Notes on Vibration Design for Piezoelectric Cooling Fan

Transcription

1 World Aadmy of Sin, Enginring and Thnology Intrnational Journal of Mhanial and Mhatronis Enginring Vol:7, No:, 3 Nots on Vibration Dsign for Pizoltri Cooling Fan Thomas Jin-Ch Liu, Yu-Shn Chn, Hsi-Yang Ho, Jyun-Ting Liu, Chih-Chun L Intrnational Sin Indx, Mhanial and Mhatronis Enginring Vol:7, No:, 3 wast.org/publiation/79 Abstrat This papr disusss som nots on th vibration dsign for th pizoltri ooling fan. Aftr rviwing th fundamntal formulas of th antilvr Eulr bam, it is not asy to find th optimal dsign of th pizoltri fan. Th xprimnts also show th ompliatd rsults of th vibration bhavior and air flow. Kywords Pizoltri ooling fan, vibration, antilvr Eulr bam, air flow. I. INTRODUCTION IEZOELECTRIC matrials and atuators ar widly Papplid in modrn thnologis du to th apability of th transfr btwn mhanial and ltri nrgy. Th pizoltri ooling fan as shown in Fig. is on of th pizoltri produts. This ooling ida was first proposd by Toda and Osaka []. With th vibrating or flapping motion, th of this ooling fan an produ th air flow to rdu th tmpratur of hot ltroni dvis. Many rsarh topis for th pizoltri ooling fan hav bn studid xprimntally and numrially []-[]. Th xprimntal, analytial and numrial mthods of solid and fluid mhanis ar adoptd in thos rsarhs. Many studis onludd that th pizoltri ooling fan onsums low powr and has good ooling prforman for th ltroni dvis. For smallr ltroni produts, th spa may not allow to st a rotary ooling fan. To solv this problm, th small-sizd pizoltri ooling fan is a good solution. Yoo t al. hav invstigatd svral dsigns of pizoltri ooling fans for th ltroni dvis []. In thir study, svral typs of pizoltri fans wr onstrutd and tstd at Hz, V, and V, rsptivly. Thy found a rlationship btwn th tip displamnt and th wind vloity whn th pizoltri fan is opratd in th fundamntal rsonan. Howvr, th fft of diffrnt working frqunis was not studid by Yoo t al. Th purpos of this papr is to disuss som nots on th vibration dsign of th pizoltri ooling fan. Th prsnt study is th fluid-strutur intration problm. Th xprimntal rsults will show th vibration bhavior, air flow Thomas Jin-Ch Liu, Assoiat Profssor, is with th Dpartmnt of Mhanial Enginring, Ming Chi Univrsity of Thnology, Taishan, Nw Taipi City, Taiwan (orrsponding author to provid phon: xt 59; -mail: jinh@mail.mut.du.tw). Y.S. Chn, H.Y. Ho and J.T. Liu ar graduat studnts in th Graduat Institut of Eltro-Mhanial Enginring, Ming Chi Univrsity of Thnology, Taishan, Nw Taipi City, Taiwan. C.C. L is an undrgraduat studnt in th Dpartmnt of Mhanial Enginring, Ming Chi Univrsity of Thnology, Taishan, Nw Taipi City, Taiwan. and ooling prforman of th pizoltri ooling fan. Fig. Pizoltri ooling fan and ooling mhanism (a: pizoltri ooling fan; b: pizoltri atuator; : ; d: fixtur; : ltri powr; f: ltroni dvi; g: air flow; δ t : total tip displamnt) II. PROBLEM STATEMENTS Fig. shows th gomtry of th pizoltri ooling fan in this study. Th paramtrs L, L, L 3, W b, and W p ar main dimnsions. Th thiknsss t, t p, t, t g, and t b blong to th thin-film ltrod, pizoltri atuator, oppr ltrod, glu, and, rsptivly. As shown in Fig., th atuator with two bondd pizoltri matrials is namd as th bimorph atuator. Th pizoltri matrial is atuatd by th ltri fild btwn two ltrods. Whn th voltag (ltri potntial) diffrn is applid on both ltrods, th pizoltri atuator dforms or bnds du to th ltri fild. To prform th vibrating assoiatd with th air flow, th pizoltri ooling fan must b fixd and subjtd to th ltri powr with th altrnativ urrnt (AC). Fig. 3 shows th boundary onditions of th pizoltri ooling fan. Th oppr ltrod is groundd (V = V), and two thin-film ltrods ar subjtd to th AC voltag V = V amp sin(πft) V. In abov quation, th paramtrs f and t ar th AC frquny and tim, rsptivly. Th ltro-mhanial oupling bhavior of th transvrsly isotropi pizoltri matrial is ruld by th onstitutiv quation undr th Cartsian oordinat x -x -x 3 [7], []: T T T T3 T = 3 T D D D3 3 3 sym S 3 S S (a) S3 S3 S E E E3 Intrnational Sholarly and Sintifi Rsarh & Innovation 7() 3 9 sholar.wast.org/37-9/79

2 World Aadmy of Sin, Enginring and Thnology Intrnational Journal of Mhanial and Mhatronis Enginring Vol:7, No:, 3 = ( ) (b) As shown in Fig. and, th matrials usd for of th ar th PET plastis and SUS 3 stainlss stl. whr T, S, D, E,, and ε ar th strss, strain, ltri displamnt, ltri fild, lasti onstant, pizoltri onstant, and prmittivity, rsptivly. In (), th poling dirtion of th pizoltri matrial is along th x 3 -axis. In this study, th bimorph atuator is mad of th pizoltri rami PZT-5H. Fig. 3 shows th poling dirtions (P vtors) of both pizoltri matrials of th bimorph. Du to th rlativly thin thiknss, th thin-film ltrod and glu an b ignord in th analysis. Intrnational Sin Indx, Mhanial and Mhatronis Enginring Vol:7, No:, 3 wast.org/publiation/79 Fig. Gomtry of pizoltri ooling fan Fig. 3 Boundary onditions of pizoltri ooling fan III. EXPERIMENTAL STUDIES: VIBRATION BEHAVIOR AND AIR FLOW Fig. shows th xprimntal quipmnts for masuring th air flow in this study. Th pizoltri ooling fan is atuatd by th AC voltag (i.., V =V amp sin(πft)) mad from th ltri signal sour and amplifir. Th input of th voltag V is applid on th pizoltri atuator. Th air flow vloity from th pizoltri fan is masurd by th anmomtr and snsor. Also, th total tip displamnt of th vibrating is masurd by th lasr displamnt snsor as shown in Fig. 5. Th pizoltri ooling fans as shown in Fig ar usd in th xprimnts. Th dimnsions ar L =mm, L =3mm, L 3 =3mm, W b =mm, W p =mm, t p =.3mm, and t =.mm. Fig. Exprimntal quipmnts for air flow in this study Layout figur Photo Fig. 5 Exprimntal quipmnts for tip displamnt Fig. Pizoltri ooling fan PET Stainlss stl Intrnational Sholarly and Sintifi Rsarh & Innovation 7() 3 95 sholar.wast.org/37-9/79

3 World Aadmy of Sin, Enginring and Thnology Intrnational Journal of Mhanial and Mhatronis Enginring Vol:7, No:, 3 Intrnational Sin Indx, Mhanial and Mhatronis Enginring Vol:7, No:, 3 wast.org/publiation/79 Fig. 7 shows th vibration prforman of th pizoltri ooling fan with PET (t b =.5mm). It vibrats rsonantly undr its first-mod natural frquny f =7.5Hz. Th rsonant vibration prforms th maximum flapping displamnt. As shown in Fig. whn th applid frquny is shiftd out of th natural frquny, th flapping displamnt (total tip displamnt) of th drass rapidly. Whn th PET s with t b =.5mm and t b =.mm ar usd, th variations of th air flow vloity v air and tip displamnt δ t with ar rsptivly shown in Figs. 9 and. It prsnts th non-linar phnomna du to th flxibl proprty and largr dformation. Th rsults show that th largr voltag applid on th pizoltri atuator an indu largr flapping displamnt (total tip displamnt) and air flow. In othr words, th largr th tip displamnt is, th largr th air flow vloity is. Th ffts of th thiknss on th air flow and tip displamnt ar also onsidrd. Du to diffrnt strutural stiffnss, th natural frqunis of t b =.5mm and t b =.mm ar f =7.5Hz and f =.5Hz, rsptivly. In Fig., th tip displamnts of t b =.mm ar always largr than thos of t b =.5mm. Howvr, Fig. 9 shows that th air flow vloity of t b =.mm ar not always largr than thos of t b =.5mm. Whn V amp >75V, th as of t b =.5mm gts largr air flow. In this voltag rang, highr working frquny of t b =.5mm (7.5Hz >.5Hz) dominats th air flow. Whn th stl s ar usd, similar ompliatd rsults ar obtaind. Th stl thiknsss ar t b =.5mm, t b =.mm, and t b =.mm. From th xprimntal masurmnt, thir natural frqunis ar f =9.5Hz, f =Hz, and f =.5Hz, rsptivly. Th variations of v air and δ t with V amp ar rsptivly shown in Figs. and. Th as of t b =.mm has largr air flow and tip displamnt than othr two ass with thinnr or thikr thiknss. Th thiknss affts th natural frquny and tip displamnt so that th air flow prforms ompliatd rsults in Fig. Howvr, th as of t b =.mm shows th approximatly linar rlationship btwn v air and V amp. This linar as agrs with thos of Yoo t al. []. Th pizoltri ooling fan must work at th natural frquny to prform th rsonant vibration. Th largr tip dfltion is also xptd. Abov two phnomna an produ largr air flow for th ooling pross. Howvr, th natural frquny of th pizoltri fan must b high nough. Othrwis, low working frquny will produ small air flow vn if th tip dfltion boms vry larg. In addition, vry high natural frquny should b avoidd du to th larg ltri powr onsumption and low fatigu lif. Fig. 7 Vibration of pizoltri ooling fan with PET pizoltri fan and anmomtr, rsonant vibration undr 7.5Hz. total tip displamnt δ t applid frquny f (Hz) Fig. Variation of tip displamnt with applid frquny of pizoltri fan with PET (V amp = V) Intrnational Sholarly and Sintifi Rsarh & Innovation 7() 3 9 sholar.wast.org/37-9/79

4 World Aadmy of Sin, Enginring and Thnology Intrnational Journal of Mhanial and Mhatronis Enginring Vol:7, No:, 3.. t b =.5 mm (f = 7.5 Hz) t b =. mm (f =.5 Hz) t b =. mm (f =.5 Hz) t b =. mm (f = Hz) t b =.5 mm (f = 9.5 Hz) air flow vloity v air (m/s).... total tip displamnt δ t. Intrnational Sin Indx, Mhanial and Mhatronis Enginring Vol:7, No:, 3 wast.org/publiation/79 Fig. 9 Rlationship btwn v air and V amp of pizoltri fan with PET total tip displamnt δ t t b =.5 mm (f = 7.5 Hz) t b =. mm (f =.5 Hz) Fig. Rlationship btwn δ t and V amp of pizoltri fan with PET air flow vloity vair (m/s) t b =. mm (f =.5 Hz) t b =. mm (f = Hz) t b =.5 mm (f = 9.5 Hz) Fig. Rlationship btwn v air and V amp of pizoltri fan with stl Fig. Rlationship btwn δ t and V amp of pizoltri fan with stl As a simplifiation, th antilvr Eulr bam modl an b usd to stimat th bhaviors of th pizoltri fan. Th tip dfltion δ of th antilvr Eulr bam is [9]: 3 FL δ = () 3E I whr F, L, E Y, and I, ar th for, lngth, Young s modulus and momnt of inrtia, rsptivly. In addition, aording to th vibration thory, th natural frquny f of th first mod shap of th Eulr bam is []: Y 3.5 EY I f = (3) π ml whr m is th lngth dnsity of mass. It should b notd that () and (3) may indu opposit dsign idas for maximizing th air flow vloity. For xampl, largr thiknss (largr valu of I) an prform highr natural frquny, but it will indu smallr tip dfltion. This paradox and ompliatd phnomnon aus th onfusion of using () and (3) for dsigning th pizoltri ooling fan. Figs. 9 to also show this ompliatd phnomnon and onfusion. From abov xprimntal rsults and disussions, it is diffiult to find an optimal dsign of th pizoltri ooling fan by th onpts of () and (3). IV. EXPERIMENTAL STUDIES: COOLING PERFORMANCE In this stion, th ooling prforman of th pizoltri fan is onfirmd. Th dimnsions of th pizoltri fan ar L =mm, L =3mm, L 3 =3mm, W b =mm, W p =mm, t b =.5mm, t p =.3mm, and t =.mm. Th matrial usd for of th is th PET plastis. Fig. 3 shows th xprimntal quipmnts for th ooling prforman. Th hatr and hatsink will b oold by th pizoltri fan. Th tmpratur at th masuring point is masurd by th thrmo-oupl and thrmo-mtr. Intrnational Sholarly and Sintifi Rsarh & Innovation 7() 3 97 sholar.wast.org/37-9/79

5 World Aadmy of Sin, Enginring and Thnology Intrnational Journal of Mhanial and Mhatronis Enginring Vol:7, No:, 3 Fig. shows th tmpratur history data at th masuring point. At s, th pizoltri fan is turnd on and th air flow is produd. At s, th tmpratur hang of th hatr is ΔT= C. Th pizoltri fan provs its ooling apability for th hot dvi. ooling fan hav bn disussd in this short papr. For this fluid-strutur intration problm, it is not asy to find th optimal dsign of th pizoltri fan by th formulas of th antilvr Eulr bam. It is worth rating an optimal dsign pross in th futur. Howvr, in th dsign pross, th largr air flow an b obtaind by th trial-and-rror mthod but it is not sintifi. ACKNOWLEDGMENTS Th authors ar gratful to th Ming Chi Univrsity of Thnology for th finanial support undr th ontrat numbr -Start-Aadmi-Rsarh-E-. Intrnational Sin Indx, Mhanial and Mhatronis Enginring Vol:7, No:, 3 wast.org/publiation/79 Fig. 3 Exprimntal quipmnts for ooling prforman layout figur photo of hatr and hatsink tmpratur ( o C) REFERENCES [] M. Toda and S. Osaka, Vibrational fan using th pizoltri polymr PVF, Prodings of th IEEE, vol. 7, pp. 7 73, 979. [] J.H. Yoo, J.I. Hong and W. Cao, Pizoltri rami bimorph oupld to thin mtal plat as ooling fan for ltroni dvis, Snsors and Atuators, vol. 79, pp.,. [3] T. Aikalin, S.V. Garimlla, A. Raman and J. Ptroski, Charatrization and optimization of th thrmal prforman of miniatur pizoltri fans, Intrnational Journal of Hat and Fluid Flow, vol., pp., 7. [] M. Kimbr and S.V. Garimlla, Masurmnt and prdition of th ooling haratristis of a gnralizd vibrating pizoltri fan, Intrnational Journal of Hat and Mass Transfr, vol. 5, pp. 7 7, 9. [5] W.J. Shu, R.T. Huang and C.C. Wang, Influn of bonding glus on th vibration of pizoltri fans, Snsors and Atuators A: Physial, vol., pp. 5,. [] H.K. Ma, H.C. Su, C.L. Liu and W.H. Ho, Invstigation of a pizoltri fan mbddd in a hat sink, Intrnational Communiations in Hat and Mass Transfr, vol. 39, pp. 3 9,. [7] J. Yang, Analysis of Pizoltri Dvis. Singapor: World Sintifi Publishing,. [] T.J.C. Liu, Fratur mhanis and rak ontat analyss of th ativ rpair of multi-layrd pizoltri paths bondd on rakd struturs, Thortial and Applid Fratur Mhanis, vol. 7, pp.-3, 7. [9] J.M. Gr and B.J. Goodno, Mhanis of Matrials. th Ed., Singapor: Cngag Larning, 3. [] L. Mirovith, Fundamntals of Vibrations. Nw York: MGraw-Hill,. 5 tim (s) Fig. Tmpratur vrsus tim V. CONCLUSIONS Som nots on th vibration dsign for th pizoltri Intrnational Sholarly and Sintifi Rsarh & Innovation 7() 3 9 sholar.wast.org/37-9/79