Abstract:
Disclosed is a method and apparatus to increase convection heat transfer in an electrical system. The increase in convection heat transfer is achieved by applying a heat source in the vicinity of an electronic element. This effectively increases the amount of airflow across the electronic element.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to methods and apparatus for promoting heat transfer. More particularly, the present invention relates to methods and apparatus for promoting an increase of convection heat transfer in systems employing electronic components. 
     2. Description of Related Art 
     As integrated circuit packages and devices have become smaller, with shorter circuit traces and increased internal signal speeds, greater power density has resulted, causing increased heating of the devices and a need for improved heat sinking and better thermal management. 
     A few methods and/or apparatus are commonly employed for providing such thermal management. Some of those include: heat conduction, where through a material, such as aluminum, heat flows from a warmer temperature to a cooler temperature; natural convection, which relies on airflow for cooling without any external forces applied to the air; forced convection where fans or blowers move air in a direction parallel to the surface of an element from which heat is being removed; and impingement cooling where the air is blown at the element to be cooled in a direction perpendicular to its surface. 
     Although not required, often, heat sinks are provided with each of the above methods and/or apparatus to improve the removal of heat from the element. Commonly, cooling fins or vanes are employed with the heat sinks for this purpose. Each of the indicated methods and/or apparatus for cooling has a disadvantage when implemented with today&#39;s ultra dense and sensitive integrated circuits and/or electronic devices. The heat produced by current integrated circuits can reach staggering temperature levels. Accordingly, a conventional heat sink, which relies solely upon convection heat transfer, is incapable of property cooling, and therefore, maintaining such integrated circuits at an acceptable operational temperature. 
     Forced convection and impingement cooling are capable of overcoming the deficiency of natural convection heat transfer. Specifically, each of forced convection and impingement cooling implements an air moving device to increase the mass flow of air across the element. This requires the installation of a fan and a predetermined supply voltage for operating the fan. The larger the increase in mass flow of air that is desired, the higher capacity fan and/or the larger the supply voltage. However, even if the element is to be cooled with a minimally sized fan, which requires a very small supply voltage, the acoustic signature of the fan may disrupt the desired operational characteristics of the integrated circuit being cooled. In many situations such a disruption in the operational characteristics of the integrated circuit is unacceptable. 
     SUMMARY OF THE INVENTION 
     The present invention provides a novel method and apparatus to increase convection heat transfer in an electrical system. The increase in convection heat transfer is achieved by introducing a heat source in the vicinity of an element to be cooled, thereby increasing convection heat transfer, i.e. increasing the amount of airflow across the element. 
     In addition, according to the present invention, a novel method of manufacturing an apparatus to increase convection heat transfer in an electronic system is provided. The method of manufacture includes the use of an electronic device, which is. preferably cooled using a heat source and an optional heat sink. The heat source is used to increase the convection heat transfer. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The present invention will become more fully understood from the detailed description given hereinbelow and the accompanying drawings which are given by way of illustration only and thus are not limitative of the present invention, and wherein: 
     FIG. 1 is a perspective view of various structural elements which may be used to accomplish the method of the present invention; 
     FIG. 2 is a perspective view of the same structural elements illustrated in FIG. 1, but in assembled form; 
     FIG. 3 is a perspective view of an electronics enclosure employing the method according to the present invention; and 
     FIG. 4 illustrates a side view of the electronics enclosure depicted in FIG.  3 . 
    
    
     DETAILED DESCRIPTION 
     FIG. 1 is a perspective view of various structural elements which may be used to accomplish the method and apparatus of the present invention. However, it should be readily understood from the following description that the elements shown in FIG. 1 are intended to be merely illustrative of the principles of the present invention, and should not be construed as limiting. 
     As seen in FIG. 1, the illustrated device includes an electrical device  1 . This electrical device  1  may be, but is not limited to, an integrated circuit (e.g. a microprocessor or the like). In order to promote convection heat transfer away from the electrical device  1 , a heat sink  3  is attached to a surface of the electrical device  1 . The heat sink  3  is attached to the electrical device  1  using a heat conducting material to thereby promote even heat transfer from the electrical device  1  to the heat sink  3 . The use of such a heat conducting material is useful to maximize a high efficiency thermal interface between the electrical device  1  and the heat sink  3 . 
     As is further seen in FIG. 1, the illustrated device further includes a cover  7  attached to a top surface of the heat sink  3 . In particular, the cover  7  is attached to the top edges of vanes  9 . The vanes  9  of the heat sink are relatively thin vertical members, which extend from a base of the heat sink  3 . These vanes  9  are often made of a metal material, however, they may also be made of another heat conducting material. The cover  7  attached to the vanes  9  creates a plurality of enclosed lengthwise passages. The cover  7  is preferably a metal plate. Each of the lengthwise passages is defined between two consecutive vanes  9 . The lengthwise passages have openings  11  and  13  at top and bottom edges of the device, respectively. These passages are for promoting convection heat transfer. During the convection heat transfer air will enter the passages through one of the openings  11  and  13  and then exit the passages via one of the openings  11  and  13 . For example, if the air enters the passages via opening  13 , then it will exit the passages via opening  11 . 
     A heat source  5  is then attached to one of the edges of the device, along either of the openings  11  and  13 . The heat source  5  has a through opening  15  to thereby ensure that airflow through the lengthwise passages is uninhibited. The heat source may be a heating device that converts electric current to heat by means of resistors that emit radiant energy. Resistors may be composed of metal-alloy wire, nonmetallic carbon compounds, or printed circuits. Heating elements may have exposed resistor coils mounted on insulators, metallic resistors embedded in refractory insulation and encased in protective metal, or a printed circuit encased in glass. Alternatively, the heat source  5  may be another conventional device used for generating heat. 
     As is shown in FIG. 2, activation of the heat source  5  creates an increase of an input airflow  17  through the plurality of passages formed by the vanes  9 , the cover  7  and the heat source  5 . The input airflow  17  passing between the plurality of passages effectively cools the vanes  9 , thereby indirectly cooling the electronic device  1 . The input airflow  17  is exhausted form the device via the plurality of passages and the through passage  15 . 
     Alternatively, the heat source  5  may be used with an electronic device  1 , which does not employ a heat sink  3  and a cover  7 . In this case, the heat source  5  may be used in the vicinity of the electronic device  1  to enhance heat transfer. However, care should be taken to ensure the heat source  5  does not increase the temperature of the electronic device  1 . 
     Another embodiment according to the principles of the present invention is shown in FIG.  3 . FIG. 3 illustrates an electronics enclosure  19  having a plurality of circuit boards  21  contained therein. Vents or air passages  23  are integrated in a top  25  and bottom  27  of the enclosure  19 . A heat source  29  is placed in the vicinity of the top  25 , and preferably, directly on the top  25 . The heat source  29  may be a heating device of the same type described hereinabove. As an example, the heat source  29  may formed having a meandering (having a winding or turning structure) or matrix structure, such that the air passages  23  are left exposed. The heat source  29  depicted in FIG. 3 has a meandering structure. Several heat sources may also be used if desired. For example, heat sources may be placed near or in the passages; however, care must be taken to ensure that the temperature element to be cooled is not increased. Moreover, the placement of the air passages  23  in the figures is for illustration only. For example, the air passages  23  may be placed in other locations on the electronics enclosure  19 , while still achieving the objects of the present invention. 
     FIG. 4 illustrates a side view of the electronics enclosure  19  depicted in FIG.  3 . The rectangular broken-line figure shown within the confines of the electronics enclosure  19  is one of the plurality of circuit boards  21  depicted in FIG.  3 . FIG. 4 further illustrates heat source  29 , which is applied to the top  25  of the electronics enclosure  19 . When the heat source  29  is operational an airflow  31 , which passes through the air passages  23  in the bottom  27 , increases. The airflow  31  flows past the circuit boards  21  and reduces the temperature of the circuit boards  21  and any component disposed thereon. Specifically, the airflow  31  flows between the plurality of circuit boards  21 . The airflow  31  then exits the electronics enclosure  19  via the air passages  23  and passes through the openings in the heat source&#39;s  29  meandering or matrix structure. 
     While the enclosure  19  shown in the figures has multiple passages, defined by multiple circuit boards, the illustration thereof is merely illustrative. For example, heat producing elements disposed within a single passage may also be cooled using the method of the present invention. Specifically, vents located in the vicinity of the top and bottom of a passage, and a heat source applied to the vicinity of the top vents, will effectively reduce the temperature of the elements. 
     The devices shown in the figures have been depicted using individual elements, which are combined to implement the present invention. However, is should be readily understood that the devices depicted may be constructed as integral units when manufactured. 
     Additionally, the present invention has been illustrated and described using devices having a relatively small size. However, the method according the present invention is also applicable to larger scale applications. For example, an expansive ventilated enclosure (e.g. a room having heat sensitive equipment) may be cooled using the method of the present invention. In particular, using vents in a floor and roof and the addition of a heat source in the vicinity of the roof will increase a mass airflow through the room, thereby cooling any equipment contained in the room. 
     According to the principles of the present invention, the novel method disclosed hereinabove significantly increases the transfer of heat away from the electronic device  1  and/or electronics enclosure  19 . For example, as is seen in FIGS. 1 and 2, the use of the heat source  5  results in an increase in the heat transfer coefficients by about 50%. The significant increase in heat transfer coefficients is a result of an increase in the temperature gradient from the top to the bottom of the device (or bottom to the top if the heat source  5  is attached to the bottom of the electronic device  1 ). However, because heat naturally rises, it is preferable to position the heat source  5  in the vicinity of the top of the device, thereby increasing the transfer of heat away from the device. 
     The invention thus being described, it will be obvious that the same may be varied in many ways. Such variations are not to be regarded as a departure from the spirit and scope of the invention, and all such modifications as would be obvious to one skilled in the art are intended to be included within the scope of the following claims.