22 first by lo­cating the drawn hole into the hole of inlet 18 of the neck flange 46. The remaining baffle members are then slid in as described earlier.

[0026] While the details concerning the respective paths of the first and second fluids are described later, it will be appreciated by a comparison of Figs. 2 and 3, that the in­let 54 for the first heat exchange fluid is oriented to couple incoming fluid into the nest of tubes occupying Sector V of the baffle assembly. Construction details con­cerning the tubes are better understood with reference to Figs. 4, 5 and 8.

[0027] Fig. 4 is an enlarged longitudinal partial section of the assembled end assembly 14 illustrating, in part, a rep­resentative of one of the heat exchange tubes. Fig. 5 is an enlarged sectional view of a portion of expanded sur­face tubing taken about section line 5 in Fig. 4. Fig. 8 is a port section of the assembled end assembly 16 illus­trating in part a representative of one the heat exchange tubes.

[0028] As shown in Figs. 4, 5 and 8, the tubing 75 generally com­prises an outer skin 96 and an inner skin 57 pressed to­gether along a helical area of contact so that a gap or cavity 110 effectively spirals the length of the tube between adjacent spiral contact areas. If, for example, the outer skin 96 of a tube 75 in Sector I (Fig. 3) frac­tures, the second fluid in Sector I will enter the spiral cavity 110 and, in accordance with the invention, as sub­sequently described, such fracture will be detected by the venting of such fluid from within the cavity 110 to atmos­phere. Similarly, when the inner skin 57 is breached, the first fluid will enter the spiral cavity 110 and will thereafter be vented to atmosphere in accordance with the invention as subsequently described.

[0029] The configuration of tube 75 has been designed to improve the heat transfer coefficient over conventional enhanced surface tubes. This improvement is achieved by providing a relatively wide groove where the outer skin 96 and the inner skin 57 are pressed together, yielding greater area of metal contact 122. Additionally, by increasing the distance 124 between the grooves to allow a thicker wetted surface to form, an increased heat transfer coefficient is provided. While it is known that enhanced surface tubing significantly increases the heat transfer of a particular tube diameter in heat exchange equipment, Applicant has developed a particular configuration wherein the control­ling parameters are optimized. In particular, applicant has found that a groove width 122 of approximately 3,1 mm and depth of approximately 2,4 mm assures good turbula­tion of the fluids on both sides of the tube while maxi­mizing heat transfer without collapsing the tube during manufacture. The pitch 124 of the optimal tube is found to be 14,3 mm. A gap 110 of 76 µm was employed to meet venting regulations but should be kept at a mini­mum to ensure maximum heat transfer.

[0030] Before describing the fluid flow paths in the heat ex­changer, attention is directed to the assembly procedure, whereby the interrelationship of the various components will be more easily appreciated. With initial reference to Fig. 1, the inner tube sheet 42 is first mounted onto the neck flange 46 by means of locating dowels 70ʹ pro­truding from the flange and receiving holes 38 in the tube sheet 42. The dowels and dowel-receiving holes are similar to dowel 70 and holes 56 associated with tube sheet 40 of the inlet assembly and illustrated in Fig. 2A.

[0031] The tube sheet 42, which is similar to plate 40 (Fig. 2A) includes a pattern of holes sized to accomodate the outer skins 96 of the tubes 75. The hole pattern corresponds to the pattern of the tubes 75 shown in Fig. 3.

[0032] Reference is made to Fig. 8, a fragmentary sectional view of the outlet end of the heat exchanger 10. Each of the tubes 75, to be inserted into chamber 22 through a respec­tive one of the holes in the innertube sheet 42, includes a bushing 104 which has been inserted over the end of the tube. The bushing 104 includes a through-hole having a stepped wall 104a such that the larger internal diameter portion of the bushing engages the outer skin 96 of tube 75, while the smaller diameter portion of the bushing engages the inner skin 57 of tube 75. A general swedging tool may then be inserted into the tube, as is known in the art, to expand the tubes within the bushing and there­by effect respective seals between the bushing and the in­ner and the outer skins, with the gap 110 between the in­ner and outer skins being sealed against the step 104a of 30 the internal bushing wall.

[0033] As the tube/bushing sub-assemblies are inserted into respective holes of the inner tube sheet 42, the leading face of each bushing contacts a gasket similar to gasket 67 against the outer face of the plate 42.

[0034] Before describing the completion of the outlet end assembly 16, attention is redirected to inlet end assembly 14. Re­turning to Figs. 1 and 2A, the neck flange 44 is shown to include a number of peripheral apertures 33 and a longitu­dinally extending, peripheral dowel 70. The dowel 70 is adapted to pass through location holes respectively formed in the components of end assembly 14 when the components are mounted onto the flange 44.

[0035] Accordingly, a gasket assembly comprising a tube sheet 40 interjacent two gaskets 68, 69 is mounted onto the flange 44. The tube sheet and gasket 68 include aligned hole patterns corresponding to the layout of tube holes 95 so that the tubes 75 extend outward therethrough. As will be subsequently appreciated, the gasket assembly and the corresponding gasket assembly of outlet assembly 16 define the ends of chamber 22 for the second heat transfer fluid.

[0036] After the gasket 68 has been mounted against the tube sheet 40, a generally annular bushing 41 is placed about each tube 75 and slide back against the gasket assembly. The bushing 41 straddles the termination of outer tube skin 96. As shown in Fig. 4, each bushing 41 includes a pair O-rings 102, 103 for forming a tube expansion region 43 communicating with gap 110 in tube 75. Into tube expansion region 43 is a hole III which connects to gap 110 to allow the tube to vent to atmosphere.

[0037] Next, gasket 67 is fitted over the protruding inner tube 57 of tube 75. A pressure flange 32 is then correctly oriented via dowel 70 and assembled onto the neck flange 44. The axially inner face of pressure flange 32 butts against the gasket 67 which is against the outer face of the bushings 41, resulting in an outer annular portion 32a which circumvents the protruding bushings 41 and which is adepted to sealingly contact the gaskets 67 and 68 to de­ fine a vent chamber 45 between the flange 32 and tube sheet 40. The vent passage is completed with a vent hole 47 in pressure flange annular portion 32a.

[0038] The aforedescribed arrangement is directed towards pre­venting the contamination of one of the heat exchange fluids by the other. Should the outer skin 96 of a tube 75 fracture and permit the second fluid to enter and travel along helical gap 110, the fluid will enter region 43 pass through hole 111 then to atmosphere through hole 47. The second fluid will not escape from gap 110 at the outlet assembly 16 since the expansion of tube 75 into bushing 104 at that end has sealed that bushing across the gap.

[0039] As shown in Fig. 4, bushing 41 includes a through-hole 111 through which any fluid in gap 110 will escape. The escap­ing fluid falls downward through chamber 45 and out of the end assembly via through-hole 47 in the bottom periphery of the pressure flange 32a and is detected by means herein­after set forth so that the tube 75 can be replaced before a subsequent fracture in inner skin 57 or other event per­mits a mixing of the first and second fluids. Similarly, a fracture of the inner skin 57 results in first fluid being restricted to region 43 and escaping via hole 111 and 47.

[0040] The pressure flange 32 additionally comprises a central portion 32b relatively recessed from the gasket-contacting surface of the annular portion 32a. The recessed portion contains a pattern of through-passages 95 located in align­ment with the axially extending inner sleeves 57 that pro­trude from bushings 41. The axially inward face of the re­cessed portion 32b surrounds each passage 95 thereby sealingly contacts the axially outward face of the respec­tive bushing against gasket 67. The inner sleeves 57 extend into, but do not protrude from the axially outward side of, passages 95.

[0041] The axially outer face of the pressure flange 32 includes an end baffle arrangement 28 comprising annular portion 28a circumscribing the through-holes 95 together with a generally Y-shaped portion comprising generally radially extending bars 52a, b,and c. The bars 52a, b, and c and annular portion 28a are adapted to sealingly contact the interior face of each cap 24 via a gasket 29 and to there­by form a series of pressure chambers, as better explained by reference to Figs 6 and 7.

[0042] Figs 6 and 7 are cross-sectional views of portions of the inlet and outlet end assemblies taken along the lines 6-6 and 7-7, respectively, of Fig. 1. As can be seen, the end assemblies are substantially similar. The plurality of bolt receiving holes 149 is provided about the outer periphery of pressure flange 32, 34.

[0043] End baffle 28, 30 illustrated in Figs.6 and 7 as comprising an annular steel portion 28a, 30a, with radial vane arrange­ments 52a, b, c, and 59a, b, c. The relative orientations of the vanes 28, 30 by a 72° rotational offset. Apertures 56, 38 in the annular portion of the baffles are provided for insertion about positioning dowels 70, 70ʹ to provide the correct relative orientations of the vane arrangements within the end assemblies 14 and 16. Accordingly, the welding of neck flange 46 onto shell 12 at a rotational offset of 72° from the orientation of neck flange 44 per­mits identical components to be used in end assemblies 14, 16 except for bushings 41, 104.

[0044] The end baffles 28, 30 vanes define pressure chambers in the end assemblies 14, 16 that provide a fluid flow con­tinuum for reversing the direction of the first heat ex­change fluid within the thermal exchange tubes. The dashed circles 54 and 62 indicate the locations of the inlet port 54 and the outlet port 62 with respect to the vane arrange­ ments 28 and 30 respectively. As can be seen, the radial fins of each arrangement subtend two obtuse and acute angle. In an actual reduction to practice of the invention, an acute angle of 72° and obtuse angles of 144° were em­ployed.

[0045] The through passages 95 which the ends of the inner tube sleeves 57 engage into are shown in Figs. 6 and 7. The axially outer faces 28a, 30a are illustratively divided into in 72° segments denoted "A" through "E" and "Aʹ" through "Eʹ", respectively. The three radial vanes of each end baffle cooperate with the interior of the respective end cap 24, 26 to define three end chambers at each end of the heat exchanger.

[0046] The flow of the first heat exchange fluid through the heat exchanger occurs in the following sequence: the fluid enters the heat exchanger 10 under pressure at inlet port 54 (Fig. 6), distributing itself over the 72° section A to thereby enter inner tube 57 nest of heat transfer tubes 75 that are telescopically engaged within the passages 95 of the pressure plate 32. The fluid then travels in the tubes through the heat transfer chamber 22 to the 144° section of the pressure chamber in the outlet end assembly 16 comprising the Aʹ and Eʹ segments (Fig. 7). As the fluid emerges from the tubes in section Aʹ under pressure, its only outlet from this section of the end chamber is the path commencing with the set of channels of section Eʹ, through which it enters tubes 57 that transport the fluid back through the heat exchange chamber 22 to the inlet end 14 section. Emerging from the pipes of segment E (Fig. 6), the fluid can only enter the channels within segment D for transmission once again through the heat exchange chamber 22, and so forth. The end of one inner sleeve 57 within each of the defined segments of the end pressure chambers has been identified according to the direction of first fluid flow in the tube nest of that segment, a "dot" in­dicating fluid flow emerging from the plane of the paper and a "cross" indicating flow into the plane of the paper. One can see that, by means of the particular design and relative orientations of the end baffles 28 and 30, a multi-­pass fluid flow path is established for the first fluid through the heat transfer chamber 22.

[0047] Having described the multi-pass flow path of the first fluid, the path of the second fluid is next described. Turning to Fig. 3, the second fluid has been mentioned as entering section I of chamber 22 via inlet 18. Radial arms 134 are sealed against tube sheet 40, (better appreciated by reference to Fig. 2) and therefore cannot pass out of section I via the #1 fluid outlet end 16 of the exchanger. The second fluid accordingly flows towards the #1 fluid inlet end 14 until it reaches the interface of segment I and inner tube sheet 40. While the entire radially direc­ted length of radial arm 134 is sealed against tube sheet 40, a portion of the axially remote end of radial arm 134 terminates short of the tube sheet permitting the second fluid to flow around the remote end of arm 134 and back towards the outlet end 14 (Fig. 1) via segment II (Fig. 3) of the chamber 22.

[0048] Similarly, the radial arm of baffle 78 terminates short of tube sheet 42, permitting the second fluid to pass into section III and flow towards the inlet end 14 (Fig. 1). From section III, the second fluid similarly flows through section IV and V egressing from the chamber 22 via outlet 20 at the completion of its pass through section V.

[0049] One manner for terminating the end of the appropriate shown in Fig. 2B, wherein a generally "C" shaped notch 210 co­operates with the tube sheet to form a conduit between ad­jacent segment, while the remaining radial lengths of the arms seal against the tube sheet.

[0050] Fig. 3 displays a "dot" and "cross" symbol in a representa­tive tube 75 of each nest to indicate the flow direction of first fluid in the respective segment. A "dot" indicates flow out of the plane of the page, while a "cross" indi­cates a flow into the plane. Similarly, the flow direction of the second fluid is shown by a like symbol in each segment exterior to the tube 75 therein.

[0051] As evident from Fig. 3, the first and second fluids flow in opposite directions in each of the sections I-V. As is also evident from Fig. 3, the first fluid will be at one temperature extreme (e.g., coldest) in section V, and pro­gressively hotter (to follow the example) in each succes­sive section IV-I as it flows through successive segments in a clockwise direction. The second fluid, on the other hand, is at its temperature extreme (e.g., hottest) in section I, wherein the first fluid is hottest flows through successive segments in a counter-clockwise direction, and exits from section V, at its coldest, where the first liquid is also at its coldest. Thus, the two fluids con­tinue to exchange heat undirectionally throughout their counterflow in the heat exchanger.

[0052] To minimize the risk of temperature-induced stress in the shell resulting from temperature differences between each of the sections I-V, a thin circulating layer of second fluid is provided in the annular, axially extending space 145 between the circumferential arms of the baffle assem­bly and the inner circumferential wall of chamber 22. The space 145 is, as previously mentioned, provided by legs 76a, 78a, 80a, 82a and 84a which support the baffle assem­bly radially inward from the chamber 22 wall. As also previously mentioned, the outlet 20 for the second fluid does not include a sleeve such as sleeve 71 of inlet 18, thereby permitting egressing second fluid to "leak" into, and fill, the space. Accordingly, the temperature of the shell is maintained generally uniform about its circum­ference.

[0053] The second fluid (assumed to be refrigerant for illustra­tive purposes) in segment I is warmest, is successively colder in segments II-V. Accordingly, the second fluid in space 145 radially adjacent to section I will be war­mer, and less dense, than the second fluid in space 145 radially adjacent to section V. Accordingly, the second fluid in space 145 will tend to rise counter-clockwise in Fig. 3. Once the second fluid reaches the 12 o'clock position, gravity causes it to flow downward, completing the loop. Once the space is filled, no additional fluid enters the space, and fluid in the space will slowly circulate counter-clockwise to minimize temperature-induc­ed stresses in the shell.

[0054] Assembly of the heat exchanger 10 is completed by posi­tioning the end caps 24, 26 onto the neck flange 44, 46. Bolts 48 are inserted through the apertures 33 in both neck flanges with their heads pointed towards the opposite of the heat exchanger. Nuts 50 are then tightened onto the bolts to secure the end assemblies 14, 16.

[0055] The holes 149 in the pressure flanges 32, 34 are threaded to engage the bolts 48. Accordingly, the removal of nuts 50 permits disassembly of the end caps 24, 26 for visual inspection of the end baffles without breaking the seal between the pressure flanges 32, 34 and respective neck flanges 44, 46. The tubes 75 may accordingly be inspected through apertures 95 without the voiding of the second fluid in chamber 22. This is particularly adavantageous when the second fluid is a refrigerant.

[0056] Should the need arise to replace any of the tubes 75, the end assemblies can be easily disassembled. The expanded tube/bushing combination requiring replacement can simply be axially slid out of the heat exchanger with the O-rings of the bushing 41 permitting the axial sliding movement. A replacement bushing/expanded tube combination can then be axially slid through the inner tube sheet 33, chamber 22, and the bushing 41 refitted to the replaced tube.

[0057] Turning to end assembly 16 (Fig. 8), it will be appreciated that any leakage of second heat transfer fluid through gas­kets associated with the inner tube sheet 42 or the pres­sure flange 34 will be drawn into vent chamber 151 and vent to atmosphere by the same method as end assembly 14.

[0058] Another feature of the described embodiment is directed to the temperature-induced dimensional changes in the tubes 75. In the heat exchanger described herein, higher outlet temperatures of the first fluid have been provided using a five segment chamber with successive counterflowing first and second fluids to increase surface contact time. Because the segments I-V represent different temperature zones within the heat exchanger, the tubes 75 of each segment will expand to a greater or lesser degree than the tubes of the remaining segments.

[0059] Accordingly, the aforedescribed configuration permits each tube 75 to freely expand to the extent required, thereby meeting design codes governing such heat exchangers.

[0060] As appreciated from Fig. 8, the tube ends in end assembly 16 a relatively fixed owing to the securing of bushes 104 into which the tubes have been expanded. Referring to Fig. 4, however, it will be appreciated that the other end of the tube 75 is permitted to "float" axially so that temperature-induced changes in standardized tube length may be accomodated during operation of the heat ex­changer. Specifically, outer skin 96 of tube 75 may slide axially within the O-ring without loss of sealing contact therebetween. Similarly, inner skin 57 may slide axially within the O-ring without loss of sealing contact between the two. Because skin 57 and skin 96 are joined together by metal contact area 122, tube 75 is one tube of a tube within a tube design and skins 57 and 96 move simultaneous­ly.

[0061] Because the sealed region between the two O-rings remains intact, venting is maintained while the tubes are per­mitted to expand. The heat exchanger thereby herein meets the design specification of the ASME pressure vessel codes in the United States, as well as corresponding foreign codes.

[0062] Those skilled in the art will recognize that the foregoing of the preferred embodiment is illustrative in nature and that many modifications and variations are apparent with­out departing from the spirit of the invention. It is accordingly intended that the scope of the invention be defined solely by the appended claims and that claims be given the broadest interpretation possible, consistent with the prior art, so as to include all such modifications and variations and equivalent embodiments.

Claims

1. A heat exchanger comprising:

a) a generally tubular shell (12) extending between axially opposed ends and having first inlet means (54) and first outlet means (62) for respectively permitting the in­gress and egress of a first heat exchange fluid and a second inlet means (18) and a second outlet means (20) for respectively permitting the ingress and egress of a second heat exchange fluid,

b) a pair of end assemblies (14, 16) coupled to the axially opposed ends of the shell (12) to define an internal chamber (22) therein, and

c) a plurality of multi-walled tubes (75) having inner and outer walls (57, 96) and extending axially within the internal chamber (22) between the end assemblies (14, 16) at each end, said end assemblies (14, 16) comprising each

d) a tube sheet (40, 42) having a plurality of axially ex­tending apertures therethrough, each receiving an outer wall (96) of a different multi-walled tube (75), said tube sheet (40, 42) is provided together with further means (210) for establishing a flow path of the second fluid through the internal chamber (22),

e) a center flange (32,34) disposed on a side of the tube sheet (40, 42) opposite the internal chamber (22), said center flange (32, 34) is provided with a plurality of axially extending apertures (95) therethrough, each re­ceiving an inner wall (57) of a different multi-walled tube (75), and

f) means (24, 28; 26, 30) for coupling the first heat ex­changer fluid into the inner walls (57) of at least a plurality of the tube members (75),
characterized in that

g) at least in one end assembly (14) the outer wall (96) and the inner wall (57) of each multi-walled tube (75) are supported by the tube sheet (40) and the center flange (32) with an axially movable relationship, re­spectively,

h) the center flange (32, 34) is disposed in an axially spaced relationship to the tube sheet (40, 42), and

i) sealing means (41, 67, 68, 102, 103; 104) are provided between the tube sheet (40, 42) and the center flange (32, 34) for sealing the outer wall (96) of each tube (75) in an axially movable relationship to the tube sheet (40, 42) and for sealing the inner wall (57) of each tube (75) in an axially movable relationship to the center flange (32, 34).

2. A heat exchanger according to claim 1, characterized in that the means for sealing includes for each multi-wall­ed tube (75) a bushing (41, 104) disposed between the tube sheet (40, 42) and center flange (32, 34) with an internal bore therethrough having a diameter at an end adjacent the tube sheet (40, 42) selected to movably receive the outer wall (96) of the tube (75) in a sealing relationship, the bushing internal bore having a diameter at an end adjacent the center flange (32, 34) that is smaller than the diame­ter at the end adjacent the tube sheet (40, 42) and select­ed to movably receive the inner wall (57) of the tube (75) in a sealing relationship.

3. A heat exchanger according to claim 2, characterized in that the means for sealing includes for each bushing (41, 104) a first seal (103) slideably sealing the smaller diameter bore to an inner tube wall (57) passing there­through and a second seal (102) slideably sealing the lar­ger diameter bore to an outer tube wall (96) extending partway therethrough.

4. A heat exchanger according to claim 3, characterized in that the first and second seals (103, 102) being O-ring seals.

5. A heat exchanger according to claim 2, 3, or 4, characterized in that the means for sealing including means (68) for sealing each bushing (41, 104) against the tube sheet (40, 42) at an end adjacent the tube sheet (40, 42) and means (67) for sealing each bushing (41, 104) against the center flange (32, 34) at an end adjacent the center flange (32, 34).

6. A heat exchanger according to claim 2, 3 or 4, characterized by a vent chamber (45, 151) defined between the tube sheet (40, 42) and center flange (32, 34), means (47) for providing a fluid flow path between the vent cham­ber (45) and the exterior of the heat exchanger (10), and a radial bore (111) extending through each bushing (41, 104) at a location axially positioned between a transition from the larger diameter bore to the smaller diameter bore and the end of the outer tube wall (96) extending partway through the larger diameter bore.

7. A heat exchanger according to claim 1, characterized in that the pair of end assemblies (1, 16) defines the in­ternal chamber (22) with an intermediate region and two nonintermediate end regions (45, 151) disposed on opposite sides of the intermediate region.

8. A heat exchanger according to claim 1 or 2, charac­terized in that the tube members (75) each include an inner tube (57) having a wall of uniform thickness and a spiral groove formed therein and an outer tube (96) disposed con­centrically about the inner tube (57) and having a uniform­ly thick wall with a spiral groove formed therein which mates with the spiral groove of the inner tube (57) such that an inner surface of the outer tube wall engages an outer surface of the inner tube wall along the mating grooves of the inner and outer tubes (57, 96).

9. A heat exchanger according to claim 8, characterized in that the inner and outer tubes (57, 96) define a spi­rally extending cavity (110) therebetween and between adja­cent spiral groove contact areas, the spiral in the inner and outer tubes (57, 96) having a width of substantially 3,1 mm, a depth of substantially 2,4 mm and a pitch of sub­stantially 14,3 mm.

10. A heat exchanger according to one of the claims 7 to 9, characterized in that the nonintermediate end regions (45, 151) communicate via the tube members (75).

11. A heat exchanger according to one of the claims 2 to 10, characterized by the sealing being achieved at one end of the tube members (75) by expanding the walls of the multi-walled tube members (75) into the bore of the bushing (104) and gaskets on both sides of the bushing wall and at the other end by the provision of tappered sealing rings.

Drawing