喷射器内闪急沸腾雾化特性研究

发布时间：2018-05-24 15:12

本文选题：CFD + 闪急沸腾雾化　；参考：《青岛科技大学》2017年硕士论文

【摘要】：气液喷射器作为一种具有高强度混合效果的流体装置,近年来在化工、能源、环保等领域已有广泛应用,其性能好坏关键在于雾化过程中形成的液滴大小及分布情况。闪急沸腾雾化作为一种新型高效喷射雾化装置,能够获得比传统雾化装置更加细小和均匀的液滴分布。目前虽然对闪急沸腾雾化的研究较多,但大多数集中在发动机的燃油特性的研究中,而在化工领域研究很少。而且由于影响闪急沸腾雾化特性的因素较多,闪急沸腾雾化流场结构复杂,导致影响雾化特性因素的研究不够系统全面。本课题主要从喷嘴结构以及操作条件两方面入手,以改善液体雾化为最终目的,采用计算流体动力学(CFD)模拟的方法,系统地研究喷射压力、喷嘴结构对喷嘴内流型变化的影响规律,建立了新的流型判定模型;在此基础上,进一步对喷嘴结构和操作条件对闪急沸腾雾化特性的影响进行了分析,对传统雾化与闪急沸腾雾化的不同雾化特性和机理进行了比较,获得了如下结论:一、建立了利用CFD方法判断喷嘴内流型变化的数学模型,并利用文献实验数据对模型进行了验证。并利用模型研究了喷射压力、入口倒角半径与喷嘴直径的比r/d、喷嘴长度与喷嘴直径的比L/d对喷嘴内流型变化的影响,结论如下:(1)研究表明,喷射压力越大,喷嘴内更容易产生空穴区。r/d越大,越不容易产生空穴现象。对已经形成柱塞流的喷嘴,通过增大L/d值可以使得喷嘴内形成的柱塞流再次转变为局部空穴流。(2)得到平孔喷嘴内流型变化与r/d和L/d之间的关系,建立了新的流型判断模型并与目前平孔喷嘴内流型判断经验模型进行比较,验证了其准确性。本文所建立的模型有助于对已有的柱塞流经验判断公式的修正。二、通过耦合气泡喷嘴模型和液体蒸发模型,建立了喷射器闪急沸腾雾化的CFD模型,并对模型可靠性进行了验证。并基于模型对影响闪急沸腾雾化特性的各因素进行了研究,结论如下:(1)采用汽化率表示液体过热度,在其它工况条件一定的前提下,增大喷射液体的汽化率,可以使喷射液体在喷嘴出口处受到气体的冲击力增加,从而改善雾化质量。(2)仅仅改变表面张力时,随着液滴表面张力的减小,雾化形成的液滴SMD值减小,液滴分布范围变小,分布更加均匀。(3)密度对液滴雾化特性的影响与表面张力相反,随着液滴密度的增大,雾化形成的液滴SMD(索特平均直径)值减小,分布更加均匀。(4)在本文模拟过程中,粘度在小于0.01 kg/(m·s)时,其变化对雾化特性的影响较小;当粘度大于0.01 kg/(m·s)时,粘度对液滴粒径产生影响,粘度越大,SMD值越大。其影响效果与表面张力类似,均是对液滴的破碎起到了阻尼作用。三、对传统雾化与闪急沸腾雾化的特性进行了对比分析。分别在闪急沸腾雾化与传统雾化保持相同喷射量和相同喷射压力的情况下,对闪急沸腾雾化与传统雾化效果进行了比较,结果表明在相同条件下,闪急沸腾雾化形成的液滴平均粒径更小,分布更均匀,显示出闪急沸腾雾化较传统雾化装置相比更有优势。
[Abstract]:As a fluid device with high strength mixing effect, gas liquid ejector has been widely used in the fields of chemical, energy and environmental protection in recent years. The key of its performance is the size and distribution of droplets in the process of atomization. Flash boiling atomization can be used as a new type of high efficient spray atomizing device, which can be compared with traditional atomization. The device has more finer and even distribution of droplets. Although there are many researches on flash boiling, most of them are concentrated in the study of the fuel characteristics of the engine, but few in the chemical field. And because there are many factors affecting the atomization characteristics of flash boiling, the structure of the atomization flow field is complex, which leads to the effect of atomization. The study of sex factors is not systematic and comprehensive. This topic mainly starts with the two aspects of the nozzle structure and operating conditions, in order to improve the liquid atomization as the ultimate goal. The method of computational fluid dynamics (CFD) simulation is used to systematically study the effect of the jet pressure and the nozzle structure on the flow pattern in the nozzle, and a new flow pattern determination model is established. On this basis, the influence of the nozzle structure and operating conditions on the atomization characteristics of flash boiling is analyzed. The different atomization characteristics and mechanism of the traditional atomization and flash boiling atomization are compared. The following conclusions are obtained: first, a mathematical model is established to judge the change of inner flow pattern of the nozzle by CFD method, and the literature is used in the literature. The model was verified by the experimental data, and the effect of the injection pressure, the radius of the inlet angle and the diameter of the nozzle r/d, the effect of the nozzle length and the diameter of the nozzle on the change of the flow pattern in the nozzle were studied. The conclusions are as follows: (1) the study shows that the larger the injection pressure is, the greater the.R/d in the cavity area is produced in the nozzle, the less easily it is produced. Hole phenomenon. For the nozzle which has formed the plunger flow, the plunger flow formed in the nozzle can be changed to the local cavitation flow by increasing the L/d value. (2) the relationship between the change of the flow pattern of the nozzle and the r/d and the L/d is obtained. A new flow pattern judgment model is established and compared with the current model of the inner flow pattern judgement of the flat nozzle. The model established in this paper helps to correct the empirical formula of the existing plunger flow. Two, by coupling the bubble nozzle model and the liquid evaporation model, the CFD model of the ejector flash boiling atomization is established, and the reliability of the model is verified. The following factors are studied and the conclusions are as follows: (1) using the vaporization rate to express the liquid overheat, increasing the vaporization rate of the jet liquid under the condition of other conditions, can increase the impact force of the jet at the outlet of the nozzle, thus improving the mass of the atomization. (2) only when the surface tension is changed, the surface tension of the droplet is with the surface tension. The droplet SMD value decreases, the droplet distribution range becomes smaller and the distribution is more uniform. (3) the influence of density on the droplet atomization characteristics is opposite to the surface tension. With the increase of the droplet density, the droplet SMD (SOT mean diameter) decreases and the distribution is more uniform. (4) the viscosity of the droplet is less than 0.01 kg/ during the simulation process. When m. S), the change has little influence on the atomization characteristics; when the viscosity is greater than 0.01 kg/ (M. S), the viscosity has an effect on the droplet size, the greater the viscosity and the greater the SMD value. The effect is similar to the surface tension, and all of the droplets are damped. Three, the characteristics of the atomization and flash boiling are compared and analyzed. In the case of flash boiling atomization and traditional atomization keeping the same injection amount and the same injection pressure, the effect of flash boiling atomization and traditional atomization is compared. The results show that under the same conditions, the average particle size of the droplet formed by the flash boiling atomization is smaller and the distribution is more uniform, showing that the flash boiling atomization is more than the traditional atomization device. It's more advantageous than that.
【学位授予单位】：青岛科技大学
【学位级别】：硕士
【学位授予年份】：2017
【分类号】：TQ027.32

【参考文献】