Abstract:
A front-to-back cooling system allows cooling of an apparatus containing two orthogonal sets of modules. Each set of modules is independently cooled. A vertical set of modules is cooled with vertical air flow across the modules that enters from a front of the apparatus and exhausts from a back of the apparatus. A horizontal set of modules is cooled with horizontal front-to-back air flow. When the horizontal set of modules is at the front of the apparatus, a plenum extending exterior to the vertical set of modules allows exhausting horizontally flowing air to the rear of the apparatus. When the horizontal set of modules is at the rear of the apparatus, a plenum extending exterior to the vertical set of modules allows moving air from the front of the apparatus to a chamber holding the horizontal modules.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is a divisional of U.S. Ser. No. 12/167,604, filed on Jul. 3, 2008, entitled “FRONT-TO-BACK COOLING SYSTEM FOR MODULAR SYSTEMS WITH ORTHOGONAL MIDPLANE CONFIGURATION”, by Gunes Aybay, et al., currently pending. 
    
    
     STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT 
     Not applicable. 
     REFERENCE TO A COMPACT DISK APPENDIX 
     Not applicable. 
     TECHNICAL FIELD 
     The present invention relates to the field of cooling systems, and in particular to cooling of a modular system with orthogonal modules. 
     BACKGROUND ART 
     Systems that require very high bandwidth any-to-any connectivity among a set of modules typically use an orthogonal mid-plane configuration. In this configuration, a set of cards are plugged into the front side of the mid-plane in vertical configuration and another set of cards are plugged into the rear side of the mid-plane in horizontal configuration. This layout enables each front card to be directly connected to each rear card, and makes it possible to eliminate the use of PCB signal traces on the mid-plane to carry high speed signals. 
     However, the orthogonal configuration also creates a cooling challenge, especially in applications where front-to-back cooling is required. Vertical cards can be cooled using conventional cooling mechanisms with front air intake and rear air exhaust, but cooling the horizontal cards while maintaining overall front-to-back air flow is challenging. 
     If front-to-back cooling is not required, the horizontal card cage can be cooled using side-to-side air flow. However, many rack mount environments require front-to-back air cooling. One solution has been to divert air taken from a front intake to the back and run it up in a column next to the horizontal cards. Such a mechanism typically uses a set of fans or blowers to create the air pressure across the horizontal cards. However, the amount of air flow that is provided in such a system is typically limited due the number of turns in the air path. Also, the placement of one or two fan blades along the sides of the horizontal cards can severely limit the PCB area and panel surface that is available. 
     SUMMARY OF INVENTION 
     In one embodiment, a method of cooling an apparatus comprises: forming a plenum on a side of a first chamber of the apparatus, open to a front of the apparatus, partitioning the apparatus with an air-permeable barrier, forming a second chamber separated from the plenum and the first chamber by the air-permeable barrier, pulling air from the front of the apparatus via the plenum through the air-permeable barrier into the second chamber, and exhausting air from the second chamber to a rear of the apparatus. 
     In another embodiment, a method of cooling an apparatus comprises: cooling a first plurality of modules oriented in a first direction, comprising: pushing air from an edge of each of the first plurality of modules in the first direction, and pulling air from an opposite edge of each of the first plurality of modules in the first direction, and cooling a second plurality of modules oriented in a second direction, orthogonal to the first direction, comprising: moving air in the second direction across the second plurality of modules and through a plenum extending exterior to a first chamber containing the first plurality of modules, and exhausting air from the apparatus. 
     In yet another embodiment, a method of cooling an apparatus comprises: forming a plenum on a side of a first chamber containing a first plurality of modules, moving air from a front of the apparatus through the plenum into a second chamber containing a second plurality of modules, the second plurality of modules mounted orthogonal to the first plurality of modules, and exhausting air to a rear of the apparatus from the second chamber. 
     In yet another embodiment, a cooling system for an apparatus comprises: a first chamber, a plenum formed exterior to the first chamber and fluidly isolated from the first chamber, a second chamber in fluid communication with the plenum, a cooling system for the first chamber, comprising: a first fan, configured to push air across the first chamber, and a second fan, configured to pull air from the first chamber, and a cooling system for the second chamber, comprising: a third fan, configured to move air through the plenum into the second chamber. 
     In yet another embodiment, a method of cooling an apparatus comprises: forming a first plenum on a side of a first chamber containing a first plurality of modules, moving air from a front of the apparatus across a second plurality of modules, the second plurality of modules mounted orthogonal to the first plurality of modules in a second chamber, and exhausting air from the second plurality of modules through the first plenum to a rear of the apparatus. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
       The accompanying drawings, which are incorporated in and constitute a part of this specification, illustrate an implementation of apparatus and methods consistent with the present invention and, together with the detailed description, serve to explain advantages and principles consistent with the invention. In the drawings, 
         FIG. 1  is a top perspective view illustrating an apparatus with orthogonal modules according to one embodiment; 
         FIG. 2  is a rear perspective view of the apparatus of  FIG. 1 ; 
         FIG. 3  is a front perspective view of the apparatus of  FIG. 1 ; 
         FIG. 4  is a side cutaway perspective view of the apparatus of  FIG. 1 ; 
         FIG. 5  is a perspective view illustrating another embodiment of an apparatus with orthogonal modules; 
         FIGS. 6-7  are additional perspective vies of the apparatus of  FIG. 5 ; 
         FIG. 8  is a front perspective view illustrating yet another embodiment of an apparatus with orthogonal modules; 
         FIG. 9  is a rear perspective view of the apparatus of  FIG. 8 ; 
         FIG. 10  is a top perspective view of the apparatus of  FIG. 8 ; and 
         FIG. 11  is a side cutaway perspective of the apparatus of  FIG. 8 . 
     
    
    
     DESCRIPTION OF EMBODIMENTS 
       FIG. 1  is a top perspective view illustrating an apparatus  100  with orthogonal modules according to one embodiment. The apparatus  100  can be, for example, an enterprise class router, and the modules are typically circuit boards. But the disclosed technique can be used in any apparatus with orthogonal modules. In this embodiment, the apparatus  100  contains a plurality of modules  110  oriented vertically in a front section of the apparatus  100  and a plurality of modules  130  oriented in a horizontal direction in a rear section of the apparatus  100 . Modules  110  and  130  are cross-connected through a mid-plane  120 . In this embodiment, the vertical modules  110  are enclosed by an enclosure  170  on either side forming a plenum  150  on either side of the vertical modules  110  extending from the front of the apparatus  100  past the mid-plane  120 . An air-permeable barrier  160  is placed between each of the modules  130 , forming a rear chamber of the apparatus  100 . In some embodiments, barrier  160  is a perforated rippled material where the perforation pattern can be figured to create a pressure difference between the front section on one side of the barrier  160  and the rear section on the other side of the barrier  160 . This pressure difference can achieve a more uniform air flow across more of the surface area of modules  130 . As shown in  FIG. 1 , fans or blowers  140  are placed at a rear portion of the modules  130 . The fans or blowers  140  pull air from the front of the apparatus  100  through the plenum  150  and through the barrier  160  across the modules  130  providing cooling to the modules  130 . Heated air is then exhausted through openings on the rear of the apparatus  100  as described below. As shown in  FIG. 1 , in some embodiments, two blowers  140  are positioned centrally at the rear of each module  130 . In other embodiments, a single fan or blower  140  could be used. Alternately, the fan or fans  140  could be positioned in other locations on the modules  130  as desirable for uniform air flow across the surface of the modules  130  or to provide higher air flow across portions of the surface area of the modules  130  that generate proportionally more heat than other portions of the modules  130 . 
     Turning to  FIG. 2 , a front view of the apparatus  100  shows the plenums  150  on either side of the enclosure  170  surrounding the vertically oriented modules  110 . Additionally,  FIG. 2  shows an independent cooling system for the modules  110 . A plenum  240  is formed beneath the vertically oriented modules  110  and a lower fan tray  220  contains a plurality of fans that push air vertically across the surfaces of the modules  110  to provide cooling to the modules  110 . An upper fan tray  230  contains a plurality of fans that pull heated air from the modules  110  and exhaust the heated air toward the rear of the apparatus  100  as described below. A plurality of power supplies  210  are shown in  FIG. 2  at the bottom of the apparatus  100 . In some embodiments, each of these power supply units provides its own front-to-back air cooling path from front openings or inlets in the power supply units  210 . 
     Turning to  FIG. 3 , a rear view in perspective of the apparatus  100  illustrates the outlets where heated air is exhausted to the rear of the apparatus  100 . A collection of power supply exhaust outlets  310  correspond to the power supply inlets  210  of  FIG. 2 . A pair of exhaust outlets  330  is also shown for each of the modules  130 , corresponding to the two fans or blowers  140  illustrated in  FIG. 1 . Finally, outlets  320  provide exhaust outlets for heated air that have cooled the vertical modules  110  and is exhausted from the upper fan tray  230 . 
       FIG. 4  illustrates the air flow path across the vertical modules  110 . As shown in  FIG. 4 , an upper plenum  410  is formed above the upper fan tray  230  and the horizontally oriented modules  130  to provide an air path to the exhaust outlets  320  illustrated in  FIG. 3 . 
     In another embodiment, instead of pulling air from the front of the apparatus  100  across the horizontal modules  130 , as illustrated in  FIG. 1 , apparatus  500  pushes air across horizontal modules. One or more blowers or fans  510  are positioned toward the front of the apparatus  500  in a plenum  520 . The fans  510  push air through the plenum  520  formed along the side of vertical modules, not shown in  FIG. 5  for clarity of the drawing. Putting the fans  510  in the plenum  520  can allow for better filtering and cleaner air throughout the air path across the rear horizontally mounted modules than the negative pressure system illustrated in  FIGS. 1-4 . In some embodiments, filters can be placed at the inlets of the plenum  520  in front of the fans  510 , but are not shown in  FIG. 5  for clarity of the drawing. A barrier  530  is placed at the outlets of the fans  510 . As best shown in  FIG. 7 , openings  710  are formed in the barrier  530  to better control air flow through the plenum  520 . Air pushed through the plenum  520  is then pushed across the surfaces of the horizontal outlets  540  and exhausted through the rear of the apparatus  500 . As shown in  FIGS. 5 and 6 , the apparatus  500  has a cooling system for the vertically oriented modules that is same as illustrated  FIGS. 1-4 . The only difference between the embodiments of  FIGS. 1-4  and  FIGS. 5-7  is that instead of pulling the air through the plenum and across the cards as in  FIGS. 1-4 , the apparatus  500  pushes the air from the front through the plenum  520  and across the horizontal outlets  540 . The numbered configuration and placement of fans shown in  FIGS. 5-7  are exemplary and illustrative only and other numbers configuration and placement of fans can be used. 
     In apparatus  100 , as illustrated in  FIGS. 1-4  (and similarly in apparatus  500 , illustrated in  FIGS. 5-7 ), the vertically oriented modules  110  are in a front section of the apparatus  100  and horizontally mounted modules  130  are positioned in a rear section of the apparatus  100 . In other embodiments, vertically oriented modules can be placed in the rear, and horizontally oriented modules can be placed in the front of the apparatus.  FIGS. 8-11  illustrate such an apparatus according to one embodiment. 
     Turning now to  FIG. 8 , a front perspective view illustrates an apparatus  800  that contains front mounted horizontal modules  810 . As with apparatus  100 , power supplies  830  are cooled from air flow from the front. Inlets  820  provide air to cool the rear mounted vertical modules of the apparatus  800 . Openings  840  in each of the horizontal modules  810  provide an air path for cooling the horizontally mounted modules  810 . 
       FIG. 9  is a rear perspective view of the apparatus  800  of  FIG. 8 . Vertically mounted modules  930  are cooled by an upper fan tray  920  pulling air from inlets  820  of  FIG. 8 , then pushing that air downward across the surfaces of the vertically mounted modules  930 . A lower fan tray  910  contains exhaust fans that pull the heated air from the vertically oriented modules  930 , exhausting the heated air through plenums  960  formed below the lower fan tray to the rear of apparatus  800 . An end closure  940  holding the vertically oriented modules  930  forms a plenum  950  on either side of the vertically oriented modules  930  to exhaust heated air from the horizontally oriented modules  810 . 
     Turning to  FIG. 10 , a top view shows the cooling path for the horizontal modules  810 . Cool air is pulled in through the openings  840  shown in  FIG. 8 , and pulled across the surface of the modules  810  to a radial blower  1020  mounted on either side of each of the modules  810 . The radial blowers  1020  then exhaust the heated air through the plenums  950  to the rear of the apparatus  800 . As in the apparatus  100  of  FIG. 1 , a mid-plane  1010  connects the horizontally mounted modules  810  and the vertically mounted modules  930 . Although described above as radial blowers, any desirable fan or blower can be used. The placement, configuration and number of blowers are exemplary and illustrative only, and other numbers configurations and placements can be used. 
       FIG. 11 , a side view in perspective, shows the cooling path for the vertical rear modules  930  described above and the cooling path  1110  for power supplies at the bottom of the apparatus  800 . A plenum  1130  provides air passage from the front of the apparatus  800  through inlets  820  to the upper fan tray  920  which then pushes air vertically downward across the surfaces of the modules  930 , where the lower fan tray  910  exhausts the air through plenum  960  to the rear of the apparatus  800 . A wall  1120  provides a portion of an enclosure above the horizontally mounted modules  810  to form the plenum  1130 . 
     While certain exemplary embodiments have been described in details and shown in the accompanying drawings, it is to be understood that such embodiments are merely illustrative of and not devised without departing from the basic scope thereof, which is determined by the claims that follow. By way of example and not limitation, the specific electrical components utilized may be replaced by known equivalents or other arrangements of components which function similarly and provide substantially the same result.