Note: Descriptions are shown in the official language in which they were submitted.
This invention relates to a method of e~aporative
heat exchange in which water from wh;ch heat is to be
extracted is sprayed in such fashion as to induce concurrent
air flow with resulting mixing~ heat exchange and partial
evaporation of the water and more particularly such a method
in which the water is repeate~ly sprayed in a series of
stages each involving inducing a new supply oF air to the
heat exchange.
In general, an evaporative heat exchanger is
designed to deal with certain load conditions which are
imposed by the needs of the use to which the apparatus is
put. These include volume of water to be cooled per unit
time, the amount or range of cooling of said water and air
temperatures both absolute and relative to the temperatures
of the water to be cooled.
To meet a higher load condition the designer of a
conventional cooling tower has the option to increase the
physical size of the unit or to a limited extent increase
the air quantity with a resultant increase in input energy
or both. In the case of an injector cooling tower (as
described in U.S. patent No. 3,807,145 issued to applicant
on April 30, 1974), much more flexibility is possible by
changes in the pressure of the water spray, and therefore
input energy to drive the water pumps.
Surprisingly it has been found, as a part of this
invention, that with ;njector cooling ~owers one can meet -
higher designed heat load conditions without increase in
equipment and without increase in input energy to drive the
water pumps. ~
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BAC 32
1 In an injector type cooling tower in which the
2 water itself pumps the air~ the air and water necessarily
3 flow concurrently and therefore the initial temperature
4 differences between the air and water tends to decrease as
the fluids flow together through the apparatus~ Since
6 temperature difference has an e~ect on the efficiency of
7 the heat exchange, it is apparent that this type of ~pparatus
8 suffers from the effects of low temperature dif~erence as
9 the designed approach temperature is reached. Yet, accord-
ing to the method of the present invention it is possible
11 to reduce this efect of low temperature differential in
12 injector type cooling towers by exposing the water to a
13 series of stages thereby taking advantage of large air-
14 water initial or entering temperature differences. This
lS advantage along with the greatly increased heat transfer
16 efficiencies achieved by series exposure to water and air
17 dramatically decrease the size of unit necessary to deal
18 with a particular heat load and without increase in pumping
19 energy.
.
Other objects and advantages of the invention will
21 be apparent from the following detailed description thereof
22 in conjunction with the annexed drawings wherein:
23 FIGURE 1 is an isometric view of two injector type
24 cooling towers connected to operate in accordance with the
25 principles of the present invention; and ~-
26 FIGURE 2 is a graph in which physical size of the
27 injector is plotted~against heat loads to demonstrate the - ~ -
28 advantages of the~ method of the present invention in compari-
29 son to conventional methods.
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BAC-32IA
~ 9
1 FIGURE 3 is a schematic representation of a
three stage cooling tower system connected to operate
3 in accordance with the principles of the present invention.
4 FIGURE 4 is an isometric view of two injector
type cooling towers connected to operate simllar to
6 FIGURE 1 but where the second pump is eliminated by
7 utili~ing gravity feed~
8 PIGURE 5 is an isometric view of four injector
9 type cooling towers connected to operate similar to
10 PIGURE 4 but where the capacity per uni~ height of the
11 installation is maximized. .
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Referring first to Figure 1, it will be seen that
two injector type evaporative cooling towers are illustrated.
The details of the injector towers of Figure 1 are shown in
the above mentioned U.S. patent No. 3,807,145. While the
units shown are structurally identical, to facilitate
distinguishing them in the following discussion, the left
unit as viewed ;n ~igure 1 w;ll be referred to as the f;rst
stage whereas the right one will be referred to as ~he second
stage. Reference numerals for like parts will bear the
subscr;pt "a when referring to the second stage.
Each unit of each stage comprises an air entry
mouth 10, lOa, a throat 11, llag and downstream of the throat
a diffusion or expansion region 12, 12a. Beyond the expansion
region there is a bank of mist eliminators 13, 13a, and an
1~ air exhaust reg;on, 14, 14a, prov;ded w;th vanes 15, l~a to
direct the exhausting air upwardly and outwardly from the
apparatus.
Water to have heat extracted from it is pumped by
a pump 16 from a heat load to header 17 of the first stage
of the present method. Header 17 supplies a series of
horizontal conduits 18 extending across the air entry mouth
10 of the unit. Each of the conduits 18 is provided with
nozzles 19 spaced along its length. The water to have heat
extracted from it is sprayed from these no~zles into the
throat 11, and this has the e-Ffect of drawing in air from
the surrounding atmosphere which thus constitutes the source
of air for the present system. The air and water co-mingle,
some of the water eva~porates, the air is exhausted through
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sAC-3~A
1 the outlet 14 and the water is collected in a sump 20.
2 This water is extracted from the sump 20, drawn through a
3 pipe 21 by a pump 22 which delivers it to the manifold 17a
4 of the second unit, said manifold 17a serving the pipes 18a
each of which are provided with nozzles l9a in the manner
6 of the first stage. The heat exchange process of the first
7 stage is repeated in the second stage with the difference
8 that the water supplied through ~he nozzles l9a is water
9 which has already had heat extracted from it in passage
through the first stage. The source of air for the two
11 units is, however, the same so that water issuing from
12 nozzle~ 19 and l9a is exposed to the same temperature air.
13 The water issuing from the second unit is collected in a
14 sump 20a and delivered through a pipe 23 to the heat load.
In order better to demonstrate the value of the
16 multistage operations cons~ituting the present invention,
17 reference is made to ~he following examples~
18
19 EXa~PLE 1
Suppose a load of 100,000 GPM ~gallons per minute)
21 with a required water temperature reduction o~ 40F from
22 125F to 85F. Suppose also an ambient air wet bulb temper-
23 ature of 72F at entry (mouth 10 of Figure 13. A single
24 unit of the type shown in Figure 1 adequate to deal with
such a load would require a throat cross section area (11 of
26 Figure 1) of about 80,640 square feet and 2900 BHP (brake
27 horsepower) with a 79.4F wet bulb at exhaust ~14 of
28 Figure 1). Such a unit is very large and proportionately
29 expensive to huild and maintain. ~Yet if instead o~ using
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1 such a unit, the staging method of the present invantion
2 is employed, the following dramatic reduction in si2e is
3 achieved:
4 First St~
5 Flow 100,000 ~PM
6 Load 125~ to 97.5F
7 Throa~ area 15 ,120 ~quare feet
8 Energy 1450 BHP
9 Air temperature 72F. wet bulb at 10 of Figure 1
10 Air temperature 90.1F. we~ bulb at 14 of Figure 1
11 _cond Sta~e -
12 Flow 100,000 GPM
13 Load 97.5 to 85F. :
14 Throat area 15,120 square feet
15 Energ~ 1450 BHP
16. Air temperature 72F. wet bulb at lOa of Figuxe 1
17 Air temperature. 81.2F. wet bulb at 14a of Figure 1 ;:
18 Throat area, irst stage, 15,120 square feet
19 throat area, second ~tage, 15,120 square ~eet = 30,240 square
feet. Throat area single unit less sum of throat areas of
21 stages 1 and 2 is: 80,640 square feet - 2(15,120) = 50,400
22 square feet or 62% saved in unit size by practicing the
23 present method.
24 Thus, it is seen that the reduction in needed ~:
throat cross section is more than 50,000 square feet.
26 ~- When two:stages are connected in-serie~ as shown
27 in Figure l of ~he-drawings it is apparant that energy is
28 put into the wa~e~ at two places. ~If half of khe energy
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29 requir~d by a large single unit i~put in at each of these
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BAC 32 :
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l places the total will be the same. Brake horsepower is a
2 function of pressure ~or any given flow (GPM); thus, if
3 half the pressure is applied in each of two places in series
4 the sum will be the same (1450 B~P + 1450 BHP = 2900 BHP~.
Hence, in this example, there is no increase in
6 BHP along with a savings of 50t400 square feet in throat
7 area or 62%.
8 A second example dealing with a much smaller ;... : :
9 water ~low is further demonstrative of the savings in size
to be achieved by practicing the present method:
11 EXAMPLE 2
.
12 single Unit -
13 Flow lO00 GPM
14 Load 103 - 85F ~ 18 Range
15 Throat area 360 square feet ~;
16 Energy 41.2 ~HP
17 Wet bulb air temperature at entry 78F.
18 Wet bulb air tempexatuxe at exit 82.9F.
19 First Sta~e -
20 Flow . - lO00 GPM
21 Load 103 - 91F.
22 Throat area 95 square feet
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23 Energy 20.6 BHP
24 Wet bulb air temperature at entry 78F.
Wet bulb air temperature at exit~ 87.6~F~
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BAC 3
l Second Sta~e -
2 Flow lO00 GPM
3 Load 91 - 85F.
4 Throat area 95 ~quare feet
5 Energy 20.6 BHP
6 We~ bulb air temperature at entry 7~F.
7 Wet bulb air temperature at exit 82.9F.
8 Thus for this second example, there is achieved
9 a savings of 170 square feet or about 47.2% in throat area
at the same brake horsepower.
ll To illustrate further the effects of the present
12 invention reference is made to Figure 2. ~ere is plotted
13 for both single and series staging of injector cooling
14 towers, physical size index as the ordinate versus range
as the abscissa. This plot is for a constant design
16 approach temperature. To be sure that Figure 2 and the
17 examples above are understood, the term "range" is used to
18 define the range of cooling to which the water is to be
l9 subjected. To cool water from 125 to 100 is a range of
25. The expression "approaah~tempexature" means the
21 aif ference ~etween the wet bulb temperature of the entering
22 air, see Pigure l~ mouths lO - lQa, and the leaving water
23 temperature, see Figure l at~sumps 20 - 20a.~
24 ~ In Figure 2, the ordinate is an index of physical
size. Since certain proportians~are necessary in injeator
26 cooling towers, a practical index of size is the throat
27 area if a venturi i5 used~and if~water~is sprayed into a ~ -
28 tube of uniform section then the area af that section is an
29 ~ index of size. Ts - ~f means simply range as~ defined abo~e~
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BAC-32IA
1 Thus, by staging, the input energy can be
2 decreased substantially from that of the single unit before
3 the value of the index of physical size of staging becomes
4 equal to that of the single unit.
FIGURE 1 illustrates two stages of cooling with
6 the water in series, it is contemplated as a part of the
7 invention that stages in excess of two will be used ~o
8 meet certain operating conditlons. As shown in PIGURE 3
9 for ex~mple, there are provided three stages connected in
series by a common water line 30 with individual pumps
11 32a, 32b and 32c interposed in the line 30 in advance
12 of each stage.
13 In addition, the pumps in advance of the second
14 and successive stages may be eliminated by mounting the
first stage vertically above the second, the second above
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16 the ~hird and so forth, and using the liquid head created
`17 to~produce the operating pressure of the lower stage. This
18 arrangement is shown in FIGURES 4 and 5.
19 FIGURE 4 shows a two stage arrangement wherein
the liquid feed to the second stage originates from a
21 collecting sump in the upper stage and is transported by a
Z2 downcomer of approximate height h to the lower stage. The
23 oper~ating pressure of the second stage is equivalent to h `:~
24 plus the sump operating level above it, less any frictional
25 losses. The operating pressure is dependent on ~and there- -
26 fore versatility is possible by inc~easing or decreasing the
27 distance h ~ between stages to meet specific design conditions.
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l FIGURE 5 shows two sets of two stage units. The
2 first stage A is coupled with the second stage A in a manner
3 similar to FIGURE 4. The first stage B is also coupled to
4 second s~age B in a manner similar to FIGURE 4. The insertion
of the first stage B of height ~ between the two A stages
6 serves to utilize this area. In comparing F:IGURF,S 4 and 5;
7 if the height of the stage is equal to ~ in FIGURE 4, the
total cooling capacity for a total height of 3~ in FIG. 4
g is one half of that for FIGURE 5 with a height of 4 h . There-
fore by inserting stages between the stages the capacity can
11 be doubled for a 33% height increase. It should be recog-
12 nized that first stages A and B are cooling in parallel
13 relationship and second stages A and B also are cooling in
14 parallel relationship.
The arrangements shown in PIGURES 4 and 5 can be
16 advantageous when -compared to FIGURES 1 and 3. The pump
17 arrangement of PIGURES l and 3 require that all the pumps
18 be handling identical flow rates otherwise overflowing or
19 pumping dry one ~of the sumps can occur. By gravity feed,
a constant flow rate from the pump to the first stage, first
21 stage to second stage, second stage to successive stages is
22 assured.
23 ~ Th;e invention may be embodied in other specific
24 forms without- departing from the spirit or essential charac-
,
terlstics hereof. The embodlment and the modi~ication
26 described are therefore to be considered in all respects as
27 illustrative and~not restrictlve, the scope of the invention
28 being indicated by the appended claims rather than by the
29 foregoing description, and all changes which come within the
.
meaning and range of equivalency of the claims are there~ore
31 intended to be embraced ~herein.
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