Abstract:

Liquid film breakup mode at disk rim of centrifuge particle generator directly determines droplet shapes and sizes, which is a key factor to affect product qualities. A critical transition coefficient for spinning disk particle generator was proposed to characterize liquid film breakup transition characteristics from film to ligament, to extend to other breakup modes, and to establish critical equations for transition from direct droplet to ligament, ligament to fully ligament, and fully ligament to sheet. The experimental results of three working fluids and two disks indicated that disk surface wettability played key role for liquid film to become direct droplet or to transit from direct droplet to ligament, which incomplete wetting caused random critical volume flow rate with no direct correlation between disk diameter and critical volume flow rate. Critical volume flow rate increased with increasing disk diameter in fully-ligament and film modes. In general, the increase of liquid flow rate, rotation speed, liquid density, and viscosity drove towards film breakup mode. However, high surface tension force maintained liquid film in direct drop or ligament even at large flow rate and rotation speed. Moreover, increasing disk diameter enhanced both centrifugal force and surface tension and breakup mode did not change unless the force balance was lost.

Key words: fluid mechanics, model, experimental validation, breakup mode, spinning disk, transition characteristics

摘要：

液膜在离心粒化器边缘的破碎模式直接决定了雾化后的液滴形态和尺寸分布，是影响物料品质的关键因素。针对转盘粒化器，提出临界转变系数表征液膜由膜状向纤维状破碎的转变条件，并拓展至其他破碎模式，建立了滴状向纤维状、完全纤维状及纤维状向膜状破碎转变的临界关系。结果表明，转盘表面润湿性对于液膜呈滴状以及滴状向纤维状模式转变影响显著，未完全润湿导致临界流量存在一定的随机性，转盘直径与临界流量间无明确规律；而完全纤维状以及膜状时，大直径转盘临界流量明显升高。转速、流量、密度及黏度的提高，破碎模式趋向于膜状；而增大表面张力，即使对于较大流量和转速，液膜也能维持纤维状或滴状模式。调整转盘直径将引起表面张力与离心力同时变化，若未打破平衡，其破碎模式不会改变。研究结果为转盘粒化器的设计与优化提供了可借鉴的理论与应用基础。

关键词: 流体力学, 模型, 实验验证, 破碎模式, 转盘, 转变特性