The unsteady flow characteristic research on the initial period flow of micro channel

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1 Avalable onlne Journal of Chemcal and Pharmaceutcal Research, 2014, 6(6): Research Artcle ISSN : CODEN(USA) : JCPRC5 The unsteady flow characterstc research on the ntal perod flow of mcro channel Wang Xaorong, Zhang Jnxn, Tan Guzhong, Xue Long and Cao Welong Insttute of Mechancal Engneerng, JangSu Unversty of Scence and Technology, Zhenang, Chna ABSTRACT To obtan stable soluton flow s very mportant to bologcal cell mcro necton; ths paper adopts the method of computatonal flud dynamcs, unsteady flow dynamc characterstcs of the concal mcro channel ntal flow were researched. The ndependence of the model grd was verfed; the error between ext speed and the theoretcal value s wthn 5%. Establshed the mcro channel gas-lqud two phase unsteady flow model, under dfferent nlet pressure, flux and flow resstance characterstcs of the soluton n the concal mcro channel were studed. Through the study found that flux s fluctuaton n the ntal perod of the mcro channel flow, under the mnmum nlet pressure that can flow, except the tme lqud flm flow fluctuaton broken, flow tends to be stable wthn the entre crculaton tme, and the flow s very small. Wth the ncrease of nlet pressure, mcro channel flow ncreasng, wthn flow tme flux volatlty ncreases, and the greater the nlet pressure, the earler the volatlty moments. Mcro channel flow resstance change over tme, the smaller the nlet pressure, the greater the resstance and the nstantaneous maxmum flow resstance after flow stablty. The results show that Choose nlet pressure slghtly hgher than the crtcal flow pressure can get good lqudty; flow s stable and easy to control. The study provdes reference for the research of bologcal mcro flud necton. Key words: Mcrochannel; mcroflow; bologcal necton; flow characterstc INTRODUCTION Mcro channel devce has excellent performance and s wdely appled n bologcal cell necton, mcro flow heat exchange, mcro fludc devce, boncs, prnter nozzle, and transmsson of reactants, partcle separaton and the mcro flow sensor [1-4]. Wth the development of mcro/nano technology, more attenton pad to the study of mcro channel flow and heat transfer, the research of mcro-scale flow and heat transfer not only provde wder space for the applcaton of MEMS technology, but also has very mportant academc sgnfcance to enrch and perfect the theory of flud mechancs [5-7]. At present, the study of mcro channel flow characterstcs are mostly steady flow and the flud resstance characterstcs after flow stablty. Alma Halelfadl focused on analytcal optmzaton of a rectangular mcro channel heat snk, they analyzed the effects of the temperature, the channel aspect rato, the channel wall rato to the flow characterstc [8]. Na Lu had studed the pressure drop durng condensaton of R152a n crcular and square mcro channels.the results show that heat-transfer coeffcents and pressure drop both ncrease wth ncreasng mass flux and vapor mass qualty whle decrease wth ncreasng saturaton temperature. Channel geometry has much effect on heat transfer at low mass fluxes whle has lttle effect on pressure drop [9]. Yan Han have nvestgated the characterstcs of gas flow n mcro channels under the coupled effects of random surface roughness and velocty slp by the method of computatonal flud dynamcs [10]. Due to the phenomenon of capllary n mcro channel, t needs to overcome the surface tenson n the process of ntal flow to flow, so flux fluctuaton and uneven phenomenon exst n flow process of the ntal flow and the 2020

2 Wang Xaorong et al J. Chem. Pharm. Res., 2014, 6(6): research s relatvely small. But gven the flow stablty s of great sgnfcance for necton, the ntal moments flux has great nfluence on the subsequent mcro flud flow. Due to the ntal flow cannot obtan the quanttatve soluton by adustng bologcal mcro necton machne, so t s necessary to smulate the flow process of mcro channel ntal flow. In ths paper, through the smulaton of soluton flow process n mcro channel ntal perod, the flow characterstcs are analyzed and the results can provde references to the research n the feld of mcro flud necton. 1. MICRO CHANNEL FLOW PROCESS SIMULATION 2.1 Control equaton Due to Kn < 0.1, so the control equaton s stll contnuous equaton and Naver - Stockes equaton: dρ + ρ = 0 dt (1) du 2 u u ρ = ρf + + p + µ µ dt 3 x (2) Due to the flow of ncompressble flow, thus: = 0 (3) 1 p 1 u = + µ ρ x ρ x (4) The above equaton can be wrtten as follows: ϕ ( µ ϕ) = Γ ϕ + Sϕ x (5) Therento, φ s the general dependent varable, S φ s all the other phase that cannot be represented as convecton or dffuson tem. 2.2 Calculaton model and boundary condtons Ths artcle uses the taper ppe channel to smulate process of mcro needle necton, shaft secton of channel model s shown n fgure1, crcular dameter of channel secton s D and d respectvely, long s L, workng medum s water. Boundary condtons are shown n fgure 2, nlet pressure s gven, outlet pressure s atmospherc pressure, and no slp wall for adabatc wall, ntal flow areaⅠ s water, regonalⅡ s ar, temperature s 293K, the effect of surface tenson s consdered. Fg 1 Channel model smplfed fgure Fg 2 Boundary condtons 2. NUMERICAL CALCULATION Grd computng area fgure s shown n fgure3, the grd total quantty s Before the formal calculaton, t needs to verfy the result of calculaton s not dependent on the grd and the correctness of the nspecton procedures, for ppe of the dameter D and length L lamnar flow feld, numercal smulaton was done, and compared the velocty dstrbuton at the ext calculated wth the analytcal soluton of the ppe lamnar flow feld. Due to the ppe geometrc symmetry, only calculates half of the flow feld, the calculaton results are shown n fgure 4, compared wth the theoretcal value, the error of numercal calculaton results s less than 5%. 2021

3 Wang Xaorong et al J. Chem. Pharm. Res., 2014, 6(6): Fg 3 Grd of computng doman Fg 4 Entrance velocty dagram 3. CALCULATION RESULTS AND ANALYSIS 3.1 The nfluence of dfferent nlet pressure on the flux For the above channel, mcro needle necton channel flow characterstcs were calculated when the nlet pressure P n = , 0.095, 0.10, 0.12 MPa, ncludng the P n = MPa, whch s the mnmum nlet pressure mcro needle syrnge can flow, fgure5 s the volume fracton velocty vector dagram of P n = MPa, fgure6 s the mcro channel mass flow rate under dfferent nlet pressure. t=0.1us t=1us t=10us Fg5 P n = MPa flow state dagram at dfferent tme 4.0x x10-8 Q(Kg/s) 2.0x x Fg 6 Mass flow rate varaton over tme The fgure5 shows that at the ntal flow moment, for the water n the mcro channel, and the outsde world s the gas, lqud membrane formed at the gas and lqud uncton, lqud membrane have a retardng effect on flow, ths effect s called surface tenson and the sze of surface tenson s wth the relevant of the shape of the lqud flm. In order to observe the flow state of water near the lqud flm easly, the mcro channel ext flow area was ntercepted and amplfed whch s shown n fgure5. When the P n =, the ntal stage of the mcro channel flow, due to the nfluence of surface tenson, lqud membrane formed at the ext, and no lqud flow nsde the mcro needle syrnge; As tme ncreases, the lqud flm ncreases gradually, when t=1 us, lqud flm reaches crtcal broken state, water reflux near the lqud membrane, t ndcates that there are nverse pressure gradent; When lqud membrane broken, water spewng from the mcro channel; when t=10 us, the mcro channel flow levelng off, spewng water near the mcro channel ext formed a mushroom head flow area. Wth the ncrease of nlet pressure, n nstantaneous of lqud membrane broken, flow peak ncreases, and the flow s greater volatlty n the short term. When the P n = MPa, flow gradually become stable after lqud flm crushng, the late flow was stable n kg/s, whch s the smallest flux. When the P n ncreases to, wth the ncrease of tme flows slowly rsng, when t=10 us, the flux s kg/s. When the P n =, flow ncreased gradually after lqud flm crushng, when t=9 us, flow surged, from kg/s to

4 f Wang Xaorong et al J. Chem. Pharm. Res., 2014, 6(6): kg/s, when the P n =, flow surge moment s t=0.58 us ahead of tme, flux sharply ncreased from kg/s to kg/s. Vsble, when P n =, under the mnmum nlet pressure of the mcro channel flow, except flow fluctuaton when the lqud flm broken, the entre crculaton tme flow tends to be stable, and the flux s very small. Wth the ncrease of nlet pressure, mcro channel flow ncrease, and flux of mcro channel ncreased, and n the crculaton tme flux volatlty ncreased, the greater the nlet pressure the earler the volatlty moments. 3.2 Influence of dfferent nlet pressure on the drag coeffcent Flow s ncompressble flow, the frcton coeffcent f s functon of mport and export pressure dfference P, form s as follows: 2D h P f = 2 ρu L Therento, U s cross secton average speed; ρ s flud average densty, D h and L are respectvely the hydraulc dameter and length of mcro channel. Fgures 7 and 8 are outlet pressure and velocty changng wth tme curve respectvely under dfferent nlet pressure, when the nlet pressure s 0.925MPa, export pressure s about 0.9MPa, far hgher than the other three curves, and the outlet pressure over tme slowly decreases, and ext velocty s relatvely stable; When the nlet pressure ncreased to, at 8.5us export pressure plummeted to 0.002MPa, ext velocty reached 4.5 m/s at the same tme, the syrnge wll spt out a lot of water at the moment, t s dffcult to complete quanttatve necton; When the nlet pressure s, export pressure drop moment s to 6 us n advance, and ext velocty ncreases to 5.5 m/s. All the above, when the nlet pressure s crtcal flow pressure, outlet pressure s bgger, flow gently, easy to control. In order to study the nfluence of nlet pressure change on the change of the frcton factor, fgure9 s f changes under dfferent nlet pressure. It can be found that ntal moment due to lqud flm has not been destroyed, so lqud flow velocty s zero n the mcro needle channel, the flow resstance s nfnty, when lqud membrane damaged, the nstantaneous flow resstance s almost zero. Resstance coeffcent decreases wth the ncrease of nlet pressure, drag coeffcent s reduced, the peak decreased, and the peak moment n advance, that shows ncrease he nlet pressure can mprove the flow ablty of flud, but the flow fluctuaton s bgger, t s not conducve to quanttatve necton, and the nlet pressure s too small, mcro channel lqudty becomes bad, and even can't flow. Choose nlet pressure slghtly hgher than the crtcal flow pressure can get good lqudty; flow s stable and easy to control. (6) P out (MPa) V out (m/s) Fg 7 Outlet pressure varaton wth tme 50 0 Fg 8 Ext velocty varaton over tme Fg9 Frcton coeffcent varaton over tme 2023

5 Wang Xaorong et al J. Chem. Pharm. Res., 2014, 6(6): CONCLUSION (1) The flow s fluctuatng n the early perod of the mcro channel flow, under the mnmum nlet pressure that can flow, except the flow fluctuaton at the lqud flm of broken tme, flow tends to be stable throughout the crculaton tme, and flux s very small. Mcro channel flow ncrease wth the ncrease of nlet pressure, and flow volatlty ncreased at whole crculaton tme, and the greater the nlet pressure, the earler the volatlty moments. (2) The mcro channel flow resstance changes over tme, the smaller the nlet pressure, the greater the resstance after flow stablty, the greater the nstantaneous maxmum flow resstance too. (3) Choose nlet pressure slghtly hgher than the crtcal flow pressure can get good lqudty; flow s stable and easy to control. Acknowledgments The authors wsh to thank the Natonal Natural Scence Foundaton of Educaton Department n JangSu Provnce for contract 12KJB410001, the Natonal Natural Scence Foundaton of Chna for contract , under whch the present work was possble. REFERENCES [1] Huang, L.; Lee, M. S.; Saleh, K.; Aute, V.; Radermacher, R. Appled Thermal Engneerng 2014, 65, pp [2] Afzal, A.; Km, K. Chemcal Engneerng Scence 2014, 116, pp [3] Nand, T. K.; Chattopadhyay, H. Internatonal Communcatons n Heat and Mass Transfer 2014, 56, pp [4] Martínez-Ballester, S.; Corberán, J.; Gonzálvez-Macá, J. Internatonal Journal of Refrgeraton 2013, 36, pp [5] Duan, Z.; He, B. Internatonal Communcatons n Heat and Mass Transfer 2014, 56, pp [6] Ganapathy, H.; Shooshtar, A.; Choo, K.; Dessatoun, S.; Alshehh, M.; Ohad, M. Internatonal Journal of Heat and Mass Transfer 2013, 65, pp [7] Cha, L.; Xa, G.; Zhou, M.; L, J. Internatonal Communcatons n Heat and Mass Transfer 2011, 38, pp [8] Halelfadl, S.; Adham, A. M.; Mohd-Ghazal, N.; Maré, T.; Estellé, P.; Ahmad, R. Appled Thermal Engneerng 2014, 62, pp [9] Lu, N.; L, J. M.; Sun, J.; Wang, H. S. Expermental Thermal and Flud Scence 2013, 47, pp [10] Yan Han Zhang Wen-Mng Hu Ka-Mng Lu Yan Meng Guang.Investgaton on characterstcs of flow n mcrochannels wth random surface roughness. Acta Phys. Sn 2013, pp