CA1069429A - Method and apparatus of multi stage injector cooling - Google Patents

Abstract

A B S T R A C T
This application illustrates staging of injector type evaporative heat exchangers in such a way that the water to have heat extracted from it flows through the stages in series but comes into contact with a new volume of air at each stage.
Dramatic reductions in size of unit required to deal with high loads is achieved without increase in horsepower requirements.

Description

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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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.

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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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~ 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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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~

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 .
29 requir~d by a large single unit i~put in at each of these : ~ 6 - - .

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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:

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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 ..... .... . .

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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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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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 . . .
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.

Claims (11)

The embodiments of the invention in which an exclu-sive property or privilege is claimed are defined as follows:

1. A multiple stage injector type liquid cooling system comprising first and second injector type liquid cooling units, the first unit containing a confined region having an end open to a source of first gas at a wet bulb temperature lower than that of the spray liquid, liquid spray means positioned to direct liquid sprays into said confined region to induce flow of first gas from said source there-through for mixing and partial evaporation of said liquid, separator means positioned in said confined region downstream of said liquid spray means for separating said liquid from said first gas exiting from said confined region, liquid collection means positioned below said separator means to collect the separated liquid at a first temperature above the wet bulb temperature of the separated first gas, means for passing the liquid from the liquid collection means of the first liquid cooling unit to a liquid spray means of a second cooling unit, said second cooling unit containing a confined region having an open end to a source of second gas at a wet bulb temperature no higher than that of the first gas at said first mentioned source, said liquid spray means of said confined region in said second cooling unit being positioned to cause said sprays to induce flow of said second gas from said source into said confined region for mixing and partial evaporation of said liquid, separator means in said confined region of said second unit positioned in said confined region downstream of said liquid spray means for separating said second gas and liquid and liquid collection means positioned below said separator means in said confined region of said second unit for collecting the liquid at a second temperature above the wet bulb temperature of the separated second gas but below the wet bulb temperature of the separated first gas, the combined total cross sectional area of both said confined regions being less than the cross sectional area of a single similar confined region capable of cooling said liquid to said second temperature and wherein the said means for passing liquid from the collection means of the first unit to the liquid spray means of the second unit is by force of gravity.

2. A multiple stage injector system according to Claim 1, wherein the means for passing liquid includes a pump for forcing liquid through the liquid spray means of said second cooling unit under pressure.

3. A multiple stage injector system according to Claim 1, wherein said cooling units are positioned so as to share the same source of air.

4. A multiple stage injector system according to Claim 1, wherein said cooling units are of substantially equal size and capacity.

5. A multiple stage injector system according to Claim 1, wherein said cooling units are positioned to share a common source of fresh air and to share a common discharge area for the exit air.

6. A multiple stage injector cooling system according to Claim 1, comprising two pairs of multiple stage injector cooling systems and means for passing liquid from the collection means of the first cooling unit of a pair to the liquid spray means of the second cooling unit of said pair, said means being the force of gravity.

7. A multiple stage injector cooling system according to Claim 6, wherein 4 injector units are stacked one above the other, the first being on the lowest level and the fourth on tile highest level, wherein the liquid to be cooled is initially sprayed in units 4 and 3 and then the liquid from units 4 and 3 is passed by gravity to units 2 and 1 respectively.

8. The method of extracting heat from water that comprises spraying said water into a confined region having an end open to a source of atmospheric air at a wet bulb temperature lower than that of said spray water, causing said spray to induce a first air flow from said source into said confined region for mixing and partial evaporation of said water, exhausting said first air, collecting the remaining water at a first temperature above the wet bulb temperature of the exhausting first air, and spraying the collected water into another confined region having an end also open to said source of atmospheric air, causing the spray of said collected water to induce a second air flow from said source into said other confined region for mixing and partial evaporation of said collected water and collecting the latter at a second temperature above the wet bulb temperature of the exhausting second air but below the wet bulb temperature of the exhausted first air, the combined total cross sectional areas of both said confined regions being less than the cross sectional area of a single similar confined region capable of cooling said water to said second temperature and wherein the water at the first temperature is sprayed into said other confined region by force of gravity.

9. The method of Claim 8, wherein the water at said second temperature is further sprayed successively into one or more confined regions each of said regions having an end open to a source of atmospheric air at a wet bulb temperature no higher than at said first mentioned source.

10. The method of Claim 8, in which the energy of the water sprayed into said first and said other confined region is equal.

11. The method of Claim 8, in which said first and said other confined region are of substantially equal size.