Patent Application
20140034283
1. Field
The present application relates to devices that generate ions and electrical fields to motivate flow of fluids, such as air, and more particularly, to operational control of electrohydrodynamic (EHD) air movers and/or electrode conditioning mechanisms suitable for use as part of a thermal management solution to dissipate heat.
2. Related Art
Many modern electronic devices (including desktop and laptop computers, all-in-one computers, televisions, video displays and projectors) employ forced air flow as part of a thermal management solution. Mechanical air movers such as fans or blowers have conventionally been employed in many such devices. However, in some applications and devices, mechanical air mover operation may result in undesirable levels of noise or vibration that may degrade the user experience. In some cases, physical scale or flow paths that would otherwise be necessary to accommodate a mechanical air mover may be incompatible with, or unacceptably limit, the design, scale or form factor of a particular design. Worse still, at the extremely thin device form factors popular in certain consumer electronics (e.g., laptops, pad-type computers, televisions, smartphones, book readers and media players), mechanical air mover designs (if even accommodatable) tend to exhibit poor cooling efficiencies. As a result, battery life may be adversely affected or, as a practical matter, device performance throttled to a level compatible with passive cooling.
Technologies have been developed that employ electric fields and principles of ionic movement of a fluid to motivate air flow. Devices that operate based on such principles are variously referred to in the literature as ionic wind machines, electric wind machines, corona wind pumps, electro-fluid-dynamics (EFD) devices, electrohydrodynamic (EHD) thrusters and EHD gas pumps. Some aspects of the technology have been exploited in devices referred to as electrostatic air cleaners or electrostatic precipitators and, indeed, some practical large scale device applications of the technology date back to the early 1900s. More recently, researchers have considered the utility of EHD air movers as part of a thermal management solution in consumer electronics devices. See generally, N. E. Jewell-Larsen, H. Ran, Y. Zhang, M. Schwiebert and K. A. Honer, Electrohydrodynamic (EHD) Cooled Laptop, in proceedings of 25th Annual Semiconductor Thermal Measurement and Management Symposium (March 2009).
In some cases, an ion flow or EHD air mover may improve cooling efficiency and thermal management in some devices and/or applications, while reducing noise, vibration and power consumption. Likewise, EHD air mover designs may provide or facilitate systems or devices that have reduced overall device lifetime costs, device size or volume, and/or improved electronic device performance or user experience.
Ozone (03), while naturally occurring, can also be produced during operation of various electronics devices including EHD devices, photocopiers, laser printers and electrostatic air cleaners, and by certain kinds of electric motors and generators, etc. At high concentrations, ozone can be undesirable and, accordingly, techniques to reduce ozone concentrations are desired. Indeed, techniques have been developed to catalytically or reactively break down ozone (O3) into the more stable diatomic molecular form (O2) of oxygen. See e.g., U.S. Pat. No. 6,603,268 to Lee and U.S. Patent Application Publication 2010-0116469, naming Jewell Larsen et al. as inventors, each of which is commonly-owned by the assignee of the present application.
Improved techniques for ozone management and/or abatement are desired for, or for use in conjunction with, EHD air movers.
It has been discovered that an controller for an EHD air mover may, in its operational control decision logic, advantageously consider factors beyond simple ventilating air flow or cooling demands of the system in which it resides. In particular, control actions and, in some cases, the observables directly sensed or modeled, may be selected to improve efficacy of ozone reduction strategies. For example, efficacy of an ozone reducing catalyst may be improved by controller-ordered rest at selected times during the operation of a system in which the EHD air mover resides.
In some systems in which an ozone reducing catalyst is employed to reduce net ozone introduced by an EHD air mover systems, efficacy of the ozone reducing catalyst has been found to decrease over time. For example, after tens of hours EHD air mover operation and related ozone generation, certain ozone catalyst preparations, such as e.g., Mn02 bearing catalysts, have been observed to exhibit significantly reduced efficacy. Although the particular mechanisms involved in saturation or efficacy reduction of the catalyst are not fully understood, it is possible that a portion of catalyst surface is covered by adsorbed species including oxygen atoms (not necessarily O3 or O2 molecules).
To address such efficacy reduction or saturation, a variety of strategies have been employed. In some cases, an additional consumable catalyst or ozone reducer, such as silver (or a silver containing compound), may be applied in situ to offset the efficacy reduction or saturation of a primary catalyst. In systems in which successive in situ applications of an additional consumable catalyst are employed as part of a steady state ozone reduction strategy, frequency of applications can be increased.
In some cases, a primary catalyst may be allowed to rest by reducing EHD air mover power and generated ozone flux. Rest may be particularly effective for catalyst materials such as manganese dioxide (MnO2), which may be provided on heat transfer surfaces and elsewhere along an EHD-motivated air flow path. In some cases, catalyst rest may be scheduled opportunely in terms of observed or predicable use patterns. In some cases, commanded reductions in EHD power and motivated air flow (notwithstanding cooling demands of the otherwise cooled and ventilated system) may be employed to thermally enhance the effects of such rest. Such a strategy may be particularly effective when a least a portion of the surface area of the primary catalyst is provide on, or otherwise thermally coupled to, heat transfer surfaces such as fins of a heat sink.
In some embodiments in accordance with the present invention, an apparatus includes an electrohydrodynamic (EHD) fluid mover, ozone reducing catalyst bearing heat transfer surfaces and a controller. The electrohydrodynamic (EHD) fluid mover includes emitter and collector electrodes energizable to motivate fluid flow therebetween. The ozone reducing catalyst bearing heat transfer surfaces are downstream of the emitter electrode in a flow path of the motivated fluid flow. The controller is operable to, at respective times throughout the operating life of the EHD fluid mover, selectively employ at least one ozone reduction enhancement response selected from a set of responses that includes: (i) triggering a conditioning mechanism to apply an additional, but at least partially consumable, ozone reducing catalyst to a surface of the emitter electrode.
In some cases, timing of the selectively employed ozone reduction enhancement response is based, at least in part, on operating time of the EHD fluid mover since a most recent application the additional ozone reducing catalyst to the emitter electrode. In some cases, timing of the selectively employed ozone reduction enhancement response is based, at least in part, on an estimate of saturation of the ozone reducing catalyst bearing heat transfer surfaces.
In some cases, the selected-from set of responses further includes: (ii) reducing EHD fluid flow and thereby temporarily increasing temperature of the ozone reducing catalyst on the heat transfer surfaces.
In some embodiments, the apparatus also includes a heat source thermally coupled to the ozone reducing catalyst bearing heat transfer surfaces, wherein during periods of generally low thermal management demands, the controller preferentially employs the temporary increase in temperature to rejuvenate and thereby maintain efficacy of the ozone reducing catalyst on the heat transfer surfaces. In some cases, the controller is operable to trigger the reduced EHD fluid flow response notwithstanding an unmet thermal management demand of the heat source. In some cases, the heat source includes one or more of a processor, a graphics or memory subsystem, an illumination source, an optoelectronic device and an RF transceiver.
In some embodiments, the controller is operable to trigger the reduced EHD fluid flow based on an estimation of decreased efficacy of the ozone reducing catalyst on the heat transfer surfaces. Duration of the triggered reduction EHD fluid flow is based on an estimation of ozone reducing catalyst rejuvenation at the temporarily increased temperature. In some cases, during periods of generally high user activity, the controller limits use of the conditioning mechanism to apply the additional but consumable ozone reducing catalyst and preferentially employs the rejuvenation at temporarily increased temperature.
In some embodiments, the selected-from set of responses further includes: (iii) resistively heating the surface of the emitter electrode by causing a current to flow along a longitudinal extent thereof. In some cases, the emitter electrode is coupled in a conductive loop, and the apparatus further includes an inductive coupler proximate a portion of the conductive loop to induce the current flow.
Some embodiments include the aforementioned conditioning mechanism, and the included conditioning mechanism is operable in response to the triggering to travel over the surface of the emitter electrode in frictional engagement therewith. In some cases, the conditioning mechanism includes an abrasive in frictional engagement with the emitter electrode, the conditioning mechanism further operable to, at successive times throughout the operating life of the EHD fluid mover, frictionally remove at least some otherwise detrimental material accumulation from the emitter electrode. In some cases, the conditioning mechanism includes one or more surfaces configured for tandem travel over at least a portion of the collector electrode.
In some cases, the emitter electrode is a conductive wire having a diameter of less than about 40 microns. In some cases, the ozone reducing catalyst on the heat transfer surfaces exhibits decreasing oxygen saturation as a function of temperature and time. In some cases, the ozone reducing catalyst on the heat transfer surfaces includes manganese dioxide (MnO2). In some cases, the additional but consumable ozone reducing catalyst applied to the emitter electrode surface includes silver (Ag). In some cases, the additional but consumable ozone reducing catalyst applied to the emitter electrode surface includes a preparation of silver (Ag) and graphite.
In some embodiments, the apparatus is embodied at least in part as a thermal management system for an electronic system, wherein the controller includes functional code executable on a processor of the electronic system. In some embodiments, the controller is implemented, at least in part, as a device driver executable on a processor of an electronic system. In some embodiments, the controller is implemented, at least in part, as part of a thermal management system.
In some embodiments in accordance with the present invention, a method includes (A) energizing emitter and collector electrodes of an electrohydrodynamic (EHD) fluid mover to motivate fluid flow over ozone reducing catalyst bearing heat transfer surfaces downstream of the emitter electrode in a flow path of the motivated fluid flow and (B) at respective times throughout the operating life of the EHD fluid mover, selectively (i) applying an additional, but at least partially consumable, ozone reducing catalyst to a surface of the emitter electrode; and (ii) reducing EHD motivated fluid flow notwithstanding an unmet thermal management demand of a heat source and thereby temporarily increasing temperature of the ozone reducing catalyst on the heat transfer surfaces.
In some cases, timing of the applying is based, at least in part, on operating time of the EHD fluid mover since a most recent application the additional ozone reducing catalyst to the emitter electrode. In some cases, timing of the reducing is based, at least in part, on an estimate of saturation of the ozone reducing catalyst bearing heat transfer surfaces.
In some embodiments, the method further includes maintaining the reduced EHD motivated fluid flow for a period of generally low thermal management demands to rejuvenate and thereby maintain efficacy of the ozone reducing catalyst on the heat transfer surfaces. In some embodiments, the method further includes, at successive times throughout the operating life of the EHD fluid mover, frictionally removing at least some otherwise detrimental material accumulation from the emitter electrode.
In some embodiments, the method further includes, monitoring temperature of the ozone reducing catalyst on the heat transfer surfaces, monitoring energy applied to the EHD fluid mover, and estimating decreased efficacy of the ozone reducing catalyst on the heat transfer surfaces based on the monitored temperature and applied energy. In some embodiments, the method further includes estimating ozone reducing catalyst rejuvenation based on the monitored temperature and time of reduced EHD motivated fluid flow.
In some embodiments in accordance with the present invention, a system includes an enclosure, a heat source and a controller. The enclosure has inlet and outlet ventilation boundaries and a fluid flow path therebetween. The heat source is thermally coupled to heat transfer surfaces in the fluid flow path. The controller is operable to, at respective times throughout the operating life of an EHD fluid mover to motivate fluid along the flow path, selectively trigger (i) application of an at least partially consumable ozone reducing catalyst to an emitter electrode of an EHD fluid mover and (ii) reduction of EHD motivated fluid flow notwithstanding an unmet thermal management demand of the heat source and a temporary increase in temperature of an ozone reducing catalyst on the heat transfer surfaces.
In some cases, the controller includes functional code executable on a processor of the system to control an EHD fluid mover. In some embodiments, the system further includes the EHD fluid mover and the ozone reducing catalyst on the heat transfer surfaces.
In some embodiments in accordance with the present invention, an apparatus includes an electrohydrodynamic (EHD) fluid mover, a conditioning mechanism, and a controller. The EHD fluid mover includes emitter and collector electrodes energizable to motivate fluid flow therebetween. The conditioning mechanism is operable to cause one of a conditioning surface and the emitter electrode to travel over the other in frictional engagement. The controller is operable to initiate the travel at times that do not coincide with a fixed interval, but rather in correspondence with one or more of (i) a period of at least reduced user activity, (ii) startup of the system and (iii) shutdown of the system.
In some cases, the emitter electrode is positionally fixed and the conditioning surface travels thereover. The controller is further operable to substantially de-energize the electrodes during the travel. In some cases, the conditioning surface is positionally fixed and the emitter electrode travels thereover. In some cases, the conditioning mechanism is further responsive to the controller to cause at least one additional conditioning surface to travel over a portion of the collector electrode at times that do not coincide with a fixed interval, but rather in correspondence with one or more of (i) the period of at least reduced user activity, (ii) the startup and (iii) the shutdown. In some cases, the travel of the conditioning surface and the travel of the additional conditioning surface are in tandem.
In some embodiments, the apparatus further includes ozone reducing material downstream of the EHD fluid mover and exposed to the motivated fluid flow. In some cases, at least some of the ozone reducing material is formed on exposed heat transfer surfaces. In some cases, the ozone reducing material includes an ozone catalyst and the controller is operable to de-energize the electrode during operation of the apparatus in response to detection or prediction of reduced efficacy of the ozone catalyst.
In some embodiments, the controller and the conditioning surface travel initiated thereby are responsive to power management states of the apparatus.
The present invention may be better understood, and its numerous objects, features, and advantages made apparent to those skilled in the art by referencing the accompanying drawings.
As will be appreciated, many of the designs and techniques described herein have particular applicability to the thermal management challenges of densely-packed devices and small form-factors typical of modern consumer electronics. Indeed, some of the EHD fluid/air mover designs and techniques described herein facilitate active thermal management in electronics whose thinness or industrial design precludes or limits the viability of mechanical air movers such as fans, blowers, etc. In some embodiments, such EHD fluid/air movers may be fully integrated in an operational system such as a pad-type or laptop computer, a projector or video display device, a set-top box, etc. In other embodiments, such EHD fluid/air movers may take the form of subassemblies or enclosures adapted for use in providing such systems with EHD motivated flows.
In general, a variety of scales, geometries and other design variations are envisioned for electrostatically operative surfaces that provide field shaping or that functionally constitute a collector electrode, together with a variety of positional interrelationships between such electrostatically operative surfaces and the emitter and/or collector electrodes of a given EHD device. For purposes of illustration, we focus on certain exemplary embodiments and certain surface profiles and positional interrelationships with other components. For example, in much of the description herein, generally planar collector electrodes are formed as or on respective parallel surfaces that define opposing walls of a fluid flow channel and which are positioned proximate to a corona discharge-type emitter wire that is displaced (upstream) from leading portions of the respective collector electrodes. Nonetheless, other embodiments may employ other configurations or other ion generation techniques and will nonetheless be understood in the descriptive context provided herein.
In the present application, some aspects of embodiments illustrated and described herein are referred to as electrohydrodynamic fluid accelerator devices, also referred to as “EHD devices,” “EHD fluid accelerators,” “EHD fluid movers,” “ion fluid movers” and the like. For purposes of illustration, some embodiments are described relative to particular EHD device configurations in which a corona discharge at, or proximate to, an emitter electrode operates to generate ions that are accelerated in the presence of an electrical field, thereby motivating fluid flow. While corona discharge-type devices provide a useful descriptive context, it will be understood (based on the present description) that other ion generation techniques may also be employed. For example, in some embodiments, techniques such as silent discharge, AC discharge, dielectric barrier discharge (DBD), or the like, may be used to generate ions that are in turn accelerated in the presence of an electrical field and motivate fluid flow.
Using heat transfer surfaces that, in some embodiments, take the form of heat transfer fins, heat dissipated by electronics (e.g., microprocessors, graphics units, etc.) and/or other components can be transferred to the EHD motivated fluid flow and exhausted from an enclosure through a ventilation boundary. Typically, when a thermal management system is integrated into an operational environment, heat transfer paths (often implemented as heat pipes or using other technologies) are provided to transfer heat from where it is dissipated (or generated) to a location (or locations) within the enclosure where air flow motivated by an EHD device (or devices) flows over heat transfer surfaces.
For illustration, heat transfer fins are depicted with respect to various exemplary embodiments. However, as will be appreciated based on the description herein, in some embodiments, conventional arrays of heat sink fins need not be provided and EHD motivated fluid flow over exposed interior surfaces, whether proximate a heat generating device (such as a processor, memory, RF section, optoelectronics or illumination source) or removed therefrom, may provide sufficient heat transfer. In each case, provision of ozone catalytic or reactive surfaces/materials on heat transfer surfaces may be desirable. Typically, heat transfer surfaces, field shaping surfaces and dominant ion collecting surfaces of a collector electrode present differing design challenges and, relative to some embodiments, may be provided using different structures or with different surface conditioning. However, in some embodiments, a single structure may be both electrostatically operative (e.g., to shape fields or collect ions) and provide heat transfer into an EHD motivated fluid flow.
Basic principles of electrohydrodynamic (EHD) fluid flow are well understood in the art and, in this regard, an article by Jewell-Larsen, N. et al., entitled “Modeling of corona-induced electrohydrodynamic flow with COMSOL multiphysics” (in the Proceedings of the ESA Annual Meeting on Electrostatics 2008) (hereafter, “the Jewell-Larsen Modeling article”), provides a useful summary. Likewise, U.S. Pat. No. 6,504,308, filed Oct. 14, 1999, naming Krichtafovitch et al. and entitled “Electrostatic Fluid Accelerator” describes certain electrode and high voltage power supply configurations useful in some EHD devices. U.S. Pat. No. 6,504,308, together with sections I (Introduction), II (Background), and III (Numerical Modeling) of the Jewell-Larsen Modeling article are hereby incorporated by reference herein for all that they teach.
Summarizing briefly with reference to the illustration in
EHD fluid mover designs illustrated herein generally include a single elongate wire, corona discharge type emitter electrode, although (more generally) multiple emitter electrodes and other emitter geometries may be employed. Typically, corona discharge type emitter electrodes include a portion (or portions) that exhibit(s) a small radius of curvature and may take the form of a wire, rod, edge or point(s). Other shapes for corona discharge electrodes are also possible; for example, the corona discharge electrode may take the shape of barbed wire, wide metallic strips, and serrated plates or non-serrated plates having sharp or thin parts that facilitate ion production at the portion of the electrode with the small radius of curvature when high voltage is applied. In general, corona discharge electrodes may be fabricated in a wide range of materials. For example, in some embodiments, a corona discharge type emitter electrode is formed of Palladium Nickel (PdNi) plated Tungsten (W) wire with a Rhodium (Rh) coating. In some embodiments, compositions such as described in U.S. Pat. No. 7,157,704, filed Dec. 2, 2003, entitled “Corona Discharge Electrode and Method of Operating the Same” and naming Krichtafovitch et al. as inventors may be employed. U.S. Pat. No. 7,157,704 is incorporated herein for the limited purpose of describing materials for some emitter electrodes that may be employed in some corona discharge-type embodiments. In general, a high voltage power supply creates the electric field between corona discharge electrodes and collector electrodes.
EHD fluid mover designs illustrated herein include ion collection surfaces positioned downstream of one or more corona discharge electrodes. Often, ion collection surfaces of an EHD fluid mover portion include leading surfaces of generally planar collector electrodes extending downstream of the corona discharge electrode(s). In small form factor designs that seek to minimize flow channel height, collector electrode surfaces may be positioned against, or may partially define opposing walls of, the flow channel. In some cases, a collector electrode may do double-duty as heat transfer surfaces. In some cases, a fluid permeable ion collection surface may be provided.
In general, collector electrode surfaces may be fabricated of, or with, any suitable conductive material or surface, such as aluminum or copper. Alternatively, as disclosed in U.S. Pat. No. 6,919,698 to Krichtafovitch, collector electrodes (referred to therein as “accelerating” electrodes) may be formed of a body of high resistivity material that readily conducts a corona current, but for which a result voltage drop along current paths through the body of high resistivity collector electrode material provides a reduction of surface potential, thereby damping or limiting an incipient sparking event. Examples of such relatively high resistance materials include carbon filled plastic, silicon, gallium arsenide, indium phosphide, boron nitride, silicon carbide, and cadmium selenide. U.S. Pat. No. 6,919,698 is incorporated herein for the limited purpose of describing materials for some collector electrodes that may be employed in some embodiments. Note that in some embodiments described herein, a surface conditioning or coating of high resistivity material (as contrasted with bulk high resistivity) may be employed.
Given the substantial voltage differential and short distances involved (perhaps 1 mm or less) between emitter electrode 191 and leading surfaces of collector electrodes 192, a strong electrical field is developed which imposes a net downstream motive force on positively charged ions (or particles) in the fluid. Field lines illustrate (generally) spatial aspects of the resulting electric field and spacing of the illustrated field lines is indicative of field strength.
As will be understood by persons of ordinary skill in the art, corona discharge principles may be employed to generate ions in the intense electric field closely proximate the surface of a corona-discharge type emitter electrode. Thus, in corona discharge type embodiments in accord with
Notwithstanding the descriptive focus on corona discharge type emitter electrode configurations, persons of ordinary skill in the art will appreciate that ions may be generated by other techniques such as silent discharge, AC discharge, dielectric barrier discharge (DBD), or the like, and once generated, may, in turn, be accelerated in the presence of electrical fields to motivate fluid flow as described herein. For avoidance of doubt, emitter electrodes need not be of a corona discharge type in all embodiments. Also for avoidance of doubt, power supply voltage magnitudes, polarities and waveforms (if any) described with respect to particular embodiments are purely illustrative and may differ for other embodiments.
In the illustrated cross-sectional view of
In the illustrated perspective view of
Further details regarding suitable cleaning/conditioning mechanisms for in situ application of a consumable catalyst that includes silver (Ag) to an emitter electrode of certain EHD air mover configurations such as illustrated herein may be found in commonly-owned, U.S. Provisional Application No. 61/582,305, filed Dec. 31, 2011, entitled “System and Method for In-Situ conditioning of Emitter Electrode with Silver” and naming Jewell-Larsen, Honer, Gao and Schwiebert as inventors, which is incorporated herein by reference.
While the techniques and implementations of the EHD devices discussed herein have been described with reference to exemplary embodiments, it will be understood by those skilled in the art that various changes may be made and equivalents may be substituted for elements thereof without departing from the scope of the appended claims. For example, while operative embodiments have been illustrated and/or described herein with reference to an illustrative microcontroller implementation that may be programmed by persons of ordinary skill in the art having benefit of the present disclosure in accord with functional flows and/or operational characteristics described herein, other concrete implementations are also contemplated. In some cases, operational control circuits (or portions of circuits) illustrated and/or described herein may be implemented (sometimes together with a programmable microcontroller) as one or more application specific integrated circuits (ASICs).
Although operative embodiments have been illustrated and/or described herein with respect to a particular illustrative power supply voltage configuration in which emitter electrodes are coupled to high positive voltage, field shaping dielectric surfaces accumulate positive charge, and collector electrodes are coupled to ground, it will be appreciated by persons of ordinary skill in the art having access to the present disclosure that other configurations are also possible. Grounded emitter embodiments are contemplated, as are embodiments in which voltages coupled to emitter and collector electrodes straddle a ground potential or have different polarity.
In addition, many modifications may be made to adapt a particular situation or material to the teachings without departing from the essential scope thereof. Therefore, the particular embodiments, implementations and techniques disclosed herein, some of which indicate the best mode contemplated for carrying out these embodiments, implementations and techniques, are not intended to limit the scope of the appended claims.
