Abstract:
An apparatus and method for controlling the temperature of an integrated circuit device includes a refrigerant system having a coolant loop containing refrigerant, an evaporator, a compressor, and a condenser. The condenser has a variable speed fan controlled to maintain the temperature of the refrigerant at a predetermined value. In a refrigeration system used to cool an integrated circuit device, a method for controlling refrigerant pressure by comparing the refrigerant temperature at a predetermined location to a predetermined value and varying the cooling applied to the condenser.

Description:
BACKGROUND OF THE INVENTION  
         [0001]    The present invention relates generally to integrated circuit devices such as the microprocessors of computers and more particularly to the cooling of such devices to below ambient temperatures for improved efficiency and enhanced speed of operation.  
           [0002]    It is well known in the electronics industry that cooling integrated circuit devices to below ambient temperatures substantially improves the efficiency and speed at which such devices can operate. Such cooling is particularly beneficial in microprocessors that form the heart of modern day computers. For example, it has been found that the performance of a desktop computer can be significantly improved by cooling the microprocessor to temperatures of −40 degrees Centigrade or below.  
           [0003]    Various methods and apparatus are known in the art for removing the thermal heat generated by integrated circuit devices. For example, KryoTech, Inc., the assignee of the present invention, has previously developed a refrigeration system for cooling an integrated circuit device in a desktop computer. This refrigeration system operates by circulating refrigerant fluid to a thermal head engaging the microprocessor.  
           [0004]    The thermal head defined a flow channel through which the refrigerant fluid would pass as it circulated around the closed loop of the refrigeration system. Due to its design, the thermal head functioned as an evaporator where the refrigerant fluid was converted from liquid to gaseous form. In accordance with known thermodynamic principles, thermal energy was thus removed from the location of the microprocessor. The gaseous refrigerant drawn from the evaporator by a compressor was then fed back to a condenser where the thermal energy was removed.  
           [0005]    As one skilled in the art will appreciate, size limitations require the refrigeration system to be relatively small with a relatively low volume of refrigerant. As a result, slight changes in ambient air temperature directly affect the system&#39;s performance. For example, a decrease in ambient temperature causes the continuous operation fan to remove more heat from the gaseous refrigerant in the condenser. This results in liquid refrigerant exiting the condenser at a lower temperature and pressure. Given the small volume of refrigerant available, even a slight decrease in ambient temperature can reduce liquid refrigerant pressure excessively and significantly reduce the cooling capacity of the refrigeration system.  
         SUMMARY OF THE INVENTION  
         [0006]    In one aspect, the present invention provides an integrated circuit device cooled by a refrigeration system. In this embodiment, the refrigeration system comprises a coolant loop containing a refrigerant, an evaporator, a compressor, and a condenser.  
           [0007]    The evaporator is in thermal contact with the integrated circuit device and defines a flow channel for passage of the refrigerant to remove thermal energy from the integrated circuit device. The compressor increases the pressure of the refrigerant exiting the evaporator. The condenser is located between the compressor and the evaporator and includes a variable speed fan to force air across the condenser. A temperature sensor in thermal contact with the refrigerant provides a signal to a controller for varying the speed of the fan to maintain the refrigerant at a predetermined temperature.  
           [0008]    Other aspects of the present invention provide a refrigerant system for cooling an integrated circuit device. The refrigerant system comprises a coolant loop containing refrigerant, an evaporator, a compressor, and a condenser.  
           [0009]    The evaporator is in thermal contact with the integrated circuit device and has an inlet plenum and an exhaust plenum. The evaporator further defines a flow channel between the inlet plenum and exhaust plenum, and the refrigerant passes through the flow channel to absorb thermal energy from the integrated circuit device, changing the refrigerant to a gaseous state. The compressor has a suction and a discharge, and the coolant loop connects the evaporator exhaust plenum to the compressor suction. The gaseous refrigerant passes through the compressor and is discharged at a higher pressure. The condenser connects between the compressor discharge and the evaporator inlet plenum. The condenser includes a variable speed fan to remove thermal energy from the gaseous refrigerant passing through the condenser, changing the gaseous refrigerant to a liquid state. A temperature sensor in thermal contact with the refrigerant provides a signal to a controller for varying the speed of the fan to maintain the refrigerant at a predetermined temperature.  
           [0010]    In some exemplary embodiments, the temperature sensor measures the temperature of the refrigerant between the condenser and the evaporator. In other exemplary embodiments, the coolant loop includes a capillary tube between the condenser and the evaporator for restricting flow of the refrigerant from the condenser to the evaporator. It will often be desirable that the capillary tube produces a refrigerant pressure entering the capillary tube of more than 225 pounds per square inch.  
           [0011]    Still further aspects of the present invention are provided by a method used to cool an integrated circuit device. The method uses a refrigeration system to circulate a refrigerant throughout a coolant loop including a compressor, a condenser, and an evaporator. The method controls refrigerant pressure by providing a variable speed fan operational across the condenser for removing thermal energy from the refrigerant. The method detects a temperature of the refrigerant at a predetermined location and compares the temperature to a predetermined value. If the temperature exceeds the predetermined value, indicating that the refrigerant pressure is too high, the method increases the variable speed of the fan to reduce the temperature. If the predetermined value exceeds the temperature, indicating that the refrigerant pressure is too low, the method decreases the variable speed of the fan to increase the temperature. In an exemplary embodiment, the predetermined location is between the condenser and the evaporator.  
           [0012]    Other objects, features and aspects of the present invention are discussed in greater detail below. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0013]    A full and enabling disclosure of the present invention, including the best mode thereof, to one of ordinary skill in the art, is set forth more particularly in the remainder of the specification, including reference to the accompanying drawings, in which:  
         [0014]    [0014]FIG. 1 is a perspective view of a computer having a refrigeration system constructed in accordance with the present invention;  
         [0015]    [0015]FIG. 2 is a diagrammatic representation of the refrigeration system that is installed in the computer of FIG. 1; and  
         [0016]    [0016]FIG. 3 is a schematic diagram of preferred controller circuitry for use in the refrigeration system of FIG. 2. 
     
    
       [0017]    Repeat use of reference characters in the present specification and drawings is intended to represent same or analogous features or elements of the invention.  
       DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT  
       [0018]    Reference will now be made in detail to presently preferred embodiments of the invention, one or more examples of which are illustrated in the accompanying drawings. Each example is provided by way of explanation of the invention, not limitation of the invention. In fact, it will be apparent to those skilled in the art that modifications and variations can be made in the present invention without departing from the scope or spirit thereof. For instance, features illustrated or described as part of one embodiment may be used on another embodiment to yield a still further embodiment. Thus, it is intended that the present invention covers such modifications and variations as come within the scope of the appended claims and their equivalents.  
         [0019]    [0019]FIG. 1 illustrates a computer  10  including a refrigeration system  20  constructed in accordance with the present invention. The refrigeration system  20  operates to cool an integrated circuit device, such as the computer&#39;s microprocessor  12  (FIG. 2). It should be understood, however, that the present invention is not limited to cooling a microprocessor  12  but is equally applicable to cooling any integrated circuit device that can benefit from lower operating temperatures.  
         [0020]    As shown, the computer  10  generally includes a mother board  14 , various other devices, a power supply  16 , and a housing  18 . The mother board  14  provides a centralized platform for locating various electronic components, including the microprocessor  12 .  
         [0021]    Referring to FIGS. 1 and 2, the general components of the refrigeration system  20  include a coolant loop  30 , an evaporator  40 , a compressor  60 , and a condenser  70 .  
         [0022]    The coolant loop  30  comprises flexible tubing  32  made from copper, stainless steel, or a synthetic material to connect the various components of the refrigeration system  20  in series. The flexible tubing  32  contains a refrigerant  34 , such as R404a, R507a, R134a, or other suitable substitute, for circulation throughout the refrigeration system  20 . During circulation, the refrigerant  34  changes between gaseous and liquid states to alternately absorb and release thermal energy. Insulation material  36  surrounds the flexible tubing over portions of the coolant loop  30  that contain refrigerant  34  below the local ambient dew point to prevent condensation from forming.  
         [0023]    The length and inner diameter of the coolant loop  30  depends on the location in the refrigeration system  20 . For example, between the condenser  70  and the evaporator  40 , the coolant loop  30  necks down to form a capillary tube  38 . In presently preferred embodiments, the capillary tube  38  may be approximately ten feet long and have an inner diameter of approximately 0.026 inches. In this configuration, the capillary tube  38  ensures refrigerant pressure at its inlet will be greater than 110 pounds per square inch, preferably between 225 and 250 pounds per square inch. It should be understood by one of ordinary skill in the art that integrated circuit devices having different thermal demands may require variations in the length and inner diameter of the flexible tubing  32 , and these variations are within the scope of the present invention.  
         [0024]    The evaporator  40  mounts directly on the integrated circuit device, in this illustration a microprocessor  12  of a computer  10 . The evaporator  40  is formed from a highly thermally conductive material, such as brass or copper, to maximize heat transfer from the microprocessor  12 . The evaporator  40  includes an inlet plenum  42  for receiving the refrigerant  34 . The inlet plenum  42  opens to a flow channel  44  which traverses the interior of the evaporator  40  and provides maximum surface area for the refrigerant  34 . The flow channel  44  terminates at an exhaust plenum  46  for exhausting the refrigerant  34  from the evaporator  40 .  
         [0025]    A mounting assembly  50  fixedly attaches the evaporator  40  to the microprocessor  12 . In general, the mounting assembly  50  includes an upper section  52  and a lower section  53  which attach by way of fasteners  54 , such as bolts that extend through mating flanges. Other methods of fastening are known in the art and within the scope of the present invention. In this manner, the mounting assembly  50  defines an airtight chamber  56  around the evaporator  40  and the microprocessor  12  to isolate the cooled components from ambient air. Heating elements  58  imbedded in the upper  52  and lower  53  sections maintain the exterior surface of the mounting assembly  50  above the local ambient dew point, thus preventing condensation from forming.  
         [0026]    The preceding description of the evaporator  40  and mounting assembly  50  is by way of example only and is not intended to limit the scope of the present invention. A more detailed description of a preferred construction of an evaporator and mounting assembly is described in pending patent application filed by Lewis S. Wayburn, Derek E. Gage, Andrew M. Hayes, and R. Walton Barker on Jul. 24, 2001, titled “Integrated Circuit Cooling Apparatus”, assigned to KryoTech, Inc., the assignee of the present invention, and incorporated here by reference.  
         [0027]    The compressor  60  includes a suction  62  and a discharge  64  and connects downstream of the evaporator exhaust plenum  46 . As is understood by one of ordinary skill in the art, the compressor  60  functions to increase the pressure of the gaseous refrigerant  34 . The compressor  60  operates at a constant rate from a constant voltage power supply (not shown), although a variable rate compressor may also be used in some embodiments.  
         [0028]    The condenser  70  connects in series between the compressor  60  and the evaporator  40 . The condenser  70  includes cooling coils  72 , a temperature sensor  74 , a controller  76 , and a variable speed fan  78 . The cooling coils  72  are formed from a highly thermally conductive material, such as brass, aluminum, stainless steel, or copper, to maximize heat transfer from the condenser  70  to the environment. The temperature sensor  74  may be a thermocouple or other suitable substitute for measuring refrigerant temperature at a predetermined location. In one embodiment, the temperature sensor  74  is in thermal contact with the coolant loop  30  between the condenser  70  and the evaporator  40 . Insulation  75  around the temperature sensor  74  enables the temperature sensor  74  to accurately measure the refrigerant temperature inside the coolant loop  30  without penetrating the coolant loop  30 . The temperature sensor  74  provides an electrical signal  82  (shown in FIG. 3) to the controller  76  responsive to the temperature of the refrigerant leaving the condenser  70 .  
         [0029]    In one embodiment, the controller includes a pulse width modulator circuit  80  (FIG. 3) to proportionally control the operating speed of fan  78  based on the electrical signal  82  from the temperature sensor  74 . The variable speed fan  78  forces ambient air across the cooling coils  72  to transfer thermal energy from the condenser  70  to the environment.  
         [0030]    The refrigeration system  20  can be an after market component capable of installation with minimal modification to the integrated circuit device. For example, referring again to FIG. 1, the refrigeration system  20  can mount adjacent to the computer housing  18 . The coolant loop  30  can supply and return the refrigerant  34  to the microprocessor  12  through a thermal bus  92  extending through a cutout  94  in the computer housing  18 . The mounting assembly  50  then attaches over the microprocessor  12  to secure the evaporator  40  in position to cool the microprocessor  12 .  
         [0031]    Referring now to FIGS. 2 and 3, the operation of the refrigeration system  20  will be described in more detail. Starting at the evaporator  40 , the liquid refrigerant  34  enters the evaporator  40  through the inlet plenum  42  where it expands into the flow channel  44 . The expansion of the liquid refrigerant  34  reduces the pressure of the refrigerant, causing the liquid refrigerant  34  to change to a gaseous state. The gaseous refrigerant  34  traverses through the flow channel  44  to quickly cool the evaporator  40 , to approximately −40 degrees Centigrade in one embodiment. The thermally conductive surface of the evaporator  40  transfers thermal energy from the microprocessor  12  to the gaseous refrigerant  34 . Simultaneously, the heating elements  58  embedded on the exterior surface of the mounting assembly  50  ensure that the exterior of the mounting assembly  50  remains above the local dew point to prevent condensation from forming.  
         [0032]    The gaseous refrigerant  34  exits the flow channel  44  at the exhaust plenum  46  and passes through the coolant loop  30  to the compressor  60 . The compressor  60  increases the pressure of the gaseous refrigerant  34 , and the gaseous refrigerant  34  exits the compressor discharge  64  at a much higher temperature and pressure.  
         [0033]    The pressurized and heated gaseous refrigerant  34  passes through the coolant loop  30  to the cooling coils  72  (shown in FIG. 1) in the condenser  70 . As the heated gaseous refrigerant  34  passes through the cooling coils  72 , the variable speed fan  78  forces ambient air across the cooling coils  72 , and the ambient air removes thermal heat from the gaseous refrigerant  34  to the environment. As the gaseous refrigerant  34  cools, the refrigerant  34  condenses into a liquid state.  
         [0034]    The liquid refrigerant  34  exits the condenser  70  and passes through the coolant loop  30 . The insulated temperature sensor  74  measures the coolant loop temperature, and thus the liquid refrigerant temperature, and provides an electrical signal  82  to the controller  76  indicative of the temperature of the liquid refrigerant  34  leaving the condenser  70 .  
         [0035]    Referring now to FIG. 3, the controller circuitry  80  compares the electrical signal  82  from the temperature sensor  74  to a predetermined temperature selected by the user to vary the speed of the variable speed fan  78 . An operational amplifier  84  amplifies the electrical signal  82  from the temperature sensor and passes the amplified signal to the input of a pulse width modulator  86 . In presently preferred embodiments, the operational amplifier  84  produces a proportional signal between about 0 and 5 volts. The pulse width modulator  86  receives the output from the operational amplifier  84  and produces a square wave having a duty cycle which is directly proportional to the magnitude of the input.  
         [0036]    The output of the pulse width modulator  86  passes to the gate of a field effect transistor  88  which is rendered conductive when the duty cycle is “on.” By adjusting the speed of the fan  78 , the controller  76  regulates the amount of ambient air that the fan forces over the cooling coils  72 , thus controlling the temperature and pressure of the liquid refrigerant  34  leaving the condenser  70 .  
         [0037]    Referring again to FIG. 2, the liquid refrigerant  34  passes through the coolant loop  30  and into the capillary tube  38 . The relatively long length and reduced inner diameter of the capillary tube  38  restrict the flow of the liquid refrigerant  34 , producing a desired higher pressure at the inlet of the capillary tube  38  through which the refrigerant passes to the evaporator  40  where the refrigeration cycle repeats.  
         [0038]    It can thus be seen that the preceding description provides one or more preferred embodiments of the present invention. It should be understood that any and all equivalent realizations of the present invention are included within the scope and spirit thereof. The embodiments depicted are presented by way of example only and are not intended as limitations upon the present invention. Thus, it should be understood by those of ordinary skill in this art that the present invention is not limited to these embodiments since modifications can be made. Therefore, it is contemplated that any and all such embodiments are included in the present invention as may fall within the literal and equivalent scope of the appended claims.