US3450198A

US3450198A - Heat exchanger

Info

Publication number: US3450198A
Application number: US532721A
Authority: US
Inventors: Alfred Brunner
Original assignee: Sulzer AG
Current assignee: Sulzer AG
Priority date: 1965-03-12
Filing date: 1966-03-08
Publication date: 1969-06-17
Anticipated expiration: 1986-06-17
Also published as: CH434501A; GB1146012A; DE1501618A1; NL6602222A; BE677707A; DE1501618C3; NL130632C; DE1501618B2

Description

Jime17,1969 I NB-RUNNER 3,450,198

HEAT EXCHANGER.

Filed March a, 1966 Sheet of 2 ALFRED BRUNNER W ZATTO EVS A. BRUNNER HEAT EXCHANGER June 17, 1969 Sheet 3 of2 Filed March 8, 1966 Inventor: AL FRED BRUNNEF? AT'T'QR EYS "United States Patent 3,450,198 HEAT EXCHANGER Alfred Brunner, Winterthur, Switzerland, assignor to Sulzer Brothers, Limited, Winterthur, Switzerland, a corporation of Switzerland Filed Mar. 8, 1966, Ser. No. 532,721 Claims priority, application Switzerland, Mar. 12, 1965,

3,499 Int. Cl. F28f 27/02 U.S. Cl. 165-101 9 Claims ABSTRACT OF THE DISCLOSURE This invention relates to a heat exchanger. More particularly, this invention relates to a heat exchanger for a nuclear reactor. Still more particularly, this invention relates to a heat exchanger of composite structure which provides a uniform pressure pattern to a medium flowing therethrough.

Heretofore, the heat exchangers of composite structure have been used in nuclear reactors for absorbing the heat carried by the reactor coolant. These heat exchangers have been comprised of a plurality of parallel connected heat exchange units having a heat absorbing medium flowing therein and have been arranged in a casing so that the reactor coolant flows directly through the heat exchanger casing over the heat exchange units.

Since the coolant usually undergoes a considerable pressure drop in passing through the heat exchanger, considerations of heat expansion make it essential for the units to be disposed in the heat exchanger in spaced relation. As a consequence, the lateral boundary walls of the units have had to be strengthened.

In order to provide a solution to the problem created by pressure drops, it has been suggested that the heat exchanger units which may be of any polygonal shape be erected in a plurality of open-ended containers having closed walls for disposition on stilts, a support lattice or a grating so that the containers are arranged alongside each other in situ with the gaps between each pair of adjacent containers bridged by sealing means at top and bottom. However, when a considerable pressure drop occurs along the coolant flow path through these heat exchangers, a positive pressure acts on the container side walls at the sealed ends which is either internal or external to the walls depending on the end of the container involved. Thus, the lateral walls must be strengthened. This requires not only extra material but also extra space since the walls have generally been made of corrugated plates.

Accordingly, it is an object of this invention to provide a heat exchanger having a plurality of spaced heat exchanger units wherein the pressure patterns in the spaces between the units is substantially the same as the pressure patterns within the units.

It is another object of this invention to provide a heat exchanger having a plurality of spaced heat exchanger units with throttling means in the spaces between the units.

It is another object of this invention to provide a heat exchanger having a plurality of spaced heat exchanger units with vertically spaced throttling plates in the spaces between the units.

It is another object of this invention to provide a plurality of spaced heat exchanger units of a heat exchanger with perforated walls in communication with each other.

Generally, this invention provides a heat exchanger comprising a plurality of open-ended spaced heat exchanger units for absorbing heat from a flow of coolant passingtherethrough with a throttling means disposed in the spaces between adjacent heat exchanger units for throttling the flow of coolant through the spaces. The throttling means includes a plurality of movably mounted spaced throttling elements which are supported on the wall of one heat exchanger unit and which bear against the wall of an adjacent heat exchanger unit at different levels.

The invention avoids any unbalanced pressure loading on the exterior walls of the units by substantially equalizing the pressures on opposite sides of the exterior walls. Further, the invention allows adjacent heat exchanger units, assuming they are of square shape, to have two opposite walls formed of i mperforate plates or sheets while the other two walls are formed of spaced apart plate strips so as to form perforated walls. In such a modification there is a direct pressure equalization between the interior of the units and the spaces between adjacent units.

Additionally, in the latter case, the invention provides some temperature equalization between the coolant flowing through the spaces between adjacent units and the coolant flowing in the units. The degree of temperature equalization can be improved by staggering the apertures in the exterior walls of adjacent units relative to each other between adjacent throttling elements so that a flow of coolant can be transversely directed from between the units into the units. The transverse flow, however, is substantially smaller than the flow of coolant in the units.

According to a further modification of the invention, the heat exchanger units are vertically disposed to each other and each is provided with tu-be bunches for the flow of heat absorbing medium therethrough which are disposed in a scaffold-like structure having longitudinal and transverse struts. The transverse struts of adjacent uni-ts are interconnected in a number of stages or tiers by the throttling elements and the longitudinal struts are aligned in parallel relation to the direction of flow of coolant over the tubes.

In like manner, the outside units of the heat exchanger are sealed or throttled with respect to the walls of the casing in which the heat exchanger is mounted.

The throttling elements comprise a sheet metal strip which is mounted on the wall of one unit at a level below the point of contact with the adjacent unit. However, the throttling elements can be formed of bar material of U- or T-shaped sections.

These and other objects and advantages will become more apparent from the following detailed description taken in conjunction with the accompanying drawings in which:

FIG. 1 illustrates a cross-sectional view of a nuclear reactor having a heat exchanger of the invention disposed therein;

FIG. 2 illustrates a partial cross-sectional view of a pan of adjacent heat exchange units of the heat exchanger of FIG. 1;

FIG. 3 illustrates an enlarged cross-sectional view of a throttling means between the heat exchanger units of FIG. 2; and

FIG. 4 illustrates a modification of the invention.

Referring to FIG. 1, a nuclear reactor in which the invention can be utilized includes a reactor core R which is received in a pressure-resistant structure, for instance, of concrete. A large number of heat exchange units E are disposed below the core R in a passage K which in this particular case forms the casing of the heat exchanger according to the invention and cover plates A are provided to seal the space between the elements and the heat exchanger casing wall. In this particular embodiment, those boundary walls of the units which are adjacent the casing wall take the form of strengthened sheetmetal walls while the spaces S between the units are interconnected in stages by throttling elements in the manner clearly apparent from FIG. 2, which will be described hereinafter.

A reactor coolant, e.g. CO flows downwards through the reactor core and passes therefrom to the heat exchanger which is formed by the units E to heat a mediume.g., water, flowing through the units E. In passing through the units E, the coolant is throttled by the tiered throttling elements in the spaces S between the units E. The coolant then passes from the heat exchanger through circulating lines L associated with circulating blowers U upwardly to re-enter the reactor core.

Referring to FIG. 2, the

heat exchanger units

1, 2 of the heat exchanger of FIG. 1, which, for example, are of square cross-section in plan, are open at top and bottom for the flow of reactor coolant therethrough in the direction indicated by arrows M. The tubes 3 through which the heat absorbing medium flows are arranged in bunches of parallel flat-type tube coils so that the coolant flows transversely over the tubes. In order to illustrate the invention with clarity, FIG. 2 shows the tubes 3 disposed in only one of the heat exchanger units but it is to be noted that all the units have similar tubes mounted therein during use. Further, in order to more clearly describe the environment of the invention, the heat exchanger is of a size which measures 2 m. x 2.5 m. x 10 m. and weighs about 100 tons.

The straight parallel portions of the tubes 3 are formed with circular ribs 4 and interconnected by unribbed reversing bends 5 to form flat parallel tube panels through which the heat absorbing medium flows. The units enclose the tube panels with a scaffold-like structure comprising longitudinal and transverse struts or the like, in the form of four bearing longitudinal struts 6 to which

transverse struts

7, 8, embodied as T bearers, are welded in a number of tiers with angle-

member bearers

9, 10 forming a top frame and bottom frame respectively. The tube panels are secured by flanges 11 to the webs 12 of the transverse struts 7, such webs forming support or bearing edges 12. The webs 12 are in turn welded to the arms of the longitudinal struts 6 which are contiguous on the opposite sides. Conveniently, the webs 12 are disposed in staggered relationship to one another on the two opposite sides of each unit.

When the units are assembled, the tube panels are placed in a plane parallel to the plane of the drawing, then introduced between the transverse struts which have the edges 12, and secured by means of the flanges 11 thereto. Only after all the tube panels are secured is the front frame welded on. In the drawing, the visible transverse struts of the rear frames of the units are indicated by reference character 8.

According to the invention, the transverse struts of adjacent units are interconnected at least in a number of stages by throttling elements. In the embodiment shown in FIG. 2, the space 13 between the

units

1 and 2 is bridged in a number of tiers by throttling elements 14, so that the flow of gas around the pipes is severely throttled in the spaces 13. Since the gas flow is intensively throttled not only by the elements 14 in the spaces 13 between adjacent units but also by the edges 12 near the unribbed tube bends, most of the gas flow is confined to the region of the ribbed straight tube portions 3. Consequently, the temperature distribution of the gas at the end of the heat exchanger is uniform over the whole crosssection. Also, there is pressure equalization in the sections between the various units and between the spaces which exist between adjacent units so that there is no unequal stressing of the insides or outsides of the various units.

As above stated, there is also some temperature equalization between the medium flowing around the tubes and the medium flowing through the spaces. Advantageously, to further improve this temperature equalizer, the units can be specially devised to produce, as compared with the lengthwise flow of the heat absorbing medium through the units, a reduced transverse flow between the units and the spaces. One way of producing such a transverse flow is for the transverse struts of adjacent units to be vertically staggered relatively to one another. Alternatively, inclined baffles can be provided near the tube bends between two transverse struts of the same unit, or else the entry cross-section of that proportion of the medium of one unit which flows through the units can be reduced relatively to the entry cross-section of the other, for instance, by appropriately devising the top frame of the angle-member bearers 9, and the outflow cross-section of another unit separated from the first-mentioned unit by a number of units can be reduced similarly in relation to the other outflow cross-sections by similarly devising the angle-member bearers 10 which form the bottom frame.

As above stated, there is noneed for the throttling elements to completely seal off the various space sections from one another; all that is needed is for the flow in the spaces to be intensively throttled. The lengthwise gas flow through the spaces which are e.g. 5 cm, wide, is small as compared with the gas flow through the units; also, the lengthwise gas flow through the spaces is mixed in the various sections with cooled gas from the units so that the gas flow from the spaces has substantially the same temperature as the gas flow in the units. Consequently, there is substantially uniform thermal stressing of the constructional elements.

Referring to FIGS. 2 and 3, the transverse struts 7 as well as the transverse struts S of adjacent units are interconnected by throttling elements 14 which are disposed in all tiers of adjacent units to be bridged; however, arrangements are of course possible wherein only some of the transverse struts of adjacent units are interconnected by throttling elements.

The throttling elements 14 take the form of sheetmetal strips which are borne by continuous projections or troughs 15 contrived on the transverse struts 7 of one unit. The strips 14 are wider, preferably about 1.4 times wider, than the longest space 13 between any two adjacent units and extend at an inclination over the space against the corresponding transverse strut 7 of the adjacent unit under a slight positive gas pressure of the coolant. The chain-dotted lines in FIG. 3 indicate how the strips 14 are secured to the strut 7 by means of numbered retaining stirrups 16, before and after the various units are slid together. Once the units have been slid together, the stirrups 16 are removed allowing the throttling strips 14 to automatically take up the inclined position shown. It the stirrups 16 are numbered, a continuous check can be made during assembly to see that all the strips 14 have definitely been released by the stirrups 1-6.

The sealing lines of the strips 14 extend horizontally between the strips 14 and the two adjacent struts 7; however, arrangements are of course possible wherein the sealing lines extend at an inclination to the vertical. This feature depends mainly upon how the various units are disposed and constructed.

Referring to FIG. 2, the space 13 is sealed at the top by a T-bar 17 and the pressure of the gaseous heat vehicle on the angle-member bearers 9 of two adjacent units. The web of the T-bar 17 in the space centers the bar while the bar flanges bridge the space.

Instead of using flattened strips 14, the transverse struts 7 of adjacent units can be interconnected in stages by U-bars 18 over the space as shown by example in chain-dotted lines in FIG. 2. In this particular embodi' ment, the units are erected on a support grating which is formed from box girders; one such grating 19 being shown in FIG. 2. The heat exchanger is so devised in accordance with the invention that the bearing box girders need not be specially sealed 01f from the units at the bottom of the heat exchanger.

The outer units of the heat exchanger can have, for instance, on their outsides, a strengthened continuous wall (FIG. 1). Preferably, however, the spaces between the outsides of the outer elements and the heat exchanger casing wall is bridged in tiers or stages by sealing elements, similarly to the tiered or stagewise sealing of the spaces between the various units.

Referring to FIG. 4, edges 21 are disposed in tiers or stages or stories on the cylindrical casing wall 20 of the heat exchanger for cooperation with the throttling elements 14 of the adjacent units. Disposed at the top is a T-bar 22 Whose web engages with a centering action in the space between the casing wall and the outer units, while the flanges of the bar bear the one on the top edge 21 of the casing wall and the other on the top bearers 9 of the outer units.

The term throttling element is not to be understood in the present context in the sense of an element eifecting a tight sealing effect; rather, the term is intended to indicate an element which serves to throttle the flow of the medium through the spaces so that the pressure pattern of the medium flowing through the spaces is substantially adapted to the pressure pattern of the medium flowing around the flow passages in the units. This effectively prevents the formation of short-circuit flows along the spaces which short-circuit flows would cause thermodynamic losses impairing eflicient heat exchange and also lead to heavy thermal stressing of the materials used for the constructional elements.

Having thus described the invention it is not intended that it be so limited as changes may be readily made therein without departing from the scope of the invention. Accordingly, it is intended that the subject matter described above and shown in the drawings be taken as illustrative and not in a limiting sense.

What is claimed is:

1. A heat exchanger comprising a plurality of openended heat exchanger units for absorbing heat from a flow of heated coolant passing therethrough, each pair of adjacent heat exchanger units being sealingly connected to each other at the end thereof and being disposed in a freely expandible manner to each other at the opposite end thereof to define a gap therebetween, and throttling means movably mounted across said gap between each said pair of adjacent heat exchanger units for throttling a flow of heated coolant passing through said gap whereby the pressure pattern of the flow of heated coolant passing through each said gap substantially corresponds to the pressure pattern of the flow of heated coolant passing through said heat exchanger units defining said gap.

2. A heat exchanger as set forth in claim 1 wherein 6 said throttling means includes a plurality of vertically spaced throttling elements longitudinally of each said gap.

3. A heat exchanger as set forth in claim 2 wherein said throttling elements comprise a flattened strip supported at one elevation on one of said heat exchanger units and bearing against an adjacent heat exchanger unit at a second elevation.

4. A heat exchanger as set forth in claim 3 wherein said second elevation is disposed above said first elevation.

5. A heat exchanger as set forth in claim 1 wherein each of said heat exchanger units has at least one perforated wall adjacent a perforated wall of an adjacent heat exchanger unit, said throttlingmeans interconnecting the imperforated areas of said adjacent perforated walls in vertical spaced tiers.

6. A heat exchange as set forth in claim 1 wherein the throttled flow of coolant between said adjacent heat exchanger units is directed transversely into the flow of coolant passing through said heat exchanger units.

7. A heat exchanger as set forth in claim 6 wherein said transverse flow of coolant is substantially smaller than said flow of coolant passing through said heat exchanger units.

8. A heat exchanger as set forth in claim 1 wherein each of said heat exchanger units includes a scaifold-like structure comprising longitudinal struts and T-shaped transverse struts connected together and a plurality of tube panels for conveying a heat absorbing medium therethrough enclosed within said scaffold-like structure, each said tube panel being secured to the web of one of said transverse struts, said throttling means interconnecting said transverse struts of each pair of adjacent heat exchanger units.

9. In combination, a plurality of spaced apart openended heat exchanger units for absorbing heat from a flow of heated coolant passing therethrough, and throttling elements movably mounted across the spaces between adjacent heat exchanger units for throttling a flow of heated coolant passing therethrough whereby the pressure pattern of the flow of heated coolant passing between said heat exchanger units substantially corresponds to the pressure pattern of the flow of heated coolant passing through said heat exchanger units.

References Cited UNITED STATES PATENTS 1,571,575 2/1926 Darrah 26320 FOREIGN PATENTS 667,720 6/ 1929 France.

ROBERT A. OLEARY, Primary Examiner. THEOPHIL W. STREULE, Assistant Examiner.

U.S. Cl. X.R. 26320