US3863711A

US3863711A - Method and apparatus for maintaining substantial uniformity in the temperature of a heat-exchanging fluid

Info

Publication number: US3863711A
Application number: US330623A
Authority: US
Inventors: Georg Beckmann; Paul Viktor Gilli; Josef Lippitsch
Original assignee: Waagner Biro AG
Current assignee: Waagner Biro AG
Priority date: 1972-02-09
Filing date: 1973-02-08
Publication date: 1975-02-04
Anticipated expiration: 1992-02-04
Also published as: GB1410425A; CH555526A; DE2304841A1; AT317258B; FR2171765A5; DE2304841B2

Abstract

A heat exchanger and method for operating the same according to which the temperature of a heat-exchanging fluid is maintained substantially uniform. The heat exchanger has two groups of tubes in which an inner heat-exchanging fluid flows while an outer heat-exchanging fluid flows across the exterior of these tubes. The groups of tubes form first and second groups with the outer fluid flowing first across the first group and then across the second group, to form an entering stream of outer fluid flowing across the first group and an exiting stream of outer fluid flowing across the second group of tubes. Each of these streams is composed of first and second stream portions which have predetermined relationships with respect to the heat exchanger axis, and through a suitable baffle structure the first portion of the entering stream is deflected to form the second portion of the exiting stream while the second portion of the entering stream is deflected to form the first portion of the exiting stream, so that in this way substantial uniformity is maintained in the temperature of the exiting stream.

Description

United States Patent [191 Beckmann et a1.

[ METHOD AND APPARATUS FOR MAINTAINING SUBSTANTIAL UNIFORMITY IN THE TEMPERATURE OF A HEAT-EXCHANGING FLUID [75] Inventors: Georg Beckmann; Paul Viktor Gilli,

both of Vienna; Josef Lippitsch, Graz, all of Austria [73] Assignee: Waagner- Biro Aktiengesellschaft, Vienna, Austria 22 Filed: Feb. 8, 1973 21 Appl. No.: 330,623

[30] Foreign Application Priority Data Feb. 9, 1972 Austria A 1027/72 [52] US. Cl. 165/145, 161/163 [51] Int. Cl F28f 9/22 [58] Field of Search ..165/140,145,l,140,141, 165/163, 159

1 51 Feb.4,l975

Primary Examiner-Charles Sukalo Attorney, Agent, or Firm-Steinberg & Blake [57] ABSTRACT A heat exchanger and method for operating the same according to which the temperature of a heatexchanging fluid is maintained substantially uniform. The heat exchanger has two groups of tubes in which an inner heat-exchanging fluid flows while an outer heat-exchanging fluid flows across the exterior of these tubes. The groups of tubes form first and second groups with the outer fluid flowing first across the first group and then across the second group, to form an entering stream of outer fluid flowing across'the first group and an exiting stream of outer fluid flowing across the second group of tubes. Each of these streams is composed of first and second stream portions which have predetermined relationships with respect to the heat exchanger axis, and through a suitable baffle structure the first portion of the entering stream is deflected to form the second portion of the exiting stream while the second portion of the entering stream isdeflected to form the first portion of the exiti ng stream, so that this wail substantial uniformity is maintained in the temperature of the exiting stream.

12 Claims, 14 Drawing Figures PATENTEU FEB 4197s SHEET 1 [IF 3 METHOD AND APPARATUS FOR MAINTAINING SUBSTANTIAL UNIFORMITY IN THE TEMPERATURE OF A HEAT-EXCHANGING FLUID BACKGROUND or THE lNVENTION The present invention relates to heat exchangers.

In particular, the present invention relates to heat exchangers in which an inner heat-exchanging fluid flows along the interior of successive groups of tubes while an outer heat-exchanging fluid flows across the exterior of these tubes, with the inner fluid flowing only once through the inner tubes. The heat exchangers of this type are particularly suitable for nuclear power plants.

With heat exchangers of this type each group of tubes has a considerable variation in the temperature of the inner fluid which flows within the tubes, so that'as a result the outer fluid forms a stream in which the temper ature is not uniform. This-lackof uniformity in the temperature of the outer stream of fluid is highly undesirable. ln order to alleviate this problem it has already been proposed to arrange the heat exchanger tubes in such a way that the tubes of one group cross each other before forming the tubes of a second group, so that through this expedient the positions occupied by the tubes of the different groups are reversed with respect to each other in order to attempt to achieve a uniformity in the temperature of the heated outer fluid. However, this type of construction is exceedingly complex because of the complex paths along which the tubes must extend. This type of construction requires a very large space and involves high costs in assembly of the components, in addition to resulting in an undesirably high pressure loss, so that such arrangements have proved to be uneconomical particularly with heat exchangers which have but one pressure vessel. It is also known to situate between two groups of tubes a throttling device or a plate which is punched wtih openings passing therethrough, in order to alleviate the above problem. This type of construction, however, has the great disadvantage of creating an undesirable loss of pressure in the outer fluid which flows across the exterior of the tubes without avoiding an undesirable formation of bodies ofthe outer fluid which do not mix with each other. Thus, the outer marginal currents of the outer fluid and the central currents thereof do not mix with each other with these known arrangements.

A further disadvantage encountered with conventional apparatus andmethod of the above type is that static or aperiodic instabilities are encountered, which is to say that with the heat exchanger tubes arranged in parallel large differences in the cross section of fluid flow and in temperatures at different parts of the fluids occur at individual groups of tubes, particularly because of the formation of bodies of the outer fluid which do not mix with the remainder of the outer fluid, and these factors create a hazardous operation which renders the operating conditions unsafe.

SUMMARY OF THE INVENTION A It is accordingly a primary object of the present ining heat-exchanging fluid without resorting to complex tubular structures.

Furthermore, it is an object of the present invention to provide a heat exchanger apparatus and a method of operation according to which it is possible to achieve the desired uniformity in the temperature of the discharging fluid without creating any substantial loss in pressure during flow of the fluid through the heat exchanger.

Also it is an object of the present invention to provide a method and apparatus of the above type which can be used either with radial or with axial heat exchangers.

' In addition it is an object of the present invention to provide a method and apparatus of the above type which require only simple inexpensive changes to be made in conventional heat exchangers.

In accordance with the method and apparatus of the present invention the heat exchanger is composed of at least two groups of tubes which have a predetermined relationship with respect to each other and the axis of the heat exchanger. An inner heat-exchanging fluid flows along the interior of these tubes while an outer heat-exchanging fluid flows across the exterior of these tubes. The outer fluid which flows across the exterior of the tubes includes an entering stream which contacts the first group of tubes and an exiting stream which contacts the second group of tubes, this entering stream being composed of first and second portions which have respectively predetermined relationships with respect to the heat exchanger axis while the exiting stream is also composed of first and second portions which have the same predetermined relationships with the heat exchanger axis as the first and second portions of the entering stream, respectively. According to the method and apparatus of the present invention the first and second portions of the entering stream are deflected before they reach the second group of tubes in such a way that the first portion of the entering stream forms the second portion of the exiting stream and the second portion of the entering stream forms the first portion of the exiting stream, so that through this interchange of the relationships between the stream portions the desired uniformity is achieved in an exceedingly simple yet highly effective manner.

Thus, the apparatus of the invention will include suitable baffles situated between the groups of tubes for deflecting the stream of outer fluid to achieve the above results. These baffles may be arranged so as to divide the stream of outer fluid into a plurality of subsidiary streams which are individually treated to achieve the above objects. Thus, where the two groups of tubes are arranged along a common axis of the heat exchanger within an outer shell which forms a means for directing theexterior gas across these tubes, the part of the gas which is situated adjacent the axis at the first group of tubes is deflected to flow along the shell at the second group of tubes while the part of the gas in the region of the shell at the first group of tubes is deflected to flow along the axis near the center of the second group of tubes. The deflection of the gas currents may be through for the partial streams and the baffles may have a helical configuration without producing any substantial reduction in the cross section of flow of the gas streams so that there is no undesirable loss of pressure.

The method and apparatus of the present invention are of particular importance in connection with heat 3 exchangers where the groups of tubes are inaccessible as is the case, for example, with nuclear steam generators or heat exchangers. Where there are no intermediate headers, as is the case with steam boilers through which the fluid flows only once, the equallizing mixing effect resulting from the use of intermediate headers, injection coolers, or the like, to contribute to the uniformity of the temperature of the outer fluid is no longer available. Since it is possible that some of the tubes will become damaged, the heat exchanger structure should have the capability of placing the damaged tubes out of operation without creating undesirable instability in the current flow, and particularly with respect to this latter problem the method and apparatus of the present invention are of special importance because any lack of uniformity in the temperature of the discharging gas which otherwise would occur by taking damaged tubes out of operation are eliminated with the method and apparatus of the present invention.

BRIEF DESCRIPTION OF DRAWINGS The invention is illustrated by way of example in the accompanying drawings which form part of this application and in which:

FIG. I is a schematic elevation view of a heat exchanger according to the invention illustrating the manner in which fluid flows;

FIGS. 2-4 are respectively schematic sectional plan views taken along lines Il-II, III-Ill, and Iv-IV of FIG. I and illustrating in addition the direction of fluid flow;

FIGS. 5 and 6 are respectively schematic sectional plan views illustrating further possible embodiments of the method and apparatus of the invention at a location between two groups of tubes;

FIG. 7 is a schematic sectional elevation of another embodiment of the method and apparatus of the invention at the location between two groups of tubes;

FIG. 8 is a schematic plan view of the structure of FIG. 7 as seen when looking down on the structure of FIG. 7 in the direction of the arrow VIII of FIG. 7;

FIGS. 9 and 10 are respectively sectional plan views of the structure of FIG. 7 taken along lines IX-IX and X-X of FIG. 7 in the direction of the arrows;

FIG. 11 is a schematic sectional plan view of the structure between the two groups of tubes, showing yet another embodiment where this structure is cylindrical rather than rectangular as shown in FIG. 8;

FIG. 12 is a sectional elevation of a radial heat exchanger, as contrasted with the axial heat exchanger of the above embodiments, which includes the method and apparatus of the present invention;

FIG. 13 is a schematic sectional elevation of yet another embodiment of the invention according to which the tubes are twisted in a predetermined manner; and

FIG. 14 is a schematic fragmentary sectional elevation of a further embodiment of a heat exchanger method and apparatus according to the invention.

DESCRIPTION OF PREFERRED EMBODIMENTS Referring to FIG. I, there is schematically illustrated therein an axial heat exchanger having a lower or first group of tubes 2 arranged around the vertical heat exchanger axis which coincides with the axis of a central vertical tube coaxially surrounded by the outer shell 17 of the heat exchanger.

The lower or first group of tubes 2 is followed by an upper or second group of tubes 3 spaced axially from the lower group of tubes 2 and also situated within the shell 17. This shell 17 forms a means for directing an outer fluid in the form of a gas upwardly across the first group of tubes 2 and then across the second groups of tubes 3. In this way the stream of outer fluid forms an entering stream 31 and an exiting stream 32.

In addition it will be noted that the lower group of tubes 2 is divided by a cylindrical partition into an inner subgroup of tubes II and an outer subgroup of tubes 12 while the upper group of tubes 3 is correspondingly divided by a cylindrical partition into an inner subgroup of tubes 13 and an outer subgroup of tubes 14. Thus, at each group the subgroups are concentric.

As a result of this arrangement the entering stream 31 is divided into inner and outer stream portions which respectively flow across the subgroups I1 and 12, while the exiting stream 32 is also divided into inner and outer stream portions which respectively flow across the subgroups l3 and 14.

In accordance with the invention, in the space 1 be tween the first group of tubes 2 and the second group of tubes 3 there is a baffle means, which includes the plates 4, serving to deflect the stream portion which flows across the inner subgroup 11 so that it will flow across the subgroup 14 while also deflecting the stream portion which flows across the subgroup 12 so that it will flow across the subgroup 13. In this way the parts of the entering stream 31 which have a particular relationship with respect to each other and with respect to the axis of the heat exchanger become interchanged with those parts of the exiting stream 32 which have the same relationship with respect to each other and with respect to the axis of the heat exchanger. In order to illustrate this action clearly, the stream portion flowing across the subgroup 12 is designated by a solid arrow 15 while the stream portion flowing across the subgroup 11 is designated by a dotted arrow 16. It will be noted that in the space 1 because of the baffle means, these arrows cross each other with the stream portions being deflected substantially radially with respect to the heat exchanger axis in substantially opposite directions, so that at the second group of tubes 3 the arrow 15 is situated at the inner subgroup I3 and the dotted arrow 16 is situated at the outer subgroup 14.

It will be noted that in addition to the above features the directions of winding of the subgroups l1 and 12 are opposite to each other to provide the opposed circular directions of flow indicated respectively by the arrows l5 and 16. Moreover, with the heat exchanger a countercurrent heat exchange is preferred according to which the inner fluid in the interior of the tubes flows downwardly while the exterior fluid flows upwardly as shown in FIG. 1. Of course, the two groups of

tubes

2 and 3 communicate with each other. In order to facilitate understanding of the invention and clarity of illustration the details of the tubes and their connections are not shown. FIGS. 2 and 4 respectively illustrate also how the gas stream portions have interchanged their relative positions while maintaining their predetermined relationship with respect to the heat exchanger axis.

As may be seen from FIG. 3, the plates 4 of the baffle means are flat plates situated respectively in planes which contain the axis of the heat exchanger, these plates being uniformly distributed about the axis in such a way that each partial gas stream is deflected through approximately 180.

FIG. 5 shows how it is possible to arrange the plates 4 in such a way that they define two groups of spaces which alternate with each other, with one group of these spaces accommodating the tubes which interconnect the

groups

2 and 3 while the remaining spaces accommodate the baffle means which includes, in addition to the plates 4, the plates which are described in greater detail below. Thus it will be seen from FIG. 5 that intermediate tube portions 5 extend through the illustrated spaces defined between the plates 4 in order to maintain the

tube groups

2 and 3 in communication with each other. These tubes 5 also act as supports. The baffles 10 are in the form of suitably twisted or curved plates shown for the sake of simplicity and clarity in only one of the spaces between a pair of successive plates 4. The configuration of the plates is such that the deflection of each partial gas stream through 180 will be achieved. Thus, with thisdeflection those parts of the stream which are close to the axis become situated close to the shell l7 while those parts which are initially close to the shell 17 become located close to the axis.

According to the embodiment of FIG. 6, instead of utilizing flat plates 4, the'one group of spaces, which alternate with the other group in which the tubes 5 are accommodated, are defined by cylindrical plates 4 spaced as illustrated in FIG. 6 to define between themselves biconcave spaces for accommodating the tubes 5. Within each cylindrical wall 4 there are the baffles 10 as described above to provide the deflection through 180 as pointed out above.

FIGS. 7-10 illustrate another embodiment according to which the heat exchanger section between the two groups of tubes is of a rectangular section with the baffle means 6, 7 taking the form of oppositely curved plates of helical configuration providing helical surfaces for guiding the partial gas streams.

As may be seen from FIG. 8, which is a top plan view of the structure shown in FIG. 7, the baffles define flow channels of pentagonal configuration, as illustrated by the heavy lines in FIG. 8, with the baffles or

walls

6 and 7 providinghelical surfaces to guide the gas so that pentagonal entrance channels illustrated by the heavy lines are transformed into pentagonal exit channels as shown by the thin lines. One of the entrance areas includes the corners -24 while the corners of an exit area are indicated by the reference characters -29. The channel walls 8 and9 are plates formed by a section through the

helical baffles

6 and 7. If desired these walls 8 and 9 can be eliminated without detracting from the desired operation of the baffle means which would then consist only of oppositely directed helical surfaces. In the plan view of FIG. 8 the heavy lines are at the front while the thin lines are at the back. The guide surfaces of the baffles are skewed backwardly and define an edge, these surfaces being hatched at the horizontal section line.

FIG. 9 is the section midway between the top and bottom of the structure of FIG. 7 while FIG. 10 shows the arrangement adjacent the bottom of the structure of FIG. 7.

As is apparent from the above description and the illustration of FIGS. 7-10, the baffle means does not create any appreciable reduction in the cross section of flow of the gas streams from the first group of tubes 2 to the second group of tubes 3, so thatas a result no undesirable loss of pressure is created during deflection of the gas currents.

In FIG. 11 there is a plan view of another embodiment which is cylindrical, rather than rectangular as shown in FIG. 8. In this case also the entrance and exit channels are illustrated with the upper edges shown in thick lines and the lower edges shown in thin lines. The designation of the helical surfaces has been carried out in FIG. 11 according to the same scheme as in FIG. 8 but in only two adjacent channels for the sake of clarity. Thus, in this case also the baffles are in the form of helical deflector plates arranged in

groups

18, 19 with partition plates being provided to define spaces through which the connecting tube portions 5 can extend.

FIG. 12 shows how the invention can be applied to a radial heat exchanger. Thus as schematically illustrated in FIG. 12, the entering stream 31 is deflected by a conventional baffle of inverted conical configuration so that the entering stream now flows radially away from the vertical axis of the heat exchanger which coincides with the axis of the inverted conical baffle 40. Thus, the entering stream will first flow across the first group of tubes 2 which are circumferentially surrounded by the second group of tubes 3 which are spaced radially from the first group of tubes 2 by the space 1. In this space 1 are situated baffles which form a baffle means for deflecting the partial gas streams in the manner indicated by the

arrows

15 and 16. Thus, an upper part of the gas stream at the tubes 2 is deflected axially to form a lower part of the gas stream at the tubes 3, while a lower part of the gas stream at the tubes 2 is deflected axially in an upward direction to form an upper part of the gas stream at the outer tubes 3. In this way it is possible to achieve with a radial heat exchanger also the results desired to provide a uniform temperature in the discharging gas stream.

Referring now to FIG. 13, there is shown therein in elevation a heat exchanger where the tubes are themselves curved so as to have the configuration of screws. Thus, this heat exchanger is also shown as having for the first group of tubes 2 the

subgroups

11 and 12 and for the second group of tubes 3 the

subgroups

13 and 14. It will be seen that the

subgroups

11 and 12 are curved spirally in opposite directions, while the same is true of the

subgroups

13 and 14, while the

subgroups

11 and 13 are twisted in the same direction and the

subgroups

12 and 14 are twisted in the same direction, so that the

subgroups

11 and 14 are twisted oppositely with respect to each other and the

subgroups

12 and 13 are twisted oppositely with respect to each other.

Therefore the portions of the entering stream 31 are directed circumferentially respectively inopposite directions and are then deflected further by baffles in the space 1 so that the outer stream at the subgroup of tubes 12 forms the inner stream portion at the subgroup 13 while the inner stream portion at the subgroup 11 forms the outer stream portion at the subgroup 14, as indicated by the arrows l5 and 16. In this way the stream portions or currents are deflected so as to reverse their relative positions. FIG. 13 shows how the entering inner heat exchanger fluid is supplied by way of a supply header 33, with this inner heatexchanging fluid discharging through a discharge header 34.

The embodiment of FIG. 14 will also achieve the results of the invention although it will be noted that in FIG. 14 the

groups

2 and 3 are not subdivided into subgroups and are twisted in the same direction. These tube groups communicate with each other in any suitable way while the space 1 between the subgroups is provided with the baffles 10 situated'between radial plates 4 in the manner described above and shown in H0. 5 or within cylindrical plates 4 as shown in FIG. 6. The several helically curved baffles which are thus distributed around the heat exchanger axis in the space 1 also deflect the entering stream after it flows beyond the tube group 2 so as to provide separate stream portions flowing in the manner indicated schematically by the solid arrow and dotted arrow 16 to provide an interchange according to which the part of the entering stream adjacent the axis becomes the part adjacent the shell 17 at the second group of tubes 3 while the part of the entering stream adjacent the shell 17 becomes the part adjacent the axis at the group of tubes 3.

Thus, with the above-described method and apparatus of the invention it becomes possible to achieve a high degree of uniformity throughout the entire body of the discharging stream 32 without requiring complex tubular arrangements and without creating any undesirable loss of pressure.

What is claimed is:

1. In a heat exchanger, first and second groups of tubes communicating with each other for directing an inner heat-exchanging fluid along the interior of said groups, said first and second groups of tubes having a predetermined relationship with respect to an axis of the heat exchanger, means for directing an outer heatexchanging fluid first across the exterior of said first group of tubes and then across the exterior of said second group of tubes to form from said outer fluid an entering stream distributed across said first group of tubes and an exiting stream distributed across said second group of tubes, said entering stream being composed of first and second stream portions which respectively have first and second relationships with respect to said axis and second exiting stream also being composed of first and second stream portions which have also said first and second relationships, respectively, with respect to said axis, and baffle means situated between said groups of tubes for deflecting said first stream portion of said entering stream to a location where said first stream portion of said entering stream forms said second stream portion of said exiting stream and for deflecting said second stream portion of said entering stream to a location where said second stream portion of said entering stream forms said first stream portion of said exiting stream, so that the temperature of said exiting stream will be substantially uniform.

2. The combination of claim 1 and wherein said second group of tubes circumferentially surrounds said first group of tubes while said baffle means deflects said first and second portions of said entering stream in opposed directions, respectively, which extend substantially parallel to said axis.

3. The combination of claim 1 and wherein said first and second groups of tubes are axially spaced from each other to occupy different locations along said axis, and said baffle means being situated in a space between said first and second groups of tubes with said axis extending through the latter space, said baffle means deflecting said first and second portions of said entering stream respectively in opposed directions which extend substantially radially with respect to said axis.

4. The combination of claim 3 and wherein said baffle means includes a plurality of baffle plates which divide said entering stream into a plurality of subsidiary streams each of which includes part of said first portion and part of said second portion of said entering stream, said baffle means deflecting each part of said first portion and each part of said second portion of said entering stream through approximately before reaching said second group of tubes.

5. The combination of claim 3 and wherein said baffle means includes a plurality of cylinders through which said subsidiary streams respectively flow, said cylinders all having parallel axes which are parallel to said heat exchanger axis.

6. The combination of claim 3 and wherein said baffle means includes plates which define two groups of spaces which alternate with each other and are distributed about said axis, and a plurality of connecting tubes extending through one of said groups of spaces for connecting said groups of tubes with each other so that they communicate with each other.

7. The combination of claim 6 and wherein said baffle means includes deflecting plates situated in the other group of spaces.

8. The combination of claim 3 and wherein said baffle means include baffle plates of helical configuration defining channels through which the outer fluid flows while travelling from said first to said second group of tubes.

9. The combination of claim 3 and wherein said first group of tubes includes an inner section and an outer section surrounding said inner section, and said sections of said first group of tubes extending spirally in respectively opposite directions for creating a whirling in the entering stream.

10. The combination of claim 3 and wherein said baffle means includes a plurality of partition plates each situated in a plane containing said axis and said plates being uniformly distributed about said axis in planes extending radially therefrom, and a plurality of deflecting plates situated between said partition plates.

11. The combination of claim 3 and wherein said means for directing the outer fluid across said groups of tubes includes an outer cylindrical wall within which said groups of tubes are located, and said baffle means extending up to said outer cylindrical wall with the latter participating in the control of the direction of flow of the outer fluid.

12. The combination of claim 1 and wherein said baffle means maintains the cross section through which the outer fluid flows from said first to said second group of tubes substantially unchanged so that deflection takes place without any substantial loss of pressure.

Claims

1. In a heat exchanger, first and second groups of tubes communicating with each other for directing an inner heatexchanging fluid along the interior of said groups, said first and second groups of tubes having a predetermined relationship with respect to an axis of the heat exchanger, means for directing an outer heat-exchanging fluid first across the exterior of said first group of tubeS and then across the exterior of said second group of tubes to form from said outer fluid an entering stream distributed across said first group of tubes and an exiting stream distributed across said second group of tubes, said entering stream being composed of first and second stream portions which respectively have first and second relationships with respect to said axis and second exiting stream also being composed of first and second stream portions which have also said first and second relationships, respectively, with respect to said axis, and baffle means situated between said groups of tubes for deflecting said first stream portion of said entering stream to a location where said first stream portion of said entering stream forms said second stream portion of said exiting stream and for deflecting said second stream portion of said entering stream to a location where said second stream portion of said entering stream forms said first stream portion of said exiting stream, so that the temperature of said exiting stream will be substantially uniform.

4. The combination of claim 3 and wherein said baffle means includes a plurality of baffle plates which divide said entering stream into a plurality of subsidiary streams each of which includes part of said first portion and part of said second portion of said entering stream, said baffle means deflecting each part of said first portion and each part of said second portion of said entering stream through approximately 180* before reaching said second group of tubes.