Abstract:
The heat dissipating apparatus is a cooling system that can be used to cool a heat-generating electronic component, such as a CPU (Central Processing Unit), within an enclosure, such as a computer. The cooling system includes a heat receiving section that is thermally and mechanically coupled to the heat-generating electronic component. Heat received in the heat receiving section is transferred to a heatsink that is coupled to the heat receiving section. To dissipate heat from the heatsink, an air flow device, such as a fan or axial blower, is provided. The air flow device is movable from a retracted position, where it is completely inside the enclosure, to an extended position, where it is at least partially outside the enclosure. In the extended position, the air flow device is able to intake air with less airflow impedance than in the retracted position. An increase in airflow to the heatsink can therefore be achieved by having the air flow device in the extended position.

Description:
CROSS-REFERENCE OF RELATED APPLICATIONS  
       [0001]     Not Applicable  
       STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT  
       [0002]     Not Applicable  
       REFERECE TO SEQUENCE LISTING, A TABLE, OR A COMMPUTER PROGRAM LISTING COMPACT DISC APPENDIX  
       [0003]     Not Applicable  
       BACKGROUND OF THE INVENTION  
       [0004]     Electronic and computer systems are equipped with heat generating electronic and integrated circuit (IC) devices and components, such as CPUs (Central Processing Units) for processing various types of data and information. The amount of heat generated by CPUs and other heat generating components is increasing significantly over time due to the increase in the processing speed and/or enhancement of versatility and functionality. Accordingly, to maintain the electronic and computer systems in general, and CPU and other heat generating components in particular in a stable and reliable state, it is necessary to increase the capability of heat removal and dissipation from the CPUs and those heat generating components.  
         [0005]     Modern electronic and computer systems typically have at least one cooling system for forcibly air cooling the CPU and/or other heat generating components. A cooling system, such as that shown in  FIG. 14 , typically comprises a heat-receiving section  1400 , a heatsink  1405 , a coupling device  1410  thermally coupling the heat-receiving section  1400  and the heatsink  1405 , and an air flow device (not shown).  
         [0006]     The heat-receiving section  1400  is made of thermally conductive material and is thermally and mechanically coupled to the CPU or other heat generating components to receive heat. The heatsink  1405  has extended surface areas such as fins made of thermally conductive materials and is thermally coupled to the heat-receiving section  1400  such that heat absorbed by the heat-receiving section  1400  can be efficiently transferred to the heatsink  1405 . The heat-receiving section  1400  can be integral with the heatsink  1405 , such as commonly found in desktop computers or may be a physically separate unit from the heatsink such as commonly found in mobile computing environments.  
         [0007]     The air flow device draws cooling air in from ambient, forces cooling air to flow past the heatsink surfaces, and exhausts the heated air out of the enclosure thus removing heat from the heat generating components. The air flow device is typically chosen from radial impellers/blowers or axial fans.  
         [0008]     For blowers, the air inlet can be at one side or both and opposite sides of a generally thin case. A single air outlet or multiple air outlets can be at the side, or the whole side can be the air outlet. As such, airflow direction at the inlet is perpendicular to that at the outlet. Axial fans, on the other hand, have the air inlet on one side of the flat surface and the outlet on the opposite side such that airflow direction at the inlet is the same as that at the outlet.  
         [0009]     The cooling capability of a cooling system is determined by, among many important factors, the size or the total exposed surface area of the heatsink and cooling air delivery capacity of the air flow device. In general, use of a big heatsink and/or a big and powerful air flow device will result in a cooling solution with higher cooling capability.  
         [0010]     However, a computer system employing a faster and hotter CPU may not have the necessary space allocated for a bigger cooling system. This is typically the case with modern mobile computers such as portable and laptop computers and other computing and data processing devices such as low profile workstations and servers. The requirement of a thin profile enclosure necessitates the use of radial blowers as air flow devices and low profile heatsinks in a mobile computer and other low profile and compact electronic device environment. Blowers invariably have low airflow delivery capacity as compared to axial fans of similar size. Moreover, physical limitations brought about by small form factor chassis enclosures also restrict airflow. In laptop computers, air intake is typically from a very narrow gap between the bottom surface of the laptop base and a working surface that the laptop rests on. The narrow gap can significantly increase airflow impedance rendering lower volumetric flow delivered by the blower.  
         [0011]     Low profile heatsinks also have limited way of effectively increasing surface areas. To increase the surface area of a thin heatsink, more fins have to be packed into a fixed width and/or longer fins in the direction of airflow have to be used. Unfortunately, an increase in surface area accomplished by the aforementioned methods will inevitably result in tighter spaces between fins thus high airflow impedance. As such, for a given blower, improvement in cooling capacity can only be achieved to a certain extent, beyond which, increase in surface area will not yield meaningful cooling capacity improvement.  
         [0012]     To meet the increasing cooling requirements for hotter CPUs, multiple heatsinks and multiple air flow devices such as blowers are used in low profile mobile computers resulting in undesirably large and heavy chassis enclosures. More cooling solutions lead to more parts, parts of increased complexity, increased effort in assembly and therefore higher costs. More blowers in a chassis enclosure also lead to high fan noise and lower reliability.  
         [0013]     To summarize, the limitation in conventional cooling solutions for low profile chassis enclosures is becoming a road blocker for manufacturers to build small form factor computers that can meet the market demand for incorporating the fastest CPUs in mobile computers as well as the smallest and most compact form factor for the mobile computers&#39; physical size.  
         [0014]     In order to meet the aforementioned market demands on CPU speed and mobile computer size simultaneously, cooling solution must be designed differently with better and improved cooling efficiency.  
       BRIEF SUMMARY OF THE INVENTION  
       [0015]     Described below is a cooling system and method designed to cool heat generating electronic components such as a CPU (Central Processing Unit) in electronic and computer system enclosures incorporating the cooling system. More particularly, the cooling system and method may be used to remove heat from high heat dissipating components located within small form factor electronic and computer devices such as mobile computers having a main body portion and a display portion connected in an operable manner to the main body portion.  
         [0016]     In this description, a laptop is used as an example device in which the cooling system is used. It will be appreciated that the cooling system as described can be used in electronic devices of other forms, non-limiting examples of which include other forms of computing and data processing devices. Furthermore, the cooling systems in this description are described using one heat receiving section and one heatsink. It should be understood that cooling systems comprising multiple heat generating components with multiple heat receiving sections, multiple heatsinks and multiple air flow devices will also work according to cooling solution principles outlined in the following description.  
         [0017]     One form of the system described below is a cooling system for a device having an enclosure and at least one heat-generating electronic component operating within the enclosure. The system includes a heat receiving section thermally and mechanically coupled to the heat-generating electronic component and a heatsink thermally and mechanically coupled to the heat receiving section. There is also an air flow device movable between a retracted position, where the air flow device is completely inside the enclosure, and an extended position, where the air flow device is at least partially outside the enclosure. The cooling system can be designed to operate with the air flow device in the retracted position as well as in the extended position. Alternatively, the cooling system can be designed to operate with the air flow device in the extended position only.  
         [0018]     In the extended position, the air flow device is adapted to direct air to the heatsink to dissipate heat that is transferred from heat generating component. When operation is required in the retracted position, the air flow device is also adapted to direct air to the heatsink for heat removal.  
         [0019]     Another form of the cooling system utilizes a blower movable between a retracted position, where the blower is completely inside the enclosure, and an extended position, where the blower is at least partially outside the enclosure. The blower in the extended position is adapted to direct air to the heatsink to dissipate heat from the heatsink. The blower can also be adapted to direct air to the heatsink for heat removal if operation is required in the retracted position.  
         [0020]     A further form of the cooling system utilizes a first blower movable between a retracted position, where the blower is completely inside the enclosure, and an extended position, where the blower is at least partially outside the enclosure; wherein the blower in the extended position is adapted to direct air into the enclosure to dissipate heat from the heatsink. There is a second blower provided underneath the first blower, the second blower being fixed in a retracted position and adapted to direct air into the enclosure in the fixed retracted position.  
         [0021]     A further form of the cooling system utilizes a lower blower fixed in a retracted position where the lower blower is completely inside the enclosure; and an upper blower located over the lower blower. The upper blower is movable between a retracted position, where the upper blower is completely inside the enclosure, and an extended position, where the upper blower is at least partially outside the enclosure. In this form, the lower blower is adapted to direct air to the heatsink for heat removal in the retracted position and the upper blower is adapted to direct air to the heatsink in the extended position.  
         [0022]     In a further form, the system utilizes an axial fan movable between a retracted position, where the fan is completely inside the enclosure, and an extended position, where the fan is at least partially outside the enclosure. The fan is adapted to direct air to the heatsink in the extended position. The fan can also be adapted to direct air to the heatsink for heat removal in the retracted position if operation of the cooling solution with the fan in retracted position is required.  
         [0023]     In a further form, the system includes a movable cover under the heatsink. An axial fan is movable between a retracted position, where the fan is completely inside the enclosure, and an extended position, where the fan is moved out from underneath the enclosure so as to be at least partially outside the enclosure. In the extended position, the movable cover is moved so as to expose an underside portion of the heatsink and the fan is moved so as to direct air to the heatsink at least through the exposed underside portion of the heatsink. The fan can also be adapted to direct air to the heatsink for heat removal in the retracted position if operation of the cooling solution with the fan in retracted position is required.  
         [0024]     A still further form of the cooling system includes a heat receiving means thermally and mechanically coupled to the heat-generating electronic component for conducting heat away from the component and a heatsink means thermally and mechanically coupled to the heat receiving means for dissipating heat from the component. There is also an air flow means for directing air into the enclosure. The air flow means is movable between a retracted position, where the air flow means is completely inside the enclosure, and an extended position, where the air flow means is at least partially outside the enclosure. The air flow means directs air to the heatsink for removing heat transferred from the heat generating component in the extended position. The air flow means can also be adapted to direct air to the heatsink for heat removal in the retracted position if operation of the cooling solution with the air flow means in retracted position is required  
         [0025]     One form of the cooling method includes the steps of transferring heat from the heat-generating electronic component to a heatsink, directing air to the heatsink to dissipate heat from the heatsink using an air flow device; and moving the air flow device from a retracted position, where the air flow device is completely inside the enclosure, to an extended position, where the air flow device is at least partially outside the enclosure.  
         [0026]     In another form, the method comprises the steps of transferring heat from the heat- generating electronic component to a heatsink; directing air to the heatsink to dissipate heat from the heatsink using a lower blower; moving an upper blower from a retracted position, where the upper blower is located over the lower blower and is completely inside the enclosure, to an extended position, where the upper blower is at least partially outside the enclosure; and directing air into the enclosure to dissipate heat from the heatsink using the upper blower.  
         [0027]     A further form of the method comprises the steps of transferring heat from the heat-generating electronic component to a heatsink; directing air to the heatsink to dissipate heat from the heatsink using an axial fan; moving a cover from underneath the heatsink so as to expose at least a portion of the underside of the heatsink; and moving the fan from a retracted position, where fan is completely inside the enclosure, to an extended position, where the fan substantially covers and directs air to the heatsink through the exposed underside portion of the heatsink for heat removal.  
         [0028]     Other features and advantages will become apparent from the description and claims that follow. 
     
    
     BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS  
       [0029]      FIG. 1A  is a perspective view of the first embodiment cooling system in a retracted position in a laptop computer.  
         [0030]      FIG. 1B  is a plan view of the cooling system of  FIG. 1A .  
         [0031]      FIG. 1C  is a side view of the cooling system of  FIG. 1A .  
         [0032]      FIG. 2A  is a perspective view of the first embodiment cooling system in an extended position.  
         [0033]      FIG. 2B  is a plan view of the cooling system of  FIG. 2A  showing the rotating out option for extension of the blower.  
         [0034]      FIG. 2C  is a plan view of the cooling system of  FIG. 2A  showing the sliding out option for extension of the blower.  
         [0035]      FIGS. 3A  to  3 D are plan views showing possible locations of the first embodiment cooling system in a laptop computer.  
         [0036]      FIG. 4A  is a side view of the second embodiment cooling system in a retracted position in a laptop computer.  
         [0037]      FIG. 4B  is a plan view of the cooling system of  FIG. 4A  in the extended position using rotating out option.  
         [0038]      FIG. 4C  is a plan view of the cooling system of  FIG. 4A  in the extended position using sliding out option.  
         [0039]      FIGS. 5A  to  5 D are plan views showing possible locations of the second embodiment cooling system in a laptop computer.  
         [0040]      FIG. 6A  is a perspective view of the third embodiment cooling system in a retracted position.  
         [0041]      FIG. 6B  is a side view of the cooling system of  FIG. 6A .  
         [0042]      FIG. 6C  is a plan view of the cooling system of  FIG. 6A .  
         [0043]      FIG. 7A  is a perspective view of the third embodiment cooling system in an extended position.  
         [0044]      FIG. 7B  is a side view of the cooling system of  FIG. 7A .  
         [0045]      FIGS. 7C and 7D  are plan views of the cooling system of  FIG. 7A  from the retracted position to extended position using rotating out option.  
         [0046]      FIGS. 7E and 7F  are plan views of the cooling system of  FIG. 7A  from the retracted position to extended position using sliding out option.  
         [0047]      FIGS. 8A  to  8 D are plan views showing possible locations of the third embodiment cooling system in a laptop computer.  
         [0048]      FIG. 9A  is a side view of the fourth embodiment cooling system in a retracted position.  
         [0049]      FIG. 9B  is a side view of the fourth embodiment cooling system in an extended position.  
         [0050]      FIGS. 10A  to  10 D are plan views showing possible locations of the fourth embodiment cooling system in a laptop computer.  
         [0051]      FIG. 11A  is a perspective view of the fifth embodiment cooling system in a retracted position in a laptop computer.  
         [0052]      FIG. 11B  is a side view of the cooling system of  FIG. 11A .  
         [0053]      FIG. 11C  is a plan view of the cooling system of  FIG. 11A .  
         [0054]      FIG. 12A  is a perspective view of the fifth embodiment cooling system in an extended position in a laptop computer.  
         [0055]      FIG. 12B  is a side view of the cooling system of  FIG. 12A .  
         [0056]      FIGS. 13A  to  13 D are plan views showing possible locations of the fifth embodiment cooling system in a laptop computer.  
         [0057]      FIG. 14  is a perspective view of some of the components in an example cooling system. 
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0058]     The cooling system of the present invention provides for the air flow device in the cooling system to move at least partially outside an electronic device enclosure within which the cooling system and the electronic components to be cooled are housed. The electronic device can perform any computing and/or data processing functions. For clarity, the movement and position of the air flow device out of the enclosure will be referred to as ‘extension’ and ‘extended’ respectively, and the movement and position of the air flow device into the enclosure will be referred to as ‘retraction’ and ‘retracted’ respectively.  
         [0059]     The extension and retraction of the air flow device may involve rotational and/or translational movements that can be easily accomplished by conventional mechanisms such as gear groups, linear motors, stepper motors, actuators or the like. The extension and retraction of the air flow device may be activated manually by a user such as by turning a thumbwheel or a push of a button that will allow an electrical motor to drive the gear group to achieve certain predetermined combination of translational and/or rotational motions. The extension and retraction can also be activated automatically. In the case of a laptop computer, the automatic activation may be triggered by opening the display panel of the laptop computer to extend the air flow device out of the enclosure and by closing the display panel of the laptop computer to retract the air flow device into the inside of the enclosure.  
         [0060]     In the case of a laptop or a mobile computing device, the extension and retraction may be based on an operating mode of the laptop. Depending on user preference and/or operation requirements, the laptop can operate in two different modes. In a battery savings mode or low power mode, the CPU operates at a low clock speed and thus consumes less power and generates less heat. In this mode, the air flow device may be configured to operate in the retracted position. In a high power mode, the CPU runs at full speed and generates maximum power. Here, the air flow device moves to the extended position. In a further alternative, the laptop can operate in only one mode with the air flow device operating in the extended position once the computer is powered on.  
         [0061]     The air flow device is typically chosen from radial impellers/blowers or axial fans. For blowers, the air inlet can be at one side or both and opposite sides of a generally thin case. A single air outlet or multiple air outlets can be at the side, or the whole side can be the air outlet. As such, airflow direction at the inlet is perpendicular to that at the outlet. Axial fans, on the other hand, have the air inlet on one side of the flat surface and the outlet on the opposite side such that airflow direction at the inlet is the same as that at the outlet.  
         [0062]      FIG. 1A  shows a laptop  100  having the first embodiment cooling system installed in a retracted position in the enclosure of the main body of the laptop  100 . The cooling system includes a blower  105  operating as an air flow device and a heatsink  110 . The heatsink  110  may be provided with extended surfaces such as plate fins, pin fins or other forms of surfaces that can be either unidirectional or omni directional depending on design requirements.  
         [0063]     In this embodiment, the blower  105  is movable between a retracted position with the blower  105  inside the enclosure and an extended position with the blower  105  extended at least partially out of the enclosure.  
         [0064]     In the retracted position, the cooling system can be adapted to work in a manner very similar to conventional cooling systems for laptop computers when operation of the cooling system in the retracted position is required.  
         [0065]      FIGS. 1B and 1C  respectively show a top and side view of the first embodiment cooling system that is operational in a retracted position in a laptop computer. The blower  105  is located inside the main body enclosure with the bottom air inlet, generally shown as  120  exposed to the exterior of the enclosure through air inlet vents at the bottom surface of the enclosure. As such, the air inlet  120  is aligned with and faces the air inlet vents which generally have a cross sectional area that is at least similar to the cross sectional area of the air inlet  120 .  
         [0066]     To facilitate airflow communication between the blower air inlet  120  and ambient through air inlet vents at the enclosure bottom, downward protruding standoffs attached to the bottom surface of the enclosure may be provided to elevate the enclosure off the working surface, such as a table top surface  130 , and create a gap to provide the air inlet  120  access to air.  
         [0067]     In operation, the blower  105  draws air from its air inlet  120 , through air inlet vents on the bottom surface of the enclosure and the gap. Referring to  FIGS. 1A  to  1 C, air drawn into the air inlet  120  of the blower  105  is discharged at the blower air outlet, represented as  135 , located on the side of the blower  105  facing the heatsink  110 . The air from the air outlet  135  then flows to the heatsink  110  whose fins are aligned such that air can flow past the fins and out into the ambient through exhaust vents  115  located on the peripheral surface  140  of the enclosure.  
         [0068]      FIG. 2A  shows the first embodiment cooling system in an extended position outside the enclosure of the main body of the laptop  200 . The blower  205  in this embodiment has been moved so that the blower  205  is at least partially outside of the laptop enclosure. In the depiction, about one-half of the blower  205  is located outside the enclosure. The extension of the blower  205  may be realized by first providing an aperture shown as  150  in  FIG. 1A  on the peripheral surface  140  and as  250  in  FIG. 2A  on the peripheral surface  240  of the laptop from which the blower  205  may extend. In one option, with reference to  FIGS. 2A and 2B , the blower outlet  235  will face the heatsink  210  when the blower  205  is in retracted position in the same way that  FIGS. 1A  to  1 C depict. The blower  205  extends out of the aperture  250  by rotating the blower  205  about a fixed pivot P, as shown in  FIG. 2B .  
         [0069]     When the blower  205  is in the extended position, air is drawn and directed into the blower chamber  260  in which the blower  205  was positioned in the retracted position to force air into and to dissipate heat from the heatsink  210 . However, instead of air being drawn into the blower only through a generally narrow gap into bottom air inlet  120  as described above in  FIG. 1B , air is drawn into the blower through bottom and top inlets  220  that are at least partially open to the ambient. As a result of the blower  205  being at least partially outside, airflow impedance at the air inlets  220  is reduced and airflow discharge from blower outlet  235  into the blower chamber  260  increases. The air from the blower chamber  260  then flows through the fins of the heatsink  210  and out through exhaust vents  115   
         [0070]     To completely extract or extend the blower  205 , the blower  205  is rotated out along a fixed pivot P so that when the blower  205  is completely outside, the outlet  235  faces the aperture  250  on the peripheral surface  240  and directs air into the blower chamber  260 .  
         [0071]     The cooling system described above can operate both in the retracted position and in the extended position. If it is required for the first embodiment cooling system to work only in the extended position, the following option can be used in addition to the rotating out option described above. The position of the air outlet  235  of the blower can be located on the side of the blower  205  opposite the aperture  250  in the retracted position as illustrated in  FIG. 2C . With the air outlet  235  facing away from the heatsink  210 , the cooling system is not operational when the blower  205  is in the retracted postion and therefore, the blower  205  is powered off in the retracted position. When extended, the blower  205  slides out through the aperture  250  so that the outlet  235  faces and directs air into the blower chamber  260 . Again, partial or full extension can be accomplished by sliding blower  205  out of the enclosure.  
         [0072]      FIGS. 3A and 3B  show possible locations of the cooling system of the first embodiment in a laptop computer. The front of the laptop, where a keyboard and pointing device are normally located is indicated as ‘F’, while the rear of the laptop is indicated as ‘R’. The blower  305  is shown in solid lines in the retracted position and is shown in broken lines in the extended position.  
         [0073]     The heatsink  310  is ideally located at a corner of the peripheral surface  340  of the enclosure with two sides bounded by the peripheral surface  340  as illustrated in  FIGS. 3A  to  3 D. This ensures that there is one side of the peripheral surface  340  from which the blower  305  may extend and intake air, and at least another side of the peripheral surface  340  from which heated exhaust flow may exit the enclosure through exhaust vents  315 .  
         [0074]     Exhaust vents  315  are disposed along the peripheral surface  340 .  FIGS. 3A and 3B  show exhaust vents  315  only on one side of the peripheral surface  340  for use with the heatsink  310  such as a plate fin or pin fin heatsink that is adapted to accommodate airflow from the blower  305  to the exhaust vents  315 , while  FIGS. 3C and 3D  show exhaust vents  315  on two sides of the peripheral surface  340  for use with the heatsink  310  such as a pin fin heatsink that is adapted for airflow from the blower  305  to two sides that form the exhaust vents  315 . While  FIGS. 3A  to  3 D show significantly complete extension of the blower  305  out of the enclosure, the extension can also be partial and can be accomplished by either sliding out or rotating out options.  
         [0075]      FIG. 4A  shows a side view of the second embodiment cooling system, which employs two blowers, the top blower  404  and the lower blower  405  stacked one atop the other, and a heatsink  410 . The heatsink  410  may be provided with extended surfaces such as plate fins, pin fins or other forms of surfaces that can be either unidirectional or omni directional depending on design requirements. As with the first embodiment, this embodiment will be described with reference to a laptop and use of the laptop on a table top working surface  430 .  
         [0076]     In this embodiment, the top blower  404  is movable between a retracted position with the top blower  404  being inside the enclosure and an extended position with the top blower  404  extended at least partially out of the enclosure. The lower blower  405  has a fixed position inside the enclosure.  
         [0077]     The lower blower  405  fixed in its position within the enclosure has the bottom air inlet  420  exposed to the exterior of the enclosure through air inlet vents at the bottom surface of the enclosure. As such, the bottom air inlet  420  is aligned with and faces the air inlet vents which generally have a cross sectional area that is at least similar to the cross sectional area of the air inlet  420 . The top air inlet  421  of the lower blower  405  can either be blocked with a solid plate or be left open.  
         [0078]     In the retracted position, the top blower  404  sits atop the lower blower  405  with its bottom air inlet  423  facing the top air inlet  421  of the lower blower  405  and with its top air inlet  424  generally blocked by a solid surface behind the top surface of the enclosure main body. As such, neither the top inlet  424  nor the bottom air inlet  423  of the upper blower  404  has direct access to air in the retracted position. Therefore, the upper blower  404  is non-operational and is always powered off in the retracted position. The location of the air outlet  436  of the upper blower  404  is determined by how upper blower  404  is extended which will be discussed later.  
         [0079]     To facilitate airflow communication between the blower air inlet  420  of the lower blower  405  and ambient through air inlet vents at the enclosure bottom, downward protruding standoffs are commonly attached to the bottom surface of the enclosure to elevate the enclosure off the working surface  430  and create a gap for access to air. In operation with both blowers  404  and  405  in the retracted position, the lower blower  405  is powered on with its bottom air inlet  420  open to ambient and its top air inlet  421  non-functional whether it is blocked or open as the top blower  405  is powered off and non-functional. Air from the ambient is drawn into the bottom air inlet  420  of the blower  405  through the gap and the air inlet vents and is discharged from the air outlet, represented by arrow  435 , located on the side of the blower  405  facing the heatsink  410  with reference to  FIG. 4C . The air from the air outlet  435  then flows into the heatsink  410  whose fins are aligned such that air can flow past the fins and out into the ambient through exhaust vents  415  located on the peripheral surface of the enclosure.  
         [0080]     An blower aperture represented as  450  in  FIG. 4C  is provided on the peripheral surface  440  of the enclosure to allow the upper blower  404  to be moved in and at least partially out of the enclosure, or more specifically, the blower chamber  460  in which the upper blower  404  was positioned in the retracted position.  
         [0081]     In operation, referring to  FIGS. 4B and 4C , the second embodiment cooling system with the upper blower  404  is extended partially outside of the enclosure. The upper blower  404  can also be extended completely outside of the enclosure if required. The upper blower  404  is then powered up and is able to draw in air from its at least partially open top inlet  424  as well as bottom air inlet  423 . The air is made to flow out of the outlet  436  into the blower chamber  460 . If the top air inlet  421  of the lower blower  405  is blocked, the air from the blower chamber  460  then flows directly through the fins of the heatsink  410  and out through exhaust vents  415 . On the other hand, if the top air inlet  421  of the lower blower  405  is open, air discharged from air outlet  436  of the upper blower  404  into the blower chamber  460  will split into two streams, one is made to flow through the heatsink  410  directly and the other is drawn into the top inlet  421  of the bottom blower  405  which is then discharged out from the blower outlet  435  of the lower blower  405  and made to flow through the heatsink  410 .  
         [0082]     The following two options can be used and more options can be devised if needed to place the outlet  436  of the upper blower  404  that will also determine how the upper blower  404  is extended out of the enclosure. One option is to have the outlet  436  of the upper blower  404  in the retracted position face the heatsink  410 . To extract or extend the upper blower  404 , the blower  404  is rotated out along a fixed pivot axis so that when the upper blower  404  is extended, the outlet  436  faces and directs air into the blower chamber  460 , as can be seen in  FIG. 4B .  
         [0083]     Alternatively, the outlet  436  of the upper blower  404  in the retracted position is located on the side opposite the blower aperture  450 . To extract or extend the upper blower  404 , the upper blower  404  slides out through the blower aperture  450  so that the outlet  436  faces and directs air into the blower chamber  460  with reference to  FIG. 4C .  
         [0084]     Based on the second embodiment described herein, a laptop employing this cooling system can operate in two different modes. In the low power operating mode, the upper blower  404  stays inside the blower chamber  460  and powered off while the lower blower  405  is powered on to direct air into heatsink  410  to dissipate heat. The heat removal capacity in this mode is limited when only the lower blower  405  is operational. In the high power operating mode, both blowers  404  and  405  are powered on with lower blower  405  staying in the retracted position while the upper blower  404  is extended from the enclosure by rotating out or sliding out. The heat removal capability in this mode is naturally higher with both blowers  404  and  405  operating and directing air to heatsink  410 .  
         [0085]     Alternatively, a laptop employing this cooling system can have a single operating mode; that is the high power operating mode described above. Once the computer is powered on, both blowers  404  and  405  are powered on with lower blower  405  staying in the retracted position while the upper blower  404  is extended from the enclosure by rotating out or sliding out.  
         [0086]      FIGS. 5A  and SB show possible locations of the second embodiment cooling system in a laptop computer. The front of the laptop, where a keyboard and pointing device are normally located is indicated as ‘F’, while the rear of the laptop is indicated as ‘R’.  
         [0087]     For clarity, only the movable upper blower  504  is shown. The lower blower  505  will have the same or similar positioning as the upper blower  504  in the retracted position. While the lower blower  505  is non-movable, the upper blower  504  can be moved from its retracted position shown with solid lines to the extended position shown with broken lines.  
         [0088]     As with the first embodiment, the heatsink  510  is preferably located at a corner with two sides bounded by the peripheral surface  540  and with the upper blower  504  as well as the lower blower  505 , in the retracted position, located next to it with reference to  FIGS. 5A  to SD. This ensures that there is one side of the peripheral surface  540  from which the upper blower  504  may extend and intake air, and at least another side of the peripheral surface  540  from which heated exhaust flow may exit the enclosure through exhaust vents  515 .  
         [0089]     Exhaust vents  515  are disposed along the peripheral surface  540 .  FIGS. 5A and 5B  show exhaust vents  515  only on one side of the peripheral surface  540  for use with the heatsink  510  such as a plate fin or pin fin heatsink that is adapted to accommodate airflow from the upper blower  504  and lower blower  505  to the exhaust vents  515 , while  FIGS. 5C and 5D  show exhaust vents  515  on two sides of the peripheral surface  540  for use with the heatsink  510  such as a pin fin heatsink that is adapted for airflow from the upper blower  504  and lower blower  505  to two sides that form the exhaust vents  515 . While  FIGS. 5A  to  5 D show significantly complete extension of the upper blower  504  out of the enclosure, the extension can also be partial and can be accomplished by either sliding out or rotating out options.  
         [0090]      FIG. 6A  shows the third embodiment cooling system, employing an axial fan  605  and a heatsink  610 . As with previous embodiments, the heatsink  610  may be provided with extended surfaces such as plate fins or pin fins or other forms of surfaces that can be either unidirectional or omni directional depending on design requirements. As noted in the Background section, the axial fan differs from the radial blower in that the airflow direction at the air inlet and that at the outlet of the fan are parallel, while airflow at the inlet(s) and that at the outlet of the blower are perpendicular to one another.  
         [0091]     In this embodiment, the axial fan  605  is movable from a retracted position inside the enclosure to an extended position at least partially outside the enclosure. Referring to  FIGS. 6A  to  6 C, the heatsink  610  is preferably located adjacent and on the side of the fan  605  that is in the retracted position. This placement of a fan next to a heatsink may be desirable due to space limitations or other design requirements.  
         [0092]     In the retracted position, the fan  605  is oriented such that airflow is from the bottom to the top with the air inlet  620  at the bottom and the air outlet  635  at the top. Air inlet vents in the form of finger guards or other types can be attached to or be an integral part of the fan air inlet  620  to prevent foreign objects from being inadvertently drawn into the air inlet  620 . Further a bottom aperture is provided on the bottom surface of the enclosure underneath the fan  605  significantly aligned with the fan inlet  620  to allow communication between air inlet  620  and air. The bottom aperture preferably has a cross sectional area that is significantly similar to that of the air inlet  620 . As an alternative, the air inlet vents can also be mounted to the bottom aperture.  
         [0093]     When operation of the cooling system in this embodiment is required with the fan  605  in the retracted position, with reference to  FIG. 6B , downward protruding standoffs are attached to the bottom surface of the enclosure to elevate the enclosure off the working surface  630  and create a gap for access to air. Further, as the heatsink  610  is located along the side of the fan  605 , air flowing out of the air outlet  635  will need to be redirected from flowing upwardly out of the fan outlet  635  to horizontally through the fins of the heatsink  610 . As shown in  FIG. 6B , a plenum  625  is provided on top of the fan outlet  635  to achieve this.  
         [0094]     In operation with the fan  605  in the retracted position, air from the ambient is drawn into the air inlet  620  of the fan  605  through the gap and the air inlet vents. The air is then discharged from the air outlet  635  located on the top of fan  605  into the plenum  625 . As shown in  FIGS. 6B and 6C , pressurized air in the plenum  625  will find its way through the heatsink fins that are aligned such that air can flow past the fins and out into the ambient through exhaust vents  615  located on the peripheral surface  640  of the enclosure.  
         [0095]     Alternatively, when operation of the fan  605  is not required in the retracted position, the plenum  625  and the downward protruding standoffs become optional.  
         [0096]     To allow the fan  605  to be moved in and out of the enclosure, and more specifically out of the fan chamber  660  in which the fan  605  was positioned in the retracted position, a fan aperture  650  is provided on the peripheral surface  640  with reference to  FIG. 6A .  FIGS. 7A  and  7 B show the third embodiment cooling system in the extended position where the axial fan  705  slides out of the enclosure through the fan aperture  750 . While the fan  705  can maintain its leveled position relative to the enclosure in the extended position, it is preferable that the fan  705  is tilted to a predetermined angle a in its extended operational position relative to the position of the fan  705  in the retracted position. As shown, a wedge shaped space is formed underneath the fan  705  between a plane that defines the air inlet  720  and the working surface  730  thus affording greater access to air compared to a generally narrow gap provided underneath the laptop using standoffs. As such, the airflow impedance at air inlet  720  is reduced and airflow rate increases as a result.  
         [0097]     In the retracted position, upwardly flowing air from the fan outlet  635  was redirected to flow to the heatsink using the plenum  625 . Now, in the extended position, a similar provision is required to redirect air flowing upwardly out of the outlet  735  into the fan chamber  760  from which the fan  705  exited. With reference to  FIG. 7B , a hood  770  is provided for this reason. The hood  770  may be retractable and extendable depending on the fan position. When the fan  705  is retracted inside the fan chamber  760 , the hood  770  is also retracted significantly conforming to the size and shape of the interior of the plenum  725 . Conversely, when the fan  705  is in the extended position outside the enclosure, the hood  770  also extends and expands if required to a predetermined size and shape. As an alternative, the hood  770  can also have a fixed size and shape that can conform to the inside of the plenum  725  when the fan  705  and the hood  770  are in the retracted position. The hood  770  acts as a plenum with a hood opening  780  facing the fan chamber  760  when the fan  705  is in the extended position.  
         [0098]     Referring to  FIGS. 7A and 7B , in operation with the fan  705  in the extended position, air is drawn into the fan inlet  720  of the fan  705  from the open sides of the wedge shaped space and discharged from the fan outlet  735  into the hood  770 . From the hood  770 , air exits the opening  780  and enters the fan chamber  760 . Pressurized air inside the fan chamber then finds its way into the heatsink  710  whose extended surfaces are adapted such that air can flow past at least the majority of the extended surfaces of the heatsink  710  and be exhausted to the ambient through the exhaust vents  715  on the peripheral surface  740  of the enclosure.  
         [0099]     The location of the hood opening  780  when the hood  770  along with the fan  705  is in the retracted position is determined by the cooling solution requirement and extension mechanism of the fan  705 .  
         [0100]     If it is required for this cooling system to work in both the retracted and extended position, the following option can be used and more options can be devised if needed. In the retracted position, the opening  780  faces the heatsink  710  with reference to  FIG. 7C . To extract or extend the fan  705 , the fan  705  is rotated out about a fixed pivot axis so that when the fan  705  is moved outside at least partially, the hood opening  780  faces and directs air into the fan chamber  760  with reference to  FIG. 7D . However, if the cooling solution is only required to operate in the extended position, in addition to the aforementioned rotate-out option with reference to  FIGS. 7C and 7D , the following option can be used. In the retracted position, the hood opening  780  faces the side opposite and significantly parallel to the aperture  750  with reference to  FIG. 7E . Since this option does not allow airflow path from the fan air outlet  735  to the exhaust vents  715  when the fan  705  is in the retracted position, the fan  705  needs to be powered off in the retracted position. To extract or extend the fan  705 , the fan  705  slides out from the fan chamber  760  through the aperture  750  with the hood opening  780  facing and directing air into the fan chamber  760  with reference to  FIG. 7F . In both options, the fan  705  can be extracted out partially or completely.  
         [0101]     Similar to previous embodiments, the cooling system in this embodiment can be adapted to allow operation in two modes or in one mode. Two operating modes involve a low cooling capacity operation with the fan  705  in the retracted position, allocation of plenum  625  and the hood opening  780  facing the heatsink  710  when the fan  705  is in the retracted position with reference to  FIG. 7C , and a high cooling capacity operation with the fan  705  in the extended position shown in  FIGS. 7A, 7B  and  7 D with the fan  705  being extracted by rotating out. Alternatively, the cooling system in this embodiment can be designed for a single mode operation; that is the cooling system will only operate with the fan  705  in the extended position illustrated in  FIGS. 7A and 7B  either by rotating out ( FIG. 7D ) and sliding out ( FIG. 7F ).  
         [0102]      FIGS. 8A  to  8 D show possible locations of the third embodiment cooling system in a laptop computer. The front of the laptop, where a keyboard and pointing device are normally located is indicated as ‘F’, while the rear of the laptop is indicated as ‘R’.  
         [0103]     The axial fan  805  is shown in solid lines in the retracted position, and in broken lines in the extended position.  FIGS. 8A  to  8 D show a substantially complete extension of the fan  805  outside of the enclosure. This is not necessary. The fan  805  can be moved outwardly so as to be only partially outside.  
         [0104]     As with earlier embodiments, the heatsink  810  is preferably located at a corner of the peripheral surface  840  of the enclosure with two sides bounded by the peripheral surface  840  and with the fan  805 , in the retracted position, located next to it with reference to  FIGS. 8A  to  8 D. This ensures there is one side of peripheral surface  840  from which the fan  805  may extend and intake air, and at least another side of peripheral surface  840  from which heated exhaust flow may exit the enclosure through exhaust vents  815 .  
         [0105]     Exhaust vents  815  are disposed along the peripheral surface  840 .  FIGS. 8A and 8B  show exhaust vents  815  only on one side of the peripheral surface  840  for use with the heatsink  810  such as a plate fin or pin fin heatsink that is adapted to accommodate airflow from the fan  805  to the exhaust vents  815 , while  FIGS. 8C and 8D  show exhaust vents  815  on two sides of the peripheral surface  840  for use with the heatsink  810  such as a pin fin heatsink that is adapted for airflow from the fan  805  to two sides that form the exhaust vents  815 . While  FIGS. 8A  to  8 D show significantly complete extension of the fan  805  out of the enclosure, the extension can also be partial and can be accomplished by either sliding out or rotating out options.  
         [0106]      FIG. 9A  shows the fourth embodiment cooling system, where an axial fan  905  is used as the air flow device to cool the heatsink  910 . As with previous embodiments, the heatsink  910  may be provided with extended surfaces such as plate fins, pin fins or other forms of surfaces that can be either unidirectional or omni directional depending on design requirements.  
         [0107]     In this embodiment, the fan  905  is movable between a retracted position with the fan  905  significantly contained inside the enclosure of an electronic device and an extended position with the fan  905  extended out of the enclosure at least partially from underneath or the bottom surface of the enclosure. Referring to  FIG. 9A , the heatsink  910  is preferably located adjacent and on the side of the fan  905  that is in the retracted position. This placement of a fan next to a heatsink may be desirable due to space limitations or other design requirements.  
         [0108]     In the retracted position, the fan  905  is oriented such that airflow is from the bottom to the top with the air inlet  920  at the bottom and with the air outlet  935  at the top. Air inlet vents in the form of finger guards or other types can be attached to or be an integral part of the fan air inlet  920  to prevent foreign objects from being inadvertently drawn into the air inlet  920 . The fan air inlet  920  is then exposed to the exterior of the enclosure through a fan aperture  950  located on the bottom surface of the enclosure underneath the fan  905  significantly aligned with the air inlet  920 . The fan aperture  950  typically has a cross sectional area that is at least the same size as the cross sectional area of the fan  905  so that the fan  905  can move inside and outside of the enclosure or more specifically the fan chamber  960  that the fan  905  occupies in the retracted position.  
         [0109]     When operation of the cooling system in this embodiment is required with the fan  905  in the retracted position, with reference to  FIG. 9A , downward protruding standoffs are attached to the bottom surface of the enclosure to elevate the enclosure off the working surface  930  and create a gap for access to air. Further, as the heatsink  910  is located along the side of the fan  905 , air flowing out of the air outlet  935  will need to be redirected from flowing upwardly out of the fan outlet  935  to horizontally through the fins on the heatsink  910 . As shown in  FIG. 9A , a plenum  925  is provided on top of the fan outlet  935  to achieve this.  
         [0110]     In operation with the fan  905  in the retracted position, air from the ambient is drawn into the air inlet  920  of the fan  905  through the gap and the fan aperture  950  at the bottom of the enclosure. The air is then discharged from the air outlet  935  located on the top of fan  905  into the plenum  925 . As shown in  FIG. 9A , pressurized air in the plenum  925  will find its way through the heatsink fins that are aligned such that air can flow past the fins and out into the ambient through exhaust vents  915  located on the peripheral surface of the enclosure.  
         [0111]     Alternatively, when operation of the fan  905  is not required in the retracted position, the plenum  925  and the downward protruding standoffs become optional.  
         [0112]      FIG. 9B  shows the fourth embodiment cooling system in an extended position. In this extended position, the axial fan  905  moves out from the bottom surface of the enclosure through the fan aperture  950 . Once outside, the fan  905  tilts relative to the position of the fan is  905  in the retracted position such that a wedge shaped space is formed with a predetermined angle β between the plane of fan air inlet  920  and the working surface  930 . The tilt angle β is adapted to provide the axial fan  905  better access to air by allowing the air inlet  920  to face the open side of the wedge shaped space and by directing discharged air from the air outlet  935  to the fan chamber  960  and to the heatsink  910 . As such, the airflow impedance at the fan inlet  920  is reduced and airflow rate increases as a result as compared to the generally narrow gap provided by standoffs and working surface  930  and small plenum  925  at the fan outlet  935  when the fan is in the retracted position.  
         [0113]     The tilted fan  905  under the enclosure will cause the enclosure to tilt with reference to the working surface  930 . While the impact of how the enclosure tilts on the operation or performance of the cooling system may not be significant, to avoid the enclosure to tilt in a way that is ergonomically unfriendly and awkward to operate, it is desirable to keep the fan  905  near or along the rear side of the enclosure. As such, the enclosure will tilt in an ergonomically friendly way when the fan  905  is in the extended position with the front edge of the enclosure being close to the working surface  930  and the rear edge elevated above the working surface  930 . To ensure that the enclosure can rest stably on the working surface  930 , supporting legs or structures that are preferably extendable and retractable preferably in sync with the extension and retraction of the fan  905  will be attached to the bottom side of the enclosure or to the fan  905  protruding downwardly toward the working surface  930 .  
         [0114]     Further, depending on the angle β of the wedge shaped space and the extent that the fan  905  extends out of the enclosure, it may also be necessary to provide airflow one or more baffles or a hood such as on shown in  FIG. 9B  as  990  at the fan outlet  935  to ensure that air discharged from the air outlet  935  does not leak into the ambient but is instead directed toward the heatsink  910 .  
         [0115]     Referring to  FIG. 9B , in operation with the fan  905  in the extended position, air is drawn into the fan inlet  920  from the open side of the wedge shaped space and discharged from the fan outlet  935  into the fan chamber  960 . Pressurized air inside the fan chamber then finds its way into the heatsink  910  whose extended surfaces are adapted such that air can flow past at least the majority of the extended surfaces of the heatsink  910  and be exhausted to the ambient through the exhaust vents  915  on the peripheral surface  940  of the enclosure.  
         [0116]     Similar to previous embodiments, the cooling system in this embodiment can be adapted to allow operation in two modes or in one mode. Two operating modes involve a low cooling capacity operation with the fan  905  in the retracted position and allocation of plenum  925  and downward protruding standoffs shown in  FIG. 9A  and a high cooling capacity operation with the fan  905  in the extended position shown in  FIG. 9B . Alternatively, the cooling system in this embodiment can be designed for a single mode operation; that is the cooling system will only operate with the fan  905  in the extended position illustrated in  FIG. 9B .  
         [0117]      FIGS. 10A  to  10 D show possible locations of the cooling system of the fourth embodiment in a laptop computer. The front of the laptop, where a keyboard and pointing device are normally located is indicated as ‘F’, while the rear of the laptop is indicated as ‘R’.  
         [0118]     The axial fan  1005  is located within the enclosure when it is in the retracted position, shown in solid lines in  FIGS. 10A  to  10 D. In the extended position, the fan  1005  moves at least partially out of the enclosure from underneath the enclosure and is tilted with respect to the position of the fan  1005  in the retracted position. This extended position is shown in broken lines in  FIGS. 10A  to  10 D.  
         [0119]     Since the fan  1005  is extended out from the bottom of the enclosure, the fan  1005  does not need to be bounded by the peripheral surface  1040  of the enclosure as compared to the discussions of embodiments one, two and three. Therefore, the heatsink  1010  can be located in the enclosure with only one side bounded by the peripheral surface  1040  with the fan  1005  located on its side as shown in  FIGS. 10A and 10B  when the heatsink  1010  has extended surfaces such as plate fins or pin fins, that are adapted to airflow between the fan  1005  and the exhaust vents  1015 .  
         [0120]     Alternatively, the heatsink  1010  shown in  FIGS. 10C and 10D  can also be located at a rear corner bounded on two sides of the peripheral surface  1040 , when the heatsink  1010  has extended surfaces, such as pin fins that are adapted for airflow between the fan  1005  and the exhaust vents  1015  on two sides of the peripheral surface  1340 . While not shown, when the heatsink  1010  is located at a rear corner, the exhaust vents  1015  can also be located at only on side of the peripheral surface  1040  when the heatsink  1010  has extended surfaces, such as plate fins or pin fins that are adapted for airflow between the fan  1005  and the exhaust vents  1015  on one of the peripheral surface  1040 .  
         [0121]      FIG. 11A  shows the fifth embodiment cooling system as installed inside the main body enclosure of a laptop computer. As with the previous two embodiments, the fifth embodiment cooling system employs an axial fan  1105  to cool a heatsink  1110 , which could have plate fins, pin fins or other forms of extended surfaces that can be either unidirectional or omni directional depending on design requirements.  
         [0122]     In this embodiment, the fan  1105  is movable between a retracted position with the fan  1105  substantially contained inside the main body enclosure and an extended position with the fan  1105  extended at least partially out of the enclosure from underneath or the bottom surface of the enclosure. Referring to  FIGS. 11A  to  11 C, the heatsink  1110  is preferably located adjacent and on the side of the fan  1105  that is in the retracted position. This placement of a fan next to a heatsink may be desirable due to space limitations or other design requirements.  
         [0123]     In the retracted position, the fan  1105  is oriented such that airflow is from the bottom to the top with the air inlet  1120  at the bottom and with the air outlet  1135  at the top. Air inlet vents in the form of finger guards or other types can be attached to or be an integral part of the fan  1105  to prevent foreign objects from being inadvertently drawn into the air inlet  1120 . The fan air inlet  1120  is then exposed to the exterior of the enclosure through a fan aperture  1150  as shown in  FIG. 11B  located on the bottom surface of the enclosure underneath the fan  1105  significantly aligned with the air inlet  1120 . The fan aperture  1150  typically has a cross sectional area that is at least the same size as the cross sectional area of the fan  1105  so that the fan  1105  can move inside and outside of the enclosure or more specifically the fan chamber  1160  that the fan  1105  occupies in the retracted position through the fan aperture  1150 .  
         [0124]     When operation of the cooling system in this embodiment is required with the fan  1105  in the retracted position, with reference to  FIG. 11B , downward protruding standoffs are attached to the bottom surface of the enclosure to elevate the enclosure off the working surface  1130  and create a gap for access to air. Further, with the heatsink  1110  being located along the side of the fan  1105 , air flowing out of the air outlet  1135  will need to be redirected from flowing upwardly out of the fan outlet  1135  to horizontally through the fins on the heatsink  1110 . As shown in  FIG. 11B , a plenum  1125  is provided on top of the fan outlet  1135  to achieve this.  
         [0125]     In operation with the fan  1105  in the retracted position, air from the ambient is drawn into the air inlet  1120  of the fan  1105  through the gap and the fan aperture  1150  at the bottom of the enclosure. The air is then discharged from the air outlet  1135  located on the top of fan  1105  into the plenum  1125 . As shown in  FIGS. 11B and 11C , pressurized air in the plenum  1125  will find its way through the heatsink fins that are aligned such that air can flow past the fins and out into the ambient through exhaust vents  1115  located on the peripheral surface  1140  of the enclosure.  
         [0126]     Alternatively, when operation of the fan  1105  is not required in the retracted position, the plenum  1125  and the downward protruding standoffs become optional.  
         [0127]     Referring to  FIG. 11B , to facilitate operation with the fan  1105  in the extended position, a heatsink aperture is provided on the bottom surface underneath the heatsink  1110 , for purposes that will later be described. The heatsink aperture has a cross sectional area that is typically at least similar to the cross sectional area of the heatsink  1110  and should be covered with a solid plate or cover when the heatsink  1105  is operating in the retracted position in order to eliminate airflow bypass.  
         [0128]     Referring to  FIGS. 12A and 12B , the fifth embodiment cooling system is shown in the extended position. In this position, the axial fan  1205  has moved out of the fan chamber  1260  from underneath through the fan aperture  1250  provided on the bottom surface of the enclosure. The fan  1205  is also moved toward the heatsink  1210  to substantially cover the underside of the heatsink  1210 . In the process, the fan  1205  maintains its bottom to top airflow direction.  
         [0129]     A mechanism is provided to move the solid cover that covers the heatsink aperture underneath the heatsink  1210 . When the fan  1205  moves toward the heatsink  1210 , the cover makes way for the incoming fan  1205 . This precise motion may be altered, for instance, by having the solid cover of the underside of the heatsink  1210  to open just before the fan  1205  is moved to the extended position. Therefore, when the fan  1205  moves into the extended position that substantially covers the heatsink  1210  from underneath, the underside of the heatsink  1210  is at least partially open to the fan outlet side  1235 . Better results can be achieved when the opening underneath the heatsink  1210  and the cross-sectional area of the heatsink  1210  exposed to the fan  1205  are adapted to allow the underside of the heatsink  1210  to be substantially covered by airflow coming out from the fan outlet  1235 .  
         [0130]     As can be seen in  FIG. 12B , once the fan  1205  is moved to cover the underside of the heatsink  1210 , the bottom surface of the enclosure will be elevated off the working surface  1230  beyond the height of the original standoffs if available, and will tilt relative to the working surface  1230  in a way determined by the location of the fan  1205 . While the impact of how the enclosure tilts on the operation or performance of the cooling system may not be significant, to avoid the enclosure to tilt in a way that is ergonomically unfriendly and awkward to operate, it is desirable to keep the fan  1205  in the extended position near the rear side of the enclosure When the fan  1205  is located near the rear edge in the extended position, the enclosure will tilt with the front edge of the enclosure being close to the working surface  1230  and the rear edge elevated from the working surface  1230  to at least the thickness of the fan. This tilt may be ergonomically desirable, for instance where the device is laptop computer with its keyboard located on the top surface, as many standard laptops and keyboards are designed.  
         [0131]     When the enclosure tilts as described, a wedge shaped space forms between the plane of the fan air inlet  1220  and the working surface  1230  allowing air inlet  1220  access to air through the open side of the wedge shaped space. To reduce airflow impedance at the fan inlet  1220 , it may be desirable to increase the tilt angle by raising the rear side of the enclosure to a predetermined height, preferably beyond the thickness of the fan by addition of supporting legs or structure under the bottom surface or under the fan  1205 . Preferably, supporting legs or structure are also adapted to ensure that the enclosure rests on the working surface  1230  stably and to be retractable and extendable preferably in sync with the retraction and extension of the fan  1205 .  
         [0132]     In this extended position, air is drawn into the fan air inlet  1220  from the open side of the wedge shaped space, as shown in  FIG. 12B , and discharged from air outlet  1235  to the heatsink  1210  from the underside. One stream of the exhaust air exits from one end of the heatsink  1210  through exhaust vents  1215  located on the peripheral surface  1240  of the enclosure. Another stream of the exhaust air exits from the second and opposite end of the heatsink  1210  into the fan chamber  1260  vacated by the fan  1205  and into the ambient through the gap between the bottom surface of the enclosure and the working surface  1230 . As such, it may be desirable to have one or more air baffles separating the fan air inlet  1220  from exhaust air stream coming out from the second end of the heatsink  1210 . With reference to  FIG. 12B , an air baffle  1290  may be installed preferably along the edge of the fan air inlet  1220  or from the underside of the enclosure bottom surface adjacent the fan air inlet  1220  extending downward all the way to the working surface  1230  to minimize hot air recirculation into fan air inlet  1220 . Further, the air one or more baffles can also act as at least a part of the aforementioned supporting legs or structure.  
         [0133]     Similar to previous embodiments, the cooling system in this embodiment can be adapted to allow operation in two modes or in one mode. Two operating modes involve a low cooling capacity operation with the fan  1105  in the retracted position and allocation of plenum  1125  and downward protruding standoffs shown in  FIGS. 11A-11C  and a high cooling capacity operation with the fan  1205  in the extended position shown in  FIGS. 12A and 12B . Alternatively, the cooling system in this embodiment can be designed for a single mode operation; that is the cooling system will only operate with the fan  1205  in the extended position illustrated in  FIGS. 12A and 12B . When the cooling system in this embodiment is only required to operate in the extended position, the cover underneath the heatsink  1210  becomes optional.  
         [0134]      FIGS. 13A  to  13 D show possible locations of the cooling system within a laptop&#39;s main body enclosure. The front of the main body, where a keyboard and pointing device are normally located is indicated as ‘F’, while the rear of the laptop is indicated as ‘R’.  
         [0135]     The axial fan  1305  is located within the enclosure when it is in the retracted position, shown in solid lines in  FIGS. 13A  to  13 D. In the extended position, the fan  1305  moves out of the enclosure from underneath the enclosure and moves to underneath the fan  1310 . This extended position is shown in broken lines in  FIGS. 13A  to  13 D.  
         [0136]     As illustrated in  FIGS. 13A and 13B , the heatsink  1310  can be located with only one side bounded by the peripheral surface  1340  of the enclosure and the fan  1305 , in the retracted position, located on its side when the heatsink  1310  has extended surfaces such as plate fins or pin fins, that are adapted to airflow between the fan  1305  and the exhaust vents  1315 .  
         [0137]     Alternatively, the heatsink  1310  shown in  FIGS. 13C and 13D  can also be located at a rear corner bounded by two sides of the peripheral surface  1340 , when the heatsink  1310  has extended surfaces, such as pin fins shown in  FIGS. 13C and 13D  that are adapted for airflow between the fan  1305  and the exhaust vents  1315  on two sides of the peripheral surface  1340 . While not shown, when the heatsink  1310  is located at a rear corner, the exhaust vents  1315  can also be located at only one side of the peripheral surface  1340  when the heatsink  1310  has extended surfaces, such as plate fins or pin fins that are adapted for airflow between the fan  1305  and the exhaust vents  1315  on one of the peripheral surface  1340 .  
         [0138]     The text above describes one or more specific embodiments of a broader invention. The invention also is carried out in a variety of alternative embodiments and thus is not limited to those described here. Those other embodiments are also within the scope of the following claims.  
         [0139]     While the invention and exemplary embodiments of the invention have been illustrated and described in general and specific terms, it should be understood that the invention may be modified and otherwise embodied in still other forms, including but not limited to all forms which are obvious variants of or equivalent to those disclosed.  
         [0140]     The preceding descriptions are by way of example and are not intended to limit or restrict the scope of the invention which is specified and defined by the appended claims.