Abstract:
Aspects of the invention pertain to cooling bundles of power distribution cables or other current carrying cables. Such cables give off heat, especially when carrying high current loads. One or more cooling members are used to secure multiple cables. The cables may be placed about a generally circular shaped member which has a central opening. Receptacles are placed along an outer perimeter of the cooling member to secure the cables. The thickness of each cooling member may vary. When multiple cooling members are used, they may be spaced at least 6 inches apart. The cooling members may be fabricated from a nonconductive material such as PVC.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     Aspects of the invention relate generally to heat dissipation in power distribution systems. More particularly, aspects provide cooling of current carrying cable bundles. 
     2. Description of Related Art 
     Power distribution systems are used in many different applications such as large scale computer systems. Such systems often use multiple cables, and each cable may support a high current. Often, two or more current carrying cables are bundled together using tie-wraps (cable ties) or other equipment. Bundling allows for convenient handling of the cables and gives the appearance of an orderly arrangement. 
     Unfortunately, current carrying cables dissipate heat. Bundling such cables together prevents efficient heat dissipation per unit time, as it keeps more heat within the core of the bundle. This may reduce the current carrying capability of the cables. It may also reduce the useful life of a given cable and may cause a fire hazard. It is possible to increase the insulation surrounding each cable. However, this increases the size and expense of the cables. 
     SUMMARY OF THE INVENTION 
     In accordance with aspects of the invention, one or more cooling discs are used to secure multiple current carrying cables while spreading the cables out in an organized manner. The cooling discs provide an efficient spatial distribution of heat so that the amount of power dissipated over time is distributed over a larger volume, effectively cooling the cables. Thus, it is not necessary to derate the cables. 
     In accordance with one embodiment, a cooling apparatus comprises at least one cooling member having an outer perimeter and an inner perimeter. The outer perimeter includes a plurality of receptacles for receiving a corresponding one of a plurality of current carrying cables. The inner perimeter defines a central opening. Each receptacle has a cross-sectional size conforming to a cross-sectional size of the corresponding cable. And each receptacle has a pair of opposing outer lips having a spacing therebetween. The spacing is less than a diameter of the corresponding cable. 
     In one example, the receptacles have a generally arcuate shape. In this case, the inner perimeter is desirably generally circular. In another example, the at least one cooling member is a thermal and electric insulator. Here, the at least one cooling member desirably comprises a thermoplastic polymer. 
     In a further example, the at least one cooling member comprises a plurality of cooling members, each of the plurality of cooling members having a thickness of less than one inch. In one alternative, upon connection to the plurality of cables, a first one of the cooling members is spaced apart from a second one of the cooling members by at least about 6 inches. In another alternative, upon connection to the plurality of cables, a first one of the cooling members is spaced apart from a second one of the cooling members by less than about 12 inches. And in another example, the at least one cooling member has a thickness of between about 0.25 to 0.5 inches. 
     In accordance with another embodiment, a cooling system comprises a plurality of cooling members and a plurality of cables configured to handle current loads. Each cooling member has an outer perimeter and an inner perimeter. The outer perimeter includes a plurality of receptacles therealong. The inner perimeter defines a central opening. Each of the plurality of cables will generate heat in relation to its current load. Each of the plurality of cables has a cross-sectional size. Each receptacle receives a corresponding one of the plurality of cables. Each receptacle has a cross-sectional size conforming to the cross-sectional size of the corresponding cable, and each receptacle has a pair of opposing outer lips having a spacing therebetween. The spacing is less than a diameter of the corresponding cable. 
     In one example, the receptacles have a generally arcuate shape. In another example, the inner perimeter is generally circular. In a further example, the cooling members are thermal and electric insulators. Here, the cooling members desirably comprise a thermoplastic polymer. 
     In yet another example, each of the plurality of cooling members has a thickness of less than one inch. In one alternative, each cooling member is spaced apart from any neighboring cooling members by at least about 6 inches. And in another alternative, each cooling member is spaced apart from any neighboring cooling members by less than about 12 inches. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  illustrates a cooling system in accordance with aspects of the invention. 
         FIG. 2  illustrates features of the system of  FIG. 1 . 
         FIGS. 3A-B  illustrate features of a cooling system in accordance with aspects of the invention. 
         FIG. 4  illustrates another cooling system configuration in accordance with aspects of the invention. 
         FIG. 5  illustrates features of the system of  FIG. 4 . 
         FIG. 6  is an image showing the use of a cooling member in accordance with aspects of the invention. 
         FIG. 7  illustrates a bundle of current carrying cables. 
     
    
    
     DETAILED DESCRIPTION 
     Aspects, features and advantages of the invention will be appreciated when considered with reference to the following description of preferred embodiments and accompanying figures. The same reference numbers in different drawings may identify the same or similar elements. Furthermore, the following description is not limiting; the scope of the invention is defined by the appended claims and equivalents. 
     As noted above, current carrying cables may dissipate significant heat per unit time. This is a function of the amount of current which is carried by the cables, the thickness of the conducting material, the insulation and the cooling and ventilation available. By way of example, the current may be 30 Amps per cable or more, depending upon the application. 
       FIG. 7  illustrates an exemplary conventional example of a bundle  10  of current carrying cables  1 - 9 . Cable  5 , being in the center of the bundle, will be the warmest because it is surrounded by the other cables. The following heat transfer equations may be used to determine the temperature of the cable at a given temperature for a given current capacity.
 
Conduction:  q″=−k ( dT/dx )
 
Convection: q″=hdT
 
Equivalent Resistance Method: Q=ΔT/R tot  
 
     Given these equations, the temperature for a given gauge of cable can be determined. In the example where cables  1 - 9  are 10 AWG wires at 20° C. ambient and 30 amps, the theoretical temperature of cable  5  would be approximately 64.1° C. The theoretical temperature of the same cable when using a cooling disk according to aspects of the invention (see  FIGS. 1-2 ) would be 48° C. When tested empirically at 20° C. ambient (derated), the temperature for cable  5  was 53° C. And when tested in the configuration shown in  FIG. 1 , the temperature for cable  5  was 36° C. This is a substantial (˜32%) decrease in the cable temperature. 
     In an embodiment, one or more cooling discs are used with current carrying cables to prevent heat buildup.  FIG. 1  illustrates a cooling system  100 , which includes a plurality of disc-type cooling members  102  and a number of current carrying cables  104  connected thereto. By way of example only, one end of the cables  104  may couple to a power supply device, while the other end of the cables  104  may couple to one or more computing devices (not shown). 
     In the example illustrated, the cooling members  102  support and space apart  9  cables  104 . However, any number of cables  104  may be connected to (and supported by) the cooling members  102 . The number of cables  104  may be limited due to the diameter of the cables, the diameter of the cooling members and/or the load carried by the cables.  FIG. 2  illustrates an enlarged view of a series of the cooling members  102  without the cables  104 . In one case, the thickness of each cooling member  102  is on the order of 0.25 to 0.5 inches. In other examples, the thickness may be less than 0.25 inches (e.g., 0.15 inches) or greater than 0.5 inches (e.g., 1 inch, 2 inches or more). 
     In this embodiment, a plurality of cooling members  102  is desirably employed to cool and support the cables  104 . The number of cooling members  102  that is used may vary depending upon the system configuration. For instance, depending upon how many feet or meters the cables must span, there may be only a few cooling members used (e.g., 2-5), or a dozen or more may be used. Desirably, cooling members  102  are spaced apart on the order of every 6 or 12 inches along the length of the cable bundle. 
       FIGS. 3A-B  illustrate a front or cutaway view of a cooling member  102  with and without the cables  104 , respectively. The front or rear side (or cutaway cross section) shown in this example illustrates that the cooling member  102  may have a generally circular perimeter  106 . The cooling member  102  may also include an inner perimeter defining a generally circular central opening  108 . The central opening  108  is preferably equidistant from the cables  104 . 
     In one example, the outer diameter (“OD”) of the cooling member  102  is determined according to the following equation: 
             OD   =     n   *       d   c     ⁡     (       1   π     +     1   3       )               
where n is equal to the number of conductors and d c  is the conductor diameter.
 
     In another example the diameter of the inner central opening (“ID”) is determined according to the following equation: 
     
       
         
           
             ID 
             = 
             
               ( 
               
                 
                   0.85 
                   * 
                   n 
                   * 
                   
                     d 
                     c 
                   
                 
                 π 
               
               ) 
             
           
         
       
     
     In a further example, the offset between adjacent cables (centerline to centerline) is determined according to the following equation: 
     
       
         
           
             Offset 
             = 
             
               ( 
               
                 
                   OD 
                   2 
                 
                 - 
                 
                   
                     0.75 
                     * 
                     
                       d 
                       c 
                     
                   
                   2 
                 
               
               ) 
             
           
         
       
     
     The spacing between each adjacent cable may be in radial coordinates or in degrees and radius (or offset). Radial coordinates (θ) may be used according to θ=360/n (in units of degrees). 
       FIG. 3B  shows that the cooling member  102  includes receptacles  110  for each of the cables  104 . In this example, the receptacles  110  are formed as arcuate or semicircular notches  112  disposed along the perimeter  106 . Here, the receptacles include opposing outer lips  114  on either side, which desirably are formed along the perimeter  106 . The outer lips  114  help protect the cables when installing them into the slots/receptacles. The receptacles  110  are desirably uniformly distributed along the perimeter  106 . The outer lips  114  forming the opening to a given receptacle have a smaller spacing (S R  in  FIG. 3B ) between them than the diameter (D C  in  FIG. 3A ). D c  represents the diameter of the slot/receptacle where the cable is received. D c  is desirably optimized for mechanical and thermal reasons. Spacing S R  need not be substantially smaller than the diameter D C ; but rather allows for the cable to be easily snapped into place or otherwise secured while permitting removal from the receptacle without damaging the cable. 
     While the receptacles  110  are shown as being substantially semicircular or arcuate, other shapes conforming to the cross-sectional configuration of the cables  104  may be employed. Similarly, the perimeter  106  and/or the central opening  108  may have non-circular geometric shapes. By way of example only, the central opening and the perimeter may be hexagonal, octagonal, nonagon, decagon, etc. These shapes may be chosen depending upon the number of cables the cooling member  102  supports. 
     The central opening  108 , the spacing between cables along the periphery of the cooling members  102 , and the spacing between neighboring cooling members all promote air cooling of the cables. In one example, the cooling members  102  also function as an insulated surface or a non-conductor. More specifically, the cooling members are desirably thermal and electric insulators. Thus, the cooling members in this case do not act as heat sinks. They also act to decouple the effects of cables acting on other cables in a bundle, for instance by reducing induction effects between cables. 
     In one alternative, the cooling members are formed of plastic or a thermoplastic polymer such as polyvinyl chloride (“PVC”). The material (or materials) used to fabricate the cooling members should be selected to withstand the same or higher temperatures as those of the insulation temperature ratings for the cables that are to be cooled. In one example, the cooling members are made via an injection molding process, although other processes may be employed. 
       FIGS. 4 and 5  illustrate an alternative cooling member configuration in accordance with additional aspects of the invention. In this configuration, an elongated disc-type cooling member  202  is formed. The member  202  may be extruded in a preconfigured length. According to one embodiment, the member  202  may be cut or separated into a number of thinner cooling members  102 . As shown in  FIG. 4 , cooling system  200 , which includes elongated disc-type cooling member  202  that may be used with number of current carrying cables  204  connected thereto. As with the embodiment of  FIG. 1 , one end of the cables  204  may couple to a power supply device, while the other end of the cables  204  may couple to one or more computing devices (not shown). 
     In the example illustrated, the cooling member  202  support and space apart  9  cables  204 . However, any number of cables  204  may be connected to (and supported by) the cooling members  202 . The number of cables  204  may be limited due to the diameter of the cables, the diameter of the cooling members and/or the load carried by the cables.  FIG. 5  illustrates a view of the cooling member  202  without the cables  204 . 
     In this embodiment, a single cooling member  202  may be employed to cool and support the cables  204 . The number of cooling members  202  that are used may vary depending upon the system configuration. For instance, depending upon how many feet or meters the cables must span, there may be only one cooling member  202  used, or a plurality of cooling members  202  may be used. The cooling member(s)  202  may be used alone or in combination with the cooling member  102  discussed above. 
     The cross-sectional configuration of the cooling member  202  is desirably equivalent to the configuration of the cooling member  102  shown in  FIGS. 3A-B . Thus, the cooling member  202  may have the generally circular perimeter  106 . The cooling member  202  may also include the generally circular central opening  108 . 
     Similarly, the receptacles  110  may be formed as arcuate or semicircular notches  112  disposed along the perimeter  106 . And as with cooling member  102 , the receptacles for cooling member  202  may include opposing outer lips  114  on either side, which desirably are formed along the perimeter  106 . The outer lips  114  forming the opening to a given receptacle have a smaller spacing (S R  in  FIG. 3B ) between them than the diameter D C  in  FIG. 3A ). Spacing S R  need not be substantially smaller than the diameter D C ; but rather allows for the cable to be easily snapped into place or otherwise secured while permitting removal from the receptacle without damaging the cable. 
     While the receptacles  110  for cooling member  202  may be substantially semicircular or arcuate, other shapes conforming to the cross-sectional configuration of the cables  204  may be employed. Similarly, the perimeter  106  and/or the central opening  108  may have non-circular geometric shapes. By way of example only, the central opening and the perimeter may be hexagonal, octagonal, nonagon, decagon, etc. These shapes may be chosen depending upon the number of cables the cooling member  102  supports. 
     The central opening  108  and the spacing between cables along the periphery of the cooling members  102  promote air cooling of the cables. In one example, the cooling member  202  also functions as an insulated surface. More specifically, the cooling member  202  is desirably a thermal and electric insulator. Thus, the cooling member in this case does not act as a heat sink. Rather, it acts to decouple the effects of cables acting on other cables in a bundle. 
       FIG. 6  illustrates a configuration  300  illustrating one of the cooling members  202  for cooling a plurality of cables  204  in an enclosure. This configuration  300  also shows the use of conventional cable ties  302  and wraps  304 , which bundle the cables  204 , which can be detrimental to the heat dissipation of the cables, particularly the cables in the interior of the bundle. While a cooling member  202  is shown, cooling members  102  may be used in place of or in combination with cooling member  202 . The use of such cooling members may reduce the temperature among the cables within a bundle by 15 degrees Celsius or more as discussed above. 
     Although aspects of the invention herein have been described with reference to particular embodiments, it is to be understood that these embodiments are merely illustrative of the principles and applications of the invention. It is therefore to be understood that numerous modifications may be made to the illustrative embodiments and that other arrangements may be devised without departing from the spirit and scope of the invention as defined by the appended claims.