Injector Type Indirect Evaporative Condensers

Abstract

An indirect evaporative heat exchanger such as a condenser operating on the injection or aspiration principle in which the air is pumped solely by the injection of water which also serves to maintain wet the surface of the tubes of the condenser.

Description

This invention relates to the art of evaporative heat exchangers of the indirect type and more particularly to an improved evaporative condenser or closed circuit evaporative cooler.

Evaporative heat exchangers of the indirect type are widely used today where it is necessary to cool or to condense a fluid such as a refrigerant which must be maintained out of contact, that is in indirect heat exchange relationship, with the heat exchange medium to which the heat is transferred. In general the principle of the indirect heat exchange evaporative cooler is that the fluid from which heat is to be extracted is flowed through tubes the exterior surface of which is maintained wet with water. Air is circulated over the wet tubes to promote evaporation of the water and the heat of vaporization necessary to support that evaporation of water is supplied from the fluid within the tubes thus bringing about the desired heat extraction and/or condensation. That portion of the cooling water which is not evaporated is recirculated and, of course, losses by evaporation are made up.

In the conventional evaporative condenser the water is sprayed to flow by gravity over the heat exchange tubes in which the refrigerant is circulated and air is flowed upwardly through the tubes counter to the water to promote evaporation. Such a system requires a water pump to pump the water to the spray heads and an air blower to pump the air. Both involve cost to construct, both consume power in use and both require maintenance.

It is therefore an object of this invention to provide an evaporative heat exchange system suitable for cooling or condensation on an indirect heat exchange basis in which the water which wets the external surface of the tubes of the system is so supplied as to induce the flow of such air as is necessary to promote efficient water evaporation, thus reducing the number and complexity of the parts by eliminating the need for moving parts in the air propulsion system with resulting savings in cost of construction and maintenance.

Another object of the present invention is to provide an evaporative heat exchanger of the indirect type characterized by compact construction of low profile and quiet operation.

Other objects and advantages of the present invention will be apparent upon consideration of the following detailed description of a preferred embodiment thereof in conjunction with the annexed drawings wherein:

FIG. 1 is a view in vertical section of an evaporative condenser constructed in accordance with the principles of the present invention;

FIG. 2 is a top plan view of the evaporative condenser of FIG. 1;

FIG. 3 is a view in section taken on the line 3--3 of FIG. 1;

FIG. 4 is a view in section taken on the line 4--4 of FIG. 1;

FIG. 5 is a fragmentary view of a water supply arrangement involving a water pump having a variable speed drive so that with its use the system can be operated below available capacity;

FIG. 6 is a view partially in vertical section and partially in elevation of a horizontal axis type evaporative condenser according to the present invention;

FIG. 7 is a view in elevation at the inlet end of the apparatus of FIG. 6; and

FIG. 8 is a view similar to FIG. 6 but showing two evaporative condensers arranged one above the other and employing a common sump.

Referring now in greater detail to the drawings, in FIG. 1 the illustrated evaporative condenser is comprised of an injector portion 10 and an air venting stack 11. The injector portion has an outer wall 12 and an inner wall 13, the latter being common to and constituting the inner wall of stack 11. Stack 11 has an outer wall 14 and, connecting the outer walls 12 and 14 at opposite ends of the apparatus are common end walls 15 and 16. The structure defined by the walls 12 -16, inclusive, has a common bottom sheet 17 which extends the width of the apparatus from wall 12 to wall 14 and the length thereof from wall 15 to wall 16.

Walls 12 and 13 are so contoured, see FIGS. 1 and 2, as to define a sort of venturi having a long rectangular mouth 18, a long rectangular throat 19 narrower than the mouth, and a long rectangular lower region 20 wider than the throat 19. Above the mouth 18 there extends lengthwise of the apparatus a water supply conduit 21. Depending from this conduit are two rows of conduits 22 and 23 each such conduit terminating in a nozzle 22n or 23 n. The nozzles 22n and 23n are adapted to spray a pattern of water generally oval in cross section with the long axes of the adjacent spray patterns generally aligned with each other and parallel to the end walls 15 and 16 of the apparatus, see FIG. 2. The water from the rows of nozzles 22n and 23n strikes the inside of the walls 12 and 13 at or near the region of the throat 19. The spray induces air flow into the system at the mouth 18. The theory of operation of the injection air pumping system of the present invention is described in greater detail in applications Ser. No. 826,638, filed May 21, 1969, and Ser. No. 869,798, filed Oct. 27, 1969, and is therefore not repeated here.

In the path of the water and air flowing downwardly in the injector 10 there are located the tubes 24 through which the fluid to be condensed or cooled is circulated. These tubes extend between a header 25 and a header 26. The fluid to be condensed or cooled is supplied to header 25 through a conduit 27 which passes through wall 15, see FIGS. 1, 3 and 4. The fluid flows through the tubes 24 which extend between header 25 and header 26, enters header 26 and is withdrawn from header 26 through a conduit 28 which also passes through wall 15.

The tubes 24 are arranged in diagonally offset pairs such as tubes 24a and 24b of FIG. 4. The tubes run from the header 25 to the back wall 16 and then forward to a position near the front wall 15, then back again to the rear wall 16, and finally forward to the header 26. Enough pairs of tubes are supplied to traverse the space between the lower end of wall 13 and the side wall 12. The arrangement of tubes is such as to expose the full length of each tube to the water spray and the flowing air so that the full length of each tube is kept wet at all times and evaporation is promoted to cool or condense the fluid flowing within the tube.

It will be observed that the tubes 24 as a group form a permeable rectangular body of substantially uniform thickness. This body has substantially the same length as the distance from wall 15 to wall 16, see FIG. 2. On the other hand, its width is greater than the width of the region 20 of the injector 12 at the horizontal plane of the lower end of the wall 13. Thus, the tubes 24, as a group, define a permeable body of uniform thickness so disposed in the apparatus that the plane of the surface of said body lies at an oblique angle to the long axis of the injector 12.

As can best be seen in FIGS. 3 and 4, the tubes 24 are physically supported from pipes 33 which are supported in L - section members 34 and 35 attached respectively to walls 16 and 15. The L - section members 34 and 35 are provided with holes along the length thereof and the supporting pipes 33 are passed through these walls and through the bends in the tube and once in position may be welded as indicated at 36. When the run of tubes is a long one, it is also customary to provide a conventional support structure in the middle of the tube bank between the end walls.

The water which issues from the nozzles 22n and 23n and which does not evaporate from the surface of tubes 24 is collected in a sump at the bottom of the apparatus. The sump is provided with a water outlet at 37 and strainer screens at 38 and 39. The water is pumped from the sump through outlet 37 to the pipe 21 by a pump, not shown. The water level is maintained by a float-controlled makeup valve, not shown. Note that this level is maintained below the lower extremity of the banks of heat exchange tubes 24. The recirculation of the water from sump outlet 37 to conduit 21 can be metered by any conventional means, such as a throttle valve or a variable capicity pump, see FIG. 5. If the amount of water supplied to conduit 21 is reduced, the amount of air pumped is also reduced and thus there is provided a convenient method for capacity control. In other words, when ambient temperatures are low or when the heat load is low, reduced water flow will throttle down the apparatus to meet the lower load condition.

In FIG. 5 a pump 40 is shown for delivering water from the outlet 37 of sump 17 to conduit 21 which serves the spray nozzles. The pump 40 is capable of operation at variable speeds. It is controlled by a variable speed motor 41 which can be operated by a temperature sensor measuring the fluid temperature within the coil or a function thereof.

Heat exchange tubes 24 are so positioned that not only are they kept wet for efficient operation as coolers or condensers, but they likewise very largely remove droplets from the water which passes through them. Accordingly, the air which also passes through them as indicated by the arrows in FIG. 1 exhausts to atmosphere through the stack 11 substantially free of droplets. If further removal of droplets is necessary, a row of mist eliminators 42 may be disposed from the front wall 15 to the back wall 16 of the apparatus in an angular position between the upper right corner of the tube system and the wall 14 approximately at the level of the sump water. These mist eliminators correspond in structure and function to those shown in application Ser. No. 869,798, filed Oct. 27, 1969.

It is to be noted that wall 13 which is common both to the injector 10 and the stack 11 is so contoured that it helps define the mouth 18, the throat 19 and the diffusion portion 20 of the injector while at the same time defining an air exhaust stack which tapers inwardly so that at the upper, exhaust end 43 thereof the air discharges at a high velocity which assists in preventing exhaust air from recirculating to the air inlet of the system. Recirculation is also inhibited by the fact that the mouth 18 of the injector lies in a plane below the plane of the upper end of the stack 11.

It will be appreciated that the heat load in the water, evaporation of which cools the fluid within the heat exchange tubes, is transferred to the exhausting air. This air therefore contains the heat load in the form of latent and sometimes sensible heat as well and is nearly saturated with water. In this condition it can no longer function to take up more heat and more water, and it is for this reason that its recirculation must be prevented; for if it were not prevented, drastic reduction in efficiency would result.

While in FIG. 1 there is shown a single elongated injector with a single stack, where additional capacity is needed it is entirely feasible to duplicate a mirror image of the apparatus shown in FIG. 1 on the opposite side of the plane of wall 14 in which case, of course, wall 14 itself is eliminated.

FIGS. 6 and 7 illustrate an embodiment of the invention in which the injector acts generally horizontally. There is a casing having an air inlet mouth 50 at one end and an air discharge portal 51 at the other end. The casing is defined by two vertical side walls 52 and 53 and sloping upper and lower walls 54 and 55. The air inlet 50 is rectangular as can be seen in FIG. 6, the long axis of the inlet being horizontal and the short axis vertical. The upper margin portion 56 of the air inlet 50 is curved to define a bell mouth and this is also true of lower margin portion 57. The bell mouth portions 56 and 57 lead through a region of convergence defined by upper and lower walls 58 and 59 to a throat region 60.

Water is sprayed into the throat region 60 from a plurality of nozzles 61. As illustrated these nozzles are arranged in four horizontal rows, each having a water supply pipe 62. All of the pipes 62 are fed from a common header 63.

The water issuing from each nozzle forms a spray which is generally oval in cross section, see FIG. 7. The pipes 62 are so spaced vertically from one another that the upper and lower edges of each spray intersect just about at the plane of the throat 60. The nozzles 61 are so spaced in relation to one another along the respective pipes 62 that the side edges of the spray just about touch one another at the plane of the throat, see again FIG. 7.

The theory of operation of these sprays in pumping air in a horizontal system is explained in application Ser. No. 144,853 filed May 19, 1971; and is therefore not repeated here.

The water sprays flowing the length of the casing inpinge against a tube bank 64 structurally and functionally similar to tube bank 24 shown in FIGS. 1, 3 and 4. The fluid to have heat extracted from it enters the tube bank 64 through conduit 65 similar in structure and function to conduit 27 of FIG. 1. The fluid leaves the tube bank 64 through conduit 66.

Note that the tube bank or coil 64 is tilted at a slight angle which approximates the angle of slope of the lower wall 55, see FIG. 6. The tilt will ensure that the coil is fully wetted across its face and throughout its depth. In view of the fact that the coil 64 itself functions somewhat as a mist eliminator, ordinarily only a single bank of mist eliminators will be necessary, and these are shown at 67. In cross section these correspond in appearance to FIG. 4 of application Ser. No. 869,798, filed Oct. 27, 1969. The air leaving outlet portal 51 having passed through eliminators 67 is guided by turning vanes 68 which direct the heat and moisture laden air up and away from the inlet mouth 50 to avoid any tendency to recirculation.

It should be noted that in a conventional evaporative condenser fans pump the air and only enough water is pumped to wet the coil surfaces. Using minimum water quantities in this way sometimes results in areas of light coverage with a tendency to form scale on the tubes. Of course, in an ejector evaporative condenser, the water serves the dual purpose of both pumping the air and wetting the coil. The total amount of energy input for such an ejector is approximately equal to the sum of the pump and fan motor horsepower of a conventional type unit. In an ejector the energy input is measured by the nozzle pressure and water flow quantity. Therefore for an equal amount of energy the amount of water pumped would be much higher than a conventional evaporative condenser. This water flow would be approximately two to three times as great per square foot of the coil cross-sectional area (as viewed from the sprays.) This additional water has the advantage of eliminating any "dry" spots which tend to scale and also promotes better heat transfer from the tubes to the water and then to the air.

The apparatus shown in FIGS. 6 and 7 has a spigot 69 for supplying makeup water to the sump 70 under the control of a float 71. Water leaves the sump 70 through a conduit 72 and is delivered by pipes, not shown, back to header 63. A blowdown arrangement is shown in which water extracted from the lowermost pipe 62 passes through a conduit 73 to one end of a trough constituting part of the bell mouth 57. Water leaves the other end of this trough through a conduit 74 which discharges through a convenient connection 75. The blowdown arrangements, the water supply arrangements, and the nozzles all are fully described in application Ser. No. 144,853 filed May 19, 1971 and need not be further discussed here.

Where increased condensing capacity is needed and it is not convenient to achieve that capacity by enlarging units such as are shown in FIGS. 6 and 7, it is possible to use multiples of these units arranged one upon the other. For example, in FIG. 8 there is shown an arrangement which is, in effect, like the unit of FIG. 6 with another similar unit located above it. In FIG. 8 the water supply, the pumping of the air, the positioning of the tubes, the structure and positioning of the mist eliminators, and of the turning vanes is the same as is shown in FIG. 6. These parts are therefore given the same numbers which they had in FIG. 6. The upper unit 80 of FIG. 8, however, does have a sump of its own different in structure from the sump 70. This sump 81 drains water through the tubes 64 of the lower evaporative condenser unit 82 to the sump 70. Except for this difference and the fact that the drain 83 underneath the nozzles 61 of the upper unit 80 is connected by a pipe 84 to the basin 81 from which it drains also through the tubes 64 of the lower unit 82 into the sump 70, these units are identical.

While the apparatus of the present invention has been described in conjunction with an evaporative condenser, it is to be understood that any type of cooling or condensing that requires the fluid from which heat is to be extracted to be maintained out of contact with the medium which extracts the heat is within the intended use of the apparatus. The term indirect heat exchange as used herein is to express the situation where a fluid from which heat is to be extracted is physically isolated (as by tubing) from contact with the medium (such as water) to which the heat is transferred. This term is used to distinguish from direct heat exchange as in a cooling tower where the water from which heat is extracted is in direct contact with the evaporating water to which the heat is transferred.

While the illustrated apparatus discloses four coil passes between the input and output headers, it is to be understood that the number of coil passes can be varied as necessary to meet the capacity requirements of the system.

The invention may be embodied in other specific forms without departing from the spirit or essential characteristics hereof. The embodiment and the modification described are therefore to be considered in all respects as illustrative and not restrictive, the scope of the invention being indicated by the appended claims rather than by the foregoing description, and all changes which come within the meaning and range of equivalency of the claims are therefore intended to be embraced therein.

Claims

What is claimed is:

1. An evaporative heat exchanger of the indirect type comprising means defining a conduit extending in a horizontal direction and having an air intake at one end exposed to the ambient, means to inject water in a horizontal direction within the conduit in the form of a plurality of sprays of sufficient divergence to contact the inner surface of the conduit and to inersect each other within the conduit, thereby to pump ambient air into the conduit at its intake end, enclosed means to receive the water issuing from the other end of said conduit, means to pump the water from said water receiving means to said injecting means, a tube bank positioned in said conduit, said tube bank comprising a plurality of tubes arranged in diagonally offset pairs which traverse the space between the walls of the conduit thereby to form a permeable body, said tube bank being positioned in the path of said water between said common plane and said water receiving means, to be impinged upon by said water sprays, said tubes being arranged and positioned in said body such that they very largely remove droplets from the water which passes between them so that the air which also passes between them is substantially free of droplets, whereby maximum water quantities are maintained on said tubes and scale formation is reduced, means to circulate a fluid from which heat is to be extracted through said tubes and means providing an air passage from said enclosed means to a region of discharge.

2. An evaporative heat exchanger as claimed in claim 1 in which said pumping means includes means to vary the rate of flow of the water to said injecting means.

3. An evaporative heat exchanger as claimed in claim 1 wherein the permeable body is of substantially uniform thickness and the plane of the face of said body is disposed at an oblique angle to the axis of the conduit.

4. An evaporative heat exchanger as claimed in claim 1 wherein mist eliminators are located in the air path between said tubes and the region of air discharge.

5. An evaporative heat exchanger of the indirect heat exchange type comprising means defining a conduit of rectangular cross section having an air intake at one end exposed to atmosphere, a throat and a region beyond the throat discharging to atmosphere, said air intake throat and region providing a generally horizontal passageway, means to inject water into said throat in the form of a series of oval section intersecting sprays which fill said throat, thereby to pump ambient air into the conduit at its intake end, the long axes of said sprays being normal to the long axis of the cross section of said conduit, means to receive water issuing from said region, means to pump the water from said water receiving means to said injection means, a plurality of tubes arranged in diagonally offset pairs which traverse the space between the walls of the conduit to define a permeable rectangular body of substantially uniform thickness to be impinged upon by said sprays, said tubes being arranged and positioned in said body such that they very largely remove droplets from the water which passes between the tubes so that the air which also passes between is substantially free of droplets, means mounting said body between said throat and said water receiving means with the plane of the face of said body at an oblique angle to the axis of said conduit and means to circulate a fluid from which heat is to be extracted through said tubes.

6. An evaporative heat exchanger according to claim 5 wherein said throat is of lesser cross sectional area than said air intake and said region beyond the throat.