壁面润湿性对微通道内Taylor流动特性的影响
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摘要
壁面润湿性不仅影响着Taylor气泡的形状,同时对通道内流体流动、相变换热等有着关键的作用。采用VOF模型对T型微通道内气液两相Taylor流动进行三维数值模拟,重点研究了接触角改变对Taylor气泡流体动力学特性的影响。模拟结果与他人实验数据对比基本吻合,验证了模型的有效性。结果表明:随着接触角增大,气泡周围液含量逐渐降低,相界面也由外凸形变为内凹形。壁面越接近润湿(或疏水)状态,气液接触面的曲率就越大;当120°≤θ≤150°时Taylor气泡稳定性变差。当θ≥150°时"拖曳流态"出现,分析指出在大接触角下气体更易贴附壁面导致接触区内流场发生变化,形成的涡流减弱了水对气相的水平剪切作用,进而引起流型转变。接触角对通道内压力有着重要影响,通道中心轴向压力曲线以θ=90°为过渡,润湿状态下呈凸函数递减且p_G>p_L,疏水状态下气液进口处的压力分配改变,曲线趋势相反。
Wall wettability affects the shape of the Taylor bubble and plays a key role in fluid flow and phase change heat transfer in the microchannel. In this paper, the VOF model was used to simulate the gas-liquid two-phase Taylor flow in T-type microchannels, and the influence of contact angle change on the hydrodynamic characteristics of Taylor bubbles was analyzed emphatically. The simulation results were basically consistent with the experimental data of others, which verified the validity of the model.The result showed that with the increase of the contact angle, the liquid content around the bubble decreased gradually, and the phase interface also changed from convex to concave. The closer of wall to the wet or hydrophobic state, the larger curvature of gas-liquid interface will be. When 120°≤θ≤150°, the stability of Taylor bubble was poor. When θ≥150°, "drag flow pattern" appeared, it was pointed out that the gas was easier to attach to the wall at large contact angle, and the vortex in the contact area weakened the horizontal shear effect of water on the gas phase, leading to the flow pattern transformation. The contact angle had an important effect on the pressure in the channel. The axial pressure curve in the center of the channel took θ=90° as the transition, it was a convex function in wet state and P_G>P_L,in the hydrophobic state that the pressure distribution at the gas-liquid inlet was changed, and the curve trend was opposite.
Wall wettability affects the shape of the Taylor bubble and plays a key role in fluid flow and phase change heat transfer in the microchannel. In this paper, the VOF model was used to simulate the gas-liquid two-phase Taylor flow in T-type microchannels, and the influence of contact angle change on the hydrodynamic characteristics of Taylor bubbles was analyzed emphatically. The simulation results were basically consistent with the experimental data of others, which verified the validity of the model.The result showed that with the increase of the contact angle, the liquid content around the bubble decreased gradually, and the phase interface also changed from convex to concave. The closer of wall to the wet or hydrophobic state, the larger curvature of gas-liquid interface will be. When 120°≤θ≤150°, the stability of Taylor bubble was poor. When θ≥150°, "drag flow pattern" appeared, it was pointed out that the gas was easier to attach to the wall at large contact angle, and the vortex in the contact area weakened the horizontal shear effect of water on the gas phase, leading to the flow pattern transformation. The contact angle had an important effect on the pressure in the channel. The axial pressure curve in the center of the channel took θ=90° as the transition, it was a convex function in wet state and P_G>P_L,in the hydrophobic state that the pressure distribution at the gas-liquid inlet was changed, and the curve trend was opposite.
引文
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[22]王维萌,马一萍,陈斌.十字交叉微通道内微液滴生成过程的数值模拟[J].化工学报, 2015, 66(5):1633-1641.WANG Weimeng, MA Yiping, CHEN Bin. Numerical simulation of droplet generation in crossing micro-channel[J]. CIESC Journal, 2015,66(5):1633-1641.
[23] IDE H, KIMURA R, KAWAJI M. Effect of channel wetting properties on flow characteristics of gas-liquid two-phase flow in a microchannel[C]//ASME-JSME-KSME Joint Fluids Engineering Conference,Hamamatsu, Japan:Fluids Engineering Division, 2011:2493-2500.
[24] BARAJAS A M, PANTON R L. The effects of contact angle on twophase flow in capillary tubes[J]. International Journal of Multiphase Flow, 1993, 19(2):337-346.
[25] KUMAR V, VASHISTH S, HOARAU Y, et al. Slug flow in curved microreactors:hydrodynamic study[J]. Chem. Eng. Sci., 2007, 62(24):7494-7504.
[26] DANG Minhui, YUE Jun, CHEN Guangwen. Numerical simulation of Taylor bubble formation in a microchannel with a coverging shape mixing junction[J]. Chemical Engineering Journal, 2015, 262:616-627.
[27]车德福,李会熊.多相流及其应用[M].西安:西安交通大学出版社,2007:624.CHE Defu, LI Huixiong. Multiphase flow and its application[M]. Xi'an:Xi'an Jiaotong University Press, 2007:624.
[28] GUO Fang, CHEN Bin. Numerical study on taylor bubble formation in a micro-channel T-junction using VOF method[J]. Microgravity Science and Technology, 2009, 21(1):51-58.
[29] SHIRTCLIFFE N J, MCHALE G, ATHERTON S, et al. An introduction to super hydrophobicity[J]. Advances in Colloid and Interface Science, 2010, 161(1):124-138.
[30] SANTOS R M, KAWAJI M. Developments on wetting effects in microfludic slug flow[J]. Chemical Engineering Communications,2012, 199(12):1626-1641.
[31] KHAN W, CHANDRA A K, KISHOR K, et al. Slug formation mechanism for air–water system in T-junction microchannel:a numerical investigation[J]. Chemical Papers, 2018, 72(11):2921-2932.
[32] YONG Yumei, YANG Chao, JIANG Yi, et al. Numerical simulation of immiscible liquid-liquid flow in microchannels using lattice Boltzmann method[J]. Science China Chemistry, 2011, 54(1):244-256.
[33]孙俊杰,郝婷婷,马学虎,等.壁面润湿性对微通道内二氧化碳-水两相流流动及传质性能的影响[J].化工学报, 2015, 66(9):3405-3412.SUN Junjie, HAO Tingting, MA Xuehu, et al. Surface wettability effect on carbon dioxide-water two-phase flow and mass transfer in rectangular microchannel[J]. CIESC Journal, 2015, 66(9):3405-3412.
[34] SANTOS R M, KAWAJI M. Numerical modeling and experimental investigation of gas-liquid slug formation in a microchannel T-junction[J]. International Journal of Multiphase Flow, 2010, 36(4):314-323.
[35] KANDLIKAR S G, LU Z, RAO N, et al. Visualization of fuel cell water transport and performance characterization under freezing conditions[R]. US Department of Energy, 2010.
[2]陈光文,袁权.微化工技术[J].化工学报, 2003, 54(4):427-439.CHEN Guangwen, YUAN Quan. Microchemical technology[J]. Journal of Chemical Industry and Engineering(China), 2003, 54(4):427-439.
[3] QIAN Dongying, LAWAL A. Numerical study on gas and liquid slugs for Taylor flow in a T-junction microchannel[J]. Chem. Eng. Sci.,2006, 61(23):7609-7625.
[4] GUPTA R, FLETCHER D F, HAYNES B S. CFD modelling of flow and heat transfer in the Taylor flow regime[J]. Chem. Eng. Sci., 2010,65(6):2094–2107.
[5] LEUNG S S Y, LIU Yang, FLETCHER D F, et al. Heat transfer in well-characterised Taylor flow[J]. Chem. Eng. Sci., 2010, 65(24):6379-6388.
[6] GUNTHER A, JHUNJHUNWALA M, THALMANN M, et al.Micromixing of miscible liquids in segmented gas-liquid flow[J].Langmuir, 2005, 21(4):1547-1555.
[7] GARSTECKI P, FISCHBACH M A, WHITESIDES G M. Design for mixing using bubbles in branched microfluidic channels[J]. Appl.Phys. Lett., 2005, 86(24):244108.
[8] LAI S M, MARTIN-ARANDA R, YEUNG K L. Knoevenagel condensation reaction in a membrane microreactor[J]. Chem.Commun., 2002, 21(2):218-219.
[9] YEUNG K L, ZHANG X F, LAU W N, et al. Experiments and modeling of membrane microreactors[J]. Catal. Today, 2005, 110(1/2):26-37.
[10] LANG P, HILL M, KROSSING I, et al. Multiphase minireactor system for direct fluorination of ethylene carbonate[J]. Chem. Eng. J., 2012,179:330–337.
[11]付涛涛,朱春英,王东继,等.微通道内气液传质特性[J].化工进展,2011, 30(s2):95-98.FU Taotao, ZHU Chunying, WANG Dongji, et al. Mass transfer characteristics for gas-liquid two-phase flow in microchannels[J].Chemical Industry and Engineering Progress, 2011, 30(s2):95-98.
[12] IRANDOUST S, ANDERSSON B. Liquid film in Taylor flow through a capillary[J]. Ind. Eng. Chem. Res., 1989, 28(11):1684-1688.
[13] BERCIC G, PINTAR A. The role of gas bubbles and liquid slug lengths on mass transport in the Taylor flow through capillaries[J].Chem. Eng. Sci., 1997, 52(21/22):3709-3719.
[14] VAN BATEN J M, KRISHNA R. CFD simulations of wall mass transfer for Taylor flow in circular capillaries[J]. Chem. Eng. Sci.,2005, 60(4):1117-1126.
[15] IRANDOUST S, ANDERSSON B. Liquid film in Taylor flow through a capillary.[J] Indus. Eng. Chem. Res., 1989, 28(11):1684-1688.
[16]乐军,陈光文,袁权,等.微通道内气-液传质研究[J].化工学报,2006, 57(6):1296-1303.LE Jun, CHEN Guangwen, YUAN Quan, et al. Mass transfer in gasliquid flow in microchannel[J]. Journal of Chemical Industry and Engineering(China), 2006, 57(6):1296-1303.
[17] DAI L, CAI W F, XIN F. Numerical study on bubble formation of a gas-liquid flow in a T-junction micro-channel[J]. Chemical Engineering and Technology, 2009, 32(12):1984-1991.
[18] TRIPLETT K A, GHIAASIAAN S M, ABDEL-KHALIK S I, et al.Gas–liquid two-phase flow in microchannels:Part II:void fraction and pressure drop[J]. International Journal of Multiphase Flow, 1999,25(3):395-410.
[19] CHEN W L,TWU M C, PAN C. Gas-liquid two-phase flow in microchannels[J]. International Journal of Multiphase Flow, 2002, 28(7):1235-1247.
[20] SERIZAWA A, FENG Ziping, KAWARA Z. Two-phase flow in microchannels[J]. Experimental Thermal and Fluid Science, 2002, 26(6/7):703-714.
[21] KAWAHARA A, SADATOMI M, NEI K, et al. Characteristics of twophase flows in a rectangular microchannel with a T-junctionn type gas-liquid mixer[J]. Heat. Transf. Eng., 2011, 32(7/8):585-594.
[22]王维萌,马一萍,陈斌.十字交叉微通道内微液滴生成过程的数值模拟[J].化工学报, 2015, 66(5):1633-1641.WANG Weimeng, MA Yiping, CHEN Bin. Numerical simulation of droplet generation in crossing micro-channel[J]. CIESC Journal, 2015,66(5):1633-1641.
[23] IDE H, KIMURA R, KAWAJI M. Effect of channel wetting properties on flow characteristics of gas-liquid two-phase flow in a microchannel[C]//ASME-JSME-KSME Joint Fluids Engineering Conference,Hamamatsu, Japan:Fluids Engineering Division, 2011:2493-2500.
[24] BARAJAS A M, PANTON R L. The effects of contact angle on twophase flow in capillary tubes[J]. International Journal of Multiphase Flow, 1993, 19(2):337-346.
[25] KUMAR V, VASHISTH S, HOARAU Y, et al. Slug flow in curved microreactors:hydrodynamic study[J]. Chem. Eng. Sci., 2007, 62(24):7494-7504.
[26] DANG Minhui, YUE Jun, CHEN Guangwen. Numerical simulation of Taylor bubble formation in a microchannel with a coverging shape mixing junction[J]. Chemical Engineering Journal, 2015, 262:616-627.
[27]车德福,李会熊.多相流及其应用[M].西安:西安交通大学出版社,2007:624.CHE Defu, LI Huixiong. Multiphase flow and its application[M]. Xi'an:Xi'an Jiaotong University Press, 2007:624.
[28] GUO Fang, CHEN Bin. Numerical study on taylor bubble formation in a micro-channel T-junction using VOF method[J]. Microgravity Science and Technology, 2009, 21(1):51-58.
[29] SHIRTCLIFFE N J, MCHALE G, ATHERTON S, et al. An introduction to super hydrophobicity[J]. Advances in Colloid and Interface Science, 2010, 161(1):124-138.
[30] SANTOS R M, KAWAJI M. Developments on wetting effects in microfludic slug flow[J]. Chemical Engineering Communications,2012, 199(12):1626-1641.
[31] KHAN W, CHANDRA A K, KISHOR K, et al. Slug formation mechanism for air–water system in T-junction microchannel:a numerical investigation[J]. Chemical Papers, 2018, 72(11):2921-2932.
[32] YONG Yumei, YANG Chao, JIANG Yi, et al. Numerical simulation of immiscible liquid-liquid flow in microchannels using lattice Boltzmann method[J]. Science China Chemistry, 2011, 54(1):244-256.
[33]孙俊杰,郝婷婷,马学虎,等.壁面润湿性对微通道内二氧化碳-水两相流流动及传质性能的影响[J].化工学报, 2015, 66(9):3405-3412.SUN Junjie, HAO Tingting, MA Xuehu, et al. Surface wettability effect on carbon dioxide-water two-phase flow and mass transfer in rectangular microchannel[J]. CIESC Journal, 2015, 66(9):3405-3412.
[34] SANTOS R M, KAWAJI M. Numerical modeling and experimental investigation of gas-liquid slug formation in a microchannel T-junction[J]. International Journal of Multiphase Flow, 2010, 36(4):314-323.
[35] KANDLIKAR S G, LU Z, RAO N, et al. Visualization of fuel cell water transport and performance characterization under freezing conditions[R]. US Department of Energy, 2010.