Abstract:
Disclosed is an apparatus for cooling unvented cabinets housing electronic equipment. A fanning unit at a bottom portion of the cabinet draws air down through the spaces between printed circuit boards which include the electronic components. A plate installed on the inside of the cabinet door creates a duct to cause cooling of the air at the door surface as it flows upward for recirculation. A heat exchange element may also be provided in the space between the equipment mounted on both sides of the cabinet.

Description:
This application is a continuation of application Ser. No. 07/519,050, filed on May 4, 1990, now abandoned. 
    
    
     BACKGROUND OF THE INVENTION 
     This invention relates to cooling of electronic components. 
     Higher heat densities in electronic equipment caused by the increasing density of integrated circuits and circuit pack configurations, has led to concern regarding the ability of unvented outdoor electronic cabinets to dissipate the heat generated by the electronics. The equipment is usually housed in shelves within an appropriate cabinet and cooled by fans. Fans can be adapted to blow recirculated coolant onto the components through a series of ducts (see, e.g., U.S. Pat. No. 3,387,648 issued to Ward, Jr., et al). Alternatively, a fan can draw air from outside the cabinet through openings in a wall of the cabinet and direct it over the components (see, e.g., U.S. Pat. No. 4,027,206 issued to Lee). Appropriate ducts can also be used to guide the air (see, e.g., U.S. Pat. No. 4,860,163 issued to Sarath). 
     Such cooling techniques, while generally adequate, are not necessarily effective in cases where a large number of high density circuit packs must be housed within a fairly small space, as in the case of subscriber loop carrier (SLC®) remote terminal channel banks. Such banks typically include channel units and common units which are each capable of generating up to 10 watts of heat. These circuit packs are mounted vertically with, typically, 28 circuit packs per shelf and 5 shelves per bank. Usually, banks are housed back-to-back in a cabinet with a small space between them. 
     The present method generally employed to cool unvented cabinets, which is to blow air into the banks, has reached the limit of its effectiveness. Attempts to increase cooling have generally involved use of heat pipes or finned heat exchangers without addressing the optimization of airflow within the cabinet. 
     It is, therefore, the objective of the invention to provide a means for enhanced cooling of electronic components mounted within an unvented cabinet by increasing internal airflow over cabinet surfaces exposed to outside air and increasing the flow of cooled internal air through the electronic equipment. 
     SUMMARY OF THE INVENTION 
     This and other objects are achieved in accordance with the invention which, in one aspect, is a cabinet for housing electronic equipment and including means for cooling said equipment. The cooling means comprises a fan mounted so as to be capable of drawing air down through said equipment, and means for providing recirculation of the air. The recirculation means includes a plate member mounted to a door of the cabinet so as to form a duct for the recirculation of the air adjacent to a surface of the door. 
     In accordance with another aspect of the invention, the recirculation means includes a heat exchanging element mounted in a spaced relationship to the equipment so that air which is recirculated in said space can be cooled by the heat exchanger. The heat exchanger element includes means for drawing air from outside the cabinet through a plurality of compartments so as to provide a cooling surface for the recirculated air in the space adjacent to said surface. 
    
    
     BRIEF DESCRIPTION OF THE DRAWING 
     These and other features of the invention are delineated in detail in the following description. In the drawing: 
     FIG. 1 is a perspective view of a cabinet including cooling means in accordance with an embodiment of the invention; 
     FIG. 2 is a cross-sectional schematic view of the cabinet of FIG. 1 taken along line 2--2; 
     FIG. 3 is a perspective view of a cabinet including cooling means in accordance with a further embodiment of the invention; 
     FIG. 4 is a cross-sectional schematic view of a portion of the cooling means of FIG. 3 taken along line 4--4; and 
     FIG. 5 is a cross-sectional schematic view of the cabinet of FIG. 3 taken along line 5--5. 
     It will be appreciated that, for purposes of illustration, these figures are not necessarily drawn to scale. 
    
    
     DETAILED DESCRIPTION 
     FIG. 1 illustrates an embodiment of the invention. The cabinet 10 includes a housing 11 and four doors 12, 13, 50 and 51 hinged on opposite surfaces of the housing. The electronic equipment protected by the housing includes banks 14 and 15 of circuit packs, e.g., 16, mounted in shelves, e.g., 17 and 18. Although not shown, multiple banks can be mounted in a cabinet position, e.g., one above the other. The front of the circuit packs of the two banks 14 and 15 face in opposite directions so as to be accessible by opening different doors. The circuit packs are of a standard type which include components, e.g., 19, formed on a circuit board 20 with a faceplate 21 at the front end for latching the board into the shelf. It will be appreciated that the full number of shelves, as well as other standard components on a remote terminal cabinet, such as protector blocks, power components, and wiring, have been omitted for the sake of clarity in the illustration. 
     At the bottom of each mounting position in the cabinet is a shelf including a fan (22 and 27 of FIG. 2) mounted so as to draw air down through the spaces between the circuit packs in the bank. The applicants discovered that drawing the air through the bank was more effective than blowing air into the bank in terms of exchanging heat between the air and the heat generating components. 
     Plates 23, 24, 52 and 53 are mounted in a spaced relationship with each door, 12, 13, 50 and 51, respectively, to provide ducts, e.g., 25 and 26 of doors 12 and 13, for recirculating air as described in more detail below. In this particular example, each plate covered essentially the entire inside surface of its respective door and was mounted to the door by screws and standoffs, but any standard mounting arrangement can be employed. The plates were made of aluminum, but other materials can also be used. The ducts formed between the plates and the doors were approximately 3 cm wide. Each plate also included a horizontal baffle, e.g., 56, mounted to a bottom portion of the plate by standard means. 
     FIG. 2 is a schematic cross-sectional view along line 2--2 of FIG. 1, with the doors in a closed position, illustrating the flow of air through the cabinet when the fans are turned on. Each rectangular block, e.g., 16, represents a channel bank (typically 5 shelves of circuit packs). As previously mentioned, the fans 22 and 27 draw air down through the banks of circuit packs as indicated by the arrows. The air is then recirculated through the ducts 25 and 26 formed between the plates 23 and 24 and the doors 12 and 13. The ducts prevent the recirculating air from entering the spaces between the faceplates of the circuit packs since the plates extend essentially the entire vertical distance occupied by the circuit packs. While the recirculating air traverses the ducts 25 and 26 it is cooled by the inside surface of the doors 12 and 13 which are made of a good heat conducting material such as aluminum. Thus, by the time the air reaches the top of the cabinet, it is cooled sufficiently so that it can again cool the circuit pack components as it is drawn down through the banks. Air circulation in the vertical space between banks is impeded by use of vertical baffles 58 and 59 attached to the shelves including fans 22 and 27. 
     Utilizing this technique, it was discovered that the rise in temperature of the hottest circuit packs was lowered by approximately 40 percent over prior schemes which forced air into the channel banks without using a door duct. 
     FIG. 3 illustrates a cabinet which further enhances cooling capabilities. The cabinet is essentially the same as that illustrated in FIG. 1 except for the addition of a heat exchange element 30. This element is inserted in a side surface of the housing and extends into the spaces between the banks 14 and 15. This element includes a metal housing 31 providing heat exchanging surfaces adjacent to each bank, and means such as fans 32 and 33 for bringing in air from the outside environment and exhausting the air back to the outside environment. The housing can include metal fins, e.g., 54, for increased heat exchange. 
     As illustrated by the arrows in the cross-sectional view of the element in FIG. 4, air brought in by fan 32 is circulated through three different main compartments 36-38 formed by U-shaped baffles 39, 40 and 41 as well as secondary compartments formed by vertical plates, e.g., 42. The air is then exhausted through fan 33. 
     This air flow produces finned heat exchange surfaces 34 and 35 which are utilized for cooling the cabinet as shown in FIG. 5, which is a cross-sectional view along line 5--5 of FIG. 3. Again, air is drawn vertically through the spaces between circuit packs in the banks by the fans 22 and 27. In addition to recirculating through ducts 25 and 26 part of the air is also recirculated in the spaces (43 and 44 of FIG. 3) between the banks which contain finned surfaces 34 and 35 of the heat exchanger element 30. In this example, the spaces 43 and 44 are approximately 3 cm wide. The recirculating air is cooled by the heat exchange surface, 34 and 35 as it traverses upward. (The air is prevented from entering the spaces between circuit packs in its upward path by the usual backplane provided for electrically interconnecting the circuit packs). The cooled air can then be drawn downward again to cool the circuit packs. 
     Thus, the embodiment shown in FIGS. 3-5 should permit additional heat exchange capabilities over the embodiment of FIGS. 1-2. 
     Various additional modifications will become apparent to those skilled in the art. All such variations which basically rely on the teachings through which the invention has advanced the art are properly considered within the scope of the invention.