Cooling tower

A cooling tower for condensing water has a hyperbolical main wall with an per portion which defines a passage for ascending vapor-laden air. The upper portion contains an annular insert serving to intercept currents of cool air which develop and tend to flow into the interior of the intermediate portion of the main wall at low wind velocities and/or to intercept turbulent air which develops and tends to flow into the intermediate portion when the wind velocity at the top of the tower is high. The insert may constitute a sheltered passageway for workmen and may be made integral with the upper portion of the main wall. The width of the annular space which is defined by the insert and upper portion of the main wall may be a whole multiple of the depth of such space, and the cross-sectional area of this space can approach one-half the cross-sectional area of the passage through which cooling air escapes from the tower by flowing upwardly within and above the insert.

BACKGROUND OF THE INVENTION 
The present invention relates to improvements in cooling towers for 
condensing water or the like. More particularly, the invention relates to 
improvements in natural-draft or mechanical-draft cooling towers of the 
type wherein the central vertical section of the main wall of the tower is 
preferably a hyperbola so that the upper region of the main wall acts not 
unlike a diffusor and promotes the flow of ascending air. 
Cooling towers often reach a height of up to and in excess of 100 meters 
and, in some instances, a height of up to and in excess of 150 meters. The 
diameter may reach or exceed 50 meters, in some instances 120 meters. 
Their main wall is often made of concrete or analogous construction 
material and is disposed above a water-distributing system which sprinkles 
water into a basin whereby the streamlets of water are contacted by air 
which enters the lower portion of the main wall and flows upwardly. It is 
also known to construct such cooling towers for cross-flow of gaseous heat 
removing medium. The towers may be designed for natural draft or 
mechanical draft; in the latter instance, the fan or fans can be mounted 
at the top of or below the main wall, i.e., the towers can be operated 
with forced draft or induced draft. A hyperbolical main wall exhibits a 
number of important advantages in that it enhances the stability and 
contributes to lower cost of the cooling tower. However, in presently 
known cooling towers with hyperbolical main walls, the aerodynamic factor 
has been neglected so that such towers are not entirely satisfactory, 
especially in the region of the upper portion of the main wall. 
The manner in which air flows in the region of the upper portion of the 
main wall exerts a pronounced influence on the mode of operation and 
efficiency of the tower. The nature of air flow at the upper portion 
depends largely on atmospheric conditions, especially on the velocity of 
wind at the crown of the tower. Thus, in the absence of any wind or when 
the velocity of wind is relatively low but the wind blows in several 
directions, thermal instability develops at the upper end of the main wall 
which brings about a rather pronounced downward flow of cool air in the 
region between the ascending column of cooling air which entrains water 
vapors into the atmosphere and the internal surface of the main wall. The 
inflowing cool air reduces the cross-sectional area (i.e., it constricts 
the ascending column of vapor-laden air so that the efficiency of the 
cooling tower decreases well below the maximum or average efficiency. This 
will be readily appreciated since such constriction of the ascending 
column of vapor-laden air increases its speed so that the length of 
intervals during which the ascending body of air is maintained in contact 
with water in the cooling tower is reduced well below the optimum length. 
The acceleration of ascending air takes place in the entire region where 
the relatively cool atmospheric air is allowed to penetrate into and to 
flow downwardly along the internal surface of the main wall. This means 
that once-cooled water must be recycled through the tower because the 
maximum temperature of water which can be reused in a plant or which can 
be released into rivers or ponds is prescribed in most industrial 
countries and is vigorously enforced by authorities. The main reason for 
the just discussed thermal instability in the region of the upper end of 
the main wall in a cooling tower wherein the main wall has a hyperbolical 
vertical sectional outline is that the pressure gradient of warmer air in 
the interior of the tower is less than the pressure gradient of 
surrounding atmospheric air. 
When the wind velocity at the top of the cooling tower increases to a 
medium or high value, the likelihood of penetration of cool air along the 
internal surface of the main wall is less pronounced. However, the rapidly 
flowing air currents are turbulent, and pronounced complex tubulence in 
the passage which is provided for escape of vapor-laden columns of 
ascending air reduces the effective cross-sectional area of the columns. 
This brings about the same drawbacks as if cool air were permitted to 
descend along the inner side of the main wall. 
SUMMARY OF THE INVENTION 
An object of the invention is to provide a novel and improved natural-draft 
or mechanical-draft cooling tower which is constructed and assembled in 
such a way that the likelihood of penetration of cool or turbulent 
atmospheric air into the passage for evacuation of vapor-laden air is 
either prevented or reduced to a small fraction of penetration in 
heretofore known cooling towers. 
Another object of the invention is to provide the cooling tower with a 
novel and improved main wall, especially as regards the aerodynamic 
characteristics of the upper portion where the column of air which has 
contacted the fluid to be cooled escapes from the column. 
A further object of the invention is to provide a cooling tower, especially 
a wet cooling tower, with novel and improved means for insuring 
predictable outflow of ascending air at the upper end of a hyperbolical 
main wall. 
An additional object of the invention is to provide a cooling tower which 
is better suited to operate with a high or optimum degree of efficiency 
irrespective of the direction, velocity and/or other characteristics of 
prevailing winds, than a conventional tower. 
The invention is embodied in a cooling tower, particularly in a wet cooling 
tower for condenser water or the like which may be of the natural-draft or 
mechanical-draft type and the lower portion of which includes a water 
distributor system, one or more dry heat exchangers or both. The cooling 
tower comprises an upright annular main wall which is preferably 
hyperbolic (i.e., its cross-sectional outline in a central vertical plane 
preferably resembles a hyperbola) so that the upper section of the main 
wall constitutes a diffusor whose cross-sectional area increases in a 
direction above and away from the ground. The main wall has an 
air-admitting lower portion which is preferably located above a water 
basin and into which air enters through gaps between suitable supports for 
the main wall, an intermediate portion or chimney, and an upper portion 
which discharges heated and vapor-laden air into the atmosphere. In 
accordance with a feature of the invention, the tower comprises a 
substantially annular insert which is preferably located in the upper 
portion of the main wall and preferably defines therewith an annular space 
which is surrounded by the internal surface of the upper portion and is 
open at the top (i.e., it has an open upper side). Thus, the space permits 
the inflow of and thereby intercepts cool atmospheric air as well as 
tubulent air tending to penetrate into the intermediate portion of the 
main wall by flowing downwardly along the internal surface of the upper 
portion. The insert and the upper portion of the main wall may form an 
annular space which is bounded from the outer side and from below, a space 
which is bounded from within and from below, or a space which is bounded 
from within and from without as well as from below. 
The novel features which are considered as characteristic of the invention 
are set forth in particular in the appended claims. The improved cooling 
tower itself, however, both as to its construction and its mode of 
operation, together with additional features and advantages thereof, will 
be best understood upon perusal of the following detailed description of 
certain specific embodiments with reference to the accompanying drawing.

DESCRIPTION OF THE PREFERRED EMBODIMENTS 
FIG. 1 shows a natural-draft wet cooling tower which includes an annular 
main wall 1 having a hyperbolical outline. The main wall 1 constitutes a 
mantle or shell and has an intermediate portion or chimney 1a, an 
air-discharging upper portion or crown 5 and an air-admitting lower 
portion 5A resting on a system of supports 10. The supports 10 are mounted 
on foundations 11 which are embedded in the ground G. The cooling tower 
further comprises a water basin 2 and a distributing system 3 which 
sprinkles water into ascending streams of air which enter in the gaps 
between the supports 10. The main wall 1 may consist of relatively thin 
concrete or another rigid or substantially rigid material the minimum 
thickness of which may be in the range of 14 centimeters. The passage 4 
through which air escapes from the main wall 1 of the tower is surrounded 
by a ring-shaped insert 6 best shown in FIG. 2. The insert 6 comprises a 
substantially cylindrical portion 8 which is spacedly surrounded by the 
internal surface 9 of the upper portion 5 of the main wall 1, and a 
substantially washer-like portion 8a which extends between the lower end 
of the cylindrical portion 8 and the upper portion 5. The portions 5, 8, 
8a define an annular space 7 which is surrounded by the internal surface 9 
and takes up a certain part of the area within the top portion 5. The 
cross-sectional area of passage 4 is substantially less than the combined 
cross-sectional area of passage 4 and the space 7. As a rule, the 
cross-sectional area of space 7 will not exceed 30 percent of the combined 
cross-sectional area of passage 4 plus space 7. 
The insert 6 constitutes but one form of means which can be mounted on or 
inserted in the upper portion 5 to intercept at least some cool air as 
well as turbulent air tending to penetrate into the space within the 
intermediate portion 1a of the main wall 1. The illustrated insert 6 has 
an L-shaped cross-sectional outline; however, it is equally within the 
purview of the invention to configurate the insert in such a way that the 
portions surrounding the annular space will have a U-shaped 
cross-sectional outline. It is also possible to use an insert having a 
U-shaped cross-sectional outline and to bond the outer leg of the U to the 
upper portion 5 of the main wall. Such outer leg then constitutes a 
component part of the upper portion 5. 
As shown in FIG. 1, the intermediate portion 1a of the main wall 1 has an 
upper part 1a' which diverges upwardly toward the upper portion 5, and a 
lower part 1a" which diverges downwardly toward the lower portion 5A. The 
width y on the space 7, as measured radially of the upper portion 5, need 
not but preferably at least equals or exceeds the extent of divergence d 
of the upper part 1a'. 
In accordance with a modification, the length of the cylindrical portion 8 
of the insert 6 shown in FIG. 2 can exceed, several times, the length of 
the upper portion 5, as considered in the axial direction of the cooling 
tower. In FIG. 2, the uppr end face 8' of the portion 8 is located at or 
close to the level of the upper end face 5' of the upper portion 5. In 
accordance with the just mentioned modification, the height of the 
ring-shaped portion 8 (indicated by broken lines, as at 108) can be 5x 
wherein x is the depth of space 7 or the length of upper portion 5. Such 
insert is even more effective as a baffle which directs cool and/or 
turbulent air upwardly and away from the intermediate portion 1a. 
The width y of the space 7 (as considered radially of the upper portion 5) 
may equal or approximate the depth x. However, it is normally preferred to 
select the dimensions of the space 7 in such a way that the width y 
exceeds the depth x or vice versa; for example, the width y may equal 3x 
or x plus n wherein n does not exceed 2x. 
This is indicated in FIG. 2 by broken lines wherein the width y' of a 
modified insert 106 equals or approximates 3x. 
In each instance, the improved insert prevents cool air from flowing along 
the internal surface 9 of the upper portion 5 toward and into the interior 
of the intermediate portion 1a of the main wall 1. The prevention may be 
total or partial; however, the insert invariably intercepts substantial 
quantities of cool air and/or turbulent air. Such air is guided along the 
external surface of the portion 8 or 108 so that its direction changes. 
Air turbulence (which creates eddy currents tending to flow downwardly 
along the internal surface 9 of the upper portion 5) is likely to develop 
at medium or high wind velocities. Such eddy currents are also deflected 
by the ring-shaped portion 8 or 108 so that they cannot descend into the 
interior of the intermediate portion 1a. The hyperbolical outline of the 
main wall 1 enhances the efficiency of the cooling tower by promoting the 
upward flow of cooling air, even when the direction and/or velocity of 
wind changes within an extremely wide range. 
It is clear that the inner diameter of the cylindrical portion 8 or 108 is 
selected with a view to insure that the passage 4 is large enough to allow 
for evacuation of vapor-laden air without undue acceleration irrespective 
of the velocity and/or direction of wind in the region of the upper 
portion 5a. Thus, the dimensioning of the passage 4 satisfies the 
thermodynamic requirements in spite of the fact that the diameter of the 
passage 4 is less than the diameter of the internal surface 9. By 
preventing the inflow of turbulent and/or cool air into the intermediate 
portion 1a, the improved insert insures that the temperature of air in the 
main wall 1 varies at a predictable rate. The cylindrical portion 8 or 108 
acts not unlike a baffle which deflects the cold air streams and/or 
turbulent air so that such air flows upwardly rather than toward the 
interior of the intermediate portion 1a. 
As mentioned above, the width y or y' of the annular space which the insert 
defines with the upper portion 5 of the main wall preferably exceeds the 
extent of divergence d of the upper part 1a' of the intermediate wall 
portion 1a. As a rule, the cross-sectional area of the part 1a' 
immediately below the upper portion 5 exceeds the cross-sectional area of 
the intermediate wall 1a between the parts 1a' and 1a" (i.e., at the lower 
end of the diffusor-like part 1a') by at least 10 percent and preferably 
by at least 15 percent. As also mentioned above, the cross-sectional area 
of the space 7 may equal up to 30 percent of the cross-sectional area of 
the space within the surface 9. In other words, the ratio of the 
cross-sectional area of space 7 to the effective cross-sectional area of 
the passage 4 may be as low as 3:7. 
It has been found that the cost of making and installing the insert 6 (or 
of building a main wall wherein the insert is integral with the upper 
portion 5) is a very small fraction of the overall cost of the cooling 
tower. On the other hand, the advantages of the insert are so pronounced 
that, in the long run, its installation in the main wall greatly enhances 
the effectiveness and contributes to more predictable cooling action 
irrespective of the prevailing wind conditions. Thus, the improvement in 
aerodynamic conditions at the top of the main wall (without in any way 
affecting the stability of the tower and/or the ability of the 
intermediate portion of the main wall to act as a chimney if the tower is 
of the natural-draft type) invariably warrants the mounting of the insert 
not only in a newly erected cooling tower but also in existing cooling 
towers. 
If the cooling tower is very large, e.g., if its maximum diameter exceeds 
50 or 100 meters, the portion 8a of the insert can be used as the floor of 
a ring-shaped passageway for workmen. In all presently known cooling 
towers, the passageway is disposed around the upper portion of the main 
wall. This constitutes a potential danger to workmen, especially if the 
tower is a wet cooling tower or a combined wet-dry cooling tower. Thus, 
when the weather is cold, vapors which are entrained by ascending cooling 
air are condensed and form icicles which depend from and adhere to the 
external passageway. A workman is likely to slip which invariably results 
in serious injuries or death, especially if the height of the tower is in 
the range of several hundred feet. The improved insert renders the 
externally mounted passageways obsolete. Moreover, the insert is 
sufficiently close to ascending heated air so that the formation of 
icicles is unlikely or impossible. 
In its simplest form, the improved insert merely consists of a washer, 
i.e., the cylindrical portion 8 or 108 shown in FIG. 2 is optional. The 
annular space which is adjacent to the internal surface of the upper 
portion is then open at the top and from within. 
FIG. 3 shows that the insert 206 may constitute the frustum of a hollow 
cone which is open at the top and bottom so that the space 207 acquiries a 
substantially triangular cross-sectional shape. The external surface 206a 
of the insert 206 tapers inwardly and away from the internal surface 9 of 
the upper portion 5. 
FIG. 4 shows that the insert 306 has a portion 308 which is similar to the 
insert 206 of FIG. 3 and a washer-like portion 308a. The cross-sectional 
outline of the space 307 is a trapezoid. 
As mentioned above, the invention can be embodied in wet cooling towers 
(such as the tower shown in FIG. 1), in combined wet-dry cooling towers, 
or in dry cooling towers. 
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 which 
fairly constitute essential characteristics of the generic and specific 
aspects of our contribution to the art and, therefore, such adaptations 
should and are intended to be comprehended within the meaning and range of 
equivalence of the claims.