火焰CVD法合成二氧化钛纳米颗粒的数值模拟
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摘要
纳米材料的广泛用途使其制备方法的研究越来越受重视。化学气相沉积法(CVD)是制备纳米粉体的一种很有效的方法，例如日常用的碳黑、钛白粉颜料(TiO_2)等都可以用该方法制得。颗粒尺寸、尺寸分布状况以及形态等特性对颗粒产品的性能都产生极大的影响，这就要求对生产装置的结构和操作参数要有很好的了解和控制。
本文应用CFD商业软件FLUENT，对火焰CVD法合成二氧化钛纳米颗粒的过程进行了数值模拟。首先对CVD法中的湍流扩散火焰进行了详细的模拟，在采用单步化学反应假设的条件下，通过比较得出非平衡壁面函数法下的RNGκ-ε模型的模拟结果与实验中观测到的火焰形状和温度场最为接近；在此基础上，将二氧化钛作为一种准气体模拟计算了火焰的温度场和各组分的浓度场。
其次引入颗粒动力学模型(Schild等人，1999)及大连理工大学化工学院谢洪勇老师的Kn修正模型。并编制了一段关于颗粒碰撞生长的计算程序，在FLUENT预先计算得到的温度场内对火焰CVD法合成纳米颗粒过程中颗粒的凝结生长过程进行了模拟。这里假定所有的先驱物TiCl_4在反应后全部转化为自由的单分子，忽略了过程中晶体与晶格的转变；接着，在高温火焰中TiO_2分子单体之间不断碰撞而凝结，长大形成单个的大颗粒。这里将气体中的颗粒或者颗粒聚集块看成一种假定的气体组分，忽略颗粒对于流体的影响。在这些假设基础上对颗粒尺寸进行了预测，模拟结果显示该模型对颗粒尺寸的预测与实验数据相差不大。文中还分析了火焰温度，氧化剂流量等对生成颗粒尺寸的影响。结果表明，温度越高就越容易形成大直径的颗粒，颗粒在火焰中的停留时间越长，生成的颗粒或聚集块的尺寸就越大。
Considerable interest lies in the synthesis and the use of nanosized particles for a variety of applications. Commodities such as carbon blacks, pigmentary titania or optical fibers for telecommunications are typical products of industrial aerosol reactors. Particle characteristics like size and size distribution or the morphology mainly influence the final product quality. This emphasizes the need for a tool for optimization of the reactor geometry and the operating parameters.
Using the commercial CFD-code FLUENT, the simulation of the growth process of Titania nanoparticle synthesized in a flame CVD process for nanoparticles is performed. With the suppose that the combustion reaction occurs in a single step, the calculated results show that the RNG k-ε turbulent model produces reasonable predictions for the temperature profile and the shape of the flame with the Non-Equilibrium wall function in comparison with other method. On the base of that, the oxidation of TiCl_4 was also included in this turbulent model with the pseudo-component titania and the effects of particles to the fluid are ignored. By using the additional fluid-particle dynamics (Schild et al. 1999)and Kn modified fuction by HongyongXie, growth processes of Titania nanoparticle in the turbulent diffusion flame was simulated, where the process of all precursor molecules converting to free TiO2 "monomer" molecules firstly when the reactions occurred; after that these monomers turned into large particles or aggregates by coagulation caused by Brown collisions between particles in the high temperature flame. Based on those assumptions, the size of particles is simulated, and the effects of flame temperature and the flow rates of oxygen on the sizes of particles and aggregates have been calculated. The results indicate a flame of higher temperature more easily leads to big particles; the size of particles or aggregates become bigger with the longer residence time.
本文应用CFD商业软件FLUENT，对火焰CVD法合成二氧化钛纳米颗粒的过程进行了数值模拟。首先对CVD法中的湍流扩散火焰进行了详细的模拟，在采用单步化学反应假设的条件下，通过比较得出非平衡壁面函数法下的RNGκ-ε模型的模拟结果与实验中观测到的火焰形状和温度场最为接近；在此基础上，将二氧化钛作为一种准气体模拟计算了火焰的温度场和各组分的浓度场。
其次引入颗粒动力学模型(Schild等人，1999)及大连理工大学化工学院谢洪勇老师的Kn修正模型。并编制了一段关于颗粒碰撞生长的计算程序，在FLUENT预先计算得到的温度场内对火焰CVD法合成纳米颗粒过程中颗粒的凝结生长过程进行了模拟。这里假定所有的先驱物TiCl_4在反应后全部转化为自由的单分子，忽略了过程中晶体与晶格的转变；接着，在高温火焰中TiO_2分子单体之间不断碰撞而凝结，长大形成单个的大颗粒。这里将气体中的颗粒或者颗粒聚集块看成一种假定的气体组分，忽略颗粒对于流体的影响。在这些假设基础上对颗粒尺寸进行了预测，模拟结果显示该模型对颗粒尺寸的预测与实验数据相差不大。文中还分析了火焰温度，氧化剂流量等对生成颗粒尺寸的影响。结果表明，温度越高就越容易形成大直径的颗粒，颗粒在火焰中的停留时间越长，生成的颗粒或聚集块的尺寸就越大。
Considerable interest lies in the synthesis and the use of nanosized particles for a variety of applications. Commodities such as carbon blacks, pigmentary titania or optical fibers for telecommunications are typical products of industrial aerosol reactors. Particle characteristics like size and size distribution or the morphology mainly influence the final product quality. This emphasizes the need for a tool for optimization of the reactor geometry and the operating parameters.
Using the commercial CFD-code FLUENT, the simulation of the growth process of Titania nanoparticle synthesized in a flame CVD process for nanoparticles is performed. With the suppose that the combustion reaction occurs in a single step, the calculated results show that the RNG k-ε turbulent model produces reasonable predictions for the temperature profile and the shape of the flame with the Non-Equilibrium wall function in comparison with other method. On the base of that, the oxidation of TiCl_4 was also included in this turbulent model with the pseudo-component titania and the effects of particles to the fluid are ignored. By using the additional fluid-particle dynamics (Schild et al. 1999)and Kn modified fuction by HongyongXie, growth processes of Titania nanoparticle in the turbulent diffusion flame was simulated, where the process of all precursor molecules converting to free TiO2 "monomer" molecules firstly when the reactions occurred; after that these monomers turned into large particles or aggregates by coagulation caused by Brown collisions between particles in the high temperature flame. Based on those assumptions, the size of particles is simulated, and the effects of flame temperature and the flow rates of oxygen on the sizes of particles and aggregates have been calculated. The results indicate a flame of higher temperature more easily leads to big particles; the size of particles or aggregates become bigger with the longer residence time.
引文
[1] 冯学董．微细粉体材料及其制备技术的现状与发展．广西机械，1999年第1期：19-22．
[2] 王俏，齐红军．超细粉体材料前景广阔．当代化工，2002，31(2)：98-100．
[3] 化工百科全书第15卷．北京：化学工业出版社．1996，515-518．
[4] 陈彩凤，陈志刚，陈雪梅，郝臣．纳米粉体的制备技术．江苏理工大学学报，2001，11(6)：98-102．
[5] 刘维平，邱定蕃，马瑞新．超细粉体制备及测量技术研究进展．IM&P化工矿物与加工，2003年第3期．
[6] 毛日华，孔之瑾，郭存济．纳米二氧化钛胶体和粉体的制备．上海大学学报，1999，5(6)：477-480．
[7] 宋晓岚，邱冠周，杨华明．超细功能粉体的机械化学合成研究进展．金属矿山，2004第7期．
[8] 谢洪勇．粉体力学与工程．北京：化学工业出版社，2003．
[9] 杨柯，刘阳，尹红．纳米二氧化钛的制备技术研究．中国陶瓷，2004，40(4)：8-12．
[10] 郭新，袁润章．化学气相淀积在无机新材料制备中的应用．材料科学与工程，1994，12(1)：58—61．
[11] 吴孟强．张其翼，陈艾．凝胶-燃烧法合成纳米晶SnO_2粉体．硅酸盐学报，2002，30(2)：247-253．
[12] 赵东林，潘正伟，周万城．激光法气相合成纳米Si／C／N复相粉体．西安工程学院学报，1998，20(4)：56-58．
[13] Wenhua Zhu, Sotiris E. Pratsinis. Flame Synthesis of Nanosize Powders——Effect of Flame Configuration and Oxidant Composition. Nanotechnology, 1996, P65.
[14] M. R. Zachariah, D. Chin, H. G. Semerjian, J. L. Katz. Comb. Sci. Tech., 1977, 17: p119.
[15] M. Choi, J. Cho, J. Lee, H. W. Kim. Measurements of Silica Aggregate Particle Growth Using Light Scattering and Thermophoretic Sampling in a Coflow Diffusion Flame. Journal of Nanoparticle Research, 1999, 1: 169-183.
[16] 谢洪勇，宁桂玲等．火焰CVD法制备纳米TiO2和纳米SiO2的实验与理论研究．过程工程学报，2002，2：183-186．
[17] 张薇，孙雪，谢洪勇．Preparation of Nano Titanium Dioxide in Propane／air Diffusion Flame．过程工程学报，2004第4卷增刊：509-514．
[18] F. E. Kruis, K. A. Kusters and S. E. Pratsinis. A Simple Model for the Evolution of the Characteristics of Aggregate Particles Undergoing Coagulation and Sintering. Aerosol Science and Technology, 1993, 19: 514-526.
[19] S. Tsantilis, S. E. Pratsinis, V. Haas. Simulation of Synthesis of Palladium Nanoparticles in a Jet Aerosol Flow Condenser. J. Aerosol Sci. 1999, 30(6): 785-803.
[20] A. Schild, A. Gutschl, H. M " uhlenweg, S. E. Pratsinis. Simulation of Nanoparticle Production in Premixed Aerosol Flow Reactors by Interfacing Fluid Mechanics and Particle Dynamics. Journal of Nanoparticle Research, 1999, 1: 305-315.
[21] Tatsuo Go, Munetaka Honda, Kunio Kato. Analysis of Flame Gas Velocity and Temperature Distribution from Double-pipe Nozzle Jet in a Production Unit for Spherical Particles by Flame Spray Method. Heat Transfer-Japanese Reseatch. 1996, 25(4): 201-213.
[22] Johannessen T., S. E. Pratsinis, H. Livbjerg. Computational Analysis of Coagulation and Coalescence in the Flame Synthesis of Titania Particles. Powder Technology, 2001, 118: 242-250.
[23] Patrick T. Spicer, Olivier Chaoul, Stavros Tsantilis, Sotiris E. Pratsinis. Titania formation by TiCl, gas phase oxidation, surface growth and coagulation. Aerosol Science, 2002, 33: 17-34.
[24] 陶文铨，数值传热学．西安：西安交通大学出版社2002：509．
[25] Fluent Inc. Fluent: User' Guide: Fluent 6. 0. USA: Fluent Inc 2001.
[26] 陆大有．工程辐射传热．北京：国防工业出版社1988：294-296．
[27] Tatsuo Go, Munetaka Honda, and Kunio Kato. Analysis of flame gas velocity and temperature distribution from double-pipe nozzle jet in a production unit for spherical particles by flame spray method. Heat Transfer-Japanese Research, 1996, 25(4): 201-213.
[28] 陈义良，张孝春，孙慈，季鹤鸣．燃烧原理．北京：航空工业出版社，1992，363-366．
[29] 朱谷君．工程传热传质学．北京：航空工业出版社，1989，514-515．
[30] 陶文铨．计算传热学的近代发展．北京：科学出版社，2000，233-234．
[31] NIST．
[32] 谢洪勇，宁桂玲，毛中强，王达望，孙雪．火焰CVD法制备TiO2纳米颗粒材料的实验与理论研究，过程工程学报，第2卷增刊(2002)183-186．
[33] 王利希．火焰CVD法合成纳米颗粒的数值模拟(硕士学位论文)．大连：大连理工大学2004．
[34] 李云．火焰CVD法合成纳米颗粒的数值模拟(硕士学位论文)．大连：大连理工大学2005．
[35] 赵和平．火焰CVD法合成纳米颗粒的数值模拟(硕士学位论文)．大连：大连理工大学2006．
[36] Kobata A., K. Kusakabe & S. Morooka. Growth and transformation of TiO2 crystallites in aerosol reactor. 1991. AIChE J. 37, 347-359.
[37] Seinfeld, J. H.. Atmospheric chemistry and physics of air pollution. New York: Wiley, 1986.
[38] Fuchs, N. A. Mechanics of aerosols. New York: Pergamon Press, 1964.
[39] T. Matsoukas, S. K. Friedlander, Dynamics of aerosol agglomerate formation, J. Colloid Interface Sci. 1462 1991, 495-506.
[40] Pratsinis S. E., H. Bai, P. Biswas, M. Frenklach & S. V. R. Mastrangelo. Kinetics of TIC14 Oxidation, J. Am. Ceram. Soc., 1990, 73, 2158-2162.
[41] T. Johannessen, "Implementing User-defined Scalars/Functions in Fluent - A practical example", Department of Chemical Engineering, Technical University of Denmark, 1999.
[42] 孙文策．工程流体力学．大连：大连理工出版社 1995：P31．
[2] 王俏，齐红军．超细粉体材料前景广阔．当代化工，2002，31(2)：98-100．
[3] 化工百科全书第15卷．北京：化学工业出版社．1996，515-518．
[4] 陈彩凤，陈志刚，陈雪梅，郝臣．纳米粉体的制备技术．江苏理工大学学报，2001，11(6)：98-102．
[5] 刘维平，邱定蕃，马瑞新．超细粉体制备及测量技术研究进展．IM&P化工矿物与加工，2003年第3期．
[6] 毛日华，孔之瑾，郭存济．纳米二氧化钛胶体和粉体的制备．上海大学学报，1999，5(6)：477-480．
[7] 宋晓岚，邱冠周，杨华明．超细功能粉体的机械化学合成研究进展．金属矿山，2004第7期．
[8] 谢洪勇．粉体力学与工程．北京：化学工业出版社，2003．
[9] 杨柯，刘阳，尹红．纳米二氧化钛的制备技术研究．中国陶瓷，2004，40(4)：8-12．
[10] 郭新，袁润章．化学气相淀积在无机新材料制备中的应用．材料科学与工程，1994，12(1)：58—61．
[11] 吴孟强．张其翼，陈艾．凝胶-燃烧法合成纳米晶SnO_2粉体．硅酸盐学报，2002，30(2)：247-253．
[12] 赵东林，潘正伟，周万城．激光法气相合成纳米Si／C／N复相粉体．西安工程学院学报，1998，20(4)：56-58．
[13] Wenhua Zhu, Sotiris E. Pratsinis. Flame Synthesis of Nanosize Powders——Effect of Flame Configuration and Oxidant Composition. Nanotechnology, 1996, P65.
[14] M. R. Zachariah, D. Chin, H. G. Semerjian, J. L. Katz. Comb. Sci. Tech., 1977, 17: p119.
[15] M. Choi, J. Cho, J. Lee, H. W. Kim. Measurements of Silica Aggregate Particle Growth Using Light Scattering and Thermophoretic Sampling in a Coflow Diffusion Flame. Journal of Nanoparticle Research, 1999, 1: 169-183.
[16] 谢洪勇，宁桂玲等．火焰CVD法制备纳米TiO2和纳米SiO2的实验与理论研究．过程工程学报，2002，2：183-186．
[17] 张薇，孙雪，谢洪勇．Preparation of Nano Titanium Dioxide in Propane／air Diffusion Flame．过程工程学报，2004第4卷增刊：509-514．
[18] F. E. Kruis, K. A. Kusters and S. E. Pratsinis. A Simple Model for the Evolution of the Characteristics of Aggregate Particles Undergoing Coagulation and Sintering. Aerosol Science and Technology, 1993, 19: 514-526.
[19] S. Tsantilis, S. E. Pratsinis, V. Haas. Simulation of Synthesis of Palladium Nanoparticles in a Jet Aerosol Flow Condenser. J. Aerosol Sci. 1999, 30(6): 785-803.
[20] A. Schild, A. Gutschl, H. M " uhlenweg, S. E. Pratsinis. Simulation of Nanoparticle Production in Premixed Aerosol Flow Reactors by Interfacing Fluid Mechanics and Particle Dynamics. Journal of Nanoparticle Research, 1999, 1: 305-315.
[21] Tatsuo Go, Munetaka Honda, Kunio Kato. Analysis of Flame Gas Velocity and Temperature Distribution from Double-pipe Nozzle Jet in a Production Unit for Spherical Particles by Flame Spray Method. Heat Transfer-Japanese Reseatch. 1996, 25(4): 201-213.
[22] Johannessen T., S. E. Pratsinis, H. Livbjerg. Computational Analysis of Coagulation and Coalescence in the Flame Synthesis of Titania Particles. Powder Technology, 2001, 118: 242-250.
[23] Patrick T. Spicer, Olivier Chaoul, Stavros Tsantilis, Sotiris E. Pratsinis. Titania formation by TiCl, gas phase oxidation, surface growth and coagulation. Aerosol Science, 2002, 33: 17-34.
[24] 陶文铨，数值传热学．西安：西安交通大学出版社2002：509．
[25] Fluent Inc. Fluent: User' Guide: Fluent 6. 0. USA: Fluent Inc 2001.
[26] 陆大有．工程辐射传热．北京：国防工业出版社1988：294-296．
[27] Tatsuo Go, Munetaka Honda, and Kunio Kato. Analysis of flame gas velocity and temperature distribution from double-pipe nozzle jet in a production unit for spherical particles by flame spray method. Heat Transfer-Japanese Research, 1996, 25(4): 201-213.
[28] 陈义良，张孝春，孙慈，季鹤鸣．燃烧原理．北京：航空工业出版社，1992，363-366．
[29] 朱谷君．工程传热传质学．北京：航空工业出版社，1989，514-515．
[30] 陶文铨．计算传热学的近代发展．北京：科学出版社，2000，233-234．
[31] NIST．
[32] 谢洪勇，宁桂玲，毛中强，王达望，孙雪．火焰CVD法制备TiO2纳米颗粒材料的实验与理论研究，过程工程学报，第2卷增刊(2002)183-186．
[33] 王利希．火焰CVD法合成纳米颗粒的数值模拟(硕士学位论文)．大连：大连理工大学2004．
[34] 李云．火焰CVD法合成纳米颗粒的数值模拟(硕士学位论文)．大连：大连理工大学2005．
[35] 赵和平．火焰CVD法合成纳米颗粒的数值模拟(硕士学位论文)．大连：大连理工大学2006．
[36] Kobata A., K. Kusakabe & S. Morooka. Growth and transformation of TiO2 crystallites in aerosol reactor. 1991. AIChE J. 37, 347-359.
[37] Seinfeld, J. H.. Atmospheric chemistry and physics of air pollution. New York: Wiley, 1986.
[38] Fuchs, N. A. Mechanics of aerosols. New York: Pergamon Press, 1964.
[39] T. Matsoukas, S. K. Friedlander, Dynamics of aerosol agglomerate formation, J. Colloid Interface Sci. 1462 1991, 495-506.
[40] Pratsinis S. E., H. Bai, P. Biswas, M. Frenklach & S. V. R. Mastrangelo. Kinetics of TIC14 Oxidation, J. Am. Ceram. Soc., 1990, 73, 2158-2162.
[41] T. Johannessen, "Implementing User-defined Scalars/Functions in Fluent - A practical example", Department of Chemical Engineering, Technical University of Denmark, 1999.
[42] 孙文策．工程流体力学．大连：大连理工出版社 1995：P31．