Abstract:
A notebook computer system that utilizes both natural convection and forced convection cooling methods is described. Specifically, at low power levels, the forced convection components are disabled to conserve energy and to reduce noise.

Description:
FIELD OF THE INVENTION  
       [0001]     The present invention pertains to the field of computer system design. More particularly, the present invention relates to a thermal management technology for notebook computers.  
       BACKGROUND OF THE INVENTION  
       [0002]     A computer system typically comprises a plurality of electronic components. Such components may include a central processing unit (CPU), a chipset, and a memory. During operation, the components dissipate heat. In addition, voltage stepping inside the computing system also generates heat. If the CPU, or any other electronic component, becomes overheated, performance may suffer and the component&#39;s life may be depreciated.  
         [0003]     A thermal management system is typically used to remove heat from a computer system. One example of a thermal management system is a single-phase loop. In a single-phase loop, a liquid is used to absorb and remove heat from a component of a computer system. The liquid is then circulated to an area of the system where the heat is purged through natural convection.  
         [0004]     A second example of a thermal management system is a refrigeration loop. A refrigeration loop typically uses a working fluid such as Freon to cool a component of a system. An evaporator picks up heat from the component. The heat causes the working fluid to change phase from a liquid to a mixture of liquid and vapor or pure vapor. A pump, working as a compressor, then transports the working fluid to a heat exchanger. The compressor compresses or increases the pressure of the gas, which results in increase in temperature of the fluid. The heat exchanger is typically coupled to a fan that rejects the heat from the working fluid to the ambient air, turning the working fluid back into a liquid. The liquid, however, is still at a high pressure. An expansion valve reduces the pressure of the working fluid and returns the working fluid to the evaporator to complete the loop.  
         [0005]     A third example of a thermal management system is a two-phase cooling loop. Like a refrigeration loop, a two-phase cooling loop also uses a pump to circulate a working fluid to cool a component of a system. A two-phase loop typically uses a working fluid such as water. An evaporator picks up heat from the component. Within the evaporator, the heat causes the working fluid to form a vapor. The working fluid is output from the evaporator to a heat exchanger, condenser, or heat sink. The heat exchanger is typically coupled to a fan that rejects the heat from the working fluid to the ambient air. The vapor condenses in the heat exchanger, converting the working fluid back to liquid. A pump is used to drive the working fluid to the evaporator to complete the loop. The fundamental difference between the refrigeration loop and the two-phase loop is that the heat exchanger in the refrigeration loop typically has a higher temperature than the heat exchanger in the two-phase loop.  
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0006]      FIG. 1  is a flowchart of a cooling loop having natural convection and forced convection cooling capabilities;  
         [0007]      FIG. 2  is an embodiment of a refrigeration loop with remote heat exchanger and display to dissipate heat;  
         [0008]      FIG. 3  is an embodiment of a notebook computer system with hinges that comprise flexible tubing to transfer a working fluid;  
         [0009]      FIG. 4  is an embodiment of a display for cooling a notebook computer system;  
         [0010]      FIG. 5  is an embodiment of plates in a notebook computer system display; and  
         [0011]      FIG. 6  is an embodiment of a notebook computer system having a spreader to distribute heat in the display.  
     
    
     DETAILED DESCRIPTION  
       [0012]     In the following detailed description, numerous specific details are set forth in order to provide a thorough understanding of the invention. However, it will be understood by those skilled in the art that the present invention may be practiced without these specific details. In other instances, well-known methods, procedures, components and circuits have not been described in detail so as not to obscure the present invention.  
         [0013]     Most applications of a notebook computer system consume only a few watts of power. Computer systems generally rely on forced convection methods that use a remote heat exchanger and fan to dissipate the heat generated by these applications.  FIG. 1  is an embodiment of a flowchart of a notebook computer system that comprises both natural convection and forced convection cooling capabilities. The computer boots in operation  110 . A cooling loop comprising natural convection and forced convection is enabled in operation  120 . This cooling loop and its components will be described in further detail below. A circuit then detects the power consumption or temperature of the CPU in operation  130 . If the power consumption by the CPU or the temperature of the CPU is greater than a predefined threshold, the cooling loop continues to cool the system through natural convection and forced convection.  
         [0014]     If, however, the circuit in operation  130  detects that the power consumption by the CPU or the temperature of the CPU is less than the predefined threshold, the forced convection components of the cooling loop are disabled in operation  140 . In other words, the fan is turned off, but the fluid continues to flow through the heat exchanger. The forced convection components may comprise a remote heat exchanger and a fan.  
         [0015]     If natural convection is primarily performed through the display of the notebook computer system, the display temperature is detected in operation  150 . The cooling loop may rely solely on this natural convection method as long as the temperature is less than a predefined temperature threshold. Otherwise, if the temperature is detected to be greater than a predefined temperature threshold, the forced convection components are enabled.  
         [0016]     The flowchart described in  FIG. 1  may be implemented in a refrigeration loop or a pumped liquid loop. Moreover, the flowchart is independent of the working fluid used to cool the computer system.  FIG. 2  depicts an example of how a system having natural convection and forced convection cooling capabilities may be implemented in a refrigeration loop.  
         [0017]     The refrigeration loop of  FIG. 2  comprises evaporator  210 , compressor or pump  220 , heat exchanger  230 , fan  235 , and display  240 . Evaporator  210  is coupled to pump  220  and display  240 . Pump  220  is coupled to heat exchanger  230 . Heat exchanger  230  is coupled to fan  235  and display  240 .  
         [0018]     The evaporator  210  is thermally coupled to a heat source. As an example, the evaporator  210  may be placed on top of a heat source. For one embodiment of the invention, the heat source may be the CPU of the notebook computer system. The evaporator  210  picks up heat from the heat source, heating the working fluid.  
         [0019]     For another embodiment of the invention, the notebook computer system may comprise a plurality of evaporators. The use of a plurality of evaporators allows heat to be absorbed by the working fluid at a number of components. Each evaporator is placed at a heat sensitive component of the notebook computer system.  
         [0020]     The working fluid changes phase inside the evaporator  210 . Prior to reaching the evaporator  210 , the working fluid comprises a liquid phase. As the working fluid picks up heat at the evaporator  210 , the working fluid may boil and form a vapor. Thus, after picking up heat from the heat source, the working fluid comprises a liquid phase and a vapor phase. The pump  220  is coupled to the evaporator  210  and pumps the working fluid exiting the evaporator  210  to the heat exchanger  230 .  
         [0021]     Inside the heat exchanger  230  or condenser, the heat in the working fluid is rejected via fan  235  to the ambient air and the vapor condenses. This heat rejection via forced convection from the fan  235  is a first heat sink the computer system.  
         [0022]     The second heat sink is the notebook display  240 , which is coupled to the heat exchanger  230 . The display  240  allows for natural convection. The display  240  will be described in further detail in  FIG. 4 .  
         [0023]     The cooling system of  FIG. 2  offers improved cooling capabilities over traditional refrigeration or two-phase loops because the cooling system of  FIG. 2  comprises a plurality of heat sinks. Moreover, the cooling system may offer improved performance. The forced convection components may be turned off when the system and its applications are generating a minimum amount of energy. As stated above, most applications consume only a few watts of power on average. The display  240  may dissipate 2-20 watts of power through natural convection and radiation. This heat sink should be sufficient for the execution of most applications on the notebook computer system. For one embodiment of the invention, the remote heat exchanger  230  and the fan  235  are only enabled when a high power application is being executed. Thus, the fan  235  is turned on to enable forced convection as soon as the load is larger than the system&#39;s natural convection cooling capabilities.  
         [0024]     For another embodiment of the invention, heat sensors are placed at a plurality of heat sensitive components of the notebook computer system. The heat sensors may be thermal diodes. The notebook computer system monitors the temperature at each of the heat sensors. The remote heat exchanger  230  and the fan  235  are enabled when the computer system detects the temperature at a component is greater than a predefined temperature. Otherwise, the notebook computer system cools itself only through passive cooling or natural convection. Therefore, the notebook computer system is normally passively cooled, but active cooling techniques are also enabled if any monitored component exceeds a threshold temperature. Selectively enabling the forced convection components allow the notebook computer system to save energy and to increase the battery life. Further, disabling the fan  235  may reduce noise.  
         [0025]      FIG. 3  depicts a notebook computer system for implementing the flowchart of  FIG. 1 . The notebook computer base  310  is coupled to hinge  312  and hinge  314 . The hinges  312  and  314  are coupled to display  240 . Evaporator  210 , pump  220 , remote heat exchanger  230 , and fan  235  may be components of notebook computer base  310 . A keyboard may be coupled to the top of the notebook computer base  310 . The working fluid of the cooling loop may be transmitted from the notebook computer base  310  to the display  240  via tubing or hoses inside the hinges  312  and  314 . The hoses that are inside hinges  312  and  314  are flexible and may be manufactured using plastic if the working fluid remains a single phase during the cooling loop. For example, the hoses may be plastic if the working fluid is liquid metal.  
         [0026]     However, working fluids that changes phase in the course of the cooling loop may require the hinges  312  and  314  to comprise metal tubing in order to ensure a hermetic seal. The metal tubing may comprise metallic bellows. Water may be a working fluid that has more than a single phase.  
         [0027]     The working fluid is delivered from the computer base  310  to the display  240  because the display  240  comprises a large surface area, which is ideal for natural convection. Natural convection is a function of a temperature gradient and area. Natural convection may be defined by the following equation: 
 
 Q=h*A*ΔT,  
 
 where Q is the heat rejected, h is the heat transfer coefficient, A is the heat rejection surface area, and ΔT is the difference between the working fluid temperature and the ambient temperature outside of the display  240 . 
 
         [0028]     The layers of the display  240  are depicted in  FIG. 4 . Display screen  410  is coupled to display circuitry  420 . Display circuitry  420  is coupled to insulation layer  430 . Insulation layer  430  is coupled to plate  440 . Plate  440  is coupled to plate  450 . Plate  450  is coupled to display  460 .  
         [0029]     The heat transfer coefficient, h, varies depending on properties of the convection surface. In this case, the chosen convection surface is the cover  460  of the notebook display  240 . To achieve maximum heat dissipation, the temperature of the working fluid must be as high as possible. The temperature of the working fluid, however, may have two limitations. The first limitation is the reliability criteria of the display screen  410 . Display circuitry  420  may comprise components that are heat sensitive. The working fluid temperature may be kept at a temperature that would prevent degradation of the display circuitry  420 .  
         [0030]     The second limitation of the working fluid temperature is the ergonomic specification of the notebook computer system. The hotter the working fluid temperature, the greater the heat dissipated from the display cover  460 . Heat dissipation increases the temperature of the display cover  460 . The temperature of the display cover  460  must be maintained such as to prevent the user of the notebook computer system from being burned.  
         [0031]     The display circuitry  420  may comprise a sensor to detect the temperature of inside the display. The sensor may be a thermal diode. For one embodiment of the invention, if the forced convection components are disabled and the sensor detects that the temperature of the display screen  410  is above a first predefined threshold, the sensor may enable the forced convection components. For another embodiment of the invention, if the forced convection components are disabled and the sensor detects that the temperature of the display cover  460  is above a second predefined threshold, the sensor may enable the forced convection components.  
         [0032]     The working fluid is kept between plate  440  and plate  450  of the notebook display  240 .  FIG. 5  depicts an embodiment of the face of plates  440  and  450 . The plates  440  and  450  have complementary features with regard to one another. Plate  440  comprises a groove  510 , flow path entrance  505 , and flow path exit  515 . Plate  450  comprises a groove  530 , flow path entrance  525 , and flow path exit  535 .  
         [0033]     The face of plate  450  is superimposed on the face of plate  440  such that the groove  530  aligns with groove  510 , flow path entrance  525  aligns with flow path entrance  505 , and flow path exit  535  aligns with flow path exit  515 . In other words, plate  450  is flipped over onto plate  440 . The grooves in the plates  440  and  450 , once placed together, form a pipe like path. Each of the plates  440  and  450  are each approximately one millimeter thick. The plates  440  and  450  may be manufactured using a metal such as aluminum or copper. The material of the plates  440  and  450 , however, must not be a material that negatively reacts with the working fluid.  
         [0034]     The groove  510  of plate  440  and the groove  530  of plate  450  provide a flow path for the working fluid. The working fluid enters the grooves at flow path entrances  505  and  525  and exit at flow path exits  515  and  535 . The flow path allows the temperature of the working fluid to be spread across the surface area of the display  240 . The more turns the grooves  510  and  530  of plates  440  and  450 , the better the temperature spreading. The temperature spreading creates a natural convection of heat that escapes through the display cover  460 . The display cover  460  may be manufactured using a plastic. Alternatively, the display cover  460  may be manufactured using a metallic material such as magnesium.  
         [0035]     To protect the display circuitry  420  from the working fluid heat, an insulating layer  430  may be placed between the display circuitry  420  and the plate  440 . The insulating layer  430 , however, is only required if the working fluid may reach a temperature hotter than the display circuitry  420  tolerance specification.  
         [0036]      FIG. 6  depicts another embodiment of the invention for implementing the flowchart of  FIG. 1 .  FIG. 6  depicts a notebook computer system having a notebook computer base  610 , hinges  612  and  614 , and display  640 . The notebook computer base  610  is coupled to hinge  612  and hinge  614 . The hinges  612  and  614  are coupled to display  640 . Evaporator  210 , pump  220 , remote heat exchanger  230 , and fan  235  may be components of notebook computer base  610 . The fan  235  may be enabled if cooling through natural convection is insufficient. A keyboard may be coupled to the top of the notebook computer base  610 . Similar to the computer system of  FIG. 3 , the working fluid of the cooling loop may be transmitted from the notebook computer base  610  to the display  640  via tubing or hoses inside the hinges  612  and  614 .  
         [0037]     The display  640  comprises display tubing  660  and spreader  650  to provide natural convection. The display tubing  660  is coupled to the hoses in hinges  612  and  614 . For one embodiment of the invention, the working fluid may be flow from hinge  612  to display tubing  660 . The working fluid may then exit the display via hinge  614 . The spreader  650  may be a flat heat pipe or a roll bond heat pipe coupled to the display tubing  660 . The spreader  650  spreads the temperature of the working fluid across the display  640  to create a natural convection of heat that escapes through the display cover.  
         [0038]     In the foregoing specification the invention has been described with reference to specific exemplary embodiments thereof. It will, however, be evident that various modification and changes may be made thereto without departure from the broader spirit and scope of the invention as set forth in the appended claims. The specification and drawings are, accordingly, to be regarded in an illustrative rather than restrictive sense.