Abstract:
An improved HTSC filter system design. An improved HTSC filter system comprises a cryocooler and dewar assembly, a heat dissipation assembly and at least one heat pipe providing a thermal coupling between said heat dissipation assembly and said cryocooler and dewar assembly. In a preferred embodiment, the cryocooler and dewar assembly is environmentally sealed within a double-walled aluminum canister, and the heat pipes are formed from stainless steel tubes having a predetermined amount of ammonia provided therein.

Description:
FIELD OF THE INVENTION  
         [0001]    The present invention relates generally to high temperature superconducting (HTSC) filter systems for use in, for example, cellular PCS systems and, more particularly, to tower mountable HTSC filter systems and enclosures.  
         BACKGROUND OF THE INVENTION  
         [0002]    Recently, substantial attention has been devoted to the development of high temperature superconducting radio frequency (RF) filters for use in, for example, cellular telecommunications systems. However, such filters are extremely temperature sensitive, and the use of such filters within tower mounted communications systems can raise significant heat management issues.  
           [0003]    One such issue, is the issue of cryocooler “cold finger” temperature regulation, which is addressed in co-pending, U.S. patent application Ser. No. 09/204,897, filed on Dec. 3, 1998 and entitled “TEMPERATURE CONTROL OF HIGH TEMPERATURE SUPERCONDUCTING THIN FILM FILTER SUBSYSTEMS,” the disclosure of which is incorporated herein by reference.  
           [0004]    However, another equally important issue, and one that is addressed herein, is the issue of heat dissipation. Stated somewhat differently, for an HTSC filter system to function properly, the heat of compression generated by a cryocooler incorporated within the system must be efficiently and reliably rejected to the ambient environment. If that heat cannot be efficiently and reliably rejected, it may have a serious impact upon system operation and, depending upon the circumstances, could result in inefficient cryocooler operation and/or cryocooler shut down.  
           [0005]    Those skilled in the art also will appreciate that, when multiple HTSC filters are deployed, for example, within a dewar cooled by a cryocooler, and the cryocooler is mounted, for example, on a telecommunications tower, substantial durability and reliability issues may arise. For example, when a system is to be mounted at the top of a tower, the system must be able to withstand significant changes in climate and weather, and the system must be reliable and require minimal maintenance. In this latter regard, reliability can be improved, and maintenance requirements reduced, through the use of a minimal number of moving parts. Thus, where a cryocooler and associated HTSC filter system are to be mounted atop a tower, it would be desirable to utilize a cryocooler including as few moving parts as is possible. Similarly, any associated heat management system should include a minimum number of moving parts.  
           [0006]    In view of the foregoing, it is believed that those of ordinary skill in the art would find an improved system for “managing” the heat of compression generated by a cryocooler within a tower-mounted HTSC filter system to be quite useful. It also is believed that those skilled in the art would find a tower-mounted HTSC that is highly reliable and utilizes a minimum number of moving parts to be useful.  
         SUMMARY OF THE INVENTION  
         [0007]    The present invention is directed to an improved heat management system and design for a tower-mounted HTSC filter system.  
           [0008]    In one particularly innovative aspect, a tower-mounted HTSC filter system in accordance with the present invention utilizes a plurality of heat pipes to carry heat away from a cryocooler body to a finned heat dissipation assembly. Moreover, an HTSC filter system in accordance with the present invention may comprise a environmentally sealed housing having, for example, a Stirling cycle cryocooler and dewar assembly mounted therein, a heat dissipation assembly coupled to a selected surface of the environmentally sealed housing, and a plurality of heat pipes providing a thermal coupling between the heat dissipation assembly and one or more heat rejecting blocks of the cryocooler.  
           [0009]    In a presently preferred embodiment, the heat pipes comprise sealed stainless steel tubes that are filled with ammonia, and the environmentally sealed housing comprises a double-walled aluminum cylindrical container.  
       
    
    
       [0010]    Other objects and features of the present invention will become apparent from consideration of the following description taken in conjunction with the accompanying drawings.  
       BRIEF DESCRIPTION OF THE DRAWINGS  
       [0011]    [0011]FIG. 1 is an exploded view of a tower-mountable HTSC filter system in accordance with the present invention.  
         [0012]    [0012]FIG. 2 is a cross-sectional view of a heat pipe in accordance with the present invention.  
         [0013]    [0013]FIG. 3 illustrates how the HTSC filter system of FIG. 1 may be mounted, for example, on a telephone pole or other tower. 
     
    
     DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS  
       [0014]    Turning now to the drawings, FIG. 1 provides an exploded illustration of a tower mountable HTSC filter system  10  in accordance with a preferred form of the present invention. As shown, the HTSC filter system  10  includes a frame  12 ; a heat dissipation assembly  14 ; an electronics plate assembly  16 ; a controller assembly  18 ; a lightning protector assembly  20 ; a capacitor assembly  21 ; and a cryocooler, dewar and heat pipe assembly  22 .  
         [0015]    Preferably, the heat dissipation assembly  14 , electronics plate assembly  16 , controller assembly  18 , lightning protector assembly  20 , capacitor assembly  21 , and cryocooler, dewar and heat pipe assembly  22  are mounted to the frame  12 , and the resulting subassembly is mounted within a housing or canister  60 . Further, in some embodiments, it may be desirable for the HTSC filter system  10  to further include, as part of the heat dissipation assembly  14 , a screened enclosure  23  including one or more fan units (not shown). However, the HTSC filter system  10  has been found to perform adequately without requiring the use of such fan units.  
         [0016]    The cryocooler, dewar and heat pipe assembly  22  comprises, for example, a Stirling cycle cryocooler unit  24 , such as that described in co-pending U.S. patent application Ser. No. 09/175,924, which is entitled “Cryocooler Motor with Split Return Iron” and is hereby incorporated by reference; a dewar assembly  26  coupled to the cryocooler unit  24 ; and a plurality of heat pipes  28 . Those skilled in the art will appreciate that the dewar assembly  26  preferably includes a heat-sink (not shown) whereon a plurality of HTSC filters (not shown) may be mounted. Such a heat-sink is shown, for example, in co-pending U.S. patent application Ser. No. 09/204,897, entitled “TEMPERATURE CONTROL OF HIGH TEMPERATURE SUPERCONDUCTING THIN FILM FILTER SUBSYSTEMS,” which was filed on Dec. 3, 1998, and is referenced above.  
         [0017]    The heat pipes  28  preferably are formed from stainless steel tubing and have a predetermined amount of ammonia provided therein. The heat pipes  28  provide a thermal coupling between the heat dissipation assembly  14  and one or more heat rejector blocks  30  provided on an exterior of the cryocooler unit  24 . It will be appreciated that the heat pipes  28  provide an efficient means for moving excess heat away from the cryocooler unit  24  and for delivering that heat to the heat dissipation assembly  14 .  
         [0018]    The heat dissipation assembly  14  preferably comprises a base plate  32  and a plurality of vertically oriented fins  34 . The base plate  32  and fins  34  preferably are formed from aluminum alloy and have high thermal conductivity. In addition, the base plate  32  preferably has a heat pipe mounting section (not shown) that is inclined 7° with respect to horizontal. The heat dissipation assembly  14  also preferably is chemically treated to improve its resistance to environmental factors such as precipitation.  
         [0019]    Turning now to FIG. 2, the heat pipes  28  preferably have a wire mesh  40 , or similar structure, provided within an evaporator end  42  thereof. The wire mesh  40  preferably comprises  120  wire-per-inch stainless steel wire mesh and is provided along an internal surface or internal diameter  44  of the heat pipe  28 . The wire mesh  40  provides an even distribution of additional surface area for evaporation of liquid ammonia. Thus, those skilled in the art will appreciate that the end  42  of each heat pipe  28  preferably is coupled to the heat rejector block  30  of a cryocooler unit  24 .  
         [0020]    As alluded to above, the heat pipes  28  preferably are shaped such that, when the heat pipes  28  are mounted and thermally coupled to a cryocooler unit  24  and related heat dissipation assembly  14 , an upper section  46  of the heat pipes  28  forms an angle of approximately 7° with respect to horizontal. This ensures that, even if an HTSC filter system  10  incorporating the heat pipes  28  is installed +/−5° from true, the upper sections  46  of the heat pipes  28  will remain tilted with respect to horizontal. This ensures proper drainage of condensed ammonia from the upper sections  46  of the heat pipes  28 .  
         [0021]    As further shown in FIG. 2, the heat pipes  28  preferably comprise 0.5 inch diameter stainless steel tubing and have end caps  50  and  52  provided at the respective ends thereof. The end caps  50  and  52  preferably are TIG welded to respective ends of a stainless steel tube  53 . In addition, a 0.25 inch diameter pinch off tube  54  is provided at one end of the stainless steel tube  53 . When loading the heat pipes  28  with ammonia, one end of the heat pipe  28  is submerged in liquid nitrogen, and condensed ammonia is flowed into the heat pipe  28  through the pinch off tube  54 . Preferably, 3.2 grams of ammonia are flowed into the heat pipes  28 . Once the condensed ammonia has been deposited within the heat pipe  28 , the pinch off tube  54  is pinched to seal the heat pipe  28  and a cap  52  is provided over the corresponding end of the heat pipe  28  to protect the tip  55  of the pinch off tube  54 .  
         [0022]    Those skilled in the art will appreciate that a heat pipe, such as the heat pipe  28  described herein, is a unique device that can move a large quantity of heat with a very low temperature drop. Indeed, the thermal conductivity of a heat pipe  28  in accordance with the present invention is likely several thousand times that of the best metal heat conductors such as copper, silver or aluminum. It also will be appreciated that a heat pipe, when used in accordance with the present invention, provides a unique heat management tool, as it has no moving parts and is capable of providing silent, reliable, long life operation when used in conjunction with, for example, an HTSC filter system or cellular communication system.  
         [0023]    Turning again to FIG. 1, in a preferred form, the HTSC filter system  10  is sealed within a double-walled aluminum canister  60 . The double-walled canister  60  protects the HTSC filter system  10  from environmental factors, exposure to sunlight, and vandalism (i.e., gunfire). Once sealed within the double-walled canister  60 , the HTSC filter system may be mounted atop a telephone pole or other tower structure as illustrated in FIG. 4.  
         [0024]    While the invention is susceptible to various modifications and alternative forms, a specific example thereof has been shown in the drawings and is herein described in detail. It should be understood, however, that the invention is not to be limited to the particular form disclosed, but to the contrary, the invention is to cover all modifications, equivalents, and alternatives falling within the spirit and scope of the appended claims.