Note: Descriptions are shown in the official language in which they were submitted.
~1991~43 USD 17 2 8
TUB~ BUNDLE SUPPORT STRUCTURE
BACKGR(:)UND OF THE INVENTIOI~
In heat exchangers employing tubes arranged in a
bundle, it is necessary to-maintain the indi~idual tubes of the
bundle in a parallel, spaced relationship. Such spacing is
important to allow t~e:eVen transfer of heat from fluids flowing
within the tubes to fluids 10wing around the outside of the
tubes. There~are advantages to employing heat exchangers as gas
turbine regenerators, vapor~generators, feed water.heaters, and
the like, in which a first fluid is passed through the tubes.and
a.second fluid is passed in coun~erflow relation to the first .,
fluid,around:the outside of the tubes along the length thereof.
In heat`exchangers of this type, it is also necessary or the
,~support.~tructure maintaining the tubes in spaced, parallel
.,relati~onsh:ip~to:be:open to permit fluid to flow by.
U.S.:Patent No. 3,916,990, issued November 4, 1975 to
'An~hon~ Ruha et al and assigned to the~assignee o~ the present
,~
application, discloses:~a heat exchanger in which a plurali-ty of
:~'.;~elonga-ted tubes~are sup~orted in a spa~ed.parallel relationship
.
2D ~::between two ~.tu~e :~sheets, and in which intermediate support units
are pro~ided~between .the tuhe sheets, the support units comprising
:a pluralL.ty of intercon ected:grid strips formed into a grid
..patternr~or permitting fluid to ~low through. The support units
: :are~prea9sembled in a ~hop by welding the strips together at
: variou~s spaced points'. Such preassembled support units or grids
; are well ~uited or straight lengths o~ tubing, for the tubes can
,be slid through the support uni-ts and into the -tube sheets.during
.,the assembly of t~e heat exchanger.
Known tube-type heat exchangers for the above-mentioned
purposes usually include a bundle of straight tubes extendin~
between inlet and outlet headers at opposite ends of a shell
or casing. A drawback of this type of heat exchanger is the
tendency of some tubes to develop high thermal stresses as a
result of relative expansion compared to other tubes in the
bundle. This is attributable to the lack o~ uniform gas flow
across the width of the bundle. A type of tube heat exchanger
which overcomes this problem includes an elongated bundle of
U-shaped tubes mounted within a large U-shaped shell or casing.
lQ In addition -to avoiding the tube s-tressing mentioned above, the
U-shaped heat exchanger is characterized by a reduction in
required materials and construction costs. For example, fewer
tube-to-tube sheet 30ints are associated with such a heat
exchanger than would be required for a conventional tube-type
heat exchanger of~equivalent capacity. However, one requirement
of such U-tube heat ~xch~ngers~ which does not apply to other
heat eXchangèrs is the need for in~ermedia-te supports in the
area o the U bend ~o prevent vibration of the tubes and to
~maintain the tube bundle in a propeYly spaced orientation.
Furthermore, where the flow outside the tubes is parallel to
the ~ubes, the~parallel flow must be maintained in the U-bend
area as well. This imposes an the int~rmP~;ate U-tube supports
the furt-her requirement of hi~h porosity to enable fluid to flow
through the support structure with very low flow resistance.
The previously mentioned preassembled grids are not
suitable ~or the area o~ the U-bend because the tubes cannot
be slid with respect to preassembled grids where the tubes bend.
Thus, it also required that the intermediate supports in the area
of the U-hend can be built up layer-by-layer as the tube bundle
~0 is buil~ up.
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SUMMARY OF THE INVENTION
Accordingly, the present invention seeks to provide a tube
support structure which is suitable for supporting a bundle of bent
tubes in an evenly spaced rela-tionship in the region of the bends
and to provide a tube support system which lends itself to being
assembled in the tube bundle as the tube bundle is being assembled.
Further, the present invention seeks to provide a support
structure capable of being assembled in place, which is being
porous, so that a heat exchange medium may flow through it and
which may be assen~led in place to accon~odate tube bundles of
various sizes and shapes.
In one broad aspect, the invention pertains to a suppor-t
structure for a bundle of tubes which comprises a plurality of
parallel strips having a plurality of indentations and a plurality
o~ flat sections, the strips being arranged in pairs, with the
indentations in each strip of a pair projecting toward and being
secured to the other strip of the pair, the indentations in each
strip being in alignment with and projecting away from the in-
dentations in the adjacent strip of an adjacent pair of strips.
Fasteners connect the flat sections of each strip of a pair of
strips to flat sections of the adjacent strip of an adjacent pair
of strips to define a support grid for a bundle of tubes.
More particularly, the tube support structure of the present
invention comprises a plurality of elongated, corrugated grid
strips arranged in pairs, stacked, and secured together by fasteners
to maintain the various tubes o a tube bundle in a prearranged,
evenly spaced pattern. The assembled pairs of strips define a
grid or matrix which mainkains the tubes of the bundle in a regular
spaced arrangement and rest~ains them from vibration. The grid
strips of the grid are reinorced in their assembled, stacked
position by key strips which extend in pairs transverse to the grid
strips a~ong opposite sides of the grid strips, the key strips in
each pair being secured to one another at their ends. The tube
bundle ma~ be supported in sections, with the support structure
~r
according to the present invention including a pluralit~ of grids
positioned in alignment with one another and spaced by elonga-ted
keeper bars which extend between adjacent sections in a direction
transverse to both the tube bundle and the key strips. Flanges
are secured to the ends of the keeper bar and are engaged with
the sides of the section to prevent adjacent sections from
shifting with respect to one another. Where one section is
positioned above another section, the keeper bars pr~vide a support
surface for the upper section. Collars are secured to some of the
tubes adjacent the grids and the keeper bars to restrain them
from movement along the tubes.
BRIEF DESCRIPTION OF THE DRAWINGS
Fig. 1 is a perspective view of a U-shaped heat e~changer
well suited to employ the support structure of the present
invention~
Fig. 2 is a cross section along the line 2-2 in Fig. 1,
schematically showing support structures according to the present
invention in position on a tube bundle;
Fig. 3 is an enlarged fragment of the cross section of
Fig. 2;
Fig. 4 is a cross section taken along the line 4-4 of
Yig. 3;
Fig. 5 is an enlarged view of a fragment of the support
structure shown in Fig. 4;
Fig. 6 is a perspective view of two pairs of grid strips
aligned for asse~ly;
Fig~ 7 is a cross section taken along the line 7-7 in
Fig. 4;
Fig. 8 is an enlarged fragment of Fig. 4;
Fig. 9 is a cross section taken along the line 9-9 in
Fig. 8;
Fig. 10 i5 a perspective view of the key strips and
~ .
grid strips shown in Fig. 9; and
Fig. 11 is a perspective view of a portion of a
keeper bar.
DETAILED DESCRIPTION OF THE RREFERRE~ E~BODIME~T
Figs. 1 and 2 illustrate a heat exchanger 10 which
is well suited for employing the support structure o~ the
present invention. The heat exchanger 10 includes an inverted
generally U-shaped housing 12 which is supported at the bottom
by a plurality of feet 14. The housing 12 includes a front wall-
16 (Fig. 2~, a rear wall 18, a pair of side walls 20 (one of
which is shown), a top closure 22, and a pair of intermediate
walls 24 and 26 connected at their upper ends by a horizontal
member 28.
As is shown in Fig. 2, a plurality of elongated
inverted U-shaped tubes 30 is disposed within the housing 12.
Each tube 30 has a first straight upflow portion 32, a U-portion
33 cont~;n;ng bends and a second straight downflow portion 34.
The inlet ends of the first skraight portions 32 are secured in
a tubesheet 36, and the outlet ends o the second straight
portions 34 are secured in a tubesheet 38. An inlet header 40
is welded ~to the underside of the tube sheet 36, and a similar
outlet header 42 is welded to the underside of the tubesheet 38.
A supply pipe 44 is adapted to deliver a first fluid, such as
air~ to the inlet header 40 and an outlet pipe 45 is adapted to
convey the first fluid away from the outlet header 42.
A series o~ preassembled grids 46 are positioned in
intermediate positions along the tubes 30 to keep the tubes 30
evenly spaced within the housing 12 and to dampen vibration of
the tubes which can occur as ~luids pass through and over the
tubes. Because the preassembled grids 46 are -to be positioned
along the straight por-tions 32 and 3~ of the -tubes 30, the tubes
~5-
3~0 can be slid through the preassembled grids 46 into position
for attachment to the tubesheets 36 and 38.
A second fluid, such as a gas, enters the housing 12
through an inlet 48, passes upwardly over the straight downflow
portion 34, across the U-portion 33, then downwardly over the
straight upflow portion 32 and out through a stack 49. Thus, it
is essential that all of the tube support struc~ures in the path
of the second fluid ~e porous to allow the second fluid to flow.
The first fluid flows through the tubes 30 in a direction opposite
1~ to the flow of the second ~luid.
~ Supports arè also needed in the area OL the bends to
prevent vibration of the tubes 30 in that area and to maintain
them in an evenly spaced relationship. The preassembled inter-
mediate grids 46 are not suitable for the bend areas, since the
bends in the tub~s 30 cannQt slide through the grids so that the
ends o~ the tubes are in a position to be secured to the tube-
sheets 36 and 38. ~s is illustrated in Fig. 3, the U-porkion
of the U-shaped heat exchanger 10 includes a plurality of -tube
supports or grids 50 which are assembled near the bends and are
porous to the flow of fluid.
A plurality of keeper bars 52 xests on the top layer of
tubes 30, most of which are shown schematically in Fig. 3, in
~parallel, spaced positions near the bends in the tubes. U-tube
,
heat exchangers;are ~typically of such a size that they are
assembled on their sides, with the U-shaped tubes 30 lying in a
horizontal plane. With the tubes 30 in such an orientation, the
.
height of the tube bundle is typically on the order of 10 feet.
As a result, it is convenient for workers to assemble the bundle
in two 5 foot high sections~ When the lower section of the tube
bundle has been assembled~ the keeper bars 52 are placed across
the top of the section~ lying on the tubes 30. Then, as -the
upper section of the tube bundle is assembled, its weight is
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4~
supported by the keeper bars 52.
Moreover, as is better illustrated in Figs. 4, 8 and
11, flanges 54 and 56 axe welded or otherwise secured to the
ends of the keeper bars 52, from which they e~tend transversely
to the length of the tubes 30, along the sides of the tube
bundle sections. This arrangement maintains the adjacent sections
of the tube bundle in alignment, preventing shifting of the
sections with respect to one another. In addition, it eliminates
any tendency for the layers of tubes 30 near the inter~ace of
the sections to spread out from their evenly spaced arrangement.
Collars 58 are welded or otherwise suitably secured to several of
the tubes 30 on which the keeper bars 52 rest, adjacent to the
edges of the keeper bars 52, in order to prevent the keeper bars
52 ~rom shifting sideways along the length o~ the tubes 30.
Although the keeper bars 52 in the er~odiment o~ the present
invention ~escribed herein are horizontally oriented between two
! adjacent sections of the tube bundle during the assembly, the tu~e
bundle can be arranged in additional sections, with keeper bars
positioned between all of the adjacent sections. Furthexmore, the
keeper bars 52 can also be oriented ~ertically during the assembly
of a tube ~undle which includes sections which are arranged side
by side.
As is schematically illustrated in Fig. 4, two adjacent
grids 50, each supporting a section of a tube bundle, have a
common boundary adjoining the keeper bars 52, one of which is
shown in Fig. 4. The grids 50 `are made of a pluxality o parallel
individual grid strips 60 which lie across the tubes 30 transverse
to the tubes 30 and to the keepex bars 52. In Fig. 4, the grid
strips 60 terminate behind -the keepe~ bar 52, leaving a small
space between the corresponding grid strips ~0 of the adjacent
grids 5Q. The row of tubes 30 o each section closest to the
boundary engage the keeper bar 52 on its opposite sides.
In Fig, 5, a portion of a cross section of a tube
bundle with the grid strips 60 in place is illustrated. Each
grid strip 60 is corrugated, defining a regular series of
deformations or indentations 62 separated by flat sections 63.
Each indentation 62 includes arcuate or curved portions 64 which
are complementary to the outer circum:Eerences of the tubes 30
and a trapezoidal crown portion 66 connecting the curved por-tions
64 and engaging a flat section 63 of an adjacent grid strip 60.
Figs. 5, 6 and 8 clearly show the arrangement of the grid strips
60 in grid strip pairs 68, sometimes called "wiggly pairs", with
the deformations or indentations 62 of each grid strip 60 extend-
ing toward and abutting the flat portions 63 of -cthe o-ther grid
skrip 60 of the pair 68. The top surface of each trapezoidal
crown portion 56 is welded or otherwise secured to the facing
surface of the flat portion 63. The securing of the grid strips
60 into pairs 68 can be done prior to the assembly of the grid
! strips 60 with the tubes 30 to help m;n;mize the time required for
tube bundle assembly. The deformations or indentations 62 in
each grid strip 60 are in alignment with and project away from
the indentations 62 in the adjacent grid strip 60 in the adjacent
pair 68, thereby co~operating to define arcuate openings si2ed
and shaped to receive the tubes 30. The flat sections 63 of the
grid strips 60 of a pair 68 are aligned with and are in abutment
with the flat sect.ions 63 of the adjacent pairs 68. The abutting
- flat sections 63 are held together by fasteners 70 such as
removable spring-loaded steel clips or other suitable connectinc3
means. It is desirable for the asse~bly of the grid 50 in the
tube bundle that the connect.ing means be suitable ~or quickly and
easily connecting the pairs 68 of cJrid strips 60. Two fasteners
70 may be used to secure the grid strip pairs 6~ between each
pair of adjacent.tubes 30, as is illustrated in Fig. 5. However,
as is shown in Fig. 8, where less strength ox rigidl-ty is
required, a single fa,stener 70 can be used between adjacent
pairs of tubes 30. For example, in the embodiment of the
invention described, the lower section of the tube bundle may
require two fasteners 70 between the -tubes 30, since the lower
section must support the weight of the upper section during
assembly. Since the upper section has no such limitation, a
single fastener 70 be-tween the tubes 30 is sufficient.
Fig. 7 shows a fragmentary cross section of a tube
bundle taken along the line 7-7 in Fig. 4 and including -the
boundary between two adjacent bundle sections. The left two
tubes 30 are part of one bundle section and are held together
by the grid strips 60 of one grid 50, while the three tubes 30
on the right side of the figure belong to another bundle section
and are held together by the grid strips 60 of anothèr grid 50.
The grids 50 of the adjacent bundle sections are in alignment
and the grid strips 60 of each grid 50 extend beyond the tubes
30. The keeper bar 52 engages the tube 30 of the adjacent
sections and has a thickness which is greater than twice the
extension of the ~rid strips 60 beyond the tube 30. Thus, the
keeper bars 52 support the adjacent sections with respect to one
another, protect the ends of the grid strips 60 and determine
the amount of space between the tubes 30 of the adjacent sections.
As can be seen from Figs. 4 and 7-10, the grid 50 of
assembled grid strips 60 is given lateral stability by pairs of
key strips 72 positioned along the sides of the grid s-trips 60
transverse to the grid s-trips 60 at selected locations along the
length of the grid strips. The key strips 72 are positioned
transverse to the tubes 3a between adjacent rows of the tubes 30
and are secured by a bridging plate 7~ welded between the key
strips 72 at their ends. ~hus, the key strips 72 keep the grid
strips 60 aligned in their stacked relationship. Additional pipe
collars 52 are secured to selec-ted tubes 30 along -~he sides of
_9~
the grids 50 to prevent the grids 50 fxom shifting laterally
along the lengths of the tubes 30.
~ s is shown in Figs. 9 and 10, reinforcing plates
76 are secured perpendiculaxly between the grid strips 60 in
the pairs 68 which are along the periphery of a grid 50 and
which, therefore, engage the bridging plates 74 of the key
strips 72. The reinforcing plates 76 are positioned in planes
conta; ni ng the bridging plates 74 to add strength to the key
strips 60 which engage the bridging plates and to distribute
the load borne by such peripheral key strips 60 to othex key
strips 60,
Thus, it can be seen that a tube bundle can quickly
be assembled by laying down a plurality of spaced grid strip
pairs 68, laying down a layer of tubes 30 across the pairs 68,
clipping additional pairs 6~ to the previous pairs 68 around
the tubes 30, laying the next l~yer of tubes 30, etc.
i . Although it is a~parent from the foregoing that the
present invention is particularly well suited for application to
tube-type heat exchangers having bends in the tubes, it is under-
stood that the scope of the present invention is not so limited~
but rather extends to other applications. Also, various other
changes and modifications may be made without departing from the
spirlt and scope of the present invention as recited in the
appended claims and their legal equivalents.
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