基于稳定域原理的液体燃料静电雾化过程模拟研究

发布时间：2018-06-10 11:48

本文选题：雾化 + 数值模拟　；参考：《南京理工大学》2016年硕士论文

【摘要】：液体石化燃料是燃烧炉最常使用的原料。液体燃料的雾化效果直接影响到其使用效率,甚至会使油嘴结焦,炉管局部结焦而出现热点导致爆管事件；此外,未完全燃烧的液体燃料滴落在冷灰斗中,也可能形成可燃蒸汽云,产生爆炸的危险性。显然,提高液体燃料的雾化效果对于改善燃烧效率、提高燃烧炉在使用过程中的安全性均具有非常重要的意义。静电雾化技术作为电流体力学的一个重要分支,近年来得到较快发展。静电雾化过程中,首先使液体在电场中带电,带电液滴表面电荷的库仑斥力在克服表面张力后可进一步形成更为细小的液滴,实现充分雾化。由于静电雾化后的液滴带有相同电荷,同种电荷间的库仑斥力可以防止液滴的二次聚集,因此具有更好的雾化效果。本文基于稳定域原理对静电雾化过程进行模拟研究。通过对静电雾化过程中的电流体力学理论、电压、电流、粒径等参数的计算公式进行分析,建立相应的模型,并进行数值仿真计算。采用ICEM进行建模,并对雾化模型进行网格划分,利用FLUENT软件对两种腔室结构内部的空间流场进行模拟分析。研究了气体流速和腔室形状对腔室内部气体流型的影响,得到了两种腔室结构下流场的稳定域。在稳定域条件下,采用多相流模型和DPM模型分别模拟液体在不同电压下和不同表面张力下泰勒锥的形成过程和液滴在不同电压、不同液体粘性、不同的液体表面张力下的二次雾化过程。在使用DPM模型来模拟空气场中的液滴雾化过程中,采用自行编制的电场力程序,用UDS加入电的方程,并通过UDF加入电场力对动量方程的影响。结果表明,当施加在喷管上的电压大小发生变化时,尽管泰勒锥的形状会发生明显改变,但是泰勒破碎形成的最初液体大小大致相同。液体性质发生改变后,泰勒锥形状和首次破碎液滴大小也会发生改变。电压为2000V、3000V、5000V条件下对二次雾化过程进行研究,证实在一定范围内提高电场强度可以明显减小液滴的平均粒径；降低液体的表面张力也可以显著降低液滴平均粒径；而液体粘性对形成的液滴粒径的影响相对较小。本文的研究方法及得到的结果不仅为稳定域原理在静电雾化过程的模拟研究提供了一种可行的方法,也为燃烧炉中液体燃料的静电雾化工艺参数的选取提供了重要的理论依据。
[Abstract]:Liquid fossil fuels are the most commonly used raw materials for combustion furnaces. The atomization effect of liquid fuel has a direct effect on its use efficiency, even coking the oil nozzle, and the hot spot in the furnace tube leads to the tube burst event. In addition, the liquid fuel that is not completely burned drops into the cold ash bucket. Flammable vapor clouds may also be formed, creating the risk of explosion. Obviously, improving the atomization effect of liquid fuel is very important for improving combustion efficiency and improving the safety of combustion furnace. As an important branch of electrohydrodynamics, electrostatic atomization technology has been developed rapidly in recent years. In the process of electrostatic atomization, the liquid is first charged in the electric field, and the Coulomb repulsion force with surface charge on the surface of the charged droplet can further form smaller droplets after surmounting the surface tension and realize full atomization. Because the droplet has the same charge after electrostatic atomization, the Coulomb repulsive force between the same charge can prevent the secondary aggregation of the droplet, so it has better atomization effect. In this paper, the electrostatic atomization process is simulated based on the stability region principle. By analyzing the calculation formulas of electrohydrodynamics theory, voltage, current, particle size and other parameters in electrostatic atomization process, the corresponding model is established and the numerical simulation is carried out. ICEM is used to model the atomization model and the atomization model is meshed. The flow field inside the two chambers is simulated and analyzed by fluent software. The effects of gas flow rate and chamber shape on the gas flow pattern in the chamber are studied. The stable region of the flow field under two chamber structures is obtained. In the stable region, the multiphase flow model and DPM model are used to simulate the formation process of Taylor cone under different voltage and different surface tension, respectively. The secondary atomization process under different surface tension of liquid. The DPM model is used to simulate the droplet atomization process in the air field. The self-compiled electric field force program is used to add the electric equation with UDS and the influence of the electric field force on the momentum equation through the addition of UDF. The results show that when the voltage applied on the nozzle changes, although the shape of the Taylor cone will change obviously, the initial liquid size formed by Taylor fragmentation is approximately the same. The shape of Taylor cone and the size of the first broken droplet will also change after the change of liquid properties. The secondary atomization process was studied at the voltage of 2000V ~ (3 000) V ~ (3 000) V ~ (5 000) V, and it was proved that increasing the electric field intensity in a certain range could obviously reduce the average particle size of the droplet, decrease the surface tension of the liquid, and decrease the average diameter of the droplet. The effect of liquid viscosity on droplet size is relatively small. The research methods and the results obtained in this paper not only provide a feasible method for the simulation of the electrostatic atomization process of the stability region principle, but also provide an important theoretical basis for the selection of the parameters of the electrostatic atomization process of the liquid fuel in the combustion furnace.
【学位授予单位】：南京理工大学
【学位级别】：硕士
【学位授予年份】：2016
【分类号】：TK16

【相似文献】