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12-9-2008

Ionic Winds for Enhanced Cooling in PortablePlatformsDavid B. GoBirck Nanotechnology Center, Purdue University; University of Notre Dame, dgo@purdue.edu

Raul A. MaturanaBirck Nanotechnology Center, Purdue University, rmaturan@purdue.edu

Rajiv K. MongiaIntel

Suresh V. GarimellaBirck Nanotechnology Center, Purdue University, sureshg@purdue.edu

Timothy S. FisherBirck Nanotechnology Center, Purdue University, tsfisher@purdue.edu

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Go, David B.; Maturana, Raul A.; Mongia, Rajiv K.; Garimella, Suresh V.; and Fisher, Timothy S., "Ionic Winds for Enhanced Coolingin Portable Platforms" (2008). Birck and NCN Publications. Paper 1502.http://dx.doi.org/10.1109/EPTC.2008.4763520

Ionic Winds for Enhanced Cooling in Portable Platforms

David B. Go#', Raul A. Maturana#, Rajiv K. Mongia$, Suresh V. Garimella#, Timothy S. Fisher#4 Purdue University, School of Mechanical Engineering and Birck Nanotechnology Center,

West Lafayette, IN 47907-2088& presently at the University ofNotre Dame, Department of Aerospace and Mechanical Engineering, Notre Dame, IN 46556

$ Intel Corporation, 2200 Mission College Blvd, M/S RNB-6-53, Santa Clara, CA 95054-1549

Abstract placed along the base of the notebook. The fan, which blowsWhile cooling of the microchip continues to receive over the heat sink, also draws low-speed, parasitic flows from

significant interest in most electronic devices, portable these vents and convectively cools the rest of the platform.platforms such as notebooks, multi-use cellular phones, and Recently, new concepts have emerged which more directlyultra-mobile personal computers (PCs) present unique thermal address the cooling of the non-processor components andmanagement challenges as well. Cooling non-processor skins of mobile devices by enhancing the heat transfer by thecomponents such as wireless devices and the skin of the parasitic air flow. For example, synthetic jets have often beendevice are becoming the important thermal management suggested for portable platforms [2][3], and recently Mongiadrivers, and volume and power constraints are limiting the et al. [4] and Go and Mongia [5] suggested employing thempracticality of including larger or additional conventional fans. for non-processor cooling applications. Experimental work byIonic wind engines are devices which generate air flow with Mongia et al. [4] and Go and Mongia [5] studied theno moving parts, and feature low power consumption and a interaction of synthetic jets and low-speed flowssmall volumetric footprint. An ionic wind is produced when representative of the parasitic flow from auxiliary vents, andpositive air ions are accelerated in a particular direction by an demonstrated that localized cooling could be increased by aselectric field, and exchange momentum with neutral air much as 25%. Piezoelectric, vibrating cantilever fans [6] havemolecules, thus generating a body force on the air. In the also been suggested as an air cooling technology for notebookpresence of an existing bulk flow, an ionic wind distorts the computers, and potentially could be used for the enhancementboundary layer and increases the local cooling effect at a of parasitic flows for cooling.heated wall. A free-standing ionic wind engine with an One concept which has been suggested by the author'selectrode gap of approximately 1 mm has been constructed. group is to utilize ionic winds to enhance the cooling capacityExperiments show that the ionic wind engine can enhance the of a bulk flow [7][8]. An ionic wind occurs when air ionslocal heat transfer coefficient of a low-speed flow by as much (typically N2+ and 02+) are drawn through interstitial air by anas 500o. The impact of the ionic wind is shown to increase electric or magnetic field. The accelerated ions collide withwith current and decrease as the bulk flow increases. neutral air molecules (N2 and 02) and exchange momentum,

causing the neutral molecules to move. The cascading effectIntroduction of the ions and neutral molecules generate a net motion or

The increased capabilities and functionality of blowing effect often called an ionic wind. In stagnant air,microprocessors has led to the recent boom in the use of ionic winds can act as a blower, and this concept has recentlyportable electronic devices over the past two decades. been developed into a replacement device for traditional rotaryPortable platforms include notebooks, multi-functional fans [9]. A method for cooling LED components has alsocellular phones, and ultra-mobile PCs. The thermal challenges been proposed based on a similar principle [10][1 1].facing the electronics industry have often focused on the However, in the presence of a bulk flow, an ionic wind has theeffects of the increasing power density of microprocessors. effect of distorting and modifying the bulk flow - called aHowever, the emergence of these portable platforms has given secondary wind. Therefore, an ionic wind can potentially berise to a new set of thermal challenges that must be addressed used to modify the boundary layer of the low-speed, parasitic[1]. The thermal management solution for a mobile device flow in notebook platforms to enhance heat transfer and coolmust also includes methods or apparatuses to cool non- non-chip components. Fig. 1 shows the basic operatingprocessor components such as memory modules and wireless principle of an ionic wind in the presence of an external bulkcards, and to cool the skin of the device which is now in flow.contact with the user. In many applications, device skin One of the most common methods of ionizingcooling can be the most important challenge. Additionally, atmospheric air and generating an ionic wind is by using abecause of size and portability constraints, the thermal corona discharge. When a sharp and a blunt electrode (assolutions must be compact, light-weight, have low power shown in Fig. 1) are held at a sufficiently high potentialconsumption, and little acoustic signal. difference in atmospheric air, naturally occurring free

In notebooks, the cooling solution typically consists of a electrons are accelerated towards the sharp electrode (anode)heat spreader on the chip with a heat pipe drawing the heat where they collide with the neutral molecules and at sufficientfrom the chip to a remote heat exchanger where a rotating fan kinetic energy strip an electron from the molecule. Theblows over the heat exchanger and releases the thermal energy resulting positive ion is then accelerated towards the bluntinto the ambient atmosphere. The non-processor components electrode where, en route, it collides with neutral molecules,and skin are typically cooled by auxiliary vents strategically exchanges momentum, and generates the ionic wind. Recent

work by the authors has studied ionic winds in the presence of978-1-4244-21 18-3/08/$25.00 ©2008 IEEE 2008 10th' Electronics Packaging Technology Conference

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bulk flows using a gap spacing between the sharp and blunt electrodes forming ionic windelectrodes of approximately 3-5 mm [7][8]. At ion currents di|169* d

near 10-50 pA and electrical power on the order of 100 mW, _iIthe ionic wind was shown to cool a heated flat plate 25 Kmore than the cooling achieved by the low-speed bulk flowalone, and enhance the bulk flow heat transfer coefficient bymore than 200% [7] [8]. Additionally, predictions frommodels for the ion transport, ion/fluid interactions(electrohydrodynamics), and heat transfer matched the cnatpdexperimental trends reasonably well and showed how the ionic Fig. 2. Free-standing ionic wind engine on a quartz substratewind accelerates the boundary layer flow near the wall and (pitdbakfreeimnlpuos).Telcrdear

.. (pa1ntedblackforexper1mentalpurposes).Theelectrodepa1r~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~........m..............................................................

advects additional heat [7].The studies above used a laborator,v set-up for the is shown in the circle.

electrodes where they were not part of an independent ionicwind generating device, and with electrodes gaps greater than3 mm. For the present work, a free-standing ionic windengine was developed on a quartz substrate with an electrodegap less than 1 mm. A miniature wind tunnel was alsoconstructed, andl the cooling performance of the free-standiing _ ,,

...'.... _~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~.......................................

ionic wind engine was characterized with and without aabbulkflow. _

boundary layer boundaryllayerprofile upstream profile downstream Fig. 3. Optical microscope image of the active region betweenof ionic wind of ionic wind the stainless steel corona wire and gold ribbon collecting

|>/ | 3/~~~~electrode.

_>/ > ( ~~~~~~~~Oneof the challenges of generating a corona discharge in

| >/ ~ionic wind 4atmospheric air is identifying the proper operating voltages forI~ ~~_ - > the device. At low voltages, a corona discharge will not form|~~->" ' ______ and the current response will be very low (~1 nA) due to

@ 1~~~~~~~~~~~~intermittent ionizing events. At sufficient electric potential,heated +J | I the onset of a corona discharge is established, and as thesurFace / Ii potential increases the current increases with the followingFig. 1. Basic operating principle of an ionic wind in the relationship 8,

presence of a bulk flow. iSo>(1I)At some upper limit, the applied potential is sufficiently highsuch that spark discharges form between the two electrodes.

Experimental Method The discharges are channels of very high ion current whereThe free-standing ionic wind engine was constructed on a breakdown of the interstitial air has occurred. Spark

quartz substrate and is shown in Fig. 2. The blunt electrode discharges can damage the electrodes, and it is desirable to(called the collecting electrode) consisted of a 25 pim thick by operate the devices in the regime between corona discharge125 pim wide gold ribbon and was attached to the quartz wafer onset and spark discharge breakdown. The device constructedusing Omega 101 Thermal Epoxy. The sharp electrode for this work demonstrated the capability of steady operation(corona wire) was a 25 pim diameter stainless steel wire. In in the desired regime. Fig. 4 shows a representative plot of theorder to more easily generate the corona discharge, the corona current response as the voltage is ramped up in discretewire was strung between two ceramic pads, and elevated ~650 increments over time. There is some variation in the currentpim above the quartz substrate. Fig. 3 shows an optical when the potential is set to produce the targeted ion current,microscope image of the device. The axial distance between and the device often experienced some drift in the current overthe electrodes was approximately 200 pim, and the true gap time even though the potential was fixed. For all the current(accounting for the elevation of the wire) was approximately values described, the current drift was within 0.5 piA from the715 ,um with a variation of ±25 ,um (±3.50 ) along the length targeted value. A number of additional devices wereof the wire. A positive electric potential was applied to the constructed in an effort to reduce the electrode spacing to lesscorona wire using a Spellman CZE high-voltage power supply than 500 pim but these were unable to maintain operationand the collecting electrode was connected to a Keithley 6485 beyond corona onset without quickly transitioning to sparkpicoammeter and grounded. breakdown.

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10 2000 ~~~~~~~~~~~~SideView9 - 1800

8 - ~~~~~~~~~~1600'0 a)C-7 1400 2cm

= 6 rl~~~~pplied potential | 400 o6 - 12~~~~~~~~~~~~~0. ionic wind engine5 - + 1000 = bulk on substrate &

lL Top View flow h ater4 ~~~~~~~~~~~800

3 - current 600 ,'

o~~~~~~~~~~~~~~~~~ 0cprob0 2 - -C 400~~~~

1 2000 0 ~~~~~~~~~~~~~~~~~~~~~~~~~~~velociy

0 5 10 15 20 25 30 35 40time, t (min) Fig. 5. Schematic of experimental apparatus for

Fig. 4. Ionic wind current and applied potential as a function characterizing the ionic wind engine.of time.

The device was placed into a custom-built miniature windtunnel so that the electrodes were perpendicular to the flowand the substrate was suspended at the centerline of the testsection. The wind tunnel was constructed from acrylic sheetswith a test section 2 cm high by 5 cm wide by 9 cm long. ASharkoon Silent Eagle 1000 axial fan was used to generate thebulk flow with speeds up to 2 m/s in suction mode. At theinlet of the wind tunnel, 50.8 mm thick honeycomb with 3.175mm cells was used to condition the flow. Bulk flow velocitymeasurements were obtained with a TSI Velocicheck 8330hand-held velocimeter inserted into the wind tunnel justdownstream of the device. The velocimeter had an accuracy Fig. 6. Image of windtunnelusedduringthe experiment.of ±0.5 m/s.

The quartz substrate was heated by a 38.1 x 38.1 mmMinco quarthin-fil ater wattaheatedto the backs o.f th The experiments were conducted by heating the substrate

sust wthin-l Oegat Oattacherm 2 thermalksgreas to using the thin-film heater so that a heat flux of approximatelysubtrtewitOeg Omgahem 21 hemalgras t1375 W/m2-K was produced at steady state, at which time theensure good thermal contact. A thin layer of Styrofoam was 1375 fwm was proed at stea taes atw timerthe

attached to the backside of the heater to limit thermal losses bulk f wasture on. er the substrate temperand ensure all the heater power passed through the substrate reahed a sthe state under thembulk flow, th tpliedand device. Prior to constructing the device on the substrate, potential on the corona wire was incremented slowly until thethe surface of the substrate was coated with Krylon Ultra Flat set of a corona discharge. The applied potential was thenBlack Spray 1602, which has a known emissivity of 0.96 [12]. set such that the response current was at the desired value.Thermal images of the device were obtained with a FLIR Again, Thesyte wasaloed tc to a steady coolingThermacam SC300 infrared camera with an uncertainty of ± 1 condition. The data presented in this work are for the steady-K. A viewing window was cut from the top of the wind tunnel state cooling of the bulk flow only as well as for the ionicand replaced with a plastic sheet which is infrared transparent.Fig. 5 shows a schematic diagram of the experimental set-up,and Fig. 6 shows a photograph of the wind tunnel. Results

Fig. 7 shows representative infrared images of thesubstrate when heated to a steady condition, under a 0.12 m/sbulk flow, and then cooled with an 8 pA ionic wind alsoactivated in the presence of the bulk flow. The temperaturedecrease of the substrate due to cooling by the ionic wind wasnearly 15 K below that already achieve by the bulk flow alone.Additionally, the ionic wind leads to enhanced cooling bothupstream and downstream of the engine, consistent withobservations in earlier experiments [7] [8]. The upstream anddownstream cooling appears to be due to cooler ambient airbeing entrained into the accelerated region of the inducedboundary layer and therefore advecting more heat away from

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the hot surface. Because of difficulties with deviceconstruction where the gap between the electrodes varied by v 65±3.500 which can affect the local electric field, the final device < 60did not operate uniformly across its width as shown in Fig. 7.The results presented in the following are for the region of r 55\maximum cooling and focus on the gap between the 50electrodes which represents the area targeted for local cooling Xenhancement, rather than the upstream or downstream regions. 0 45

055 60 65 70 75 80 85°C -0 40 bulk only

. 35

corona collecting contact 30wire electrode pad 25 b n

z~~ ~~~ 25ucino hbulk fo eoiy.Teionicwind oeae

E C

a) )0.00 0.25 0.50 0heatedbulk velocity, u (mls)

ionic wind An alternative measure of the thermal performance of thedevice is to consider the improvement in the local heat transfer

Fig. 7. Infrared images of substrate (a) heated with no flow coefficient with and without the ionic wind being activated.(b) under a 0.12 m/s bulk flow and (c) under a 0.12 m/s bulk The local heat transfer coefficient can be extracted from the

flowand cooledbyan 8 pAionicwind infrared data, and accounting for radiative heat losses, isdefined as

One of the most common ways of assessing the _ tperformance of an air cooling device for a notebook h v heaer - qradiamion (3)application is by considering the temperature rise of theXlATsurface above ambient, \T, which defines the thermal driving The percent improvement in the local heat transfer coefficientpotential for cooling of the surface of interest. For a given is then defined asheat flux, a decrease in AT indicates less thermal resistance at h -hthe surface. For the free-standing device in this work this is F =x,ionilc x,bu/k (4)defined as hxbhUdkAT=T-T (2) Four different ionic wind conditions were considered aswhere T is the temperature of the substrate andTri is the specified in Table 1. The greatest current tested was 8.0 TAmeasured temperature of the ambient air. Fig. 8 shows a plot because at higher applied potentials spark discharges wereofthe temperature rise over ambient for a steady-state heated observed. For this device, the effective current range forcondition, bulk flows ranging from 0.0 m/s to 1.0 m/s, and an steady operation between corona onset and breakdown wasionic wind in the presence of those bulk flows. The ionic 1.0 - 8.0 pA. The electrical power input ranged from 3.8wind operated at 8 pA and 2050 V for an electrical power of mW to 16.3 mW for these conditions.16.3 mW. The figure demonstrates how the ionic windenhances the performance of the bulk flow and reduces AT. It Table 1. The four different ionic wind operating conditionsis also observed thateasthe bulk flow velocity increases, the considered in this study getscuntetdws___impact of the ionic wind is reduced. Under no bulk flow, the Ionic Wind Aplelectrical P r. I . 3ionic wid cools the substrate by nearly 18 K. However, Current, (wA) Potential, @(V) Input, P (mW)under a bulk flow of nearly I m/s, the ionic wind only cools 2I 187 3.8the substrate 2-3 K beyond the cooling from the bulk flow

42.0 1875

73.8

alone. 4.0 1970 | 7.9alone. ~~~~~~~~~~~~~~6.02007 12.08.0 2043 ] 16.3

Fig. 9 shows the variation of F as a function the bulk flowvelocity. In general, the impact of the ionic wind decreases asthe bulk flow increases again confirming the observations inFig. 8. Under no bulk flow conditions, where only radiationand free convection is significant, an 8 plA ionic windenhanced the heat transfer by 680%. In the presence of a 0.12m/s bulk flow the heat transfer enhancement was

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approximately 52% and less than 10% for a 1 m/s flow. When Fig. 10 shows the enhancement in heat transfer coefficientconsidering the uncertainty in the experiment, the as a function of the electrohydrodynamic number. For theimprovement at 1 m/s across all ionic wind conditions studied range of experiments tested here, the results indicate thatis minimal. Additionally, with a low ionic wind current, the below a NEHD = 50, the enhancement is only 10% or less.improvement also decreases significantly. Thus, while the body force is greater than the inertial surface,

it is not sufficiently large to enhance heat transfer. Therefore,these results suggest that there is a lower limit to NEHD greater

60 than 0 at which heat transfer enhancement is negligible.Further study over a wider parameter space is needed to

- 50 conclusively determine the critical NEHD for heat transferenhancement.

r=408.0 gA 50

>-

0 , \>30 -. 45uA

2~0L + IU 2 . 0 °6.0F6.0 .'40-

r-0 'w~~~~~~~~~~~~~~~~~~.*135-o.OIA-I E 30

10 --OL2.0OgA 2-

o.o0 0.25 0.50 0.75 1 50 1.200.00 1.00 1.25~~~~~~~~~*~1bulk velocity, u (m/s) a-

Fig. 9. The percent improvement in local heat transfer X 2 0coefficient, F, as a function of the bulk velocity, u, for four 5Mdifferent ionic wind conditions. The uncertainty in F ranged 0 -

from 5 - 15 %. 0 50 100 150 200 250 300 350 400 450 500electrohydrodynamic number, NEHD

The ion motion induces a Coulombic body force on the Fig. 10. The percent improvement in local heat transferbulk flow which is defined as coefficient, F, as a function of the electrohydrodynamic

number, NEHD, for four different ionic wind conditions.f = p,E (5)where f is the body force, Pe is the concentration of ions (inC/i3), and E is the electric field due to the applied potential Conclusionsbetween the electrodes. The body force then appears in the In this work, a free-standing ionic wind engine has beenNavier-Stokes equations where it is balanced by inertial, constructed and experimentally investigated. The devicepressure, and viscous effects: considered had an approximately 700 ptm electrode spacing

V * (pUi) =-VP + VV2Ui + PeE (6) with an operating range of 1.0 -8.0 ,uA and electrical powerA no-imninaletoydoyamcnubrNH

input of less than 20 mW. The device was shown to cool aA non-dimensional electrohydrodynamic number (NEHD) heated surface by as much as 18 K, and increase the local heat

can be used to further understand the relationship and transfer coefficient by more than 500 when placed in theinteraction between an ionized gas and bulk flow [13]. The tresenceffa more

flow.NEHD is the ratio of the electrohydrodynamic body force to the presence of a bulk flow.inertial force (,ou2) and can be written as

Ionic wind devices have been demonstrated to be aneffective cooling technology, have low power consumption,

N - _(7) little audible signal, and are generally robust (the deviceEHD lpbu 2 studied here was tested over the course of a year). Future

work should address some of the practical challenges facingwhere i is the current, p is the density of the fluid, u is the the imple nation ofic n cooling chnology. Tospeed of the bulk flow, b is the mobility ions in air

(approximately14x10M2_Sortmoshercar1 an

date, the operating voltages of these devices are greater than(approximately 1 t4x len-gm/V-s for atmospheric air [14]), and the voltages desirable in portable platforms. The primaryIis the characteristic length ofthe system. Moreau et al [13] method of reducing voltages is to reduce the gap between

defined 1 as the length of the electrodes. However, another electrodes, although reducing the size of the sharp electrode ispossible interpretation of the characteristic length of the an alternative approach. However, most devices constructedsystem may be the gap between the electrodes because this is b h uhr ihgp esta 0 mwr nbetthe region over which the body force acts. Qualitatively, for oprt stadl wihu geeaigsakdshre. Onsmall NEHD (i. e., NEHD >* 0) the inertial force dominates the posbearactoedetheltoesainadpevtbody force and the bulk flow will be unaffected. Conversely, sprIn is toincroaea inl uha hs sdbfor large NEHD (i. e. NEHD >* x) the body force is sufficient to lwtmeauedeeti are icag. Deetiovercome the inertial force, and the bulk flow will be brirdshre aeotnbe tde o hmodified. Under that condition, it follows that heat transfer mnplto fbudr aesi eopc plctoswill also be enhanced.

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and there exists the opportunity for study of these devices for electrostatic fluid actuators," Proc. 24th Annual IEEEthe thermal management of portable platforms. Semiconductor Thermal Measurement and Management

Symposium, Semi-Therm 2008, San Jose, CA, 2008, pp.Acknowledgements 32-37.The authors gratefully acknowledge financial support from 12. NASA, data on the emissivity of a variety of black paints,Intel Corporation. Mr. Raul Maturana would also like to http://masterweb.jpl.nasa.gov/reference/paints.htm, 2003thank Dr. Sungwon Kim for assistance with acquiring the (accessed August 22, 2006)optical microscope images of the device. 13. Moreau, E., Leger, L., Touchard, G. "Effect of a DC

surface-corona discharge on a flat plate boundary layerReferences for air flow velocity up to 25 m/s," J. Electrostatics, Vol.1. Mongia, R. K., Pokharna, H., Machiroutu, S. "Mobile 64, No. 3-4, (2006), pp. 215-225.

thermal challenges in future platforms," Thermal 14. Owsenek, B. L., Seyed-Yagoobi, J., Page, R. H.Challenges in Next Generation Electronic Systems "Experimental investigation of corona wind heat transfer(THERMES 2007), ed. Garimella S. V., Fleischer, A. S., enhancement with a heated horizontal flat plate," J. HeatMillpress (Rotterdam, Netherlands 2007), pp. 283-290. Transfer, Vol. 117, No. 2, (1995), pp. 309-315.

2. Minichiello, A. L., Hartley, J. G., Glezer, A., Black, W.Z. "Thermal management of sealed electronic enclosuresusing synthetic jet technology," Proc. InterPACK '97,ASME EEP-Vol. 19-2, Advances in ElectronicPackaging, vol. 2, pp. 1809-1812, 1997.

3. Campbell, Jr., J. S, Black, W. Z. , Glezer, A., Hartley, J.G. "Thermal management of a laptop computer withsynthetic air microjets," Proc. Sixth IntersocietyConference on Thermal and ThermomechanicalPhenomena in Electrical Systems, ITherm '96, Seattle,WA, 1998, pp.43-50.

4. Mongia, R. K., Macdonald, M. A., Mccune, J. S.,Pavlova, A., Trautman, M. A., Bhattacharya, A. "Heattransfer enhancement using synthetic jets for cooling inlow form factor electronics in presence of mean flow,"Proc. 9th Electronics Packaging Technology Conference,EPTC 2007, Singapore 2007, pp. 830-835.

5. Go, D. B., Mongia, R. K. "Experimental studies onsynthetic jet cooling enhancement for portable platforms,"Proc. 11th Intersociety Conference on Thermal andThermomechanical Phenomena in Electrical Systems,ITherm '08, Orlando, FL, 2008, pp. 528-536.

6. Acikalin, A., Wait, S. M., Garimella, S. V., Raman, A."Experimental investigation of the thermal performanceof piezoelectric fans," Heat Transfer Eng., Vol. 25, No. 1(2004), pp. 4-14.

7. Go, D. B., Garimella, S. V., Fisher, T. S., Mongia, R. K."Ionic winds for locally enhanced cooling," J. Appl.Phys., Vol. 102, No. 5, (2007), art. no. 053302.

8. Go, D. B., Maturana, R. A., Fisher, T. S., Garimella, S. V."Enhancement of external forced convection by ionicwind," Int. J. Heat Mass Transfer, in press.

9. Schlitz, D., Singhal, V. "An electro-aerodynamic solid-state fan and cooling system," Proc. 24th Annual IEEESemiconductor Thermal Measurement and ManagementSymposium, Semi-Therm 2008, San Jose, CA, 2008, pp.46-49.

10. Hsu, C.-P., Jewell-Larsen, N. E., Krichtafovitch, I. A.,Montgomery, S. W., Dibene, J. T., Mamishev, A. V."Miniaturization of electrostatic fluid accelerators," J.MEMS, Vol. 16, No. 4, (2007), pp. 809-815.

11. Hsu, C.-P., Jewell-Larsen, N. E., Sticht, C.,Krichtafovitch, I. A., Mamishev, A. V. "Heat transferenhancement measurement for microfabricated

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