锥射流模式下乙醇静电喷雾液滴速度特性分析

A STUDY ON DROPLET VELOCITY OF ETHANOL DURING ELECTROSPRAYING PROCESS AT CONE-JET MODE

研究液滴在静电喷雾下的速度特性是理解喷雾形态的形成及演化的关键.结合锥射流模式下乙醇静电喷雾实验数据,建立了静电喷雾二维轴对称模型.基于离散相液滴运动方程、连续相空气运动方程、电场方程以及用户自定义函数,进行了数值求解,获得了锥射流模式下的乙醇静电喷雾形态、空间电场分布以及液滴速度场分布.考虑了不同空气入口流速的影响,得到了乙醇/空气同轴射流静电喷雾形态的变化规律.结果表明,喷雾外围液滴与空气流场有较强的相互作用,导致喷雾中轴线附近的液滴速度分布变化较小,而在喷雾外围处的液滴速度分布沿径向剧烈变化;随着空气入口速度的增大,乙醇/空气同轴射流静电喷雾形态先趋于发散,当空气入口速度大于喷雾外围液滴轴向速度时,喷雾形态则趋于聚拢.因此,除改变施加电压、液体流量和电极结构外,通过控制空气入口速度来影响喷雾液滴速度场,也可获得不同的静电喷雾效果.

An analysis on the velocity characteristics of droplets generated from electrospraying is the key to understand the formation and evolution of the spray shape.Combining with the experimental results of ethanol electrospraying at cone-jet mode,a two-dimensional axisymmetric model of electrospraying was established.Based on the droplet motion equations,air motion equations,electric field equations and user-defined functions,the model was numerically solved to obtain the spray morphology,the space electric field distribution and the droplet velocity field distribution at cone-jet mode.The effect of air inlet velocity on the spray shape and velocity field distribution of ethanol/air coaxial jet was also discussed.The results indicate that the air flow field has a strong interaction with the droplets at the periphery of the spray,leading to a smooth variation of the droplet velocity distribution near the axis of the spray,while the droplet velocity distribution at the periphery of the spray varies drastically along the radial direction.As the coaxial air inlet velocity increases,the spray shape tends to diverge first.But when the air inlet velocity increases to be greater than the axial velocity of the spray droplets,the spray shape tends to gather.Therefore,in addition to changing the applied voltage,liquid flow rate or electrode pattern,controlling the air inlet velocity to affect the spray velocity field can be an e_cient way to control the electrospraying.