Abstract:
The present invention relates to a cooling system, the cooling system having a nozzle which receives coolant from a reservoir and which faces a substrate. The nozzle may be opened and closed by a thermally responsive valve allowing the coolant to be automatically metered to the substrate, thus controlling the spatial distribution of the coolant that is applied to the substrate. This approach allows hotter areas of the substrate to receive more coolant, thus eliminating nonuniformities in the thermal profile of the substrate.

Description:
BACKGROUND OF THE INVENTION  
       [0001]     1. Field of the Invention  
         [0002]     The present invention relates to a cooling system. More specifically, it relates to a cooling system which automatically meters the coolant that is applied to a substrate, based on ambient air or substrate temperature.  
         [0003]     2. Description of the Related Art  
         [0004]     Electronic systems are being manufactured with increasingly compact geometries. In a variety of applications such as telecommunications, cellular base stations and mobile phones, automotive electronics, aerospace, power distribution systems in computers, large-scale servers, military electronics and avionics, and many others, there is a need to remove heat from compact spaces. The space and performance constraints call for sophisticated cooling techniques which are easy to implement. In many applications, the absence of compact cooling techniques has jeopardized the viability of the product. Proper use of cooling technologies can also lead to important gains in efficiency and performance.  
         [0005]     A typical approach to dissipate heat is through the use of heat pipes. Heat pipes can offer significantly better heat conduction than solid metal rods of the same dimensions, and are widely used in many applications.  
         [0006]     Heat pipes consist of a hollow tube which incorporates a wicking structure, and is partially filled with liquid. One end of the heat pipe is placed in contact with the heat-generating device. At this end of the heat pipe, the liquid evaporates, and vapor travels down the hollow center of the pipe to the other end. This end is placed into contact with a cold medium, or a heat sink, or is in contact with the surrounding air, and acts to cool the vapor in the center of the tube to the condensation temperature. This liquid, after condensation, is transported back to the hot end of the tube by capillary forces within the wicking structure.  
         [0007]     Many common designs include a substrate, often porous, which is either in close proximity to, or in direct contact with, the heat pipe. These designs often use a cooling system to disperse coolant into the substrate. To accomplish this, either the average substrate temperature or the power consumption is monitored. When the average substrate temperature is low or little power is being consumed, the pressure of the coolant fluid in the plenum drops to a minimum. As the power and temperature increase, the plenum pressure also increases. This increase in pressure also increases the flow of fluid into the substrate, thus balancing the increase in cooling requirements. If the substrate is composed of a porous media, the coolant may then spread throughout the porous media via capillary action.  
         [0008]     Variations on this general design include the use of nozzles or similar devices which disperse the coolant into the substrate.  
         [0009]     While these cooling devices achieve an average level of control of the system temperature, they suffer from a number of drawbacks. Typically, the heat load is not evenly distributed across the surface of the substrate, resulting in uneven temperature distribution on the surface areas. By only monitoring the average temperature, these devices do not compensate for such non-uniform temperatures across the substrate. This situation can result at best in inefficient use of coolant, and at worst in damage to the delicate electronics.  
         [0010]     In order to overcome these problems, what is needed is a cooling system, which controls the spatial distribution of coolant by automatically directing more coolant to hotter areas. Thus, spatial nonunifomities in temperature are reduced. Further, this design allows use of numerous nozzles, distributed above the substrate to spray only the substrates hot areas. This simplifies the design of the associated coolant plenum and pressures of the associated pump, thus addressing and solving problems associated with conventional systems.  
       SUMMARY OF THE INVENTION  
       [0011]     The present invention relates to a cooling system, the cooling system having a nozzle which receives coolant from a reservoir and which faces the substrate. The nozzle may be opened and closed by a thermally actuated valve allowing the coolant to be automatically metered to the substrate, thus controlling the coolant that is applied to the substrate. By using multiple nozzles, this approach allows hotter areas to receive more coolant than cooler areas of the substrate, thus eliminating nonuniformities in the thermal profile of the substrate without adding excessive fluid which may reduce performance.  
         [0012]     It is an object of the invention disclosed herein to provide a new and improved cooling system, which provides novel utility through the use of a unique design which allows hotter areas of the substrate to receive more coolant than low temperature areas, thus achieving more uniform cooling of the substrate.  
         [0013]     It is another object of the invention disclosed herein to provide a new and improved cooling system, which allows hotter areas of the substrate to receive more coolant than cooler areas, thus causing a greater fraction of the coolant to be evaporated, thereby improving the performance and efficiency of the system.  
         [0014]     It is an advantage of the invention disclosed herein to provide a new and improved cooling system, which can operate with lower coolant pressures, thus simplifying the design of the coolant plenum and pressures of the associated pump.  
         [0015]     It is an advantage of the invention disclosed herein to control the flow of coolant and permit spraying nozzles from using excessive fluid.  
         [0016]     These and other objects and advantages of the present invention will be fully apparent from the following description, when taken in connection with the annexed drawings. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0017]     The teachings of the present invention can be readily understood by considering the following detailed description in conjunction with the accompanying drawings, in which:  
         [0018]      FIG. 1  is a cross-sectional view of an example of a first embodiment according to the principles of the present application, of a cooling system in an open state;  
         [0019]      FIG. 2  is a cross-sectional view of an example of a first embodiment according to the principles of the present application, of a cooling system in a closed state;  
         [0020]      FIG. 3  is a cross-sectional view of an example of a second embodiment according to the principles of the present application, of a cooling system in an open state;  
         [0021]      FIG. 4  is a cross-sectional view of an example of a second embodiment according to the principles of the present application, of a cooling system in a closed state. 
     
    
     DETAILED DESCRIPTION OF EXEMPLARY EMBODIMENTS  
       [0022]     Referring now to the drawings in greater detail,  FIG. 1  shows a cross-sectional view of a first embodiment according to the principles of the present application. Cooling system  10  includes housing  20  having a substantially hollow tubular shape. Housing  20  is open at the upper end and substantially closed at the lower end. The hollow shape of housing  20  defines coolant plenum  30 . Note that the principles of the present application may be applied to a wide variety of plenum designs, hence the specific design of plenum  30  shown in  FIG. 1  is not intended to limit the scope of this application.  
         [0023]     The lower end of plenum  30  has an opening  40  which allows coolant to flow into nozzle  50 . Nozzle  50  has a hollow tubular shape. Coolant flows into nozzle  50  through opening  40  in plenum  30 .  
         [0024]     Nozzle  50  is in communication with thermally responsive valve  60 .  FIG. 1  illustrates valve  60  mounted onto substrate  70 , and substrate  70  contacting heat source  80 . In this embodiment, valve  60  responds to changes in the temperature of substrate  70 .  
         [0025]     Furthermore,  FIG. 1  illustrates valve  60  in an open state. Such an open state results from the temperature of substrate  70  increasing and thereby causing the temperature of valve  60  to increase beyond a predetermined value. In this open state, valve  60  does not obstruct the flow of coolant and thus coolant from plenum  30  flows through nozzle  50  and continues flowing through valve  60  onto substrate  70 . In this fashion, coolant flow is tuned to be distributed to the area of substrate  70  of greatest need.  
         [0026]     One type of thermally responsive valve  60  may be a bimetallic strip. Note that the principles of the present application may be applied to a variety of thermally responsive valves  60 , hence neither the specific design of thermally responsive valve  60  shown in  FIG. 1 , nor the use of bimetallic strips or nitinol as one type of such valve, are intended to limit the scope of this application.  
         [0027]      FIG. 2  illustrates the first embodiment in a closed state. In this illustration, the temperature of substrate  70  is within a predetermined normal operating range, and thus thermally responsive valve  60  is closed in response to the temperature of substrate  70 . Valve  60  is thus obstructing the flow of coolant, so that coolant is not flowing into substrate  70 .  
         [0028]      FIG. 3  illustrates an example of a second embodiment according to the principles of the present application. Cooling system  100  includes housing  200  having a substantially hollow tubular shape. Housing  200  is open at the upper end and substantially closed at the lower end. The hollow shape of housing  200  defines coolant plenum  300 . Coolant plenum  300  is under pressure. Note that the principles of the present application may be applied to a wide variety of plenum designs, hence the specific design of plenum  300  shown in  FIG. 3  is not intended to limit the scope of this application.  
         [0029]     The lower end of plenum  300  has an opening  400  which allows coolant to flow into nozzle  500 . Nozzle  500  has a hollow tubular shape. Coolant flows into nozzle  500  through opening  400  in plenum  300 .  
         [0030]     Nozzle  500  is in communication with thermally responsive valve  600 .  FIG. 3  illustrates thermally responsive valve  600  mounted onto nozzle  500 . In this second embodiment, valve  600  is not mounted on substrate  700 . Being attached to nozzle  500 , valve  600  responds to changes in ambient temperature.  FIG. 3  illustrates valve  600  in an open state. When the ambient temperature increases beyond a predetermined level, valve  600  opens, no longer obstructing the flow of coolant, and thus allows coolant from plenum  300  to flow throughout the full length of nozzle  500  onto substrate  70 . In this fashion, coolant flow can be tuned to be distributed to the area of substrate  70  of greatest need.  
         [0031]     One type of thermally responsive valve  60  may be a bimetallic strip. Note that the principles of the present application may be applied to a variety of thermally responsive valves  60 , hence neither the specific design of valve  60  shown in  FIG. 3 , nor the use of bimetallic strips as one type of such valve, are intended to limit the scope of this application.  
         [0032]     Also illustrated in  FIG. 3  are counterbalancing springs  700  which are shown mounted to the plenum housing  200  and which attach to valve  600 . Counterbalancing springs  700  accomplish the dual purposes of providing compensation for coolant pressure and also providing adjustable spring tension against valve  600 .  
         [0033]      FIG. 4  illustrates the second embodiment in a closed state. In this illustration, the ambient temperature of thermally responsive valve  600  is within a predetermined normal operating range, and thus thermally responsive valve  600  is closed in response thereto and obstructs the flow of coolant. Therefore, coolant is not flowing into substrate  70 .  
         [0034]     In operation, in the first embodiment of the invention, heat source  80  causes the temperature of substrate  70  to increase. As the temperature of substrate  70  increases and reaches a predetermined range, thermally responsive valve  60  mounted on the substrate  70  opens, allowing coolant to flow through nozzle  50  onto substrate  70 .  
         [0035]     In second embodiment of the invention, a heat source  80  may cause the temperature of substrate  70  to increase. As the temperature of substrate  70  increases, ambient temperature and potentially fluid vapor temperature surrounding thermally responsive valve  600  increases, thus heating valve  600 . When valve  600  reaches a predetermined temperature, valve  600  may open, allowing coolant to flow throughout the full length of nozzle  500  and onto substrate  70 . In one embodiment, the valve  600  may also be connected to the substrate  70  via a heat finger or other device. This may allow the valve  600  to actuate based on changes in substrate temperature.  
         [0036]     It should be apparent to those skilled in the art that the present invention may be embodied in many other specific forms without departing from the spirit or scope of the invention. Therefore, the present examples and embodiments are to be considered as illustrative and not restrictive, and the invention is not to be limited to the details given herein, but may be modified within the scope of the appended claims.