Patent Publication Number: US-2017367215-A1

Title: Cooling systems and synthetic jets configured to harvest energy and vehicles including the same

Description:
TECHNICAL FIELD 
     The present specification generally relates to cooling systems and, more particularly, to cooling systems that employ triboelectric devices for energy generation. 
     BACKGROUND 
     Power electronics devices are often utilized in high-power electrical applications, such as inverter systems for hybrid electric vehicles and electric vehicles. Power semiconductor devices, such as insulated gate bipolar transistors (IGBTs) and power transistors, for example, may be thermally coupled to a cooling device (e.g., a heat spreader and/or a heat sink), to remove non-uniform heat fluxes generated by the power semiconductor devices. Operation of the power semiconductor devices may generate high thermal loads. Power semiconductor devices are demanding increased thermal management performance of cooling devices. 
     In some cooling devices, a cooling fluid may be used to receive heat from a heat generating device, such as a power semiconductor device, through convective heat transfer and remove the heat from the heat generating device. For example, one device that may be utilized to cool a power semi-conductor device is a synthetic jet device. Generally, a synthetic jet device utilizes an oscillating diaphragm to create an airflow to cool a device. However, the synthetic jet device may generate kinetic energy that is wasted. 
     Accordingly, a need exists for alternative cooling systems for electronic device assemblies that harvest kinetic energy. 
     SUMMARY 
     In one embodiment, a cooling system includes a diaphragm, at least one conductor layer disposed on the diaphragm, at least one dielectric film layer, and a controller. The controller is programmed to operate the cooling system in a contact mode and in a non-contact mode. In the contact mode, the diaphragm is controlled to oscillate at a first amplitude such that the conductor layer contacts the dielectric film layer. In the non-contact mode, the diaphragm is controlled to oscillate at a second amplitude such that the conductor layer does not contact the dielectric film layer while the diaphragm oscillates. 
     In another embodiment, a synthetic jet device includes a diaphragm, at least one conductor layer disposed on the diaphragm, at least one dielectric film layer, and a controller. The controller is programmed to operate the synthetic jet device in a contact mode and in a non-contact mode. In the contact mode, the diaphragm is controlled to oscillate at a first amplitude such that the conductor layer contacts the dielectric film layer. In the non-contact mode, the diaphragm is controlled to oscillate at a second amplitude such that the conductor layer does not contact the dielectric film layer while the diaphragm oscillates. The oscillation of the diaphragm generates a fluid jet. 
     In yet another embodiment, a vehicle includes an electric motor; and a synthetic jet device electrically coupled to the electric motor. The synthetic jet device includes a diaphragm; at least one conductor layer disposed on the diaphragm; at least one dielectric film layer; and a controller. The controller is programmed to operate the synthetic jet device in a contact mode to operate the synthetic jet device in a non-contact mode. In the contact mode, the diaphragm is controlled to oscillate at a first amplitude such that the at least one conductor layer contacts the at least one dielectric film layer. In the non-contact mode, the diaphragm is controlled to oscillate at a second amplitude such that the at least one conductor layer does not contact the at least one dielectric film layer while the diaphragm oscillates. 
     These and additional features provided by the embodiments described herein will be more fully understood in view of the following detailed description, in conjunction with the drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The embodiments set forth in the drawings are illustrative and exemplary in nature and not intended to limit the subject matter defined by the claims. The following detailed description of the illustrative embodiments can be understood when read in conjunction with the following drawings, where like structure is indicated with like reference numerals and in which: 
         FIG. 1  schematically depicts an example cooling system including an oscillating diaphragm according to one or more embodiments described and illustrated herein; 
         FIG. 2  schematically depicts an example triboelectric device for use in the cooling system of  FIG. 1  according to one or more embodiments described and illustrated herein; 
         FIGS. 3A and 3B  schematically depict an example triboelectric device operating in contact mode according to one or more embodiments described and illustrated herein; 
         FIGS. 4A and 4B  schematically depict an example triboelectric device operating in non-contact mode according to one or more embodiments described and illustrated herein; 
         FIG. 5  is a graph illustrating the open-circuit voltage (V OC ) output of the triboelectric device according to one or more embodiments described and illustrated herein; 
         FIG. 6  is a graph illustrating the short-circuit current (I SC ) output of the triboelectric device according to one or more embodiments described and illustrated herein; and 
         FIG. 7  schematically depicts a perspective view of a vehicle including an electric motor and a power electronics module having the cooling system according to one or more embodiments described and illustrated herein. 
     
    
    
     DETAILED DESCRIPTION 
     Embodiments of the present disclosure are directed to cooling systems including a diaphragm that are operable to harvest electrical energy from the kinetic energy of the oscillating diaphragm. Particularly, embodiments described herein include a diaphragm and a controller programmed to operate the cooling system in a contact mode and a non-contact mode. For example, the controller may be programmed to operate the cooling system in a contact mode in which the diaphragm is controlled to oscillate at a first amplitude such that a conductor layer disposed on the diaphragm contacts a dielectric film layer. In the non-contact mode, the diaphragm is controlled to oscillate at a second amplitude such that the conductor layer does not contact the dielectric film layer when the diaphragm oscillates. As the diaphragm oscillates, energy produced as a result of the triboelectric effect and electrostatic induction between the conductor layer and a dielectric film may be harvested. The harvested energy may be used, for example, to power the cooling system or another electronic device, or may be stored for later use. As an example and not a limitation, the power output may be about 1.5 W/m 2  when the device operates in non-contact mode and about 2 W/m 2  when the device operates in contact mode. Various embodiments of cooling systems including triboelectric devices and vehicles incorporating the same are described in detail below. 
       FIG. 1  depicts an example cooling system  100 . In general, the cooling system  100  includes a synthetic jet device  102  and one or more heat generating elements  104 . The synthetic jet device  102  includes a diaphragm  202  between walls  105  of the synthetic jet device  102  that define a fluid housing. In particular, the walls  105  are spaced apart to define cavity  106  in which the diaphragm  202  is positioned. 
     The diaphragm  202  may be formed from a metal, plastic, glass ceramic, elastomeric material, or any other suitable material. Suitable metals include materials such as nickel, aluminum, copper and molybdenum, and alloys such as stainless steel, brass, or the like. Suitable elastomeric materials include, by way of example and not limitation, silicones, rubbers, urethanes, elastic polymers, and the like. 
     In various embodiments, the diaphragm  202  is coupled to an actuator  108  to enable displacement of the diaphragm  202  within the cavity  106 . The actuator  108  may be, for example, a piezoelectric actuator, an electric actuator, an ultrasonic actuator, an electro-restrictive actuator, a pneumatic actuator, or a magnetic actuator. As shown in  FIG. 1 , the actuator  108  is driven by a controller  110 . 
     The controller  110  may be configured as any processing or computing device capable of receiving one or more signals and producing one or more output signals to operate the cooling system  100 , and more specifically, the synthetic jet device  102 . Example processing or computing devices for the controller  110  include, but are not limited to, programmable logic controllers, analog to digital converter devices, digital to analog converter devices, general purpose microcontrollers, application specific integrated circuits, discrete electronic components, and general purpose computing devices. The functionality of the controller  110  may be provided by any combination of software, hardware and firmware. In some embodiments, the controller  110  may include a non-transitory computer-readable medium storing instructions to receive the one or more signals and produce the one or more output signals. 
     The controller  110  is operable to operate the synthetic jet device  102  in a contact mode and in a non-contact mode. More particularly, the controller  110  is programmed to oscillate the diaphragm  202 , such as through the actuator  108 , at a first amplitude corresponding to the contact mode and a second amplitude corresponding to the non-contact mode. The controller  110 , and its use to operate the synthetic jet device  102 , will be discussed in greater detail hereinbelow. 
     In operation, the controller  110  drives the actuator  108  to oscillate the diaphragm  202  within the cavity  106  of the synthetic jet device  102 . As the diaphragm  202  oscillates within the cavity  106 , it displaces fluid in the cavity  106 , which is expelled from the synthetic jet device  102  through a nozzle  112  to form a fluid jet  114 . The fluid may be air, another gas, or even a liquid. The fluid jet  114  passes over the heat generating elements  104 . Through convection, the fluid jet  114  facilitates a reduction of the temperature of the heat generating elements  104 . 
     In various embodiments, energy resulting from the oscillation of the diaphragm  202  within the cavity  106  may be harvested, such as through the use of a capacitor or battery. Accordingly, in various embodiments, the diaphragm  202  and at least one of the walls  105  of the synthetic jet device  102  form a triboelectric device  200 . 
       FIG. 2  schematically illustrates an example triboelectric device  200  in accordance with various embodiments described herein. As shown in  FIG. 2 , the triboelectric device  200  generally includes the diaphragm  202 , at least one conductor layer  204  disposed on the diaphragm  202 , and at least one dielectric film layer  206 . In the embodiment depicted in  FIG. 2 , the dielectric film layer  206  is disposed on a second conductor layer  208  which is, in turn, disposed on a cover  210 . In various embodiments, the cover  210  may be a part of the synthetic jet device  102 , such as the wall  105 . Although the embodiment in  FIG. 2  is depicted as including conductor layers  204  on opposing surfaces of the diaphragm  202 , it should be understood that in some embodiments, such as the embodiment depicted in  FIG. 1 , a conductor layer  204  may be disposed on a single surface of the diaphragm  202 . 
     The conductor layer  204  and the second conductor layer  208  serve as electrodes. Accordingly, the conductor layers  208 ,  208  may be made of aluminum, copper, gold, or another conductive material having a triboelectric series rating indicating a propensity to lose electrons. The conductor layers  204 ,  208  may be, for example, a thin film of a conductive material. Some suitable materials for the conductor layers  204 ,  208  include, by way of example and not limitation, gold thin films and aluminum foil. In various embodiments, each conductor layer  204 ,  208  is made of a material that is at a different position on a triboelectric series than the dielectric film layer  206 . Moreover, the conductor layer  204  may be the same material or a different material as the material of the second conductor layer  208 . 
     The dielectric film layer  206  may be made of one or more polymeric materials or another material with a triboelectric series rating indicating a propensity to gain electrons. The dielectric film layer  206  may be, by way of example and not limitation, polyvinyl chloride (PVC), polyimide, a polymeric organosilicon compound, such as polydimethylsiloxane (PDMS), or a fluorinated ethylene polymer, such as fluorinated ethylene propylene (FEP), polytetrafluorotethylene (PTFE), and the like. Although depicted in  FIG. 2  as being disposed on the conductor layer  208 , it is contemplated that in some embodiments, the dielectric film layer  206  may be disposed on the conductor layer  204  rather than the second conductor layer  208 . 
       FIG. 2  also depicts a load  212  coupling the conductor layer  204  to the second conductor layer  208 . The load  212  may be, by way of example and not limitation, any component suitable to consume or store electric power generated between the conductor layer  204  and the second conductor layer  208 . As non-limiting examples, the load  212  may be a capacitor, a powered electronic device, such as a sensor or a light-emitting diode (LED), or even a component of the cooling system  100 , such as the controller  110 . In embodiments in which the cooling system  100  consumes the power generated between the conductor layers  204  and  208 , the cooling system  100  may be referred to as a self-powered cooling system. In order to generate electricity, the controller  110  is programmed to operate the synthetic jet device  102  in a contact mode and in a non-contact mode, which will be discussed in turn. 
     When the controller  110  operates the synthetic jet device  102  in contact mode, the diaphragm  202  is controlled to oscillate at a first amplitude A 1  such that the conductor layer  204  contacts the dielectric film layer  206 , as shown in  FIGS. 3A and 3B . In various embodiments, as a non-limiting example, the first amplitude A 1  is between about 1 mm and about 5 mm, depending on the space between the conductor layer  204  and the dielectric film layer  206  and the thickness of the conductor layer  204  and the diaphragm  202 . Without being bound by theory, when the conductor layer  204  contacts the dielectric film layer  206 , the triboelectric effect causes electrons to be transferred from the surface of the conductor layer  204  to the dielectric film layer  206 , thereby causing a net negative charge in the dielectric film layer  206  and a net positive charge in the conductor layer  204 . As a result of the net positive charge in the conductor layer  204 , electrons flow from the conductor layer  208  to the conductor layer  204  through the load  212 . 
     The electric field generated by the separated surface charges between the conductor layer  204  and the dielectric film layer  206  will then give rise to a much higher potential on the conductor layer  204  than on the second conductor layer  208 . Such a potential difference will drive the flow of positive charges from the conductor layer  204  to the second conductor layer  208  through the load  212  until the potential difference is fully offset by the transferred charges. As a non-limiting example, the synthetic jet device  102  generates energy in an amount of between about 1.0 W/m 2  and about 3.0 W/m 2 , between about 1.5 W/m 2  and about 2.5 W/m 2 , or between about 1.75 W/m 2  and about 2.25 W/m 2  when operated in contact mode. In another non-limiting example, the synthetic jet device  102  generates about 2 W/m 2  in contact mode. 
       FIGS. 4A and 4B  schematically illustrate operation of the synthetic jet device  102  in non-contact mode. When the controller  110  operates the synthetic jet device  102  in non-contact mode, the diaphragm  202  is controlled to oscillate at a second amplitude A 2  such that the conductor layer  204  does not contact the dielectric film layer  206  while the diaphragm  202  oscillates. As shown in  FIGS. 4A and 4B , when the diaphragm  202  is oscillated at amplitude A 2 , the conductor layer  204  is spaced apart from the dielectric film layer  206  by a distance s. As a non-limiting example, the second amplitude A 2  is between about 0.5 mm and about 4.5 mm, between about 1 mm and about 4.25 mm, or between about 2 mm and about 4 mm. The distance s may, in some embodiments, be between about 0.05 mm and about 2 mm. The second amplitude A 2  is less than the first amplitude A 1  and greater than zero (i.e., A 1 &gt;A 2 &gt;0). Without being bound by theory, when the conductor layer  204  is brought into close proximity to (but not contact with) the dielectric film layer  206 , the electrostatic field between the conductor layer  204  (which has a net positive charge) and the dielectric film layer  206  (which has a net negative charge) causes the dielectric film layer  206  to become slightly polarized, which drives the flow of positive charges from the conductor layer  204  to the second conductor layer  208  through the load  212 . 
     As non-limiting examples, the synthetic jet device  102  generates energy in an amount of between about 0.5 W/m 2  and about 2.5 W/m 2 , between about 1.0 W/m 2  and about 2.0 W/m 2 , or between about 1.25 W/m 2  and about 1.75 W/m 2  when operated in non-contact mode. In one particular embodiment, the synthetic jet device  102  generates about 1.5 W/m 2  in non-contact mode. 
     In operation, the controller  110  is programmed to operate the synthetic jet device  102  in a non-contact mode for a number of cycles following operation of the synthetic jet device  102  in a contact mode for a predetermined number of cycles. For example, the controller  110  may operate the synthetic jet device  102  in a contact mode for one or more cycles, which brings the conductor layer  204  and the dielectric film layer  206  into contact with one another, producing triboelectric charges through the transfer of electrons. The predetermined number of cycles for operation of the cooling system  100  may be any number such as, without limitation, 5 cycles, 3 cycles, or even one cycle. 
     In one particular embodiment, the charge imbalance resulting from one cycle of the synthetic jet device  102  in contact mode yields an initial charge imbalance between the conductor layer  204  and the dielectric film layer  206 . As used herein, the “initial charge imbalance” is the charge imbalance that results from the transfer of electrons from the conductor layer  204  to the dielectric film layer  206  when the two layers contact one another when the synthetic jet device  102  is operated in contact mode. In some embodiments, the initial charge imbalance is achieved as a result of a single contact between the conductor layer  204  and the dielectric film layer  206  and is a value corresponding to the charge imbalance resulting from separation of the conductor layer  204  from the dielectric film layer  206 . In other embodiments, when the synthetic jet device  102  is operated in contact mode for more than one cycle in a row, the “initial charge imbalance” is the maximum charge imbalance that results during operation in contact mode. For example, the charge imbalance may increase with each contact to a maximum charge imbalance before the synthetic jet device  102  is operated in non-contact mode. The maximum charge imbalance corresponds to the initial charge imbalance for the system. Accordingly, in various embodiments, the controller  110  is programmed to operate the synthetic jet device  102  in contact mode effective to increase an existing charge balance between the conductor layer  204  and the dielectric layer  206  to the initial charge imbalance. 
     As non-limiting examples, the initial charge imbalance may be between about 10 μC/m 2  and about 100 μC/m 2 , between about 25 μC/m 2  and about 75 μC/m 2 , or between about 40 μC/m 2  and about 60 μC/m 2 . In one particular embodiment, the initial charge imbalance is about 50 μC/m 2 . 
     After operating in the contact mode for the predetermined number of cycles, the controller  110  may be programmed to then switch the synthetic jet device  102  to operation in a non-contact mode. The controller  110  may be programmed to operate the synthetic jet device  102  in non-contact mode for more than one cycle before operating the synthetic jet device  102  in contact mode again. 
     In some embodiments, the controller  110  is programmed to operate the synthetic jet device  102  in contact mode responsive to determining that the existing charge imbalance between the conductor layer  204  and the dielectric film layer  206  is below a threshold charge imbalance. The threshold charge imbalance may be, by way of example and not limitation, about 75% of the initial charge imbalance, about 60% of the initial charge imbalance, about 50% of the initial charge imbalance, or even about 40% of the initial charge imbalance. Accordingly, the controller  110  may receive charge imbalance information, compare the received charge imbalance information corresponding to an existing charge imbalance to a threshold charge imbalance stored in the memory of the controller  110 , and, when the existing charge imbalance is below the threshold charge imbalance, operate the synthetic jet device  102  in contact mode. For example, in one non-limiting example, the controller  110  may measure the voltage across the load to obtain the charge imbalance information. However, it is contemplated that the controller  110  may be configured to receive charge imbalance information in any suitable way. 
     In some other embodiments, the controller  110  may be programmed to operate the synthetic jet device  102  in contact mode responsive to determining that a predetermined amount of time has passed since the synthetic jet device  102  was last operated in contact mode. For example, the controller  110  may operate the synthetic jet device  102  in contact mode for a predetermined number of cycles (e.g., the diaphragm is oscillated at the first amplitude A 1  such that the each conductor layer  204  contacts each corresponding dielectric film layer  206  once) and record a time that corresponds to that contact. The time may be, for example, recorded in the memory of the controller  110 . Following the operation in contact mode, the controller  110  may operate the synthetic jet device  102  in non-contact mode until a predetermined period of time has passed. The predetermined period of time may be, by way of example and not limitation, 3 hours, 6 hours, 12 hours, 18 hours, 24 hours, 36 hours, or even 48 hours. When the predetermined amount of time has passed, the controller  110  may operate the synthetic jet device  102  in contact mode and record the time that a new contact between the conductor layer  204  and the dielectric film layer  206  occurs. 
     In various embodiments, the operation of the synthetic jet device  102  in non-contact mode enables the synthetic jet device  102  to produce fluid jets while energy produced as a result of the triboelectric effect and electrostatic induction is harvested without adversely impacting the cooling system  100 , and the synthetic jet device  102 , in particular. Accordingly, by programming the controller  110  to operate the synthetic jet device  102  in a contact mode and a non-contact mode, device durability can be improved because of the lack of contact between the dielectric film layer  206  and the conductor layer  24  during non-contact operation. 
     In one experimental example, a cooling system  100  included a synthetic jet device  200  in which a conductor layer  204  in the form of aluminum foil was adhered to the diaphragm and a dielectric film layer  206  in the form of fluorinate ethylene polymer was used as a contact surface with a deposited gold thin film layer as the second conductor layer  208  was adhered onto the inner surface of the upper wall  105 . Conductor layer  204  and the dielectric film layer  206  were sized and aligned to have a contacting surface area of about 7 cm 2 .  FIG. 5  is a plot illustrating the open-circuit voltage (V OC ) during the operation of the device in non-contact mode.  FIG. 6  is a plot illustrating the short-circuit current (I SC ) during the operation of the device in non-contact mode. 
     As shown in  FIGS. 5 and 6 , the peaks of the V OC  and the I SC  were up to about 40 V and about 3 μA, respectively, corresponding to a peak power density of about 0.2 W/m 2 . In the experiment, the energy was able to simultaneously light up ten light-emitting diode (LED) bulbs continuously. Accordingly, the harvested energy may be used to power electronics devices, such as LEDs, sensors, and the like. Alternatively or in addition, the harvested energy may be used to at least partially power the cooling system  100 , resulting in a self-powered cooling system. 
     As stated above, the synthetic jet devices  102  described herein may be incorporated into larger power circuits, such as inverter and/or converter circuits of an electrified vehicle, for example. The electrified vehicle may be a hybrid vehicle, a plug-in electric hybrid vehicle, an electric vehicle, or any vehicle that utilizes an electric motor. Referring now to  FIG. 7 , a vehicle  700  configured as a hybrid vehicle or a plug-in hybrid vehicle is schematically illustrated. The vehicle generally comprises a gasoline engine  770  and an electric motor  772 , both of which are configured to provide rotational movement to the wheels  780  of the vehicle  700  to propel the vehicle  700  down the road. A power circuit  702  is electrically coupled to electric motor  772  (e.g., by conductors  778 ). The power circuit  702  may be configured as an inverter and/or a converter circuit that provides electrical power to the electric motor  772 . The power circuit  702  may in turn be electrically coupled to a power source, such as a battery pack  774  (e.g., by conductors  776 ). The power circuit  702  includes one or more cooling systems  100  (see  FIG. 1 ) that include one or more triboelectric devices  200 . When the synthetic jet devices  102  of the one or more cooling systems  100  operate, electricity may be harvested and stored or used by one or more components in the vehicle  700 , such as sensors, LEDs, or other electronic power devices. 
     It should now be understood that embodiments of the present disclosure are directed to cooling systems employing synthetic jet devices from which energy may be harvested. A controller is used to operate the synthetic jet device in a contact mode and a non-contact mode to improve durability of the synthetic jet device. During operation in contact mode, a diaphragm of the synthetic jet device is oscillated at an amplitude such that a conductor layer coupled to the diaphragm contacts a dielectric film layer within the synthetic jet device to generate a charge imbalance. During operation in non-contact mode, the diaphragm is oscillated at a second amplitude such that the conductor layer and the dielectric film layer do not contact one another. Although the conductor layer and the dielectric film layer do not contact one another, the charge imbalance generated during operation in contact mode is sufficient to generate electricity as the two are brought close to one another. 
     It is noted that the term “approximately” may be utilized herein to represent the inherent degree of uncertainty that may be attributed to any quantitative comparison, value, measurement, or other representation. Such terms are also utilized herein to represent the degree by which a quantitative representation may vary from a stated reference without resulting in a change in the basic function of the subject matter at issue. 
     While particular embodiments have been illustrated and described herein, it should be understood that various other changes and modifications may be made without departing from the spirit and scope of the claimed subject matter. Moreover, although various aspects of the claimed subject matter have been described herein, such aspects need not be utilized in combination. It is therefore intended that the appended claims cover all such changes and modifications that are within the scope of the claimed subject matter.