Patent Publication Number: US-10321602-B2

Title: Air agitator assemblies

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is a divisional of U.S. application Ser. No. 14/514,440, filed on Oct. 15, 2014, titled “AIR AGITATOR ASSEMBLIES”, which is related to U.S. application Ser. No. 14/514,436, filed Oct. 15, 2014, now U.S. Pat. No. 10,028,408, issued on Jul. 17, 2018, titled “AIR AGITATOR ASSEMBLIES”, which are hereby expressly incorporated herein by reference in their entirety. 
    
    
     BACKGROUND OF THE INVENTION 
     Contemporary high-power-dissipating electronics produce heat that requires thermal management to maintain the electronics at a designed working temperature range. Heat must be removed from the electronic device to improve reliability and prevent premature failure of the electronics. Cooling techniques may be used to minimize hot spots. 
     BRIEF DESCRIPTION OF THE INVENTION 
     In one aspect, an embodiment of the invention relates to an air agitator assembly for use with a heat-emitting object having a contour, the air agitator assembly including a perforated flexible structure having a thermally absorbing first side confronting and spaced from a portion of the heat-emitting object to define an air space there between and a second side opposite the first side and where at least a portion of the first side of the perforated flexible structure has a contour that matches a contour of a corresponding portion of the heat-emitting object and at least one piezoelectric structure located on the perforated flexible structure and operably coupled to a power source wherein heat emitted from the heat-emitting object is absorbed by the first side and actuation of the at least one piezoelectric structure results in movement of the perforated flexible structure to move the volume of the air located between the hot source and the agitator assembly with the local ambient air. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       In the drawings: 
         FIGS. 1A-1B  schematically illustrate an air agitator assembly according to an embodiment of the invention. 
         FIGS. 2A-2B  schematically illustrate an air agitator assembly according to another embodiment of the invention. 
         FIG. 3  is a partially exploded view of an air agitator assembly according to yet another embodiment of the invention. 
         FIG. 4  is a cross-sectional view of an air agitator assembly according to another embodiment of the invention. 
         FIG. 5A  is an exploded perspective view of an air agitator assembly according to another embodiment. 
         FIG. 5B  is a cross-sectional view of the assembled air agitator assembly of  FIG. 5A . 
     
    
    
     DESCRIPTION OF EMBODIMENTS OF THE INVENTION 
       FIG. 1A  illustrates an air agitator assembly  10  for use with a heat-emitting object  12 . The heat-emitting object  12  may be any heat-emitting object including any electronic heat-emitting component that requires thermal management such as a microprocessor, high heat flux Printed Circuit Boards (PCBs), capacitors, electronics including MOSFETs, and any other device that needs cooling. In the accompanying  FIGS. 1 through 4 , the heat-emitting object  12  has been illustrated as a PCB for illustrative purposes only. The air agitator assembly  10  may be used with airborne, shipboard, and ground based electronics or any heat dissipating plate and device. 
     A perforated flexible plate  14  may be included in the air agitator assembly  10  and may be spaced apart from the heat-emitting object  12  and disposed in a generally confronting relationship with the heat-emitting object  12 . The perforated flexible plate has been shown partially exploded and partially offset from the heat-emitting object  12  for illustrative purposes. The perforated flexible plate  14  may be formed from any suitable flexible material including aluminum, copper, stainless steel, composite, etc. While the term plate is used, it will be understood that the perforated flexible plate  14  need not have a planar shape and may have any suitable shape including that of a different geometrical shape including a circle or non-standard-geometrical shape. Further, it will be understood that the perforated flexible plate  14  may be of any suitable thickness including that it may have a varied thickness. Perforations  16  in the perforated flexible plate  14  may take any suitable shape and size. Any number of perforations  16  may be included and such perforations  16  may be spaced from each other in any suitable manner. 
     A first side  20  of the perforated flexible plate  14  is illustrated more clearly in  FIG. 1B  as the side confronting and spaced from a portion of the heat-emitting object  12  to define an air space  18  there between. The first side  20  is thermally absorbing via radiation heat transfer. More specifically, the first side  20  may have an absorptivity that is close to 1.0. By way of non-limiting example, the first side  20  may have an absorption value equal to or greater than 0.95. The absorptivity may be achieved in any suitable manner including having the first side  20  be black in color. As an example, the black color in the paint mix is a polyurethane paint doped with carbon black to obtain the desired high emissivity value. 
     Conversely, the second side  22 , which is opposite the first side  20 , of the perforated flexible plate  14  may include a thermally reflective surface such that it is configured to minimize the absorption of heat via radiation. More specifically, the second side  22  may have a reflectivity that is close to one and an absorptivity that is close to 0.0. By way of non-limiting example, the second side  22  may have an absorption value equal to or less than 0.1 and a reflectivity value greater than 0.95. The reflectivity may be achieved in any suitable manner including by having the second side  22  be shiny and light in color. Such a radiation coating may be applied to the perforated flexible plate  14  to minimize the radiative heat transfer from hotter objects and to maximize the heat dissipation from the second surface  22 . It is understood that the second surface  22  can have a tailorable emissivity and reflectivity depending on the view factor between hot and colder components within the packaged enclosure. 
     At least one piezoelectric structure  24 , for example a piezoelectric crystal, may be located on the perforated flexible plate  14 . In the illustrated example, the piezoelectric structure  24  is located at the center of the perforated flexible plate  14 . This need not be the case, and at least one piezoelectric structure  24  may be located elsewhere. The piezoelectric structure  24  may be operably coupled to suitable power sources through connections (not shown). For example, a controllable electric source (not shown) may be utilized such that an alternating voltage of the desired magnitude and frequency may be applied to the piezoelectric structure  24 . If multiple piezoelectric structures  24  are utilized, they may be spaced from each other or stacked. 
     The air agitator assembly  10  may be mounted to the heat-emitting object  12 . By way of non-limiting example, the perforated flexible plate  14  is illustrated as being mounted to the heat-emitting object  12  at its center with fasteners  26  in the form of screws. Alternatively, the air agitator assembly  10  may be mounted to a housing or other structure such that it is spaced from the heat-emitting object  12  such that the air agitator assembly  10  is mounted next to the heat-emitting object  12 . By way of non-limiting example, it is contemplated that the two may be spaced closely such as within approximately 0.25 to 0.5 inches apart. 
     During operation, heat emitted from the heat-emitting object  12  is absorbed by the thermally absorbing first side  20  of the perforated flexible plate  14 . Such heat travels through the perforated flexible plate  14  by way of conduction and may radiate from the second side  22  into the surrounding environment. Because the perforated flexible plate  14  has one side that is highly thermally absorbing and the other highly reflective, greater heat transfer rates are achieved. It will also be understood that the highly reflective side can be tailored to a highly absorbing side depending on the view factor with cooler components within the enclosure. 
     Further, at least one piezoelectric structure  24  may be actuated and this results in movement of the perforated flexible plate  14  to move air within the volume of the air space  18 . The movement of the perforated flexible plate  14  may cause the air to circulate and agitate. Such agitation movement allows for an increase in the coefficient of convection heat transfer and the circulation allows for cooling of the air agitator assembly  10  that has absorbed part of the heat from the heat-emitting object  12  via radiation heat transfer. More specifically, when a voltage is applied to at least one piezoelectric structure  24  ends of the perforated flexible plate  14  move upwards. When a voltage of opposite polarity is applied, ends of the perforated flexible plate  14  move in the opposite direction. The actuation of the piezoelectric structure  24  causes ends of the perforated flexible plate  14  to flap. 
     In this manner, the piezoelectric structure  24  converts electrical energy into mechanical work for the perforated flexible plate  14  to oscillate. The perforated flexible plate  14  may be caused to oscillate or flap at any suitable speed including, by way of non-limiting example, at frequencies of approximately 140 Hz. As the perforated flexible plate  14  oscillates, the local boundary layer near the heat-emitting object  12  is agitated and disturbed. The disturbed boundary layer becomes an effective convective heat transfer medium. As the perforated flexible plate  14  oscillates, the boundary layer air that is located next to the heat-emitting object  12  is forced to continuously mix with the cooler air in the surrounding environment due to the air movement in-and-out of the perforations  16  that are located on the perforated flexible plate  14 . Further, the second side  22  of the perforated flexible plate  14  reflects heat from other packaged electronic devices that are in view of the heat-emitting object  12  and hotter than the heat-emitting object  12 . 
     By way of further non-limiting example,  FIGS. 2A-2B  illustrate an alternative air agitator assembly  110  according to a second embodiment of the invention. The air agitator assembly  110  is similar to the air agitator assembly  10  previously described and therefore, like parts will be identified with like numerals increased by 100, with it being understood that the description of the like parts of the air agitator assembly  10  applies to the air agitator assembly  110 , unless otherwise noted. 
     One difference is that the air agitator assembly  110  includes a second air agitator having a second perforated flexible plate  130  with perforations  132 . The second perforated flexible plate  130  is in a confronting and spaced relationship with the second side of the first perforated flexible plate  114  to define an air space  134  there between. The second perforated flexible plate  130  is similar to the first and also includes a thermally absorbing first side  136  and a reflective second side  138  opposite the first side  136  and at least one piezoelectric structure  140  located on the second perforated flexible plate  130 . The first perforated flexible plate  114  and the second perforated flexible plate  130  may be arranged in parallel such that they may obtain a desired effective radiation heat transfer. Although this need not be the case, the first perforated flexible plate  114  and the second perforated flexible plate  130  have been illustrated as being arranged such that perforations  116  and  132  in each perforated flexible plate are offset. While only two plates have been illustrated, it is contemplated that any number of plates may be arranged in such a parallel relationship. The first perforated flexible plate  114  and the second perforated flexible plate  130  may be placed at close distance from one another. 
     The air agitator assembly  110  works similarly to the air agitator assembly  10  described above including that heat emitting from the heat-emitting object  112  is absorbed by the first side  120  of the first perforated flexible plate  114  and heat emitting from the second side  122  of the first perforated flexible plate  114  is absorbed by the first side  136  of the second perforated flexible plate  130 . Further, actuation of piezoelectric structures  124  and  140  results in movement of the corresponding first perforated flexible plate  114  and the corresponding second perforated flexible plate  130  to draw air in, push out the drawn in air such that the heat-emitting object  112  is cooled by the airflows and air movement created. It is contemplated that the piezoelectric structures  124 ,  140  of the first perforated flexible plate  114  and the second perforated flexible plate  130 , respectively, are configured to be actuated simultaneously and may utilize the same power source and/or controller. Alternatively, they may be actuated separately and may utilize separate power sources and/or controllers. 
     Both the first perforated flexible plate  114  and the second perforated flexible plate  130  act to disturb the boundary layer of air along the heat-emitting object  112 . Further, both the first perforated flexible plate  114  and the second perforated flexible plate  130  act as a radiation heat shield. Because the perforations  116  and  132  are offset they occult the view factor between the heat-emitting object  112  and any higher heat-emitting components that are located nearby. 
     By way of further non-limiting example,  FIG. 3  illustrate an alternative air agitator assembly  210  according to a third embodiment of the invention. The air agitator assembly  210  is similar to the air agitator assembly  10  previously described and therefore, like parts will be identified with like numerals increased by 200, with it being understood that the description of the like parts of the air agitator assembly  10  applies to the air agitator assembly  210 , unless otherwise noted. 
     One difference is that connections  248  are illustrated as coupling the piezoelectric structure  224  to a power source  252  located directly on the perforated flexible plate  214 . Further, a controller  250  is illustrated as being included on the perforated flexible plate  214 . The controller  250  may be configured to control actuation of the power source  252  and therefore the piezoelectric structure  224 . The controller  250  may be any suitable type of controller including a Proportional Integral Differential (PID) controller or an on/off controller. During operation, the controller  250  may allow the air agitator assembly  210  to turn-off during low temperature operation, such as by way of example below 20° C., to increase the reliability of the air agitator assembly  210 . 
     By way of further non-limiting example,  FIG. 4  illustrates an alternative air agitator assembly  310  according to a fourth embodiment of the invention. The air agitator assembly  310  is similar to the air agitator assembly  210  previously described and therefore, like parts will be identified with like numerals increased by 100, with it being understood that the description of the like parts of the air agitator assembly  210  applies to the air agitator assembly  310 , unless otherwise noted. 
     One difference is that power source for the piezoelectric structure  324  is not illustrated on the heat-emitting object  312 . While it may be located on the heat-emitting object  312  it may also be located elsewhere. Further, while the controller  350  has been illustrated as being coupled to the heat-emitting object  312  it may also be located elsewhere. Another difference is that a temperature-measuring device  352  has been illustrated as being included on the heat-emitting object  312 . Such a temperature-measuring device  352  may be considered a part of the air agitator assembly  310  regardless of its location. The temperature-measuring device  352  may provide a temperature signal to the controller  350  such that the air agitator assembly  310  may be controlled based on a temperature of the heat-emitting device  312  or the air surrounding it. Any suitable temperature-measuring device  352  may be utilized including a thermocouple. 
     Again the controller  350  may be any suitable type of controller. By way of non-limiting example, when an on/off controller is used with the integrated temperature-measuring device  352 , the piezoelectric structure  324  may be activated when the allowable hot temperature is reached. For example, such a hot temperature may be, for exemplary purposes, 70° C. Alternatively, when the temperature is detected and sent to the controller  350  it is between a set hysteresis loop, as an example 20° C. to 70° C., the piezoelectric structure  324  is controlled to be either on or off. In this mode, the air agitator assembly  310  is considered in the hysteresis hot or cold mode, respectively. The hysteresis mode occurs either during a decrease in temperature from its turn-on set point or an increase in temperature from its turn-off set point. When the temperature is below it lowest set point, the power to the piezoelectric structure  324  is off. If a PID type controller is used, the hysteresis loop may be replaced by a fine temperature control with a higher tolerance. 
     By way of further non-limiting example,  FIGS. 5A-5B  illustrate an alternative air agitator assembly  410  according to a fifth embodiment of the invention. The air agitator assembly  410  is similar to the air agitator assembly  10  previously described and therefore, like parts will be identified with like numerals increased by 400, with it being understood that the description of the like parts of the air agitator assembly  10  applies to the air agitator assembly  410 , unless otherwise noted. 
     One difference is that the air agitator assembly  410  is illustrated as being used with a heat-emitting object  412  that has a contour (i.e. is not flat). For example, such a heat-emitting object  412  may be a capacitor. Further, while the perforated flexible structure  414  may include a thermally absorbing first side  420  confronting and spaced from a portion of the heat-emitting object  412  to define an air space  418  there between and a reflective second side  422  unlike the earlier embodiments the perforated flexible structure  414  has at least a portion of the first side  420  that has a contour that matches a contour of a corresponding portion of the heat-emitting object  412 . In the illustrated example, the first side  420  is rounded to better match the cylindrical shape of the heat-emitting object  412 . It will be understood that the contoured perforated flexible structure  414  may have any suitable shape and may be contoured in any suitable manner depending on the shape of the heat-emitting object. For example, the flexible structure may merely be shaped or bent plate or structure. Alternatively, it is contemplated that a thickness of the flexible structure may be varied such that the first side  420  of the perforated flexible structure  414  has a contour that matches the contour of the corresponding portion of the heat-emitting object  412 . 
     Further, the air agitator assembly  410  includes a second perforated flexible structure  430  with perforations  432 . The second perforated flexible structure  430  is in a confronting and spaced relationship with a second side of the heat-emitting object  412  to define an air space  434  there between. The second perforated flexible structure  430  is similar to the first perforated flexible structure  414  and also includes a thermally absorbing first side  436  and a reflective second side  438  opposite the first side  436  and at least one piezoelectric structure  440  located on the second perforated flexible structure  430 . The first perforated flexible structure  414  and the second perforated flexible structure  430  may be joined via portions  450  including that a screw of other fastener may be utilized to fasten the portions  450  together. As illustrated in  FIG. 5B , the first perforated flexible structure  414  and the second perforated flexible structure  430  may be mounted together such that they do not touch the heat-emitting object  412 . 
     The air agitator assembly  410  works similarly to the air agitator assembly  10  described above including that heat emitting from the heat-emitting object  412  is absorbed by the first side  420  of the first perforated flexible structure  414  and the first side  436  of the second perforated flexible structure  430 . Further, actuation of piezoelectric structures  424  and  440  results in movement of the corresponding first perforated flexible structure  414  and the corresponding second perforated flexible structure  430  to create air movement such that the heat-emitting object  112  is cooled by the airflows and air movement created. It is contemplated that the piezoelectric structures  424 ,  440  of the first perforated flexible structure  414  and the second perforated flexible structure  430 , respectively, are configured to be actuated simultaneously or in series or based on the same or different detected temperatures. Further, they may utilize the same power source and/or controller or utilize separate power sources and/or controllers. 
     In this manner both the first perforated flexible structure  414  and the second perforated flexible structure  430  act to disturb the boundary layer of air around the heat-emitting object  412 . Further, both the first perforated flexible structure  414  and the second perforated flexible structure  430  act as a radiation heat shield. It will be understood that an air agitator assembly having a contoured may be utilized with any number of perforated flexible structures over any number of sides of any heat-emitting object. Including that only a single perforated flexible structure may be utilized. Further still this may include utilizing perforated flexible structures in parallel with each other as disclosed in embodiments above. Further still, the air agitator assembly  410  may be used with one or more controllers, power sources, and/or temperature sensors. 
     The embodiments described above provide a variety of benefits including that such air agitator assemblies solve the thermal management problem of cooling electronic devices with high power dissipations, with local hot spots, or electronic components that require a uniform temperature distribution. The effective convection, provided by the oscillation of the plate and the perforations, and radiation, provided by the highly absorbing and reflective surfaces, heat transfer coefficient is expected to be approximately five times greater than natural convection. The above-described embodiments couple convection and radiation heat transfer to provide better cooling. Further, the above-described embodiments are easy to manufacture, have low electrical draw, low volume, are lightweight, and increase component reliability. Typically, standard fans are used for convection cooling in aircrafts; however, they are heavier and at times the air circulation from fans is blocked due to the high-density packaging. The above-described embodiments significantly improve cooling because the air movement is near the boundary layer of the heat-emitting object as opposed to having the air travel through a tortuous path to get to the object. Further still, depending on the attachment method, the air agitator assembly may provide additional structural integrity to the component to be cooled while it is under vibration and shock environments. 
     To the extent not already described, the different features and structures of the various embodiments may be used in combination with each other as desired. Some features may not be illustrated in all of the embodiments, but may be implemented if desired. Thus, the various features of the different embodiments may be mixed and matched as desired to form new embodiments, whether or not the new embodiments are expressly described. All combinations or permutations of features described herein are covered by this disclosure. 
     This written description uses examples to disclose the invention, including the best implementation, to enable any person skilled in the art to practice the invention, including making and using the devices or systems described and performing any incorporated methods presented. The patentable scope of the invention is defined by the claims, and may include other examples that occur to those skilled in the art. Such other examples are intended to be within the scope of the claims if they have structural elements that do not differ from the literal language of the claims, or if they include equivalent structural elements with insubstantial differences from the literal languages of the claims.