Abstract:
A reconfigurable apparatus for thermal management of an electronics module is described. The apparatus includes a pair of fans generating airflow along respective fan axes. The apparatus also includes a beat sink having one portion disposed in the airflow of the fans and another portion adapted for thermal coupling with the electronics module. The airflows from the fans are in the same direction when the apparatus is arranged in a front-to-back airflow configuration and the airflows are in opposite directions when the apparatus is arranged in a front-to-front airflow configuration. A removable flow director is included in the apparatus when the apparatus is in the front-to-front airflow configuration to direct the airflow from the first fan towards the second fan.

Description:
FIELD OF THE INVENTION 
     The invention relates generally to thermal management of electronics enclosures. More particularly, the invention relates to a reconfigurable apparatus for thermal management of horizontal enclosures. 
     BACKGROUND 
     Electronic equipment can generate significant heat during operation. The performance of the equipment is typically affected by temperature. Performance may become unreliable if the electronics are subject to high temperatures or large temperature variations. The thermal management of electronic enclosures is becoming increasingly challenging as the power density of the electronics increases. For example, a common form factor for communications equipment enclosures is the horizontal box or “pizza box”. Such enclosures are particularly challenging because the only accessible surfaces for air cooling are the front and rear panels. For some applications, only the front panel is useful for air cooling due to the mounting of the enclosure relative to other enclosures or adjacent walls. Moreover, the enclosure size must be maintained to preserve the number of enclosures that can be deployed in a fixed space. The thermal management of these enclosures has to be effective, affordable and reliable. 
     Generally, cooling is achieved by providing airflow across the electronics to remove excess heat. The airflow can introduce dust and other contaminants into the electronics environment, potentially leading to failure of the electronic components. Air filters are sometimes used to limit the dust and particulates, however, the power, size and cost of the fans are generally increased to maintain the cooling efficiency. Moreover, air filters require periodic cleaning or replacement. 
     Accordingly, there exists a need for a thermal management apparatus that meets the requirements described above. The present invention satisfies these needs and provides additional advantages. 
     SUMMARY OF THE INVENTION 
     In one aspect, the invention features an apparatus for thermal management of an electronics module. The apparatus includes a first fan to generate an inlet airflow and an exhaust airflow along a first fan axis, and a second fan to generate an inlet airflow and an exhaust airflow along a second fan axis. A flow director is disposed on the first fan axis to redirect the exhaust airflow of the first fan to the second fan along the second fan axis. The apparatus also includes a heat sink having a first portion disposed in one or both of the exhaust airflow of the first fan and the inlet airflow of the second fan. The heat sink also has a second portion that can be thermally coupled with the electronics module. The apparatus also includes an enclosure surrounding the heat sink and the electronics module. The heat sink and the enclosure define a first volume and a second volume. The first volume includes the exhaust airflow of the first fan and the inlet airflow of the second fan. The second volume includes the electronics module and is isolated from the airflows generated by the first and second fans. 
     In one embodiment the apparatus also includes a first louver disposed in the inlet airflow of the first fan and a second louver disposed in the exhaust airflow of the second fan. The first louver is configured at a first angle with respect to the first and second fan axes and the second louver is configured at a second angle with respect to the first and second fan axes that is opposite the first angle. The inlet airflow of the first fan and the exhaust airflow of the second fan are thereby spatially separate. 
     In another aspect, the invention features a reconfigurable apparatus for thermal management of an electronics module. The reconfigurable apparatus includes a first fan and a second fan generating an airflow along a first fan axis and a second axis, respectively. The second fan axis is substantially parallel to the first fan axis. The airflow from the second fan is in the same direction as the airflow from the first fan when the reconfigurable apparatus is in a first configuration. The airflow from the second fan is in an opposite direction to the airflow from the first fan when the reconfigurable apparatus is in a second configuration. The reconfigurable apparatus also includes a removable flow deflector disposed on the first fan axis when the reconfigurable apparatus is in the second configuration. The removable flow director directs the airflow of the first fan to the second fan along the second fan axis. The reconfigurable apparatus also includes a heat sink having a first portion disposed in one or both of the airflow of the first fan and the airflow of the second fan. The heat sink has a second portion that can be thermally coupled to the electronics module. 
     In one embodiment the reconfigurable apparatus also includes an enclosure surrounding the heat sink and the electronics module. The heat sink and the enclosure define a first volume and a second volume. The first volume includes the airflows generated by the first and second fans and the second volume includes the electronics module. In another embodiment the heat sink includes a thermal spreader plate that separates the first volume and the second volume. In yet another embodiment the reconfigurable apparatus includes a first louver and a second louver. The first louver is disposed on the first fan axis and is configured at a first angle with respect to the first and second fan axes. The second louver is disposed on the second fan axis and is configured at a second angle with respect to the first and second fan axes that is opposite the first angle so that an airflow exhausted through the second louver does not interfere with the airflow received at the first louver. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The above and further advantages of this invention may be better understood by referring to the following description in conjunction with the accompanying drawings, in which like numerals indicate like structural elements and features in various figures. The drawings are not necessarily to scale, emphasis instead being placed upon illustrating the principles of the invention. 
     FIG. 1A is a front view of a rack of electronics enclosures. 
     FIG. 1B is a side view of the rack of electronics enclosures of FIG.  1 A. 
     FIG. 2A is an illustration of an electronics enclosure having an embodiment of a thermal management apparatus to provide a front-to-rear airflow in accordance with the present invention. 
     FIG. 2B is an illustration of the electronics enclosure of FIG. 2A configured to provide a front-to-front airflow. 
     FIG. 3 is an exploded view of the electronics enclosure of FIG.  2 B. 
     FIG. 4 is an illustration of a louver module for a thermal management apparatus in accordance with the present invention. 
     FIG. 5 is an illustration of an enclosure having an embodiment of a thermal management apparatus in accordance with the present invention. 
    
    
     DETAILED DESCRIPTION 
     In brief overview, the invention is directed to a reliable and cost-effective apparatus for thermal management of an electronics enclosure. The apparatus does not require air filters and thus eliminates the need for filter maintenance. The apparatus allows for front-to-rear and front-to-front airflow configurations in a single electronics enclosure. In addition, enclosure size is not substantially affected by the thermal management apparatus. The apparatus can be used with any electronics enclosures, including enclosures having any combination of electronic, optical and mechanical devices that are a source of heat. 
     FIGS. 1A and 1B illustrate front and side views, respectively, of a portion of a rack  10  containing multiple electronics enclosures  14 . The enclosures  14  are closely spaced vertically (e.g., tenths of an inch separation) and have a horizontal box or “pizza box” form. Many enclosures  14  are typically mounted in the rack  10 . For example, each enclosure  14  may be less than 17 inches wide, 10 inches deep and 1.7 inches high and as many as 44 enclosures  14  can be provided in a seven foot high rack  10 . The enclosures  14  are cooled by generating an inlet airflow (solid arrows) into each enclosure from one side of the enclosure  14  and exhausting heated air (dashed arrows pointing to the right) out the opposite side of the enclosure  14 . In the illustration, a wall  18  located close to the rack  10  near the rear of the enclosures  14  obstructs the heated exhaust airflow. In another arrangement, racks are placed back-to-back resulting in heated exhaust airflows that are incident on other enclosures  14 . In either arrangement, the front-to-rear airflow is restricted and the enclosures  14  cannot be maintained at an acceptable temperature. Cooling is achieved instead by providing the inlet airflow (solid arrows) through the front of the enclosure  14  and exhausting the heated airflow (dashed arrows pointing to the left) back through the front of the enclosure  14 . Advantageously, the thermal management apparatus of the present invention does not result in a significant change in size for the enclosures  14 . Consequently, the number of enclosures  14  within the rack  10  (i.e., the density of enclosures  14 ) is unaffected by the thermal management apparatus. 
     FIG. 2A illustrates an electronics enclosure  14 ′ having a general pizza box form factor with a two part front face, or front panel,  22 ′ and  22 ″. The enclosure  14 ′ is configured for a front-to-rear airflow. A fan module  26  has two fans  28  and  30  attached to the enclosure  14 ′ at one or more openings in the front panel  22 ′. Each fan  28 ,  30  operates in parallel to generate an inlet airflow (depicted as solid arrows  34 ) along fan axes  36  and  38 , respectively. The inlet airflow  34  passes through the fins of a heat sink (not shown) inside the enclosure  14 ′. The heat sink is thermally coupled to the internal electronic components and modules to provide cooling as described below. The heated airflow (depicted as solid arrows  42 ) is exhausted through the back panel (not shown) of the enclosure  14 ′. 
     FIG. 2B illustrates the electronics enclosure  14 ′ of FIG. 2A configured for a front-to-front airflow. In this configuration the two fans  28 ,  30  are arranged in a serial fashion. Inlet fan  28  generates an inlet airflow  34  from front to rear along fan axis  36 . The inlet airflow  34  passes between some of the fins of the heat sink. The outlet fan  30  rotates in the opposite direction to the inlet fan to blow air out of the enclosure  14 ′. Thus the airflow  34 ,  42  turns within the enclosure  14 ′, passes between additional fins of the heat sink and exits through the front panel  22 ′. Thus the fans  28 ,  30  in this configuration operate in a push-pull fashion. A flow director (not shown) located inside the enclosure  14 ′ assists in redirecting the front-to-rear airflow along fan axis  36  to a rear-to-front airflow along fan axis  38 . The cooling capacity of the front-to-front configuration is less than that for the front-to-rear configuration of FIG. 2A because the total airflow is less. Thus the maximum acceptable heat generation of the enclosed electronics is less for the front-to-front configuration. 
     The redundant fan arrangement provides for a highly reliable thermal management apparatus. If one of the fans  28 ,  30  in the front-to-rear configuration of FIG. 2A fails to operate, the other fan  28 ,  30  continues to generate an inlet airflow  34  sufficient to maintain adequate cooling and continued operation of the enclosed electronics. If the inlet fan  28  in the front-to-front configuration of FIG. 2B fails to operate, the outlet fan  30  continues to pull sufficient air across the heat sink to maintain adequate cooling and continued operation of the enclosed electronics system. Similarly, if the outlet fan  30  fails to operate, the inlet fan  28  continues to push enough air across the heat sink for adequate thermal control and electronics operation. 
     FIG. 3 shows an exploded view of the electronics enclosure  14 ′ configured for front-to-front airflow as illustrated in FIG.  2 B. The enclosure  14 ′ substantially surrounds an electronics module that includes a circuit board  46  (e.g., printed circuit board (PCB)). Various components  50 ′ and  50 ″ (generally  50 ) and subsystems  54 ′ and  54 ″ (generally  54 ) are integrated to, or mounted on, the board  46 . For example, components  50  can include electrical components (e.g., transformers, transistors, processors, memory devices, etc.) and optical components (e.g., pump lasers, pin diodes, array waveguides, filters, couplers, etc.) which generate heat that needs to be removed from the enclosure  14 ′. Subsystems  54  can include, for example, power supplies, multi-chip modules, daughterboards, optical modules and other subsystems. 
     The enclosure  14 ′ also encloses a heat sink  40  that includes a thermal spreader plate  58  and multiple cooling fins  62 . Because the heights of the components  50  and subsystems  54  vary, thermal shims may be attached to the bottom of the thermal spreader plate  58  to decrease the gaps between the plate  58  and the components  50  and subsystems  54 . A thermally-conductive material (e.g., thermal putty) fills the space between each shim and the top of one of the components  50  or subsystems  54 . Heat generated by the components  50  and subsystems  54  is thus conducted through the thermal spreader plate  58  and cooling fins  62 . The enclosure  14 ′ includes a cover plate  66  that closely fits over the top of the cooling fins  62 . Thus cooling fins  62  are sealed on top by the cover plate  66  and on the bottom by the spreader plate  58 , resulting in airflow channels between the cooling fins  62 . 
     A removable flow deflector  70  is attached over one or more openings on the back panel (not shown) of the enclosure  14 ′ using, for example, screws or snaps. In other embodiments, the removable flow deflector  70  is attached to the heat spreader plate  58 , the electronics board  46  or the cover plate  70 . The removable flow deflector  70  prevents the airflow generated by the inlet fan  28  from escaping and prevents the outlet fan  30  from drawing in air through the opening. The removable flow deflector  70  can be a plate that simply covers the opening. Alternatively, the removable flow deflector  70  can have a curved surface exposed to the airflow to decrease the flow loss as the airflow changes direction. 
     An optional louver module  74  mounts to the fan module  26 . The louver module  74  controls the direction of the inlet airflow  34  and exhaust airflow  42  outside the enclosure  14 ′. 
     Referring to FIGS. 2B and 3, the fans  28 ,  30  generate the inlet airflow  34  through an inlet louver portion of the louver module  74 . The inlet airflow  34  passes through some of the airflow channels defined by the cooling fins  62 . The airflow  34 ,  42  “turns the corner” in the gap (region between arrows  78 ) between the back edge of the cooling fins  62  and the removable airflow deflector  70 . The airflow  42  continues through other airflow channels between the cooling fins  62  and exits the enclosure  14 ′ through an outlet louver portion of the lover module  74 . To convert the enclosure  14 ′ to a front-to-rear configuration, the removable flow deflector  70  is removed to expose the one or more openings in the back panel of the enclosure  14 ′. In addition, one of the fans  28 ,  30  is configured to reverse its direction of airflow by reversing the orientation of the fan  28 ,  30  on its axis or changing the polarity of the electrical power applied to the fan  28 ,  30 . 
     If the exhaust airflow  42 , which is at a higher temperature than the inlet airflow  34 , is sucked back into the enclosure  14 ′ through the inlet fan  28 , the cooling capacity of the thermal management apparatus is decreased. Recirculation of the exhaust airflow  42  does not occur if the fans  28 ,  30  are sufficiently spatially separated. If the inlet and exhaust fans  28 ,  30  are separated by only a few inches or less, it is desirable to include the louver module  74  to better separate the inlet and exhaust airflows  34 ,  42 . Referring to FIG. 4, the louver module  74  includes an inlet louver  80  and an outlet louver  82 . The inlet louver  78  has a set of vanes  86  that are tilted at an angle θ 1 , with respect to the inlet fan axis  36  and the outlet louver  82  has a set of vanes  90  that are tilted at an angle θ 2  with respect to the outlet fan axis  38 . Thus the inlet airflow  34  and exhaust airflow  42  generated by the fans  28 ,  30  are increasingly separated from each other with increasing distance from the enclosure  14 ′. This angular separation prevents the exhaust airflow  42  from being sucked back through the inlet fan  28  and recirculated through the enclosure  14 ′. 
     In conventional thermal management systems, the cooling airflow can deposit dust which accumulates on the enclosed electronics module over time. The dust acts as an insulating layer, making it difficult to cool the components and subsystems. Consequently, the enclosed electronics module can fail if the cooling efficiency continues to decrease in time. Many systems include air filters to prevent the buildup of dust, however, such systems require periodic cleaning or replacement of filters. In addition, such systems require more powerful fans to overcome airflow loss introduced by the air filter. The thermal management apparatus of the present invention maintains one volume within the enclosure that contains the electronics module and another volume for the cooling airflow. In the embodiment depicted in FIG. 3, the spreader plate  58  separates the two volumes. No significant dust is deposited on the components  50  and subsystems  54 . Thus, no air filter is required and smaller capacity cooling fans  28 ,  30  can be utilized. Consequently, the cost of the enclosure  14 ′ is reduced and no filter maintenance is necessary. 
     The thermal management apparatus of the present invention is not limited to the above described structures. For example, the electronics volume and airflow volume can be separated by a vertically oriented thermal spreader plate  58 ′ (shown in phantom) as depicted in FIG.  5 . The electronics boards (not shown) can be vertically aligned (i.e., parallel) to the thermal spreader plate  58 . In another example (not shown), one or more thermal spreader plates can be arranged horizontally for use with one or more horizontal circuit boards. The horizontal thermal spreader plates can be attached to, or be integral with, the vertical spreader plate  58 ′. 
     While the invention has been shown and described with reference to specific preferred embodiments, it should be understood by those skilled in the art that various changes in form and detail may be made therein without departing from the spirit and scope of the invention as defined by the following claims.