Abstract:
A cooling system for an electronics chassis includes a plurality of centrifugal blowers arranged to motivate cooling air through the electronics chassis. The centrifugal blowers are arranged in one or more sets, each having blowers oriented with respective inlets in mutual facing relationship. The orientation, positioning, and alignment of the centrifugal blowers facilitates a compact arrangement of the plurality of blowers that achieves increased aerodynamic efficiencies to reduce noise output and energy consumption.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application claims priority to U.S. provisional Patent Application Ser. No. 61/501,535, filed on Jun. 27, 2011 and entitled “Cooling Module with Parallel Blowers”, the content of which being incorporated herein in its entirety. 
    
    
     FIELD OF THE INVENTION 
     The present invention relates to cooling systems generally, and more particularly to cooling fan arrays specifically arranged for enhanced performance in motivating cooling fluid through an electronics chassis. 
     BACKGROUND OF THE INVENTION 
     Designers of electronic equipment have become increasingly challenged to provide high-power devices in relatively small packages. These devices require compact and highly efficient cooling systems. A typical cooling system involves moving air across one or more printed circuit boards. The flow path layout, type of air moving device, and how well it is integrated into the system are all key elements in achieving the desired performance in a small package size with limited noise. 
     One such electronic device is a telecommunications router which typically includes a series of electronics communications “cards” arrayed with cooling fans in a chassis. The desire to make routers more powerful, yet compact in size, leaves little space for cooling system components necessary to address ever-increasing heat loads. Conventional system designs often employ fans that are not well matched to the system pressures, or do not move air efficiently within the space constraints, and result in unacceptable noise and relatively large power consumption. 
     Design efforts to date typically use multiple axial fans arranged in a “tray”, as illustrated in  FIG. 1 . The fans either push cooling air through a chassis or pull warm air out from the chassis. Higher fan speeds have been used to address increased flow requirements, but as system pressures increase, designers have responded by adding additional trays of axial fans arranged in series. An example of such series of axial fan trays is illustrated in  FIG. 2 . In theory, each axial fan tray handles half of the system pressure. The conventional arrangement illustrated in  FIG. 2  sets forth an orientation with both fan trays downstream from the electronics being cooled in the electronics chassis, thereby pulling cooling air through the system. In other conventional arrangements, fan trays may be disposed upstream of the electronics being cooled, or fan trays being disposed both upstream and downstream of the electronics in a push-and-pull-through system. Relatively high aerodynamic efficiencies may be achieved with this type of air mover, but unfortunately require high rotational speeds that typically result in unacceptable acoustic levels. 
     Centrifugal blowers are better suited for the higher pressures encountered in high cooling load applications. However, centrifugal blowers have not typically been considered for electronics chassis cooling, particularly in compact arrangements, due to their relatively larger physical size. As a result, centrifugal blowers have not commonly been considered for fit within cooling system packaging space. For example, a single inlet centrifugal blower sized to match the performance of two axial fans in series can require twice the volumetric space, be less efficient, and result in a less uniform flow field. 
     It is therefore an object of the present invention to provide a cooling system that simultaneously increases performance and reduces noise of conventional air movers. 
     It is a further object of the present invention to provide a cooling arrangement that is particularly well suited for cooling densely populated electronic components, such as telecommunication edge routers. 
     SUMMARY OF THE INVENTION 
     By means of the present invention, enhanced cooling to electronics chassis may be achieved with greater efficiency and reduced acoustic levels. The present cooling system provides cooling fluid, such as cooling air, in a generally uniform flow field across electronic components for cooling thereof. The electronic components may be disposed in a chassis, such as a telecommunication edge router, server, or a power supply unit. 
     In one embodiment, a cooling fan array of the present invention is arranged for motivating cooling fluid through an interior chamber of an electronics chassis generally along a flow direction. The cooling fan array includes a frame having a cooling fluid entrance and a cooling fluid exit in fluid communication with the interior chamber, with at least one of the frame entrance and exit directing air flow therethrough along a direction parallel with the flow direction. The frame further includes a plurality of modules individually removable from and replaceable in the frame without operational interruption to others of the modules. Each of the modules includes a centrifugal blower with an impeller driven by a motor and defining an axis of rotation, wherein the blower includes an inlet arranged to intake the cooling fluid along a respective intake direction transverse to the flow direction. The blowers are arranged in the frame in one or more sets, with each set including at least two blowers oriented with respective inlets in facing relationship with one another and with respective axes of rotation being axially aligned with one another, the facing inlets being axially spaced apart by a spacing dimension that is less than 75% of a diameter dimension of the impeller within the set, such that the blowers operate in parallel to motivate the cooling fluid through the cooling fluid inlet. 
     In another embodiment, an electronics chassis of the present invention includes an interior chamber through which cooling fluid is motivated generally along a flow direction to cool electronic components. The chassis further includes a frame having an entrance through which the cooling fluid is drawn from the interior chamber, and an exit. A plurality of modules may be disposed in the frame, and are individually removable from and replaceable in the frame without operational interruption to others of the modules. Each of the modules includes a centrifugal blower with an impeller driven by a motor and defining an axis of rotation. The centrifugal blower includes dual opposed inlets arranged to intake the cooling fluid along respective intake directions transverse to the flow direction. The blowers are arranged in the frame in one or more sets, with each set including at least two blowers oriented with respective inlets in facing relationship with one another and with respective axes of rotation being axially aligned with one another, the facing inlets being axially spaced apart by a spacing dimension that is less than 75% of a diameter dimension of the impeller within the set, such that the blowers operate in parallel to motivate the cooling fluid through the frame inlet. 
     In a further embodiment, an electronics chassis includes an interior chamber through which cooling fluid is motivated generally along a flow direction to cool electronic components disposed in the interior chamber. The chassis further includes a frame having an entrance through which the cooling fluid is drawn from the interior chamber, and an exit. A plurality of modules in the frame are individually removable from and replaceable in the frame without operational interruption to others of the modules. Each of the modules includes one or more sets of two centrifugal blowers having forward-curved impellers driven in opposite circumaxial directions with respect to one another about respective impeller axes of rotation. The centrifugal blowers each have an inlet and an outlet, wherein the respective centrifugal blower inlets of the set are arranged to intake the cooling fluid along respective substantially opposite intake directions that are both transverse to the flow direction. The blowers of the set are arranged in the frame to operate in parallel to motivate the cooling fluid through the frame entrance. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is an illustration of an axial fan tray arrangement of the prior art; 
         FIG. 2  is a schematic diagram of an axial-type fan tray arrangement in series of the prior art; 
         FIG. 3  is an illustration of a cooling fan array of the present invention; 
         FIG. 4   a  is a schematic illustration of an electronics chassis of the present invention incorporating the cooling fan array of  FIG. 3 ; 
         FIG. 4   b  is a schematic illustration of an electronics chassis of the present invention incorporating a cooling fan array of the present invention; 
         FIG. 5   a  is a schematic illustration of an electronics chassis of the present invention incorporating a cooling fan array of the present invention; 
         FIG. 5   b  is a schematic illustration of a cooling fan array of the present invention; 
         FIG. 5   c  is a schematic illustration of a cooling fan array of the present invention; and 
         FIG. 6  is a chart depicting performance characteristics of a cooling fan array of the present invention. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     The objects and advantages enumerated above together with other objects, features, and advances represented by the present invention will now be presented in terms of detailed embodiments described with reference to the attached drawing figures which are intended to be representative of various embodiments of the invention. Other embodiments and aspects of the invention are recognized as being within the grasp of those having ordinary skill in the art. 
     With reference now to the drawings, and first to  FIGS. 3 and 4   a , a cooling fan array  10  includes a frame  12  having a cooling fluid entrance  14  and a cooling fluid exit  16 . Frame  12  includes a plurality of modules  18   a - 18   c  that are individually removable from and replaceable in frame  12  without operational interruption to others of modules  18   a - 18   c . Such a characteristic is known in the art as being “hot swappable”, in that each of modules  18   a - 18   c  may be removed from frame  12  for repair or replacement without interrupting or substantially affecting the operation of the remaining modules  18   a - 18   c  of housing  12 . In this manner, maintenance may be performed upon a respective module  18   a - 18   c  without requiring shut down of the entire cooling fan array  10 , which would require shut down of the electronics chassis being cooled by cooling fan array  10 . In some cases, removal of one or more of modules  18   a - 18   c  from housing  12  requires increased blower speed in the remaining modules to accommodate and maintain a desired cooling fluid flow rate through the electronics chassis. Control systems for electronically controlling the blowers of hot-swappable modules for air-cooling systems are well understood in the art. 
     Each of the modules  18   a - 18   c  in frame  12  may include one or more double-width double-inlet forward curved (DWDI-FC) centrifugal blowers  20 . In the example arrangement of  FIG. 3 , frame  12  includes three modules  18   a - 18   c , each of which includes three DWDI-FC centrifugal blowers  20 . It is to be understood, however, that frame  12  of the present invention may include any number of a plurality of modules  18   a - 18   c , with each module having, for example, one or more DWDI-FC centrifugal blowers  20 . Moreover, modules  18   a - 18   c  of frame  12  may include different numbers of DWDI-FC blowers  20 . In typical embodiments, each DWDI-FC centrifugal blower  20   a - 20   c  is driven by a motor, such as a DC brushless motor that is independently controllable by a control system to adjust and maintain desired cooling air flow characteristics through frame  12  and the associate electronics chassis. 
       FIG. 4   a  illustrates frame  12  secured to an electronics chassis  30  in an embodiment wherein cooling fan array  10  is arranged to pull air flow through a series of electronics communication cards arrayed in an interior chamber  32  of electronics chassis  30  generally along a flow direction  34  to cool the electronic components disposed at interior chamber  32  of electronics chassis  30 . Cooling fluid flow (represented by arrows) is drawn through electronics chassis  30  from an inlet  36 , into cooling fluid entrance  14  of frame  12 , and finally out from cooling fan array  10  at cooling fluid exit  16 . Centrifugal blowers  20  in parallel motivate the cooling fluid flow along flow direction  34 , and motivate the cooling fluid flow “in parallel” by each blower individually acting upon cooling fluid flow through interior chamber  32  of electronics chassis  30 . In addition, blowers  20   a - 20   c  of each of modules  18   a - 18   c  motivate the cooling fluid flow “in parallel” by receiving cooling fluids to their respective inlets that is sourced directly from cooling fluid passing through interior chamber  32 , and not as exhaust from an “upstream” blower within its associated frame  12 . It is contemplated that a plurality of frames  12  may be employed in a cooling fan array  10 , wherein the respective frames  12  may operate in series to motivate cooling fluid through electronics chassis  30 . In such case, blowers  20  of a “downstream” housing  12  would in fact receive the exhaust from an “upstream” blower. However, the blowers  20  within a respective frame  12  operate in parallel to receive substantially only “fresh” air entering frame  12  through cooling fluid entrance  14 . 
     Blowers  20 , such as blowers  20   aa - 20   ac  each include dual opposed inlets  22 ,  24  arranged to intake the cooling fluid along respective intake directions  26 ,  28  which are transverse to flow direction  34 . Such an arrangement is best viewed in  FIG. 4   b , which is identical to the system illustrated in  FIG. 4   a  with the exception of the cooling fluid outlet directionality. Cooling fluid exit  16  of the embodiment illustrated in  FIG. 4   a  is transverse to flow direction  34 , while cooling fluid exit  16  of the embodiment illustrated in  FIG. 4   b  permits outflow parallel to flow direction  34 . It is contemplated that frame  12  may be provided, in some embodiments, with any suitable cooling fluid outlet arrangement and orientation, including for either or both of cooling fluid outlet directions transverse or parallel to flow direction  34 . 
     In some embodiments, each of blowers  20  include a single-scroll blower housing  42  which defines the dual-opposed inlets  22 ,  24  and a blower outlet  44 . Centrifugal blowers  20  may further include a forward-curved impeller having a diameter dimension “y”, and defining an axis of rotation  52  which extends through inlets  22 ,  24  substantially transverse to flow direction  34 . Blowers  20  each include a motor  54  for rotation of the respective impellers about their rotation axis  52 . In the illustrated embodiments, respective blowers  20  in modules  18  define sets  41  of axially adjacent blowers. For example, blowers  20   aa - 20   ac , as shown in  FIG. 4   b , represent a set  41   a  of blowers having respective impellers that axially aligned about axis of rotation  52 . In this example, blower  20   aa  is a part of module  18   a , blower  20   ab  is a part of module  18   b , and blower  20   ac  is a part of module  18   c . Thus, set  41   a  of blowers  20   aa - 20   ac  may include one or more blowers from a plurality of distinct modules  18   a - 18   c . In other embodiments, however, blower sets  41   a - 41   c  may be confined to a plurality of blowers within a single respective module  18   a - 18   c . Blower sets  41   a - 41   c  preferably include a plurality of centrifugal blowers  20  that are arranged in frame  12  with their respective impeller axes of rotation axially aligned with one another, with axially adjacent inlets of axially adjacent blowers  20  being in mutually facing relationship. In the illustrated embodiment, blowers  20   a - 20   c  of blower set  41   a  are DWDI-FC centrifugal blowers having respective impeller axes of rotation aligned along axis  52 . Axially adjacent blower inlets  24   a ,  22   b  and  24   b ,  22   c  are in facing relationship with one another drawing inlet air in opposite directions and transverse to flow direction  34 , as depicted by the air flow arrows in  FIG. 4   b . This arrangement has been discovered by the applicant to improve air flow efficiencies in motivating air flow through electronics chassis  30 . 
     In some embodiments, adjacent blower inlets  24   a ,  22   b  and  24   b ,  22   c  are not only axially aligned, but also spaced apart by a specific spacing dimension “x”. In some embodiments, such spacing dimension “x” may be less than about 0.75 (75%) of diameter dimension “y” of the impeller of blowers  20 , and more preferably between 0.5 and 0.75 (50%-75%) of diameter dimension “y” of the impeller of blowers  20 . In the event that the diameter dimension “y” of the axially adjacent pair of blowers is not equal, the spacing dimension “x” may be determined as 0.5-0.75 (50-75%) of the diameter dimension “y” of the larger impeller. Similarly, a spacing dimension “z” between a blower inlet and an axially adjacent wall, such as between blower inlet  22   a  and a side wall  9  of frame  12 , may be between about 0.2-0.5 (20-50%) of diameter dimension “y” of the respective blower impeller, and more preferably between 0.23-0.36 (23-36%) of the respective impeller diameter dimension “y”. 
     The arrangements illustrated in  FIGS. 4   a  and  4   b  have been found to provide surprisingly enhanced aerodynamic efficiency for each blower  20 , such that total power input to motivate a desired cooling fluid flow may be reduced. In addition, the surprising efficiency of the proposed arrangement reduces sound emissions, which is also a beneficial operating characteristic of the cooling fan arrays of the present invention. Such enhancements in efficiency and sound reductions may be accomplished in a housing volume that is not substantially larger than the volume assumed by conventional fan trays. Therefore, it is believed that the arrangements of the present invention substantially improve cooling fan arrays. 
     Applicants are particularly surprised to discover that the small axial spacing between adjacent blower inlets, and between a blower inlet and an axially adjacent wall, does not diminish aerodynamic performance in the operation of the centrifugal blowers.  FIG. 6  is a graphical depiction of aerodynamic performance curves at various relative dimensions for spacing “A”, wherein spacing “A” may be between a blower inlet and an axially adjacent wall, equivalent to spacing dimension “z” in  FIG. 4   b , or one-half of the spacing dimension between axially adjacent inlets, equivalent to spacing dimension “x”/2. As depicted in  FIG. 6 , the present arrangement of axially aligned centrifugal blowers with a spacing “A” of 36% of the impeller diameter exhibits aerodynamic performance that is equivalent to centrifugal blowers with “unrestricted” inlets, which are defined as having a spacing “A” that is sufficiently large to avoid disturbance to inlet air flow. In effect, therefore, the “unrestricted inlet” data in  FIG. 6  assumes an infinite spacing “A”. 
     The data graphically depicted in  FIG. 6  reveals a surprising result of the present invention, in that a centrifugal blower arrangement with a spacing “A” of 36% of an impeller diameter dimension “y” of the blower applied to motivating air through an interior chamber  32  of electronics chassis  30 , as depicted by the “system curve” of  FIG. 6 , exhibits substantially equivalent aerodynamic performance to centrifugal blowers with unrestricted inlets. Such a discovery is counter to conventional understanding of centrifugal blower aerodynamic performance, wherein restricted inlet spacing “A” consistently reduces aerodynamic performance of the blower. Applicants have surprisingly discovered that, even with centrifugal blower inlets “restricted” with a spacing “A” of 36% of the impeller diameter, can achieve aerodynamic performance equivalent to centrifugal blowers with unrestricted inlets, as measured in a cooling system application.  FIG. 6  further reveals that the present arrangement of axially aligned centrifugal blowers with a spacing “A” of 23% of the impeller diameter, as applied in motivating air through chassis  30 , is substantially equivalent to conventional centrifugal blower arrangements with a spacing “A” of 50% of the impeller diameter. 
     Applicants theorize that the discovery of unexpected aerodynamic performance at small spacing dimensions between adjacent centrifugal blowers may be at least in part the result of coinciding vortices just upstream from the respective blower inlets, wherein the coincidence of the vortices is created as a consequence of the small axial spacing dimensions. The coincident vortices may be synergistic in generating a highly efficient aerodynamic flow into the respective blower inlets. Such a finding is contrary to conventional understanding, which predicts aerodynamic performance degradation with the presence of another operating blower within the flow field of the first blower. The results depicted in  FIG. 6  clearly indicate otherwise. 
     The arrangement illustrated in  FIG. 4   b  includes a frame  12  incorporating a separation plate  62  defining an outlet plenum  64  of frame  12  which primarily separates inlets  22 ,  24  of blowers  20  from respective outlets  44 . Outlet plenum  64  is therefore fluidly connected to cooling fluid entrance  14  only through blowers  20 , such that cooling fluid is motivated through interior chamber  32  of electronics chassis  30  into cooling fluid entrance  14  and into respective inlets  22 ,  24  of blowers  20  for exhaust out through blower outlets  44 , and ultimately out through cooling fluid exit  16 . Thus, outlet plenum  64  is fluidly connected to cooling fluid exit  16 . 
     Separation plate  62  creates separation between a negative pressure side  13  from a positive pressure side  11  of frame  12 . Separation plate  62  therefore eliminates the need for separate ducts from each blower  20  in a module  18 , and reduces recirculation to negative pressure side  13  in the event of blower failure. The need for back draft dampers is therefore substantially reduced or eliminated. As illustrated in  FIG. 3 , each module  18   a - 18   c  may include a separation plate  62   a - 62   c  for separating positive and negative pressure sides  11 ,  13  of a respective module  18 . Outlet plenum  64  may further be divided by divider plates  63   a ,  63   b  to define individual module outlet plenums  64   a - 64   c . Divider plates  63   a ,  63   b  segment outlet plenum  64  as individual outlet zones from the blowers of each module  18   a - 18   c.    
     Outlets  44  of blowers  20  may be canted at an angle, such as at 45°, to promote cooling fluid exhaust more directly out through cooling fluid exit  16  along an outlet axis  58  that is substantially transverse to flow direction  34 . In other embodiments, such as that illustrated in  FIG. 4   b , blower outlets  44  may be directed axially in parallel with flow direction  34  to direct exhaust cooling fluid axially out from cooling fluid exit  16 . 
     The systems illustrated in  FIGS. 4   a  and  4   b  depict a “pull” system employing a plurality of DWDI-FC centrifugal blowers arranged to motivate the cooling fluid flow in parallel, and with parallel cooling fluid discharges. Moreover, the respective inlets  22 ,  24  of blowers  20  are arranged transverse to flow direction  34 . Such arrangement represents a substantial noise reduction in comparison to similar packaging space allocated for conventional axial fan trays. 
     A further embodiment is illustrated in  FIG. 5   a , wherein cooling fan array  110  includes a frame  112  having a cooling fluid entrance  114  and a cooling fluid exit  116 . Frame  112  includes a plurality of modules  118   a - 118   c  that are individually removable from and replaceable in frame  112  without operational interruption to others of modules  118   a - 118   c . In this embodiment, each of the modules  118  in cooling fan array  110  includes one or more sets of “forward-curved” centrifugal blowers  180 . In the example arrangement of  FIG. 5   a , each set of forward curved centrifugal blowers  180  includes two centrifugal blowers  182   a ,  182   b  placed back to back, such that inlet  184   a  of blower  182   a  is oppositely disposed from inlet  184   b  of blower  182   b . Due to such opposite orientations, the respective impellers of blowers  182   a ,  182   b  may be configured to rotate in opposite circumaxial directions with respect to one another about an axis of rotation  152 . The opposite circumaxial rotational directions have been found to generate desired cooling fluid flow characteristics through frame  112  and interior chamber  132 . Blower sets  180  may include two or more blowers  182   a ,  182   b  which may be arranged to coordinate with other blowers of the module  118  and/or array  110  to motivate cooling fluid flow through interior chamber  132  of electronics chassis  130 . Blower sets  180  may operate to motivate the cooling fluid flow along flow direction  134 , and to motivate the cooling fluid flow “in parallel”. 
     In the illustrated embodiment, each module  118   a - 118   c  includes two sets  180  of forward-curved centrifugal blowers  182   a ,  182   b . Frame  112  of the present invention, however, may include any number of a plurality of modules  118   a - 118   c , with each module having one or more sets  180  of blowers  182 . In some embodiments, respective sets  180  of blowers  182   a ,  182   b  among a plurality of modules  118  may be arranged so that their respective axes of rotation through inlets  184   a ,  184   b  are all substantially mutually aligned along a respective axis  152 ,  154 . In typical embodiments, each blower  182  may be driven by a motor, such as a DC brushless motor that is independently controllable by a control system to adjust and maintain desired cooling fluid flow characteristics through frame  112  and the associated electronics chassis  132 . 
     Blowers  182  each include a respective inlet  184  that is arranged to intake the cooling fluid along a respective intake direction  126 ,  128  which is transverse to flow direction  134 . In the embodiment illustrated in  FIG. 5   a , cooling fluid exit  116  permits outlet flow from blowers  182  along an outlet direction  135  that is substantially transverse to flow direction  134 . It is contemplated, however, that frame  112  may be provided with any suitable cooling fluid exit arrangement and orientation, including for either or both of cooling fluid outlet directions transverse or parallel to flow direction  134 . 
     It is contemplated that the blower sets  180  may be configured to provide desired cooling fluid flow in a manner similar to blowers  20  described hereinabove. Blower sets  180 , however, utilize, for example, single-inlet forward-curved centrifugal blowers placed in back to back relationship to together motivate cooling fluid flow through electronics chassis  130 . In some embodiments, respective blowers  182   a ,  182   b  may be in abutting relationship with one another, or may be spaced apart by a desired spacing dimension. Moreover, mutually facing inlets of axially adjacent blowers may preferably have a spacing dimension “x 1 ” of less than about 0.75 (75%) of a diameter dimension “y 1 ” of the impellers of respective blowers  182   a ,  182   b , and more preferably between 0.5-0.75 (50-75%) of diameter dimension “y 1 ”. The respective inlets  184   a ,  184   b  of blowers  182   a    182   b  lead to impellers which may preferably be axially aligned along a respective axis of rotation. 
     Another embodiment is illustrated in  FIG. 5   b  wherein cooling fan array  210  includes a frame  212  having a cooling fluid entrance  214  and a cooling fluid exit  216 . Frame  212  includes a plurality of modules  218   a - 218   c  that are individually removable from and replaceable in frame  212  without operational interruption to others of modules  218   a - 218   c . In this embodiment, each of the modules  218  in cooling fan array  210  includes one or more sets of centrifugal blowers  280 , which may include forward-curved impellers. In the illustrated embodiment, each set of centrifugal blowers  280  includes two centrifugal blowers  282   a ,  282   b  placed in facing relationship to one another, such that inlet  284   a  of blower  282   a  is in generally facing relationship with inlet  284   b  of blower  282   b . The respective impellers of blowers  282   a ,  282   b  may be configured to rotate in opposite circumaxial directions with respect to one another about an axis of rotation  252 . Blower sets  280  may be arranged to coordinate with other blowers of the respective module  218  and/or array  210  to motivate cooling fluid flow through the associated electronics chassis  230 . Blower sets  280  may operate to motivate the cooling fluid flow along flow direction  234 , and to motivate the cooling fluid flow “in parallel”. 
     In the illustrated embodiment, each module  218  includes one set  280  of centrifugal blowers  282   a ,  282   b . Frame  212  of the present invention, however, may include any number of a plurality of modules  218 , with each module  218  having one or more sets  280  of blowers  282 . In typical embodiments, each blower  282  may be driven by a motor, such as a DC brushless motor that is independently controllable by a control system to adjust and maintain desired cooling fluid flow characteristics through frame  212  and the associated electronics chassis  232 . 
     Blowers  282  each include a respective inlet  284  that is arranged to intake the cooling fluid along a respective intake direction  226 ,  228  that is transverse to flow direction  234 . In the embodiment illustrated in  FIG. 5   b , cooling fluid exit  216  permits outlet flow from blowers  282  along an outlet direction  235  that is in alignment/parallel to flow direction  234 . It is contemplated, however, that frame  212  may be provided with any suitable cooling fluid outlet arrangement and orientation, including for either or both of cooling fluid outlet directions transverse or parallel to flow direction  234 . 
     It is contemplated that the blower sets  280  may be configured to provide desired cooling fluid flow in a manner similar to blowers  20 ,  182  described above. Blower sets  280 , however, utilize, for example, single-inlet forward-curved centrifugal blowers placed in substantially face to face relationship to together motivate cooling fluid flow through electronics chassis  230 . Respective blowers  282   a ,  282   b  may be spaced apart by a desired spacing dimension “x 2 ” that is less than about 0.75 (75%) of the diameter dimension “y 2 ” of the impellers of blowers  282   a ,  282   b , and more preferably between 0.5-0.75 (50-75%) of diameter dimension “y 2 ”. The respective inlets  284   a ,  284   b  of blowers  282   a ,  282   b  lead to impellers which are preferably axially aligned along a respective axis of rotation  252 ,  254 . 
     A still further embodiment is illustrated in  FIG. 5   c  wherein cooling fan array  310  includes a frame  312  having a cooling fluid entrance  314  and a cooling fluid exit  316 . Frame  312  includes a plurality of modules  318   a - 318   c  that are individually removable from and replaceable in frame  312  without operational interruption to others of modules  318   a - 318   c . In this embodiment, each of the modules  318  in cooling fan array  310  includes one or more sets of centrifugal blowers  380 . In the example arrangement of  FIG. 5   c , each set of centrifugal blowers  380  includes two centrifugal blowers  382   a ,  382   b  placed front to front in generally facing relationship with one another, such that inlet  384   a  of blower  382   a  is in facing relationship with inlet  384   b  of blower  382   b . The respective impellers of blowers  382   a ,  382   b  may be configured to rotate in opposite circumaxial directions with respect to one another about an axis of rotation  352 . Blower sets  380  may include two or more blowers  382   a ,  382   b  which may be arranged to coordinate with other blowers of the module  318  and/or array  310  to motivate cooling fluid flow through the interior chamber of electronics chassis  330 . Blower sets  380  may operate to motivate the cooling fluid flow along flow direction  334 , and to motivate the cooling fluid flow “in parallel.” 
     In the illustrated embodiment, each module  318  includes one set  380  of forward-curved centrifugal blowers  382   a ,  382   b . Frame  312  of the present invention, however, may include any number of a plurality of modules  318 , with each module having one or more sets  380  of blowers  382 . In some embodiments, respective sets  380  of blowers  382   a ,  382   b  among a plurality of modules  318  may be arranged so that their respective inlets  384   a ,  384   b  are all substantially mutually aligned along a respective axis of rotation  352 . In typical embodiments, each blower  382  may be driven by a motor, such as a DC brushless motor that is independently controllable by a control system to adjust and maintain desired cooling flow characteristics through frame  312  and the associated electronics chassis  332 . 
     Blowers  382  each include a respective inlet  384  that is arranged to intake the cooling fluid along a respective intake direction  326 ,  328  which is transverse to flow direction  334 . In the embodiment illustrated in  FIG. 5   c , cooling fluid outlet  316  permits outlet flow from blowers  382  along an outlet direction  335  that is substantially transverse to flow direction  334 . 
     It is contemplated that the blower sets  380  may be configured to provide desired cooling fluid flow in a manner similar to blowers  20 ,  182 ,  282  described hereinabove. Blower sets  380 , however, utilize, for example, single inlet forward curved centrifugal blowers placed in substantially face to face relationship to together motivate cooling fluid flow through electronics chassis  330 . In some embodiments, respective blowers  382   a ,  382   b  may preferably be spaced apart by a desired spacing dimension “x 3 ” that is less than about 0.75 (75%) of a diameter dimension “y 3 ” of the impellers of blowers  282   a ,  282   b , and more preferably between 0.5-0.75 (50-75%) of diameter dimension “y 3 ”. The respective inlets  384   a ,  384   b  of blowers  382   a ,  382   b  lead to impellers which are preferably axially aligned along a respective axis of rotation  352 . 
     Table 1 represents actual performance measured on an example embodiment cooling fan array in accordance with the present invention, compared to axial fans in series, as described in “prior art”  FIGS. 1 and 2 . 
     
       
         
               
               
               
               
             
               
               
               
               
             
           
               
                   
                 TABLE 1 
               
               
                   
                   
               
               
                   
                   
                   
                 Delta from 
               
               
                   
                 Example 
                 Axial Fans in series 
                 Example 
               
               
                   
                 Embodiment 
                 (FIG. 1&amp;2) 
                 Embodiment 
               
               
                   
                   
               
             
             
               
                   
               
             
          
           
               
                 Air Flow 
                 295 cfm 
                 295 cfm 
                 — 
               
               
                 Static Pressure 
                 2.9 in. of H 2 O 
                 2.9 in. of H 2 O 
                 — 
               
               
                 Tip Speed 
                 5700 ft/min 
                 13,000 ft/min 
                 +128% 
               
               
                 Sound Power 
                 Est. 75 dBA 
                 Est. 90 dBA 
                 +15 dBA 
               
               
                 Physical Volume 
                 27 × 10 5  mm 3   
                 21 × 10 5  mm 3   
                  −22% 
               
               
                   
               
             
          
         
       
     
     Table 2 represents actual performance of an example embodiment cooling fan array in accordance with the present invention, compared to conventional single width, single inlet centrifugal blowers. 
     
       
         
               
               
               
               
             
               
               
               
               
             
           
               
                   
                 TABLE 2 
               
               
                   
                   
               
               
                   
                   
                 Single width, single 
                 Delta from 
               
               
                   
                 Example 
                 inlet 
                 Example 
               
               
                   
                 Embodiment 
                 FC Centrifugal 
                 Embodiment 
               
               
                   
                   
               
             
             
               
                   
               
             
          
           
               
                 Air Flow 
                 295 cfm 
                 295 cfm 
                 — 
               
               
                 Static Pressure 
                 2.9 in. of H 2 O 
                 2.9 in. of H 2 O 
                 — 
               
               
                 Tip Speed 
                 5700 ft/min 
                 5,000 ft/min 
                  −12% 
               
               
                 Sound Power 
                 Est. 75 dBA 
                 Est. 73 dBA 
                 −2 dBA 
               
               
                 Physical Volume 
                 27 × 10 5  mm 3   
                 42 × 10 5  mm 3   
                 +155% 
               
               
                   
               
             
          
         
       
     
     It is clear from the above data that the arrangements of the present invention are capable of producing similar air performance to conventional arrangements, while substantially reducing tip speed, which is a major indicator of acoustic levels. The present arrangements also have substantially reduced volume in comparison to conventional centrifugal blower arrangements, due primarily to the discovery of desired aerodynamic performance with significantly reduced spacing dimensions “x” between respective facing inlets of axially adjacent centrifugal blowers. The surprising aerodynamic performance permits the construction of a highly compact array of centrifugal blowers to achieve either greater performance than conventional arrangements of similar size, or reduced noise output in comparison of conventional blower arrangements of similar size. 
     The cooling fan arrays of the present invention, therefore, provide substantially enhanced efficiency and reduced acoustic signatures, without requiring substantially increased volume to the housing. 
     The invention has been described herein in considerable detail in order to comply with the patent statutes, and to provide those skilled in the art with the information needed to apply the novel principles and to construct and use embodiments of the invention as required. However, it is to be understood that the invention can be carried out by specifically different methods/devices and that various modifications can be accomplished without departing from the scope of the invention itself.