Fan based heat exchanger

[0002] This application is a continuation of U.S. Ser. No. 08/723,905 filed Sep. 30, 1996, now abandoned.

[0003] The present invention relates to the cooling of electronic components which generate high amounts of heat in general and more particularly to a method and apparatus for removing heat from an electronic heat generating component in an electronic system having a small form factor.

[0004] A number of present day electronic components utilized, for example, in computer systems, generate large amounts of heat. These components, such as microprocessors and associated components are typically encapsulated in plastic or ceramic from which a plurality of leads extend. The integrated circuit (IC) is mounted to a printed circuit board either by direct soldering or through a connector which is soldered to the printed circuit board. In a typical personal computer system, a processor, which in most cases in current systems is a high speed processor which generates a great deal of heat, is mounted on a printed circuit board known as a motherboard, along with a plurality of other components that support the processor such as memory circuits. Also contained within the personal computer housing are additional circuits or circuit boards such as video cards, facsimile-modem cards, etc. The housing may also contain a power supply, supplying power to all of the various components.

[0005] As explained in co-pending application Ser. No. 08/686,856, filed May 31, 1996 and assigned to the same assignee as the present invention, the disclosure of which is hereby incorporated by reference in its entirety, it is desirable to have a high rate of heat transfer from the IC package in order to maintain junction temperatures within the IC inside safe operating limits. As noted, modern microprocessors typically employ millions of transistors in internal circuitry that requires some type of cooling mechanism to avoid excessive junction temperatures that may effect the performance of the circuit and can cause permanent degradation of the device. As noted in that application, this is a particularly difficult problem in the design of computer system enclosures which have a small form factor such as laptop and notebook computers. However, heat removal also can constitute a problem in other types of systems which have high power profile components located within a small form factor or thin profile electronic device.

[0006] Aside from the possibility of affecting the performance of the circuits in the IC and degradation of those circuits, high heat generating components which are located within consumer electronic devices, such as laptop computers, can create hot spots at certain locations along the external casing of the devices. These hot spots can be uncomfortable to touch and may even cause burns. This is a farther reason for conducting heat away from these hot spots and cooling the components generating them to avoid injury to users.

[0007] The aforementioned application describes prior art methods used to remove heat from heat generating components located within the confines of a computer enclosure, which include the simple attachment of finned-heat sinks; the development of finned-heat sinks with intricate fins; the use of large flat heat spreading plates to which an IC is directly or indirectly attached; and the thermal coupling of the integrated circuit to a heat spreading plate by a heat pipe or other low resistance thermal path. As described, more recently, forced cooling air has been used to cool one side of a heat spreading plate having an integrated circuit attached to the other side. The prior application recognizes that these prior art methods do not provide sufficient heat removal capacity and/or efficiency needed to cool current and future high performance microprocessors and other high heat generating devices in portable general purpose or other thin profile electronic devices.

[0008] The solution proposed in that application is the use of an air duct comprising a thermally conductive housing having internal fins dispersed along the internal walls of the air duct. An airflow generator, e.g., a fan, produces an airflow that is directed from an inlet port located at or near the center of the air duct to first and second exit ports located adjacent opposite ends of the duct. The heat generating integrated circuit such as a microprocessor is thermally coupled to the thermally conductive housing by means of a low resistance thermal path such as a heat pipe.

[0009] Such an arrangement efficiently removes large amounts of heat. However, the location of the inlet port near the center of the air duct as described in the aforementioned application requires openings above the air inlet in the housing of the device. In the case of a laptop computer this can cause a problem, since in many current laptop computers, a convenient place to locate such openings is not available because it would occur in the area of the keyboard.

[0010] Because of this, there is a need for an improved apparatus and method to solve the problem of cooling high heat generating components such as microprocessors within portable consumer electronic and computer devices, which retain the highly efficient cooling performance of the aforementioned application within the available space, but avoid the problem of drawing air in through the top surface of the device in order that it can be used with a device such as a laptop computer which does not have an area on its top surface available for air intake.

[0011] The present invention provides such an apparatus for cooling a heat generating component through the use of an elongated hollow heat exchanger with a fan at one end of the heat exchanger. A heat pipe has one end thermally coupled to the heat exchanger and the other end adapted to be thermally coupled to the heat generating component. When used in a small form factor, low profile electronic device such as a laptop computer, the heat generating component, e.g., a microprocessor, is coupled to the heat pipe. In the illustrated embodiment, a heat sink is thermally coupled to the heat pipe, the heat sink being in thermal contact with the heat generating component.

[0012] Various embodiments of the present invention are disclosed including one in which one end of the heat pipe is in thermal contact with the outside surface of the heat exchanger duct. Preferably there are members, e.g., fins, attached to the inner surface of the heat exchanger duct increasing its internal surface area. The heat exchanger duct may have a rectangular or cylindrical cross section.

[0013] The members on the inside may take various forms such as convoluted fins, plate fins or pin fins. In another embodiment, the heat pipe extends through the center of the hollow heat exchanger duct and a plurality of longitudinal radial fins extend between the heat pipe and the inside wall of the heat exchanger duct, supporting the heat pipe. In the illustrated embodiment, the fan draws air through the heat exchanger duct. It could equally well blow air into the heat 20 exchanger duct.

[0014] In the illustrated laptop application, the heat exchanger extends in a direction adjacent and parallel to one of the side walls of the laptop housing. An air outlet is formed in the rear wall and an air inlet in the side wall to which the heat exchanger is adjacent. The fan is disposed between the air outlet and the one end of the heat exchanger. In some embodiments there is a curved deflector between the inlet opening and the other end of the heat exchanger and/or an expansion duct between the one end of the heat exchanger and the fan.

[0015] The arrangement of the present invention allows the use of the vertical walls as an air inlet and outlet, thus avoiding interference with elements such as a keyboard on the top of the device. This is done by thermally coupling one end of a heat pipe having two ends, to the heat generating component, such as a microprocessor, thermally coupling the other end of the heat pipe to an elongated hollow heat exchanger and generating a flow of air through the hollow heat exchanger using a fan disposed at one end while drawing air in through the other end.

[0016] FIG. 1 is a perspective view of the heat exchanger according to the present invention in a notebook computer.

[0017] FIG. 2 is a plan view of the connection between the heat sink of the heat generating component and the heat exchanger via a heat pipe.

[0018] FIGS. 3A and 3B are cross sectional side and front views respectively through the heat exchanger within the housing of the computer.

[0019] FIGS. 4A-E illustrate various possible arrangements of the heat exchanger.

[0020] FIGS. 5A-5C illustrate a number of possible internal fin arrangements for a heat exchanger duct such as the duct of FIG. 4A.

[0021] FIG. 1 is a perspective view of the heat exchanger according to the present invention Illustrated is a notebook or laptop computer 11 including an enclosure with vertical side walls 27 and 30, a vertical front wall 32 and a vertical rear wall 34. As is conventional, the laptop includes a display 13. The laptop is shown with the top of its enclosure, which would contain the keyboard, removed. Only the components related to the present invention are illustrated inside the laptop 11. It will, of course, include many additional components, many of which generate heat. Within the enclosure of the notebook computer 11 is a central processing unit 15 which is a high heat generating component from which heat must be removed to both maintain the performance of the processor and also to avoid hot spots on the housing of the computer 11. The processor is connected to a heat sink 16 which in turn is thermally connected to a heat pipe 17. The heat pipe 17 is thermally coupled to an elongated hollow heat exchanger 19 with openings at its opposed ends. The heat exchanger 19 has an air inlet 21 at one end and an air outlet 23 at the other end. Air is drawn through the heat exchanger, which has a hollow interior with an increased surface area (e.g., using finned surfaces) by a fan 25. As illustrated, an expansion duct 24 can be provided at the outlet 23 coupling it to the fan 25. An air inlet 28 is formed in the side wall 27 of the housing 11 of the computer. An air outlet opening 29 is formed in the rear wall 34 of the housing 11 of the computer

[0022] The use of an elongated hollow heat exchanger 19 which has its air inlet 21 at one end and air outlet 23 at the other end permits an arrangement in which the air inlet opening 28 and the air outlet opening 29 can both be formed in vertical walls of the housing 11. Although these openings are shown as being located in the side wall 27 and rear wall 34 of the laptop 11, it would, of course, be possible to locate them in different ones of the vertical walls of the housing of the laptop 11. For example, the air inlet could be in the front wall 32 and the air outlet in the rear wall 34. Alternatively, the heat exchanger 19 could extend in a direction perpendicular to that in which it is shown with the air outlet being in the side wall 27 and the air inlet either in the front wall 33 or the side wall 35. In addition, as indicated by arrow 30, inside air is drawn into the heat exchanger aiding in the cooling of other components within the enclosure of the laptop computer 11. Furthermore, although shown as employed in a notebook or laptop computer, the present invention can also be employed with other electronic devices, particularly those having a small form factor with a low profile.

[0023] FIG. 2 shows further details concerning an arrangement according to the present invention. The heat sink 16 for the CPU 15 of FIG. 1 is in thermal contact with the heat pipe 17 which is bent at a 90° angle. The heat pipe 17 is in contact with the heat exchanger 19 along one surface thereof As illustrated, a deflector 44 can be provided to deflect air coming in the direction of arrows 43 from the opening 28 into the housing into the interior of the heat exchanger 19.

[0024] FIGS. 3A and 3B are cross sectional side and front views respectively through the heat exchanger 19 within the housing 11 of the computer. As can be seen from FIG. 3B, in one embodiment the heat exchanger includes a duct 41 with a rectangular cross section. Within the interior of the heat exchanger duct 41 are a plurality of fins 45 to increase the surface area in contact with the air moving through the duct 41. The heat pipe 17 is shown in FIG. 3B adjacent to and in thermal contact with the duct housing 41 of the heat exchanger 19. In conventional fashion, as described in the aforementioned co-pending application, the heat pipe 17 includes a wick 46 on its inner surface and contains a working fluid which is evaporated by the heat generated at the heat sink 16 associated with the heat generating component, i.e., the CPU 15. The vapor is condensed along the surface of the heat pipe in contact with the heat exchanger 19 permitting the condensed fluid to then be wicked back to the heated end of the heat pipe where it is again condensed, forming a closed system. FIG. 3A also shows the location of the fan 25 and deflector 44.

[0025] FIGS. 4A-E illustrate various possible arrangements of the heat exchanger 19. As illustrated in FIG. 4A, the heat exchanger has a duct 41 with a round or rectangular cross section at the outlet end of which is the expansion duct 24 to which the fan 29 is coupled to draw air through the duct 41. The duct 41 has fins 45 on its internal surface which direct the air through an air outlet such as the air outlet 29 shown in FIG. 1. Also included is the optional flow turning deflector 44 which is useful in the case where the air inlet is in a wall parallel to the orientation of the heat exchange duct 41 such as the air inlet opening 28 shown in FIGS. 1 and 2. FIG. 4B shows a heat exchanger duct 41 of cylindrical cross section in which the fan 29 is of the same diameter as the duct 41. Again, the optional flow turning deflector 44 at the air inlet is shown.

[0026] FIG. 4C shows a heat exchanger duct 41 which has at its outlet a flow turning and expansion duct 47 to which the fan 29 is coupled. There is no flow turning deflector at the air inlet. In this case, with reference to FIG. 1, the air inlet in the vertical wall of the housing would be located in the front wall 32 and the air outlet in the sidewall 27. FIG. 4D shows a further embodiment similar to that of FIG. 2B with a fan 29 of the same size as the duct 41. However, in this embodiment, as illustrated by FIG. 2E, which is a cross sectional view of the heat exchanger of FIG. 2D, a heat pipe 51 is located in the center of the duct 41. The heat pipe is supported by longitudinal radially extending fins

[0027] FIGS. 5A-5C illustrate a number of possible internal fin arrangements for a heat exchanger duct such as the duct 41 of FIG. 4A. In each case, the duct is shown as a rectangular duct. Thus, in FIG. 5A within the duct housing 41 of the heat exchanger 19, convoluted fins 61 are provided. In the embodiment of FIG. 5B plate fins 63 are used and in the embodiment of FIG. 53 pin fins 65 are used. These are given as examples only; any type of fin known in the art is usable for this purpose. The arrangements of FIGS. 5A, B and C can be manufactured using well established techniques, for example, the extrusion of pin or plate fins or brazing of convoluted fins such as in FIG. 5A to the base. In the arrangement of FIG. 5A the convoluted fins are bonded to the rectangular shroud or duct 41.