Patent Publication Number: US-11029093-B2

Title: Cooling tower with direct and indirect heat exchanger

Description:
BACKGROUND OF THE INVENTION 
     The present invention relates generally to an improved heat exchange apparatus such as a closed circuit fluid cooler, fluid heater, condenser, evaporator, thermal storage system, air cooler or air heater. More specifically, the present invention relates to a combination or combinations of separate indirect heat exchange sections enclosed in a housing and direct evaporative heat exchange sections arranged in the same structure to achieve improved capacity, improved performance and allowing a wet and dry mode. 
     The invention includes the use of a plate type or coil circuit tube type of heat exchanger as an indirect heat exchange section. Such indirect heat exchange section can be combined with a direct heat exchange section, which usually is comprised of a fill section over which an evaporative liquid such as water is transferred, usually in a downwardly streaming operation. Such combined indirect heat exchange section and direct heat exchange section together provide improved performance as an overall heat exchange apparatus such as a closed circuit fluid cooler, fluid heater, condenser, evaporator, air cooler or air heater. 
     Part of the improved performance of the indirect heat exchange section comprising a plate heat exchanger is the capability of the indirect heat exchange section hereinafter called a plate type heat exchanger but could can also be a coil circuit tube type heat exchanger, to provide both sensible and latent heat exchange with the evaporative liquid which is streamed or otherwise transported over and through the indirect heat exchange section. The improved performance is achieved by insuring that 100% of the plate heat exchanger is wetted while also operating at substantially higher evaporative fluid velocities resulting in higher external forced convection heat transfer coefficients relative to gravity drain indirect heat exchangers. 
     Various combinations of the heat exchange arrangements are possible in accordance with the present invention. Such arrangements could include an arrangement wherein the indirect heat exchange section is physically located within the arrangement and being above, adjacent or below the direct heat exchange section. In such arrangements, the indirect heat exchange section is comprised of a plate type heat exchanger located in a housing located within the evaporative heat exchanger. An internal fluid stream to be cooled, heated, evaporated or condensed is passed through the internal passageways of the plate type heat exchanger. An evaporative liquid is passed through the indirect heat exchange section housing and distributed through the external passageways of the plate type heat exchanger to indirectly exchange heat with the internal fluid stream. Due to varying heat loads, varying ambient conditions, economical needs to save energy or water and needs of heat exchange, the indirect heat exchanger of the present invention could be operated wherein both air and an evaporative liquid such as water are drawn or supplied across the indirect heat exchanger. This is accomplished by selectively pumping air into the indirect heat exchanger to travel with the evaporative liquid which causes increased agitation and evaporative fluid velocities hence increased external heat transfer coefficients while also allowing evaporative heat exchange to occur on the outside of the indirect heat exchanger. A dry mode of operation is made possible by pumping only air through the indirect heat exchange section housing in thermal contact with the outside of the internal passageways of the plate type heat exchanger to indirectly exchange heat with the internal fluid stream. Because of the increased efficiency of the indirect heat exchange section, the size of the indirect heat exchanger can be reduced thereby allowing more room for adding direct heat exchanger surface area and even allowing a larger diameter fan in some orientations both of which increase the improved heat exchanger capacity. Because the indirect heat exchange section is located within the improved arrangement and being above, adjacent or below the direct heat exchange section, either air or evaporative liquid or both are in direct contact with the housing of the indirect heat exchanger thereby increasing the heat transfer of the indirect heat exchange section. 
     The evaporative liquid then exits the indirect heat exchange section housing to be distributed onto and through the direct heat exchange section which is usually comprised of a fill arrangement. Air is moved over the direct heat exchange section to evaporatively cool the evaporative liquid. The evaporative liquid draining from the direct heat exchange section is typically collected in a sump and then pumped upwardly for redistribution through the indirect heat exchange section housing. 
     Accordingly, it is an object of the present invention to provide an improved heat exchange apparatus, which could be a closed circuit fluid cooler, fluid heater, condenser, evaporator, air cooler or air heater, which includes an indirect heat exchange section located within a housing and located above, below or adjacent to the direct heat exchanger all which are located within the improved heat exchange apparatus. 
     It is another object of the present invention to provide an improved heat exchange apparatus such as a closed circuit fluid cooler, fluid heater, condenser, evaporator, air cooler or air heater, including an indirect heat exchange section that comprises a plate type heat exchanger or a coil circuit tube type heat exchanger located within a housing. 
     It is another object of the present invention to provide an improved heat exchange apparatus such as a closed circuit fluid cooler, fluid heater, condenser, evaporator, air cooler or air heater, including an indirect heat exchange section located within a housing wherein either evaporative liquid, air or both evaporative liquid and air exchange heat with the housing of the indirect heat exchange section. 
     It is another object of the present invention to provide an improved heat exchange apparatus such as a closed circuit fluid cooler, fluid heater, condenser, evaporator, air cooler or air heater, including an indirect heat exchange section located within a housing wherein the customer piping between the pump and the indirect heat exchange section has been eliminated. 
     It is another object of the present invention to provide an improved heat exchange apparatus such as a closed circuit fluid cooler, fluid heater, condenser, evaporator, air cooler or air heater, including an indirect heat exchange section located within a housing wherein the cost of the housing is substantially reduced because of a lower pressure requirement. 
     It is another object of the present invention to provide an improved heat exchange apparatus such as a closed circuit fluid cooler, fluid heater, condenser, evaporator, air cooler or air heater, by decreasing the size of indirect heat exchanger while increasing the size of direct heat exchanger located within the same heat exchange apparatus while increasing the size of the fan while maintaining the size or footprint of the cooling tower in order to increase the thermal capacity and reduce the manufacturing cost for a given footprint of the cooling tower. 
     It is another object of the present invention to provide an improved heat exchange apparatus such as a closed circuit fluid cooler, fluid heater, condenser, evaporator, air cooler or air heater, including an indirect heat exchange section located within a housing wherein air streams are injected into the evaporative liquid of the indirect heat exchange section housing during wet operation. 
     It is another object of the present invention to provide an improved heat exchange apparatus such as a closed circuit fluid cooler, fluid heater, condenser, evaporator, air cooler or air heater, including an indirect heat exchange section located within a housing wherein the indirect heat exchange section may operate in a dry mode by operating an air blower that blows air through the indirect heat exchanger housing to move cold ambient air through the exterior passages of the indirect heat exchanger to indirectly and sensibly cool the internal fluid stream. 
     SUMMARY OF THE INVENTION 
     The present invention provides an improved heat exchange apparatus which typically is comprised of a combination of an indirect heat exchange section and a direct heat exchange section. The indirect heat exchange section provides improved performance by utilizing a plate type heat exchanger usually within a housing. A plurality of internal passages and external passages are formed between plates. Such plates are designed to allow an internal fluid stream to be passed through the internal passages and an evaporative liquid, air, or evaporative liquid with air to be passed through the external passages to indirectly exchange heat with the internal fluid stream within the plate heat exchanger. Such utilization of a plate heat exchanger in the closed circuit fluid cooler, fluid heater, condenser, evaporator, air cooler or air heater of the present invention provides improved performance and also allows for combined operation or alternative operation wherein only air or only an evaporative liquid or a combination of the two can be passed through or across the external passages of the plate heat exchanger. Since the housing of the indirect heat exchanger is located within the evaporative structure, the evaporative liquid moving within the housing as it is absorbing heat can be further cooled by the evaporative liquid, air, or evaporative liquid and air which is in contact and moving across the outside surface of the housing. 
     A direct heat exchange section is located beneath, adjacent or above the indirect heat exchange section. The evaporative liquid leaving the indirect heat exchange section housing passes onto and through the direct heat exchange section fill and accordingly allows heat to be drawn from such evaporative liquid by a passage of air across or through the direct heat exchange section fill by air moving therethrough. The evaporative liquid exiting the direct heat exchange section is collected in a sump and then pumped back for distribution through the indirect heat exchange section housing. While the sump is typically locating in the bottom of the evaporative heat exchanger, it is also possible to locate the sump remotely as is known in the art. 
     The present invention further concerns the design of an improved heat exchange apparatus that has a direct heat exchanger, usually a fill pack and an indirect heat exchanger, usually a plate type heat exchanger. The size of the more expensive indirect heat exchanger can be decreased while the size of the inexpensive direct heat exchanger can be increased. In addition, because some indirect and direct evaporative heat exchangers have the indirect heat exchanger and fan located at the top, the fan and indirect heat exchanger compete for precious footprint and in this improved heat exchange apparatus, since the indirect heat exchanger is smaller or located adjacent or under the direct heat exchange section, the fan diameter may be increased while maintaining the size or footprint of the cooling tower in order to increase the thermal capacity and reduce the manufacturing cost for a given footprint of the cooling tower. 
     The size reduction of the indirect heat exchanger can be achieved by increasing the rate of sensible heat transfer between the evaporative liquid and the indirect heat exchanger. In general, the rate of sensible heat transfer is increased when the velocity of liquid traveling across the surface of indirect heat exchanger is increased. Since the pull of gravity is constant and cannot be increased, the velocity of the evaporative liquid that is naturally flowing over the external surface of prior art indirect heat exchange sections is limited and cannot be substantially increased. Without significantly increasing this cooling tower liquid velocity, it is difficult to increase the rate of sensible heat transfer between the evaporative liquid and the surface of the indirect heat exchanger plates. In one embodiment of this invention, the plates of the indirect heat exchanger are enclosed in a water tight housing and then a pump is used to force a larger quantity of evaporative liquid into the housing and then rapidly through the plurality of passages between adjacent plates. Because the forced liquid velocity can be substantially higher than the naturally flowing liquid by gravity, a higher sensible heat transfer rate between the evaporative liquid and the external surface of the plates is achieved. 
     Because the indirect heat exchanger plates are typically made out of metal or of a highly conductive plastic, which is typically more expensive than the fill pack of the direct heat exchange section which are usually made of plastic, the overall manufacturing cost of the cooling tower can be reduced substantially. By increasing the rate of sensible heat transfer significantly without reducing the size of indirect heat exchanger plates significantly, the overall cooling tower&#39;s thermal capacity is increased without increasing the cooling tower footprint. 
     The overall cooling tower performance could additionally be increased by injecting air streams into the indirect heat exchange section housing during wet operation. The injected air stream, which becomes air bubbles inside the housing when filled with evaporative liquid, increases the heat transfer rate by both agitating and increasing the evaporative liquid&#39;s local velocity. Further, the injected air into the evaporative liquid allows evaporative heat transfer to occur in addition to sensible cooling by just the evaporative fluid alone. 
     In another embodiment, the indirect heat exchange section housing can be drained of evaporative liquid while still having the ability to cool the internal fluid stream within the indirect heat exchange section plate passageways. This can be achieved by operating an air blower that is attached to the plate housing to move cold ambient air through the plate housing through the passages outside the plate internal passageways to indirectly sensibly cool the internal fluid inside the plate passageways with ambient air. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       In the drawings, 
         FIG. 1  is a side view of the first embodiment using a plate type heat exchanger in the housing of the indirect heat exchange section in accordance with the present invention 
         FIG. 1A  is a side view of the first embodiment using a coil circuit tube type heat exchanger in the housing of the indirect heat exchange section in accordance with the present invention 
         FIG. 1B  is a side view of the first embodiment using a different water distribution system to direct the evaporative fluid to the direct heat exchanger in accordance with the present invention; 
         FIG. 2  is a side view of a second embodiment of a heat exchanger in accordance with the present invention; 
         FIG. 3  is a side view of a third embodiment of a heat exchanger in accordance with the present invention; 
         FIG. 4  is a side view of a fourth embodiment of a heat exchanger in accordance with the present invention; 
         FIG. 5  is a side view of a fifth embodiment of a heat exchanger in accordance with the present invention; 
         FIG. 6  is a side view of a sixth embodiment of a heat exchanger in accordance with the present invention; 
         FIG. 7  is a side view of a seventh embodiment of a heat exchanger in accordance with the present invention; 
         FIG. 8  is a side view of an eighth embodiment of a heat exchanger in accordance with the present invention; 
         FIG. 9  is a perspective view of the indirect heat exchange section having a plate type heat exchanger located inside a housing in accordance with an embodiment of the present invention; 
         FIG. 10  is a cutaway view of the indirect heat exchange section having a plate type heat exchanger located inside a housing in accordance with an embodiment of the present invention 
         FIG. 11  is a cutaway view of the indirect heat exchange section having a coil circuit tube type exchanger located inside a housing in accordance with an embodiment of the present. 
     
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT 
     Referring now to  FIG. 1  of the drawings, a first embodiment of the present invention is shown generally as heat exchanger  20 , which is generally in the form of a closed circuit cooling tower. 
     Such heat exchanger generally is present in a closed circuit cooling tower with indirect heat exchange section  25  located above direct heat exchange section  24 . 
     Direct heat exchange section  24  is typically comprised of fill usually comprised of sheets of polyvinyl chloride. Direct heat exchange section  24  receives air through air inlet  28  on the outside of heat exchanger  20 , with air being drawn generally across and somewhat upwardly through direct heat exchange section  24  by fan  26  rotated by motor  27 . 
     Indirect heat exchange section  25  is usually comprised of a plurality of plate type heat exchangers has preferably internal fluid inlet  21  and internal fluid outlet  22  and is positioned inside housing  34 . It should be understood that the operation of internal fluid inlet  21  and internal fluid outlet  22  can be reversed if it is desired. 
     An evaporative cooling tower liquid, usually water, flows downwardly from water distribution assembly  23  such that the evaporative cooling tower liquid falls downwardly onto and through direct heat exchange section  24 . While falling downwardly and through direct heat exchange section  24 , a small portion of cooling tower liquid is evaporated by moving air and latent heat transfer takes place from the evaporative cooling tower liquid to air. It should be noted that in some applications, condensation takes place from air into cooling tower liquid. 
     The cooling tower liquid that passes downwardly and through direct heat exchange section  24  is then collected in sump  31  and is pumped by pump  29  to indirect section housing  34  and through indirect heat exchange section  25  then back to water distribution assembly  23 . Water distribution assembly  23  can be comprised of a variety of pipes with openings and using orifices or spray nozzles  36  as shown in  FIG. 1  or as shown in  FIG. 1B , may have gravity water basin  35  with orifices or nozzles  36  or can be of other water distribution assemblies as known in the art. 
     In  FIG. 1 , indirect heat exchange section  25  is usually comprised of a plate type heat exchanger  32  but can be any type of indirect heat exchanger such as and not limited to a coil circuit tube type heat exchanger as known in the art. A fluid to be cooled, condensed, heated, or evaporated passes within the joined plates or cassettes of plate type heat exchanger  32 . It should be further understood that the heat exchanger  25  can be situated in any available location within the improved heat exchange apparatus in any position because the evaporative liquid is pumped through the indirect heat exchange section. An advantage of having indirect heat exchange section  25  and direct heat exchange section  24  located within the improved heat exchanger  20  is that the piping between indirect heat exchange section  25  and water distribution assembly  23  is minimized and customer piping is eliminated. Another advantage of having indirect heat exchange section  25  and direct heat exchange section  24  located within the improved heat exchanger  20  is that indirect heat exchanger  25  is in very close proximity to water distribution assembly  23 , requiring much lower pressure to pump the evaporative liquid hence the pressure rating and cost of housing  34  may be substantially reduced. 
     In  FIG. 1A , indirect heat exchanger  30  may be constructed of tubes and inlet header  22  and outlet header  21  in any configuration and material as known in the art as long as it is enclosed by housing  34 . 
     In  FIGS. 1,1A, and 1B , fan  26  is shown to induce airflow through direct heat exchange section  24  but can also be a forced air type as known in the art and is not a limitation of the invention. This is true for all subsequent Figures as well. 
     Referring now to  FIG. 2  of the drawings, a second embodiment of the present invention is shown generally as heat exchanger  10 , which is generally in the form of a closed circuit cooling tower. 
     Such heat exchanger generally is present in a closed circuit cooling tower with indirect heat exchange section  5  located below direct heat exchange section  4 . Direct heat exchange section  4  is typically comprised of fill usually comprised of sheets of polyvinyl chloride. Direct heat exchange section  4  receives air through air inlet  8  on the outside of heat exchanger  10 , with air being drawn generally across and somewhat upwardly through direct heat exchange section  4  by fan  6  rotated by motor  7 . 
     Indirect heat exchange section  5  is usually comprised of plate type heat exchanger  12  having fluid inlet  1  and fluid outlet  2  and is positioned inside housing  16 . It should be understood that fluid inlet  1  and fluid outlet  2  can be reversed if it is desired. 
     An evaporative cooling tower liquid, usually water, flows downwardly from water distribution assembly  3  such that the cooling tower liquid falls downwardly onto and through direct heat exchange section  4 . While falling downwardly and through direct heat exchange section  4 , a small portion of cooling tower liquid is evaporated by moving air and latent heat transfer takes place from the evaporative cooling tower liquid to air. It should be noted that in some applications, condensation takes places from air into cooling tower liquid. 
     The evaporative cooling tower liquid that passes downwardly and through direct heat exchange section  4  and collected in sump  11  is pumped by pump  9  to indirect heat exchange housing  16  and through indirect heat exchange section  5  then back to water distribution assembly  3 . Water distribution assembly  3  can be comprised of a variety of pipes with openings or nozzles  13  as shown, or any other water distribution arrangement such as using spray nozzles, troughs, or other water distribution assemblies. 
     Indirect heat exchange section  5  enclosed in housing  16  is usually comprised of a plurality of plate type heat exchangers  12  but can be any type of indirect heat exchanger such as and not limited to a coil circuit tube type heat exchanger as known in the art. A fluid to be cooled, condensed, heated, or evaporated passes within the joined plates or cassettes of plate type heat exchanger  12 . 
     An advantage of placing indirect heat exchange section  5  into sump  11  is that evaporative cooling tower water flows over the surface of the housing  16  of indirect heat exchange section  5  and heat transfer takes place because the cold water in sump  11  cools the surface of housing  16  of indirect heat exchange section  5  further cooling the fluid within the plurality of plates  12 . When heat transfer takes place between housing  16  and sump water  11 , sump water  11  becomes hotter and the sump water top surface can be used as an added evaporative surface to the fill and increase the overall efficiency of the cooling tower. 
     Indirect heat exchange section  5  may be either fully or partially submerged in cold water sump  11 . Another advantage of placing indirect heat exchange section  5  into sump  11  is that there is room now for a larger or taller direct heat exchange section  4  thereby increasing the capacity of the unit. An advantage of having indirect heat exchange section  5  and direct heat exchange section  4  located within the improved heat exchanger  10  is that the piping between indirect heat exchange section  5  and water distribution assembly  3  is minimized and customer piping is eliminated. 
     Referring now to  FIG. 3  of the drawings, a third embodiment of the present invention is shown generally as heat exchanger  40 , which is generally in the form of a closed circuit cooling tower. 
     Such heat exchanger generally is present in a closed circuit cooling tower with indirect heat exchange section  45  located in air plenum  53  next to and toward the lower half of direct heat exchange section  44 . It should be understood that positioning indirect heat exchange section  45  in the air plenum  53  adjacent to direct heat exchanger  44 , allows for easier access and cleaning of indirect heat exchanger  45  while allowing a larger size (full height) direct heat exchange section  44  in the design. 
     Direct heat exchange section  44  is typically comprised of fill usually comprised of sheets of polyvinyl chloride. Direct heat exchange section  44  receives air through air inlet  48  on the outside of heat exchanger  40 , with air being drawn generally across and somewhat upwardly through direct heat exchange section  44  by fan  46  rotated by motor  47 . 
     Indirect heat exchange section  45  is usually comprised of a plurality of plate type heat exchangers  52  having fluid inlet  41  and fluid outlet  42  and positioned inside housing  56 . It should be understood that the operation of fluid inlet  41  and fluid outlet  42  can be reversed if it is desired. 
     An evaporative cooling tower liquid, usually water, flows downwardly from water distribution assembly  43  such that the evaporative cooling tower liquid falls downwardly onto and through direct heat exchange section  44 . While falling downwardly and through direct heat exchange section  44 , a small portion of cooling tower liquid is evaporated by moving air and latent heat transfer takes place from cooling tower liquid to air. It should be noted that in some applications, condensation takes places from air into cooling tower liquid. 
     The evaporative cooling tower liquid that passes downwardly onto and through direct heat exchange section  44  and collected in sump  51  is pumped by pump  49  to indirect heat exchange housing  56  and through indirect heat exchange section  45  then back to water distribution assembly  43 . Water distribution assembly  43  can be comprised of a variety of pipes with openings or nozzles  36 , or be of any other water distribution arrangement such as using spray nozzles, troughs, or other water distribution assemblies. 
     Indirect heat exchange section  45  is usually comprised of a plurality of plate type heat exchangers  52  but can be any type of indirect heat exchanger such as and not limited to a coil circuit tube type heat exchanger as known in the art. A fluid to be cooled, condensed, heated, or evaporated passes within the joined plates or cassettes of plate type heat exchangers  52 . 
     Air  54  exits from direct heat exchange section  44  and flows into discharge air plenum  53  on the way to fan  46  then flows over the surface of housing  56  of indirect heat exchange section  45  and heat transfer takes place. In the case in which direct heat exchange section  44  is used to cool evaporative cooling tower liquid, air  54  cools the surface of housing  56  of indirect heat exchange section  45 , which is an added benefit from placing heat exchanger  45  in discharge air plenum  53 . It is possible to mount the indirect section at any height within air plenum  53  where the air will be in heat exchange with housing  56 . 
     An advantage of having indirect heat exchange section  45  and direct heat exchange section  44  located within the improved heat exchanger  40  is that the piping between indirect heat exchange section  45  and water distribution assembly  43  is minimized and customer piping is eliminated. 
     Referring now to  FIG. 4  of the drawings, a fourth embodiment of the present invention is shown generally as heat exchanger  90 , which is generally in the form of a closed circuit cooling tower. 
     Such heat exchanger generally is present in a closed circuit cooling tower with direct heat exchange section  94  underneath water distribution assembly  93  with indirect heat exchange section  95  located in sump  101 . 
     Direct heat exchange section  94  is typically comprised of fill usually comprised of sheets of polyvinyl chloride. Direct heat exchange section  94  receives air through air inlets  98  on the outside of heat exchanger  90 , with air being drawn generally upwardly through direct heat exchange section  94  by fan  96  rotated by motor  97 . 
     Indirect heat exchange section  95  is usually comprised of a plurality of plate type heat exchangers  102  having fluid inlet  91  and fluid outlet  92  positioned in housing  105 . It should be understood that the operation of fluid inlet  91  and fluid outlet  92  can be reversed if it is desired. 
     An evaporative cooling tower liquid, usually water, flows downwardly from water distribution assembly  93  such that the cooling tower liquid falls downwardly onto and through direct heat exchange section  94 . While falling downwardly onto and through direct heat exchange section  94 , a small portion of cooling tower liquid is evaporated by moving air and latent heat transfer takes place from cooling tower liquid to air. It should be noted that in some applications, condensation takes places from air into cooling tower liquid. 
     The cooling tower liquid that passes downwardly onto and through direct heat exchange section  94  and collected in sump  101  is pumped by pump  99  to housing  105  then through indirect heat exchange section  95  then back to water distribution assembly  93 . Water distribution assembly  93  can be comprised of a variety of pipes with openings or nozzles  100 , or any other water distribution arrangement such as using spray nozzles, troughs, or other water distribution assemblies. 
     Indirect heat exchange section  95  is usually comprised of a plurality of plate type heat exchangers  102  but can be any type of indirect heat exchanger such as and not limited to a coil circuit tube type heat exchanger as known in the art. A fluid to be cooled, condensed, heated, or evaporated passes within the joined plates or cassettes of plate type heat exchanger  102 . 
     It can be noted that by placing the indirect heat exchange section  95  under the direct heat exchange section  94 , there is room for a greater size (taller) direct heat exchange section  94 . An advantage of placing indirect heat exchange section  95  into sump  101  is that cold evaporative cooling tower water flows over the surface of the housing  105  of indirect heat exchange section  95  and heat transfer takes place. In the case in which direct heat exchange section  94  is used to cool the evaporative cooling tower liquid, the cold water in sump  101  cools the surface of housing  105  of indirect heat exchange section  95  further cooling the fluid within the plurality of plates  102  which is an added benefit. Indirect heat exchange section  95  may be either fully or partially submerged in cold water sump  101 . 
     An advantage of having indirect heat exchange section  95  and direct heat exchange section  94  located within the improved heat exchanger  90  is that the piping between indirect heat exchange section  95  and water distribution assembly  93  is minimized and customer piping is eliminated. 
     Referring now to  FIG. 5  of the drawings, a fifth embodiment of the present invention is shown generally as heat exchanger  110 , which is generally in the form of a closed circuit cooling tower. 
     Such heat exchanger generally is present in a closed circuit cooling tower with indirect heat exchange section  115  located underneath direct heat exchanger  114  and at least partially above the pool of evaporative cooling tower liquid in sump  121 . 
     Direct heat exchange section  114  is typically comprised of fill usually comprised of sheets of polyvinyl chloride. Direct heat exchange section  114  receives air through air inlets  118  on the outside of heat exchanger  110 , with air being drawn generally upwardly through direct heat exchange section  114  by fan  116  rotated by motor  117 . 
     Indirect heat exchange section  115  is usually comprised of a plurality of plate type heat exchangers  122  having fluid inlet  111  and fluid outlet  112  and positioned inside housing  125 . It should be understood that the operation of fluid inlet  111  and fluid outlet  112  can be reversed if it is desired. 
     An evaporative cooling tower liquid, usually water, flows downwardly from water distribution assembly  113  such that the cooling tower liquid falls downwardly onto and through direct heat exchange section  114 . While falling downwardly onto and through direct heat exchange section  114 , a small portion of cooling tower liquid is evaporated by moving air and latent heat transfer takes place from cooling tower liquid to air. It should be noted that in some applications, condensation takes places from air into cooling tower liquid. 
     The evaporative cooling tower liquid that passes downwardly onto and through direct heat exchange section  114  and collected in sump  121  is pumped by pump  119  to housing  125  through indirect heat exchange section  115  then back to water distribution assembly  113 . Water distribution assembly  113  can be comprised of a variety of pipes with openings, orifices or nozzles  120 , or any other water distribution arrangement such as using spray nozzles, troughs, or other water distribution assemblies. 
     Indirect heat exchange section  115  is usually comprised of a plurality of plate type heat exchangers  122  but can be any type of indirect heat exchanger such as and not limited to a coil circuit tube type heat exchanger as known in the art. A fluid to be cooled, condensed, heated, or evaporated passes within the joined plates or cassettes of plate type heat exchanger  122 . 
     Some of the air entering through air inlet  118  on the way to direct heat exchange section  114  blows over and cools the surface of housing  125  of indirect heat exchange section  115  which in turn further cools plate type heat exchangers  122 . 
     An advantage of having indirect heat exchange section  115  and direct heat exchange section  114  located within the improved heat exchanger  110  is that the piping between indirect heat exchange section  115  and water distribution assembly  113  is minimized and customer piping is eliminated. 
     Referring now to  FIG. 6  of the drawings, a sixth embodiment of the present invention is shown generally as heat exchanger  130 , which is generally in the form of a closed circuit cooling tower. 
     Such heat exchanger generally is present in a closed circuit cooling tower with direct heat exchange section  134  underneath water distribution assembly  133  indirect heat exchange section  135  located underneath redistribution pan  149  and positioned above cooling tower liquid in sump  141 . 
     Direct heat exchange section  134  is typically comprised of fill usually comprised of sheets of polyvinyl chloride. Direct heat exchange section  134  receives air through air inlets  138  on the outside of heat exchanger  130 , with air being drawn generally upwardly through direct heat exchange section  134  by fan  136  rotated by motor  137 . 
     Indirect heat exchange section  135  is usually comprised of a plurality of plate type heat exchangers  142  having fluid inlet  131  and fluid outlet  132  and positioned inside housing  145 . It should be understood that the operation of fluid inlet  131  and fluid outlet  132  can be reversed if it is desired. 
     An evaporative cooling tower liquid, usually water, flows downwardly from water distribution assembly  133  such that the cooling tower liquid falls downwardly onto and through direct heat exchange section  134 . While falling downwardly onto and through direct heat exchange section  134 , a small portion of cooling tower liquid is evaporated by moving air and latent heat transfer takes place from cooling tower liquid to air. It should be noted that in some applications, condensation takes places from air into cooling tower liquid. 
     The evaporative cooled cooling tower liquid that passes downwardly onto and through direct heat exchange section  134  gets collected in redistribution pan  149  and is re-sprayed onto indirect heat exchange section housing  145 . The redistribution pan  149  guides the evaporative cooling tower water over housing  145  such that the housing is cooled and indirectly helps to cool indirect heat exchange section  135 . The evaporative cooling tower liquid is then collected in sump  141  and is pumped by pump  139  to housing  145  then through indirect heat exchange section  135  then back to water distribution assembly  133 . Water distribution assembly  133  can be comprised of a variety of pipes with openings, orifices or nozzles  140 , or any other water distribution arrangement such as using spray nozzles, troughs, or other water distribution assemblies. 
     Indirect heat exchange section  135  is usually comprised of a plurality of plate type heat exchangers  142  but can be any type of indirect heat exchanger such as and not limited to a coil circuit tube type heat exchanger as known in the art. A fluid to be cooled, condensed, heated, or evaporated passes within the joined plates or cassettes of plate type heat exchanger  142 . 
     An advantage of having indirect heat exchange section  145  and direct heat exchange section  134  located within the improved heat exchanger  130  is that the piping between indirect heat exchange section  145  and water distribution assembly  133  is minimized and customer piping is eliminated. 
     Referring now to  FIG. 7  of the drawings, a seventh embodiment of the present invention is shown generally as heat exchanger  150 , which is generally in the form of a closed circuit cooling tower. 
     Such heat exchanger generally is present in a closed circuit cooling tower with indirect heat exchange section  155  located in plenum  163  adjacent to and towards the lower half of direct heat exchange section  154 . It should be noted that indirect heat exchanger  155  can be located above, below or adjacent to direct heat exchanger  154  as shown in other Figures but is presented as adjacent to direct heat exchanger  154  for illustrative purposes. 
     Direct heat exchange section  154  is typically comprised of fill usually comprised of sheets of polyvinyl chloride. Direct heat exchange section  154  receives air through air inlet  158  on the outside of heat exchanger  150 , with air being drawn generally across and somewhat upwardly through direct heat exchange section  154  by fan  156  rotated by motor  157 . 
     Indirect heat exchange section  155  is usually comprised of a plurality of plate type heat exchangers  162  having fluid inlet  151  and fluid outlet  152 . It should be understood that the operation of fluid inlet  151  and fluid outlet  152  can be reversed if it is desired. 
     An evaporative cooling tower liquid, usually water, flows downwardly from water distribution assembly  153  such that the evaporative cooling tower liquid falls downwardly onto and through direct heat exchange section  154 . While falling downwardly onto and through direct heat exchange section  154 , a small portion of cooling tower liquid is evaporated by moving air and latent heat transfer takes place from cooling tower liquid to air. It should be noted that in some applications, condensation takes places from air into cooling tower liquid. 
     The evaporative cooling tower liquid that passes downwardly onto and through direct heat exchange section  154  and collected in sump  161  is pumped by pump  159  to housing  169  then through indirect heat exchange section  155  then back to water distribution assembly  153 . Water distribution assembly  153  can be comprised of a variety of pipes with openings, orifices or nozzles  160 , or any other water distribution arrangement such as using spray nozzles, troughs, or other water distribution assemblies. 
     Indirect heat exchange section  155  is positioned in housing  169  and is usually comprised of a plurality of plate type heat exchangers  162 . A fluid to be cooled, condensed, heated, or evaporated passes within the joined plates or cassettes of plate type heat exchangers  162 . 
     Air  164  exits from direct heat exchange section  154  into plenum  163  on the way to fan  156  and flows over housing  169  of indirect heat exchange section  155  and heat transfer takes place. In the case in which direct heat exchange section  154  is used to cool the evaporative cooling tower liquid, air  164  cools housing  169  of indirect heat exchange section  155 , which in turn cools the evaporative cooling tower liquid and plate type heat exchanger  162  inside indirect heat exchange section  155 . 
     In embodiment  150 , air pump  166  is attached to heat exchanger  150  and supplies pressurized ambient air to air distribution tube  167  inside and near the bottom of housing  169  and indirect heat exchange section  155 . It is to be noted that the source of pressurized air also could be the facility that uses heat exchanger  150  such as from an available pressured air source. Check valve  168  prevents evaporative cooling tower liquid from flowing into air pump  166  when air pump  166  is turned off. During operation streams of air bubbles come out from air distribution tube  167  and travel upward with evaporative cooling tower liquid that is pumped by pump  159 . Injecting air bubbles into the evaporative cooling tower liquid that travels through the plurality of liquid passages within plurality plate type heat exchangers  162  increases the agitation and increases the velocity of the evaporative cooling tower liquid and also serves to enhance the heat transfer between the cooling tower water/air mixture compared to the evaporative cooling tower water alone. With the evaporative cooling tower liquid traveling at a higher speed, the sensible heat transfer rate between the evaporative cooling tower liquid and the surface of plurality of plate type heat exchangers  162  increases, and with the presence of air bubbles in the evaporative cooling tower liquid, latent heat transfer may now take place, increasing the overall thermal capacity of the heat exchanger  150 . 
     It should be noted that indirect heat exchange section  155  may be located under the direct heat exchange section as shown in  FIGS. 4, 5 &amp; 6  with the air being drawn generally upwards through the direct heat exchange section and is not a limitation of the invention. 
     An advantage of having indirect heat exchange section  155  and direct heat exchange section  154  located within improved heat exchanger  150  is that the piping between indirect heat exchange section  155  and water distribution assembly  153  is minimized and customer piping is eliminated. 
     Referring now to  FIG. 8  of the drawings, an eighth embodiment of the present invention is shown generally as heat exchanger  60 , which is generally in the form of a closed circuit cooling tower. Such heat exchanger generally is present in a closed circuit cooling tower with indirect heat exchange section  65  located in plenum  73  adjacent to and towards the lower half of direct heat exchange section  64 . It should be noted that indirect heat exchanger  65  can be located above, below or adjacent to direct heat exchanger  64  as shown in other Figures but is presented as adjacent to direct heat exchanger  64  for illustrative purposes. 
     Direct heat exchange section  64  is typically comprised of fill usually comprised of sheets of polyvinyl chloride. Direct heat exchange section  64  receives air through air inlet  68  on the outside of heat exchanger  60 , with air being drawn generally across and somewhat upwardly through direct heat exchange section  64  by fan  66  rotated by motor  67 . It should be noted that indirect heat exchange section  65  may be located under the direct heat exchange section as shown in  FIGS. 4, 5 &amp; 6  with the air being drawn generally upwards through the direct heat exchange section and is not a limitation of the invention. 
     Indirect heat exchange section  65  is usually comprised of a plurality of plate type heat exchangers  72  positioned in housing  83  having internal fluid inlet  61  and fluid outlet  62 . It should be understood that the operation of fluid inlet  61  and fluid outlet  62  can be reversed if it is desired. 
     An evaporative cooling tower liquid, usually water, flows downwardly from water distribution assembly  63  such that the evaporative cooling tower liquid falls downwardly onto and through direct heat exchange section  64 . While falling downwardly onto and through direct heat exchange section  64 , a small portion of cooling tower liquid is evaporated by moving air and latent heat transfer takes place from cooling tower liquid to air. It should be noted that in some applications, condensation takes places from air into cooling tower liquid. 
     The evaporative cooling tower liquid that passes downwardly onto and through direct heat exchange section  64  and collected in sump  71  is pumped by pump  69  to housing  83  then through indirect heat exchange section  65  then back to water distribution assembly  63 . Water distribution assembly  63  can be comprised of a variety of pipes with openings, orifices or nozzles  70 , or any other water distribution arrangement such as using spray nozzles, troughs, or other water distribution assemblies. 
     Indirect heat exchange section  65  is usually comprised of a plurality of plate type heat exchangers  72  but can be any type of indirect heat exchanger such as and not limited to a coil circuit tube type heat exchanger as known in the art. A fluid to be cooled, condensed, heated, or evaporated passes within the joined plates or cassettes of plate type heat exchangers  72 . 
     Air  74  exits from direct heat exchange section  64  into plenum  73 . Air  74  on the way to fan  66  flows over housing  83  of indirect heat exchange section  65  and heat transfer takes place. In the case in which direct heat exchange section  64  is used to cool evaporative cooling tower liquid, air  74  cools housing  83  of indirect heat exchange section  65  which in turn cools the evaporative cooling tower liquid and then plate type heat exchangers  72  inside indirect heat exchange section  65 . 
     Embodiment  60  has a wet and a dry mode of operation to cool indirect heat exchanger  65 . During wet operation, air valves  78  and  79  are closed and air blower fan  81  is turned off while liquid valves  76  and  80  are open. Air valves  78  and  79 , and also water valves  76  and  80  may be manually or automatically operated as known in the art and is not a limitation of the invention. During dry operation, liquid valves  76  and  80  are closed and air valves  78  and  79  are opened. Alternatively, air outlet valve  78  and water valve  76  may be omitted and air may discharge through distribution  63 . During dry operation fan motor  67  is turned off and air blower fan  81  blows cold ambient air into housing  83  of indirect heat exchange section  65 . Cold, ambient air cools down the plurality of plate type heat exchangers  72  using sensible heat transfer and the heated air exits through air exit  77  and then to outside of heat exchanger  60 . 
     An advantage of having indirect heat exchange section  65  and direct heat exchange section  64  located within the improved heat exchanger  60  is that the piping between indirect heat exchange section  65  and water distribution assembly  63  is minimized and customer piping is eliminated. 
     Referring now to  FIGS. 9 and 10 , a perspective view and a cutaway side view, respectively, of indirect heat exchange section  200  in accordance with the present invention are shown. 
     Indirect heat exchange section  200  is shown to be comprised of a plurality of plate type heat exchangers  201 , process fluid inlet  202 , process fluid outlet  203 , evaporative cooling tower fluid outlet  204  and inlet  205 , inlet and outlet plate header end caps  207  and housing  206 . It should be understood that the operation of the internal process fluid inlet  202  and process fluid outlet  203  can be reversed if it is desired. 
     Internal, closed circuit cooling tower process fluid enters the plurality of plate type heat exchangers  201  through process fluid inlet  202  and is separated from the exterior of the plurality of plate type heat exchangers  201  and from the evaporative cooling tower fluid that enters through cooling tower fluid inlet  205  of housing  206 . Housing  206  may be designed such that it can be easily removed for cleaning the exterior of plate type heat exchangers  201  and is not a limitation of this invention. 
     As shown by directional arrows  208 , internal process fluid flows through a plurality of internal parallel passageways of plate type heat exchangers  201  and exits through process fluid outlet  203 . As shown by cooling tower fluid directional arrows  209 , exterior evaporative cooling tower fluid enters housing  206  through fluid inlet  205  and flows through a plurality of external passageways within plate type heat exchangers  201  and comes out of housing  206  through fluid outlet  204 . 
     While flowing through the plurality of passageways within plate type heat exchangers  201 , sensible heat transfer takes place between the evaporative cooling tower fluid and plate type heat exchangers  201 . 
     In all the embodiments of the present invention, plate type heat exchanger  201  can be comprised of various metals such as stainless steel or other corrosion resistant steels and alloys. It is also possible that such plates can be comprised of other materials that would lead to good heat exchange between the fluid within the plate and the evaporative cooling tower liquid or air passing outwardly therefrom. Such materials could be aluminum or copper; various alloys, or plastics that provide corrosion resistance and good heat exchange and are not a limitation of the invention. 
     Referring now to  FIG. 11 , a side view of a coil circuit tube type heat exchanger of indirect heat exchange section  300  in accordance with the present invention is shown. 
     Indirect heat exchange section  300  is shown to be comprised of a plurality of coil circuit tube type heat exchangers  301 , process fluid inlet  302 , process fluid outlet  303 , evaporative cooling tower fluid outlet  304  and inlet  305 , inlet and outlet header end caps  307  and housing  306 . It should be understood that the operation of the internal process fluid inlet  302  and process fluid outlet  303  can be reversed if it is desired. 
     Internal, closed circuit cooling tower process fluid enters the plurality of coil circuit tube type heat exchange  301  through process fluid inlet  302  and is separated from the exterior of the plurality of coil circuit tube type heat exchangers  301  and from the evaporative cooling tower fluid that enters through cooling tower fluid inlet  305  of housing  306 . Housing  306  may be designed such that it can be easily removed for cleaning the exterior of coil circuit tube type heat exchangers  301  and is not a limitation of this invention. 
     As shown by directional arrows  308 , internal process fluid flows through a plurality of internal parallel passageways of coil circuit tube type heat exchangers  301  and exits through process fluid outlet  303 . As shown by evaporative cooling tower fluid directional arrows  309 , exterior evaporative cooling tower fluid enters housing  306  through fluid inlet  305  and flows through a plurality of external passageways within plate type heat exchangers  301  and comes out of housing  306  through fluid outlet  304 . 
     While flowing through the plurality of passageways within plate type heat exchangers  301 , sensible heat transfer takes place between the evaporative cooling tower fluid and coil circuit tube type heat exchangers  301 . 
     In all the embodiments of the present invention, coil circuit tube type heat exchangers  301  can be comprised of various metals such as stainless steel or other corrosion resistant steels and alloys. It is also possible that such tubes can be comprised of other materials that would lead to good heat exchange between the fluid within the plate and the evaporative cooling tower liquid or air passing outwardly therefrom. Such materials could be aluminum or copper; various alloys, or plastics that provide corrosion resistance and good heat exchange and are not a limitation of the invention.