Abstract:
A passive thermoacoustic cooling apparatus for cooling of components such as miniaturized microelectronics is disclosed. The passive thermoacoustic cooling apparatus includes resonant cavities, a temperature-difference element and a heat conduction element. The temperature-difference element is integrated with the system of resonant cavities for conversion of heat into acoustic power. The heat conducting element connects a heat source to the temperature-difference element, which transmits heat from the source to one end of the temperature-difference component. Due to established temperature gradient across hot and cold ends of the temperature-difference element, acoustic standing wave arises in the resonant cavity system. Forced air convection is thereby generated to cool the heat source.

Description:
BACKGROUND  
       [0001]     1. Field of the Invention  
         [0002]     The present invention relates in general to a thermoacoustic heat management apparatus. More particularly, this invention relates to a passive thermoacoustic heat dissipation apparatus for the cooling of equipment by air convection induced by the equipment itself via thermoacoustic effect.  
         [0003]     2. Description of the Related Art  
         [0004]     Heat dissipation devices for semiconductor integrated circuit devices such as microprocessors can be generally categorized as active and passive devices. Fans driven by electric motors or circulating work fluids circulated by pumps are examples of active heat dissipation systems, and simple heat sinks with structured fins aimed at enlarging air contact surface area are examples of passive devices. A motor driven fan requires an active supply of electric power for the fan blades to forcefully circulate the airflow inside the equipment so that heat generated by the equipment can be removed. By contrast, a passive finned heat sink consumes no power but relies on the air convection to facilitate equipment cooling. Active, heat dissipation systems may be optimized for cooling but consumes additional power and are frequently accompanied by problems such as mechanical vibration and increased size. On the other hand, passive devices may be simple and power-saving, yet they are limited in their effectiveness of heat dissipation within the realm of reasonable physical sizes and dimensions of both the devices themselves and the equipments they serve.  
         [0005]     Thermoacoustic effect is a known phenomenon of energy conversion between acoustic and thermal energy forms in both directions. Construction of thermal engines and pumps are possible based on thermoacoustic effect. For example, heat dissipation devices based on thermoacoustic effect have the benefit of simple construction and good potential of miniaturization. Devices making use of the air convection generated by thermoacoustic effect for equipment cooling purpose are known in the art.  
         [0006]     For example, U.S. Pat. No. 4,858,717 “Acoustic convective system” to Trinh et al. U.S. Pat. No. and 6,059,020 “Apparatus for acoustic cooling automotive electronics” to Jairazbhoy et al. disclosed the use of thermoacoustic effect in generating air convection for the purpose of heat dissipation. Devices such as loudspeakers were used as the sound-generating means to implement thermoacoustic energy conversion for initiation and sustain of convection airflows. With supplied energy source to a thermoacoustic apparatus, refrigeration is possible. U.S. Pat. No. 6,804,967 “High frequency thermoacoustic refrigerator” to Symko et al. described the use of piezoelectric actuators operating in high-frequency acoustic ranges up to 4 kHz. The system described was allegedly capable of producing temperature differences of about 40 degrees Celsius and achieving refrigeration temperature of −20 degrees. All these prior art thermoacoustic devices and systems required supplied power sources for operation. Although Wheatley et al. disclosed in U.S. Pat. No. 4,858,441 “Heat-driven acoustic cooling engine having no moving parts” a system operating on a waste heat source, however, that heat source is additional and is in fact another form of required supply power source. Therefore, all these prior thermoacoustic apparatuses are considered active systems due to the fact of their requirement of a dedicated energy source.  
       SUMMARY OF THE INVENTION  
       [0007]     There is therefore the need for a passive thermoacoustic heat dissipation apparatus that does not require a supplied energy source for operation.  
         [0008]     The present invention therefore provides a thermoacoustic heat dissipation apparatus for passive cooling of a heat source, said apparatus operating solely on said heat source to be cooled without any additional energy source, said apparatus comprising at least one temperature difference element having a hot end and a cold end; a heat conduction element connected to said hot end of said temperature difference element and to said heat source for conduction of heat from said heat source to said temperature difference element; and at least one cavity casing defining a resonance cavity therein and internally enclosing said temperature difference element and said heat conduction element; wherein said temperature difference element being positioned inside said resonance cavity at a location sustaining a thermoacoustic effect by the generation of a standing wave therein; said cold end of said temperature difference element facing toward an open end of said resonance cavity; and said temperature difference element having an air-passing porous body structure allowing connectivity between the air at the hot and cold ends thereof inside said resonance cavity.  
         [0009]     The present invention also provides a thermoacoustic heat dissipation apparatus for passive cooling of a heat source, said apparatus operating solely on said heat source to be cooled without any additional energy source, said apparatus comprising at least one temperature difference element having a hot end and a cold end; a heat conduction element connected to said hot end of said temperature difference element and to said heat source for conduction of heat from said heat source to said temperature difference element; and at least one cavity casing defining a resonance cavity therein and internally enclosing said temperature difference element and said heat conduction element; wherein said temperature difference element being positioned inside said resonance cavity at a location sustaining a thermoacoustic effect by the generation of a standing wave therein; said cold end of said temperature difference element facing toward an open end of said resonance cavity; said temperature difference element having an air-passing porous body structure allowing connectivity between the air at the hot and cold ends thereof inside said resonance cavity; and said heat source to be cooled enclosing the end of said resonance cavity opposite to said open end of said resonance cavity.  
         [0010]     The present invention further provides a thermoacoustic heat dissipation apparatus for passive cooling of a heat source, said apparatus operating solely on said heat source to be cooled without any additional energy source, said apparatus comprising at least one temperature difference element having a hot end and a cold end; a heat conduction element connected to said hot end of said temperature difference element and to said heat source for conduction of heat from said heat source to said temperature difference element; and a resonance cavity system comprising an aggregation of a plurality of cavity casings each defining a resonance cavity therein, said resonance cavity system internally enclosing and embedding said temperature difference element and said heat conduction element; wherein said temperature difference element being positioned inside each of said resonance cavities at a location sustaining a thermoacoustic effect by the generation of a standing wave therein; and said temperature difference element having an air-passing porous body structure allowing connectivity between the air at the hot and cold ends thereof inside said resonance cavity. 
     
    
     BRIEF DESCRIPTION OF THE DRAWING  
       [0011]      FIG. 1  schematically illustrates the cross section of a passive thermoacoustic heat dissipation apparatus in accordance with a preferred embodiment of the present invention.  
         [0012]      FIG. 2  schematically illustrates the cross section of a passive thermoacoustic heat dissipation apparatus of the present invention having multiple resonance cavities.  
         [0013]      FIG. 3  schematically outlines the distribution of resonance cavities of the apparatus of  FIG. 2 .  
         [0014]      FIGS. 4A and 4B  schematically shows the cross sectional view of the temperature difference element of the apparatus of  FIG. 2 .  
         [0015]      FIG. 5  schematically illustrates the cross section of another embodiment of the passive thermoacoustic heat dissipation apparatus of the present invention.  
         [0016]      FIG. 6  schematically illustrates the cross section of yet another embodiment of the passive thermoacoustic heat dissipation apparatus of the present invention.  
         [0017]      FIG. 7  schematically illustrates the cross section of still another embodiment of the passive thermoacoustic heat dissipation apparatus of the present invention.  
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT  
       [0018]     A preferred embodiment of the thermoacoustic heat dissipation apparatus in accordance with the present invention is schematically illustrated in  FIG. 1 . The thermoacoustic heat dissipation apparatus identified by  100  has a heat conduction element  12  and a temperature difference element  11  generally enclosed in a resonance cavity  13 . Standing waves generated as a result of thermoacoustic effect by the resonance cavity  13  appear within the space generally defined by the cavity casing  16 . One end of the generally elongated resonance cavity  13  as illustrated in the drawing is closed by a heat source  14  to be cooled. The other end of the cavity  13  remains open.  
         [0019]     Longitudinal length of the resonance cavity  13  can be selected to be a quarter of the acoustic wavelength of the basic frequency at which resonance tends to occur. Air pressure distribution for the standing wave in the resonance cavity most likely to appear is schematically shown in  FIG. 1  as curve  15 . Curve  15  represents the air pressure over the vertical direction as a function of the length along the horizontal longitudinal direction of the cavity  13 .  
         [0020]     One end of the temperature difference element  11  facing toward the open end of the cavity  13  is the cold end  112  and the opposite is hot end  111 . The temperature difference element  11  is located close to the center of the resonance cavity  13  along the longitudinal direction and is made of a material such as a ceramics, fiberglass, plastics or wood that is porous and preferably with low thermal conductivity coefficient.  
         [0021]     By contrast, heat conduction element  12  is made of a material, typically metallic or alloy that has a high coefficient of thermal conductivity. Heat conduction element  12  can be made in the form of elongated conductor such as a wire, rod or plate with one end physically in contact with the heat source  14 , a source of heat that is to be dissipated, and the other with the hot end  111  of the temperature difference element  11 . This establishes a temperature gradient across the ends of the temperature difference element  11  that can initiate a thermoacoustic conversion in the system.  
         [0022]     There can be more than one resonance cavities in the system of a passive heat dissipation apparatus in accordance with the present invention.  FIG. 2  schematically illustrates the cross section of a passive thermoacoustic heat dissipation apparatus of the present invention having an integrated system of multiple resonance cavities. As is shown in  FIG. 2 , heat conduction element  22  and temperature difference element  11  of the thermoacoustic heat dissipation apparatus  200  are generally enclosed and embedded in a system of resonance cavities  23 .  
         [0023]     In a preferred embodiment, structural body of the heat conduction element  22  is made and configured to a shape that essentially makes up, or, complements, each and every half of all the resonance cavities  23  in the system of their portions to the left of the temperature difference element  11 . In other words, sections generally identified as reference numeral  22  in  FIG. 2  become the equivalents of the cavity casing  16  of the depicted apparatus  100  of  FIG. 1 . Standing waves generated as a result of thermoacoustic effect by each of the resonance cavities  23  appear within the space generally defined by each set of the cavity casings  26 .  
         [0024]      FIG. 3  schematically outlines the distribution of resonance cavities of the apparatus of  FIG. 2  in a cross-sectional view taken along the C-C line. The cross-sectional view shows that the multiple cavities  23  of the system are distributed over the entire heat dissipation apparatus ( 200  of  FIG. 2 ) in a base  37  shown here in phantom line. Each resonance cavities  23  illustrated in  FIG. 3  is in the shape of a circle, indicating that each of the cavities is essentially an elongated cylindrical tube, a configuration convenient for the initiation of acoustic resonance and therefore the desired thermoacoustic effect. The entire heat dissipation apparatus  200  of  FIG. 2  thus becomes essentially a gross circular disc, with each of the resonance cavity tubes aligned substantially perpendicular to the plane of the gross disc.  
         [0025]     One end of each of the generally elongated resonance cavities  23 , as is shown in  FIG. 2 , is closed by a heat source  14 . The other end of each cavity  23  remains open. Longitudinal length of all resonance cavities  23  can be selected to be a quarter of the acoustic wavelength of the basic frequency at which resonance tends to occur. Air pressure distribution for the standing wave in the resonance cavities most likely to appear is schematically shown as curves  15 . Again, curves  15  represent the air pressure over the vertical direction as a function of the length along the horizontal longitudinal direction of each of the cavities  23 .  
         [0026]     One end of the temperature difference element  11  facing toward the open end of the cavities  23  is the cold end  112  and the opposite is hot end  111 . The temperature difference element  11  is located close to the center of all resonance cavities  23  along the longitudinal direction thereof and is made of a material such as a ceramics, fiberglass, plastics or wood that is porous and preferably with low thermal conductivity coefficient.  FIGS. 4A and 4B  schematically shows the cross sectional view of the temperature difference element of the apparatus of  FIG. 2  taken along the D-D line.  FIG. 4A  demonstrates that the temperature difference element  11  for the system of  FIG. 2  can be made of porous material generally exhibiting a grid-like porous structure  47 . On the other hand, the laminated structure  48  of  FIG. 4B  allowing for air connectivity between the layers from the hot to the cold ends of each of the resonance cavities in the system of  FIG. 2  is another example of applicable structure.  
         [0027]     On the other hand, the gross heat conduction element  22  for the system of  FIG. 2  is made of a material, typically metallic or alloy that has a high coefficient of thermal conductivity. Each portion of the heat conduction elements is made to constitute a portion of its corresponding resonance cavity with one end physically in contact with the heat source  14 , a source of heat that is to be dissipated, and the other with the hot end  111  of the temperature difference element  11 . This establishes a temperature gradient across the ends of the temperature difference element  11  that can initiate a thermoacoustic conversion in the system.  
         [0028]      FIG. 5  schematically illustrates the cross section of another embodiment of the passive thermoacoustic heat dissipation apparatus of the present invention. The thermoacoustic heat dissipation apparatus  500  shown has a heat conduction element  52  and a temperature difference element  11  generally enclosed in a resonance cavity  53 . Standing waves generated as a result of thermoacoustic effect by the resonance cavity  53  appear within the space generally defined by the cavity casing  56 . Both ends of the generally elongated resonance cavity  53  as illustrated are open in this system  500 . Longitudinal length of the resonance cavity  53  can be selected to be a quarter of the acoustic wavelength of the basic frequency at which resonance tends to occur. Air pressure distribution for the standing wave in the resonance cavity most likely to appear is schematically as curve  55 . Curve  55  represents the air pressure over the vertical direction as a function of the length along the horizontal longitudinal direction of the cavity  53 .  
         [0029]     The temperature difference element  11  is located approximately at a position about one-fourth the total length of the entire cavity  53  along the longitudinal direction. One end of the temperature difference element  11  facing toward the longer opening of the cavity  53  is the hot end  111  and the opposite is cold end  112 . The temperature difference element  11  is made of a material such as a ceramics, fiberglass, plastics or wood that is porous and preferably with low thermal conductivity coefficient. By contrast, Heat conduction element  52  is made of a material, typically metallic or alloy that has a high coefficient of thermal conductivity.  
         [0030]     Heat conduction element  52  can be made in the form of a heat conductor structure with one end physically extending out of the resonance cavity  53  of the system  500  and is in contact with the heat source  14 , the source of heat that is to be dissipated. Another structural end of the heat conduction element  52  is configured to remain inside the cavity  53  and made in contact with the hot end  111  of the temperature difference element  11 . This establishes a temperature gradient across the ends of the temperature difference element  11  that can initiate a thermoacoustic conversion in the system.  
         [0031]     More than one temperature difference elements can be used for a passive thermoacoustic heat dissipation apparatus in accordance with the present invention.  FIG. 6  schematically illustrates the cross section of yet another embodiment of the passive thermoacoustic heat dissipation apparatus  600  in accordance with the present invention featuring two temperature difference elements  610  and  620 . This system  600  is similar to  500  of  FIG. 5  except that a second temperature difference element is installed opposite to element  11  of system  500  also at a location approximately one-fourth the length of the resonance cavity measuring from the opposite end. Installation of the two temperature difference elements  610  and  620  in the system  600  is symmetric. As is illustrated in  FIG. 6 , the heat conduction element  62 , which is an enlarged version of its counterpart  52  in the system  500  of  FIG. 5 , is install between and in physical contact with the two temperature difference elements  610  and  620 . Cold ends  612  and  622  of the elements face outward toward the opening of the cavity  63 , and hot ends  611  and  612  face inward. This system  600  is also capable of establishing temperature gradients across the ends of the temperature difference elements  610  and  620  that collaborate to initiate a thermoacoustic conversion in the system due to the arising standing wave  65  in the cavity  63 .  
         [0032]      FIG. 7  schematically illustrates the cross section of still another embodiment of the passive thermoacoustic heat dissipation apparatus  700  of the present invention. This system  700  can be considered to be an aggregation of a multiple of devices such as illustrated and described in  FIG. 6 . Note that the aggregation can be both stacking in the vertical direction and expansion in the horizontal. Two temperature difference elements  710  and  720  shown in the drawing can each be a gross version of their counterpart in the system  600  of  FIG. 6 . Specifically each of them can be constructed as a single structure to pass through the cavity casing of all the aggregated units. In a preferred embodiment, elements  710  and  720  are positioned at the one-fourth length location of the aggregated resonance cavities  73  measuring from both open ends of the cavities of the system. Orientation of the hot and cold ends can be the same as in the system  600  of  FIG. 6 . The system  700  is capable sustaining a thermoacoustic conversion of amplified rate in the system  700  than  600  due to the arising standing wave  75  in the cavities  73 .  
         [0033]     Preferred embodiments of the passive thermoacoustic heat dissipation apparatus of the present invention as described in the above paragraphs via reference to accompany drawing include apparatuses suitable for cooling or heat dissipation applications such as for semiconductor integrated circuit devices in electronic equipments. Typical examples include CPU&#39;s, graphic processing units (GPU&#39;s), and core logic ASIC&#39;s (application specific IC) for computer systems including PC&#39;s, game machines and set-top boxes such as home entertainment systems. In these applications, a passive thermoacoustic apparatus of the present invention can be installed to the top heat dissipation planes of these IC devices similar to the manner modern PC CPU&#39;s are installed with heat sinks, either passive or active ones with fans. In some of these applications, a passive thermoacoustic apparatus of the present invention makes use of the IC device being cooled as a portion of the thermoacoustic system since they are used to close one end of the resonance cavity, for example, in the examples of  FIGS. 1 and 2 .  
         [0034]     While the above is a full description of the specific embodiments, various modifications, alternative constructions and equivalents may be used. Therefore, the above description and illustrations should not be taken as limiting the scope of the present invention, which is defined by the appended claims.