US3888305A

US3888305A - Cooling tower

Info

Publication number: US3888305A
Application number: US475151A
Authority: US
Inventors: Hans-Bernd Gerz
Original assignee: GEA Happel GmbH and Co KG
Current assignee: GEA Happel GmbH and Co KG; GEA Luftkuehlergesellschaft Happel GmbH and Co KG
Priority date: 1974-02-08
Filing date: 1974-05-31
Publication date: 1975-06-10
Anticipated expiration: 1992-06-10
Also published as: DE2405999C3; JPS50110141A; DE2405999A1; JPS5242246B2; ES425061A1; ZA742242B; IT1003963B; DE2405999B2

Abstract

An upright peripheral tower wall has a lower region with air inlet apertures and an upper region with an air outlet. An upper annulus of first heat-exchange elements is arranged inwardly adjacent the wall, and a downwardly offset second small-diameter lower annulus of heat-exchange elements is inwardly spaced from the upper annulus, the elements of each annulus being upwardly and inwardly inclined and having upper and lower end portions, and at least some of the elements of each annulus acting as condensers. A supply conduit is centrally located within the confines of the tower wall for supplying vaporous medium. A plurality of straight connecting pipes radiate substantially horizontally from the supply conduit and communicate with the upper portions of the first elements, and a plurality of substantially horizontal condensate collecting tubes communicate with the lower end portions of the first elements and also with the upper end portions of the second elements, so as to convey both condensate and vaporous medium from the first to the second elements.

Description

United States Patent Gerz June 10, 1975 COOLING TOWER [75] Inventor: Hans-Bernd Gerz, Bochum, Pr'mary Exammer Alben Davis Germany Attorney, Agent, or F1rm-M1chael S. Striker [73] Assignee: Gea Luftkuhlergesellschaft Happel GmbH & KG, Bochum, Germany [57] ABSTRACT An upright peripheral tower wall has a lower region [22] Flled: May 1974 with air inlet apertures and an upper region with an air 2 AppL 475 5 outlet. An upper annulus of first heat-exchange elements is arranged mwardly ad acent the wall, and a downwardly ofi'set second smalkdiameter lower annul l Foreign Application Data lus of heat-exchange elements is inwardly spaced from Feb. 8, 1974 Germany .t 2405999 the upper annulus, the elements of each annulus being upwardly and inwardly inclined and having upper and [52] US. Cl. 165/113; 60/693; l65/l25; lower end portions, and at least some of the elements l65/l29; l65/DIG. 1 of each annulus acting as condensers. A supply con- [51] Int. Cl. F28b l/06; F28b 9/l0 duit is centrally located within the confines of the [58] Field of Search l65/l 10, l l l, 125, 129, tower wall for supplying vaporous medium. A plurality l65/l 22, 113, DIG. 1; 60/685, 690-693 of straight connecting pipes radiate substantially horizontally from the supply conduit and communicate [56] References Cited with the upper portions of the first elements, and a UNITED STATES PATENTS plurality of substantially horizontal condensate col- 3,4009 9/1968 Richards 65/129 X lecting tubes communicate with the lower end por- 3519'068 M970 Harris a 3L I [GS/'22 X tlons of the first elements and also with the upper end 3,776,306 l2/|973 Michd U I65 I 1 portions of the second elements, so as to convey both 3.844344 1011974 Kliemann et al [65/110 Condensate and vaporous medium from the first lo the FOREIGN PATENTS OR APPLlCATlONS l,039,2l8 8/1966 United Kingdom l6S/l I] second elements.

13 Claims, 3 Drawing Figures PATENTEDJUH 1 0 1915 PATENTEUJUH 1 0 I975 SHEU FIG. 3

COOLING TOWER BACKGROUND OF THE INVENTION The present invention relates in general to a cooling tower, and more particularly to a cooling tower for condensation of vaporous media, particularly for condensation of discharged turbine steam.

It is already known to provide so-called natural-draft cooling towers having an apertured circumferential wall through which air can enter into the interior of the tower to flow around heat exchange elements through which a vaporous medium to be condensed such as steam is circulated. The heat exchanger which takes place results in the desired condensation.

These known arrangements utilizing the so-called direct condensation system provide certain problems which have not heretofore been solved. In particular, it is exceedingly difficult to have the entire heat exchange surface which is provided, be contacted with steam to be condensed. On the other hand, if there is no contacting to this extent, then it has been observed that within the heat exchange elements, particularly at the end where the condensation takes place, there will develop stagnent pockets of gas which substantially influence the condensation formation in a disadvantageous sense. A further drawback of these prior art constructions is the danger of excessive cooling of the condensate, which may lead at least in the winter-time to freezing of the condensate. Furthermore, such excessive cooling of the condensate and the formation of pockets of gas have been found to lead to corrosion at the interior of the heat-exchange elements, and thus to an undesirable reduction of their useful life.

Investigations have shown that the reason for the incomplete contacting of the installed heat-exchange surface area with steam or other vaporous media to be condensed, is based upon various factors, an important one of which is the irregularity of the speed of flow of the cooling air within the installation. Another important factor is the differential inflow conditions of the steam, as the vaporous medium to be condensed will hereafter be called for short, and these inflow conditions are largely the result of differential length of the distributing pipes, of bends or curvatures in the pipes, and of manufacturing irregularites in the different pipes.

Concerning the question of the flow speed of cooling air, it is well known that in natural draft cooling towers, whether they be of the dry or wet variety, higher air speeds will develop at the center of the cooling tower than at its periphery. This means that air speeds must be expected which vary over the radius of the cooling tower, and consequently the art has made attempts to overcome this problem in an effort to eliminate these irregularities. Thus, one prior -art construction arranges the heat-exchange elements in a conical pattern, the cone having an upright axis which coincides with the upright axis of the cooling tower itself, and having a base which is located above the upper edge of the air inlet openings formed in the peripheral wall of the cooling tower. The cone is inclined downwardly towards the center of the cooling tower and the arrangement is intended to assure that the air speed in horizontal direction below the heat-exchange elements is constant, and that the air distribution to the various heatexchange elements is uniform.

Another prior-art construction utilizes heatexchange elements which are distributed at different levels of the cooling tower, essentially in correspondence with the force of the draft or air stream which differs at different locations of the cooling tower cross section. The elements located at or near the center of the cooling tower are located at a higher level than those at or near the circumferential wall of the tower, and this arrangement also is intended to assure that a uniform or near-uniform cooling of all heat-exchange elements will be obtained.

It is clear that the prior art attempts to obtain a uni form distribution of the cooling air to the heatexchange elements. However, the upward flow of air through the heat-exchange elements is determined by the product of the cooling tower draft height and by the density difference of the cooling air; this means that when the heat-exchange capacity of the cooling tower varies, the initially obtained uniformity of cooling air speed will be disturbed again. If the cooling tower serves condensation purposes, there is the added difficulty that approximately rectangular heat-exchange elements must be installed in a substantially circular cooling tower cross section, so that only a portion of the cooling tower cross section is available for the air flow, which, of course, again produces disturbences in the air flow.

Another consideration that must be taken into account where condensation is to be obtained, is that the pressure losses at the steam or vapor side must be as low as possible, because high pressure losses will lead in condensation arrangements of the direct-system type to a substantial decrease of the condensing temperature, and thus to a reduction of the temperature differential. The reasons for higher pressure losses is in part to be found in the spacing between the location at which the steam or vapor arises, for instance a turbine, and the cooling tower. A much larger and more significant role is played by the fact that in the air cooled condensation systems of the direct type, the supply of steam to the heat-exchange elements takes place via a plurality of bends, elbows and curves formed in the distributing pipes.

SUMMARY OF THE INVENTION Accordingly, it is an object of the present invention to overcome the disadvantages of the prior art.

More particularly, it is an object of the present invention to provide a cooling tower for condensation of vaporous media, using the so-called direct system and producing the least possible pressure loss at the steam side while assuring a uniform distribution of the amount of steam to be condensed to the various heatexchanger elements.

An additional object of the invention is to provide such a cooling tower of the type outlined above, in which the disdavantages resulting in the prior art from the non-uniform flow speed of the cooling air, are fully or at least substantially avoided.

In keeping with the above objects, and with others which will become apparent hereafter, one feature of the invention resides in a cooling tower for condensation of vaporous media which, briefly stated, comprises an upright peripheral tower wall having a lower region with air inlet apertures, and an upper region with an air outlet. At least one upper annulus of first heatexchange elements is provided inwardly adjacent the wall, and at least one downwardly offset second lower annulus of heat-exchange elements is inwardly spaced from the upper annulus. The elements of each annulus are upwardly and inwardly inclined and have upper and lower end portions, and at least some of the elements of each annulus act as condensers. A supply conduit is located centrally within the confines of the tower wall for supplying vaporous medium. A plurality of straight connecting pipes radiate substantially horizontally from the supply conduit and communicate with the upper end portions of the first elements. A plurality of substantially horizontal condensate collecting tubes communicate with the lower end portions of the first elements and also with the upper end portions of the second elements, so as to convey both condensate and vaporous medium from the first to the second elements.

The cooling tower outlined above provides an aircooled condensation system of the direct type in which an exact dimensioning of the connecting pipes and tubes, in conjunction with the arrangement of the first and second heat-exchange elements in two or more vertically spaced annuli, assures that a minimum of bends. elbows, and curvatures will be present in the various pipes and tubes. This means that the steam or other vaporous medium is supplied from the central supply conduit directly and in an essentially straight line, to the first heat'exchange elements which are located inwardly adjacent the wall of the tower. These pipes in effect radiate in the manner of spokes.

By providing a large-dimensioned construction of the steam distributor head located at the inner end of the supply conduit, a quieting stage is obtained which aids substantially in the desired uniformity of steam distribution. The distributor and connecting pipes can be produced more precisely and more economically, because they are identical with one another, and particularly the uniformity of manufacture which is thus possible serves to eliminate undesired pressure differentials within the vapor spaces. Stagnant gas inclusions as a result of pressure differentials are thus eliminated, and this in turn eliminates disadvantageous influences on the condensation capacity of the arrangement, in contradistinction to the prior art, as avoiding the danger of corrosion within the heatexchange elements and substantially decreasing the danger that freezing of con densate might take place in winter operation.

The connecting pipes are of identical length, so that their flow speed is also identical and the steam is supplied uniformly from the supply conduit to the first heat-exchange elements The essentially straight-line radial supply of steam to the heat-exchange elements is also maintained when steam and condensate is to be supplied from the first heat-exchanger elements to the second heatexchanger elements, in that the upper ends of the second heatexchange elements are located substantially at the same level as the lower ends of the first heat exchange elements, and the consensate collecting tubes are arranged at this level and serve not only to transfer condensate from the first heat-exchange elements, but also steam, Since this again provides for an essentially straight-line transfer of steam from the first to the second heabexchange elements, that is from the upper to the lower annulus, it decreases the influencing of the heat-exchange elements by the pecularities of air flow in the cooling tower. The development of stagnant gas pockets is avoided, because the heat-exchange elements of the upper annulus are operated with a substantial excess of steam, meaning that a substantial quantity of excess steam is transferred from the condenser heat-exchange elements of the upper annulus to the condenser heat-exchange elements of .11 lower annulus. The essentially straight-line connection of these heat-exchange elements by the horizontal condensate collecting tubes. assures a stepping effect towards the center of the cooling tower, which is advantageous and assures that the flow of cooling air is substantially uniform with respect to the various heat-exchange elements.

The construction according to the present invention obtains a largely uniform distribution of steam to be condensed. and similarly the cooling of the heat exchange elements by the incoming air is largely uniform over the entire cooling tower cross section. No lost heat-exchange surfaces exist, that is heat-exchange surfaces in contactwith internal stagnant gas pockets, so that disadvantageous influences upon the condensing capabilities of the cooling tower are not to be expected.

Moreover, the construction according to the present invention decreases the danger of corrosion acting upon the heat-exchange elements, and avoids excessive cooling of the condensate and thus the danger that the condensate might freeze in winter operation.

The straight line supply of steam from the central supply conduit to the first heat-exchange elements, and from there in form of a substantial excess quantity of steam to the second heat-exchange elements, assures that the pressure-loss caused dropping of the condensation temperature is reduced and a reduction of the temperature differential resulting in the condensation is largely avoided.

A currently preferred embodiment of the invention provides for the second heat-exchange elements which act as condensers to be located in the radially outer region of the lower annulus, and their associated condensate collecting tubes are simultaneously operative as the steam supply tubes supplying steam to the heatexchange elements which act as dephlegmators and are arranged in the radially inner region of the lower annulus. This results in a stage-like condensation in which the first condensation stage and the last condensation stage respectively have the greatest and the smallest spacing from the center axis of the cooling tower. The first and the second condensation stage are formed by heat-exchange elements which act as condensers, and the last condensation stage is formed by heat-exchange elements acting as dephlegmators. Essentially straight radial conduits connect the individual condensation stages directly, and substantial excess quantities of steam travel from the heatexchange elements of the upper annulus which act as condensers, to the heatexchan ge elements of the lower annulus, which also act as condensers, as well as from these latter to the heatexchange elements which act as dephlegmators, in the lower annulus. The development of inert gas pockets with the disadvantages resulting therefrom, is avoided with such a construction.

A further embodiment of the invention may also utilize a construction wherein the heat-exchange elements acting in the lower annulus as dephlegmators might be located in the outer region of the lower annulus, and the heat-exchange elements acting as the condensers might be located in the inner region of the lower annulus.

It is also possible to have circumferentially adjacent condensate collecting tubes of heat-exchange elements of the upper annulus united to form a common conduit for the heat-exchange elements of the inner annulus. In this case, it is advantageous, if the number of heatexchange elements in the upper and lower annulus is identical, and the heat-exchange elements of the inner conduit are circumferentially offset substantially midway between two successive elements of the upper annulus. The heat-exchange elements are arranged in roof-shape, that is upwardly and inwardly inclined, and their inner narrow sides facing towards the center axis of the tower are located directly adjacent one another. The inner line of demarcation of each annulus is thus formed by a polygon which provides for a space-saving construction and advantageous utilization of the available tower cross section.

A particularly good utilization of the cooling tower cross section by the heat-exchange elements is also obtained if the radical spacing of the inner edges of the heat-exchange elements of the upper annulus from the central axis of the tower is equal to approximately twothirds of the spacing of the outer edges from the tower axis, and if the radial spacing of the inner edges of the elements in the lower annulus with respect to the tower axis, is approximately equal to one-third of the spacing of the outer edges of the elements of the upper annulus. Such as construction has various advantages. including an advantageous relationship with respect to the stepwise condensation. Approximately two-thirds of the total quantity of steam are treated in the heat-exchange elements of the upper annulus, and the remaining third of excess steam enters into the heat-exchange elements of the lower annulus which act as condensers, and is treated to two-thirds of its quantity. The remaining third then passes into those heat-exchange elements of the lower annulus which act as dephlegmators and is treated therein. The tube length of the heat-exchange elements of the other annulus with respect to that of the heat-exchange elements of the lower annulus could be approximately in a ratio of 2 l, and the width of the individual heat-exchange elements can be constant throughout. This affords a very simple construction and assembly which is less expensive than herebefore.

The heat-exchange elements of the lower annulus can be more steeply inclined than those of the upper annulus. The operation of the tower can be regulated by accommodating blocking arrangements, such as valves and the like, in the connecting pipes. The heatexchange elements of either or both of the annuli can be provided with shutters which are known per se from the art to vary the air flow. Thus, portions of the tower cross section in which no heat-exchange elements are located, can be blocked against the passage of air in known manner. in order to prevent a bypass of the air and the disadvantages resulting therefrom with respect to the condensing capacity of the arrangement.

Those heat-exchange elements which act as dephlegmators may have connected with them at least one venting conduit which is under the influence of one or more evacuating devices, that is which exert suction. It is preferable, however, if several venting conduits with separate suction device or devices are in communication with groups of these heat-exchange elements acting as dephlegmators, according to the sectorarrangement of these heat-exchange elements. This has the advantage that in case of changing air flow conditions, a self-regulation with respect to the end pressure in the respective vent conduit will be obtained.

The condensate outlet conduit can be connected in known manner via siphons or conduit loops with a common collecting space, or downwardly from condensation stage to condensation stage.

The novel features which are considered as characteristic for the invention are set forth in particular in the appended claims. The invention itself, however, both as to its construction and its method of operation, together with additional objects and advantages thereof, will be best understood from the following description of specific embodiments when read in connection with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWING FIG. 1 is a side elevational view, with the bottom portion in vertical section, of a cooling tower according to an embodiment of the invention;

FIG. 2 is a horizontal section through FIG. 1, taken on line II II of that FIGURE; and

FIG. 3 is a vertical cross section through FIG. 1, taken on line III III of that FIGURE.

DESCRIPTION OF THE PREFERRED EMBODIMENTS Referring now to the drawing in detail, in which FIGS. 1, 2 and 3 show a single exemplary embodiment of the invention, it will be seen that reference numeral 1 identifies an upright cooling tower of circular cross section. The cooling tower 1 has a circumferential wall 2 of known construction and conventional shape. The lower region of the wall 2 is provided with air inlet openings 3 oflarge cross section, through which air can enter in radial direction, the flow direction of the air being indicated by the arrows X. Reference numeral 4 identifies an upright central opening through which the air leaves the cooling tower l.

Arranged upwardly of the air inlet openings 3 within the cross section of the cooling tower, are two verti cally spaced concentric stages or annuli A and B of heat-

exchange elements

5, 5' and 5". The heatexchange elements 5, 5' and S" are each provided with a plurality of parallel finned tubes through which vaporous medium to be condensed, such as steam or the like, is to be circulated. The construction of such heatexchange elements is well known from the art and requires no discussion. The exterior of the heat-exchange elements is to be contacted by the air admitted through the inlet openings 3. A plurality of adjacent ones of the heat-

exchange elements

5, 5 or 5" is always joined in a roof shape, being upwardly and inwardly inclined, as shown in FIG. 3.

The thus formed roofs'" or assemblies 6 of heatexchange elements in the upper annulus A and the assemblies 7 of the lower annulus B, are radially oriented and have respective

narrow edges

9 and 10 which are located immediately adjacent one another and which face inwardly toward the center axis 8 of the cooling tower. The assemblies 7 of the lower annulus B are circumferentially offset with respect to the assemblies 6 of the upper annulus A by half the distance between two consecutive ones of the assemblies 6. The number of assemblies 6 is identical with the number of assemblies '7.

We claim:

The length of the assemblies 6 and 7 in radial direction of the cooling tower is so selected that the radial spacing of the inner edges 9 of the assemblies 6 from the axis 8 equals approximately two-thirds of the spacing of the outer edges 11 from the same axis 8. The radial spacing of the inner edges 10 of the assemblies 7 from the axis 8 equals approximately one-third of the spacing of the outer edges 11 of the assemblies 6 from the axis 8.

In operation of the construction according to the present invention the vapor to be cooled, such as steam, initially is admitted into a relatively large cross section central supply conduit 12 located on the axis 8 and having an upper distributor head formed with a channel l3 of annular configuration, the outer and inner diameter of which increase constantly in the direction towards the upper outlet opening 4 of the cooling tower l. The increase of the inner diameter in each vertically superposed horizontal plane is greater than that of the outer diameter. The channel 13 thus has a configuration which in vertical cross section is approximately V-shaped, as clearly shown in FIG. 1. Radially directed straight-lines substantially horizontal steam distributing connecting pipes extend in spoke-like manner from the ends 14 of the channel 13 and communicate with the upper ends l6 of the heat-exchange elements 5 of the annulus A. The upper ends 16 of the heat-exchange elements in the sets 6 are formed by pipe sections constituting an axial extension of the re spective pipe 15. Connected to this pipe section are the finned tube of the individual heat-exchange elements 5 which extend downwardly therefrom at an angle and terminate in pipe-like horizontal compensate collecting tubes 17. The heat-exchange elements 5 in the assemblies 6 of the annulus A act as condensers.

The steam which has been precipitated as condensate in the assemblies 6 of the upper annulus A is discharged via the horizontal condensate collecting tubes 17. Since the heat-exchange elements 5 in the assemblies 6 operate at a substantial excess of steam, it follows that the condensate collecting tubes 17 act not only for discharge of condensate but also as overflow and supply conduits for steam which is supplied by them to heatexchange elements 5' of the lower and inner annulus B.

The condensate collecting tubes 17 of the adjacent heat-exchange elements 5 of any two consecutive assemblies 6 extend in horizontal direction towards axis 8 in a V-shaped manner, and in the region between the upper and lower annuli A and B they join and here constitute the upper ends 18 of the assemblies 7 of the lower annulus B.

These assemblies 7 are so constructed that approximately three-fifths of the heat-exchange elements 5 forming the assemblies 7 act as condensers, and the remaining two-fifths are constituted by the heatexchange elements 5" which act as dephlegmators. The operation of condensers and dephlegmators is well known in the art and requires no discussion. E.g. see DT-PS l,()66,596 and DT-AS 1,451,131, which shows the operation of condensers and dephlegmators. The heat-exchange elements 5' are located in the outer regions 19 of the assemblies 7, whereas the heatexchange elements 5" are located in the inner regions 20 of the assemblies 7.

The excess steam in the annulus A, approximately one-third of the total quantity of steam to be condensed, enters into the upper end portions 18 of the assemblies 7, is here in part precipitated to the extent of approximately two-thirds of the incoming amount of steam in the heat-exchange elements 5', and is discharged as condensate from the condensate collecting conduits 21 which communicate with the lower ends of the assemblies 7. This means that even the heatexchange elements 5' still operate at a substantial steam excess. Thus, the collecting conduits 21 of this second condensation stage act as overflow conduits for excess steam which is supplied to the heat-exchange elements 5" that act as dephlegmators and it constitute the third stage. Here, again, the supply of steam takes place in an essentially straight line via the conduits 21, and the condensate which is obtained in the heatexchange elements 5" is again discharged. The removal of all condensate from the various stages takes place via conduit 26.

The heat-

exchange elements

5, 5', 5" of the annulus A, the annulus B or both of the annuli, can be provided with shutter-like covers 22 which are well known in the art and which serve to regulate the flow of cooling air to these elements. It is also possible to provide valves in the pipes 15 intermediate the conduit 12 and the assemblies 6 to regulate the steam flow. Those crosssectional portions of the tower in which no

heatexchange elements

5, 5' and 5" are located, for instance the portions 23, can be blocked in known manner against the flow of air therethrough.

One or more venting conduits 24 are connected with that portion 20 of the annulus B which is composed of the heat-exchange elements 5" acting as deplegmators. One or more suction-producing devices 25 communicate with the conduit or conduits 24 to produce suction therein. It is advantageous if each sector is provided with a separate conduit 24 and a separate suction device 25. The suction devices and the operation of the conduits 24 are well known in the art and require no detailed discussion.

It will be understood that each of the elements described above, or two or more together, may also find a useful application in other types of constructions differing from the types described above.

While the invention has been illustrated and described as embodied in a cooling tower for condensation of vaporous media, it is not intended to be limited to the details shown, since various modifications and structural changes may be made without departing in any way from the spirit of the present invention.

Without further analysis, the foregoing will so fully reveal the gist of the present invention that others can, by applying current knowledge, readily adapt it for various applications without omitting features that from the standpoint of prior art, fairly constitute essential characteristics of the generic or specific aspects of this invention and, therefore, such adaptations should and are intended to be comprehended within the meaning and range of equivalence of the following claims.

What is claimed as new and desired to be protected by Letters Patent is set forth in the appended claims.

I claim:

1. A cooling tower for condensation of vaporous media, comprising an upright peripheral tower wall having a lower region with air inlet apertures, and an upper region with an air outlet; at least one upper annulus of first heat-exchange elements inwardly adjacent said wall, and at least one downwardly offset second lower annulus of heat-exchange elements inwardly spaced from said upper annulus, the elements of each annulus being upwardly and inwardly inclined and having upper and lower end portions, and at least some of said elements of each annulus acting as condensers; a supply conduit centrally within the confines of said tower wall for supplying vaporous medium; a plurality of straight connecting pipes radiating substantially horizontally from said supply conduit and communicating with said upper end portions of said first elements; and a plurality of substantially horizontal condensate collecting tubes communicating with said lower end portions of said first elements and also communicating with said upper end portions of said second elements, so as to convey both condensate and vaporous medium from said first to said second elements.

2. A cooling tower as defined in claim 1, wherein the second elements acting as condensers are provided at radially outer locations of said lower annulus, and wherein some of said second elements act as dephlegmators and are located at radially inner locations of said second annulus and connected with said second elements acting as condensers by respective ones of said tubes.

3. A cooling tower as defined in claim 1, wherein the two tubes of respective pairs of adjacent first elements communicate with one another.

4. A cooling tower as defined in claim 1, wherein the number of elements in said upper and lower annulus is identical.

5. A cooling tower as defined in claim 1, wherein the second elements are circumferentially offset relative to the first and are each located substantially midway between two circumferentially successive ones of said first elements.

6. A cooling tower as defined in claim I, wherein the distance between the central axis surrounded by said wall and the radially innermost portions of said first elements equals substantially two-thirds of the same distance to the radially outermost portions of said second elements.

7. A cooling tower as defined in claim 1, wherein the radial distance between the central axis surrounded by said wall and the radially innermost portions of said second elements equals substantially one-third of the same distance to the radially outermost portions of said first elements.

8. A cooling tower as defined in claim 1, wherein said second elements are inclined upwardly at a steeper angle than said first elements.

9. A cooling tower as defined in claim 1, and further comprising blocking means in said pipes for blocking the flow of vaporous medium therethrough.

10. A cooling tower as defined in claim 1; and further comprising airflow-varying shutters associated with said elements of at least one of said annuli.

11. A cooling tower as defined in claim 1, wherein said wall surrounds an internal space having a crosssection which is in parts free of said heat-exchange elements; and further comprising means blocking said parts against the passage of air.

12. A cooling tower as defined in claim 2; further comprising suction-exerting venting conduit means communicating with said elements which act as dephlegmators.

13. A cooling tower as defined in claim 12, wherein said venting conduit means comprises a plurality of venting conduits each communicating with some of said elements acting as dephlegmators.

Claims

6. A cooling tower as defined in claim 1, wherein the distance between the central axis surrounded by said wall and the radially innermost portions of said first elements equals substantially two-thirds of the same distance to the radially outermost portions of said second elements.

11. A cooling tower as defined in Claim 1, wherein said wall surrounds an internal space having a cross-section which is in parts free of said heat-exchange elements; and further comprising means blocking said parts against the passage of air.