EP0259895B1

EP0259895B1 - Shell and tube heat exchanger

Info

Publication number: EP0259895B1
Application number: EP19870113723
Authority: EP
Inventors: Kevin Sulzberger
Original assignee: TUI Industries Inc
Current assignee: TUI Industries Inc
Priority date: 1983-03-28
Filing date: 1984-03-27
Publication date: 1990-07-18
Also published as: EP0259895A1; DE3479153D1; CA1264735A; EP0120497B1; EP0120497A3; DE3482777D1; DK168684A; DK168684D0; EP0120497A2

Description

The present invention relates to a heat exchanger as defined in the precharacterizing portion of claim 1.
A heat exchanger of this kind is already known from EP-A 0 052 522. Said heat exchanger comprising

a) a pair of end assemblies having first inlet means and first outlet means, respectively, for permitting the ingress and egress of a first heat exchange fluid,
b) a generally tubular shell extending between the pair of end assemblies with the end assemblies being disposed at axially opposed ends of the shell to define an internal chamber within the shell and between the end assemblies, and having a second inlet means and a second outlet means, respectively, for permitting the ingress and egress of a second heat exchange fluid,
c) a plurality of multi-walled tubes having inner and outer tubes and extending axially within the internal chamber betrween the end assemblies at each end, said end assemblies comprising each:
d) a tube sheet having a plurality of axially extending apertures therethrough, each receiving an outer tube of a different multi-walled tube, said tube sheet being provided with a baffle assembly in the internal chamber establishing a flow path of the second fluid through the internal chamber,
e) a center flange disposed on a side of the tube sheet opposite the internal chamber, said center flange being provided with a plurality of axially extending apertures therethrough, each receiving an inner tube of the different multi-walled tube, and
f) an end assembly arrangement for coupling the first heat exchanger fluid into the inner tubes of at least a plurality of the multi-walled tubes,
g) in at least one end assembly the center flange defining a vent chamber between the center flange and tube sheet which vent chamber is in communication with the space between the inner tube and the outer tube of each of the multi-walled tubes.

Furthermore, it is known from US-A 2 762 611 to seal outer walls of tubes to a tube sheet in an axially movable relationship in order to allow a thermal expansion of the tubes.
It is an object of the present invention to provide a heat exchanger having a better maintainability and simultaneously an improved construction in order to reduce temperature-induced stresses in the connecting parts between the tube sheet, the center flange and the multi-walled tubes and to detect any leakage flow upon failure of one of the tubes.'
The heat exchanger according to the invention is characterized in that

h) at least in one end assembly the outer tube and the inner tube of each multi-walled tube are supported by the tube sheet and the center flange with an axially movable relationship, respectively, and
i) sealing means including a bushing are provided between the tube sheet and the center flange for sealing the outer tube and inner tube of each multi-walled tube in an axially movable relationship to the bushing and for sealing the bushing to the tube sheet and to the center flange, each bushing being provided with a radial bore for allowing communication between said space and said vent chamber.

Further particulars of the invention are claimed in the dependant claims 2 to 11.
The invention is more fully described with reference to the accompanying drawings in which:

Fig. 1 is a side elevation view partially broken of a heat exchanger,
Fig. 2 is an exploded perspective view of the fluid #1 inlet end assembly, the opposed or outlet end assembly being substantially the same,
Fig. 3 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. 4 is an enlarged cross-sectional view of a portion of enhanced surface tubing taken about the indicated section line 5 of Fig. 3, and
Fig. 5 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.

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.
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.
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 Fig. 2, a plurality of heat exchange multi-walled tubes 75 and a chamber-partitioning longitudinally extending baffle assembly 74 are positioned within the chamber 22 to effect a multi-pass, contraflow thermal exhange process, during operation, between the first and second fluids within the chamber 22 and the inner multi-walled tubes 75 thereby facilitating the transfer of heat therebetween.
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 rotationally offset 72° from each other prior to affixation to the shell.
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 2, 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.
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.
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 multi-walled tubes 75.
Fig. 3 is an enlaged longitudinal partial section of the assembled end assembly 14 illustrating, in part, a representative of one of the heat exchange tubes. Fig. 4 is an enlarged sectional view of a portion of expanded surface tubing taken about section line 5 in Fig. 3. Fig 5 is a port section of the assembled end assembly 16 illustrating in part a representative of one of the heat exchange tubes.
As shown in Figs. 3, 4 and 5, the multi-walled tube 75 generally comprises an outer tube 96 and an inner tube 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 tube 96 of the multi-walled tube 75 fractures, the second fluid will enter the spiral cavity 110 and, 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 tube 57 is breached, the first fluid will enter the spiral cavity 110 and will thereafter be vented to atmosphere.
The configuration of multi-walled 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 tube 96 and the inner tube 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.
Next, attention is directed to the assembly procedure, whereby the interrelationship of the various components will be more easily appreciated. With initial references to Fig. 1, the inner tube sheet 42 is first mounted onto the neck flange 46 by. means of locating dowels 70' 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. 2.
The tube sheet 42, which is similar to plate 40 (Fig. 2) includes a pattern of holes sized to accomo- date the outer tubes 96 of the multi-walled tubes 75.
Reference is made to Fig. 5, a fragmentary sectional view of the outlet end of the heat exchanger 10. Each of the multi-walled 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 stopped wall 104a such that the larger internal diameter portion of the bushing engages the outer tube 96 of multi-walled tube 75, while the smaller diameter portion of the bushing engages the inner tube 57 of multi-walled tube 75. A general swaging 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 tubes, with the gap 110 between the inner and outer tubes being sealed against the step 104a of the internal bushing wall.
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.
Next attention is redirected to inlet end assembly 14. Returning to Figs. 1 and 2, 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.
Accordingly, a gasket assembly comprising a tube sheet 40 interjacent two gaskets 68, 69 is mounted onto the flange 44. The tube sheet 40 and gasket 68 include aligned hole patterns corresponding to the layout of tube holes 95 so that the multi-walled 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.
After the gasket 68 has been mounted against the tube sheet 40, a generally annular bushing 41 is placed about each multi-walled tube 75 and slid back against the gasket assembly. The bushing 41 straddles the termination of outer tube 96. As shown in Fig. 3, each bushing 41 includes a pair of 0- rings 102, 103 for forming a tube expansion region 43 communicating with gap 110 in multi-walled tube 75. Into tube expansion region 3 is a hole 111 which connects to gap 110 to allow the tube to vent to atmosphere.
Next, gasket 67 is fitted over the protruding inner tube 57 of multi-walled tube 75. A pressure flange 32 is then correctly orientated 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 adapted to sealingly contact the gaskets 67 and 68 to define 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.
The aforedescribed arrangement is directed towards preventing the contamination of one of the heat exchange fluids by the other. Should the outer tube 96 of a multi-walled 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 multi-walled tube 75 into bushing 104 at that end has sealed that bushing across the gap.
As shown in Fig. 3, 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 multi-walled tube 75 can be replaced before a subsequent fracture in inner tube 57 or other event permits a mixing of the first and second fluids. Similarly, a fracture of the inner tube 57 results in first fluid being restricted to region 43 and escaping via hole 111 and 47.
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 tubes 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 tubes 57 extend into, but do not protrude from the axially outward side of passage 95.
The axially outer face of the pressure flange 32 includes an end baffle arrangement comprising annular portion 28a circumscribing the thorugh-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 end cap 24 via a gasket 29 and to thereby form a series of pressure chambers.
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 end of the heat exchanger. Nuts 50 are then tightened onto the bolts to secure the end assemblies 14, 16.
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 multi-walled tubes 75 may accordingly be inspected through apertures 95 without the voiding of the second fluid in chamber 22. This is particularly advantageous when the second fluid is a refrigerant.
Should the need arise to replace any of the multi-walled 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 0-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.
Turning to end assembly 16 (Fig. 5), 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.
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 represent different temperature zones within the heat exchanger, the multi-walled tubes 75 of each segment will expand to a greater or lesser degree than the tubes of the remaining segments.
Accordingly, the aforedescribed configuration permits each multi-walled tube 75 to freely expand to the extent required, thereby meeting design codes governing such heat exchangers.
As appreciated from Fig. 5, the tube ends in end assembly 16 are relativelly fixed owing to the securing of bushes 104 into which the tubes have been expanded. Referring to Fig. 3, however, it will be appreciated that the other end of the multi-walled 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 tube 96 of multi-walled tube 75 may slide axially within the 0-ring without loss of sealing contact therebetween. Similarly, inner tube 57 may slide axially within the 0-ring without loss of sealing contact between the two. Because tube 57 and tube 96 are joined together by metal contact area 122, multi-walled tube 75 is one tube of a tube within a tube design and tubes 57 and 96 move simultaneously.
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.

Claims

1. A heat exchanger comprising

a) a pair of end assemblies (14, 16) having first inlet means (54) and first outlet means (62) for respectively permitting the ingress and egress of a first heat exchange fluid,

b) a generally tubular shell (12) extending between the pair of end assemblies (14, 16) with the end assemblies (14, 16) being disposed at axially opposed ends of the shell to define an internal chamber (22) within the shell and between the end assemblies (14, 16) and having a second inlet means (18) and a second outlet means (20), respectively, for permitting the ingress and egress of a second heat exchange fluid,

c) a plurality of multi-walled tubes (75) having inner and outer tubes (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 tube (96) of a different multi-walled tube (75), said tube sheet (40, 42) being provided with a baffle assembly (74) in the internal chamber (22) 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) being provided with a plurality of axially extending apertures (95) therethrough, each receiving an inner tube (57) of the different multi-walled tube (75), and

f) an end assembly arrangement (24, 28; 26, 30) for coupling the first heat exchanger fluid into the inner tubes (57) of at least a plurality of the multi-walled tubes (75), .

g) in at least one end assembly (14) the center flange (32) defining a vent chamber (45) between the center flange (32) and tube sheet (40) which vent chamber (45) is in communication with the space between the inner tube (57) and the outer tube (96) of each of the multi-walled tubes (75), characterized in that

h) at least in one end assembly (14) the outer tube (96) and the inner tube (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, and

i) sealing means (41, 67, 68,102,103; 104) including a bushing (41, 104) are provided between the tube sheet (40, 42) and the center flange (32, 34) for sealing the outer tube (96) and inner tube (57) of each multi-walled tube (75) in an axially movable relationship to the bushing (41) and for sealing the bushing (41) to the tube sheet (40, 42) and to the center flange (32, 34), each bushing (41, 104) being provided with a radial bore (111) for allowing communication between said space and said vent chamber (45).

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

3. A heat exchanger according to claim 1 and 2, characterized in that the sealing means includes for each bushing (41, 104) a first seal (103) slideably sealing the smaller diameter bore to the inner tube (57) passing therethrough and a second seal (102) slideably sealing the larger diameter bore to the outer tube (96) extending partway therethrough.

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

5. A heat exchanger according to claim 2, 3 or 4, characterized in that the sealing means includes 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 means (47) for providing a fluid flow path between the vent chamber (45) and the exterior of the heat exchanger (10), and in that said radial bore (111) in each bushing (41, 104) is arranged 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 (96) extending partway through the larger diameter bore.

7. A heat exchanger according to claim 1, characterized in that the pair of end assemblies (14, 16) defines the internal chamber (22) as 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 multi-walled tubes (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 (96) engages an outer surface of the inner tube (57) 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 having 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 multi-walled tubes (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 multi-walled tubes (75) by expanding the walls of the multi-walled tubes (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 tapered sealing rings.