Splashing phnomna of room tmpratur liqui mtal roplt striking on th pool of th sam liqui unr ambint air nvironmnt Haiyan Li 1, Shngfu Mi 1, Li Wang 1, Yunxia Gao 1, an Jing Liu 1,2* 1 Bijing Ky Lab of CryoBiomical Enginring & Ky Laboratory of Cryognics, Tchnical Institut of Physics an Chmistry, Chins Acamy of Scincs, Bijing 100190, P. R. China 2 Dpartmnt of Biomical Enginring, School of Micin, Tsinghua Univrsity, Bijing 100084, P. R. China * Arss for corrsponnc: Dr. Jing Liu Bijing Ky Lab of CryoBiomical Enginring & Ky Lab of Cryognics, Tchnical Institut of Physics an Chmistry, Chins Acamy of Scincs, Bijing 100190, P. R. China E-mail: jliu@mail.ipc.ac.cn Tl. +86-10-82543765 Fax: +86-10-82543767 1
Abstract: In this articl, th flui ynamics of room tmpratur liqui mtal (RTLM) roplt impacting onto a pool of th sam liqui in ambint air was invstigat. A sris of xprimnts wr conuct in orr to isclos th influnc of th oxiation ffct on th impact ynamics. Th roplt shap an impact phnomnology wr rcor with th ai of a high-sp igital camra. Th impact nrgy stor in th splash structurs was stimat via a thortical mol an svral morphological paramtrs obtain from instantanous imags of th splash. It was obsrv that th roplt shap an th splashing morphology of RTLM wr rastically iffrnt from thos of watr, so was th impact ynamics btwn room tmpratur LM pool an high tmpratur LM pool. Th nrgy analysis isclos that th hight of th jt is highly snsitiv to th viscosity of th flui, which is subjct to th oxiation ffct an tmpratur ffct simultanously, an thus prfctly xplain th phnomna. Ths basic finings ar important for th application of RTLM in a sris of nwly mrging tchnologis such as liqui mtal bas spray cooling, ink-jt print lctronics, intrfac matrial painting an coating, mtallurgy, an 3D packags, tc. Kywor: Splashing phnomna; Room tmpratur liqui mtal; Droplt impact ynamics; Oxiation ffct; High sp vio 1. Introuction Th room tmpratur liqui mtal (RTLM) or alloy gnrally has high thrmal an lctrical conuctivity, as wll as small vapor prssur. Som mtal fluis vn coul stay at liqui phas within an xtnsiv tmpratur rang, say from thir mlting points nar or far blow room tmpratur until upwarly to abov 2000 C (Stin 1966). With such particular charactristics istinguishing from convntional liquis, th RTLMs wr rcntly foun highly sirabl in a sris of mrging important aras. For xampl, th gallium-bas thrmal intrfac matrial (Gao an Liu 2012) an RTLMs print lctronics (Gao t al. 2012; Li t al. 2012; Zhng t al. 2013) rval thir unconvntional mrits whn a small amount of oxis wr inclu. Among th many proprtis, th outcom of a RTLM roplt with oxis impacting onto a surfac (ry, wt, liqui pools, tc.) is spcially a funamntal flui ynamic problm, which is not only of scintific intrst but also significant for quit a fw nwly mrging practics, such as ink-jt print lctronics, spray cooling, intrfac matrial painting an coating, nhancing boiling, mtallurgy, an 3D packags (Antkowiak t al. 2011). Impact of roplts hav bn an important topic for many yars, an som typical trns hav bn intifi for watr an aquous solutions in prcing paprs (Manzllo an Yang 2002; Sabaini an Alkschbirs 2004; Yarin 2006; Pan an Hung 2010; Lagubau t al. 2012). Howvr, up to now, only vry fw stuis wr vr invstigat on th impact ynamics of RTLMs. Hsiao t al. (Hsiao t al. 1988) rport th onst of cntral jt using th xprimntal ata for mrcury. As is known 2
to all, mrcury is subjct to th inhrnt toxicity, which hinrs its larg-scal applications in th abov fils. On th othr han, unlik most RTLMs, mrcury is a kin of spcial matrial that is not apt to form oxi skin whn xpos to th atmosphr. In such sns, th outcom of mrcury woul not b takn as a rprsntativ of RTLMs. In fact, among th fw works rgaring th mtal roplt impact ynamics, oxiation ffct is usually avoi by protctiv atmosphr for simplicity (Pasanih-Far t al. 1998). This howvr i not rflct th practical situation sinc most applications ar in ambint air. Du to th lack of systmatic information within th opn litratur on th impact morphology of th RTLMs with oxis, which ar xpct to hav subtly iffrnt physics than that of watr an aquous solutions, it is vry ncssary to carry out a funamntal invstigation on this important issu. Th motivation for th prsnt stuy is to xplor th nw phnomna that may aris whn th RTLM roplt impacting on th liqui surfac in ambint air, an thus isclos th influnc of oxiation ffct on th impact ynamics. Th masurmnt is conuct for th normal impacts of a singl RTLM roplt striking onto a pool of th sam liqui to provi th basis for mor complx situations,.g. multipl roplts, obliqu impact, an so on. 2. Exprimntal mthos 2.1. Sampl prparation Gallium-inium alloy (GaIn 24.5 ) is slct as th xprimntal fluis, sinc it has a mlting tmpratur of 15.5 C, which is far blow th room tmpratur of 25 C. Its nsity, surfac tnsion an ynamic viscosity ar 6280 kg/m 3, 0.624 N/m an 1.6956 10-3 Pa s, rspctivly, at tmpratur of 25 C (Morly t al. 2008), which ar largr than thos of watr. GaIn 24.5 was prpar from gallium an inium mtals with purity of 99.99 prcnt. Such raw matrials with a wight ratio of 75.5:24.5 wr a into th bakr an hat at 100 C. Thn a magntic stirrr was utiliz to stir th mixtur aftr thy wr all mlt to achiv uniform mixing. Consiring th fact that GaIn 24.5 is asily subjct to oxiation, th claning procssing prior to th xprimnt is ncssary to assur th finit initial stat. For this purpos, 10 ml 30 % NaOH solution was a slowly to th alloy, an th mixtur was stirr at room tmpratur for short prios of tim until th contnts of th bakr compris obvious two-phas structur, i.., an aquous phas an a mtallic phas. Thn, th GaIn 24.5 alloy was xtract from th mixtur by a syring. 2.2. Exprimntal apparatus Th xprimnts wr prform using a stup consisting of th roplt gnrator, targt surfac, hating lmnt, an imaging systm, as shown in Fig. 1. Th GaIn 24.5 liqui pool was contain in a transparnt plastic cylinr, with 85 mm in iamtr an 15 mm in hight. Th syring (10 ml) fill with clan GaIn 24.5 was mount horizontally in a syring pump (Longr LSP10-1B). A flat tipp stainlss 3
stl nl attach to a travlling vrnir (0.01 mm accuracy) was position vrtically abov th cntr of th liqui containr, with its trmination connct to th outlt of th syring through silicon rubbr tubing. Thus, th roplt was gnrat using th syring pump programm to ispns th liqui at a rat of 0.5 ml/min, an form at th tip of th nl, thn tach off unr its own wight. Droplt impact ynamics wr captur using a high-sp igital camra (IDT, NR4-S3, USA) at 5000 frams pr scon with a rsolution of 512 512 pixls an a span of 2.825 s. Th camra was fitt with a Nikon 85-mm micro lns to obtain th rquir spatial rsolution to captur th impact, an it was align at an angl θ = 10 with rspct to th horizontal to acquir th status of hight an horizontal surfac simultanously. An xposur tim of 198 μs was synchroniz with a 1000 W tungstn light, an a high-powr LED lamp was takn as compnsatory light to aquatly illuminat th impact rgion. Th light sourcs wr kpt as far away from th tst surfac as possibl to mitigat hating of th roplt an liqui surfac. Th lights wr switch on only in th procss which bgan from th ropping of th roplt an n aftr roplt impact, an th total tim whn th lights kpt on was no mor than 5 s pr xprimnt. Th camra was connct to a PC, which contain th corrsponing control softwar. Th captur imags wr rcor using th softwar, an thn th impact vlocity an gomtric paramtrs of th roplt an splashing can b quantitativly xtract from th instantanous imags with th ai of th softwar. In viw of th 10 own angl of th camra, paramtrs in th vrtical irction incluing impact vlocity an splashing hight tc. masur from th imags wr moifi through iviing by cos10. It shoul b not that Fig. 1 (a) was us to clarify th ffcts of roplt siz an th impact vlocity at room tmpratur on th impact ynamic. Bsis that, a hating unit consisting of two hating ros an an aluminum block was a to tst th influnc of pool tmpratur, as shown in Fig. 1 (b). Th hating ros wr powr from a voltag rgulator. Consiring th poor hat rsistanc of th plastic containr, a stainlss stl on was mploy insta in this cas. Th tmpraturs for th pool an block wr masur simultanously using Typ T thrmocoupls. 3. Rsults an iscussion 3.1. Droplt shaps As is notic, most of th prvious litraturs wr bas on th assumption that th roplts wr sphrical, although th shap of roplts moving through a flui will always b rnr slightly llipsoial by aroynamic forcs (Rin 1993). Howvr, this is not th cas in our xprimntal work. As is wll known, common RTLMs lik gallium an its alloys tn to form oxi skin in th room tmpratur atmosphr, which will prvnt furthr oxiation. It has bn isclos that th surfac of gallium-inium alloy roplt bcam oxiiz uring th ispnsing action in lss than 0.25 s (Liu t al. 2012), an th componnt of oxi skin was mainly gallium oxi (Dicky t al. 2008). Zrnic an Swatik (1969) hav vr rport thir 4
masurmnts of th surfac tnsion of a pnant roplt of EGaIn (GaIn 25 ) at ambint conitions, which was ~624 mn/m, whras th surfac tnsion of GaIn 25 without oxi skin was ~435 mn/m (Dicky t al. 2008). Obviously, th influnc of th ambint gas cannot b nglct for RTLMs although this simplification is normally mploy for watr s cas. Fig. 2 (a) shows th ffct of ambint gas on RTLM roplt vivily. During th falling, th oxi skin prvnts th roplt from rlasing th surfac nrgy frly, thus, th tail is hl until th impact. In orr to furthr vrify th rol of oxiation for th shap of th roplt, th xprimnt is rpat in th NaOH solution as shown in Fig. 2 (b). A small tail is still obsrv at th initial stag of th tachmnt, but it isappars graually with th falling as anticipat. NaOH solution has bn prviously prsnt to rmov th oxis, an it also provis an inrt nvironmnt for GaIn 24.5 (Taylor an Rancourt 1998). For comparison, th fr falling of a ioniz watr roplt in ambint air is illustrat in Fig. 2 (c), attachmnt is also obsrv at th initial momnt of tachmnt but th watr roplt contracts an forms a sphrical shap within a short tim u to surfac tnsion. This outcom is similar with that xhibit in Fig. 2 (b), xcpt for th shap of th pnant roplt, which is bliv as th rsult of iffrnc of th buoyancy. All ths imags ar obtain with th sam innr iamtr of nl of 1 mm, an falling hight of 900 mm. In viw of th non-sphrical roplt, quivalnt roplt iamtr is introuc, which is fin as th roplt iamtr whn taking th roplt as sphr, which can b calculat from i.. 3 6 m (1) 3 6m (2) whr m is th roplt mass, which can b obtain by wighing th pnant roplt. Th calculat quivalnt roplt iamtr an th masur roplt horizontal with from th imags for th sam siz nl ar compar in Fig. 3. Hr, th roplt horizontal with is masur at th maximum horizontal with of th roplt from th imag just prior to th impact as obsrv. Th rror bars rprsnt a rlativly stanar uncrtainty in trmining th an, with th stanar viation of 0.09 mm an 0.04 mm, i.. maximum uncrtainty of 1 % an 3 %, rspctivly. It can b not that an ar clos to ach othr whn th small siz nl is mploy. But thir iscrpancy nlargs with th incras of th nl siz. Normally, in xprimnts th impact nrgy is a most important paramtr, among which, surfac nrgy is a critical contributing on for roplt shap. Thrfor, th pnnc on th Wbr ( W ) numbr of th roplt will b iscuss in th following. W numbr is th ratio of th kintic nrgy to th surfac 5
nrgy of th impinging roplt, which is fin as W 2 V D (3) whr V is th roplt impact vlocity, D is th charactristic lngth, an an rspctivly th nsity an surfac tnsion of th liqui. Th nsity an surfac tnsion in this stuy ar bas on proprtis of th impacting roplt xtract from th prvious litratur. On th othr han, in viw of th particularity of RTLMs, th oxiation ffct of which can improv th viscosity of RTLM roplt (Gao t al. 2012), th viscosity is not inclu in th W numbr. Thus, th Rynols ( R ) numbr rlating th inrtia an th viscosity is introuc hr to scrib th impact procss, which is fin as whr is th ynamic viscosity. R VD (4) During th falling procss, gravity is also an important paramtr, thus Frou ( Fr ) numbrs fin as th ratio of inrtia to gravitational forcs is of significanc, which is xprss as whr g is th gravitational acclration. V Fr (5) gd Bas on Eqs. (3 5), it can b conclu that charactristic lngth an impact vlocity ar ky paramtrs for th spcific flui. Th siz of th roplt is vari through us of iffrnt-siz nls, whil th impact vlocity is ajust by varying th falling hight of th impacting roplt, i.. th istanc btwn th nl tip an th surfac of th liqui pool. Tabl 1 an Tabl 2 list main paramtrs for th cass of vari roplt siz an vari impact vlocity rspctivly. In tabls, i is th innr iamtr of nl, H is th rlas hight, Fr, W an R ar th paramtrs taking as charactristic lngth, whil Fr, W an R ar th paramtrs taking as charactristic lngth. Th uncrtaintis in th xprimnts ar stimat as ±5%. Th calculations inicat that thr is no big iffrnc for imnsionlss numbrs whthr accptabl viation whn taking th roplt as sphr. or is utiliz. Thus, thr is an 6
Tabl 1 Main xprimntal paramtrs ( V 4.2m/s ) i (mm) (mm) (mm) Fr Fr W W R R 0.4 2.7 2.7 25.81989 25.96096 479.3331 474.138 42000 41544.8 1 3.4 4.1 23.00895 21.07214 603.6046 719.6622 52888.89 63058.05 1.6 3.9 4.5 21.48345 20.01671 692.37 797.5556 60666.67 69883.21 2.2 4.3 5.2 20.45983 18.62492 763.3823 921.2075 66888.89 80717.81 Tabl 2 Main xprimntal paramtrs ( 3.4mm, 4.1mm ) H (mm) V (m/s) Fr Fr W W R R 300 2.4 13.14797 12.04117 197.0954 234.994 30222.22 36033.53 500 2.9 15.88713 14.54974 287.7729 343.1076 36518.52 43540.51 700 3.5 19.17412 17.56003 419.1699 499.7703 44074.07 52548.9 900 4.2 23.00895 21.07204 603.6046 719.6693 52888.89 63058.68 3.2. Impact procss Rpat xprimnts wr prform at various roplt sizs, impact vlocitis an pool tmpraturs. Sinc xprimnts at various roplt sizs an impact vlocitis conuct at room tmpratur isplay similar qualitativ trns, Fig. 4 is mploy as a rprsntativ of th two cass. In this sris, th quivalnt roplt iamtr an impact vlocity ar 4.1 mm an 4.2 m/s rspctivly at room tmpratur for an Fr numbr of 21, W numbr of 720 an R numbr of 63058. Th imag just prior to th obsrv impact was chosn as th onst tim imag in ach squnc. In th first milliscons aftr th roplt impact, th inrtia rivs th flui to form an xpaning cavity an th bulk flui aroun th impact point flows upwar bcaus of continuity. Thn vry small roplts ar jct from th top of th cavity at 2.6 ms, which is trm as th charactristic of crown. Accoring to Engl s work, th crown is mainly compos of targt liqui, but usually also contains som of th roplt liqui that lins th cavity (Engl 1966). In aition, it is not that th jct roplts ar not sphrical, but fusiform, which is bliv to b caus by oxiation of th roplt liqui an surfac targt liqui. Th crown continus to grow in hight an siz with tim proucing mor sconary 7
roplts, an rachs its maximum of 9 mm, masur from th pool surfac to th uppr g of th cavity, aftr about 20 ms, an thn starts to subsi until changs into a wav swll at 50 ms. This las to th formation of th cntral jt that carris roplt liqui at its top an rachs a maximum of 28 mm at about 110 ms. With th jt rising th nck bcoms narrow u to th inwar pull of th surfac tnsion, but no roplt sparats from th tip of th jt. Thn, th jt sinks to form a scon cratr at about 200 ms aftr th initial roplt impact. As th roplt continus its ownwar motion a smooth capillary wav front movs outwars. Splashing hights for iffrnt roplt sizs an impact vlocitis ar compar in Fig. 5 (a) an (b) rspctivly, an th intrval btwn vry two ata is 10 ms. All th masurmnts ar takn rlativ to th initial pool surfac lvl. It is obsrv that th maximum crown (minor pak) an jt (major pak) hight basically incras with th incras roplt siz an impact vlocity, an incrass of roplt siz an impact vlocity also la to th xtnsion of th tim from th impact to th formation of a scon cratr. As for th cass unr various pool tmpraturs, th quivalnt roplt iamtr an impact vlocity wr still fix at 4.1 mm an 4.2 m/s, whil th liqui pool was hat from 50 C to 200 C. Fig. 6 shows th impact ynamics at 200 C. At a tim of 20 ms aftr impact, th crown rachs th maximum of 8 mm. Aftr th crown collapss at 50 ms, a slnr high-sp thin jt is jct upwar, whos hight rachs a maximum valu of 40 mm at about 85 ms. Hr, th jt hight is fin as th hight th liqui jt riss abov th fr surfac prior to jt brakup. It is clarly largr than th maximum hight rach by th jt of th cas as shown in Fig. 4. Intrstingly, two ncks ar form graually, partitioning th jt into thr parts. Thn th uppr two parts pinch off togthr at about 90 ms. This shoul b caus by th crasing rag that prvnts th liqui from taking apart, an is also apprhnsibl from th nrgy aspct of viscous issipation. Th tach tip roplt riss furthr whil th jt quitly subsis into th bulk liqui. Th roplt tach latr bgins laving th fil of viw (100 ms). Excpt for ths faturs th whol procss procs in th usual way. In ths cass, th formation of a crown an/or th ris of a cntral jt ar usually rgar as th main faturs of splashing, an sconary roplts ar prouc from th rim of crown an th tip of cntral jt sinc th crown an cntral jt ar normally unstabl (Okawa t al. 2006). A quantitativ comparison for iffrnt pool tmpraturs is unrtakn by comparing th splashing hight as a function of tim in Fig. 7. Not that th jt hight os not inclu tip roplts that brak off from th jt. Thus whn th roplt braks off from th jt, th jt hight as a function of tim appars to jump iscontinuously. This obsrvation was also ma by Morton t al. in thir xprimnts for watr (Morton t al. 2000). Furthrmor, it os not sms that th variation of spashing hight an th momnt of braking off oby a crtain law with th incras of pool tmpratur, but th maxmum hight is finitly highr than th cas without hating. It may b xplain that hating contributs to th impact nrgy. Th nrgy stor at iffrnt stags of th splash can b roughly stimat using a simpl mol, on th basis of nrgy consrvation an a simplification of th impact structurs gomtry. In a first approach, th volution of th splash can b analyz 8
by consiring two stags (Fig. 8): (a) Th momnt of impact; (b) Th maximum amplitu of th jt. For simplicity, th roplt can b consir to b a sphr, an th jt a liqui cylinr. Th nrgy consrvation of th two stags can b xprss as follows Qim Qj QD Q (6) whr Q im is th roplt impact nrgy, Q j is th nrgy rquir to prouc th jt, Q D is th issipat viscous nrgy an Q rprsnts othr issipativ nrgis (as hat an soun). Th roplt impact nrgy ( Q ), can b trmin from th kintic an potntial nrgis (gravitational an surfac), as xprss in Eq. (7) im whr h is th pth of th targt liqui. Qim mg H h mg 4 2 2 Th nrgy ncssary to crat th jt ( Q ) can b trmin using Eq. (8) j 2 (7) 2 j 2 j j Qj g H j 2H j 2 2 2 2 whr th first an scon trms in th Eq. (8) ar th gravitational an surfac nrgis, rspctivly; j an (8) H j ar th iamtr an hights of th jt, which wr trmin from instantanous picturs of th splash in stag two. Th isconnct roplts wr not consir uring trmination of H j. Givn th conitions that th quivalnt roplt iamtr an impact vlocity is 4.1 mm an 4.2 m/s at room tmpratur, th paramtrs, calculat nrgis for th impact roplt an jt ar shown in Tabl 3. Th calculat impact nrgy is 3 Q im 1.9 10 J, an th nrgy rquir to prouc th jt is Q j 4 9.6 10 J. Approximatly 50 % of th impact nrgy is stor in th jt. In othr wors, narly half of th impact nrgy is rlas u to viscous issipation as othr issipativ nrgis only account for a small fraction. Consiring th issipat viscous nrgy mainly pns on th viscosity (Sabaini an Alkschbirs 2004), th viscosity may thus b th major caus laing to th iffrnc btwn th room tmpratur an high tmpratur cass. For RTLMs, th viscosity is subjct to th oxiation an tmpratur ffcts simultanously. Th combin ffct btwn thm las to th particular impact phnomnology. 9
Tabl 3 Paramtrs an nrgis obtain from th splash in GaIn 24.5 m H h Q im j h j Q j (g) (mm) (mm) (N/m) (mm) (10-3 J) (kg/m 3 ) (mm) (mm) (10-3 J) 0.22 900 15 0.624 4.1 1.9 6280 5.8 27.5 0. 96 3.3. Splashing shaps Fig. 9 shows th comparison of th rprsntativ roplts an splashing shaps ovr th procss for both GaIn 24.5 an ioniz watr with th sam innr iamtr of nl of 1 mm, an falling hight of 900 mm. In watr s cas (Fig. 9 (a)), sphrical roplt an sconary roplt ar obsrv no surprisingly, which is consistnt with Manzllo work (Manzllo an Yang 2002). Howvr, th ynamic viscosity (1.7 10 3 m 2 /s) of GaIn 24.5 is highr than that of watr (1.002 10 3 Pa s), an vn much highr whn subjct to surfac oxiation, thus sconary roplt is har to form unr th ffct of lvat viscous forc, as shown in Fig. 9 (b). With th incras of th tmpratur of th pool, as illustrat in Fig. 9 (c), th viscosity of GaIn 24.5 roplt crass aftr coalscnc, an th viscous forc raging th liqui wakns, thus th sconary roplt forms. Yt, th most ramatic iffrnc from th watr s cas is that th tip tach is not sphrical, but fusiform. This is bliv to b caus by th srious surfac oxiation of GaIn 24.5 at high tmpratur. Th imags ar obtain with th sam innr iamtr of nl of 1 mm, an falling hight of 900 mm. Th influncs of th falling hight, innr iamtr of nl an pool tmpratur on th GaIn 24.5 roplt shaps ar pict in Fig. 10. It can b foun that th tail is apparntly mor pronounc as innr iamtr of nl incrass, whil th influncs of falling hight an pool tmpratur appar much lss. Th formr is in accoranc with th fact that largr innr iamtr of nl las to th largr surfac ara of roplt, thrby mor oxis formation aroun th surfac. Th rais falling hight prolongs th falling tim of th roplt, but th oxi skin prvnts th roplt from furthr oxiation. Thus th contnt of oxis os not incras with th tim xposing to th ambint air; whil th pool tmpratur is inpnnt of th tmpratur of mtal roplt uring th arly stags of roplt impact, i.. th tmpratur of mtal roplt quals to its initial tmpratur (Aziz an Chanra 2000). Furthrmor, as is wll known, whn a col watr roplt is brought into irct contact with a hot watr pool, it is possibl that th coolr watr roplt may vaporiz so rapily that an xplosion may occur. Ths xplosions hav bn trm as vapor xplosions, xplosiv boiling, or rapi vapor xplosions (Manzllo t al. 2003). In contrast, it is not a concrn for th RTLMs with boiling point of abov 2000 C. This is also rgar as th supriority of RTLMs ovr watr for high tmpratur applications. 10
4. Conclusions In this stuy, th splashing ynamics of RTLM roplts with oxi skin impinging vrtically on a pool compos of th sam liqui wr visualiz an quantitativly invstigat using a high sp camra. Th influncs of th roplt siz, impact vlocity an pool tmpratur on th flui striking ynamics wr rval on th basis of xprimntal obsrvations, imag ata procssing, an mchanism intrprtation. It was foun that th roplt siz an th impact vlocity isplay similar proportional trns with rspct to th splashing hight, but i not accompany with th sconary roplt sparation; whil th incras of pool tmpratur ramatically intnsifi th splashing ffct, with th fusiform sconary roplt tach from a cntral jt. Th Fr numbr covr in this work is from 20 to 26, whil W numbr is from 479 to 763, an R numbr from 42000 to 66889, which ar all calculat with th quivalnt roplt iamtr introuc spcially for th non-sphrical roplt. It has bn isclos by th prsnt work that thr xist funamntally istinct iffrncs btwn th impact bhavior of GaIn 24.5 roplts an that of ioniz watr roplts. Th rason can b attribut to th oxi skin of th RTLM which woul significantly affct th apparanc of th roplts an th splashing morphology. Th nrgy analysis furthr confirm th spculation. Ths finings ar xpct to b important for th application of RTLM in a sris of nwly mrging tchnological fils such as liqui mtal bas ink-jt print lctronics, spray cooling, intrfac matrial painting an coating, nhancing boiling, mtallurgy, 3D packags, an so on. Acknowlgmnts Th authors thank Prof. Yixin Zhou for valuabl iscussions. REFERENCES Antkowiak, A., Auoly, B., Jossran, C., Nukirch, S., Rivtti, M., 2011. Instant fabrication an slction of fol structurs using rop impact. PNAS 26, 10400 10404. Aziz, S.D., Chanra, S., 2000. Impact, rcoil an splashing of moltn mtal roplts. Int J Hat Mass Tran 16, 2841 2857. Dicky, M.D., Chichi, R.C., Larsn, R.J., Wiss, E.A., Witz, D.A., Whitsis, G.M., 2008. Eutctic gallium-inium (EGaIn): A liqui mtal alloy for th formation of stabl structurs in microchannls at room tmpratur. Av Funct Matr 7, 1097 1104. Engl, O.G., 1966. Cratr pth in flui impacts. J Appl Phys 4, 1798 1808. 11
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Figurs an captions: Fig. 1 Schmatic of th xprimntal stup: a Without hating unit; b With hating unit unr th pool. 13
Fig. 2 Imags of fr falling: a GaIn 24.5 roplt in ambint air; b In th NaOH solution; c A ioniz watr roplt in ambint air. Fig. 3 Comparison of th quivalnt roplt iamtr with masur irctly from th imags for th sam siz nl. an th roplt horizontal 14
Fig. 4 Instantanous imags of impact procss, obtain with a GaIn 24.5 roplt of th horizontal with 4.1mm impacting a pool of th sam liqui at impact vlocity V 4.2m/s an room tmpratur. 15
Fig. 5 a Comparison of th splashing hights for iffrnt roplt horizontal with; b Comparison of th splashing hights for iffrnt impact vlocitis. 16
Fig. 6 Instantanous imags of impact procss, obtain with a GaIn 24.5 roplt of th horizontal with 4.1mm impacting a pool of th sam liqui at vlocity V 4.2m/s an pool tmpratur T 200 C. Fig. 7 Comparison of th splashing hights for iffrnt pool tmpraturs. 17
Fig. 8 Schmatic rprsntation of two stags of th splash: a Th momnt of th impact; b Th maximum hight of th jt. Fig. 9 Comparison of roplt an splashing shaps uring th splashing procss at th sam momnt: a Dioniz watr (25 C); b GaIn 24.5 (25 C); c GaIn 24.5 (200 C). 18
Fig. 10 Comparison of GaIn 24.5 roplt shaps at th initial momnt ( t 0ms ) for iffrnt innr iamtr of nl, falling hight an pool tmpratur. 19