Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
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AIR CHANNE~ING DEVICE FOR MIXING DRY
AND HUMID AIR STR~AMS OF A
~OMBINED WET AND DRY ATMOSPHERIC COOLER
I. DESCRIPTION
Field of the Invention
The present invention relates to installations for
placing a liquid in contact with a gas and more particularly
to combined atmospheric coolers or cooling towers in which a
liquid to be cooled, for example water, is placed in direct
contact in one heat exchange unit and in indirect contact in
another heat exchange unit with a cooling gas, for example,
air of the atmosphere.
Background of the Invention
Combined wet and dry coolers usually comprise one
or more openings constituting a first air inlet anfl a wet
heat exchange unit in which the air from the first inlet is
placed in direct contact with the liquid to be cooled and a
dry heat exchanger unit whose exchange elements may be
disposed vertically at the periphery of the tower adjacent
one or more openings constituting a second air inlet in
parallel with the first. In the dry heat exchange unit the
air is not in direct contact with the liquid, the latter
flowing in heat exchange elements, for example, finned tubes
or smooth tubes of metal or synthetic material. These
coolers may employ a natural draught or a forced draught
produced by suction or blower fans.
Such combined coolers are designed to avoid at the
air outlet of the installation the formation of clouds which
usually occurs at the air outlet of conventional wet coolers.
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In the past avoidance oE air outlet clouds has only been
partly achieved and there often remain cloudy streams which
result from an insufficien-t mixture of the hot and humid air,
which issues from the wet exchanger and flows at the centre
of the tower, with the hot dry air which issues from the
dry heat exchanger.
To overcome this problem of the mixture of the two
air streams, it is known to dispose inside the cooling tower
deflecting surfaces which produce turbulence in the dry air
current and directs it toward the centre of the tower.
In some arrangements, these deflecting surfaces are
formed by curved guide vanes which engage the humid air current
and impart a giratory motion to the dry air to improve mixing
of the two air streams.
It is also known in the prior art to provide a cooling
tower at the base of which the gas stream which enters the in-
stallation passes through at least one heat exchange device,
and at least one deflector disposed in the tower above the heat
exchange device and adapted to direct at least a part of the
gas stream toward the periphery of the tower.
Summary of the Invention
According to the invention, there is provided a device
for mixing dry and humid air streams o~ a combined atmospheric
cooler employing parallel air streams, comprising: a wet heat
exchange unit and a dry heat exchange unit disposed in parallel
in the air streams, the device for mixing the dry and humid
air streams comprising; air inlet means for the wet heat ex-
change unit, air inlet means for the dry heat exchange unit,
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commOn air outlet means for both the wet and dry heat
exchange units, air stream deflecting surfaces, the:
deflecting surfaces formed by a plurality of spaced
apart channel forming members which are open in the
direction of the air outlet means of the cooler, the.
spaced channel forming members defining alternate gas
passages for the humid and the dry air streams, the
channel forming members extending in the space located
between the wet heat exchange unit and the dry heat ex-
10change unit, the channel forming members further extend-
ing on a converging slope from the region in which the
dry air stream exits from the dry exchange unit which is
the nearest to the wet heat exchange unit and toward the
centre of the cooler, and wherein the channel forming
members have V- Or U- shapes in cross-section.
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Brief Description o the Drawings
Further features of the invention will be apparent
from the ensuing description with references to the
accompanying drawings which are give~ solely by way o
example and in which:
FIG. 1 is an eleva-tional and sectional view of
a cooler unit having a suction fan to which the invention is
applied;
FIG. 2 is a side sectional view of the unit shown
in FIG. l;
FIG. 3 is a sectional view taken on line 3-3 of
FIG. l;
FIG. 4 is an elevational and sectional view of a
cooler unit similar to that of FIGS. 1 to 3;
FIG. 5 is a side sectional view of the unit shown
in FIG. 4;
FIG. 6 is a sectional view taken on line 6-6 of
FIG. 4;
FIG. 7 is a plan sectional view of another
embodiment of a cooler unit to which the invention is
applied;
FIG. 8 is a side sectional view of the unit shown
in FIG. 7; and
FIG. 9 is an elevational sectional view of a cross-
current cooler to which the invention is applied.
Detailed Description of the Invention
In FIG. 1, the invention is considered as being
applied to a cooler unit having a suction fan.
The installation of FIG. 1 comprises a tower 1
which terminates in its upper part in a sleeve 2 and a
diffuser 2a. A suction fan 3 is mounted in the circular
orifice of the sleeve 2.
The tower 1 has at its base lower peripheral
openings 4 Eorming an air inlet for a wet heat exchange unit
5. This wet heat exchange unit is of the type in which the
air of the atmosphere, which enters ihe openings 4, is in
direct contact with the water from a distribution system 6.
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This wet heat exchange unit or contacting unit 5, which
extends throughout, or substantially throughout, the inner
section of the tower is of the so-called "cross-current"
type, that is to say the type in which the air stream
travels in an upward direction opposed to the downward
movement of the water.
The water supplied by the distribution system 6
is received in a basin 7.
Disposed above the distribution system 6 is a
droplet separator 8 formed, for example, by panels of
parallel corrugated sheets, the crests of the corrugations
being horizontal and defining therebetween a sinuous path
along which there is removed from the rising air stream a
part of the droplets that it contains in suspension after
it has been put in contact with the water.
Above the wet heat exchange unit 5, the tower
comprises upper peripheral openings 9 forming air inlets
for a pair of dry heat exchange unit 10. The part of the
tower 1 provided with the openings 9 constitutes a chamber
11 for mixin~ the humid and dry air streams coming respec-
tively from the wet heat exchange unit 5 and the dry heat
exchange unit 10. Disposed in the chamber 11 are air
channeling members 12 which extend upwardly from the
periphery oE the chamber toward the centre of the chamber.
In the embodiment shown in FIGS. 1 to 3, the
channels 12, formed of a pair of elements, formed in a
V-shaped section or configuration which has a constant angle
and a pointed bottom, the height of the elements decreasing
in a direction from the periphery of the cooler toward the
interior thereof.
The cooler described with reference to FIGS. 1
and 3 has a rectangular section so that the channels 12 are
disposed in such manner as to converge below the circular
orifice of the sleeve 2 of the suction fan 3 (FIG. 3). With
convergent channels such as those of the presently described
embodiment of a cooler according to the invention, obstruc-
tion of the centre of the cooler by an excessive density of
channels should ~e avoided. This is achieved in the
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presently described embodiment by the fact that the channels
12 are formed of elements which decrease in width in the
direction of the centre o~ the cooler.
If the channels ha~e a constant width, it may be
necessary to provide, among the channels which lead to the
centre region of the cooler, certain channels of shorter
length, for example every other channel, whereas the
peripheral ends of all of the channels being in alignment
at the periphery of the tower.
When the cooler has a circular section, the
channels are preferably disposed radially.
In the presently described embodiment, the channels
12 are maintained in position by guys 13.
The material of construction of the channels is
preferably light in weight and resistant to corrosion due to
the hot and humid air. Asbestos-cement, aluminum, galvanized
steel, wood, or plastic are suitable for the construction of
such channels.
The bottom-of the channels does not have to be
airtight. The V-section channels, formed by planar plates
or elements may have a gap therebetween. The gap permits
water which might condense or fall into the channel to flow
in the lower section and the entry of humid air coming ~rom
the wet heat exchanger - which improves the mixture, provided
that it occurs to a limited extent and avoids hindering the
flow of the dry air stream.
In the embodiment just described, the channels
are rectilinear and have a decreasing V-shaped section.
However, it is possib]e to envlsage the use of
U-shaped sections with a rounded bottom or other cross-
sectional shapes. Moreover, the channels may also be curved,
in which case the ends thereof facing the inlet openings 9
would be horizontal and would have a relatively slight slope,
whereas the ends thereof comm~micating with the centre ~art
of the cooler would have an inclination in the neighborhood
of vertical.
Moreover, each channel may have a constant section
throughout the length thereof, which renders it particularly
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easy and inexpensive to make.
The device just described operates in the following
manner:
The channels 12 which extend upwardly from the
periphery of the chamber 11 toward the centre of the latter
constitute an obstacle for the xising air stream from the
wet heat exchange unit 5, which obstacle creates a pa~sageway
for entry of the air issuing from the dry heat exchange
device 10.
The air which issues from the dry heat exchange
unit 10 in the region of a channel 12 travels along the
latter without being disturbed by the air issuing from the
wet heat exchange unit 5, whereas, in the absence of such
channels, it would be urged back to the periphery of the
cooler by the humid air.
As the width of the channels 12 decreases in the
direction away from the dry heat exchange unit, there is a
decrease in the flow of dry air conveyed by each of these
channels. This decrease in the dry air flow of each channel
12 corresponds to an emission of dry air throughout the
length of the channel toward the outlet end of the cooler,
which effectively contributes to the good mixing of the dry
and humid air stream.
The pressure drop due to the channels 12 is very low
since the bottoms of the channels are profiled so as to
deviate the humid air stream without creation of whirling and
disturbances which cause high pressure drop and the divergent
part of each channel 12 does not produce a sudden widening
of the section available for the humid air stream which would
also produce high pressure drop.
It will, however, be noted that on the downstream
side of the longitudinal edges of the channels 12, there is a
zone of a slight whirling which promotes mixing of the dry
and humid air streams.
As the dry air is guided in its travel toward the
centre of the tower, the humid air stream is not urged so much
toward the centre but is directed more toward the periphery of
the tower in the regions devoid of channels 12.
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The cooler shown in FIGS. 4 to 6 differs from that
of FIGS. 1 to 3 i,n -that the device for mixing the dry and
humid air streams is formed by two channels 14 arranged in
the form of a chevron, each channel being formed by two
branches 15 which meet in the centre part of the chamber 11
located above the wet heat exchanger device 5. The channels
14 join the two air inlets 9 of the dry heat exchange unit
10 below the suction orifice of the fan 3.
In the presently described embodiment, the channels
14 have a uniform section and their two branches 15 meet at
a sufficient distance below the suction orifice of the fan 3
to avoid disturbing the operation of the fan and provide
sufficient access to the humid air.
As can be seen in FIG. 5, the channels 14 have a
semi-circular cross-sectional shape and are supported by bars
16 secured to the cooler.
The device shown in FIGS. 4 to 6 operates in a
similar manner to the device shown in FIG. 3.
The cooler shown ln FIGS. 7 and 8 is a cooler
employing horizontal air flow.
It comprises a cross-current wet heat exchanyer 17
including an air inlet 18 and a water distribution system
formed by spray nozzles 19 which are supplied with water, for
example, by an open reservoir 20. The streaming water is
received in basin 21.
Placed at the outlet of the wet heat exchange unit
17 is a dry heat exchange unit 22 comprising inlets 23 which
are perpendicular to the air inlet 18 of the wet heat exchange
unit 17 which is, for examp,le, formed by two heat exchangers
each of which is formed by a set of vertical smooth tubes 24
made of plastics material.
The dry heat exchange unit 22 defines with the wet
heat exchange unit 17 the chamber 25 for mixing the dry and
humid air streams.
The cooler further comprises a suction fan 26 for
drawing the air mixture out of the chamber 25. The fan 26
is mounted in a sleeve 27 which defines the suction orifice
of the fan.
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Disposed in the mixing chamber 25 are the channels
~8 which are placed horizontally and converge to~Jard the
axis of symmetry of the cooler in the direction of the fan
26.
As can be seen in FIG. a, the channels 28 are
disposed in the mixing chamber 25 in such manner that their
openings face the suction orifice of the cooler.
FIG. 8 also shows that the channels 28 are
arranged in groups of channels which are parallel and are in
superimposed relation.
In the presently described embodiment, the channels
28 are rectilinear and have a decreasing cross-section.
It will be understood that all the modifications
of shape envisaged for the channels of the coolers described
with reference to FIGS. 1 to 6 may also be adopted for the
cooler of FIGS. 7 and 8.
If curved channels are used, the ends of the latter
in the vlcinity of the air inlets 23 of the dry heat exchange
unit 22 must be parallel, or slightly inclined, to the
direction of the air issuing from this unit, whereas their
opposite ends must be parallel, or slightly inclined, to the
general direction in which the air issues from the cooler.
The cooler shown in FIG. 9 comprises cross-current
wet heat exchanye units 30 including air inlets 31, reservoirs
32 for supplying water to the heat exchange units and a basin
33 for receiving the water. Disposed above the reservoirs 32
for the water, are dry heat exchange units 34 having air
inlets 35 and a suction fan 36 is placed in a sleeve 37
surmounted by a diffuser 38 above the dry exchange units 3~.
Disposed in the space de~ined by the wet heat
exchange units 30 and the dry heat exchange units 34 are
channels 39 which deflect the dry air streams and are held
in position by guys 40.
In contrast to the units shown in FIGS. 1 to 6, in
which the peripheral ends of the channels are disposed in the
immediate vicinity of the dry heat exchange units, the
channels 39 have their peripheral ends placed immediately
above the lower edges of the reservoirs 32 containing the
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water for the wet heat exchang~ units.
Statement of Industrial Application
.
Wet and dry air streams from a combined wet and
dry atmospheric cooler are mixed to reduce the tendency for
cloud formation when the air streams issue from the cooler
et
