CA1121338A - Heat exchanger and atmospheric cooler incorporating the same - Google Patents

Abstract

III. ABSTRACT

A heat exchanger for exchanging heat between a fluid and a gas includes a fluid distributor and a fluid collector spaced from the fluid distributor, and a plurality of flexible heat exchange to tubes arrayed in space substan-tially parallel arrangement, extending between the fluid distributor and the fluid collector with means being provided for directing a gas between the tubes of the array character-ized in that the flexible tubes are supported only at their ends from the fluid distributor and fluid collector to hang freely between the fluid distributor and fluid collector, and the tubes have a curved profile in a verticle plane.

Description

~.'Z~ ~;3~3 HEAT EXCllANGER AND AT~IOSP~IERIC COOLER
INCORPORATING THE SAME

I. DESCRIPTIO
Technical Field This invention relates to a heat exchanger between at least one fluid, for example water, and a gas, for example the atmosphere, of the type comprising a battery of flexible heat exchanger tubes which are parallel to one another and fixed at each end in a tube plate of a distributing and/or collecti.ng device for said fluid, the latter circulating in the heat exchanger tubes while the gas passes about the outside surfaces of the battery of tubes.
The invention also relates to the application of such heat exchangers to atmospheric coolers of the "dry" type : 15 in which the fluid to be cooled is placed in indirect contact with the air of the atmosphere through the wallsof the tubes of the exchanger; to atmospheric coolers of the "combined" type which comprises both at least one exchanger of the aforementioned type and at least one "wet" exchange unit in which the liquid, which may or may not be the fluid circulating in the exchanger : ~ubes, is placed in-direct contact with the air of the atmos-- . phere; and to atmospheric coolers of the "hybrid" type in which the tubes of the exchanger of the aforementioned type are externally wetted by the liquid which may or may not be the: fluid circulating in the tubes of the exchanger.
The air passing throug'n the coolers is moved either by a natural draught, l~hich may or may not be assi.sted by fans, or solely by blower and suction fans.

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3~8 The use of flexible tubes> for example, of plastic material for the construc~ion of heat exchangers is known in the art. In most of such exchangers the plastic tubes are rectilinear in length and circular in cross-section and of the water-water type of exchanger and not oF the fluid-gas type such as those employed in atmospheric coolers. In the prior art the feature of the flexibility of the tubes is only utilized at the ends of the exchanger for the purpose of group-ing them in a compact manner for connection to the distribut-ing and/or collecting headers.
Other prior art discloses exchangers having flexibletubes of plastics material of great length disposed horizon-tally and capable of conforming to the various contours of coolers. In these exchangers, the tubes are held under ten-sion in the region of their tube spacers where the tubes maybe caused to bend, etc. Thus, the curvilinear contours of coolers may be approached by a polygonal contour of the tubes of the exchangers. The flexibility of the tubes permits the tubes of the exchanger to conEorm to the shape of the cooler.
However, the very great length o-f the tubes and the high co-efficient of expansion of the plastics material from which they are made results in very large variations in length of the tubes which must then be absorbed. This constitutes a sub-stantial complication in the design of large flexible plastic 1 25 tube exchangers.
This problem of expansion o-f plastic tubes has, at least in part, been solved by suspending the battery of tubes~
at least in a part, of their length from a rigid support struc-ture by . , ,:

` ~ 2~33~ -by suspens,ion members to which spacer devices for the tubes are hooked. The spacer devices interconnect the tubes at intervals along the length of the battery and the suspension members are inclined in such manner as to place the tubes under tension. Although this arrangement is very eEfective, it is useful generally only for exchangers whose tubes are horizontal. Furthermore such systems require the presence of expensive supporting and suspending equipment.
BRIEF SUMMARY OF INVENTION
Broadly speaking the present invention provides a heat exchanger for exchanging heat between at least one fluid and a gas, comprising a fluid distributor and a fluid collector spaced from the distributor, a plurality of flexible heat exchange tubes carried in spaced subs-tantially parallel arrange-ment;
It means connecting one end of each tube to the fluid distributor;
means connecting the other end of each tube to the fluid collector;
means for directing a gas between the tubes of the array;
characterized in that the flexible tubes are support-ed only at their two ends and have a length exceeding the dis-tance between the distributor and the collector to hang freely between the ends under the effect of their weight and to have a curYed profile,in a vertical plane; and wherein the distribu-tor and the col],ector between which the exchanger tubes extend are disposed at different heights and arehorizontaIly offset from each other.

~ Z~ ~3~3 This arrangement has the-following advantages? It has great simplicity of construction relative to those of prior art exchangers. It permits the construction of ex-changers having varied configurations. Further, by its design, it solves, without the use of exterior means, the problem of the heat expansion of the tubes which, as men-tioned before, is particularly crucial when tubes of syn-thetic material are employed~

` BRIEF DESCRIPTION OF THE DRAWING
Further features and advantages of the invention will be apparent from the ensuing description of various embodi-ments which are given solely by way oE examples and are illustrated in the accompanying drawings~ ln which:
FIG. l is a side elevational View~ partly in section, of a dry type forced draught atmospheri~c cooler equipped with heat exchangers according to the invention;
FIG. 2 is a top plan view, with a part cut away, of the cooler shown in Fig. l;
FIG~ 3 is a front elevational view of the cooler sho~n in FIG. l;

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;~ ' ~ .3 FIG. ~ is a perspective detailed view of a device for spacing the tubes of the e~changers of the cooler shown in FIGS. 1 to 3;
~ IG. 5 is a view similar to FI~. l of a dry type atmospheric cooler provided with an exchanger according to another ~orm of the present invention;
FIG. 6 is a view similar to FIG. l of an atmospheric cooler provided with e~changers similar to those shown ;n FIG. l;
FIG. 7 is a top plan view, with a part cut a~ay, of the cooler shown in PIG. 6;
FIG. 8 is a sectional view of some tubes of the ex-changer shown in FIGS. 6 and 7 with a modified spacer device;
FIG. 9 is a view similar to FIG. 6 of another type o~ combined atmospheric cooler provided w;th exchangers accord-ing to the invention;
FIG. 10 is a top plxn view of the exchanger shown inFIG. 9;
FIG. 11 is an elevational view of a dry type natural draught atmospheric cooler provided ~ith an exchanger accord-ing to the invention;
FIG. 12 is a sectional view taken on line 12-12 of FIG. 11; and FIG. 13 is a uiew similar to ~IG. 11 of a further modified form of the invention . ~

2,5 Detailed Description of Invention ~ ~ith reference to FI'GS. 1 to 4, ~here is sho-~n a dry type atmospheric cooler A of the mechanical or forced draught type and of rectangular shape in hori,zontal section. The cooler-A includes a chanber 1 deined by two lateral walls 2 and 2 ! which are supported by a metal framework 3 on two of the sides of the cooler, and by two open sides 4 and 4' con-stituting tne air inlets on the two other sides of the cooler.
The chamber 1 is surmounted by a roof 5 in the shape of a truncated pyramid which terminates in a circular sleeve 6 in which there is mounted a fan 7 driven by a motor not shown for clarity o~ the drawing.
Disposcd inside the chamber 1 ar~ two heat exchanger banks 8 and 8 constructed according to the present invention.

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Each exchanger 8-8' comprises a battery 9 of flexible tubes lO~formed of synthetic material. These tubes.~10 are`parallel to one another and connected in a sealed manner at the lower ends in opposed tube plates 1~ of a water distributing box 12 supplyillg l~ater or other liquid to be cooled to the-tubes 10.
The distribution box 12 extends throughout the length of the cooler at equal distances from the two open air inlet sides ~-4' and above the ground 14 so that a liquid distributing pipe 13 can be connected to the l~ater box 12.
The tubes 10 of each battery 9 extend upwardly from the water bo~ 12 and are connected in a sealed manner at their upper ends to a tube plate 15 of respective water boxes 16 which collect the cooled liquid which is then discharged from the ~ater boxes 16 by discharge pipes 17. The water boxes 16 1~ each extend in a direction parallel to the distributing water box 12 in the upper part of the chamber 1 where they define the upper edge o~ the air inlets 4-4' and they are supported by the metal framework 3 which has only been shown diagrammatically in order to render the dral~in~ more clear.
The tubes 10 (FIG. 4) of the exchangers 8-8' are made from a synthetic material which is ~supple or~flexible, resists the relativlely elevated temperatures of`opêration and has relatively good heat conductivity. Suitable synthetic material having su-ch properties are organic polymers, for example, pol,ybut~ne or cross-linked polyethylene.
The~diameter of the tubes is preferably relatively small to permit good heat exchange, for example, 5 to 20 mm, and the tubes are disposed when viewing the exchangers 8-8' in a transverse vertical plane, as in FIG. 1, in a series of parallel paths the number of which may be, for example 8 to 40.
The tubes 10 are sealed to the tube plates 11 and 15 by suitable sealed connectors as is wel1 known in the art.
As can be seen in FIG. 1, the tubes 10 hang freely between their ends connected to the tube plates 11 and 15, and in order to ensure that they do not touch each other, they are grouped in a number of nests 18 by spacer devices 19, one em-r bodiment of which is sho~n in more detail in FIG. ~. The ,: .

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spacer devices 19 are formed by a number oE strips 20 which are clamped together by means of a frame 21 and are provided with notches defining in opposed pairs passages ~or the tubes 10. The spacer devices maintain air passages between the tubes, which are preferably disposed in a staggered relation, by off-setting adjacent t~lbe paths so that the passages constrain the air to follow sinuous paths between the tubes.
The tubes 10 have a length greater than the distance between the tube plates 11 and 15 so that the tubes have a curved profile in a vertical plane as shown in FIG. 1. How-ever, the later is diagrammatic and is not intended to re-produce the real curvature of the tubes in an exact manner since this curvature depends to a large extent on the length of the tubes.
The operation of the cooler shown in FIGS. 1 to 4 is quite conventional and will therefore not be described in detail. However, the li~uid to be cooled, for example, water, is supplied by pumping means (not shown) to the distributing water box 12 by way of the supply pi~e 13. In the water box 12, the liquid is distributecl among the tubes 10 of the two exchangers 8-~' and flows to~ard the collecting water boxes 16. In the course of its pa~sage through the tubes, the liquid is cooled by atmosphere air Yhich enters the cooler by way of the air inlets 4-4' and passes through the batteries ~ in the direction indicated by the arrows F in FIG. 1. The heated air is drawn off by the fan 7 and thereafter expelled to the atmos-phere through the sleeve 6.
It will be noted that, in the illustrated embodiment, the lateral walls 2-2' terminate at a distance above the ground 14 and more precisely at the height of the distributing water box 12 so that there are ~ormed two laterial air inlets which improve the flow of air into the cooler. However, by way of a modification, the lateral walls 2-2' may extend to the ground 14.
The embodiment shown in FIG. 5, in which the same reference numerals as used in FIGS. 1 to 3 increased by the .

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number 100 have been employed for designating similar parts, differs from that of FIGS. 1 to 3 by having only a single exchanger 10~. It will also be noted that there is no lower water box and the tubes o~ the exchanger 108 extend from one of the upper water boxes 116a, which constitutes a distributing ~ater box supplied with fluid by a supply pipe 117a, to the other water box 116b, which constitutes a collecting water box as in the preceding embodimen~ ater box 116b is placed at the same height as the ~ater box 116a. The tubes of the ex-changer 108 have a length which is substantially twice thatof the tubes of the exchangers 8-8 and hang freely between the - ~ater boxes 116a and 116b. The embodiment o FIG. 5 has the advantage over the embodiment of FIGS. 1 to 3 by eliminating a water box, but it increases on the other hand, the risk of tube stoppage by stagnant deposits in their lower parts. This risk may be reduced and even avoided by the use of good quality fluid to be cooled, and a relatively high fluid ~low rate.
~ IGS. 6 and 7 show a combined cooler which differs essentailly from the cooler ol FIGS. 1 to 3 in that it com-prises two wet type exchange llnits 222-222 each mounted in front of a portion of a dry t,~pe e~changer 208 so that each stream o~ cooling air of the atmosphere travels through a wet exchange unit 222-222 and a dry exchanger in series.
The collector water boxes 216 are provided with a plurality of dlscharge pipes 217a instead of a single pipe as in the case of the cooler of ~IGS. 1 to 3, and these pipes 217a operate as feed pipes for two tanks 223 from the two water boxes 216 respectively.
The tanks 223 are provided at the bottoms thereof -with spreader nozzles through which the liquid, which has been partly cooled în the exchanger 208, is poured over the associated exchange units 222-222'. The wet exchange elements may be either of the type in which the liquid flows in the form of thin films or of the splash type. Disposed under each - 35 exchange unit 222-222' is a basin 224-224' for receiving the cooled liquid .

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which flows from the exchange units 222-222~ and is there-after discharged from each basin by discharge pipes 225.
Disposed betl~een each ~et exchange unit 222-222' and the associated dry exchclnger 208 are t~o droplet sepa-rators 22G. Sucll droplet separators are conventional. Thedroplet separators are important in reducing the vapor plum issuing from the exit ring 206. I~hen droplet separators are employed the first rows of tubes are not required to evaporate the air born ~ater from coolers 222-222'. In this form of cooler, the lateral walls 20~-204' extend down to the ground owing to the presence of the wet exchange units 222-222' in which atmospheric air must -flow in cross-current manner with respect to the liquid to be cooled.
As shown in more detail in FIG. 8, the spacer de-~ices for the tubes of the exchangers 208-208' are different from those of the exchangers 8-8'. The spacer device comprise split rings or discs 227, for example of plastics material, which are mounted on the tubes 210 and whose radial width determines the spacing bet~een the tubes. Moreover, the tubes 210 may be rendered rigid in nests by any suitable connecting means between the tubes or spacers.
Generally, any suitable spacer device other than those shown in FIGS. ~ and 8 may be employed, for example, projections on the tubes to maintain the spacing between the tubes of the exchanger according to the invention.
The coolèr shown in FIGS. 6 and 7 operates in a con-ventional manner of a combined cooler having series circulation of the liquid to be cooled and of the atmospheric air.
FIGS. 9 and 10 show another type of combined cooler in which the liquid to be cooled also circulates in series in a dry ~ype exchanger ancl in a ~iet type exchanger but in which the two exchangers have parallel streams of air which become mixed only after having passed through the two e~changers. In these FIGS., 300 series reference numerals have been used to de-signate elements corresponding to these illustrated in FIGS. 1 and 2.
The pipes of the exchangers 308-30~ are supplied with liquid from above by pipes 317 which are connected to the upper water boxes 316-316' through a series of parallel pipes 317. The liquid, partly cooled in each of the two exchangers 308-30S' which are disposed on each side of the cooler above the wet exchanger 322, is received in the lower water boxes 312-312 which distribute the liquid to respective supply tanlcs 323-323' which in turn supply the li~uid to the distri-bution system 328 of the counter-current wet exchange unit 322.
The cooler of FIGS. 9 and 10 operates in a similar manner to prior art combined coolers having parallel air streams.
Note simply that, by way of a modification, the circulation of the liquid in the dry exchangers 308-308' and wet exchanger 322 could occur in parallel instead of being in series and that, moreover, the cooler, instead of being of rectangular shape, could have a circular shape in which case a single upper water box of circular shape and a single lower water box would be - employed.
FIGS. 1] and 12 show the application oE an exchanger having hanging tubes according to the invention to a natural draught cooling tower of the hyperbolic type. The tower com-prises a shell 429 in the form of a thin concrete shell and a network 430 of crossed girders supporting the shell via a ~
circular lintel 431 which defines a peripheral air inlet 404.
At the level of the circular lintel 43] is located the upper water supply box 416 which is continuous or formed by a succession of short rectilinear, aligned segments. The water box 416 supplies the battery ~09 of flexible plastics tubes the lower ends of which are connected to the lower cir-cular water box 412 whose overall diameter is less than that of the supply water box 416.
This difference between the diameters results in a difference between the spacings of the tubes. At the lower water box, the spacing in the tangential direction is smaller. This decreased tube spacing may be compensated for with respect to the passage of the air, by an increase in spacing of tubes at the lower end in a radial direction.
The diameter of present towers, at the level of the lintels is very large, and of the order of 100 to 200 metres, and the difference ~tween ~he overal di eters of the lower

3~3 -and upper water boxes (-~hich has been exaggerated in the drawing for reasons of clarity) is relatively small, of the order o-f a fe~ metres to around 20 metres a-t the most, and thus presents no serious problem concerning the variation in the spacing of tlle tubes.
FIG. 13 also shows a naturcLl draught cooling tower of the hyperbolic type in ~hich the battery 509 of plastics tubes assumes an outwardly 1aired configuration from the lintel 531 to the lower water box 512 which has a diameter larger than that of the upper water box 516.
A-t the level of the ~iater box 512, the slightly larger spacing of the tubes with respect to that existing at the upper water box 516 ccmpensates for the tendency o a decreasing air flow between the lintel and the ground.
In the embodiments shown in FIGS. 11 and 12, as in that shown in FIG. 3, the battery 409 or 509 is formed by a plurality of rows of tubes each defining a surface of revolution.
It will be understood that many modifications may be made in the embodiments described hereinbefore without de-parting from the scope of the invention. Thus, for example, the fluid inside the dry exchangers of the wet-dry combined coolers, such as those shown in FIGS. 6 to 10, could be dif-ferent from the fluid in the wet exchangers. In an advantageous -manner and for reducing the vapor plume from the wet section, the fluid may have a substantially higher temperature in the wet section. The fluid supply circuits ~fluid for the dry exchanger; water or aqueous solution for the wet exchanger) would then be completely distinct.
Further, the air of the coolers may be moved either by means of suction or blower fans, which urge the air through the exchangers, or by a natural draught chimney which may or may not be assisted by fans. The we~ exchange units may be of any known types, in particular of the counter-current or cross-current type, in which the tol~er fill may be of the film or splashing or combined types. The wet and dry exchangers rnay be connected in parallel or in series in the stream of air and, or the latter case, the dry exchanger may be upstream or down-stream of the IYet exchanger in this stream of air.

The exchangers according to the invention could also be designed not solely as a dry exchanger but as a hybrid exchallger.
~ lodifications may also be made in the water boxes.
5 For example, the direction of flu;d supply, namely up~rardly or downwardly as the case may be, could be reversed relative to that whlch has been described or shown in the various em-bodiments. ~nother modification would be to provide batteries having multiple passes by partitioning the ~rater boxes longi-10 tudinally or transversely as is known in the prior aTt. Ifthere is an even number of passes, the same ~rater box could serve as a distributing device and collecting device for the liquid.

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Claims (8)

THE EMBODIMENTS OF THE INVENTION IN WHICH AN EXCLUSIVE
PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:

1. A heat exchanger for exchanging heat between at least one fluid and a gas, comprising a fluid distributor and a fluid collector spaced from said distributor, a plurality of flexible heat exchange tubes carried in spaced substan-tially parallel arrangement;
means connecting one end of each tube to the fluid distributor;
means connecting the other end of each tube to the fluid collector;
means for directing a gas between the tubes of the array;
characterized in that the said flexible tubes are supported only at their two ends and have a length exceeding the distance between said distributor and said collector to hang freely between said ends under the effect of their weight and to have a curved profile in a vertical plane;

and wherein said distributor and said collector between which the exchanger tubes extend are disposed at different heights and are horizontally offset from each other.

2. A heat exchanger as claimed in claim 1, wherein, said distributor and collector devices have a rectilinear shape and said tubes are further formed in a plurality of parallel layers of tubes.

3. A heat exchanger as claimed in claim 1, wherein the fluid comprises water and the gas comprises air.

4. A heat exchanger as claimed in claim 1, wherein said distributor and collector are oriented substantially perpen-dicular to the adjacent ends of the exchanger tubes.

5. A heat exchanger as defined in claim 1, wherein the exchanger tubes are maintained spaced apart by spacer devices provided at intervals along said tubes.

6. A heat exchanger as claimed in claim 1, comprising two heat exchangers having a common lower fluid distributor which extends in the middle of the heat exchanger tubes there-of, and said tubes diverge from said common distributor device toward two respective upper collector devices.

7. A heat exchanger as claimed in claim 6, further in-cluding at least one heat exchange unit of the wet type.

8. A heat exchanger as claimed in claim 1, wherein the heat exchanger is of the type comprising a natural draught tower of circular section provided at its base with a peripheral air inlet, and wherein one of said distributors and collectors of the heat exchanger extends along the upper edge of the air inlet opening and the other is radially offset relative to the lower edge of said air inlet opening.