PATENT DOCUMENT

Publication Number: US-10606325-B2
Application Number: US-201815994753-A
Country: US
Kind Code: B2

Title: Thermal management components for electronic devices

Abstract:
A thermal management system that includes a fan assembly, a heat exchanger, and an insulating box is described. The fan assembly can have two impellers and a housing that includes two scroll portions. An internal portion of the scroll wall can be truncated. A motor housing can be connected to the fan housing via multiple struts. The struts can be oriented angularly with a tangential component and can slope inward to increase the effective inlet area. The heat exchanger can be formed of a fin stack that has a curved body that defines an airflow path that turns radially from the inlet to the exhaust. The heat exchanger can have an inlet that is smaller than the exhaust. The heat exchanger can be connected to one or more heat pipes. The insulating box can have a grid that directs air to certain specific directions.

Claims:
What is claimed is: 
     
       1. An electronic device, comprising:
 a housing that defines an internal volume and outlet vents leading to the internal volume, the housing further comprising a first region and a second region separate from the first region; 
 an air mover assembly located in the internal volume, the air mover assembly comprising an exhaust outlet; 
 a first heat-generating component located in the first region; 
 a second heat-generating component located in the second region; and 
 a heat exchanger capable of receiving an airflow from the exhaust outlet and passing the air out of the housing, the heat exchanger thermally connected to the first heat-generating component and the second heat-generating component, the heat exchanger comprising:
 a first set of heat pipes arranged to transfer heat from the first heat-generating component; and 
 a second set of heat pipes arranged to transfer heat from the second heat-generating component, wherein the first set of heat pipes is interleaved with the second set of heat pipes; and 
 
 an insulating box located in the internal volume between an exhaust of the heat exchanger and the outlet vents. 
 
     
     
       2. The electronic device as recited in  claim 1 , wherein the heat exchanger comprises fins stacked together to form a finstack. 
     
     
       3. The electronic device as recited in  claim 1 , wherein the heat exchanger turns the airflow radially from an inlet of the heat exchanger to an exhaust of the heat exchanger. 
     
     
       4. The electronic device as recited in  claim 1 , wherein the insulating box including strips that define a grid. 
     
     
       5. The electronic device as recited in  claim 4 , further comprising a stand that is rotationally coupled to the housing, wherein the outlet vents are covered by the stand, and wherein the insulating box is configured to contour air to exit the electronic device to avoid the stand. 
     
     
       6. The electronic device as recited in  claim 4 , wherein the strips have triangular cross sections so that the insulating box is configured to contour air to exit the housing in a direction away from incoming air. 
     
     
       7. The electronic device as recited in  claim 1 , wherein the air mover assembly comprises:
 a first air mover operable to move air from the first region towards the exhaust outlet; and 
 a second air mover operable to move air from the second region towards the exhaust outlet, and wherein when the air mover assembly is operating, the first air mover and the second air mover maintain a non-zero speed differential that is less than 15%. 
 
     
     
       8. The electronic device as recited in  claim 1 , wherein the exhaust outlet defines a single exhaust outlet. 
     
     
       9. An electronic device, comprising:
 a housing that defines an internal volume and outlet vents leading to the internal volume, the housing further comprising a first region and a second region separate from the first region; 
 an air mover assembly located in the internal volume, the air mover assembly comprising an exhaust outlet, 
 a first heat-generating component located in the first region; 
 a second heat-generating component located in the second region; and 
 a heat exchanger capable of receiving an airflow from the exhaust outlet and passing the air out of the housing, the heat exchanger thermally connected to the first heat-generating component and the second heat-generating component; and 
 an insulating box located in the internal volume between an exhaust of the heat exchanger and the outlet vents, wherein the insulating box including strips that define a grid. 
 
     
     
       10. The electronic device as recited in  claim 9 , wherein the heat exchanger comprises:
 a first set of heat pipes arranged to transfer heat from the first heat-generating component; and 
 a second set of heat pipes arranged to transfer heat from the second heat-generating component, wherein the first set of heat pipes is interleaved with the second set of heat pipes. 
 
     
     
       11. The electronic device as recited in  claim 9 , wherein the heat exchanger comprises fins stacked together to form a finstack. 
     
     
       12. The electronic device as recited in  claim 9 , wherein the heat exchanger turns the airflow radially from an inlet of the heat exchanger to an exhaust of the heat exchanger. 
     
     
       13. The electronic device as recited in  claim 9 , further comprising a stand that is rotationally coupled to the housing, wherein the outlet vents are covered by the stand, and wherein the insulating box is configured to contour air to exit the electronic device to avoid the stand. 
     
     
       14. The electronic device as recited in  claim 9 , wherein the strips have triangular cross sections so that the insulating box is configured to contour air to exit the housing in a direction away from incoming air. 
     
     
       15. The electronic device as recited in  claim 9 , wherein the air mover assembly comprises:
 a first air mover operable to move air from the first region towards the exhaust outlet; and 
 a second air mover operable to move air from the second region towards the exhaust outlet, and wherein when the air mover assembly is operating, the first air mover and the second air mover maintain a non-zero speed differential that is less than 15%.

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This application claims the benefit of U.S. Provisional Application No. 62/514,676, filed Jun. 2, 2017, entitled “THERMAL MANAGEMENT COMPONENTS FOR ELECTRONIC DEVICES”, which is incorporated by reference herein in its entirety. 
    
    
     FIELD 
     Embodiments of the present invention relate generally to thermal management components for electronic devices. More specifically, the described embodiments include devices and structures that improve the cooling efficiency of electronic devices. 
     BACKGROUND 
     Most electronic devices generate enough heat to require some forms of cooling processes in order to dissipate the heat and prevent overheating conditions in the device. One way devices are kept cool is by circulating air into and out of electronic device enclosures. As the sizes of electronic devices are becoming increasingly more compact, the efficiency of cooling processes should be improved. 
     SUMMARY 
     This paper describes various components and structure of an electronic device that improves the heat dissipation efficiency of the electronic device. 
     According to an embodiment, an electronic device is described. The electronic device can include a housing that defines an internal volume. The internal volume can include a first region and a second region. The first and second region can be disposed about a midline. The housing can carry an air mover assembly that includes a single exhaust, a first air mover operable to move air primarily from the first region towards the exhaust in a first airflow and a second air mover operable to move air primarily from the second region towards the exhaust in a second airflow. The first and second airflows can merge to form a combined airflow upstream of the exhaust. The electronic device can further include a first heat-generating component located in the first region, a second heat-generating component located in the second region, and a heat exchanger connected to and capable of receiving the combined airflow from the single exhaust and directing the airflow out of the housing. The heat exchanger can be thermal conductively connected to the first and second heat-generating components. 
     According to another embodiment, a fan assembly for an electronic device is described. The fan assembly can include a housing that includes a single exhaust, separate inlet openings and two impellers, each impeller being fed via separate inlet openings. Each of the inlet openings can receive airflows that are independent of each other. A truncated interior wall can allow the independent airflows to merge and form a combined airflow upstream of the exhaust. A single exhaust can receive the combined airflow and pass the combined airflow out of the fan housing. The housing can further include a motor housing integrally formed with struts that slope inward and that are angularly oriented to align a tangential component of the local airflow. The struts can connect the fan housing to the circumference of the motor housing. 
     According to yet another embodiment, a heat exchanger for an electronic device is described. The heat exchanger can include fins. Each of the fins can be characterized as having a first side edge and a second side edge that is non-adjacent to the first side edge. The fins can be stacked together such that first side edges of the fins cooperate to define an inlet of the heat exchanger and second side edges of the fins cooperate to define an exhaust of the heat exchanger. The first side edges can be non-parallel to the second side edges such that an airflow path of the heat exchanger can turn radially from the inlet to the exhaust. 
     Other aspects and advantages of the invention will become apparent from the following detailed description taken in conjunction with the accompanying drawings which illustrate, by way of example, the principles of the described embodiments. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The disclosure will be readily understood by the following detailed description in conjunction with the accompanying drawings, wherein like reference numerals designate like structural elements, and in which: 
         FIG. 1  illustrates a front view of an electronic device in accordance with some embodiments. 
         FIG. 2  illustrates a rear view of an electronic device in accordance with some embodiments. 
         FIG. 3  illustrates a cross-sectional side view of an electronic device in accordance with some embodiments. 
         FIG. 4A  illustrates a rear internal view showing some internal components of an electronic device in accordance with some embodiments. 
         FIG. 4B  illustrates a block diagram of several internal components of an electronic device in accordance with some embodiments. 
         FIGS. 5A and 5B  illustrate different perspective views of a fan assembly in accordance with some embodiments. 
         FIGS. 6A and 6B  illustrate a first and second surface views of the fan assembly shown in  FIGS. 5A and 5B . 
         FIG. 7A  illustrates a first cross-sectional view of the fan assembly shown in  FIG. 6A  along the line  602 . In  FIG. 7A , the fan assembly is illustrated to be in position with enclosures of an electronic device in accordance with some embodiments. 
         FIG. 7B  illustrates a second cross-sectional view of the fan assembly shown in  FIG. 6A  along the line  600 . 
         FIG. 8  illustrates a portion of an impeller of a fan assembly in accordance with some embodiments. 
         FIGS. 9A and 9B  illustrate different flow distribution profiles of fan assemblies in relation to different scroll wall designs. 
         FIG. 10  illustrates a perspective view of a heat exchanger in accordance with some embodiments. 
         FIG. 11  illustrates a side view of the heat exchanger shown in  FIG. 10 . 
         FIG. 12  illustrates a heat exchanger connecting to two heat-generating components via heat pipes in accordance with some embodiments. 
         FIGS. 13A and 13B  illustrate cross-sectional views of inlets of heat exchangers in accordance with some embodiments. 
         FIG. 14  illustrates an insulating box in accordance with some embodiments. 
         FIG. 15  illustrates a rear view of the outgoing airflow of an electronic device with the insulating box shown in  FIG. 14 . 
         FIG. 16  illustrates a cross-section view of the insulating box in position with a heat exchanger and a part of housing of an electronic device in accordance with some embodiments. 
         FIG. 17  illustrates a flowchart depicting a process to regulate the speeds of impellers of a fan assembly in accordance with some embodiments. 
     
    
    
     Those skilled in the art will appreciate and understand that, according to common practice, various features of the drawings discussed below are not necessarily drawn to scale, and that dimensions of various features and elements of the drawings can be expanded or reduced to more clearly illustrate the embodiments of the present invention described herein. 
     DETAILED DESCRIPTION 
     Representative applications of methods and apparatus according to the present application are described in this section. These examples are being provided solely to add context and aid in the understanding of the described embodiments. It will thus be apparent to one skilled in the art that the described embodiments may be practiced without some or all of these specific details. In other instances, well known process steps have not been described in detail in order to avoid unnecessarily obscuring the described embodiments. Other applications are possible, such that the following examples should not be taken as limiting. 
     In the following detailed description, references are made to the accompanying drawings, which form a part of the description and in which are shown, by way of illustration, specific embodiments in accordance with the described embodiments. Although these embodiments are described in sufficient detail to enable one skilled in the art to practice the described embodiments, it is understood that these examples are not limiting; such that other embodiments may be used, and changes may be made without departing from the spirit and scope of the described embodiments. 
     Increasingly, electronic devices can use more powerful processing and storage components while simultaneously continue to shrink in overall size. One way to further reduce the size of an electronic device is to taper the edges of the housing. Unfortunately such tapering of the housing can reduce the internal space of the electronic device in which internal components can be fitted. Although cooling devices can be used to dissipate heat accumulated at and near heat-generating components, significant airflow is often required to adequately cool those components. Optimizing the airflow inside an electronic device can be challenging, as increasing the sizes of cooling devices can sometimes be prohibited by the space restrictions imposed by structures around the cooling devices. 
     Embodiments described herein relate to devices, systems, and methods that improve the heat dissipation efficiency of an electronic device. In terms of the overall architecture, a thermal management system of the electronic device in accordance with some embodiments can include inlet and outlet vents on the housing of the electronic device, a fan assembly, a heat exchanger, and an insulating box. Air can be drawn into the internal volume of the electronic device by the fan assembly through the inlet vents. The exhaust of the fan assembly can be connected to the heat exchanger so that air can be blown through the heat exchanger, which can be thermally connected to heat-generating components. The heated air from the heat exchanger can then exit the electronic device at the outlet vents, which can be located above the inlet vents so that the heated air will not re-circulate back into the electronic device. 
     The components of the thermal management system in accordance with some embodiments can be arranged in a first side and a second side (for example, left and right but the arrangement can also be in other directions) of the electronic device to promote a more even temperature distribution in the electronic device. In some embodiments, the fan assembly can be a double impeller fan assembly so that air is drawn from both sides of the electronic device. A first impeller can be located in the first side and a second impeller can be located in the second side so that the first impeller and the second impeller are operable to move air primarily from the first side and from the second side, respectively. Two major heat-generating components, such as a central processing unit (CPU) and a graphics processing unit (GPU), can be separately located on each side of the internal volume. The first heat-generating component can be connected through heat pipes to the heat exchanger from a first side of the heat exchanger while the second heat-generating component can be connected through heat pipes to the heat exchanger from a second side of the heat exchanger. In some cases, a processor in communication with temperature sensors can control the double impeller fan assembly to adjust the speeds of the impellers based on the temperatures and/or the activity levels of the heat-generating components. For example, if a heat-generating component on the first side is generating a larger amount of heat compared to another heat-generating component on the second side, the speed of the first impeller can increase above the speed of the second impeller to promote air circulation on the first side of the electronic device. 
     A fan assembly, in accordance with some embodiments, can include different features that improve aerodynamic efficiency, reduce turbulence and promote more uniform flow without increasing its size. The fan assembly can be a double impeller fan assembly having two scroll portions arranged symmetrically along a midline. The housing parts of the two scroll portions can be integrated to form a single fan housing having a single exhaust outlet. Along the midline where the two scroll portions merge, an internal wall of the fan housing that is largely along the midline can be truncated such that the separate airflow distributions from the two scroll portions can merge and settle before reaching the exhaust. This truncation of that internal wall can promote more uniform flow distribution and can increase the flow rate of the fan assembly. 
     For each scroll portion, the fan assembly can include an impeller inside the fan housing. The fan housing can have a first opening above the impeller and a second circular opening below the impeller, or vice versa. Both openings can serve as inlets through which air is drawn into the fan assembly. The impeller can be driven by a motor that is located inside a circular motor housing and be supported by a bearing that is also located inside the motor housing. The motor housing can be located at the center of the second opening and can be mounted to the fan housing through a number of struts. Because some of the space of the second opening is occupied by the motor housing and the struts, the second opening can be divided by the struts into multiple opening spaces. For the same reason, the total opening spaces of the second opening can be smaller than that of the first opening. Hence, the first opening can serve as a primary inlet while the opening spaces of the second opening can serve as secondary inlets. 
     The fan assembly can be positioned and oriented in the electronic device to maximize the efficiency of both primary and second inlets. For example, the fan assembly can be positioned relative to a main logic board (MLB) of the electronic device such that air drawn through the primary inlet mainly comes from a first side of the MLB while air drawn through the second inlet mainly comes from a second side of the MLB opposite the first side. The ratio of airflow rate of the primary inlet to that of the secondary inlets can match the desired ratio of airflow rate of the first side of the MLB to that of the second side so that cooling can be optimized. In addition, the impeller&#39;s blade-support disc can be positioned at an elevation (i.e. vertical level relative to the height of the impeller) that matches the airflow ratio of the primary inlet to the secondary inlets to maximize the efficiency of the fan assembly. 
     To improve the aerodynamic efficiency of the fan assembly, especially near the secondary inlets, the struts can be specifically shaped, oriented, and positioned in certain ways. Viewed from the surface of the fan assembly, the struts can be oriented tangentially to the circumference of the circular motor housing. This orientation aligns with the airflow at the secondary inlets and, thus, reduces entrance losses and the impedance on the airflow. Also, the clock position of the struts at the second opening can be specifically determined to avoid high airflow suction regions because the airflow at the second opening is not uniform at different clock positions. Viewed from the cross section of the fan assembly, the struts can slope towards the impeller (i.e. sinking toward the interior of the fan housing). The sloped struts can increase the height of the opening spaces that serve as the secondary inlets, thereby increasing the effective size of the secondary inlets. 
     A heat exchanger, in accordance with some embodiments, can work well with other components described herein and at the same time improve aerodynamic and heat dissipation efficiency of the electronic device. The inlet of the heat exchanger can be connected to the exhaust of a fan assembly while the exhaust of the heat exchanger can be connected to the outlet vents of the housing of the electronic device. Hence, the design of the heat exchanger may be affected by the fan assembly and the outlet vents. For example, to increase the airflow of the fan assembly, the exhaust of the fan assembly can be wide but short in height because the height of the fan assembly may be restricted by the thickness of the electronic device. On the other hand, the outlet-vent area of the housing can be in a rectangular shape that is close to a square. Therefore, a heat exchanger that fits this system may be required to transition from a flattened inlet to a nearly square exhaust. The heat exchanger in accordance with some embodiments can include multiple cooling fins that are fastened together. The heat exchanger can include an inlet that is in a trapezoidal shape and an exhaust that is close to a square. The cooling fins can be oriented at slightly different angles so that the cooling fins gradually taper towards the legs of the trapezoid. This configuration can allow airflow to smoothly transition from the shape of the inlet to the shape of the exhaust. 
     Moreover, the heat exchanger can be connected to one or more heat pipes that draw heat conductively from some heat-generating components. The heat pipes can be flattened and be oriented based on the airflow of the heat exchanger so that the airflow is not impeded by the presence of the heat pipes. In some cases, two heat-generating components can be connected to the heat exchanger from opposite sides of the heat exchanger. Each of the two heat-generating components can be connected to two or more heat pipes. At the heat exchanger, the heat pipes from the first heat-generating component and the heat pipes from the second heat-generating component can be arranged in an interleaved manner so that both heat-generating components can be evenly cooled. 
     In some embodiments, an insulating box can be arranged between the heat exchanger and the outlet vents. The insulating box can be a grid like structure and can include vertical and horizontal strips that cooperate to form multiple openings for air to pass through the insulating box. The insulating box can cover the housing near the area of output vents on the side of housing that is facing the heat exchanger. The insulating box can be formed from a polymer material so that the insulating box can provide thermal insulation to the housing at the area of output vents to reduce the temperature of the housing at that area. Moreover, the vertical and horizontal strips can have aerodynamically contoured edges so that the airflow meeting the strips can be driven according to the orientations and the shapes of the strips. The strips can point to certain specific directions so that air can be directed by the insulating box to exit the electronic device at certain preferred angles that promote air circulation of the electronic device. For example, in some cases, each of the horizontal strips of insulating box can be in a triangular shape and be oriented such that a vertex of the triangle can point to the heat exchanger and a side of the triangle can slope upward. Hence, the horizontal strips can direct the air to exit the electronic device at a slightly upward direction. As such, heated air will not re-enter the electronic device through the inlet vents, which can be located below the outlet vents. In some cases, the outlet vents can be hidden behind a stand of the electronic device. The vertical strips of insulating box can be separated into a first group and a second group. The first group can point sideway in a first direction while the second group can point sideway in a second direction opposite the first direction. Hence, the vertical strips can direct the air to exit the electronic device at either sideway direction (instead of exiting straight) so that majority of the outgoing air will not impinge on the stand. 
     These and other embodiments are discussed below with reference to  FIGS. 1-17 ; however, those skilled in the art will readily appreciate that the detailed description given herein with respect to these figures is for explanatory purposes only and should not be construed as limiting. 
       FIG. 1  illustrates an exemplary front view of an electronic device  100  in accordance with some embodiments. Electronic device  100  can contain a display portion  102 . Display portion  102  can be made from any modern display technology such as liquid crystal display (LCD, or organic light emitting diode (OLED) technology). Display portion  102  can be covered and protected by display cover  104  which can be made of any thin translucent material such as glass or hardened plastic. As shown display cover  104  can extend past the edges of display portion  102 , giving the top portion of electronic device  100  a uniform appearance. Housing  106  and display cover  104  can cooperate to form an enclosure that encases the internal components of electronic device  100 . Housing  106  can be made of any rigid material sturdy enough to support the internal components. Electronic device  100  can be supported by stand  108 . Stand  108  can be rotatably connected to the back of housing  106 , allowing housing  106  to rotate at least up and down for adjusting the view angle of display portion  102 . 
       FIG. 2  shows an exemplary rear view of electronic device  100  illustrating the positions of vents and the directions of airflow in and out of electronic device  100  in accordance with some embodiments. Electronic device  100  can include a first set of inlet vents  202  and a second set of inlet vents  204 . Second set of inlet vents  204  can be located along a bottom edge of housing  106 . Second set of inlet vents  204  are represented by dashed boxes because the second set of inlet vents  204  may not be visible from a rear view of electronic device  100 . Electronic device  100  can additionally include a set of outlet vents  206  that can be located above both the first and second sets of inlet vents  202  and  204 . Incoming cool air  208  can enter through the inlet vents  202  and  204  and circulate inside housing  106  to carry heat away from the internal components. Heated outgoing air  210  can then be expelled through the outlet vents  206  and carry the heat away from electronic device  100 . 
     An insulating box  212  (represented by a dashed box) can be located inside housing  106  and at the area of outlet vents  206 . The insulating box  212  can control the direction of the outgoing air  210  so that outgoing air  210  can exit leftward for the left column of output vents  206  and can exit rightward for the right column of output vents  206 . The insulating box  212  can also adjust the vertical angle of outgoing air  210  so that outgoing air  210  can be expelled in a direction away from incoming air thereby minimizing any thermal interaction between the two airflows. More specifically, since the inlet vents  202  and  204  can be located below outlet vents  206 , directing the outgoing air  210  to exit at some slightly upward directions (or at least horizontally) can promote air circulation and prevent heated air from re-entering electronic device  100 . The structure of an exemplary insulating box will be discussed in a more detailed manner below. It should be noted that the set of outlet vents  206  can be positioned behind stand  108  so that the vents  206  can be hidden from sight. The second set of inlet vents  204  can also be positioned at the bottom edge of housing  106  so that the vents  204  are less noticeable. Those positions of the vents can improve the appearance of the electronic device  100 . 
       FIG. 3  shows a cross-sectional view of electronic device  100  and illustrates an internal volume  300  defined by housing  106  of electronic device  100  in accordance with some embodiments. As shown, housing  106  can have a convex shape so that internal volume  300  can be thicker near the center and become narrower as housing  106  tapers towards the edges (which can include top, bottom and side edges). This convex shape of housing  106  can allow electronic device  100  to be perceived as having a very thin body and to be aesthetically pleasing. 
     Electronic device  100  can include a fan assembly  302 , a heat exchanger  304 , and the insulating box  212 . Detailed exemplary structures of those internal components will be discussed below. Fan assembly  302  can be an air mover assembly that is responsible for drawing air into and expelling air out of housing  106 . Fan assembly  302  can be arranged just above the thickest portion of internal volume  300 , thereby nearly maximizing the amount of room allowed for fan assembly  302  and the amount of air accessible to fan assembly  302 . Fan assembly  302  can be mechanically coupled to heat exchanger  304  that can receive the airflow from an exhaust of fan assembly  302  and pass the heated airflow out of internal volume  300  and housing  106 . Heat exchanger  304  can be coupled to one or more heat pipes  306  that conductively draw heat from some heat-generating components. At the exhaust side  308  of heat exchanger  304 , the insulating box  212  can be located to adjust the travel angle of outgoing air. 
       FIG. 3  also illustrates an advantage of having two sets of inlet vents  202  and  204  in accordance with some embodiments. A printed circuit board (PCB)  310  or other heat-generating component can be located in the internal volume  300  and can be used to bifurcate a portion of internal volume  300  into a front portion  312  that is near display portion  102  and a back portion  314  that is near the backside of housing  106 . As illustrated by the airflow arrows, having a first set of inlet vents  202  at the backside of housing  106  can allow air to enter internal volume  300  through the back portion  314 . In addition, having a second set of inlet vents  204  at the bottom edge of housing  106  can allow air to enter internal volume  300  through the front portion  312 . Hence, having both sets of inlet vents  202  and  204  can allow air to travel though both sides of PCB  310  to promote heat dissipation of PCB  310 . In some embodiments, the total size of the first set of inlet vents  202  relative to the total size of the second set of inlet vents  204  can depend on the relative approximate volume ratio of back portion  314  to front portion  312 . For example, if the volume of back portion  314  to the volume of front portion  312  is roughly 2:1, the total size of first set of inlet vents  202  can be approximately double of the total size of second set of inlet vents  204 . This arrangement can allow maximum efficiency of airflow in internal volume  300 . 
       FIG. 4A  illustrates a rear cross-section view of electronic device  100  in accordance with some embodiments.  FIG. 4A  shows fan assembly  302 , heat exchanger  304 , inlet vents  202  and  204 , and outlet vents  206 . Housing  106  can be described as an area being divided by a dashed midline into a first region and a second region, illustrated herein as a left region and a right region. It should be noted that housing  106  can also be divided into any other suitable divisions such as top and bottom, specific quadrants, or other identifiable, symmetrical or not, regions. Fan assembly  302  can be a centrifugal fan assembly with two air movers  406  and  408  that draw air from both sides of internal volume  300 . In some cases, the air movers can include impellers that are driven by motors. A first air mover  406  can be located in the first region and a second air mover  408  can be located in the second region so that first air mover  406  is operable to move air primarily from the first region and second air mover  408  is operable to move air primarily from the second region. Heat exchanger  304  can be coupled with multiple heat pipes  306  that are connected to one or more heat generating components so that heat exchanger  304  is thermal conductively connected with the one or more heat-generating components. In the particular configuration shown in  FIG. 4A , a first heat-generating component  402  can be located in the first region while a second heat-generating component  404  can be located in the second region. Two heat pipes  306  can thermal conductively connect first heat-generating component  402  to heat exchanger  304  to allow heat generated from first heat-generating component  402  to transfer conductively to heat exchanger  304 . Other two heat pipes  306  can thermal conductively connect second heat-generating component  404  to heat exchanger  304 . The detailed arrangement among the heat-generating components, the heat pipes and the heat exchanger will be discussed below. 
     First heat-generating component  402  can be a central processing unit (CPU) of electronic device  100  and second heat-generating component  404  can be a graphics processing unit (GPU) of electronic device  100 , or vice versa. The CPU and GPU can be major heat-generating sources in electronic device  100 . First heat-generating component  402  and second heat-generating component  404  can be separately positioned at each side of electronic device  100 . For example, from the perspective shown in  FIG. 4A , first heat-generating component  402  can be located in the first region while second heat-generating component  404  can be located in the second region. The separation of first and second heat-generating components  402  and  404  can improve thermal distribution inside electronic device  100 , thus improving heat dissipation efficiency of electronic device  100 . In addition, the fan assembly  302  can have one air mover rotate faster than another air mover to avoid acoustic modulation, which will be discussed in detail below. Separating two heat-generating components to different sides can allow the heat-generating component with more heat generation to be located on the same side as the faster air mover. For example, if the GPU usually generates more heat than the CPU, the GPU can be located on the same side as the faster air mover. 
       FIG. 4B  is a block diagram illustrating the relationship among fan assembly  302 , heat exchanger  304 , first heat-generating component  402 , and second heat-generating component  404 . First heat-generating component  402  and second heat-generating component  404  can be located on opposite sides of a housing of an electronic device. Heat exchanger  304  can be conductively connected to heat-generating components  402  and  404  through heat pipes  306  to draw heat away from those processors. Fan assembly  302  can draw air to travel through the surface of heat-generating components  402  and  404  to further carry heat away from those processors through convection. The air drawn into fan assembly  302  can then be expelled through heat exchanger  304  and exit the electronic device  100 . In addition, either or both heat-generating components  402  and  404  can be electrically connected to fan assembly  302  so that heat-generating components  402  and/or  404  can control the speeds of the two air movers  406  and  408  of fan assembly  302 . First and second heat-generating components  402  and  404  can include or be connected to temperature sensors  410  and  412 . In some cases, the speeds of the air movers  406  and  408  can be adjusted based on the temperatures and/or activity levels of first heat-generating component  402  and second heat-generating component  404 . Which air mover rotates faster can depend on the relative temperatures and/or activity levels of heat-generating components  402  and  404 . For example, when first heat-generating component  402 , which can be a processor, is performing a large amount of calculations, first heat-generating component  402  can cause air mover  406  (which can be located on the same side as first heat-generating component  402 ) to rotate faster than air mover  408 . This can increase the airflow of the electronic device on the side of first heat-generating component  402 , thus promoting heat dissipation of first heat-generating component  402 . In some cases, although one air mover is rotating faster than another, the speed difference between the impeller can be maintained at about 6-10%, for reasons that will be discussed in more detail below. In other cases, the speed difference can be other than 6-10% as required based upon the differences in temperature and/or activity level of heat-generating components  402  and  404 . 
     Referring to  FIGS. 5A-7B , an exemplary air mover assembly is illustrated. The air mover assembly can take the form of a fan assembly  500  that can include a fan housing  502  that carries two air movers. In the particular embodiment shown in the figures, the air movers can include impellers  504  and  506  that are driven by motors. Fan assembly  500  can also include a single exhaust outlet  508  that can be in a trapezoidal shape and multiple inlet openings  510  and  512 . Each air mover of fan assembly  500  can receive air from different regions of an electronic device and can form separate airflows. Fan assembly  500  can then merge the separate airflows into a single combined airflow and pass the combined airflow though the single exhaust  508 . 
     At each impeller, there can be a first opening that serves as a primary inlet  510  on the side that is shown in  FIGS. 5A and 6A . On the other side of fan assembly  500  shown in  FIGS. 5B and 6B , another opening can be present at each impeller. A motor housing  516  can be located at the center of that opening and can be connected to fan housing  502  through multiple struts  518 . Since motor housing  516  and struts  518  occupy some space of that opening, the opening is divided into multiple secondary inlets  512 . Impellers  504  and  506  can be driven by motors  514  that are located inside motor housing  516 . Each motor housing  516  can also include a bearing that supports the impeller. 
     To control and power a motor  514 , a flexible circuit (flex)  520 , or another suitable connector and/or cabling arrangement, can connect motor  514  to a control circuit that can include a processor (not shown). For each impeller, a recessed channel  522  can be located along one of the struts  518  and extend through fan housing  502 . Flex  520 , or other suitable connectors such as wires, can be a thin piece of connector that is located inside channel  522 . Flex  520  can generally be flush with the surface of fan housing  502  so that flex  520  does not significantly affect the inlet airflow of fan assembly  500 . In  FIG. 5B , the flex on the left side is omitted in order to show the recessed channel  522 . 
     In accordance with some embodiments, struts  518  can be shaped, oriented and positioned in certain ways to reduce aero-acoustic noise, aerodynamic losses, and turbulence of fan assembly  500 , thus increasing the general heat dissipation efficiency of fan assembly  500 . Each strut  518  can have two edges  524  and  526  (labeled in one of the struts  518  at the left impeller shown in  FIG. 6B ). Described in terms of the direction of airflow, edge  524  can be referred to as forward edge  524  while edge  526  can be referred to as backward edge  526  because the airflow direction is from backward edge  526  to forward edge  524 . Backward edges  526  of struts  518  can be tangential to the circumference of circular motor housing  516 . As indicated by the arrows  528  (shown in  FIG. 6B ), air can enter fan housing  502  through an inlet  512  and the air can encounter a strut  518 . Instead of being oriented radially (i.e. perpendicular to the circumference of motor housing  516 ), a strut  518  can be angularly oriented with a tangential component relative to the airflow. This tangential orientation can avoid the air encountering a strut  518  at a significant angle (or perpendicular) so that the air is not forced to make an abrupt turn, which would increase aerodynamic losses and can potentially cause flow separation and create more turbulence. Hence, this tangential orientation can decrease the aerodynamic losses created when air is being drawn into the fan housing  502 , thus decreasing aerodynamic resistance and improving aero-acoustic noise of fan assembly  500 . 
     In some cases struts  518  are not planar to the surface of fan housing  502 . Instead, struts  518  can sink (i.e. sloped inward) into fan housing  502 , which is best shown in  FIGS. 5B and 7A . The sunken struts  518  can further decrease aerodynamic resistance because the sunken struts  518  can effectively increase the size of opening of secondary inlets  512  by increasing the cross-sectional area of the secondary inlets  512 . To illustrate this point, imagine the struts were planar to the surface of fan housing  502 . In other words, from the cross-sectional view of  FIG. 7A , a planar strut would extend from fan housing  502  to motor housing  516  in a horizontal direction (as contrast to a sunken strut  518  that is also going inward as shown in the figures). As a result, those planar struts would define inlets that would have no depth and have smaller cross-sectional area through which air enters. In contrast, the sunken struts  518  can allow secondary inlets  512  to have a significant larger cross-sectional area that allows air to enter. Put differently, the sunken struts  518  can allow secondary inlets  512  to become three-dimensional because secondary inlets  512  can have opening space from the view of  FIG. 6B  and also opening space from the view of  FIGS. 7A and 7B  (cross-sectional). The sunken struts  518  can increase the effective size of secondary inlets  512 , improve flow quality, and thus increase the overall aerodynamic efficiency of fan assembly  500 . 
       FIG. 7B  illustrates the airflow direction inside fan assembly  500 . In general, after air is drawn into fan housing  502 , the air is required to make a 180-degree turn before the air reaches a leading edge of a blade of an impeller. The sunken struts  518  can simplify the flow path of air entering fan housing  502  and provide more space for the airflow to change direction. 
     In accordance with some embodiments, struts  518  can also be positioned at certain special angular positions relative to the fan housing  502  in order to further increase airflow. The angular positions of struts  518  refer to the clock positions of struts  518  relative to fan housing  502 , when viewed from  FIG. 6B . For example, in the particular case shown in  FIG. 6B , the three struts  518  can roughly be evenly spaced apart at approximately 120-degree separations and be positioned at approximately 0 degrees, 120 degrees, and 240 degrees. However, the three struts can also be located at other angular positions, such as at 60 degrees, 180 degrees, and 300 degrees. The angular positions of the struts  518  can depend on the pressure distribution of the area around secondary inlets  512 . The pressure distribution of the area around secondary inlets  512  may not be uniform, meaning some locations of the area can have a higher airflow than other locations. The exact angular positions of struts  518  can be determined based on the pressure distribution of the area around secondary inlets  512  to make sure struts  518  are not blocking any of the high airflow locations. In other words, secondary inlets  512 , which are defined by struts  518 , can be located at some high airflow areas to increase the efficiency of fan assembly  500 . For example, as shown in  FIG. 6B , a scroll cut-off region of each impeller is labeled as element  530 . Scroll cut-off region  530  can be a high suction region that relatively has a very high airflow. In  FIG. 6B , struts  518  can be located at angular positions that avoid scroll cut-off region  530  so that an inlet  512  is located at the same angular position as the scroll cut-off region  530 . 
     It should be noted that while  FIG. 6B  illustrates one possible exemplary arrangement of struts  518  in terms of their angular positions, those skilled in the art should understand that the angular positions of struts  518  can be determined empirically based on the pressure distribution. Also, there can be any numbers of struts  518  and struts  518  do not have to be spaced apart evenly in the angular direction. 
     Referring to  FIGS. 7A, 7B, and 8  and focusing on the impellers  504  and  506 , impellers  504  and  506  each can include a sculpted body that increases the aerodynamic efficiency of fan assembly  500 . For simplicity, impeller  506  is discussed. Impeller  506  can include an impeller disc  532  that divides impeller  506  into two portions  534  and  536 . Portion  534  can be on the side of the primary inlet  510  while portion  536  can be on the side of motor housing  516 . In some cases, portions  534  and  536  can be proportionally sized based on the airflow contributions of primary inlet  510  versus the secondary inlets  512 . In other words, if more air can be drawn into the fan assembly  500  through primary inlet  510 , the size of portion  534  can be relatively larger than the size of portion  536 , or vice versa. Impeller  506  can include an impeller hub  538  that carries rotational components such as a shaft  542  and a bearing  540  that is connected to motor  514  in the motor housing  516 . Impeller hub  538  can have a curved surface that is shaped to reduce resistance against airflow, thereby reducing entrance losses. Impeller disc  532  can carry multiple blades  544  that are positioned relatively vertically. The inner side of each blade  544  can have a somewhat hyperboloid shape in which blade  544  progressively encroach towards the center of rotation of impeller disc  532 . Put differently, at both portions  534  and  536 , each blade  544  has the largest chord length at a vertical level near impeller disc  532  then gradually tapers to a smaller chord length away from the center of the impeller  506  in a concave manner at the leading edge. Together with impeller hub  538 , parts of blades  544  in portion  534  can define a well  546  that is recessed from the surface of fan housing  502 . Well  546  can be in a half-torus shape. Similarly, together with motor housing  516 , parts of blades  544  in portion  536  can define a well  548  that is recessed from the opposite surface of fan housing  502 . Well  548  can also be in a half-torus shape. Well  546  and well  548  can be associated with the volumes of air that are drawn into fan housing  502 . The larger the well  546 , the more air can be drawn into fan housing  502  from the side of primary inlet  510 . 
     In some embodiments, the depth of well  546  relative to the depth of well  548  can be in a specific ratio to maximize the aerodynamic efficiency of fan assembly  500 . In  FIG. 7A , the depth of well  546  is labeled as D 1  while the depth of well  548  is labeled as D 2 . The ratio of D 1  to D 2  can be associated with the ratio of airflow in portion  534  to airflow in portion  536 . D 1  and D 2  can depend on the shape of impeller  506  such as the relative position of impeller disc  532 . For example, if the impeller disc  532  is positioned more towards primary inlet  510 , D 1  will decrease while D 2  will increase. According to some embodiments, the ratio of D 1  to D 2  can be associated with the spaces external to fan assembly  500 . In  FIG. 7A , enclosures of an electronic device are shown. For example, element  550  can be the housing  106  while element  552  can be the backside of display portion  102 . The space between fan assembly  500  and a housing can be called plenum. First plenum  554  can be the space at a first surface of fan assembly  500  and between fan assembly  500  and element  550  while second plenum  556  can be the space at a second surface of fan assembly  500  and between fan assembly  500  and element  552 . The first height of first plenum  554  is labeled as P 1  while the second height of second plenum  556  is labeled as P 2 . The ratio of D 1  to D 2  can correspond to the ratio of P 1  to P 2 . In one case, both ratios can be 2:1. In other words, since the space of first plenum  554  can be larger than the space of second plenum  556 , more air can flow through first plenum  554 . Consequently, impeller  506  can also be shaped such that well  546  is deeper than well  548 . As such, the primary inlet  510  side of impeller  506  can have higher capacity to drive more airflow through fan assembly  500 . In some cases, the ratio of D 1  to D 2  can also be based on the ratio of the airflow at portion  314  to the airflow at portion  312  in  FIG. 3 . 
       FIG. 8  illustrates the shape of blades  544  of impeller  506  in accordance with some embodiments. The suction side  802  and pressure side  804  can form a thin and sharp blade. The blade can have a sharp trailing edge  806  instead of a rounded edge. The shape of the blades  544  can improve aerodynamic performance of the impeller by preventing leakage of high-pressure airflow from pressure side  804  of the blade to suction side  802  of the blade, at the trailing edge  806 . 
     Referring to  FIGS. 5A, 9A and 9B  and focusing on fan housing  502 , fan assembly  500  can include two scroll portions  558  and  560 . Scroll portions  558  and  560  can be arranged symmetrically along a dashed midline shown in  FIG. 5A . Scroll portions  558  and  560  can have scroll wall  562  that defines the flow path of air inside fan housing  502 . Scroll wall  562  can block area  564 , which can be in a triangular shape with two inwardly curved sides. Without scroll wall  562  at area  564 , air expelled from impeller  504  and air expelled from impeller  506  can encounter each other at opposite direction, which can create turbulence. Scroll wall  562  at area  564  can allow air to turn smoothly into the direction of the exhaust  508  while building up air pressure through the scroll, thus promoting less turbulent airflow with higher pressure. From the position where the streams of air from both impellers  504  and  506  turn into a similar or same direction, the scroll wall that become part of an interior wall can be truncated to allow two streams of air to merge and settle before exiting exhaust  508 . Therefore, the scroll wall can be truncated at a location between the exhaust  508  and a point where the scroll wall first becomes generally perpendicular to the exhaust  508 . Described differently, a portion of interior wall of the fan housing along a portion of the midline of the fan assembly can be truncated such that air from both scroll portion  558  and  560  can merge before the exhaust  508 . 
       FIGS. 9A and 9B  illustrate the improvement of flow distribution when scroll wall  562  is truncated.  FIG. 9A  shows a truncated scroll wall  562  and  FIG. 9B  shows a scroll wall that continues through the exhaust  508 . The un-truncated part of scroll wall in  FIG. 9B  is labeled as element  566 . The flow distribution profile in  FIG. 9A  is labeled as element  568  while the flow distribution profile in  FIG. 9B  is labeled as element  570 . As shown in  FIG. 9A , the truncated scroll wall  562  can allow a more uniform flow distribution  568 . On the contrary, the un-truncated part  566  of scroll wall in  FIG. 9B  creates a velocity deficit region at the exhaust  508  as shown in flow distribution profile  570 . The more uniform flow distribution  568  represents a combined airflow from both scroll portions that can be characterized as being generally less turbulent in nature. This uniform flow distribution  568  can reduce the shear (velocity gradient) in the outgoing airflow, which generally will result in less aero-acoustic noise and less turbulence. 
     In some embodiments, although impellers  504  and  506  can be a same type of impeller with similar or same size and shape, there can be a speed differential between impellers  504  and  506 . In some cases, the speeds of rotation of the two impellers  504  and  506  can maintain a non-zero speed differential of about 6% to 10% (e.g. one rotating at a speed of +4% from a reference level and another rotating at a speed of −4% from the reference level). The speed differential can be maintained at any speed levels. For example, both impellers  504  and  506  can have variable speeds depending on the temperature of the electronic device and/or other heat dissipation need, but a speed differential can be maintained across different speeds. The speed differential can improve the aero-acoustic noise and improve the sound quality of fan assembly  500 . When both impellers  504  and  506  are operating at a same speed, the frequency of the impeller blades and the motors driving both impellers  504  and  506  may modulate and may excite fan housing  502 , creating loud noise. By spacing out the frequencies, such type of modulation can be avoided. Also, both impellers  504  and  506  are discharging into a same pressurized area near exhaust  508 , impellers  504  and  506  can surge periodically under unusual high back pressure, resulting, for example, from severe blockage of the output vents if the speeds of both impellers are elevated and the target speeds of both impellers are the same. This can create some undesirable oscillation. Spacing out the speeds of impellers  504  and  506  slightly can avoid causing the impellers to surge periodically. 
     In some cases, one of the impellers  504  and  506  can always rotate faster than another impeller. For example, if a first heat-generating component has a higher heat generation than the second heat-generating component, the impeller on the side of the heat-generating component can be configured to rotate faster than the impeller on the side of the second heat-generating component. In one particular case, the component with a higher heat generation can be the GPU of the electronic device when compared to the CPU. In other cases, which impeller rotates faster can be adaptive based on the temperatures of the heat-generating components. 
     Referring to  FIGS. 10 and 11 , a heat exchanger  1000  in accordance with some embodiments is shown.  FIG. 10  is a perspective view of heat exchanger  1000  and  FIG. 11  is a side view of heat exchanger  1000 . Heat exchanger  1000  can be used as the heat exchanger  304  shown in  FIGS. 3 and 4 . Heat exchanger  1000  can include multiple cooling fins  1002  that can be made from metal sheets or other suitable thermal conductive materials. The cooling fins  1002  can be attached together by any suitable mechanical fastening or attachment mechanisms including zipper, adhesive, and/or welding. Each cooling fin  1002  can have a similar shape so that the cooling fins  1002  can stack together to form a finstack. 
     In one exemplary shape, each cooling fin  1002  can be characterized as having a first side edge  1004 , a second side edge  1006 , a inner curved edge  1008  and an outer curved edge  1010  that cooperate to define a surface having a J-shape. First side edge  1004  and second side edge  1006  can be straight edges and can be opposite. In other words, first side edge  1004  and second side edge  1006  can be non-adjacent to each other so that they do not meet. Inner curved edge  1008  and outer curved edge  1010  can be curved edges that are opposite. First side edge  1004  and second side edge  1006  can be adjacent to inner curved edge  1008  and outer curved edge  1010 . Cooling fins  1002  can be stacked together such that the first side edges  1004  of cooling fins  1002  can cooperate to define an inlet  1012  (labeled by a dashed box) and the second side edges  1006  can cooperate to define an exhaust  1014  (labeled by another dashed box). First side edges  1004  can be non-parallel to second side edges  1006  such that an airflow path of heat exchanger  1000  can turn radially from inlet  1012  to exhaust  1014 . 
     In general, inlet  1012  can be coupled to an exhaust of a fan assembly while exhaust  1014  can be coupled to outlet vents of the main housing of an electronic device. Heat exchanger  1000  can have a curved body that turns the airflow radially from inlet  1012  to exhaust  1014 . Hence, air expelled from a fan assembly can undergo further heat exchange when the air flows though heat exchanger  1000 . Heat exchanger  1000  can include multiple slots  1016  for insertions of heat pipes that carry heat conductively from heat-generating components such as processors. It should be noted that each cooling fin  1002  can include those slots  1016  so that heat pipes can be inserted all the way through heat exchanger  1000 . When the heat carried from the heat pipes reaches heat exchanger  1000 , the air flowing thought heat exchanger  1000  can transfer heat from the heat pipes and carry the heat away from the electronic device. 
     Heat exchanger  1000  in accordance with some embodiments can work well with other component described herein. Other components in electronic device  100  may create restriction to a heat exchanger, which can best be explained by referring back to  FIGS. 3 and 4A . An effective heat exchanger for electronic device  100  is required to address the heat dissipation need of electronic device  100  while being able to fit the form factor of a housing  106  that can sometimes have a convex shape. To increase the capacity of fan assembly  302 , the size of the exhaust of fan assembly  302  is required to increase. However, to fit into a relative thin internal volume  300 , the height of the exhaust (which is along x-direction when fan assembly  302  is oriented as shown in  FIG. 3 ) can be limited by the form factor of housing  106 . Hence, to increase the capacity of fan assembly  302 , the width of the exhaust needs to be widened. For example, if fan assembly  500  is used as fan assembly  302 , fan assembly  500  has a relatively wide exhaust because of the double impeller design. On the other hand, the width of outlet vents  206  can be limited by the width of stand  108  because output vents  206  should be hidden behind stand  108 . Hence, to increase the capacity of outlet vents  206 , the height of outlet vents  206  can be increased. Also, the area size of outlet vents  206  should be larger than the area size of the exhaust of fan assembly  302  to promote the airflow. In addition, a heat exchanger for electronic device  100  can be positioned near the center of electronic device  100 , where a hinge portion  320  is located. 
     Referring to  FIGS. 10 and 11 , heat exchanger  1000  can be an exemplary heat exchanger that effectively addresses the heat dissipation need for electronic device  100 . Inlet  1012  of heat exchanger  1000  can be wide so that heat exchanger  1000  can be used with a fan assembly that has a wide exhaust. Exhaust  1014  of heat exchanger  1000  can be narrower than inlet  1012  but taller than inlet  1012 . In other words, trapezoidal inlet  1012  can have a first base width W 1  (the narrower base of the trapezoid) and a first height H 1 , while rectangular exhaust  1014  can have a second width W 2  that is smaller than the first base width W 1  and a second height H 2  that is larger than the first height H 1 . Exhaust  1014  can have a rectangular shape that is close to a square. Hence, exhaust  1014  can match output vents  206  that are hidden behind stand  108 . In some embodiments, the area ratio of inlet  1012  to exhaust  1014  can be between 1:2 and 1:3. Having exhaust  1014  being larger than inlet  1012  can promote airflow from inlet  1012  to exhaust  1014 . As shown in the side view  FIG. 11 , the cooling fins  1002  of heat exchanger  1000  can generally be curved and in a J-shape so that airflow can smoothly make a 90-degree turn radially or an almost 90-degree turn radially. The smooth turn of airflow and transition from a smaller inlet  1012  to a larger exhaust  1014  can reduce turbulence in heat exchanger  1000 . In addition, slots  1016  can be flattened so that the heat pipes that are inserted into heat exchanger  1000  do not impede the airflow. Also, slots  1016  can be aligned along a curve of airflow path to further reduce the interference of airflow. Hence, the orientations of slots  1016  gradually turn from the direction of airflow at inlet  1012  to the direction of airflow at exhaust  1014 . 
     Referring to  FIG. 12 , heat exchanger  1000  can be coupled to one or more heat-generating components through multiple heat pipes. In the particular configuration shown in  FIG. 12 , heat exchanger  1000  can be coupled to a first processor  1018  on one side of heat exchanger  1000  and coupled to a second processor  1020  on an opposite side of heat exchanger  1000 . Having two processors  1018  and  1020  positioned in opposite sides can allow more uniform heat distribution within an internal volume of an electronic device and allow a better heat management through the double impeller fan assembly  500  as illustrated in  FIG. 4B . Each processor  1018  or  1020  can be connected to heat exchanger  1000  through two heat pipes  1022 . Heat pipes  1022  can include a heat transfer medium such as a sealed pipe containing heat-exchanging fluid therein. To increase the heat exchange capacity of a heat pipe, the size of the heat pipe can be increased. However, as the diameter or the height of the heat pipe increases, the heat pipe can interfere with the airflow of heat exchanger  1000 . Hence, in accordance to some embodiments, two flattened heat pipes  1022  having low profile cross sections are used for connecting a heat-generating component to heat exchanger  1000 . Increasing the number of heat pipes  1022  for each heat-generating component can increase the heat exchange capacity of the heat pipes without sacrificing the low turbulent airflow of heat exchanger  1000 . 
     In addition, having two or more heat pipes for each heat-generating component can promote more even heat dissipation among the heat-generating components. If first processor  1018  and second processor  1020  are each connected to heat exchanger  1000  only through a single heat pipe, the heat pipe of either one of the processors will be positioned upstream of another heat pipe in heat exchanger  1000 . Upstream here refers to the direction of airflow in heat exchanger  1000  that is flowing from inlet  1012  (more upstream) to exhaust  1014  (more downstream). Having one heat pipe always upstream of another heat pipe means that the processor that is connected to the more upstream heat pipe will usually get a better cooling compared to the other processor because the air is usually cooler in the upstream. In contrast, as shown in the configuration of  FIG. 12 , first processor  1018  and second processor  1020  can each be connected to two heat pipes  1022 . Those heat pipes  1022  can be interleaved heat pipes that are connected to heat exchanger  1000  in an alternating order. In other words, from upstream to downstream, a first set of heat pipes that include the first and third heat pipes  1022  can be thermal conductively connected to first processor  1018  while a second set of heat pipes that include the second and fourth heat pipes  1022  can be thermal conductively connected to second processor  1020 . Because the set of heat pipes for first processor  1018  and the set of heat pipes for second processor  1020  are interleaved, a difference in the capability of heat transfer from the first and second processors  1018  and  1020  is minimized. 
     Referring to  FIGS. 13A and 13B , cross-sectional views of inlets  1012  of heat exchanger  1000  in accordance with different embodiments are shown. It should be noted that inlet  1012  can be in a trapezoidal shape to allow heat exchanger  1000  to smoothly transition from a wider but shorter inlet (such as inlet  1012  shown in  FIGS. 10 and 11 , above) to a narrower but taller exhaust (such as exhaust  1014  shown in  FIGS. 10 and 11 , above). More particularly, as illustrated in  FIG. 13A , heat exchanger  1000  can have cooling fins  1002  that form individual trapezoids that, when combined, allow a transition from the inlet to the exhaust in accordance with an embodiment. For example, a middle fin  1002   a  can be generally perpendicular to the parallel edges (i.e. the top and the base) of the inlet  1012 , whereas other cooling fins such as  1002   b  and  1002   c  can be gradually tapered towards the two legs  1026  and  1028  of trapezoidal inlet  1012 . In other words, a middle fin can be generally perpendicular to a base of trapezoidal inlet  1012 ; a first group of fins can be gradually tapered towards a first leg  1026 ; and a second group of fins can be gradually tapered towards a second leg  1028 . 
       FIG. 13B  illustrates another exemplary cross-sectional view of inlet  1012  in accordance with an embodiment. Cooling fins  1002  can be divided in groups of fins that are parallel. In one case, each group can include four cooling fins  1002 , although the exact number of cooling fins  1002  in each group can vary. The cooling fins  1002  in each group can have the same orientation while the cooling fins  1002  among different groups can have different orientations. For example, two middle groups of cooling fins  1002  can be generally perpendicular to the parallel edges of the trapezoid. Other groups can be gradually tapered towards the two legs  1026  and  1028  of the trapezoid. Each group of cooling fins  1002  can include a transition fin  1024  positioned between groups of cooling fins  1002 . The transition fins  1024  can facilitate the arrangement of the groups of cooling fins  1002  such that the groups can become gradually tapered towards the two legs  1026  and  1028  of the trapezoidal inlet  1012 . The transition fins  1024  can allow the groups of cooling fins  1002  to be aligned more easily. Grouping the cooling fins  1002  can allow easier assembly of heat exchanger  1000  as fins can be manufactured in groups and then the groups can be attached together by any suitable fastening or attachment mechanisms afterward. In some embodiments, each of the cooling fins  1002  and/or transition fins  1024  include features that help facilitate proper spacing between groups of fins. Each cooling fin  1002  includes features of equal length proximate the parallel edges of the trapezoid to facilitate a parallel arrangement with an adjacent fin. In contrast, each transition fin  1024  includes features of different lengths proximate the parallel edges of the trapezoid to facilitate a non-parallel arrangement of a group of cooling fins  1002  with an adjacent group of cooling fins  1002 . In some embodiments, the features are bent edges of the cooling fins  1002  and transition fins  1024 . 
       FIG. 14  illustrates an insulating box  1400  in accordance with some embodiments. Insulating box  1400  can be formed from a polymer material and can be positioned between the exhaust of a heat exchanger and the outlet vents of an electronic device. For example, insulating box  1400  can be an exemplary insulating box  212  shown in  FIG. 3  that is positioned between heat exchanger  304  and outlet vents  206 . 
     As shown in  FIG. 14 , insulating box  1400  can include a first side portion  1402  and a second side portion  1404 . The side portions can also be referred to as a left portion and a right portion, but it should be understood that insulating box  1400  can also be divided into any other suitable divisions such as top and bottom, specific quadrants, or other identifiable, symmetrical or not, regions. Side portions  1402  and  1404  can have multiple vertical and horizontal strips  1406 ,  1408 , and  1410  that cooperate to form grids. When insulating box  1400  is mounted on housing  106  of electronic device  100 , first side portion  1402  can be located on the left (viewed from the back of the electronic device) side of outlet vents  206  while second side portion  1404  can located be on the right side of outlet vents  206 . The vertical strips  1406  of first side portion  1402  can be oriented towards a first sideway direction while the vertical strips  1408  of second side portion  1404  can be oriented towards a second sideway direction opposite the first sideway direction. For example, in one case the first sideway direction can be towards the left and the second sideway direction can be towards the right. Vertical and horizontal strips  1406 ,  1408 , and  1410  can each have aerodynamically contoured edges so that airflow meeting a strip can be driven according to the shape and orientation of the strip. The gird formed by the vertical and horizontal strips  1406 ,  1408 , and  1410  can include multiple openings  1412  that allow heated air to pass through insulating box  1400 . 
     The insulating box  1400  can serve multiple purposes. First, insulating box  1400  can provide thermal insulation to the back of housing  106  of electronic device  100  to reduce the temperature of the housing  106  near the area of output vents  206 . As shown in  FIG. 15 , insulating box  1400  (represented by a dashed box) is located at the area of output vents  206  of housing  106  of electronic device  100 . The area of output vents  206  can be one of the hottest areas of housing  106  because heated air from a heat exchanger passes through that area to exit housing  106 . In some embodiments, the strips of insulating box  1400  can be aligned with the grills of housing  106  that define the output vents  206 . In other words, the insulating box  1400  can largely cover the interior part of housing  106  at the area of output vents  206 . Since insulating box  1400  can be formed from a polymer material, the covering of housing  106  by insulating box  1400  can provide thermal insulation of housing  106  from the heated air that passes through outlet vents  206 . 
     Also, the insulating box  1400  can direct air to exit electronic device  100  at certain preferred angles so that the air circulation and heat dissipation of electronic device  100  can be improved. Vertical strips  1406  on the first portion  1402  can point in a first direction while vertical strips  1408  on the second portion  1404  can point in a second direction opposite the first direction. Hence, the vertical strips can contour air exiting housing  106  sideway (instead exiting housing  106  straight), as shown in the arrows in  FIG. 15 . Since outlet vents  206  can be positioned behind stand  108 , the splitting of the outgoing airflow into two or more directions can avoid at least portion of the airflow impinging on stand  108 . Hence, insulating box  1400  can promote heat dissipating and air circulation of electronic device  100  because at least majority of the heated air will not hit the stand  108 , then reflect and/or accumulate at the area between  106  housing and stand  108 . 
     Referring to  FIG. 16 , a cross-sectional view of insulating box  1400  mounted on housing  106  is shown. Insulating box  1400  can be connected to the exhaust  1014  of heat exchanger  1000 .  FIG. 16  shows that the horizontal strips  1410  of insulating box  1400  can be in a triangular shape with the vertex of the triangle pointing towards exhaust  1014  of heat exchanger  1000  and the base of the triangle aligned with the horizontal grills  1414  of housing  106 . The triangular horizontal strips  1410  can prevent air from impinging on horizontal grills  1414  of housing  106 . The impingement of air onto horizontal grills  1414  can create turbulence as the air hitting grills  1414  can be reflected back towards the exhaust  1014 . Triangular horizontal strips  1410  can also contour air to exit housing  106  in a horizontal or some slightly upward directions. As shown in  FIG. 16 , the airflow coming out from exhaust  1014  can have a direction with a downward component. If triangular horizontal strips  1410  are not present, heated air can exit housing  106  at a downward direction and can be re-circulated back into housing  106  by intermingling with air entering inlet vents  202  that are located below outlet vents  206  (shown in  FIGS. 3 and 4 ). Triangular horizontal strips  1410  can change the exit directions of the air to promote better heat circulation and to prevent heated air from re-entering the housing  106 . 
       FIG. 17  illustrates a flow chart of an exemplary process  1700  for regulating rotational speeds of two impellers in a double impeller fan assembly in accordance with some embodiments. A processor, which can be the CPU of an electronic device or a dedicated processor, can control and regulate the speeds of the two impellers. The electronic device can have two major heat-generating components. The first heat-generating component can be located on a first side of the electronic device and the second heat-generating component can be located on a second side of the electronic device. The first impeller of the fan assembly can also be located on the first side and the second impeller of the fan assembly can be located on the second side. Process  1700  can begin at step  1702 , where the temperatures of both the first heat-generating component and the second heat-generating component can be monitored. At decision stage  1704 , the processor can determine whether the first heat-generating component or second heat-generating component has a higher temperature and whether the temperature difference is greater than a predetermined threshold value. If the temperature of the first heat-generating component is higher than that of the second heat-generating component by the threshold value, at step  1706  the processor can cause the first impeller to rotate faster than the second impeller, thereby forming a relative speed relationship between the first and second impellers. If the temperature of the second heat-generating component is higher than that of the first heat-generating component by the threshold value, at step  1708  the processor can reverse the relative speed relationship by causing the second impeller to rotate faster than the first impeller. In some cases, the relative speed relationship can be limited to a maximum speed difference of less than 15%. In other cases, the speed differential can be more than 15% when the temperature difference between the heat-generating components is large. Also, in some cases, when the difference in temperatures between the first and second heat-generating components is less than the threshold value, the current relative speed relationship can be maintained, meaning that a faster impeller can continue to rotate faster than the other impeller. However, in some cases the threshold value can be set at zero, meaning that the relative speed relationship can be reserved whenever a temperature difference is detected. Process  1700  can be continuously repeated. The temperatures of both components can continue to be monitored and the relative speed relationship of the impellers can adaptively be adjusted based on the temperatures. 
     The various aspects, embodiments, implementations or features of the described embodiments can be used separately or in any combination. Various aspects of the described embodiments can be implemented by software, hardware or a combination of hardware and software. The described embodiments can also be embodied as computer readable code on a computer readable medium for controlling manufacturing operations or as computer readable code on a computer readable medium for controlling a manufacturing line. The computer readable medium is any data storage device that can store data that can thereafter be read by a computer system. Examples of the computer readable medium include read-only memory, random-access memory, CD-ROMs, HDDs, DVDs, magnetic tape, and optical data storage devices. The computer readable medium can also be distributed over network-coupled computer systems so that the computer readable code is stored and executed in a distributed fashion. 
     The foregoing description, for purposes of explanation, used specific nomenclature to provide a thorough understanding of the described embodiments. However, it will be apparent to one skilled in the art that the specific details are not required in order to practice the described embodiments. Thus, the foregoing descriptions of the specific embodiments described herein are presented for purposes of illustration and description. They are not targeted to be exhaustive or to limit the embodiments to the precise forms disclosed. It will be apparent to one of ordinary skill in the art that many modifications and variations are possible in view of the above teachings.

Metadata:
Filing Date: 20180531
Publication Date: 20200331
Grant Date: 20200331
Priority Date: 20170602
Inventors: DEGNER, BRETT W.
PRATHER, ERIC R.
SMITH, WILLIAM K.
AIELLO, ANTHONY JOSEPH
DYBENKO, JESSE T.
NAGHIB LAHOUTI, ARASH
LAURENT, KRISTOPHER P.
Assignee: APPLE INC
CPC Classifications: [{"code": "F28D15/0275", "inventive": true, "first": false, "tree": "[]"}, {"code": "G06F2200/1612", "inventive": false, "first": false, "tree": "[]"}, {"code": "F04D29/441", "inventive": true, "first": false, "tree": "[]"}, {"code": "G06F1/20", "inventive": true, "first": true, "tree": "[]"}, {"code": "G06F1/206", "inventive": true, "first": false, "tree": "[]"}, {"code": "H05K7/20972", "inventive": true, "first": false, "tree": "[]"}, {"code": "G06F2200/1631", "inventive": false, "first": false, "tree": "[]"}, {"code": "F28F1/325", "inventive": true, "first": false, "tree": "[]"}, {"code": "F04D25/166", "inventive": true, "first": false, "tree": "[]"}, {"code": "G06F1/1601", "inventive": true, "first": false, "tree": "[]"}, {"code": "H05K7/20336", "inventive": true, "first": false, "tree": "[]"}, {"code": "F28D2021/0029", "inventive": false, "first": false, "tree": "[]"}, {"code": "H05K7/20972", "inventive": true, "first": false, "tree": "[]"}, {"code": "F04D25/166", "inventive": true, "first": false, "tree": "[]"}, {"code": "H05K7/20136", "inventive": true, "first": false, "tree": "[]"}, {"code": "F28D15/0275", "inventive": true, "first": false, "tree": "[]"}, {"code": "G06F1/206", "inventive": true, "first": false, "tree": "[]"}, {"code": "F04D29/4226", "inventive": true, "first": false, "tree": "[]"}, {"code": "F28F2250/102", "inventive": false, "first": false, "tree": "[]"}, {"code": "F04D29/4246", "inventive": true, "first": false, "tree": "[]"}, {"code": "G06F1/20", "inventive": true, "first": false, "tree": "[]"}, {"code": "F04D29/4246", "inventive": true, "first": false, "tree": "[]"}, {"code": "F28D2021/0029", "inventive": false, "first": false, "tree": "[]"}, {"code": "H05K7/20172", "inventive": true, "first": false, "tree": "[]"}, {"code": "F28F2250/102", "inventive": false, "first": false, "tree": "[]"}, {"code": "G06F2200/1631", "inventive": false, "first": false, "tree": "[]"}, {"code": "H05K7/20154", "inventive": true, "first": false, "tree": "[]"}, {"code": "G06F1/16", "inventive": true, "first": false, "tree": "[]"}, {"code": "G06F1/16", "inventive": true, "first": false, "tree": "[]"}, {"code": "G06F1/1601", "inventive": true, "first": false, "tree": "[]"}, {"code": "F28F2250/08", "inventive": false, "first": false, "tree": "[]"}, {"code": "F28F2250/08", "inventive": false, "first": false, "tree": "[]"}, {"code": "F04D29/441", "inventive": true, "first": false, "tree": "[]"}, {"code": "G06F2200/1612", "inventive": false, "first": false, "tree": "[]"}, {"code": "G06F1/206", "inventive": true, "first": false, "tree": "[]"}, {"code": "F04D29/4226", "inventive": true, "first": false, "tree": "[]"}, {"code": "F28D15/0275", "inventive": true, "first": false, "tree": "[]"}, {"code": "G06F1/1601", "inventive": true, "first": false, "tree": "[]"}, {"code": "F04D29/441", "inventive": true, "first": false, "tree": "[]"}, {"code": "H05K7/20972", "inventive": true, "first": false, "tree": "[]"}, {"code": "H05K7/20154", "inventive": true, "first": false, "tree": "[]"}, {"code": "G06F1/16", "inventive": true, "first": false, "tree": "[]"}, {"code": "H05K7/20336", "inventive": true, "first": false, "tree": "[]"}, {"code": "F28F2250/08", "inventive": false, "first": false, "tree": "[]"}, {"code": "F28F2250/102", "inventive": false, "first": false, "tree": "[]"}, {"code": "G06F2200/1631", "inventive": false, "first": false, "tree": "[]"}, {"code": "H05K7/20136", "inventive": true, "first": false, "tree": "[]"}, {"code": "F04D25/166", "inventive": true, "first": false, "tree": "[]"}, {"code": "H05K7/20172", "inventive": true, "first": false, "tree": "[]"}, {"code": "F04D29/4246", "inventive": true, "first": false, "tree": "[]"}, {"code": "G06F1/20", "inventive": true, "first": true, "tree": "[]"}, {"code": "F28F1/325", "inventive": true, "first": false, "tree": "[]"}, {"code": "G06F2200/1612", "inventive": false, "first": false, "tree": "[]"}, {"code": "F28D2021/0029", "inventive": false, "first": false, "tree": "[]"}, {"code": "F28F1/325", "inventive": true, "first": true, "tree": "[]"}]
Family ID: 64460473