Patent Application
20090188650
This description relates to liquid distribution in evaporative heat rejection systems.
Evaporative heat rejection systems that include indirect, direct and a combination of direct and indirect heat transfer sections are commonly employed.
An evaporative liquid (generally water) can be distributed across an indirect heat transfer section that typically includes a series of individual, enclosed circuits or loops for cooling or condensing a working fluid within the circuits or loops. When an evaporative heat rejection system is used as a closed-loop cooling tower or evaporative condenser, heat can be indirectly transferred from the working fluid through the enclosed loops or circuits to the surrounding film of evaporative liquid that flows over the enclosed circuits, thereby warming the evaporative liquid. Heat is then removed from the evaporative liquid through transfer to an air stream. These enclosed loops or circuits can be a series of tubes or assembly of coils that may be circular in cross section or which may have non-circular cross sections, such as those disclosed in U.S. Pat. No. 4,755,331, the disclosure of which is incorporated herein by reference.
Heat also can be removed from a working fluid through direct transfer to an air stream in a direct evaporative heat transfer section. In a direct evaporative heat transfer section the working fluid can be directed onto a solid surface area, commonly referred to as wet deck fill, from which a small portion of the working fluid evaporates, thereby cooling the remaining portion of the working fluid. Thus, a working fluid can also function as an evaporative liquid when passing through a wet deck fill. A wet deck fill may include a variety of constructions such as wooden slats, corrugated metal sheets, stacks of formed plastic sheets, etc. For example, a certain type of fill is disclosed in U.S. Pat. No. 5,124,087, the disclosure of which is incorporated herein by reference.
Evaporative liquid has been distributed over indirect and direct heat transfer sections using a variety of different systems and methods. Many of these systems and methods involve spraying the evaporative liquid from a plurality of nozzles. However, nozzles are prone to clogging with dirt and other contaminants, thus reducing the evaporative liquid from being distributed over at least a portion of the heat transfer section and thereby reducing the efficiency of the evaporative heat rejection system. In addition, using multiple nozzles in an evaporative heat rejection system adds to the complexity and the cost of the system.
In a first general aspect, a liquid distribution system for an evaporative heat rejection system that includes a heat transfer surface is disclosed. The liquid distribution system includes a plurality of liquid conduits adapted to transport liquid for distribution over the heat transfer surface, and each liquid conduit having at least one orifice. At least a first orifice in a first conduit and a second orifice in a second conduit are positioned such that when the liquid is transported under a predetermined pressure thought the conduits, the liquid is emitted from the first and second orifices in first and second streams, respectively, that collide at a collision site, thus causing liquid to be scattered from the collision site and distributed over the heat transfer surface.
In another general aspect, an evaporative heat rejection system can include an indirect heat transfer section with a liquid distribution system positioned above the indirect heat transfer section. The liquid distribution system includes a plurality of liquid conduits that each has at least one orifice, where the conduits are adapted to transport liquid for distribution over the indirect heat transfer section. At least a first orifice in a first liquid conduit and a second orifice in a second liquid conduit are positioned in the first conduit and the second conduit, respectively, such that when the liquid is transported under a predetermined pressure through the conduits, the liquid is emitted from the first and second orifices in first and second streams, respectively, that collide at a collision site. The collision of the two streams can cause liquid to be scattered from the collision site and distributed over the indirect heat transfer section, such that the liquid drains through the indirect heat transfer section. The evaporative heat rejection system also can include a direct heat transfer section, a liquid collector, and a pump. The direct heat transfer section can be positioned to receive liquid that has been distributed over and drained through the indirect heat transfer section, such that the liquid drains through the direct heat transfer section. The liquid collector is configured to receive substantially all of the liquid that drains through the direct heat transfer section. The pump is operably connected to the liquid collector and configured to return liquid from the liquid collector to the liquid distribution system.
In another general aspect a method of distributing liquid over a heat transfer surface of an evaporative heat rejection system includes providing liquid at a predetermined pressure and transporting the liquid at the predetermined pressure through a plurality of liquid conduits, where each liquid conduit has at least one orifice. At least a first orifice in a first liquid conduit and a second orifice in a second liquid conduit are positioned in the first conduit and the second conduit, respectively, such that when the liquid is transported under the predetermined pressure thought the conduits, the liquid is emitted from the first and second orifices in first and second streams, respectively, that collide at a collision site. The collision of the first and second streams causes liquid to be scattered from the collision site and distributed over the heat transfer surface.
Implementations can include one or more of the following features. For example, the first orifice and the second can be positioned in the first conduit and the second conduit, respectively, such that the first stream and the second stream are emitted at angles of between −45° and +45° with respect to the horizontal direction. The first stream and the second stream can be emitted at an angle of between −25° and +10° with respect to the horizontal direction.
The first and second liquid conduits can be substantially parallel to each other. The plurality of liquid conduits can be arranged in an array of substantially parallel conduits, and conduits at edges of the array can include orifices on one side of the conduit facing other conduits of the array, and interior conduits of the array can include orifices on each side of the conduit facing other conduits of the array, and conduits at edges of the array can have cross-sectional areas that are smaller than cross-sectional areas of interior conduits of the array. The plurality of liquid conduits can be arranged in an array of substantially parallel conduits, and the heat transfer surface can include heat exchange coils oriented substantially perpendicularly to the plurality of conduits arranged in an array.
The liquid distribution system can include a manifold coupled to first ends of the first and second liquid conduits, where the manifold is adapted to transport liquid to the first and second liquid conduits, and where each of the first and second liquid conduits includes a plurality of orifices along a length of the conduit, and where orifices located at ends of each of the conduits proximate to the manifold are larger than orifices located at ends of the conduits distal to the manifold.
The first orifice and the second orifice can include holes through a wall of the first and second conduit, respectively, and radii of the first and second orifices at an inner surface of the respective wall can be larger than radii of the first and second orifices at an outer surface of the respective wall. The first orifice and the second orifice can include adjustable inserts configured to adjust the direction of liquid that flows out of the orifices. The heat transfer surface of the first general aspect can include an indirect heat transfer section and a direct heat transfer section, and the liquid distribution system can be positioned above the indirect heat transfer section.
Liquid can be collected after it has been distributed over and drained through the heat transfer surface, and the liquid can be returned to be provided again at the predetermined pressure and to be transported again through the plurality of conduits.
Other advantages and features will be apparent from the description, the drawings, and the claims.
Evaporative heat rejection systems can be designed and employed in a wide variety of constructions and arrangements. For example, evaporative heat rejection systems can include indirect heat transfer surfaces and/or direct heat transfer surfaces. In addition, evaporative heat rejection systems can use cross flow distribution of air over the heat transfer surface(s) (i.e., substantially perpendicular to the direction of water flow in the system), parallel flow of air over the heat transfer surface(s) (i.e., substantially in the same direction of water flow in the system), counter flow of air over the heat transfer surface(s) (i.e., substantially in the opposite direction of water flow in the system), or any combination of air flow known to those skilled in the art of evaporative heat rejection systems. While several of such arrangements are illustrated herein, other implementations and constructions are also possible. For example, implementations that are built in a factory typically are constructed in one- or two-piece modules, while field-built equipment may include separate components or units erected in place at an installation site and may not be arranged within a common housing.
As explained above, a particular implementation of the indirect heat transfer section 30 can include one or more heat transfer working fluid conduits 32 having a surface that receives liquid distributed from the liquid distribution system 22. These conduits may take several forms including a series of individual coils or tubes 54 connected by headers 56 to provide an array of tubes, so that the array increases a surface area for engagement with the liquid that is distributed from the liquid distribution system 22. A specific type of coil arrangement is disclosed in U.S. Pat. No. 4,755,331 in which the tubes have elliptical cross sections, although circular cross sections as described in that patent may also be utilized, as well as other cross-sectional configurations. In another implementation, the conduit may take the form of a hollow plate with passages formed therein for the working fluid to flow through while presenting a surface area of the plate for the non-evaporated liquid to flow over in an indirect heat transfer relationship. A series of such plates can be utilized with the plates oriented vertically with appropriate connections and headers for distributing the working fluid through the plates. Hereinafter the heat transfer working fluid conduit 32 may be referred to more simply as the heat exchanger coil, heat transfer coil, or simply coil.
The heat transfer coil(s) 32 of the exemplary implementation shown in
Because the evaporative liquid descending through the indirect heat transfer section 30 progressively warms up as it falls through the heat transfer coil(s) 32, in some implementations the working fluid can be introduced into the heat transfer coil(s) 32 at a lower portion 42 of the coil(s) and can progress upwardly through the coil(s) to exit at a higher portion 44 of the coil(s), so that the working fluid will cool as it moves upwardly through the coil(s), and at the uppermost portion of the heat transfer coil(s) the working fluid will be the coolest, as will be the evaporative liquid distributed from the liquid distribution system 22. Thus, the working fluid will be able to be cooled to a temperature approaching the ambient wet bulb temperature. If the working fluid is a gas to be condensed, it can flow from an upper end 44 of the coil 32 to a lower end 42 of the coil due to drainage requirements (i.e., so that the liquid component of the working fluid will drain under gravity out of the lower portion 42 of the coil(s) 32, while the gaseous portion of the working fluid flows in the upper part of the coil(s).
The air moving device 28 can be an axial bladed fan, which can be positioned, for example, above the indirect heat transfer section 30, a centrifugal fan, or any device that moves air over the heat transfer section. A series of air inlet openings 48 can be provided in the housing 34 below the heat transfer section 30 such that air is drawn into the housing 34, through the heat transfer section 30 to exit, for example, at a top of the housing through a large opening 50 positioned above the air moving device 28. In this arrangement, which can be known an induced draft counterflow system, a drift eliminator 52 can be provided between the liquid distribution system 22 and the air moving device 28 to remove entrained liquid droplets in the air stream prior to the air stream exiting the housing. Many different types and constructions of drift eliminators are known, including closely spaced metal, plastic or wood slats or louvers that permit air flow therethrough but that collect fine water droplets in the air. In the arrangement illustrated, the collected water droplets will fall, under the force of gravity, onto the indirect heat exchange system with the other distributed liquid. An example of an eliminator is disclosed in U.S. Pat. No. 6,315,804.
In addition to fans, many other types of air moving devices will be apparent to those skilled in the art including blowers of various constructions, movable diaphragms, and even air moving devices with no moving parts, such as convection chimneys. The position of the air outlet opening 50 may vary and may be located in a sidewall of the housing 34, rather than a top wall, to create a cross flow system, if space requirements warrant. Air can also be drawn downwardly over the indirect section 30 in a concurrent, or parallel, flow arrangement rather than the counter flow arrangement illustrated in
A liquid collector 38 can be positioned to collect liquid that drains out of the indirect heat transfer section 30. For example, the liquid collector can be a sump positioned below the indirect heat transfer section 30, such that liquid that drains out of the indirect heat transfer section 30 collects in the sump, where it can mix adiabatically and reach a uniform temperature. In one implementation, the liquid that drains out of the indirect heat transfer section 30 can be cooled before being recirculated to the liquid distribution system 22 for distribution over the indirect heat transfer section 30. An example implementation of a structure and technique for cooling the liquid is described below in connection with
A liquid recirculation system 40 (e.g., one or more pumps and associated piping) can be coupled to the liquid collector 38 and to the liquid distribution system to return the evaporative liquid from the liquid collector 38 to the liquid distribution system 22. In one implementation, the recirulation system 40 can couple the liquid collector 38 to the liquid distribution system 22 directly. In another implementation, prior to returning the evaporative liquid from the liquid collector 38 to the liquid distribution system 22 the liquid can be passed through a cooling system (not shown in
The housing 34 is illustrated as being constructed of substantially vertical outer walls arranged generally perpendicular to one another so as to form a generally rectilinear shape. This particular shape, while convenient and economical to manufacture, is not necessary or critical to performance of the heat rejection system 10, and the shape of the housing 34 can vary widely. For example, the housing could have a circular cross section or other geometrical shape and, in fact, various components could be located in different housings, it not being critical that all of the elements be located in a single housing.
In one implementation, the liquid distribution system 22 can include a manifold 24 (also known as a header) that receives evaporative liquid from the liquid recirculation system 40. The manifold 24 can be coupled to a plurality of liquid conduits 26 that receive the evaporative liquid and distribute the evaporative liquid over a heat transfer surface (e.g., the indirect heat transfer section 30) of the evaporative heat rejection system 10. The fluid conduits 26 can be any type of conduit including tubes or pipes and can be made of any type of material including polyvinylchloride (PVC), stainless steel, or rubber tubing. In the implementation shown in
Fluid conduits can include one or more orifices located in the side walls of the conduit, such that liquid received into the conduit (e.g., from the manifold 206) can be emitted out of the orifices in streams of liquid for distribution over a heat transfer surface of the evaporative heat rejection system. Orifices of the liquid conduits can be arranged in the fluid distribution system, such that when liquid is emitted from two different orifices in a first stream and a second stream, respectively, the streams collide and scatter liquid over the heat transfer surface, as described in more detail below with respect to
In one implementation, the fluid conduits 204a, 204b, 204c, 204d, and 204e can be arranged in an array 202 of parallel conduits, and conduits 204b, 204c, and 204d in the interior of the array and that have a neighboring conduit on either side in the array can have orifices on either side of the conduit, so that liquid streams can be emitted toward neighboring conduits on either side of the conduit 204b, 204c, and 204d. Conduits 204a and 204e at the edges of the array that have only one neighboring conduit in the array can have orifices on only one side of the conduit 204a and 204e, so that liquid streams can be emitted toward the only neighboring conduit. In such an implementation, because conduits 204a and 204e at the edges of the array 202 have fewer orifices than conduits 204b, 204c, and 204d in the interior of the array, to provide the a liquid stream emitted from an orifice 208a in the edge conduit 204a having the same flow rate (e.g., as measured in gallons per minute) as a liquid stream emitted from an orifice 208b in the interior conduit 204b, the cross-sectional area (e.g., the diameter) of the edge orifice 204a can be smaller than the cross-sectional area of the interior conduit 204b. For example, edge conduits 204a and 204e can have a diameter of about three inches, while the interior conduits 204b, 204c, and 204d can have a diameter of about four inches. This is but one implementation of the liquid distribution system, and other configurations are also contemplated. Fluid conduits 204a and 204e may also have orifices on both sides.
In addition, in implementations in which conduits 204a, 204b, 204c, 204d, or 204e are closed at one end and connected to a manifold supplying pressurized liquid at the other end, because the static pressure within a conduit is higher at an end distal to the manifold than at an end proximate to the manifold, liquid maybe emitted from an orifice 218d at a distal end of a conduit 204e at a higher velocity than it is emitted form an orifice 218p at a proximate end of the conduit 204e. Therefore, in an example implementation, to ensure that approximately equal amounts of liquid are emitted from orifices at the proximate ends as from the distal ends, the orifices 218d at the proximate ends can be larger than the orifices 218p at the distal ends, and orifices located between the distal and proximate ends can have intermediate values for their diameters, such that approximately equal amounts of liquid are emitted from all orifices along the length of a conduit. However, in other implementations, the orifices can be the same size along the length of the conduit, or the orifices at the distal ends can be larger than the orifices at the proximate ends.
Fluid conduits 204a, 204b, 204c, 204d, and 204e can be made of various different materials. For example, the fluid conduits can be made from plastic pipe, including PVC pipe, metal pipe, including stainless steel pipe, rubber or Tygon® tubing, wood or any other materials. Orifices 208a, 208b, 208c, 208d, and 208e can be created in the conduits 204a, 204b, 204c, 204d, and 204e in any manner. For example, the orifices can be simply drilled into a PVC pipe, or stamped into a metal pipe. Physical parameters, such as the pressure at which the liquid is provided to the conduits 204a, 204b, 204c, 204d, and 204e, the length and diameter of the conduits 204a, 204b, 204c, 204d, and 204e, the size of the orifices 208a, 208b, 208c, 208d, and 208e, the number of orifices 208a, 208b, 208c, 208d, and 208e per conduit, and the distance between neighboring conduits, can be selected to allow liquid to be provided at a desired flow rate from the orifices, such that when liquid streams are emitted from facing orifices the streams collide and scatter liquid from the collision site over a desired area in the heat rejection system 10. For example, in one implementation, five foot long PVC conduits 204a, 204b, 204c, 204d, and 204e can be spaced about 26 inches apart. Interior conduits 204b, 204c, and 204d can have a diameter of about four inches, and edge conduits 204a and 204e can have a diameter of about three inches. Orifices 208a, 208b, 208c, 208d, and 208e having a diameter of about ⅝ inch can be drilled in the conduits and can be spaced about 12 inches apart along the length of the conduits. The orifices 208a, 208b, 208c, 208d, and 208e can have a hydraulic diameter of about ¾ inch. The conduits 204a, 204b, 204c, 204d, and 204e can be located at a vertical distance of about 12 inches above the coils 32 of the indirect heat transfer section 30. In general, the system design and the parameters chosen for the various structural elements of the system can be guided by the underlying fluid dynamics, namely the momentum and pressure of the liquid, to achieve a desired distribution of an amount of fluid per minute over a known area. Because the orifices can be relatively large openings having a simple shape with no mechanical elements to impede the flow of liquid, and because liquid can flow through the orifices at a relatively high flow rate, the orifices are relatively unlikely to gather debris and have a reduced tendency to clog compared to traditional nozzles.
In one implementation, the conduits 204a, 204b, 204c, 204d, and 204e can be arranged such that they are substantially parallel to each other. In other implementations, conduits can be arranged at angles to each other, e.g., at ninety or sixty degree angles to each other, such that the conduits form an array of rectangles or equilateral triangles, respectively.
The orifices 304 and 308 can be positioned in the conduits 302 and 306, such that the first and second streams 310 and 312, respectively, are emitted from their respective conduits at angles to the horizontal direction that range from about −45° to about +45° or that range from about −25° to about +10°. By angling the streams 310 and 312 down slightly from the horizontal direction, water droplets may be less likely to splash upward, away from the coils 32 (shown in
The liquid can be collected after it has been distributed over and drained through the heat transfer surface (step 606). For example, the liquid can be collected in the sump 38 after it has drained through the coils 32 of the indirect heat transfer section 30 (where the sump 38, the coils 32, and the heat transfer section 30 are shown in
The body 712 of the direct heat transfer section 724 can include one or more elements that have a large surface area with a plurality of air passageways extending therethrough. The body surface can take many different forms. In one form, the body 712 can include a stack of spaced apart plastic sheet materials, for example, with the sheets oriented vertically such that the evaporative liquid is distributed onto the surface of sheets to flow downwardly, while air passages are formed between the spaced sheets so as to allow a flow of air over the sheets as the liquid is flowing over the sheets. In another implementation, the sheet material can be non-planar so as to provide a series of convolutions to increase the surface area for the liquid to flow over, while still providing a plurality of air flow passageways through the body. The body 712 can also include a series of spaced slats or even a series of spaced tubes. Persons skilled in the art recognize such body constructions by the term wet deck fill and hereinafter the body 712 may be referred to as the wet deck fill or simply fill. A particular type of wet deck fill is disclosed in U.S. Pat. No. 5,124,087, the disclosure of which is incorporated herein by reference.
The liquid distributed from the liquid distribution system 722 that enters the top of the wet deck fill 712 is relatively hot, but as the liquid flows through the wet deck fill 712, it is cooled evaporatively by air that is drawn into the heat rejection system 700 and that flows through the wet deck fill 712. In an efficient system, the liquid flowing through the wet deck fill 712 approaches the ambient wet bulb temperature of the air being drawn into the housing 734 of the heat rejection system 700.
The air moving device 728 can be an axial bladed fan, positioned above the heat transfer section 724, a centrifugal fan, or any device that moves air over the heat transfer section. A series of air inlet openings 748 can be provided in the housing 734 below the heat transfer section 730 such that air is drawn into the housing 734, up through the heat transfer section 724 to exit at a top of the housing through a large opening 750 positioned above the air moving device 728. A drift eliminator 752 can be provided between the liquid distribution system 722 and the air moving device 728 to remove entrained liquid droplets in the air stream prior to the air stream exiting the housing. Many different types and constructions of drift eliminators are known, including closely spaced metal, plastic or wood slats or louvers that permit air flow therethrough but that collect fine water droplets in the air. In the arrangement illustrated, the collected water droplets will fall, under the force of gravity, onto the direct heat exchange system with the other distributed liquid.
In addition to fans, many other types of air moving devices will be apparent to those skilled in the art including blowers of various constructions, movable diaphragms, and even air moving devices with no moving parts, such as convection chimneys. The position of the air outlet opening 750 may vary and may be located in a sidewall of the housing 734, rather than a top wall, to create a cross flow system, if space requirements warrant. Air can also be drawn downwardly over the direct section 724 in a concurrent, or parallel, flow arrangement rather than the counter flow arrangement illustrated in
A liquid collector 738 can be positioned to collect liquid that drains out of the wet deck fill 712. For example, the liquid collector can be a sump positioned below the wet deck fill 712, such that liquid that drains out of the wet deck fill 712 collects in the sump, where it can mix adiabatically and reach a uniform temperature, which can be close to the entering wet bulb temperature of the system. A drain pipe 739 coupled to the liquid collector 738 can route liquid to a pump 741 that provides the cooled liquid to another system (e.g., an air conditioning system).
The housing 734 is illustrated as being constructed of substantially vertical outer walls arranged generally perpendicular to one another so as to form a generally rectilinear shape. This particular shape, while convenient and economical to manufacture, is not necessary or critical to performance of the heat rejection system 700, and the shape of the housing 734 can vary widely. For example, the housing could have a circular cross section or other geometrical shape and, in fact, various components could be located in different housings, it not being critical that all of the elements be located in a single housing.
The liquid distribution system 722 can include a manifold (also known as a header) coupled to a plurality of liquid conduits 726 that receive the liquid from the manifold and distribute the liquid over a heat transfer surface (e.g., the direct heat transfer section 724) of the evaporative heat rejection system 700. The fluid conduits 726 can be any type of conduit including tubes or pipes and can be made of any type of material including polyvinylchloride (PVC), stainless steel, or rubber tubing. The fluid conduits 726 are arranged to provide a relatively even distribution of liquid over a heat transfer surface (e.g., the direct heat transfer section 724) of the evaporative heat rejection system 700 and to allow for a flow of air to be drawn up through the wet deck fill 712 and to exit through the opening 750.
An air moving device 828 (e.g., a fan) can be provided to generate two separate air streams through the fluid conduits 832 of the indirect section 830 and over the surface of the body 812 of the direct heat transfer section 824 causing a small portion of the evaporative liquid flowing through both the indirect heat transfer section 830 and direct heat transfer section 824 to evaporate, thereby cooling the remaining portion of the flowing evaporative liquid.
As explained above, a particular implementation of the indirect heat transfer section 830 can include one or more heat transfer working fluid conduits 832 having a surface that receives liquid distributed from the liquid distribution system 822. These conduits may take several forms including a series of individual coils or tubes 854 connected by headers 856 to provide an array of tubes, so that the array increases a surface area for engagement with the liquid that is distributed from the liquid distribution system 822. In another implementation, the conduit may take the form of a hollow plate with passages formed therein for the working fluid to flow through while presenting a surface area of the plate for the evaporative liquid to flow over in an indirect heat transfer relationship. A series of such plates can be utilized with the plates oriented vertically with appropriate connections and headers for distributing the working fluid through the plates.
The heat transfer coil(s) 832 of the exemplary implementation shown in
The evaporative liquid descending through the indirect heat transfer section 830 progressively absorbs heat from the working fluid in the conduits of the heat transfer coil 832. Additionally, the evaporative liquid rejects heat into the airstream via evaporation while descending over the conduits of the heat transfer coil 832. Because the airstream flows concurrently with the evaporative liquid (downward), both the airstream and the evaporative liquid progressively approach the temperature of the working fluid within the fluid conduits at the lower portion 842 of the heat transfer coil 832 as they descend in an efficient indirect heat transfer section. In the lower portion of the coil 842 the evaporative liquid is warmest within the evaporative heat rejection system. In some implementations the working fluid can be introduced into the heat transfer coil(s) 832 at a lower portion 842 of the coil(s) and can progress upwardly through the coil(s) to exit at a higher portion 844 of the coil(s), so that the working fluid will cool as it moves upwardly through the coil(s) 832, and at the uppermost portion of the heat transfer coil(s) 832 the working fluid will be the coolest, as will be the evaporative liquid distributed from the liquid distribution system 822. Thus, the working fluid will be able to be cooled to a temperature approaching the entering ambient wet bulb temperature of the system, which is the temperature the liquid distributed from the liquid distribution system 822 approaches in an efficient system. If the working fluid is a gas to be condensed, it can flow from an upper end 844 of the coil 832 to a lower end 842 of the coil 832 due to drainage requirements (i.e., so that the liquid component of the working fluid will drain under gravity, velocity, and pressure influences out of the lower portion 842 of the coil(s) 832, while the gaseous portion of the working fluid flows in the upper part of the coil(s).
The body 812 of the direct heat transfer section can include one or more elements that have a large surface area with a plurality of air passageways extending therethrough. The body surface can take many different forms. In one form, the body 812 can include a stack of spaced apart plastic sheet materials, for example, with the sheets oriented vertically such that the evaporative liquid is distributed onto the surface of sheets to flow downwardly, while air passages are formed between the spaced sheets so as to allow a flow of air over the sheets as the evaporative liquid is flowing over the sheets. In another implementation, the sheet material can be non-planar so as to provide a series of convolutions to increase the surface area for the evaporative liquid to flow over, while still providing a plurality of air flow passageways through the body 812. The body 812 can also include a series of spaced slats or even a series of spaced tubes. Persons skilled in the art recognize such body constructions by the term wet deck fill and hereinafter the body 812 may be referred to as the wet deck fill or simply fill.
The evaporative liquid that drains out of the indirect heat exchange section 830 and that enters the top of the wet deck fill 812 is relatively hot as described above. As the evaporative liquid flows through the wet deck fill 812, it is cooled evaporatively by air that is drawn in to the evaporative heat rejection system 800 and that flows through the wet deck fill 812. In an efficient system, the evaporative liquid flowing through the wet deck fill 812 approaches the entering ambient wet bulb temperature of the air entering the housing 834 of the evaporative heat rejection system 800.
The air moving device 828 can be an axial bladed fan, positioned to induce air concurrently through the indirect section 830 with respect to the evaporative liquid, and cross flow through the direct section 824 with respect to the evaporative liquid, a centrifugal fan, or any device that moves air over the heat transfer section(s). A series of air inlet openings 848a, 848b can be provided in the housing 834 such that air is induced through the indirect section 830 concurrently with respect to the evaporative liquid, and cross flow through the direct section 824 with respect to the evaporative liquid. Drift eliminators 852a, 852b can be provided between the direct 824 and indirect 830 heat transfer sections and the air moving device 828 to remove entrained liquid droplets in the air stream prior to the air stream exiting the housing. The drift eliminators may also be positioned such that air streams travelling through the direct 824 and indirect 830 sections exit through their respective drift eliminators 852a, 852b and do not stray into the other heat transfer section. Many different types and constructions of drift eliminators are known, including closely spaced metal, plastic or wood slats or louvers that permit air flow therethrough but that collect fine water droplets in the air.
In addition to fans, many other types of air moving devices will be apparent to those skilled in the art including blowers of various constructions, movable diaphragms, and even air moving devices with no moving parts, such as convection chimneys. The position of the air outlet opening 850 may vary and may be located in sidewall of the housing 834, rather than a top wall, to create a horizontal discharge system, if space requirements warrant. Air can also be drawn upwardly through the direct section 824 in a counter flow arrangement rather than the cross flow arrangement illustrated in
A liquid collector 838 can be positioned to collect evaporative liquid that drains out of the direct heat transfer section 824. For example, the liquid collector can be a sump positioned below the direct heat transfer section 824, such that evaporative liquid that drains out of the direct heat transfer section 824 collects in the sump 838, where it can mix adiabatically and reach a uniform temperature. The evaporative liquid that drains out of the direct heat transfer section 824 can be cooled additionally in an external system before being recirculated to the liquid distribution system 822 for distribution over the indirect heat transfer section 830.
A liquid recirculation system 840 (e.g., one or more pumps and associated piping) can be coupled to the liquid collector 838 and to the liquid distribution system 822 to return the evaporative liquid from the liquid collector 838 to the liquid distributor 822. For example, a drain pipe 839 coupled to the liquid collector 838 can route evaporative liquid to a pump 841 that returns the evaporative liquid through piping 843 to the liquid distribution system 822. The pump 841 can provide the evaporative liquid to the liquid distribution system 822 at a predetermined pressure above the ambient atmospheric pressure. Although a single pump 841 is shown close to the bottom of the evaporative heat rejection system 800, more than one pump can be used to return the evaporative liquid to the liquid distribution system 822, and the pump(s) can be positioned anywhere within the evaporative heat rejection system 800.
The housing 834 is illustrated as being constructed of substantially vertical outer walls arranged generally perpendicular to one another so as to form a generally rectilinear shape. This particular shape, while convenient and economical to manufacture, is not necessary or critical to performance of the heat rejection system 800, and the shape of the housing 834 can vary widely. For example, the housing could have a circular cross section or other geometrical shape and, in fact, various components could be located in different housings, it not being critical that all of the elements be located in a single housing.
In one implementation, the liquid distribution system 822 can include a manifold 825 (also known as a header) that receives evaporative liquid from the liquid recirculation system 840. The manifold 825 can be coupled to a plurality of liquid conduits 826 that receive the evaporative liquid and distribute the evaporative liquid over a heat transfer surface (e.g., the indirect heat transfer section 830) of the evaporative heat rejection system 800. The fluid conduits 826 can be any type of conduit including tubes or pipes and can be made of any type of material including polyvinylchloride (PVC), stainless steel, or rubber tubing. In the implementation shown in
While certain features of the described implementations have been illustrated as described herein, many modifications, substitutions, changes and equivalents will now occur to those skilled in the art. For example, the evaporative heat rejection system need not be a particular implementation of the heat rejection systems disclosed herein. Rather, the heat rejection system 10, 700, 800 can be any type of evaporative heat rejection system, including a cross-flow heat rejection system, a concurrent flow heat rejection system, a counter flow heat rejection system, a heat rejection system having only one of an indirect or direct cooling section, or a heat rejection system in which the indirect and direct cooling sections are not aligned vertically. Other modifications are also possible. It is, therefore, to be understood that the appended claims are intended to cover all such modifications and changes as fall within the true spirit of the embodiments of the invention.
