大會(huì)2015集ms4216納米通道流體流動(dòng)耗散粒子動(dòng)力學(xué)模擬

*（中國(guó)科學(xué)院過程工程研究所,中國(guó)科學(xué)院綠色過程與工程重點(diǎn)實(shí)驗(yàn)室，北京+（中國(guó)科學(xué)院大學(xué)，北京 滑移修正的子動(dòng)力學(xué)（moleculardynamics,）為主的離散模擬方法成為人們研究納Thma等人6采用對(duì)水在碳納米管中的流動(dòng)進(jìn)行模擬觀察到遠(yuǎn)高于理論值認(rèn)為因碳納米管天然的疏水性而產(chǎn)Alxiadi等人7對(duì)水分子在碳納米管中的結(jié)構(gòu)進(jìn)行了深入探討擬發(fā)現(xiàn)了納米管中流體性質(zhì)鏈動(dòng)然能夠較為準(zhǔn)確地計(jì)結(jié)計(jì)難以應(yīng)用于樣本數(shù)較大的體質(zhì)的統(tǒng)計(jì)。耗散粒子動(dòng)力學(xué)（dissipativeparticle設(shè)通道中心處z=0,壁面處

=-

-v(z) (z-D

Q=

d

dz)=-

??= ,vx(Z)={{Z=D =

DzZ進(jìn)而可知通量計(jì)算公式為

vx(??)=0

[ [??

??∫??(??)

'

在后文中我們將用耗散粒子動(dòng)力學(xué)模擬對(duì)此公式進(jìn)行驗(yàn)證 f=∑FC+FD+FR i≠ 三種力的作用形式分別為FC= FR=σωR(r)ζij?t-

其中，rij=ri-rj,rij=|rij|eij=rij/rij,vij=vi-vj。參數(shù)aij為斥力系數(shù)，表示兩珠子間斥力的最大值。σ和γ分別為噪聲因子與摩擦系數(shù)，二者之間應(yīng)滿足一定關(guān)系：σ2=2γkBT，ωD=(ωR)2 σ=3.0γ=15?? 4.5；代表權(quán)函數(shù)，其一般形式為{0 r>ωC=ωD=（ωR）2=1- {0 r> 體系中所涉層壁面珠子（厚度為1）呈面心擬過程中在其位置上震動(dòng)以維過增大最外層流體之間的排斥力實(shí)現(xiàn)間的排斥力是通過調(diào)節(jié)保守力參數(shù)a來調(diào)a的大小在宏觀現(xiàn)為壁面的疏水性質(zhì)圖2為流體在壁面上的接觸角隨a變化關(guān)系的模擬結(jié)a取值強(qiáng)為將疏水性控制在合理的范圍對(duì)流動(dòng)們?cè)谀M過程中將參數(shù)a的取值設(shè)為：20/22/25/28/30/32/35/3840層壁面珠子作用參數(shù)統(tǒng)一取為50。contactcontact0 a本研究中的密度均為流體珠子數(shù)密度。在首先進(jìn)行的納米通道平衡密度的模擬中ρ 在納應(yīng)造成的不可忽略的密度不均勻性是產(chǎn)生其它變化的根們選取了3a35體系中的密度分布（圖4）進(jìn)行說明：在壁面/層狀結(jié)構(gòu)7使流體密度呈現(xiàn)震蕩間距蕩幅度逐漸減弱并趨近于宏觀們將流體區(qū)域劃分為靠近壁面的非均勻區(qū)與遠(yuǎn)圖4中標(biāo)明；無論流體處于無外inhomogeneousinhomogeneousbulk 4ρ0- - z圖4.兩平板組成的納米通道內(nèi)密度分布4ρ0 為了探究通道空間尺寸與壁面疏水性質(zhì)是否對(duì)們分別改變上述兩個(gè)變結(jié)圖5為疏水性相同（a35）但空間尺寸不同的通道中近壁面處為了結(jié)觀們?cè)O(shè)壁面處為位置坐標(biāo)圖僅1時(shí)曲線這可以解釋為：在極為導(dǎo)致流體呈現(xiàn)這一結(jié)果對(duì)我們來說具有重要意義雖然我們無法對(duì)所有尺寸的通道一一進(jìn)行模擬可以對(duì)各尺寸通道中的密度分布情況進(jìn)行推測(cè)質(zhì)處蕩規(guī)律與范圍則不難寬總流體區(qū)域的比率逐漸對(duì)流動(dòng)的影響也相應(yīng)動(dòng)規(guī)律也逐漸趨于宏觀流動(dòng)動(dòng)區(qū)域內(nèi)的流體將聚集在緊密排列的鏈狀結(jié)這一結(jié)構(gòu)將使流動(dòng)更有效率16圖6為相同543ρ210- - - -圖6.壁面疏水性對(duì)近壁處密度分布的影響xμ=-τzxdv(z)x z- z-

Ai<τzx(z)=V∑mvi,z[vi,x-ux(z)]δ(zi-z)-2 Ai<

)Θ( 54423ρ 210

bulk- - - - 圖8.不同大小通道內(nèi)流速分布：(aD=6,a=35；(b) 。vx vx

“”=1D=6中，9-通量的變化規(guī):D=L - particleparticlecountervelocityintegration0 圖10兩種通量統(tǒng)計(jì)方法比較ε 圖12中展示了不同通道ε隨平板間距的變顯看出??受平板間性質(zhì)間距較小時(shí)ε值較間ε值逐漸減小并最終趨于1對(duì)于同樣強(qiáng)ε值這一變化趨勢(shì)與Guo等人17針對(duì)水與碳納米管體系的分子模結(jié)這種現(xiàn)象可以得到很好的解釋壁面疏水性增大而增大的規(guī)律與流率變強(qiáng)受限空間中流體的集中有序排布進(jìn)一步促進(jìn)流動(dòng)圍內(nèi)出現(xiàn)ε隨減小而急劇增大的現(xiàn)Q g圖11通量隨驅(qū)動(dòng)力變化876ε4321 .們通過式（7）計(jì)算了a25a35兩種計(jì)算值與模擬結(jié)果基本一致（圖13們認(rèn)為納米通道內(nèi)流體的不均勻分布是造成流動(dòng)主體流動(dòng)慮間變化的計(jì)算式不再適用于納下的流動(dòng)變化重新引入運(yùn)動(dòng)方程后推導(dǎo)得到的通量計(jì)算公式則與0 圖13通量模擬結(jié)果與計(jì)算結(jié)果的比FornasieroF,ParkH,HoltJ,StadermannM,GrigoropoulosC,NoyA,BakajinO.Ionexclusionbysub-2-nmcarbonnanotubepores.ProceedingsoftheNationalAcademyofSciencesoftheUnitedStatesofAmerica,2008,105:17250-17255HoltJ,ParkH,WangY,StadermannM,ArtyukhinA,GrigoropoulosC,NoyA,BakajinO.FastMassTransportThroughSub–2-NanometerCarbonNanotubes.Science,2006,343:752-754MajumderM,ChopraN,AndrewsR,HindsB.Nanoscalehydrodynamics:Enhancedflowincarbonnanotubes.Nature,2005,438:44VerweijH,SchilloM,LiJ.FastMassTransportThroughCarbonNanotubeMembranes.Small,2007,3:SparreboomW,BergA,EijkelJ.Transportinnanofluidicsystems:areviewoftheoryandapplications.NewJournalofPhysics,2010,12:1-23ThomasJ,McGaugheyA.Reassessingfastwatertransportthroughcarbonnanotubes.Nanoletters,2008,AlexiadisA,KassinosS.MolecularSimulationofWaterinCarbonNanotubes.ChemicalReviews.2008,108:KasiteropoulouD,KarakasidisT,LiakopoulosA.DissipativeParticleDynamicsinvestigationofparametersaffectingplanarnanochannelflow.MaterialsScienceandEngineeringB,2011,176:1574–1579FengR,XenosM,GirdharG,KangW,DavenportJ,DengY,BluesteinD.Viscousflowsimulationinastenosismodelusingdiscreteparticledynamics:acomparisonbetweenDPDandCFD.BiomechModelMechanobiol,2012,11:119-129YanK,ChenY-Z,LiuG-R,HanJ,WangJ-S,HadjiconstantinouN.Dissipativeparticledynamicssimulationoffield-dependentDNAmobilityinnanoslits.MicrofluidNanofluid,2012,12:157–163RitosK,MattiaD,CalabroF,ReeseJM.FlowenhancementinnanotubesofdifferentmaterialsandJournalofChemicalPhysics,12HoogerbruggeP,KoelmanJ.Simulationmicroscopichydrodynamicphenomenawithdissipativeparticledynamics.EurophysicsLetters,1992,19:155-16013EspanolP,WarrenP.statisticalmechanicsofdissipativeparticledynamics.EurophysicsLetters,1995,30:14GrootRD,WarrenPB.Dissipativeparticledynamics:Bridgingthegapbetweenatomisticandmesoscopicsimulation.JournalofChemicalPhysics,1997,107:4423-443515CannonJ,HessO.Fundamentaldynamicsofflowthroughcarbonnanotubemembranes.MicrofluidNanofluid,2010,8:21-3116IrvingJH，KirkwoodJG.Thestatisticalmechanicaltheoryoftransportprocesses.IV.Theequationofhydrodynamics.JournalofChemicalPhysics,1950,18:81717SuJ,GuoH.Effectofnanochanneldimensiononthetransportofwatermolecules.JournalofPhysicalChemistry.B,2012,116:5925-5932DissipativeParticleDynamicsSimulationofFlowwithinWangYuying1,2XuJunbo1Yang(1KeyLaboratoryofGreenProcessandEngineering,InstituteofProcessEngineering,ChineseAcademyofSciences,Beijing100190,(2UniversityofChineseAcademyofSciences,Beijing100049,AbstractThebasiclawofflowwithinnanochannelsisinvestigatedbythedissipativeparticledynamicssimulationandtheoreticalanalysis.Theinfluencesofwall/fluidinteractionsandthedimensionsofthechannelsarediscussedrespectivelybyexaminingthedensityprofiles,velocityprofilesandfluxes.Theresultsshowdensityandviscosityinhomogeneitiesnearthewall/fluidinterfaces,whicharedeterminedbythewall/fluidinteractionswhilethedimensionsortheflowrateshavenoeffect.Theflowpatternvariesfortheinhomogeneities,andinparticular,plugflowcanbeobservedinahydrophobicandhighlyconfinedcondition.Furthermore,thetransportoffluidissignificantlyenhanced.Theenhancement,definedastheratioofthesimulatedfluxtothefluxcalculatedbytheHagen-Poiseuillerelation,k