Abstract:
A fluid-flow balancer mimics the air-flow resistance of a component omitted from an electronic system so that omission causes little or no disruption to or alteration of the flow of a cooling fluid. This prevents overheating that such disruption or alteration may otherwise cause. In addition, the fluid-flow balancer may also mimic the EMI suppression characteristics of the omitted component. Thus, a system not fully populated with components can still be adequately cooled and shielded without changing the cooling or shielding systems.

Description:
BACKGROUND OF THE INVENTION 
     Electronic systems, such as computers typically include a protective case, one or more circuit boards mounted inside the case, and one or more components such as a processor or a power supply mounted to each of the boards. In operation, the components generate heat that the system must remove from the case to prevent overheating and the damage it may cause. 
     To remove the heat, the system typically includes one or more fans that draw cool air into the case, circulate the drawn air within the case such that it absorbs the heat generated by the components, and expel the heated air from the case. The rate at which the heat is removed is typically proportional to the rate at which the air flows into and out of the case. The greater the flow rate, the greater the heat-removal rate and vice versa. 
     To prevent hot spots within the case, however, the system designer typically must consider the size, location, and orientation of the boards and components when designing the cooling system. The boards and components add resistance to the airflow paths within the case. Because the air will follow the paths of least resistance, components that lie along high-resistance paths may overheat if the cooling system is not designed to provide adequate flow rates along these high-resistance paths. Therefore, the designer analyzes the layout of the boards and components and determines the size, speed, and placement of the cooling fans that will provide adequate flow rates along all of the airflow paths for the lowest cost. Factors that affect the cost of the cooling system include the number of fans, the amount of power they consume, and how difficult it is to manufacture/install the cooling system. 
     Furthermore, to keep electromagnetic interference (EMI) to an acceptable level, the designer typically must consider the layout of the boards and components within the case when designating an EMI shielding system. 
     To take advantage of the economies of scale in mass production, most models of a system include the same cooling and shielding systems, but may include different circuit boards or components. For example, a high-end model of a data server may include a mother board with four processors mounted thereto, while a low-end model of the same server might include the same board with only one processor mounted thereto. To ensure that a system that includes all of the possible boards and components is properly cooled and shielded the cooling and shielding systems are typically designed for such a fully populated system. Consequently, when one or more of the components or boards are omitted from the system, the airflow and EMI footprint of the system may change such that the cooling system, shielding system, or both are no longer adequate. 
     FIGS. 1 and 2 illustrate the effect that an omitted component can have on the air flow within an electronic system. 
     FIG. 1 illustrates an electronic system  20  that includes components  22  and  24  attached to the circuit boards  26 ,  28  and  30 . Air flows along paths  32 ,  34  and  36  between the circuit boards  26 ,  28  and  30  to remove heat from the components  22  and  24 . Because the cooling system (not shown in FIGS. 1 and 2) is designed for the fully populated system  20 , the air flow adequately cools the components  22  and  24 . 
     But, as FIG. 2 illustrates, when the component  24  is removed from the circuit board  28 , the air flowing along the path  34  does not encounter the resistance of the omitted component  24 . Consequently, assuming the same overall air flow into the case as in FIG. 1, air flow along the path  34  increases and the air flow along the paths  32  and  36  decreases. Consequently, the components  22  on the boards  26  and  30  may overheat. One solution is to increase the overall air flow (e.g. by increasing the fan speed) to a level where the flow along the paths  32  and  34  is sufficient to cool the components  22  on the boards  26  and  30 . However, this often increases the amount of power consumed by the cooling system and may reduce the life of the cooling fans. It also may increase costs if a technician has to manually adjust the fan speed of each partially populated system. 
     Still referring to FIGS. 1 and 2, the omission of the component  24  from a circuit board of an electronics system can change the EMI footprint in a similar manner, and tailoring the EMI shielding for each different system can be prohibitively expensive. 
     SUMMARY OF THE INVENTION 
     In one aspect of the invention, a fluid-flow balancer for taking the place of a system component having an air-flow resistance includes a flow-resistance element and a mount. The flow-resistance element is operable to mimic the air-flow resistance of the component, and the mount is operable to mount the flow-resistance member within the system. 
     By mimicking the air-flow resistance of an omitted component, such a balancer can maintain the flow along the air paths within a system at proper levels without tweaking or redesigning the cooling system. In a related aspect of the invention, the balancer also mimics the EMI suppression provided by the omitted component. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a view of an electronic system and the air flow paths over three populated circuit boards. 
     FIG. 2 illustrates the change in air flow over the circuit boards of FIG. 1 when an electronic component is omitted from one of the circuit boards. 
     FIG. 3 is a view of a circuit board that incorporates two fluid-flow balancers according to an embodiment of the invention. 
     FIG. 4 is a perspective view of one of the fluid-flow balancers of FIG. 3 according to an embodiment of the invention. 
     FIG. 5 is a block diagram of an electronic system that includes the circuit board of FIG.  3 . 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     The following discussion is presented to enable one skilled in the art to make and use the invention. Various modifications to the disclosed embodiments will be readily apparent to those skilled in the art, and the generic principles herein may be applied to other embodiments and applications without departing from the spirit and scope of the present invention as defined by the appended claims. Thus, the present invention is not intended to be limited to the embodiments shown, but is to be accorded the widest scope consistent with the principles and features disclosed herein. 
     Although air is typically circulated within an electronic system to remove heat generated by components therein, other types of gases or fluids could be used. Consequently, although air, air flow and air-flow resistance are referred to throughout this specification, it is understood that air, air flow and air-flow resistance respectively include any desired type of gas or fluid, gas-flow or fluid-flow, and gas-flow resistance or fluid-flow resistance. 
     FIG. 3 is a side view of a circuit board  40  that includes two fluid-flow balancers  42  according to an embodiment of the invention. Each balancer  42  mimics the air-flow resistance of a respective component  44  (shown in dashed line) that is omitted from the board  40 . In addition, each balancer  42  suppresses EMI from other electronic components within the system (FIG. 5) in which the board  40  is installed that would normally be suppressed by the respective omitted components  44 . Therefore, the balancers  42  reduce or eliminate changes in the system air flow and EMI shielding caused by the omission of components from the board  40 . Consequently, other system components not shown in FIG. 3 remain adequately cooled and shielded. 
     In one embodiment, the circuit board  40  includes two processing/power supply units  44 , and the two fluid-flow balancers  42 . The fluid-flow balancers  42  are respectively attached to regions of the circuit board  40  where the additional processing/power-supply units  44  would be attached to populate the circuit board  40 , but have been omitted. Such an omission may be for any reason such as a customer (not shown) not needing the extra processing power, and thus not wanting the extra expense, of including four processor/power-supply units  44  on the board  40 . 
     Each fluid-flow balancer  42  includes a flow-resistance member  50  that mimics the air-flow resistance of a processing/power-supply unit  44 , and a mount  52  that mounts the flow-resistance member  50  to the circuit board  40 . Each flow-resistance member  50  extends in a perpendicular or substantially perpendicular direction relative to the circuit board  40  and into the air flow along the path  54 . Thus, the air flow along the path  54  encounters the same or substantially the same flow resistance an air flow along the path  54  would encounter if both processing/power-supply units  44  were mounted to the circuit board  40 . Each mount  52  covers or substantially covers the omitted unit&#39;s footprint on the circuit board  40  to maintain the system&#39;s designed EMI characteristics. Consequently, the air flow along the path  56  is not reduced by the omission, of the units  44 , and thus adequately cools the installed units  44  on the underside of the board  40 . 
     Still referring to FIG. 3 in one embodiment, four standoffs  58  (only two shown for each balancer  42 ) suspend each fluid-flow balancer  42  above the circuit board  40 . The standoffs  58  can be sized to suspend each fluid-flow balancer  42  at any desired height above the board  40 . For example, the standoffs  58  can be sized to locate each mount  52  to the same or substantially the same height as the top of each omitted processing/power-supply unit  44 . 
     In operation, each fluid-flow balancer  42  resists the air flow along the path  54  to maintain the proper level of air flow along the paths  54  and  56 . As discussed in greater detail in conjunction with FIG. 4, the flow-resistance member  50  resists the air flow along the path  54  by obstructing a portion of this air flow and permitting another portion of this air flow to pass unimpeded through the member  50 . Without the flow-resistance provided by each fluid-flow balancer  42 , the air flow along the path  54  would increase (due to less resistance) and the air flow along the path  56  would decrease and may not adequately cool the processing/power-supply units  44 . 
     Still referring to FIG. 3, other embodiments of the fluid flow balancer  42  are contemplated. For example, the flow-resistance member  50  may extend in a direction that is not perpendicular or substantially perpendicular to the circuit board  40 . And although the fluid-flow balancers  42  are attached to a respective region of the circuit board  40  where processor/power-supply units  44  have been omitted, the balancers  42  can be mounted to other regions of the circuit board where a system component has not been omitted. For example, the balancers can be attached to a fully populated circuit board in a region that does not include a component. This may be desirable to alter the designed air flow through all or a portion of the system. In another example, a substitute component may be mounted to a region of the circuit board in place of a system component, and the fluid-flow balancer may be mounted above or adjacent the substitute component. This may be desirable if the substitute component has an air-flow flow resistance that is different than the omitted system component and/or alters the system&#39;s EMI characteristics. 
     FIG. 4 is a perspective view of one of the fluid-flow balancers  42  in FIG. 3 according to an embodiment of the invention. As previously discussed, the fluid-flow balancer  42  includes a flow-resistance member  50  that mimics the air-flow resistance of an omitted component such as a processing/power-supply unit  44  (FIG. 3) and a mount  52  for mounting the flow-resistance member  50  onto the board  40  (FIG.  3 ). 
     In one embodiment, the flow-resistance member  50  includes a flow-resistance plate  60  designed to mimic the air-flow resistance of the processor of the unit  44  and another flow-resistance plate  62  designed to mimic the air-flow resistance of the power supply of the unit  44 . The flow-resistance plate  60  is flat or substantially flat and includes a plurality of holes  64  arranged in a rectangular pattern. Each hole  64  is the same or substantially the same size and extends through the flow-resistance plate  60  to allow air to flow through the plate  60 . The plate  60  has an area equal to the length of a side  68  times the width of an edge  66 . The plurality of holes  64  define a hole area that equals the sum of all the individual areas of each hole  64 . When the air flow contacts the flow-resistance plate  60  from a direction perpendicular or substantially perpendicular to the plate  60 , a portion of the air flows through the holes  64  and another portion of the air is obstructed by the remainder of the plate  60 . Thus, the arrangement of the holes  64  in the plate  60  and the ratio of the hole area to the plate area are designed so that the plate  60  mimics the air-flow resistance of the omitted processor. Likewise, the flow-resistance plate  62  includes a plurality of holes  70  arranged in a rectangular pattern. Thus, the arrangement of the holes  70  and the ratio of their area to the area of the plate  62  are designed so that the plate  62  mimics the air-flow resistance of the omitted power supply. 
     In other embodiments, the flow-resistance plates  60  and  62  can be modified to mimic the air-flow resistance of other electronic components having an air-flow resistance different than the processor and the power supply of the processor/power-supply unit  44  (FIG.  3 ). For instance, such modifications can include arranging the holes  64  in a pattern other than a rectangular pattern or changing the size of the holes. For example, the flow-resistance plate  60  can include one hole sized as desired or the plate  60  can include regions where holes are clustered together and other regions without a hole. Additionally, such modifications can include changing the ratio of the hole area to the plate area. For example, increasing this ratio decreases the air-flow resistance of the flow-resistance plate and vice-versa. 
     Other embodiments of the air-flow resistance member  50  are contemplated. For example, although the flow-resistance plates  60  and  62  include circular holes  64  and  70  respectively, the plates  60  and  62  can include holes having any desired shape, such as a square, a triangle, or curved slots. Furthermore, although the holes  64  are the same or substantially the same size and the holes  70  are the same or substantially the same size, the holes  64  can have different sizes and the holes  70  can have different sizes. 
     Still referring to FIG. 4, in one embodiment, the mount  52  includes mounting plates  76  and  78  for mounting the flow-resistance members  60  and  62 , respectively, to the circuit board  40  (FIG.  3 ). The mounting plates  76  and  78  are flat or substantially flat and parallel or substantially parallel relative to each other. Four screws  88 , each located at one of the respective corners  80  and  82  of the mounting plate  76  and at the corners  84  and  86  of the mounting plate  78 , attach the fluid-flow balancer  42  to the circuit board  40 . Four coil springs  90  each disposed between the head  92  of each screw  88  and the respective one of the corners  80 ,  82 ,  84 , and  86  urge the heads  92  away from the respective corners. When the screws  88  are attached to the circuit board  48 , the springs  92  force the mounting plates  76  and  78  against the standoffs  58  (FIG.  3 ). In one embodiment, the standoffs  58  are designed such that the plates  76  and  78  have the same or substantially the same height as the processor and power supply, respectively, of the omitted processor/power-supply unit  44  (FIG.  3 ). 
     Furthermore, the fluid-flow balancer  42  can be made from conventional metal such as aluminum for providing EMI shielding when the balancer  42  is attached to the circuit board  40  (FIG.  3 ). In embodiments where shielding is not desired, the fluid-flow balancer  42  can be made from other materials such as conventional plastics. 
     Still referring to FIG. 4, other embodiments of the fluid-flow balancer  42  are contemplated. For example, the flow-resistance member  50  can include fewer or more than two flow-resistance plates. In addition, the mount  52  can include fewer or more than two mounting plates. 
     FIG. 5 is a block diagram of an electronic system  90  that incorporates one or more fluid-flow balancers  42  (FIGS.  3  and  4 ). The system  90  includes computer circuitry  94 , which includes the circuit board  40  (FIG. 3) and a memory  96 , for performing computer functions such as executing software to perform desired calculations and tasks. The board  40  includes one or more processor/power-supply units  44  coupled to the memory  96 , and includes one or more of the balancers  42  in place of omitted processor/power-supply units  44 . One or more input devices  98 , such as a keyboard, mouse, or microphone, are coupled to the computer circuitry  94  and allow an operator (not shown) to input data thereto. One or more output devices  100  are coupled to the computer circuitry  94  to provide to the operator data generated by the computer circuitry  94 . Examples of such output devices  100  include a printer and a video display unit. One or more data-storage devices  102  are coupled to the computer circuitry  94  to store data on or to retrieve data from external storage media (not shown). Examples of such storage devices  102  and the corresponding storage media include drives that accept hard and floppy disks, tape cassettes, and compact disk read-only memories (CD ROMS).