US3420297A

US3420297A - Heat exchanger tube support and spacing structure

Info

Publication number: US3420297A
Application number: US633602A
Authority: US
Inventors: Nicholas D Romanos
Original assignee: Combustion Engineering Inc
Current assignee: Combustion Engineering Inc
Priority date: 1967-04-25
Filing date: 1967-04-25
Publication date: 1969-01-07
Anticipated expiration: 1986-01-07
Also published as: CH489745A; GB1189951A; FR1576446A; DE1751179A1; DE6609726U

Description

N. D. ROMANOS Jan. 7, 1969 HEAT EXCHANGER TUBE SUPPORT AND SPACING STRUCTURE Filed April 25', 1967 Z of sheet INVENTOR. A//c//o/.As P. EOMANOS Mdm? ,4 TroeNEy Jan. 7, 1969 N. D. RoMANos HEAT EXCHANGER TUBE SUPPORT AND SPACING STRUCTURE Filed April 25, 1967 sheet 3 ors INVENTOR. A//cf/a/.As Q QOMANQS ArrozA/EY United State-s Patent O 4 Claims Int. Cl. F2811 1/04 ABSTRACT F THE DISCLOSURE A tube support structure for positively spacing and providing anti-vibration support for heat exchanger tubes arranged in a tube bundle. Tube spa-cer struts are disposed in two, axially spaced and angularly related layers extending between adjacent rows of tubes. The tube spacer strut layers are supported in axially spaced relation by means of strut support beams that are arranged in a grid-like fashion on periodic spacing through the plane of support, thereby resulting in a less expensive tube support structure that provides an increase in available fluid ow area through the plane of support.

Background of the invention In heat exchangers of the shell and tube type it is customary to arrange the tubes, which are long, thin-Walled members, in closely spaced relation in the form of a tube bundle. Axial support of the tube bundle is normally obtained by attaching the ends of the tubes to a tube sheet. In many applications the fluid velocities present in the primary fiuid, lusually conducted by the tubes, and the secondary fiuid, in which the tube bundle is immersed, gave rise to a significant amount of vibration that can be potentially dangerous to heat exchanger operation in that it can be the cause of tube failure. Vibrations within the apparatus can also occur as a result of external shock loading. In such applications means must be employed to laterally support the tubes so as to reduce the eitects of these vibrations. Such means have commonly taken the form of spacing devices which po-sitively separate adjacent tubes in the tube bundle such that they cannot contact each other as a result of the vibration present in the heat exchanger.

Several structural arrangements have been proposed to perform this function. One type involves a plurality of apertured plates which are axially spaced within the tube bundle extending laterally thereof. The plates contain one of these groups of apertures through which the tubes of the tube bundle extend and another group which permits axial fiow of secondary fluid. A second type of tube support employs a plurality of relatively thin spacer bars that extend between adjacent rows of tubes. The bars are disposed in two groups which intersect one another and are connected at their intersections so as to form a gridlike structure. This type of tube support is commonly referred to as an egg crate support.

Each lof these types of lateral tube support arrangements suffers from certain manifest disadvantages. In both arrangements the amount of available fiow area through the plane of support is considerably reduced such that high pressure losses are experienced in the secondary fluid fiowing through the heat exchanger. Moreover, the cost of constructing each of these types of tube supports is relatively expensive. The apertured plate form of support requires the provision of several thousand apertures either by drilling or stamping to accommodate the large number of tubes present in tube bundles employed for high capacity heat exchangers and another several thousand drilled or stamped apertures to accommodate secondary Huid flow through the support. The egg crate type' of support, while providing somewhat more available flow area through the plane of support than does the apertured plate arrangement, nonetheless creates creates a certain amount of pressure loss in the secondary fluid flowing through t-he support. This form of support s also expensive due to the fact that milled slotsl must be provided in all the spacer bars so that the bars of each lgroup can be mutually connected at their points of intersection.

Summary of the invention A principal object of the present invention is to provide inexpensive means for positively spacing each of the tubes in a tube bundle in a manner that will lminimize the effect of system Vibration on the tubes, yet, at the same time, will reduce the amount of pressure loss suffered by the secondary fluid in flowing through the plane of support. This objective is obtained by employing a grid-like structure formed of two groups of strut support beams that are interconnected at their intersections in conventional egg crate fashion but which are disposed on periodic spacing through the tube bundle instead of between each adjacent tube row as is presently the convention. These beams are slotted on one edge, one group being slotted along its top edge and the other along its bottom edge so as to receive two groups of tube spacer struts which extend through the spaces Ibetween the intermediate tube rows and which are axially spaced 4from one another by a dimension approximating the height of the strut support beams.

Because the two groups of tube spacer struts are axially spaced from one another on each plane of support, the amount of available Huid flow area through the tube support struts is significantly increased. This results, therefore, in a proportionate reduction in the amount of pressure loss experienced by the secondary fiuid in flowing through the tube support structure. Additionally, fabrication costs of the present arrangement are considerably reduced as compared with those required for a conventional egg crate tube support structure where all of the tube spacer members must be provided with machined slots to permit their interconnection at each intersection. In the present novel apparatus only the strut support `beams need be slotted and, since they are disposed on a periodic spacing between every tenth or so adjacent tube rows, their number represents only a fraction of that which requires machining in a conventional arrangement. The tube spacer struts which comprise the majority of the tube spacer members in the arrangement can be formed of simple rod or bar stock and require no machining. Thus the amount of total machining, and thereby the cost re'- quired to fabricate the structure, is materially reduced.

Description of the drawings FIGURE 5 is a section taken along line `5--5 of FIG- URE 2.

Description of the preferred embodiment Referring to the drawings there is shown in FIGURE 1 a heat exchanger 10 in the form of a substantially con'- ventional shell and tube type vapor generator-embodying the invention. The heat exchanger 10 comprises averti',- cally arranged shell 12 defining an evaporation Vchamber 14 and a vapor dome 16. In the evaporation chamber 14 is located a tube bundle 18 comprising a plurality of U-shaped tubes 20. The lower end of the tube bundle 18 is vertically supported by means of a tube sheet 22 wherein tube seats 24 are provided to receive the ends of the tubes 20 and to place them in fluid communication with the inlet and

outlet compartments

26 and 28, respectively, of the primary lluid manifold section 30 of the vapor generator. The tube bundle 18 includes a plurality of long, closely spaced U-tubes 20 which are disposed in lparallel rows with their arcuately-formed end portions 32 concentrically arranged, so that the innermost end portions are of relatively small radius and the outermost end portions are lof relatively large radius, with the remaining intermediate end portions being of progressively graduated radii. Since the tube bundle 18 conforms to the cylindrical shape of the evaporation chamber 14, more tubes 20 are provided in the central tube rows and the rows of tubes radially removed from the central rows have a gradually decreasing number of tubes. The disposition of the tubes in this manner leads to a regular tube pattern within the tube bundle comprising the tube rows and intermediate intersecting lanes or spaces. The angles at which the lanes intersect is determined by the distance between tubes and the tubular pitch.

Surrounding the periphery of the tube bundle 18 is a generally cylindrical baffle member 34 that is concentrically spaced from the wall of the shell 12 to form, on its interior, the evaporation chamber- 14 and, about its exterior, an `annular fluid passage 36. As shown in FIGURE 1 the bottom end of the baille 34 is vertically spaced from the tube sheet 22 in order to establish fluid communication between the passage 36 and the evaporation chamber 14. Thus, secondary liquid admitted to the vapor generator by an appropriate nozzle (not shown) communicating with the interior of the shell 12. is caused to flow down the annular passage 36 and thence to the evaporation chamber 14 where it forms a body of liquid therein that immerses the tube bundle 18.

In operation, when hot primary fluid is passed through Y the tubes 20 of the tube bundle 18 by circulation of the fluid through the inlet and

outlet compartments

26 and 28 of the primary fluid manifold 31 and secondary liquid is introduced to the evaporation chamber 14 from the feedwater inlet nozzle a transfer of heat is effected from the primary lluid to the secondary liquid. This transfer to heat results in the transformation of some of the liquid to vapor which rises from the evaporation chamber 14 to the vapor dome 16 and is removed therefrom by appropriate means (not shown). The transfer of heat from the primary fluid to the secondary liquid also creates, by means of thermal siphonic action, a circulation of secondary liquid through the liquid body. Flow of the more dense, cooler secondary liquid occurs in a downward direction through the annular passage 36 and, of the heated, less dense liquid upwardly through the evaporation chamber 14.

The flow of primary fluid through the tubes 20 and the circulation of secondary liquid through the vessel is at a sufllciently high velocity as to have the tendency to create vibrations within the unit. Vibrations may also occur as a result of external shock loading of the unit which, together with the internal vibrations of the system, have a potentially deleterious effect on the tubes. Therefore, in order to prevent or alleviate the adverse effects of these vi-brations on the tubes 20 a number of lateral support structures indicated as 40 in FIGURE l are positioned within the heat exchanger at axially spaced positions therealong.

According to the invention each of the support structures 40 comprises an annular frame that embraces the periphery of the tube bundle 18, being formed by a pair of axially spaced rings 42. The rings 42 attach two groups of structural members indicated as

strut support beams

44a and 44b which are straight, elongated bars disposed laterally between opposite portions of the rings 42 and attached at their ends as by means of welding. The

beams

44a and 44b are periodically spaced and arranged so as to extend on edge along lanes defined between adjacent tube rows through the bundle. Disposition of the beams between every tenth or twelfth tube row has been found to -be adequate in most cases, but this of course may vary according to the size of the tubes employed in the tube bundle and the amount of vibration experienced within the heat exchanger. As shown, the beams 44a of one group cross those 44b of the other group at an angle determined by the arrangement of tubes 20` within the tube bundle 18 so as to form a grid-like structure.

All of the

strut support beams

44a and 44b are identically formed as shown in FIGURE 4 with two sets of

slots

46 and 48 cut into one side edge. Slots 46 are cut to a depth approximately midway through the beams and are spaced apart a distance equal to that corresponding to the number of tube rows between the beams in the arrangement illustrated. These slots 46 function to effect locking interconnection of

beams

44a and 44b at their intersections. Slots 48, on the other hand, are adapted to mount a number of tube support struts 50 and are therefore cut only to the depth necessary to secure these struts. The slots are disposed on a spacing that corresponds to the lateral spacing between adjacent tube rows in the tube bundle 18.

In fabricating the tube support structure the beams 44a are arranged with the

slots

46 and 48 disposed along the upper edge and the beams 44b with the comparable slots disposed along their lower edge. The slots 46 in the respective beams are arranged so as to oppose one another and each beam is then secured by forcing it into the slots 46 in the other, thereby resulting in a grid-like structure wherein the upper side edge of the beams in one group and those along the lower edge of the other group are slotted. Thereafter, tube support struts 50 which are also arranged in two groups, indicated as 50a and 50b, are mounted in the edges of the respective strut support beams in the slots 48. The struts 50 may be formed of straight bars having a lateral dimension which corresponds to that of the spacing between adjacent tube rows. As shown in FIGURE 3 of the drawings, the struts 50a extend parallel to the strut support beams 44b and are mounted in slots 48 on the upper edge of the beams 44a. The struts 50h extend parallel to the beams 44a and are mounted in slots 48 on the lower edge of the beams 44b. The assembly is completed by attaching the rings 42 to the ends of the beams 44 and struts 50 as by means of welding. The rings 42 are axially spaced, therefore, by means of the ends of the strut support beams 44. The struts 50a are welded to the underside edge of the upper ring 42 while the struts 5011 are attached to the upper side edge of the lower ring.

With reference to FIGURES l and 5 of the drawing, each of the tube support structures 40 can be mounted in axially spaced locations along the length of the tube bundle by appropriate attachment to the inner surface of the annular baffle 34. According to the preferred embodiment such attachment is obtained by providing bracket members 52 weldedly or otherwise secured to the baille 34 and adapted to vertically support each of the support structures 40 by engaging the lower ring 42.

By providing anti-vibration tube support apparatus according to the present novel arrangement several particularly advantageous results are obtained. First, because the tube spacer struts and the strut support beams are formed with a lateral dimension that corresponds to the spacing between adjacent rows of tubes the tubes are positively spaced from one another and thereby rendered less affected by vibrations that occur within the heat exchanger. Secondly, because the majority of the tube spacing members are constructed of struts formed from simple bar stock and require no machining, the only machining required is that necessary to provide slots in the strut support beams which comprise only about $40 of the tube spacing members. This, therefore, results in a proportionate reduction in the cost of machining required to fabricate the apparatus. Thirdly, because the tube support struts are arranged in groups that are axially spaced from one another and therefore do not intersect at the plane of support, there is provided approximately 30% more ilow area through the tube suport structure at each plane of support. This increase in available llow area results in =a proportionate reduction in the amount of pressure loss experienced by the secondary liquid in flowing through each tube support structure.

It will be understood that various changes in the details, materials and arrangements of parts which have been herein described and illustrated in order to explain the nature of the invention, may be made by those skilled in the =art Within the principle and scope of the invention as expressed in the appended claims.

What is claimed is:

1. Anti-vibration support aparatus for positively spacing a plurality of tubes arranged in a tube bundle, said tubes extending parallel to the axis of said tube bundle and being disposed in a regular pattern of tube rows spaced by sets of intersecting lanes comprising:

(a) means forming a frame embracing the periphery of said tube bundle;

(b) a plurality of spacer struts extending along lanes 'between adjacent tube rows and having their ends attached to opposite portions of said frame, said spacer struts being arranged in a pair of axially spaced, angularly disposed layers of parallel struts, the struts of one of said layers extending through one set of lanes and the struts of said other layer extending through said intersecting lanes; and

(c) means for supporting said spacer strut layers in axially spaced relation, said means including:

(i) a plurality of strut support beams arranged in a pair of angularly related groups 0f parallel beams, the beams of one group extending along periodically spaced lanes in one of said sets of lanes and the beams in said other group extending along periodically spaced lanes in said set of intersecting lanes;

(ii) means for attaching the ends of said beams to opposite portions of said frame; and

(iii) means on the beam of each group for mounting the struts of the respective spacer strut layers.

2. Apparatus as recited in claim 1 including means for connecting said groups of beams in intersecting relation.

3. Apparatus as recited in claim 2 wherein all of said beams are identically formed and including:

(a) a -rst set of slots formed along one edge thereof for mounting said tube spacer struts;

(b) and a second set of slots formed along one edge thereof for connecting said groups of beams in intersecting relation.

4. Apparatus as recited in claim 3 wherein said rst and second sets of slots are formed on the same edge of said beams.

References Cited UNITED STATES PATENTS 1,882,474 10/ 1932 Black 165-162 1,946,234 2/ 1934 Price 165-162 1,967,961 7/ 1934 Metten 165--162 FOREIGN PATENTS 878,232 9/ 1961 Great Britain. 962,011 6/ 1964 Great Britain.

35 ROBERT A. -OLEARY, Primary Examiner.

MANUEL A. ANTONAKAS, Assistant Examiner.