Abstract:
A synthetic jet ejector ( 501 ) is provided which includes a diaphragm ( 503 ) and a chassis ( 505 ). The chassis has first and second major surfaces which are equipped with a set of interlocking features ( 509 ) such that a first instance of the synthetic jet ejector releasably attaches to a second instance of the synthetic jet ejector by way of the interlocking features.

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
       [0001]    This application claims the benefit of priority from U.S. provisional application No. 61/768,090, filed Feb. 22, 2013, having the same title, and the same inventors, and which is incorporated herein by reference in its entirety. 
     
    
     FIELD OF THE DISCLOSURE 
       [0002]    The present disclosure relates generally to synthetic jet ejectors, and more particularly to versatile and modular synthetic jet ejectors and systems incorporating the same. 
       BACKGROUND OF THE DISCLOSURE 
       [0003]    A variety of thermal management devices are known to the art, including conventional fan based systems, piezoelectric systems, and synthetic jet ejectors. The latter type of system has emerged as a highly efficient and versatile thermal management solution, especially in applications where thermal management is required at the local level. 
         [0004]    Various examples of synthetic jet ejectors are known to the art. Earlier examples are described in U.S. Pat. No. 5,758,823 (Glezer et al.), entitled “Synthetic Jet Actuator and Applications Thereof”; U.S. Pat. No. 5,894,990 (Glezer et al.), entitled “Synthetic Jet Actuator and Applications Thereof”; U.S. Pat. No. 5,988,522 (Glezer et al.), entitled Synthetic Jet Actuators for Modifying the Direction of Fluid Flows”; U.S. Pat. No. 6,056,204 (Glezer et al.), entitled “Synthetic Jet Actuators for Mixing Applications”; U.S. Pat. No. 6,123,145 (Glezer et al.), entitled Synthetic Jet Actuators for Cooling Heated Bodies and Environments”; and U.S. Pat. No. 6,588,497 (Glezer et al.), entitled “System and Method for Thermal Management by Synthetic Jet Ejector Channel Cooling Techniques”. 
         [0005]    Further advances have been made in the art of synthetic jet ejectors, both with respect to synthetic jet ejector technology in general and with respect to the applications of this technology. Some examples of these advances are described in U.S. 20100263838 (Mahalingam et al.), entitled “Synthetic Jet Ejector for Augmentation of Pumped Liquid Loop Cooling and Enhancement of Pool and Flow Boiling”; U.S. 20100039012 (Grimm), entitled “Advanced Synjet Cooler Design For LED Light Modules”; U.S. 20100033071 (Heffington et al.), entitled “Thermal management of LED Illumination Devices”; U.S. 20090141065 (Darbin et al.), entitled “Method and Apparatus for Controlling Diaphragm Displacement in Synthetic Jet Actuators”; U.S. 20090109625 (Booth et al.), entitled Light Fixture with Multiple LEDs and Synthetic Jet Thermal Management System”; U.S. 20090084866 (Grimm et al.), entitled Vibration Balanced Synthetic Jet Ejector”; U.S. 20080295997 (Heffington et al.), entitled Synthetic Jet Ejector with Viewing Window and Temporal Aliasing”; U.S. 20080219007 (Heffington et al.), entitled “Thermal Management System for LED Array”; U.S. 20080151541 (Heffington et al.), entitled “Thermal Management System for LED Array”; U.S. 20080043061 (Glezer et al.), entitled “Methods for Reducing the Non-Linear Behavior of Actuators Used for Synthetic Jets”; U.S. 20080009187 (Grimm et al.), entitled “Moldable Housing design for Synthetic Jet Ejector”; U.S. 20080006393 (Grimm), entitled Vibration Isolation System for Synthetic Jet Devices”; U.S. 20070272393 (Reichenbach), entitled “Electronics Package for Synthetic Jet Ejectors”; U.S. 20070141453 (Mahalingam et al.), entitled “Thermal Management of Batteries using Synthetic Jets”; U.S. 20070096118 (Mahalingam et al.), entitled “Synthetic Jet Cooling System for LED Module”; U.S. 20070081027 (Beltran et al.), entitled “Acoustic Resonator for Synthetic Jet Generation for Thermal Management”; U.S. 20070023169 (Mahalingam et al.), entitled “Synthetic Jet Ejector for Augmentation of Pumped Liquid Loop Cooling and Enhancement of Pool and Flow Boiling”; U.S. 20070119573 (Mahalingam et al.), entitled “Synthetic Jet Ejector for the Thermal Management of PCI Cards”; U.S. 20070119575 (Glezer et al.), entitled “Synthetic Jet Heat Pipe Thermal Management System”; U.S. 20070127210 (Mahalingam et al.), entitled “Thermal Management System for Distributed Heat Sources”; U.S. 20070141453 (Mahalingam et al.), entitled “Thermal Management of Batteries using Synthetic Jets”; U.S. Pat. No. 7,252,140 (Glezer et al.), entitled “Apparatus and Method for Enhanced Heat Transfer”; U.S. Pat. No. 7,606,029 (Mahalingam et al.), entitled “Thermal Management System for Distributed Heat Sources”; U.S. Pat. No. 7,607,470 (Glezer et al.), entitled “Synthetic Jet Heat Pipe Thermal Management System”; U.S. Pat. No. 7,760,499 (Darbin et al.), entitled “Thermal Management System for Card Cages”; U.S. Pat. No. 7,768,779 (Heffington et al.), entitled “Synthetic Jet Ejector with Viewing Window and Temporal Aliasing”; U.S. Pat. No. 7,784,972 (Heffington et al.), entitled “Thermal Management System for LED Array”; and U.S. Pat. No. 7,819,556 (Heffington et al.), entitled “Thermal Management System for LED Array”. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0006]      FIGS. 1A-1C  are illustrations depicting the manner in which a synthetic jet actuator operates. 
           [0007]      FIG. 2  is a top view of a laptop which utilizes synthetic jet ejectors for spot or skin cooling. 
           [0008]      FIG. 3  is a side view of a segment of the laptop of  FIG. 2 . 
           [0009]      FIG. 4  is (from top to bottom) a side view and top view of a channel for a synthetic jet ejector in the laptop of  FIG. 2 . 
           [0010]      FIG. 5  is an illustration of two systems utilized to generate the data depicted in the graphs of  FIGS. 6-8 ; the first of the two systems is a fan-based thermal management system, and the second of the two systems is a fan-based thermal management system which is augmented by a synthetic jet ejector. 
           [0011]      FIG. 6  is a graph showing heat dissipated at 70° C. as a function of flow rate (in cubic feet per minute) for the two systems of  FIG. 5 . 
           [0012]      FIG. 7  is a graph showing thermal effectiveness as a function of flow rate (in cubic feet per minute) for the two systems of  FIG. 5 . 
           [0013]      FIG. 8  is a graph showing heat transfer coefficient as a function of flow rate (in cubic feet per minute) for the two systems of  FIG. 5 . 
           [0014]      FIG. 9  is an illustration of a portable device equipped with a synthetic jet based thermal management system. 
           [0015]      FIG. 10  is an illustration of a synthetic jet ejector having a modular design. 
           [0016]      FIG. 11  is an illustration showing various configurations which the modular synthetic jet ejector of  FIG. 10  can be assembled into. 
       
    
    
     SUMMARY OF THE DISCLOSURE 
       [0017]    In one aspect, a device is provided which comprises (a) a plurality of heat sources arranged in a channel, wherein each heat source has a top; and (b) a synthetic jet ejector disposed in said channel; wherein said synthetic jet ejector directs a synthetic jet across the tops of said heat sources. 
         [0018]    In another aspect, a computer is provided which comprises (a) a plurality of heat sources; (b) a heat sink spaced apart from said heat sources; (c) a plurality of thermal conductors, each of which is in thermal contact with said heat sink and one of said heat sources; and (d) a synthetic jet ejector which directs a synthetic jet onto or across a surface of said heat sink. 
         [0019]    In a further aspect, a synthetic jet ejector is provided which comprises (a) a diaphragm; and (b) a chassis having first and second major surfaces which are equipped with a first set of interlocking features such that a first instance of the synthetic jet ejector releasably attaches to a second instance of the synthetic jet ejector by way of said first set of interlocking features. 
       DETAILED DESCRIPTION 
       [0020]    The structure of a synthetic jet ejector may be appreciated with respect to  FIG. 1   a . The synthetic jet ejector  101  depicted therein comprises a housing  103  which defines and encloses an internal chamber  105 . The housing  103  and chamber  105  may take virtually any geometric configuration, but for purposes of discussion and understanding, the housing  103  is shown in cross-section in  FIG. 1   a  to have a rigid side wall  107 , a rigid front wall  109 , and a rear diaphragm  111  that is flexible to an extent to permit movement of the diaphragm  111  inwardly and outwardly relative to the chamber  105 . The front wall  109  has an orifice  113  therein which may be of various geometric shapes. The orifice  113  diametrically opposes the rear diaphragm  111  and fluidically connects the internal chamber  105  to an external environment having ambient fluid  115 . 
         [0021]    The movement of the flexible diaphragm  111  may be controlled by any suitable control system  117 . For example, the diaphragm may be moved by a voice coil actuator. The diaphragm  111  may also be equipped with a metal layer, and a metal electrode may be disposed adjacent to, but spaced from, the metal layer so that the diaphragm  111  can be moved via an electrical bias imposed between the electrode and the metal layer. Moreover, the generation of the electrical bias can be controlled by any suitable device, for example but not limited to, a computer, logic processor, or signal generator. The control system  117  can cause the diaphragm  111  to move periodically or to modulate in time-harmonic motion, thus forcing fluid in and out of the orifice  113 . 
         [0022]    Alternatively, a piezoelectric actuator could be attached to the diaphragm  111 . The control system would, in that case, cause the piezoelectric actuator to vibrate and thereby move the diaphragm  111  in time-harmonic motion. The method of causing the diaphragm  111  to modulate is not particularly limited to any particular means or structure. 
         [0023]    The operation of the synthetic jet ejector  101  will now be described with reference to  FIG. 1   b - FIG. 1   c .  FIG. 1   b  depicts the synthetic jet ejector  101  as the diaphragm  111  is controlled to move inward into the chamber  105 , as depicted by arrow  125 . The chamber  105  has its volume decreased and fluid is ejected through the orifice  113 . As the fluid exits the chamber  105  through the orifice  113 , the flow separates at the (preferably sharp) edges of the orifice  113  and creates vortex sheets  121 . These vortex sheets  121  roll into vortices  123  and begin to move away from the edges of the orifice  109  in the direction indicated by arrow  119 . 
         [0024]      FIG. 1   c  depicts the synthetic jet ejector  101  as the diaphragm  111  is controlled to move outward with respect to the chamber  105 , as depicted by arrow  127 . The chamber  105  has its volume increased and ambient fluid  115  rushes into the chamber  105  as depicted by the set of arrows  129 . The diaphragm  111  is controlled by the control system  117  so that, when the diaphragm  111  moves away from the chamber  105 , the vortices  123  are already removed from the edges of the orifice  113  and thus are not affected by the ambient fluid  115  being drawn into the chamber  105 . Meanwhile, a jet of ambient fluid  115  is synthesized by the vortices  123 , thus creating strong entrainment of ambient fluid drawn from large distances away from the orifice  109 . 
         [0025]    Despite the many advances in synthetic jet ejector technology, a need for further advances in this technology still exists. For example, challenges exist in the implementation of synthetic jet based thermal management systems in laptop and handheld devices, where spatial and geometric constraints make conventional thermal management systems impractical. Similarly, a need exists in the art for a means by which synthetic jet ejectors may be readily modified by end users according to constrains imposed by the end use application, without necessitating a redesign or customization of the synthetic jet ejector or thermal management system. These needs may be met by the systems and methodologies disclosed herein. 
         [0026]    It has now been found that synthetic jet ejectors may be utilized advantageously to augment the fluidic flow provided by fan-based thermal management systems—especially in devices having spatial or design constraints—through the provision of channels, passageways or other measures in the host device. This is especially so in such applications involving the thermal management of computing devices, where the turbulent, localized flow provided by synthetic jet ejectors complements the global fluidic flow provided by fans by enhancing heat transfer through boundary layer disruption along the surfaces of a heat sink. 
         [0027]      FIGS. 2-4  illustrate a particular, non-limiting embodiment of a laptop computer  201  which incorporates an embodiment of a thermal management system in accordance with the teachings herein. The laptop computer  201  in this particular embodiment includes a chassis  203 , an inlet  205  (disposed on the bottom of the laptop  201 ), an outlet  207  (disposed on the side of the laptop  201 ), a fan  209  which drives air from the inlet  205  to the outlet  207  through a heat exchanger  211 , a hard disk drive (HDD)  213 , a battery  215 , a DVD  217 , memory cards  219 , and a motherboard  221 . The motherboard  221  has mounted on it a central processing unit (CPU)  223  with associated first voltage regulator (VR1)  225  and second voltage regulator (VR2)  227 , a memory controller hub (MCH)  229 , a graphics card  231 , an input/output controller hub (ICH)  233 , a system voltage regulator  235 , and a PCMCIA (Personal Computer Memory Card International Association) card  237 . 
         [0028]    With reference to  FIG. 3 , the memory cards  219  in the laptop computer  201  of  FIG. 2  are disposed beneath the motherboard  221  on a platform  239  which is spaced apart from the motherboard  221 . In the particular embodiment depicted, the gap between the motherboard  221  and the platform  239  is about 1.5 mm, and the gap between the upper surface of the memory cards  219  and the motherboard  221  is about 1 mm, although it will be appreciated that the systems and methodologies disclosed herein are not necessarily limited to any particular dimensions. This gap creates a channel  241  through which a flow of air may be created for thermal management purposes, and which has inlet  211  and outlet  213  disposed on opposing ends thereof. 
         [0029]    With reference to  FIG. 4 , a synthetic jet ejector  243  is disposed on one side of the channel  241  and operates to create one or more synthetic jets  245  which are directed along the longitudinal axis of the channel  241 . The synthetic jets  245  create turbulence in the ambient fluid, thus disrupting the thermal boundary layer across the surfaces of the memory cards  219  and enhancing thermal transfer between the surfaces of the memory cards  219  and the ambient fluid, where it may be rejected to the external environment. 
         [0030]    The thermal management system further includes the fan  215  (see  FIG. 2 ) which is adapted to create a global flow of air from the inlet  211  to the outlet  213 , and a synthetic jet ejector  243  which is disposed in the channel  241  and which is adapted to augment the global flow of air. More specifically, the synthetic jet ejector  243  directs one or more synthetic jets  245  across the tops of the heat sources (in this case, memory cards  219 ), and in doing so disrupts the boundary layer at the interface between the heat source and the airflow in the channel  241 . This, in turn, improves the rate of heat transfer from the heat source to the air. 
         [0031]      FIGS. 5-8  illustrate the improvement in heat dissipation, thermal effectiveness and heat transfer coefficient, respectively, in a system in which a synthetic jet ejector is utilized to augment a fan-based thermal management system. The data was derived from tests on the systems  301 ,  303  depicted in  FIG. 5 , in which a wall  305  has a first side  307  that is heated (i.e., exposed to a heat source), and a second side  309  that is exposed to a fluidic flow. In the system  301  depicted in  FIG. 5(   a ), a fan  311  (or “blower”) is utilized alone to provide the fluidic flow, while in the system  303  of  FIG. 5(   b ), the flow created by the fan (not shown) is augmented by a synthetic jet ejector  313 . As seen in  FIGS. 6-8 , when the system is augmented with a synthetic jet ejector as in the system  303  of  FIG. 5(   b ), notable enhancements in performance are achieved across a range of conditions. 
         [0032]      FIG. 6  illustrates the amount of heat dissipated across the wall  303  in the systems of  FIGS. 5(   a ) and  5 ( b ) at 70° C. as a function of flow rate (in cubic feet per minute). As seen therein, at lower flow rates, the heat dissipated by the two systems is comparable. However, at higher flow rates, the amount of heat dissipation achieved with the system of  FIG. 5(   b ), in which fluidic flow is augmented with a synthetic jet ejector, is substantially higher. Indeed, at flow rates above about 0.2 CFM, the percent improvement in heat dissipation achieved with the system of  FIG. 5(   b ) is about 30-45% higher than that achieved with the system of  FIG. 5(   a ). 
         [0033]      FIG. 7  illustrates the thermal effectiveness (a unitless measure of the efficiency with which heat is transported across the wall  303 ) in the systems of  FIGS. 5(   a ) and  5 ( b ) as a function of flow rate (in CFM). As seen therein, the thermal effectiveness of the system of  FIG. 5(   b ) is greater than that of the system of  FIG. 5(   a ) across all flow rates. 
         [0034]      FIG. 8  illustrates the heat transfer coefficient (that is, the proportionality coefficient between the heat flux and the temperature difference) in the systems of  FIGS. 5(   a ) and  5 ( b ) as a function of Reynolds Number (Re). As seen therein, the heat transfer coefficients of the system of  FIG. 5(   b ) are higher than those of the system of  FIG. 5(   a ), with the difference being especially pronounced at higher Reynolds numbers. 
         [0035]      FIG. 9  illustrates how a thermal management system of the type disclosed herein may be modified to accommodate the spatial and geometric constraints of a hand-held device which may be, for example, a smart phone, a personal digital assistant, a handheld computer, or the like. The device  401  depicted therein has a chassis  403  within which is disposed a plurality of heat sources  405 , each of which is in thermal communication with a heat sink  407  by way of a thermal conductor  409 . The thermal conductors  409  preferably comprise graphene, but may be any other suitable thermally conductive material. 
         [0036]    A synthetic jet ejector  413  is provided which is disposed adjacent to the heat sink  407 , and which may also act as the acoustical speaker for the device  401 . The synthetic jet ejector  413  is preferably adapted to direct a synthetic jet  411  into each of the channels formed by adjacent pairs of heat fins in the heat sink  407 . Consequently, heat from the heat sources  405  is transferred to the heat sink  407  and then rejected to the ambient environment. It will be appreciated, of course, that the use of such thermal conductors  409  allows the heat sources  405  to be thermally managed wherever they are disposed within the device  401 , and thus permits significant design flexibility. 
         [0037]      FIG. 10  depicts a particular, non-limiting embodiment of a modular synthetic jet ejector  501  in accordance with the teachings herein. The synthetic jet ejector  501  depicted therein includes a diaphragm  503 , a chassis  505  and a surround  507  which extends between the diaphragm  503  and the chassis  505 . The chassis  505  is equipped with mechanical features  509  and nozzle features  511  on first and second sides thereof, and is also equipped with electrical terminals  513 . 
         [0038]    In use, almost any number of instances of modular synthetic jet ejectors which are the same as, or similar to, the type depicted in  FIG. 10  may be attached in a variety of ways as shown in  FIG. 11  by using the mechanical features (element  509  in  FIG. 10 ) to secure the instances of the modular synthetic jet ejector  602  together. Thus, for example, the modular synthetic jet ejector  602  may be connected in a side-to-side fashion as in the first configuration  601 , or may be stacked as in the second configuration  603 , to provide twice the flow. The third  605  and fourth  607  configurations illustrate the effect of adding additional instances of the modular synthetic jet ejectors  602  to the foregoing configurations. 
         [0039]    Several variations are possible with respect to the devices and methodologies disclosed herein. For example, the modular synthetic jet ejectors disclosed herein may be assembled into various articles through various means. In addition to the use of mechanical features to secure the modular units together, various adhesives or fasteners may also be used for this purpose, alone or in addition to such mechanical features. By way of example, in some embodiments, mechanical features may be used to register the modular unit with another modular unit or with a host device or substrate, and a suitable adhesive or fastener may be utilized to fasten the modular units together, or to fasten the modular units to a host device or substrate. 
         [0040]    It will further be appreciated that the modular synthetic jet ejector units disclosed herein may be attached or assembled into various devices having various shapes. For example, the resulting device may be L-shaped or T-shaped. 
         [0041]    It will also be appreciated that the devices disclosed herein may be powered or controlled by a host device. By way of example, such devices may be incorporated into mobile technology platforms such as, for example, cell phones, smart phones, tablet PCs, and laptop PCs, and may be controlled by the electronic circuitry of the host device. The operating parameters of the incorporated device may be accessible by the host operating system so that the device can be controlled or programmed by software resident on the device. For example, the frequency at which a diaphragm in an incorporated synthetic jet ejector vibrates may be a programmable variable accessible by software operating on the host device. 
         [0042]    It will also be appreciated that the devices disclosed herein may have synthetic jet actuators whose chambers are formed by one or more surfaces of the host device. By way of example, the modular synthetic jet actuators disclosed herein may have a chamber with a first surface formed by the host device motherboard, and a second surface formed by the host device chassis. 
         [0043]    It will further be appreciated that the devices and methodologies disclosed herein may be utilized to cool or provide thermal management to a variety of heat sources. These include, but are not limited to, any of the components of computers (including those disclosed in the laptop computer of  FIG. 2 ) or computational devices, including the components of laptop computers, desktop computers, and handheld computers or devices such as, for example, mobile phones or personal digital assistants (PDAs). 
         [0044]    It will also be appreciated that various dimensions may be utilized in the channels and passageways in the devices and methodologies disclosed herein and illustrated, for example, in  FIG. 4 . In some embodiments, the tops of heat sources disposed in such passageways are spaced apart from the opposing surface of the passageway by a distance which is preferably within the range of about 0.75 mm to about 1.25 mm, more preferably within the range of about 0.85 mm to about 1.15 mm, and most preferably by a distance of about 1 mm. These passageways preferably have channels with first and second opposing surfaces which are spaced apart by a distance within the range of about 3 mm to about 9 mm, which are more preferably spaced apart by a distance within the range of about 5 mm to about 7 mm, and which are most preferably spaced apart by a distance of about 6 mm. These passageways preferably have a width within the range of about 25 mm to about 50 mm, more preferably have a width of about 30 mm to about 40 mm, and most preferably have a width of about 35 mm. 
         [0045]    It will also be appreciated that the foregoing passageways may have various geometries. Thus, for example, while it is preferred that these passageways have a geometry that is rectangular in cross-section, embodiments are possible in which the passageway has a geometry that is circular, elliptical, polygonal, or irregular in cross-section. 
         [0046]    Finally, it will be appreciated that various types of synthetic jet ejectors may be utilized in the foregoing devices and methodologies. These include synthetic jet ejectors which are based on voice coil technologies, as well as those based on piezoelectric or piezoceramic actuators. 
         [0047]    The above description of the present invention is illustrative, and is not intended to be limiting. It will thus be appreciated that various additions, substitutions and modifications may be made to the above described embodiments without departing from the scope of the present invention. Accordingly, the scope of the present invention should be construed in reference to the appended claims.