摘要
毛细管精馏是上个世纪70年代开始应用的一种新型的分离技术,它主要用于分离二元共沸的液体混合物。毛细管精馏的原理完全不同于传统精馏的传质机理,它依靠气-液界面的表面张力使蒸汽在毛细管中发生毛细管凝结,通过凝结液与管道壁面之间的界面作用力,改变组分的活度,从而改变二组分的相对挥发度,突破共沸点。目前,由于技术保密原因,国内外关于毛细管精馏工艺技术基础理论方面的文献报道很少,因此对毛细管精馏中毛细管道内两相流特性的研究,将有助于揭示毛细管精馏的传质机理,掌握这项技术的工艺条件。
利用计算流体力学软件FLUENT6.2对毛细管内的凝结液滴进行气-液两相流模拟。在2D物理模型下,发现当We数小于20后,表面张力和壁面粘性力对液滴的形态基本无影响,管长对流动的影响也很小,与直管道相比,管道倾角和弯道使液滴的破裂程度更大,并增加了液滴的流出时间,通过与文献实验对比,验证了模拟结果的有效性。
在3D模型中,比较了不同管道截面下,液滴的变形和破裂情况,发现方形管道截面下,固-液两相界面作用程度大于圆形管道截面,多孔不锈钢板的气液平衡数据证明了这一结论的合理性。在方形管道模型下,对液滴前后压差进行了量纲分析和回归计算,利用回归公式计算出的不同表面张力的物质在毛细管道中形成液滴的压差,可以与文献实验数据较好的吻合。在蒸汽量较大的条件下,管道中的液滴常会凝聚成小段的液柱,通过模拟液柱在上升过程中又破裂成小液滴的过程,并利用液滴粒径分布方程,建立了液柱和液滴运动的联系。
Capillary distillation is a new-type separation process dating back to the1970s,which is mainly used for the separation of the binary azeotropic liquid mixtures. Theprinciple of capillary distillation is totally different from conventional distillationprocess. It relies on the surface tension of the gas-liquid interface to make vaporcondensedinthecapillary,andthenutilizestheinterfacialforcebetweenthetubewallandthecondensedliquidtoalterthecomponentactivity,therebychangingtherelativevolatility to break azeotropic point of the two components. Nowadays, due to thetechnical privacy protection, there are few literatures that can be found at home andabroadregardingthefundamentaltheoryofcapillarydistillation,soaninsightintothecharacteristics of two-phase flow in capillary would be helpful for the application ofthetechnologyinChina.
FLUENT6.2, a commercial computational fluid dynamics (CFD) package, wereadopted for the numerical simulation of gas-liquid two-phase flow in the capillary.Under2Dmodel,itcouldbeseenthatboththesurfaceintentionandthewalladhesionhad almost no effect on the shape of droplet, and the capillary length also did littleeffect on the flow. Besides, compared to vertical-straight pipe, the inclined or bendpipe could dramatically increase the breakup degree of droplet, and prolong theoutflow time. The simulation results were found to be in good agreement with theliteraturedata.
As for 3D model, a series of capillaries which had different shape of crosssection were used to simulate the deformation and breakup of a droplet. The squarecapillarywas found to have greater interfacial interaction than the circular one, whichwas proved by the vapor-liquid equilibrium data of the sintered porous stainless steelplate. Under square model, using dimensional analysis and regression calculationdealt with pressure drop over the droplet,and the computed values of the pressuredropofmaterialsthathaddifferentsurfaceintentionfitwellwiththeliteraturedata.Inthe high vapor rate condition, the droplet can assemble to liquid column. To simulatethe process of the liquid column breaking up into small droplets when the liquidcolumn moved upward in capillary and the correlation between liquid column anddropletmotionwasdevelopedthroughdrop-size-distributionequation.
引文
[1]时钧,余国棕.化学工程手册,化学工业出版设,北京,1996.
[2]王正烈,周亚平,物理化学,高等教育出版社,北京,2001.
[3]Ling Tao, Michael F, Malone, Synthesis of azeotropic distillation systems withrecycles,Ind.Eng.Chem.Res.,2003,42(8):1783~1794.
[4]Yeh G.C, Ratigan B.J, Correnti M.S, Separation of liquid mixtures by capillarydistillation,Desalination,1991,81:129-161.
[5]George Chiayou Yeh. Separation of liquid mixtures. US Patent: 4118285,1978-10-03.
[6]Yeh G.C, Shah M.S, Yeh B.V. Vapor-Liquid Equilibria of NonelectrolyteSolutions in Small Capillaries.1. Experimental Determination of EquilibriumCompositions.Langmuir,1986(2):90-96.
[7]YehG.C,YehBV,SchmidtST,Vapor-Liquidequilibriumincapillarydistillation,April15-20,1991.
[8]马沛生,常贺英,夏淑倩等,化工热力学,化学工业出版社,北京,2005.
[9]顾惕人,朱涉瑶,李外郎等,表面化学,科学出版社,北京,1994.
[10]Yeh G.C, Capillary Distillation, Paper presented at the National Meeting ofA.I.Ch.E.Denver,CO,Aug.29,1983.
[11]Yeh G.C, Schmidt S T, Vapor-Liquid Equilibria of Nonelectrolyte in smallCapillaries, Summer Research Project(Chem.Eng), Villanova University, PA(1984and1985)
[12]Abu Al-Rub F A, Datta R. Separation of 2-Propanol-Water Mixture withCapillaryPorousPlates.Sep.Sci.Technol.1999,34(5):725-742.
[13]孔祥言,高等渗流力学,中国科学技术大学出版社,合肥,1999.
[14]N.S.J.Wong , The effects of capillary plates on vapor-liquid equilibrium inaqueous alcohol systems ,Master Thesis ,Dept.Chem.Eng.McGill University ,Montreals,1997.
[15]Abu Al-Rub F A, Datta, R. Separation of 2-Propanol-Water Mixture withCapillaryPorousPlates,Sep.Sci.Technol.1999,34(5):725-742.
[16]Abu Al-Rub F A, Datta R, Theoretical study of the vapor-liquid equilibriuminsidecapillaryporousplates,FluidphaseEquilibria162(1992):83.
[17]Kuehl SJ,Goldschmidt VW. Steady flows of R-22 through capillary tubes: testdata.ASHRAETrans,1990,96(1):719-728.
[18]Stabler LA.Theory and use of a capillary tube for liquid refrigerant control.RefrigeratingEngineering,1948,55(1):55-9.
[19]Mikol EP.Adiabatic single and two-phase flow in small bore tubes.ASHRAEJournal,1963,57(11):75-86.
[20]J.M.van Baten,R Krishna,CFD simulations of wall mass transfer for Taylor flowincircularcapillaries,ChemicalEngineeringScience,2005(60):1117-1126.
[21]Taha Taha, Z.F.Cui, CFD modeling of slug flow inside square capillaries,ChemicalEngineeringScience,2006(61):665-675.
[22]A.K.Gupta, S.Basu, Deformation of an oil droplet on a solid substrate in simpleshearflow,ChemicalEngineeringScience,2008(63):5496-5502.
[23]Mikol EP, Dudley JC.Visual and photographic study of the inception ofvaporization in adiabatic flow. Transactions of the ASME, Series D: Journal ofBasicEngineering,1964,6:257-264.
[24]Koizumi H, Yokoyama K.Characteristics of refrigerant flow in capillary tubeASHRAETransactions,1980,86(2):19-27.
[25]Motta,SFY,Parise,JAR,Braga,SL. A visual study of R-404A/oil flow throughadiabatic capillary tubes. International Journal of Refrigeration, 2002,25(5):586-596
[26]Beyer.M, Battger.A, Carl.H, et al .Influence of the pipe diameter on the structureof the gas-liquid interface in a vertical two-phase pipe flow. Nuclear Technology,2005,152(1):3-22.
[27]Kuehl SJ, Goldschmidt VW.Steady flow of R-22 through capillary tubes: testdata.ASHRAETrans,1990,96(1):719-728.
[28]Motta SFY, Braga SL, Parise JAR. Critical flow of refrigerants through adiabaticcapillary tubes: Experimental study of zeotropic mixtures R-407C and R-404aASHRAETransactions,2000,106(PA):534-549
[29]Trisaksri V, Wongwises S. Correlations for sizing adiabatic capillary tubes.InternationalJournalofEnergyResearch,2003,27:1145-1164
[30]Melo C, Neto CB, Ferreira RTS.Empirical correlations for the modeling ofR-134a flow through adiabatic capillary tubes. ASHRAE Transactions, 1999,105(PA):51-59
[31]Bittle RR,Carter JA,Oliver JV.Extended insight into the metastable liquid regionbehaviorinanadiabaticcapillarytube.HVAC&RResearch,2001,7(2):107-123.
[32]Suresh Reddy K V N, Ravi Kumar Y L, Prasad D H L, Vapor-Liquid Equilibriaand Excess Enthalpies for Binary Systems of Dimethoxymethane withHydrocarbons,J.ChemEngData2006,51,326-329
[33]Gorasia JN, Dubey N, Jain KK.Computer-aided design of capillaries of differentconfigurations.ASHRAETransactions,1991(pt1):132-138.
[34]Sami SM, Tribes C.Numerical prediction of capillary tube behaviour with pureand binary alternative refrigerants. Applied Thermal Engineering, 1998,18(6):491-502.
[35]Kuehl SJ, Goldschmidt W.Modeling of steady flows of R-22 through capillarytubes.ASHRAETransactions1991,(pt1):139-148.
[36]Rallison J.M, Acrivos A.A numerical study of the deformation and burst of aviscousdropinanextensionalflow.JFluidMech,1978,89:191-200.
[37]Chi B K, Leal L G.A theoretical study of the motion of a viscous drop toward afluidinterfaceatlowReynoldsnumber.JFluidMech,1989,201:123-146.
[38]Stone H.A.Dynamics of drop deformation and breakup in viscous fluids .AnnuRevFluidMech,1994,26:65-102.
[39]Manabu Yamaguchi, Takashi Katayama. Formation of single charged drops inliquid media under a uniform electric field. Journal of Chemical Engineering ofJapan,1982,15(5):40-45.
[40]Brady Michael R,Abiven Claude,Vlachos Pavlos P,et al.Time-resolvedspray-droplet velocity and size measurements via single camera laser sheetimagingandplanarDPIV.ASMEFluidsEngDivPublFED,2002(258):51-59.
[41]Pinczewski.W.V. Droplet sizes on sieve plates operating in the spray regime.Transactionsoftheinstitutionofchemicalengineers,1977,55(1):46-52
[42]Jun H.S, Hwang W.R. Experiments on characteristic deformation and break upbehaviors of an immiscible drop in a screw channel flow. International PolymerProcessing,2004,19(3):218-224.
[43]Sachin Velankar, Hua Zhou, et al, CFD evaluation of drop retraction methods forthe measurement of interfacial tension of surfactant-laden drops. Journal ofColloidandInterfaceScience272(2004):172-185.
[44]Robert A, Johnson and Ali Borhan. Pressure-driven motion of surfactant-ladendrops through cylindrical capillaries: effect of surfactant solubility. Journal ofColloidandInterfaceScience,261(2003):529-541.
[45]丁祖荣,流体力学,高等教育出版社,北京,2003.
[46]陈钟祥,吴望一等,流体通过多孔材料的流动,石油工业出版社,北京,1984.
[47]吴颂平,刘赵淼,计算流体力学基础及其应用,机械工业出版社,北京,2007
[48]王福军,计算流体动力学分析—CFD软件原理与应用,清华大学出版社,北京,2004
[49]韩占忠,王敬,兰小平等,FLUENT—流体工程仿真计算实例与应用,北京理工大学出版社,北京,2004
[50]王瑞金,Fluent技术基础与应用实例,清华大学出版社,北京,2007.
[51]刘培生,多孔材料引论,清华大学出版社,北京,2004.
[52]徐如人,分子筛与多孔材料化学,科学出版社,北京,2004
[53]Yilmaz.Tuncay, Unal.Saban. General equation for the design of capillary tubes.JournallfFluidsEngineering,TransactionsoftheASME,1996,118(1):150-154.
[54]江帆,黄鹏,Fluent高级应用与实例分析,清华大学出版社,北京,2008.
[55]Abu Al-Rub F A, Distillation in capillaryporous media for separation of biomassethanol-watermixture,Ph.D.Thesis,TheUniversityofIowa,1994.
[56]奚正平,汤慧萍等,烧结金属多孔材料,冶金工业出版社,北京,2009
[57]于召亮,秦太验,练国平,微型管中液滴流动的三维数值模拟,力学与实践,2007,29(2):31-33
[58]Hideo Ide,Tohru Fukano,Experimental research on the correlations of holdup andfrictional pressure drop in air-water two-phase flow in a capillary rectangularchannel,ExperimentalThermalandFluidScience,2005(29):833-841.