Patent Publication Number: US-2007103862-A1

Title: Chassis with positive pressure

Description:
BACKGROUND OF THE INVENTION  
      1. Field of the Invention  
      The disclosure relates generally to a chassis for an electronic system and, more specifically, to a computer chassis for use in a dirty environment.  
      2. Description of the Related Art  
      Electronic systems, such as computers, are vulnerable to particulate matter. For example, particulate matter can prevent hard drives and/or optical drives from properly reading media. Additionally, particulate matter can build up on cooling devices, such as a heat sink, which decreases the efficiency of the cooling device. Issues related to particulate matter, however, do not arise often in relatively clean environments, such as a typical office or home. Furthermore, where uptime of the electronic system is of particular importance, one manner of addressing these issues has been to place the electronic system in a clean room.  
      The use of a clean room environment, however, is not feasible in many applications. For example, in a situation where a computer is used to control equipment on a factory floor, placing the computer in a clean room creates issues associated with connecting the computer to the equipment as well as easily accessing the computer while operating the equipment. Therefore, in many instances, it is desirable to place the electronic system, such as a computer, adjacent the equipment, even if the environment is filled with particulate matter.  
      One particular feature (i.e., the cooling fan) commonly found in computer chassis further exacerbates the problem of preventing particulate matter from entering the chassis of the computer. Although a common technique has been to place filters over the cooling fans, in most instances, there are many opening in the computer chassis, besides the location of the cooling fan, where particulate matter can enter the chassis. For example, a computer chassis commonly has seams along edges of adjacent pieces of the chassis in addition to holes, such as mounting holes, within the chassis. There are also several much larger openings within the chassis that are adapted to receive expansion cards, input/output connectors, etc. through which particulate matter can enter the chassis. As a result of these multitude of openings, a common computer chassis acts as a veritable sieve that allows particulate-laden air to enter the chassis.  
      Another solution to preventing particular matter from entering a computer is to simply make the chassis airtight. This solution, however, is not commonly adopted since the solution is often too expensive to be practicable. Furthermore, maintaining the integrity of any seals within the computer chassis can also be expensive. There is, therefore, a need for a low-cost chassis system for an electronic system that reduces the amount of particulate-laden air entering the chassis of the electronic system.  
     BRIEF SUMMARY OF THE INVENTION  
      Embodiments of the invention address deficiencies of the art in respect to an electronic system chassis and provide a novel and non-obvious device for reducing the amount of particulate-laden air entering the chassis of the electronic system. In this regard, the chassis for an electronic device, such as a computer, includes a plurality of fans attached to a single face of the chassis with each of the fans directing a fluid into an interior of the chassis and towards a second face of the chassis. The second face of the chassis has a greatest total area of output openings within the chassis, and a positive pressure exists between the interior of the chassis and an exterior of the chassis at all the output openings within the chassis. At least one detachable filter is disposed over the plurality of fans, and at least one hexagon-shaped bezel is disposed between the plurality of fans and the at least one filter.  
      In certain aspects of the chassis, a percentage of a total area of the plurality of fans on the single face to a total area of the single face of which the fans are disposed may be greater than approximately 18.0%, and in other aspects, greater than 24.0%. An average velocity of the fluid exiting the chassis at the output openings may be greater than 9 ft/second, and in other aspects, greater than 12 ft/second. A percentage of a total area of all the output openings to a total area bounded by the chassis may be greater than 1.5%, and in other aspects, greater than 2.0%. A volume of the interior of the chassis may be less than 1.5 ft 3 .  
      Additional aspects of the invention will be set forth in part in the description which follows, and in part will be obvious from the description, or may be learned by practice of the invention. The aspects of the invention will be realized and attained by means of the elements and combinations particularly pointed out in the appended claims. It is to be understood that both the foregoing general description and the following detailed description are exemplary and explanatory only and are not restrictive of the invention, as claimed. 
    
    
     BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS  
      The accompanying drawings, which are incorporated in and constitute part of this specification, illustrate embodiments of the invention and together with the description, serve to explain the principles of the invention. The embodiments illustrated herein are presently preferred, it being understood, however, that the invention is not limited to the precise arrangements and instrumentalities shown, wherein:  
       FIG. 1A  is a schematic illustration of a base of a chassis in accordance with the inventive arrangements;  
       FIG. 1B  is a schematic illustration of a cover of a chassis in accordance with the inventive arrangements;  
       FIG. 2  is an enlarged view of a bezel; and  
       FIGS. 3A and 3B  are respective front and rear view of a filter for covering cooling fans within the chassis.  
    
    
     DETAILED DESCRIPTION OF THE INVENTION  
       FIGS. 1A and 1B  illustrate an electronic system chassis  10  for reducing particulate matter entering the chassis  10 . As illustrated, the chassis  10  may include a chassis cover  10 A and a chassis basis  10 B that when combined define the external dimensions of the chassis  10  and bound the interior of the chassis  10 . As is known in the art, many type of chassis configurations are known (e.g., the chassis may include a body and a hinged or sliding panel), and the present chassis  10  is not limited as to a particular configuration of defining the external dimensions of the chassis  10  and bounding an interior of the chassis  10 . The chassis  10  is not limited as to the particular electronic system housed within the chassis  10 .  
      Although not limited in this manner, an example of an electronic system housed within the chassis  10  is a computer system that may include, for example, a power supply  14 , an optical drive  16 , a floppy drive  18 , a hard drive  20 , and a mother board (not shown). Additionally, the chassis  10  may have an interior volume of less than 1.5 ft 3 .  
      A plurality of fans  12  ( 12 A,  12 B,  12 C,  12 D) are configured to introduce a cooling fluid, such as air, from the exterior of the chassis  10  into the interior of the chassis  10 , and the plurality of fans  12  may be directly attached to the chassis  10 . Although the plurality of fans  12  may be located on differing faces of the chassis  10 , in one aspect of the chassis  10 , each of the fans  12  are located on a common face of the chassis  10 .  
      The fans  12  may also be located on a face of the chassis  10  opposite a face of the chassis  10  having a greatest surface area of openings within the chassis  10 . By locating the fans  12  on a face of the chassis  10  opposite a face of the chassis  10  having a greatest surface area of openings a more direct path of air can be provided from the fans  12  to the greatest surface area of openings within the chassis  10 . In this manner, a propensity for “hot spots” (i.e., areas of reduced air circulation) to develop within the interior of the chassis  10  can be reduced.  
      Typically, the rear face  10 R of the chassis  10  has a greater surface area of openings within the chassis  10 . For example, the rear face  10 R commonly includes expansion card slots  24  and a slot  26  to accept the I/O panel connectors of a mother board (not shown). In contrast, the top, bottom, and side faces of the chassis  10  typically have few openings, such as mounting holes  22 . In certain aspects of the chassis  10 , a percentage of a total area of all the output openings to a total area bounded by the chassis  10  is greater than 1.5%. In other aspects of the chassis  10 , the percentage of a total area of all the output openings to the total area bounded by the chassis  10  is greater than 2.0%.  
      As illustrated, the fans  12  are located on a front face  10 F of the chassis  10 . Although the present chassis  10  has been described as having the fans  12  located in a front face  10 F of the chassis  10  and the greatest surface area of openings within the rear face  10 R of the chassis  10 , the present chassis  10  is not limited in this manner since the location of the greatest surface area of openings within a particular chassis may vary from one configuration of chassis to another.  
      Although a single fan  12  can be sized to produce the same amount of airflow through the interior of the chassis  10  as the amount of airflow produced by a plurality of fans  12 , the use of a plurality of fans  12  (e.g., four fans  12  as shown in  FIG. 1A ), creates a more even distribution of airflow across a given cross-section of the chassis  10 , which also reduces the propensity for hot spots to develop within the interior of the chassis  10 . In certain aspects of the chassis  10 , a percentage of a total output area of the fans  12  on a particular face  10 F of the chassis  10  to the total area of the particular face  10 F of the chassis is greater than 18.0%. In other aspects of the chassis  10 , the percentage of the total output area of the fans  12  on the particular face  10 F of the chassis  10  to the total area of the particular face  10 F of the chassis is greater than 24.0%. As this percentage increases, a more uniform airflow through the interior of the chassis  10  may be provided.  
      Unlike a typical chassis  10 , in which the fan(s)  12  are sized (e.g., Cubic Feet per Minute—CFM) primary to cool the internal components within the interior of the chassis  10 , the plurality of fans  12  are sized, not only to cool the internal components within the interior of the chassis  10 , but also to create a positive pressure differential between the interior of the chassis  10  and the exterior of the chassis  10 . Furthermore, the plurality of fans  12  may be sized to create a positive pressure differential at all of the output openings within the chassis  10 . In this manner, particulate matter can be prevented from entering the chassis  10 . The CFM ratings of the fans  12  are derated to compensate for a filter  28  placed over the fans  12  and any back pressure associated with obstructions within the interior of the chassis  10  or a result of a protective bezel  27  in front of the fans  12 . The cumulative CFM rating of all the fans  12  may also be derated for any other fans (e.g., within the power supply  14 ) that create a negative pressure differential within the chassis  10  (i.e., expel air from the chassis  10 ).  
      In certain aspects of the invention, the fans  12  are sized to produce an average velocity of air exiting the chassis  10  that is greater than 9 ft/second. In other aspects of the chassis, the fans  12  are sized to produce an average velocity of air exiting the chassis  10  that is greater than 12 ft/second. The average velocity of air exiting the chassis  10  is a function of (i) the volume of air entering the chassis for a given time period (e.g., the derated cumulative CFM for the fans  12 ), which given a steady-state condition is also the volume of air exiting the chassis  10  for a given time period, and (ii) the area of output openings within the chassis  10 .  
      A protective bezel  27  is disposed in front of each of the fans  12 , and an enlarged portion of a bezel  27  is illustrated in  FIG. 2 . As is known to those skilled in the art, a bezel  27  can serve several functions. For example, the bezel  27  protects the fan  12  by preventing large objects (e.g., fingers, pencils) from impinging upon the fan  12 , and the bezel  27  can also support a filter  28  disposed over the bezel  27 . Any bezel  27  capable of performing any of the above-described functions is acceptable for use with the chassis  10 . However, in a current aspect of the chassis  10 , the bezel  27  is formed from hexagon-shaped cells. In so doing, the hexagon-shaped cells provide the bezel  27  within additional strength. Also, the hexagon-shaped cells comply with UL/CE (i.e., safety) and FCC (i.e., RF) requirements.  
       FIGS. 3A and 3B  illustrate a filter  28  capable of being used with the chassis  10 . Either a combination of filters  28  (not shown) or a single filter  28  may be located over the intake for each of the fans  12 . In so doing, all air entering the chassis  10  will be channeled through the filter  28 . The filter  28  includes filter material  30  and a frame  32 . As is recognized by one skilled in the art, the many types of filter materials are known, and the filter material  30  to be used with the filter  28  may be selected depending upon he particular environment in which the chassis  10  will be used and/or the depending upon the particular particulate matter to be filtered out.  
      The frame  32  is used to connect the filter  28  to the chassis  10 , and any frame  32  capable of connecting the filter  28  to the chassis  10  is acceptable for use with the filter  28 . Although not limited in this manner, the frame  32  may be formed from a magnetic material that can magnetically adhere to the chassis  10 . The use of magnetic material for the frame  32  allows the filter  28  to be easily removed from the chassis  10  and/or replaced. The frame  32  may also be configured to not interfere with the passage of air into the fans  12  by being positioned away from and at the periphery of the fans  12 .  
     EXAMPLE  
      The chassis has a height of 6.25″, a depth of 16.25″, and a width of 17,″ which yields an internal volume of approximately 1 ft 3  and a total area bounded by the chassis  10  as 2×((6.25″×16.25″)+(6.25″×17″)+(16.25″×17″)) or 968 in 2 . The area of the output openings of the chassis were determined to be approximately 17.2 in 2 , which is broken down into 509 holes in a rear bezel for 9.72 in 2 , a slot cover of 0.36 in 2 , 4 rack mount screw holes for 0.057 in 2 , and 7.065 in 2  for a power supply exhaust opening. The percentage of an area (17.2 in 2 ) of all the output openings to the total area (968 in 2 ) bounded by the chassis  10  is 1.8%.  
      The area of the input openings of the chassis is determined to be approximately 17.73 in 2 , which is broken down into 3 cooling fans having a 3″ diameter with a hexagon bezel covering 16% of the opening. This yields a percentage of an area of the fans on the face to total area of the face of (3*π*(1.5″) 2 ) to (6.25″*17″) or approximately 20.0%. The volume of air through the 3 cooling fans per a given time period is calculated based upon a rated 36.88 CFM per fan. Each fan is derated 60% to compensate for the filter, back pressure, and the bezel over each fan. This yields a total of 66.4 CFM for the 3 cooling fans.  
      The above-described chassis, therefore, achieved a input opening to output opening ratio of 17.73:17.2 or approximately 1:1. Furthermore, the time to completely replace the internal volume of air within the chassis is calculated to be 1 ft 3 *(60 seconds/66 * ft 3 ) or approximately 0.9 seconds. The calculated velocity of the air through the output openings is (1 ft 3 )/((0.9 seconds)*((17.2 in 2 )*(1 ft 2  /144 in 2 ))) or approximately 9.3 ft/second.