Patent Publication Number: US-6702004-B2

Title: Heat exchange method and apparatus

Description:
FIELD OF THE INVENTION 
     The present invention relates to a method and apparatus for the disposal of heat utilizing a heat exchange liquid in combination with a heat exchange gas. More particularly, the present invention relates to an apparatus for providing an evaporative heat exchanger wherein the heat exchanger is employed, for example, to dispose of large quantities of heat generated by various industrial processes. 
     BACKGROUND OF THE INVENTION 
     Evaporative heat exchangers are widely used in many applications where it is necessary to cool or condense fluid and/or gas that must be maintained out of contact with the heat exchange medium to which the heat is transferred. For example, air conditioning systems for large buildings employ evaporative heat exchangers for carrying out a portion of the heat exchange that is essential to the cooling process. In these systems, air inside the building is forced passed coils containing a cooled refrigerant gas thereby transferring heat from inside the building into the refrigerant gas. The warmed refrigerant is then piped outside the building where the excess heat must be removed from the refrigerant so that the refrigerant gas can be re-cooled and the cooling process continued. In addition, industrial processes such as chemical production, metals production, plastics production, food processing, electricity generation, etc., generate heat that must be dissipated and/or disposed of, often by the use evaporative heat exchangers. In all of the foregoing processes and numerous other processes that require the step of dissipating or disposing of heat, evaporative heat exchangers have been employed. 
     The general principle of the evaporative heat exchange process involves the fluid or gas from which heat is to be extracted flowing through tubes or conduits having an exterior surface that is continuously wetted with an evaporative liquid, usually water. Air is circulated over the wet tubes to promote evaporation of the water and the heat of vaporization necessary for evaporation of the water is supplied from the fluid or gas within the tubes resulting in heat extraction. The portion of the cooling water which is not evaporated is recirculated and losses of fluid due to evaporation are replenished. 
     Conventional evaporative heat exchangers are presently in widespread use in such areas as factory complexes, chemical processing plants, hospitals, apartment and/or condominium complexes, warehouses and electric generating stations. These heat exchangers usually include an upwardly extending frame structure supporting an array of tubes which form a coil assembly. An air passage is formed by the support structure within which the coil assembly is disposed. A spray section is provided usually above the coil assembly to spray water down over the individual tubes of the coil assembly. A fan is arranged to blow air into the air passage near the bottom thereof and up between the tubes in a counter flow relationship to the downwardly flowing spray water. Heat from the fluid or gas passing through the coil assembly tubes is transferred through the tube walls to the water sprayed over the tubes. As the flowing air contacts the spray water on the tubes, partial evaporation of some of the spray water occurs along with a transfer of heat from the spray water to the air. The air then proceeds to flow out of the heat exchanger system. The remaining unevaporated spray water collects at the bottom of the conduit and is pumped back up and out through the spray section in a recirculatory fashion. 
     Current practice for improving the above described heat transfer process includes increasing the surface area of the heat exchange tubes. This can be accomplished by increasing the number of coil assembly tubes employed in the evaporative heat exchanger by “packing” the tubes into a tight an array as possible, maximizing the tubular surface available for heat transfer. The tightly packed coils also increase the velocity of the air flowing between adjacent tube segments. The resulting high relative velocity between the air and water promotes evaporation and thereby enhances heat transfer. 
     Another practice currently employed to increase heat transfer surface area is the use of closely spaced fins which extend outwardly, in a vertical direction from the surface of the tubes. The fins are usually constructed from a heat conductive material, where they function to conduct heat from the tube surface and offer additional surface area for heat exchange. 
     In addition, another method currently used to increase heat exchange is the use of splash type fill structures placed between individual tubes in a coil assembly that can function to provide additional water surface area for heat transfer. 
     These current practices can have drawbacks. For example, the use of additional tubes requires additional coil plan area along with increased fan horsepower needed to move the air through the tightly packed coil assembly, increasing unit cost as well as operating cost. In addition, placement of fins between the individual tubes may make the heat exchanger more susceptible to fouling and particle build up. Further, indiscriminate placement of fill sheets within coils assemblies can cause performance degradation by hindering air flow, and the fill sheets can act as an insulator where they abut the tubes, and/or can cause heat already transferred to the air to be transferred back to the cooling water. 
     Accordingly, it is desirable to provide a method and apparatus for effectuating desirable, evaporative heat exchange that can offer a substantial reduction in parts, improved efficiency and or reduction of complex and costly assembly of components. It is also desirable to provide increased evaporative heat exchange without undesirably increasing the size of the unit, the manufacturing cost of the unit, and/or operating cost of the unit. 
     SUMMARY OF THE INVENTION 
     The foregoing needs are met, at least in part, by the present invention where, in one embodiment, an evaporative apparatus for use in a counter flow heat exchange assembly is provided having a plurality of generally vertical arrays adjacently spaced laterally to each other. Each of the individual arrays includes a plurality of generally horizontal conduits extending across the heat exchange assembly in spaced relation to each other at different vertical levels of the counter flow heat exchange assembly. The arrays additionally have connector portions that connect the vertically adjacent conduits to each other. The evaporative apparatus also includes a plurality of generally vertical partitions each extending between at least some of the conduits in each of the arrays and at least some of the partitions extending between less than all conduits of each of the arrays. 
     In accordance with another embodiment of the present invention, an evaporative apparatus for use in a counter flow heat exchange is provided having a means for exchanging heat from a substance to be cooled having a first height, and a means for spraying a cooling fluid onto the heat exchanging means. The evaporative apparatus additionally has a means for passing air over the heat exchanging means along with a means for partitioning the cooling fluid and the air. The partitioning means includes a plurality of generally vertical partitions each having a second height less than the first height of the heat exchanging means. 
     In accordance with yet another embodiment of the invention, an evaporative apparatus for use in a counter flow heat exchange assembly is provided having a plurality of generally vertical arrays adjacently spaced laterally to each other. The arrays are each arranged along respective generally vertical centerlines and include a plurality of generally horizontal conduits. The arrays each have a diameter and extend across the heat exchange assembly in spaced relation to each other at different vertical levels of the counter flow heat exchange assembly. The arrays have connector portions for connecting vertically adjacent conduits to each other, and the adjacent vertical arrays have a centerline-to-centerline distance therebetween that is greater than the diameter of each the conduits. The arrays additionally include a plurality of generally vertical partitions each extending between at least some conduits of each array. 
     In yet another embodiment of the present invention, an evaporative apparatus for use in a counter flow heat exchange assembly having a means for exchanging heat from a substance to be cooled, wherein the means includes a plurality of arrays of conduits is provided. The arrays have a first diameter and are spaced by a centerline to centerline distance between the conduits. In addition, the evaporative apparatus has a means for spraying a cooling fluid onto the heat exchanging means along with a means for passing air over the heat exchanging means. The evaporative apparatus also includes a means for partitioning the cooling fluid and the air and a means for spacing adjacent arrays such that they have a centerline to centerline distance therebetween that is greater than the first diameter of the conduits. 
     In accordance with yet a further embodiment of the invention, a partition for a heat exchanging apparatus having conduits in generally vertical arrays, is provided. The partition includes a plurality of saddle portions for engaging the conduits and a plurality of dimple portions for engaging the conduits. The saddle portions and dimple portion additionally provide spacing between laterally adjacent vertical arrays, wherein the saddle portions and the dimple portions are positioned in staggered vertical levels with respect to one another on opposed sides of the ribs. The partition additionally has a plurality of horizontal channels where portions of the partition have been removed. The channels are vertically spaced apart from one another and extend horizontally between said saddles. 
     In another aspect of the invention, a method is provided for heat exchange comprising the steps of: providing a heat exchange assembly having a plurality of generally vertical arrays adjacently spaced laterally to each other, the arrays each comprising a plurality of generally horizontal conduits extending across the heat exchange assembly in spaced relation to each other at different vertical levels of the heat exchange assembly, each array having connector portions that connect vertically adjacent conduits to each other; providing a plurality of generally vertical partitions each extending between at least some of the conduits in each of the arrays and between less than all conduits of each of the arrays; flowing a substance to be cooled through the conduits; spraying a fluid onto the partitions and the conduits; and passing air over the partitions and the conduits. 
     In yet another aspect of the present invention, a method for exchanging heat is provided comprising the steps of: exchanging heat from a substance to be cooled that passes through a plurality of conduits; spraying a cooling fluid onto the conduits; passing air over the conduits; and partitioning the cooling fluid and the air flow via at least one partition having a plurality of generally vertical partitions each having a second height less than the first height of the heat exchanging means. 
     In accordance with yet another aspect of the present invention, a method for exchanging heat is provided comprising the steps of: providing a heat exchange assembly having a plurality of generally vertical arrays adjacently spaced laterally to each other, the arrays each arranged along a respective, generally vertical centerline and the arrays each comprising a plurality of generally horizontal conduits extending across the heat exchange assembly in spaced relation to each other at different vertical levels of the heat exchange assembly, each array having connector portions for connecting vertically adjacent conduits to each other; providing a plurality of generally vertical partitions each extending between at least some conduits of each array, and adjacent ones of the vertical arrays have a centerline-to-centerline distance therebetween that is greater than the diameter of each said conduit; flowing a substance to be cooled through the conduits; spraying a fluid onto the vertical partitions and outer surfaces of the conduits; and passing air over the individual conduits. 
     In this respect, before explaining at least one embodiment of the invention in detail, it is to be understood that the invention is not limited in its application to the details of construction and to the arrangements of the components set forth in the following description or illustrated in the drawings. The invention is capable of other embodiments and of being practiced and carried out in various ways. Also, it is to be understood that the phraseology and terminology employed herein, as well as the abstract, are for the purpose of description and should not be regarded as limiting. 
     As such, those skilled in the art will appreciate that the conception upon which this disclosure is based may readily be utilized as a basis for the designing of other structures, methods and systems for carrying out the several purposes of the present invention. It is important, therefore, that the claims be regarded as including such equivalent constructions insofar as they do not depart from the spirit and scope of the present invention. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a cutaway isometric view of an evaporative heat exchanger employing a heat exchange coil circuit in accordance with an embodiment of the present invention. 
     FIG. 2 is a perspective view showing of two coil arrays and a single partition in accordance with an embodiment of the present invention. 
     FIG. 3 is a front view of the partition depicted in FIG. 2 with the coil array removed, showing horizontal channels in accordance with an embodiment of the invention. 
     FIG. 4 is a front view showing one coil array and one partition as depicted in FIG. 1 disposed on a support structure for an evaporative heat exchanger. 
     FIG. 5 is a cross-sectional view of one embodiment showing a plurality of coil arrays and partitions. 
     FIG. 6 is a cross-sectional view of another embodiment, showing a plurality of coil arrays and partitions. 
     FIG. 7 is a schematic end view of two coil arrays and partitions illustrating the spacing of laterally adjacent coil arrays. 
     FIG. 8 is a graph of the temperature profile of heat exchange fluids as they pass through a plurality of coil arrays in accordance with an embodiment having a partition between all of the conduits in an array. 
     FIG. 9 is a graph of the temperature profile of heat exchange fluids as they pass through a plurality of coil arrays similar to those in FIG. 6 having a partition between less than all of the conduits in an array. 
    
    
     DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS OF THE INVENTION 
     Referring now to the figures wherein like reference numerals indicate like elements, FIGS. 1-9 illustrate presently preferred embodiments of a evaporative heat exchanger apparatus. While in the embodiments depicted the exchanger is a counter flow heat exchanger, it should be understood that the present invention is not limited in its application to heat transfer. 
     Referring now to FIG. 1, a counter flow evaporative heat exchanger apparatus, generally designated  10 , is illustrated. The exchanger apparatus  10  includes a coil assembly  11  having a plurality of coil arrays  12 , a generally vertical air passage  13 , a cooling fluid spray assembly  14 , and upper mist eliminators  16 , a cooling air current generator employing a fan unit  18 , and a base  20  having a lower fluid collection basin therein. More particularly, the vertical passage  13  is of generally rectangular, uniform cross-section and includes vertical front and rear walls  22 ,  24  and vertical side walls  26 ,  28 . The walls  22 ,  24 ,  26 ,  28 , extend upwardly from the base  20  and confine the mist eliminators  16  which extends across substantially the entire cross section of the vertical air passage  13 . The side walls  22 ,  24  and front and rear walls  26 ,  28  combine to form an interior within which the air passage  13 , the cooling fluid spray assembly  14 , and the coil assembly  11  are located. The cooling air current generator  18  is preferably positioned adjacent side wall  28 . 
     The walls and other structural elements that form vertical passage  13  are preferably formed from mill galvanized steel, but may be composed of other suitable materials such as stainless steel, hot dipped galvanized steel, epoxy coated steel, and/or fiber reinforced plastics (FRP). The fan unit  18  of the air current generator has an outlet cowl which projects through the side wall  28  and into the air passage  13  preferably above the base  20  and the collection basin therein. 
     As shown in FIG. 1, a recirculation line  30  is located on the side wall  28  and extends between a first and second recirculation port (not pictured) and a recirculation pump  32 . The lower port extends through the wall  28  and into the collection basin located in the base  20 . The recirculation line  30  extends from the lower port to the pump  30  and to the upper port, returning the cooling fluid to the spray assembly  14 . 
     The cooling fluid spray assembly  14  includes a plurality of pipes and nozzles positioned directly above the coil assembly  11  for distribution of a cooling liquid, preferably water, onto the individual coil arrays  12  of the coil assembly  11 . The water is supplied to the coil assembly  11  by way of the recirculation line  30  previously described and enters the spray assembly  14 . 
     The mist eliminator  16  generally includes a multitude of closely spaced, elongated strips that are canted along their length and forms an opening through the top of the conduit  10  for the air currents to exit. 
     Referring now particularly to FIGS. 1-7, the coil assembly  11  includes a plurality of the individual vertical coil arrays  12 . The coil assembly  11  has an upper inlet manifold  31  for distributing the fluid to be cooled or condensed to the various coil arrays  12  along with a lower outlet manifold  33  for returning cooling fluid from the coil arrays  12  to the process in which it is used. 
     As can be observed specifically in FIGS. 2-6, each coil array  12  is preferably in the form of a cooling tube  35  bent into a plurality of generally horizontal conduits  36 . Each horizontal conduit  36  is connected to its counterparts above and/or below in the array by way of u-bend portions  37 . Each array  12  carrys fluid from the upper manifold to the lower manifold. The u-bends  37  and horizontal conduits  36  preferably form a serpentine arrangement for each array having 180 degree bends near each of the side walls  26 ,  28 . The aforementioned arrangement results in each array extending generally horizontally across the interior of the air passage  13  in a back and forth orientation at different levels along a vertical plane. Each array is parallel to additional, laterally spaced adjacent arrays  12  that make up the coil assembly  11 . A fill sheet portion  38  extends vertically between designated horizontal conduits  36  of the coil circuit  12  and provides a partition for the air passage  13 . 
     The conduits  36  are preferably formed from copper alloy, however other materials suitable for conducting heat energy such as aluminum, steel and/or stainless steel derivatives may be utilized. As depicted, the conduits  36  are cylindrical in shape, however the tubes may vary in shape for example, square, oval, or rectangular. In addition, the cooling tubes  35  may vary in diameter. Although unitary tubes  35  are preferred, the horizontal conduits  36  may be individual tubes with a connector at each end providing fluid connection between vertically adjacent conduits. Also, the conduits  36  are preferably generally parallel to one another and generally horizontal. References to parallel and/or horizontal in this application refer to generally or substantially parallel and do not indicate any particular degree of the same. 
     As depicted in FIGS. 2-6, the fill sheet  38  extends vertically between vertically adjacent horizontal conduits  36  of an individual coil array  12 . The fill sheet  38  is preferably one continuous piece that runs generally parallel with the coil array  12  along the centerline of the conduits  36 . At the conduits  36 , the fill sheet  38  runs peripherally around one side of the conduit  36  via saddles  42  and dimples  44  described in more detail below. The fill sheet  38  is preferably a textured relatively thin sheet formed from polyvinyl chloride (PVC) or light metallic material. The sheet  38  is preferably about 1.5% to 3.5% of the cooling tube diameter, however sheets having more or less thickness may be employed. In addition, the sheet  38  has diagnonally corrugated areas  39  with a peak-to-peak corrugation that preferably ranges from about 25% of the cooling tube diameter to about 75% of the cooling tube diameter. The sheet  38  also includes vertical support ribs  40  that provide strength and support to the sheet  38  along with supporting the conduits  36  via the saddles  42  and dimples  44 . The saddles  42  are disposed on one side of each rib  40  and dimples  44  on the opposite side. 
     As can be viewed in FIGS. 2-6, the saddles  42  and dimples  44  are arranged at different levels or elevations, in an alternating, offset fashion. The ribs  40  provide both elevational spacing between horizontal conduits  36  within a single array  12  and adjacent spacing between laterally neighboring arrays  12 . The sheet  38  includes horizontal channels  46  where portions of the fill sheet are removed. The conduits  36  are disposed in the channels  46 . These channels  46  are preferably aligned with the saddles  42  of the fill sheet  38 . As depicted in FIGS. 4 and 5, the vertical staggering between conduits  36  of neighboring coil arrays  12 , orients the conduits  36  so that conduits at one level of an individual array  12  are essentially rationally centered between conduits  36  of a neighboring array  12  at the next higher and next lower level. 
     FIG. 4 illustrates a support structure  50  that provides vertical support of the conduits  36 . 
     FIG. 7 illustrates how the saddles  42  retain the conduits  36  and provide elevational spacing between the individual conduits  36  of the an array  12 . The saddles  42  preferably have a depth such that when a conduit  36  is retained, the edges of the fill sheet adjacent the conduit  36  are substantially aligned with the centerline of the conduit  36 . The spacing between each conduit  36  within a single array  12  is dependent upon the diameter of the conduit being utilized. Thus, conduit diameter is determinative of saddle spacing. Elevational spacing of the conduits  36  from about 200% to 1000% of the diameter of the conduit  36  is preferred. More preferably, this distance is approximately 530% of the diameter of the conduit  36  being employed. 
     The dimples  44  are further utilized for providing spacing between conduits of separate, laterally neighboring coil arrays  12 . As illustrated in FIG. 7, the dimples  44  are preferably curved indentations capable of engaging a portion of a conduits  36  of a neighboring coil circuit  12 . The dimples  44  and saddles  42  can be alternatively shaped to engage tubes of varying geometries. 
     The dimples  44  in combination with the ribs  40  provide a spacing distance between conduits of neighboring arrays that is preferably equal to approximately 110% to 150% the diameter of the conduits  36  utilized in the array  12 . More preferably, this distance is about 130% the cooling tube diameter. Due to the above described spatial arrangement, a vertical clear line of sight exists through the coil assembly  11 . This clear line of sight refers to the fact that two adjacent arrays  12  have a centerline distance (D) greater than the outer diameter (d) of the conduit  36  utilized, as depicted in FIG.  6 . The aforementioned spacial relationship creates a vertical channel between the circuits that is free and unobstructed. As a result of this clear sight line, air flow through the coil assembly is not hindered and pressure loss is reduced. 
     The saddles  42  and dimples  44  combine to provide support to the fill sheets  38  along with providing a mechanism for attaching the sheets to the conduits  36 . As a result of the aforementioned utilization of the vertical ribs  40  in combination with saddles  42  and dimples  44 , the need for a separate mechanical attaching means to affix the fill sheet to the conduit  36  is eliminated. In addition, the need for attaching the fill sheet  38  to each individual conduit  36  with fixtures at a multitude of places is eliminated. 
     Referring now to FIGS. 2 and 3, horizontal channels  46  are depicted extending parallel across the width of the fill sheet  38 . As previously described, the channels  46  are aligned with the saddles  42  of the ribs  40  and provide a window like opening for the cooling tubes  36 . Preferably the edges of the channels  46  do not touch or contact the conduits  36 . This orientation is preferred especially in applications where the fill sheets are constructed from materials that are non-conductive, for example plastics and plastic derivatives. These non-conductive materials can often function as insulators when they touch the conduits  36 . In addition, these channels  46  allow for the entire surface area of the cooling tube to be exposed to the cooling fluid and air currents, (except in the regions touching the saddles  42  and dimples  44 ), improving the amount of heat transfer by the individual tubes. 
     During operation of the evaporative heat exchanger  10 , a fluid to be cooled or condensed, such as water or gas, flows into the exchanger  10  via an inlet port. This fluid is then distributed by the upper manifold to the individual arrays  12  that make up the coil assembly  11 . The fluid being cooled then proceeds to flow through the various conduits  36 , back and forth across the interior of the air passage  13  at different levels therein until it reaches the lower manifold where it is transferred out of the evaporative heat exchanger  10 . As the fluid being cooled flows through the coil assembly  11 , water is sprayed from the spray assembly  14  onto the fill sheets  38  and conduits  36  of each, separate array  12  while air from the air current generator  18  is blown up between the individual conduit tubes  36 . The upwardly flowing air then passes through the mist eliminator  16  and out of the system. 
     More particularly, during its flow through the conduits  36 , the fluid to be cooled gives up heat to the conduit walls of the conduits  36 . The heat passes outwardly through the walls to the water flowing over the outer surface of the conduit. Meanwhile the water is simultaneously coming into evaporative contact with the upwardly moving air and the water gives up heat to the air both by normal contact transfer and by partial evaporation. 
     The present invention improves the aforementioned heat exchange process by increasing the heat exchange capabilities and affording the process to be more efficient. The addition of fill sheets  38  functions to provide increased air-water interface by producing more water surface area that may contact both the conduits  36  and the air currents. The fills sheets  38 , in combination with the spacing of the cooling tubes previously described, create clear vertical sight lines through the coil assembly  11 . This results in an increased, more efficient heat transfer without requiring increased coil plan area and/or air current generator horsepower. In addition, the fill sheets  38  function to direct water between cooling tubes  36 , improving water flow over the entire tube surface, significantly reducing the likelihood of evaporative fouling and/or dry spots on the cooling tube surfaces. Another benefit of placing the fill sheets within the coil circuits is the sheets  38  allow the recirculating spray system to operate at lower flow rates, affording the heat exchange unit to employ pumps that are less expensive to purchase and operate. 
     As depicted in FIG. 5, the fill sheets  38  are preferably disposed between the conduits  36  in the bottom section and middle of the arrays  12 , but not between conduit  36  at the top of the array  12 . Referring specifically to FIGS. 7 and 8, the recirculating water temperature is coldest at the top of the exchanger unit  10  while the air wet-bulb temperature is the hottest. As previously described, the fill sheets  38  provide additional water surface area for heat transfer. In FIG. 8, sheets  38  of embodiment FIG. 4 are provided between all conduits  36 . The partitions in the lower portions of the coils in embodiments FIGS. 4 and 5 function to lower the recirculating water temperature to a lower temperature differential between the recirculating water temperature and air wet-bulb temperature. This allows the temperature differential between the process fluid and the wet-bulb temperature to be lower than a coil without partitions. In embodiment FIG. 5, the recirculating water temperature is much lower than the effluent wet-bulb temperature of the air in region A. In region A, the recirculating water gains heat from the process fluid and from the air. In region A, transferring heat from the air to the recirculating water lowers the amount of heat that can be transferred from the process fluid to the water. Lowering the amount of heat removed from the process fluid raises the exit process fluid temperature. 
     To minimize this effect it is advantageous in some embodiments to employ the fill sheets  38  only between conduits  36  in lower and middle portions of the array  12  so that the sheets  38  do not extend between all vertically adjacent conduits, reducing the likelihood that heat will be transferred back from the air to the recirculating water, making the counter flow heat exchanger less efficient. FIG. 9 shows a graph of the resulting desirable temperatures, corresponding to the embodiment of FIG.  6 . 
     The many features and advantages of the invention are apparent from the detailed specification, and thus, it is intended by the appended claims to cover all such features and advantages of the invention which fall within the true spirits and scope of the invention. Further, since numerous modifications and variations will readily occur to those skilled in the art, it is not desired to limit the invention to the exact construction and operation illustrated and described, and accordingly, all suitable modifications and equivalents may be resorted to, falling within the scope of the invention.