液滴在球形粉尘表面的动力润湿特性

Kinetic wetting characteristics of droplet on the surface of spherical dust

  • 摘要: 液滴撞击、润湿粉尘现象在喷雾除尘中广泛存在,该润湿过程具有明显的动力学特征。为进一步理解液滴对粉尘的动力润湿特性,以液滴形态为监测对象,在欧拉框架下采用VOF数值模拟法,对液滴进行表面追踪,研究了液滴撞击球形尘粒前的形变特征及其与尘粒撞击过程中的动力润湿特性,分析了液滴撞击速度、液尘粒径比与无量纲展铺系数、无量纲液滴中心高度的关系。结果表明:在近尘时,随着液尘粒径比的增大,液滴形变程度降低。液滴速度越大,其形变程度越大。随着粒径降低,液滴抵抗形变能力逐渐增强。液滴撞击尘粒后,界面处存有气泡,阻碍液滴润湿尘粒,且气泡可发生断裂。液滴速度越大,气泡在压力和剪切应力作用下断裂越快。液滴展铺过程中,速度越大,越易达到最大展铺系数和最小液滴中心高度。随着液尘粒径比增大,初始无量纲液滴中心高度增大。液滴撞击尘粒表面后,无量纲液滴中心高度逐渐降低,其变化幅度逐渐降低。尘粒粒径分别为20,200,2 000 μm时,随着液尘粒径比增大,无量纲展铺系数相应减小,液尘粒径比大于1时,增大液滴粒径不会提高对尘粒的包裹程度;展铺结束后,有少部分微液滴滞留在尘粒表面。尘粒粒径为2 μm、粒径比在0.5~1.5时,液滴展铺过程受到明显抑制,尽管粒径比大于1时无量纲展铺系数最大值稍有增加,但增加量十分微小;展铺结束后,液滴整体滞留在尘粒表面。

     

    Abstract: The phenomenon of droplet impinging and wetting on dust exists widely in the process of spray dedusting.The wetting process has obvious dynamic characteristics.In order to further understand the kinetic wetting phenomenon in the process of droplet to spherical dust,this study took droplet morphology as a research target.In Eulerian framework,the VOF numerical simulation method was used to track the droplet surface.Droplet deformation and kinetic wetting characteristics were studied.The effects of droplet impact velocity,particle size ratio on dimensionless spreading coefficient and droplet center height were analyzed.The results show that when approaching the dust particle,as particle size ratio increases,the droplet deformation decreases.The greater droplet velocity,the greater deformation.With the decrease of particle size,the resistance of droplet to deformation is gradually enhanced.After the droplets hit the dust particle,bubbles appear at the interface,which prevent the droplet from wetting the dust particle,and can be broken later.The greater droplet velocity,the faster bubbles is broken by pressure and shear stress.In the droplet spreading process,the larger velocity,the easier to reach the maximum spreading coefficient and the minimum droplet center height.As the particle size ratio increases,the initial dimensionless droplet center height increases.After the droplet hits the dust particle,the dimensionless droplet center height gradually decreases,and the curve changes from steep to gentle.When dust particle size is 20,200 and 2 000 μm respectively,the dimensionless spreading coefficient decreases with the increase of the particle size ratio.When the particle size ratio is greater than 1,increasing the droplet diameter will not improve the wettability.After the spreading,a small part of the droplet will remain on dust particle surface.When the dust particle size is 2 μm and the particle size ratio is between 0.5~1.5,the droplet spreading process is obviously inhibited.Although the maximum value of dimensionless spreading coefficient increases slightly when the particle size ratio is greater than 1,the increase is very small.After the spreading,the droplet remains on the dust particle surface completely.

     

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