Abstract：Urea is produced in a tower with falling liquid droplets to enhance the evaporation and drying of the urea particles. The physical process has a liquid column feeding an atomizer. This study analyzes the effect of the nozzle diameter, liquid velocity and air flow velocity on the urea maximum drop diameter. A model is developed to predict the critical heights of the liquid column and the maximum drop diameter. The model predictions agree well with the experimental data, indicating its ability to predict the maximum drop diameter. The atomizer nozzle diameter and the tangential velocity at the orifice strongly influence the drop size, while the liquid velocity at the orifice has little impact on the maximum drop diameter. The air flow velocity in the tower also affects the maximum drop diameter when the air flow velocity is greater than 1.5 m·s-1, but the effect is very small for the air flow velocity less than 1.5 m·s-1. Thus, the maximum drop diameter can be increased by increasing the atomizer nozzle diameter and the tangential velocity at the orifice. Secondary breakup will occur with large drops falling in the tower during cooling and solidification. The critical Weber number gives the maximum drop diameter of urea in the tower for granulation processing about 4 mm.
[1] Lefebver A H. Atomization and Spray [M]. New York, NY, USA: Hemisphere Publishing Corporation, 1989.
[2] Lefebver A H. Gas Turbine Combustion [M]. New York, NY, USA: Hemisphere Publishing Corporation, 1983.
[3] 中国寰球化学工程公司. 氮肥工艺手册: 尿素 [M]. 北京: 化学工业出版社, 1988.China Huanqiu Contracting & Engineering Corp (HQC). Manual of Nitrogen Fertilizer Processing: Urea [M]. Beijing: Chemical Industry Press, 1988. (in Chinese)
[4] 孔珑. 工程流体力学 [M]. 北京: 中国电力出版社, 2007.KONG Long. Engineering Fluid Mechanics [M]. Beijing: China Electric Power Press, 2007. (in Chinese)
[5] Chandrasehar S. Hydrodynamic and Hydromagnetic Stability [M]. Oxford, UK: Oxford University Press, 1961.
[6] Rizk N K, Lefebvre A H. The influence of liquid film thickness on air blast atomization [J]. ASME Journal of Engineering for Power, 1980, 102: 706-710.
[7] Varga C M, Lasheras J C, Hopfinger E J. Initial breakup of a small-diameter liquid jet by a high-speed gas stream [J]. Journal of Fluid Mechanics, 2003, 497: 405-434.
[8] Semiao V, Andrade P, Carvatho M D G. Spray characterization: Numerical prediction of SMD and droplet size distribution [J]. Fuel, 1996, 75(15): 1707-1714.
[9] 王振国, 吴晋湘, 鄢小清, 等. 气液同轴离心式喷嘴喷雾流场数值模拟 [J]. 推进技术, 1996,17(3): 43-49.WANG Zhenguo, WU Jinxiang, YAN Xiaoqing, et al. Numerical simulation of spray flow processes in coaxial swirling injector [J]. Journal of Propulsion Technology, 1996, 17(3): 43-49. (in Chinese)
[10] Li J, Renardy Y Y, Renardy M. Numerical simulation of breakup of a viscous drop in simple shear flow through a volume-of-fluid method [J]. Physics of Fluids, 2000, 12(2): 269-282.
[11] 解茂昭.燃油喷雾场结构与雾化机理 [J].力学与实践, 1990, 12(4): 9-15.XIE Maozhao. Spray field structure of fuel and atomization mechanism [J]. Mechanics and Engineering, 1990, 12(4): 9-15. (in Chinese)
[12] Pilch M, Erdman C A. Use of break-up time data and velocity history data to predict the maximum size of stable fragments for acceleration-induced break-up of a liquid drop [J]. International Journal of Multiphase Flow, 1987, 13(6): 741-757.
[13] 甘晓华. 航空燃气轮机燃油喷嘴技术 [M]. 北京: 国防工业出版社, 2006.GAN Xiaohua. Technology of Fuel Nozzle in Aviation Gas Turbine [M]. Beijing: National Defense Industry Press, 2006. (in Chinese)
[14] 岑可法, 姚强, 曹欣玉, 等. 煤浆燃烧、 流动、 传热和气化的理论与应用技术 [M].杭州: 浙江大学出版社, 1995.CEN Kefa, YAO Qiang, CAO Xinyu, et al. Theory and Application Technology of Combustion, Flow, Heat Transfer and Gasification of Coal Slurry [M]. Hangzhou: Zhejiang University Press, 1995. (in Chinese)
[15] Scweitzer P H. Mechanisms of disintegration of liquid jets [J]. Journal of Applied Physics, 1937, 8(8): 513-521.
[16] Hinze J O. Fundamentals of the hydrodynamic mechanism of splitting in dispersion process [J]. AIChE Journal, 1955, 1(3): 289-295.
[17] Giffen T, Muraszew A. The Atomization of Liquid Fuels [M]. New York, NY, USA: John Wiley & Sons, 1953.
[18] 刘孝弟, 褚晓斌, 蒋刚. 尿素造粒机理研究 [J]. 化肥工业, 2015, 42(3): 21-28.LIU Xiaodi, CHU Xiaobin, JIANG Gang. Study of mechanism of urea granulation [J]. Chemical Fertilizer Industry, 2015, 42(3): 21-28. (in Chinese)
2016, Vol. 56 
