Electronic system adapted for passive convective cooling and staged use of electrohydrodynamic (ehd) and mechanical air movers for quiet forced convection assist

Abstract

Flow paths, duct work, ventilation boundaries, and/or placement of EHD and mechanical air mover within a electronic device enclosure can all affect the efficacy of a thermal management solution that seeks to provide silent air cooling over a significant thermal operating envelope with staged introduction of electrohydrodynamic (EHD) and mechanical air mover devices. For electronic devices in which it is desirable to employ passive, unforced convective cooling over a portion of the thermal operating envelope, practical designs for consumer electronics form factors may be quite sensitive to flow path, duct work and ventilation boundary design as well as to the placement of EHD and mechanical air mover components relative thereto and to each other. A range of inventive solutions that have been developed to address some or all of these design challenges.

1 . An electronic system comprising:
 an enclosure having inlet and outlet ventilation boundaries;   a flow path defined within the enclosure between the inlet and outlet ventilation boundaries;   heat transfer surfaces thermally coupled to one or more thermal sources within the enclosure that, during operation of the electronic system, generate heat, the heat transfer surfaces introduced into the flow path to dissipate heat through passive cooling and forced convection cooling;   an EHD air mover selectively operable to motivate air flow along the flow path for forced convection cooling of at least a portion of the heat transfer surfaces; and   a mechanical air mover selectively operable to contribute to the air flow over at least a portion of the heat transfer surfaces.   
     
     
         2 . The electronic system of  claim 1 ,
 wherein the EHD air mover is configured to provide forced convection cooling upon detection of a first performance threshold value, and the mechanical air mover is configured to provide active cooling upon detection of a second performance threshold value.   
     
     
         3 . The electronic system of  claim 2 ,
 wherein the EHD air mover and mechanical air mover are both configured to provide forced convection cooling upon detection of a third performance threshold value.   
     
     
         4 . The electronic system of  claim 2 ,
 wherein the first and second performance threshold values characterize at least one of a temperature, loading, output, and heat generation of the one or more of the plurality of electronic components.   
     
     
         5 . The electronic system of  claim 1 ,
 wherein the EHD air mover and the mechanical air mover motivate air in series along the air flow path during joint operation.   
     
     
         6 . The electronic system of  claim 1 ,
 wherein the EHD air mover and the mechanical air mover motivate air in parallel over respective heat transfer surfaces during concurrent operation.   
     
     
         7 . The electronic system of  claim 1 ,
 wherein the EHD air mover is positioned upstream of the mechanical air mover and the mechanical air mover includes an ozone reducing material.   
     
     
         8 . The electronic system of  claim 1 , further comprising
 air flow gating moveable to provide a low impedance path during passive cooling and EHD air mover operation, at least in part, through other than the mechanical air mover.   
     
     
         9 . The electronic system of  claim 1 , further comprising
 ozone reducing material provided on a surface downstream of the EHD air mover relative to the air flow.   
     
     
         10 . The electronic system of  claim 9 ,
 wherein the ozone reducing material is provided on at least one of the mechanical fan, heat transfer surfaces, surfaces exposed to an internal plenum, and ducting surfaces.   
     
     
         11 . An electronic system comprising:
 an enclosure having inlet and outlet ventilation boundaries;   an EHD air mover disposed within the enclosure to motivate air flow along a flow path between the inlet and outlet ventilation boundaries;   heat transfer surfaces thermally coupled to one or more thermal sources within the enclosure that, during operation of the electronic system, generate heat, the heat transfer surfaces introduced into the flow path downstream of the EHD air mover and including an ozone reducing surface treatment; and   a mechanical air mover that is selectively operable to contribute to the air flow without, during periods when the mechanical air mover does not substantially contribute, substantially impeding the air flow over at least a portion of the heat transfer surfaces.   
     
     
         12 . The electronic system of  claim 11 ,
 wherein flow restrictions otherwise imposed by the mechanical air mover during periods when the mechanical air mover does not substantially contribute to the air flow are mitigated by providing a low-speed idle power to the mechanical air mover.   
     
     
         13 . The electronic system of  claim 11 ,
 wherein flow restrictions of the mechanical air mover are mitigated using a bypass path.   
     
     
         14 . The electronic system of  claim 13 ,
 wherein the bypass path includes the EHD air mover.   
     
     
         15 . The electronic system of  claim 11 ,
 operable in a passively ventilated mode, and   wherein the flow path is oriented to, during passively ventilated operation of the electronic system, allow unforced convective air flow upward from the heat transfer surfaces, wherein draw of replacement air is substantially unimpeded by the mechanical air mover.   
     
     
         16 . The electronic system of  claim 15 ,
 wherein in the passively ventilated mode, the unforced convective flow is drawn primarily through the EHD air mover rather than the mechanical air mover.   
     
     
         17 . The electronic system of  claim 11 ,
 wherein the mechanical air mover precedes the EHD air mover in the flow path.   
     
     
         18 . The electronic system of  claim 11 ,
 wherein the mechanical air mover follows the EHD air mover in the flow path and includes an ozone reducing surface treatment on at least one of the air mover housing and the air mover blades.   
     
     
         19 . The electronic system of  claim 11 , further comprising:
 a valve that merges respective air flow contributions of the mechanical air mover and the EHD air mover.   
     
     
         20 . The electronic system of  claim 11 ,
 wherein the EHD air mover and the mechanical air mover direct respective air flows over separate portions of the heat transfer surfaces.   
     
     
         21 . An electronic system comprising:
 an enclosure having inlet and outlet ventilation boundaries; and   an EHD air mover and a mechanical air mover, each selectively operable and each disposed within the enclosure to motivate air flow along a flow path between the inlet and outlet ventilation boundaries;   a unitary set of heat transfer surfaces thermally coupled to one or more thermal sources within the enclosure that, during operation of the electronic system, generate heat,   wherein air flow from the EHD air mover traverses a first subset of the heat transfer surfaces and wherein air flow from the mechanical air mover traverses a second subset of the heat transfer surfaces at least partially distinct from the first subset.   
     
     
         22 . The electronic system of  claim 21 ,
 wherein the first and second subsets exhibit at least one of dissimilar fin pitch, dissimilar fin depth, dissimilar fin height, dissimilar fin material, dissimilar thickness, dissimilar angle of attack and dissimilar leading or trailing edge profile.   
     
     
         23 . The electronic system of  claim 21 ,
 wherein the first and second subsets present dissimilar traversal length to respective air flows.   
     
     
         24 . The electronic system of  claim 21 ,
 operable in a passively ventilated mode, and   wherein the flow path is oriented to, during passively ventilated operation of the electronic system, allow unforced convective air flow upward through at least the first subset of the heat transfer surfaces, wherein draw of replacement air is substantially unimpeded by the mechanical air mover.   
     
     
         25 . The electronic system of  claim 24 ,
 wherein in the passively ventilated mode, the unforced convective flow is drawn primarily through the EHD air mover rather than the mechanical air mover.   
     
     
         26 . An electronic system comprising:
 an enclosure having inlet and outlet ventilation boundaries;   a flow path defined within the enclosure between the inlet and outlet ventilation boundaries;   heat transfer surfaces thermally coupled to one or more thermal sources within the enclosure that, during operation of the electronic system, generate heat, the heat transfer surfaces introduced into the flow path to dissipate heat through passive cooling and forced convection cooling;   an EHD air mover selectively operable to motivate air flow along the flow path for forced convection cooling of at least a portion of the heat transfer surfaces; and   a mechanical air mover selectively operable to contribute to the air flow over at least a portion of the heat transfer surfaces;   wherein the electronic system is operable in a first silent cooling state characterized primarily by passive cooling;   wherein the electronic system is further operable in a second silent cooling state in which the EHD air mover provides forced convection cooling;   wherein the electronic system is further operable in a third cooling state in which the mechanical air mover operates, with or without EHD air mover, at a lower capacity to provide nearly silent forced convection below about 35 dBa; and   wherein the electronic system is further operable in a fourth cooling state in which the mechanical air mover is operable at a higher capacity to provide forced convection cooling below about 40 dBa.   
     
     
         27 . The electronic system of  claim 26 ,
 wherein forced convection cooling in the second silent cooling state is performed at below about 20 dBa.   
     
     
         28 . The electronic system of  claim 26 ,
 wherein forced convection cooling in the third forced convection cooling state is performed at below about 28 dBa.   
     
     
         29 . An electronic system comprising:
 an enclosure that exhibits a generally planar major surface with a substantial taper in thickness from a central portion thereof toward one or more peripheral edge portions thereof;   an elongate set of heat transfer surfaces thermally coupled to one or more thermal sources within the enclosure that, during operation of the electronic system, generate heat;   an EHD air mover operable to motivate air flow along a flow path that traverses the elongate set of heat transfer surfaces and out through an outlet ventilation boundary of the enclosure; and   a mechanical air mover selectively operable to boost air flow through the EHD air mover along the flow path that traverses the elongate set of heat transfer surfaces and out through the outlet ventilation boundary,   wherein the EHD air mover and the elongate set of heat transfer surfaces are positioned within the enclosure proximate at least a first one of the peripheral edge portions wherein the substantial taper provides no more than about 10 mm of thickness, and   wherein the mechanical air mover is displaced from the EHD air mover and the elongate set of heat transfer surfaces at a position within the enclosure wherein thickness is at least two times (2×) that at the first peripheral edge portion.   
     
     
         30 . The electronic system of  claim 27 ,
 wherein the electronic system includes a display, and   wherein orientation of the electronic system during operation places the first peripheral edge portion upward such that the flow path through the EHD air mover and the elongate set of heat transfer surfaces is generally vertical.   
     
     
         31 . The electronic system of  claim 30 ,
 wherein the thermal sources include one or more processors of the electronic system positioned within the central portion.   
     
     
         32 . The electronic system of  claim 27 ,
 operable in a passively ventilated mode, and   wherein the flow path is oriented to, during passively ventilated operation of the electronic system, allow unforced convective air flow upward through the elongate set of heat transfer surfaces, wherein draw of replacement air is through EHD air mover.   
     
     
         33 . The electronic system of  claim 27 ,
 wherein the EHD air mover and the elongate set of heat transfer surfaces are positioned within the enclosure proximate at least a first one of the peripheral edge portions wherein the substantial taper provides no more than about 5 mm of thickness.   
     
     
         34 . A method of forced convection cooling comprising:
 energizing an EHD air mover disposed within an enclosure to motivate air flow along a flow path between inlet and outlet ventilation boundaries of the enclosure;   reducing power to the EHD air mover for cleaning operations;   cleaning one or more electrodes of the EHD air mover; and   augmenting air flow provided by a mechanical air mover during the cleaning.   
     
     
         35 . The method of  claim 34 ,
 wherein the augmented air flow discharges from the enclosure material removed from the one or more electrodes of the EHD air mover.   
     
     
         36 . The method of  claim 34 ,
 wherein the augmented air flow provided by the mechanical air mover is of a substantially similar flow rate to combined air flow provided during operation of both the EHD air mover and the mechanical air mover.   
     
     
         37 . The method of  claim 34 ,
 wherein cleaning is performed by at least one of heating, vibrating, and frictionally engaging the electrode.