Abstract:
A cooling system for telecommunication equipment including a heat exchanger having outwardly protruding, parallel fins to dissipate heat. Each pair of fins forming an elongated channel. The system includes an ejector positioned within each channel to direct pressurized air through the channels while dragging ambient air through the channels along with the pressurized air. The pressurized and ambient air passing through the channels increases the ability of the fins to dissipate heat. Since the source of pressurized air can be remote from the telecommunications equipment in a protected and easily accessed location, the ejectors provide a rugged cooling mechanism adjacent the heat exchanger with no moving parts.

Description:
BACKGROUND  
         [0001]    1. Field of the Invention  
           [0002]    The present invention, in certain respects, relates to cooling electronic equipment. In other respects, the present invention relates to cooling telecommunication equipment in harsh environments.  
           [0003]    2. Description of Background Information  
           [0004]    There is an ongoing need to cool high power electronic equipment efficiently and reliably. This is especially true with cellular communication base station antennas. These antennas are generally mounted atop high towers or masts in order to effectively transmit and receive signals. The environment in which these antennas are positioned is often hostile due to high temperatures, dust and other particles in the air, as well as to birds and insects. Therefore, previous attempts to cool such antennas have been ineffective. Atop towers and masts, use of conventional fans and blowers have limited life expectancy and are difficult to service. Natural convection heat exchangers are also deficient due to their excessive size and weight, which results in decreased efficiency. A harsh environment further decreases the efficiency of natural convention heat exchangers.  
           [0005]    Thus, there is a need for an efficient cooling system that is impervious to environmental conditions.  
         SUMMARY OF THE INVENTION  
         [0006]    The present invention is provided to improve cooling systems and cooling methods for electrical systems. More specifically, improved systems and methods are presented to provide a cooling system for electrical equipment of active cellular communication base station antennas that is efficient and that can be employed in hostile environmental conditions.  
           [0007]    A cooling system of the invention can include a finned, heat exchanger connected to a base station antenna atop a tower or pole. Air nozzles can be positioned in between pairs of fins and pressurized air forced through the nozzles blows between the pairs of fins to cool the fins. Ambient air surrounding the fins and nozzles can be dragged along with the pressurized air to further aid in cooling the fins. The pressurized air can be supplied to the nozzles from a remote source off the tower or pole so that the air source can be easily accessed or repaired. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0008]    The present invention is further described in the detailed description which follows, by reference to the noted drawings by way of non-limiting exemplary embodiments, in which like reference numerals represent similar parts throughout the several views of the drawings, and wherein:  
         [0009]    [0009]FIG. 1 is a perspective view of a cellular communication base station antenna system illustrating a cooling system of the present invention;  
         [0010]    [0010]FIG. 2 is a front view of a portion of the cooling system illustrated in FIG. 1;  
         [0011]    [0011]FIG. 3 is a bottom view of the cooling system illustrated in FIG. 2;  
         [0012]    [0012]FIG. 4 is a sectional view of the cooling system taken along line  4 - 4  in FIG. 3;  
         [0013]    [0013]FIG. 5 is a schematic view of the pneumatic system of the cooling system illustrated in FIG. 1;  
         [0014]    [0014]FIG. 6 is a cross-sectional view of the cooling system taken along line  6 - 6  in FIG. 4;  
         [0015]    [0015]FIG. 7A is a front view of the cooling system similar to FIG. 2, but with a partial enclosure member installed thereon;  
         [0016]    [0016]FIG. 7B is a bottom view of the cooling system illustrated in FIG. 7A with the partial enclosure member in place;  
         [0017]    [0017]FIG. 8A is a front view of the cooling system similar to FIG. 2, but with a full enclosure member installed thereon;  
         [0018]    [0018]FIG. 8B is a bottom view of the cooling system illustrated in FIG. 8A with the full enclosure member in place;  
         [0019]    [0019]FIG. 9 is an alternate embodiment of the cooling system illustrating horizontally extending fins and nozzles;  
         [0020]    [0020]FIG. 10 is an alternate embodiment of the cooling system illustrating a pair of stacked heat exchangers;  
         [0021]    [0021]FIG. 11 is a bottom view of an embodiment of the cooling system for which testing was performed;  
         [0022]    [0022]FIG. 12 is a perspective of the cooling system shown in FIG. 11 showing a series of power resistors conductively connected thereto;  
         [0023]    [0023]FIG. 13 is a chart showing measured air flow velocities for heat exchanger channels with and without a cover on the heat exchanger;  
         [0024]    [0024]FIG. 14 is a graph showing the computed relation between the mean temperature difference and the velocity of air flow through the heat exchanger channels;  
         [0025]    [0025]FIG. 15 is similar to FIG. 2 but illustrates the nozzles and manifold at the bottom of the heat exchanger;  
         [0026]    [0026]FIG. 16 is a longitudinal cross-sectional view of the nozzle of the invention similar to FIG. 4, but illustrating a cover in a closed position mounted on the nozzle, with no air flowing through the nozzle; and  
         [0027]    [0027]FIG. 17 is a cross-sectional view similar to FIG. 16, but illustrating the cover in an open position with air flowing through the nozzle. 
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0028]    The cooling system of the invention is applicable to a variety of systems needing to more efficiently dissipate heat. The cooling system of the invention is particularly useful with systems having a heat dissipating element positioned in an environment that is not environmentally suited rotating fans or that is not easily accessible. FIG. 1 illustrates a particular embodiment of the invention where the elements dissipating heat are both in hostile environmental conditions and not easily accessible. That is, FIG. 1 generally illustrates an active cellular communication base station antenna system  10  utilizing a cooling system  12  of the present invention. Since the cooling system  12  has no moving parts at the remote location of the antenna subsystem  14 , a more efficient and durable cooling system is achieved for the antenna system  10 .  
         [0029]    The base station antenna system  10  includes an antenna subsystem  14  mounted in a raised fashion on a support structure  16 . Control equipment  20  for the antenna subsystem  14  is preferably positioned remote from the support structure  16 , for example, on a base  17 . The cooling system  12  can include a finned heat exchanger  22  connected to the antenna subsystem  14  for dissipating heat generated by the antenna subsystem  14 , an ejector assembly  24  having nozzles or ejectors  26  positioned between each pair of fins, and an air compressing mechanism  23  that can be located remote from the ejectors  26  and the antenna subsystem, for example, on base  17 .  
         [0030]    The antenna subsystem  14  can be of any type and is illustrated as being mounted on a support structure such as mast  16  as illustrated in FIG. 1. Of course, antenna subsystem  14  can be mounted on any appropriate support structure that raises the antenna to its appropriate height. This may include a truss structure and can include support structures  16  mounted on the ground or on another structure, such as a building. Control equipment  20  for the base station antenna system  10  can be positioned as appropriate and is preferably positioned remote from the support structure  16  and on base  17 . The control equipment  20  for the base station antenna system  10  can be operatively connected to the antenna subsystem  14  in a usual manner, such as via a series of cables  21 .  
         [0031]    The heat exchanger  22  is conductively connected to one or more electrical or heat producing components of the antenna subsystem  14 . As such, heat generated by the antenna subsystem  14  is drawn therefrom into the heat exchanger  22 , by heat conduction. The heat exchanger  22  can be formed of a highly heat conductive material to aid in the heat conduction process. Heat generated by the electrical components of the antenna subsystem  14  flows through the conductive connectors into the heat exchanger  22 .  
         [0032]    As shown in FIGS. 2 and 3, the heat exchanger  22  can be equipped with a series of spaced, heat dissipating fins  32  that extend outwardly from a body portion  34  of the heat exchanger. The fins  32  increase the area of an exterior surface  35  of the heat exchanger  22  and therefore increase the heat exchanging capacity of the heat exchanger  22 . Heat flowing into the heat exchanger  22  from the antenna subsystem  14  is liberated from the exterior surface  35  into the atmosphere through heat convection. The fins  32  can be formed in various configurations depending on the desired heat exchanging properties. For example, the fins  32  can be substantially flat or can be corrugated.  
         [0033]    Natural convection from ambient airflow dissipates heat from the heat exchanger  22  and provides a flow of cooling medium such as atmospheric air across the exterior surface  35  of the heat exchanger  22 . An increase in the area of the exterior surface  35 , such as by adding fins  32 , corresponds to an increase in heat dissipation possible by the heat exchanger  22 .  
         [0034]    As illustrated in FIGS. 1 and 2, the ejector assembly  24  has a series of ejectors or nozzles  26  that can be connected to a manifold structure  28 . The manifold structure  28  can be, in turn, connected to a conduit  30  that extends from the compressing mechanism  23  so that air can be supplied to the manifold  28  by conduit  30 .  
         [0035]    Although the manifold structure  28  can take numerous forms, one form is illustrated in FIGS. 2 and 3. The illustrated manifold structure  28  can extend along the heat exchanger  22  transverse to the fins  32  while extending through the fins  32  and can include a series of ejectors  26  connected thereto. The manifold structure can be connected to the conduit  30  on one end  36 , while being sealed on an opposite end  38 . As such, pressurized air from the compressor  23  can enter the manifold structure  28  at the end  36  thereof and can exit through each of the ejectors  26 . The manifold structure  28  can be a tubular member with a series of spaced openings for attachment to ejectors  26 , which correspond to the cavities between each pair of fins  32 . The manifold structure  28  can be formed of any suitable material. Preferably, manifold  28  is formed from a non-corrosive material such as stainless steel or plastics. As illustrated in FIG. 1, the manifold structure  28  may be mounted to a portion of the antenna subsystem  14 , for example with a pair of connecting members  39  (see also FIG. 2), such that the ejectors  26  are disposed between corresponding fins  32  of the heat exchanger  22 . The manifold  28  may be mounted on the bottom side of the finned heat exchanger, thus using the natural convection flow effect of upwardly increasing temperature.  
         [0036]    As illustrated in FIG. 4, an ejector  26  can be secured within a corresponding opening  40  within the manifold structure  28  in any appropriate manner. For example, the ejectors  26  may be securely press-fit within the corresponding openings  40 , or that they may be welded in position. Also, it may be advantageous for the ejectors  26  to be removably connected to the manifold structure  28 , such as by a threaded connection, as illustrated.  
         [0037]    As further shown in FIG. 4, each of the ejectors  26  has a central opening  42  that extends longitudinally though an ejector body  44 . One (entry) end  48  of the central opening  42  is communicated with an air pathway  46  of the manifold structure  28 , while an opposite (exit) end  50  of the central opening  42  communicates with the atmosphere. The central opening  42  may be configured with a venturi shape, as shown in FIG. 4 to increase the velocity of air flowing therethrough. Although the dimensions of the nozzle can vary depending upon the desired performance and size characteristics, the entry end  48  can exhibit an approximately 120 degree converging funnel shape and the central opening  42  can exhibit an approximately 10-20 degree diverging funnel shape. Also, the exit diameter  110  of the nozzle is preferably approximately 1.5 times larger than the restrictor diameter  120 , as seen in FIG. 4.  
         [0038]    It may be advantageous for each ejector  26  to include a polymer cover to protect the exit end  50  of the central opening  42 . One preferred design is a “duckbill” elastomeric cover  52  which remains closed as seen in FIG. 16 when no air passes through nozzle  26  and then, as seen in FIG. 17, cover  52  opens when air is forced through nozzle  26 . Thus, the cover  52  can keep unwanted debris from entering nozzle  26  and keeps the nozzle  26  free from clogging.  
         [0039]    As shown in FIG. 1, it may be preferable for the heat exchanger  22  and the ejector assembly  24  to be mounted on the antenna subsystem  14  such that the ejectors  26  point generally downwardly. In this manner, the central openings  42  of the ejectors  26  may be less prone to contamination and/or damage than in an upwardly pointing configuration. On the other hand, as seen in FIG. 15, upwardly pointing nozzles are thermally more effective, as the flow increases by natural convection effects.  
         [0040]    It is noted that the cooling system of the present invention can be made generally impervious to environmental conditions by enclosing all of the mechanical mechanisms such as an air compressor  23  within an enclosure  18 , as shown in FIG. 1. It is noted that the compressing mechanism  23  may require relatively little maintenance, since it can be disposed within the enclosure  18  and is not exposed to severe environmental conditions. Furthermore, the conduit  30  may be formed of any appropriate material such as weather resistant hose or pipe to avoid degradation of the conduit  30 , for example, a suitable medium-pressure polymer hose or non-corrosive pipe could be employed. The other structures such as the manifold structure  28  and the ejectors  26  may also be formed of non-corrosive materials to avoid degradation. In a case where the compressing mechanism  23  requires servicing, the compressing structure  23  is readily accessible and serviceable.  
         [0041]    The general operation of the cooling system of the present invention is as follows. FIG. 5 shows a schematic diagram representing the cooling system  12  of the present invention. As shown, the compressing mechanism  23  preferably includes an electric motor  54 , which is operatively coupled to a pneumatic compressing structure  56 . The pneumatic compressing structure  56  compresses air from the atmosphere through a serviceable inlet filter  57  and produces a flow of compressed air. The compressing structure  56  is connected to a valve  58 , which allows the compressing structure  56  to be isolated and the flow of compressed air to be redirected, preferably into the atmosphere, so that the various components of the cooling system  12  may be serviced. A gauge  60  is communicated with the air flow between the compressing structure  56  and the valve  58  to monitor the pressure of the air therein. A pressure reducing valve  62  maintains the air flow to the ejector assembly  24  at a constant pressure. It may also be advantageous to include a micronic filter  64 , which screens particles from the air flow in order to prevent clogging of the central openings  42  of the ejectors  26 . The air flow is then communicated to the ejector assembly  24  via the conduit  30 .  
         [0042]    Referring to FIG. 6, the compressing mechanism  23  produces a compressed fluid such as compressed air  25 , which is directed to the ejectors  26 . The ejectors  26  then emit and direct a pressurized stream of air (indicated at A in FIG. 6) between the corresponding fins  32  of the heat exchanger  22 . The stream of air A then flows generally between the fins  32  and within a channel or cavity  66 , cooperatively formed between adjacent fins  32  and a surface  33  of the body portion  34 , along the length of the heat exchanger  22 .  
         [0043]    The venturi configuration of the central openings  42 , as described previously, serves to increase the velocity of the pressurized air flowing through the ejectors  26 . Therefore, upon exit from each ejector  26 , the corresponding stream of air A has a relatively high velocity. It is preferred that the velocity will be as high as possible. Sonic or supersonic velocities give better cooling performance. It is noted that a velocity of the total air flow in between the fins of about 2 m/sec may be advantageous for inducing efficient forced convection. The high velocity air A exiting the ejector  26  “pulls” or “drags” the atmospheric air proximate the exit end  50  of the ejector  26  producing a pressure differential (i.e., a suction force toward the exit end  50 ). As such, air from the atmosphere is pulled (indicated at B in FIG. 6) into the stream of air (indicated at C in FIG. 6) exiting the ejector  26  and forced down the channel  66 . Therefore, volumetric flow rate of air traveling across the exterior surface  35  of the heat exchanger  22  is increased, effectively increasing the heat dissipation capacity of the heat exchanger  22 .  
         [0044]    Various configurations are possible for the cooling system  1 . For example, the shape and spacing of the fins  32  can be varied as well as the shape and specific dimensions of the ejectors  26  to obtain desired relationships and cooling characteristics for the desired implementation of the cooling system. Additionally, the manner of providing compressed air or other fluid to ejectors  26  can take various forms, such utilizing a single, integrally formed manifold  28 .  
         [0045]    There are various additional embodiments of the cooling system of the present invention that are possible. The embodiments shown and described herein are exemplary examples and are illustrated with respect to the illustrated system of FIGS.  1 - 6 . Other embodiments are, of course, possible.  
         [0046]    [0046]FIGS. 7A and 7B show a partial enclosure member  70  attached to the heat exchanger  22 . The partial enclosure member  70  serves to overlay and enclose a portion of the channels  66  of the heat exchanger  22 . The partial enclosure member  70  prevents the air stream from exiting the corresponding channels  66  prior to reaching the far end of each channel  66  to thereby maintain a high volumetric flow rate across the heat exchanger  22 . Since the air stream is substantially prevented from dispersing into the atmosphere until the stream passes over a significant surface area of the heat exchanger  22 , the efficiency of the cooling system  12  may be enhanced. Enclosure member  70  can be positioned at various positions with respect to the nozzles  26 . For example, the enclosure member  70  can begin to cover the channels  66  at the nozzles  26  such that the edge  71  of the cover  70  is aligned with the nozzles  26  and is positioned over the nozzles  26 , as illustrated in FIG. 7A. Alternatively, the beginning of the cover  70  can be positioned upstream or downstream of channel  66  with respect to each nozzle  26  to permit the desired amount of ambient air adjacent each nozzle  26  to be “dragged” into and through channel  66  by the air exiting from nozzle  26 .  
         [0047]    [0047]FIGS. 8A and 8B show a full enclosure member  72  attached to the heat exchanger  22 . Similar to the embodiment illustrated in FIGS. 7A and 7B, the air streams are directed over a significant surface area of the heat exchanger  22  to enhance the efficiency thereof. Member  72  has an edge  73  that is preferably positioned over the nozzles  26 . With either of the embodiments shown in FIGS. 7A through 8B, it may be preferable for the enclosure members  70 ,  72  to be relatively unrestrictive to heat flow. In other words, it may be preferable for the enclosure members  70 ,  72  to be substantially impregnable to air flow, to maintain the air stream integrity, while allowing heat to readily dissipate therethrough to prevent heat build-up within the heat exchanger  22 . It is contemplated that among the many options in forming the enclosure members  70  and  72 , a relatively thin polymer sheet-like member may be utilized as the enclosure members  70 ,  72 . It is also contemplated that a relatively thin sheet-like metallic member may also be utilized for the enclosure members  70 ,  72 , this may be preferred due to the addition of heat dissipating surfaces.  
         [0048]    [0048]FIG. 9 illustrates an additional embodiment of a heat exchanger  22 ′ and ejector assembly  24 ′ of the cooling system of the present invention. In this embodiment, the heat exchanger  22 ′ includes a laterally extending, longitudinally spaced series of fins  32 ′. Additionally, for this embodiment, the manifold structure  28  may extend the length of the heat exchanger  22 ′ and include a greater amount of ejectors  26 ′ disposed within channels  66 ′ of the heat exchanger  22 ′. As shown, the ejector assembly  24 ′ utilizes a larger number of ejectors  26 ′ as compared with the embodiment illustrated in FIGS.  1 - 8 B. It is noted that a rate of air flow through each ejector  26 ′ may be relatively lower than that through each ejector  26  since more ejectors  26 ′ are used, however, as shown, the air streams (indicated at D in FIG. 9) have a relatively shorter distance to travel if the fins  32 ′ are shorter and are directed along a width of the heat exchanger  22 ′. As such, an average flow rate across the heat exchanger  22 ′ may be comparable to that across heat exchanger  22 . This embodiment may have the advantage of producing lower temperature differences between air entering the channels  66  and the air exiting the channels  66  to ambient air, thus, keeping the heat exchanger at a more uniform temperature.  
         [0049]    [0049]FIG. 10 shows yet another embodiment of the invention in the form of a set of stacked heat exchangers  82 . It is contemplated that two or more heat exchangers  82  may be utilized in this embodiment. As shown, this embodiment includes one ejector assembly  24  for each of the heat exchangers  82 . The ejector assemblies  24  are interconnected at a connecting structure  84 , which is connected to the conduit  30 . This embodiment may be used to enhance the efficiency of the cooling system of the present invention, or may be used to cool separate components of the antenna subsystem  14   
         [0050]    The following includes a tested configuration of the cooling system of the invention along with observations and data from conducted tests. The tested configuration and resulting data is not meant to be limiting with respect to the scope of the present invention but illustrates specific performance characteristics associated with a specific configuration of an apparatus employing some of the principles of the invention.  
         [0051]    [0051]FIGS. 11 and 12 show a test embodiment of a heat exchanger at  100  and ejector assembly  101 , as tested. The ejector assembly  101  includes a series of fifteen laterally spaced ejectors  102 . As shown, the heat exchanger  100  includes sixteen fins  104 , extending upwardly from a body portion  105  of the heat exchanger  100 . The fins  104  extend the length of the heat exchanger  100  and are laterally spaced from each other along the width of the body portion  105 . There is approximately 13 mm between adjacent fins  104 , forming fifteen channels (c 1  to c 15 ), each having a width of approximately 13 mm, across the width of the heat exchanger  100 . Each channel c 1  to c 15  has a cross-sectional area of approximately 2.4 cm 2 , providing a total flow area of approximately 36 cm 2 .  
         [0052]    As further shown, four power resistors  106  are attached to an opposite side of the body portion  105 . The power resistors  106  allow the amount of heat input to the heat exchanger  100  to be predetermined and controlled. A pair of thermocouples  108  measure a temperature gradient of the heat exchanger  100  between one end (proximate the ejector assembly) and an opposite end (opposite the ejector assembly  101 ) thereof.  
         [0053]    The test were conducted under 3 bar and 3.5 bar (gauge) pressures feeding the ejector assembly  101 . The heat load from the power resistors  106  was 147 watts. The ambient temperature was 26° C. and varied ±1° C. during the test period.  
         [0054]    [0054]FIG. 13 shows the measured air velocities within the channels (c 1 -c 15 ) of the heat exchanger  100  with a cover (similar to the embodiment illustrated in FIG. 7A) and without a cover (similar to the embodiment illustrated in FIG. 2). The average air velocity was approximately 2.17 m/sec. The average temperature difference between the thermocouples  108  was approximately 12.6° C. The amplification ratio between the volumetric flow rate of the air through the channels (c 1 -c 15 ) and the air exiting the ejectors  102  was found to be c=30.5; meaning the volume flow rate of air through the channels was 30.5 times the volume flow rate of air through the ejectors. Furthermore, the convection factor of the heat exchanger  100 , as tested with the ejector assembly  101 , was approximately 38 W/(m 2 ° C.), compared with approximately 5.5 W/(m 2 ° C.) for natural convection.  
         [0055]    [0055]FIG. 14 shows a computed model of the relation between the air speed (in m/sec) of the air flowing through the channels of the heat exchanger and the average temperature difference (in degrees Celsius) between the temperature of the fins of the heat exchanger and the temperature of the ambient air. As shown, for natural convection (air speed equal to approximately 0 m/sec), the mean temperature difference is approximately 88° C., while for an air speed of approximately 2.5 m/sec, the mean temperature difference is approximately 11° C.; meaning heat is more rapidly liberated from the heat exchanger under forced convection. As stated previously, the average air velocity as tested was approximately 2.17 m/sec. From the computed model described above, this velocity corresponds to a mean temperature difference of approximately 13° C. The measured mean temperature difference of the cooling system, as tested, was approximately 14° C., which closely correlates to the computed model. As such, it is shown that the computed efficiency of the cooling system is possible with the present invention.  
         [0056]    While the invention has been described with reference to the certain illustrated embodiments, the words which have been used herein are words of description, rather than words or limitation. Changes may be made, within the purview of the appended claims, without departing from the scope and spirit of the invention in its aspects. Although the invention has been described herein with reference to particular structures, acts, and materials, the invention is not to be limited to the particulars disclosed, but rather extends to all equivalent structures, acts, and materials, such as are within the scope of the appended claims.