Abstract:

When impact velocity of liquid droplets reaches to a critical breakthrough condition, subdroplets will be generated and passed through mesh screen membrane in droplet-capturing devices of gas-liquid separators, which could cause severe performance and safety concern of downstream processes. Critical breakthrough velocity was measured on various mesh screens by visualization experiment and was studied for its dependence on factors including diameter and wettability of liquid droplets as well as structure parameters and inclination angle of mesh screen. Critical breakthrough was governed by normal dynamic pressure together with water hammer pressure in competing with capillary pressure. The normal dynamic pressure was a dynamic pressure component with regards to inclination angle of mesh screen. Water hammer pressure was created by significant water compression within a very short time of droplet impact on mesh screen membrane, and was related to the number of mesh pores in droplet projection area. The capillary pressure was related to location of liquid-gas interface in mesh pore and wettability of mesh screen. Both water hammer pressure and capillary pressure were affected by structure parameters of mesh screen. A non-dimensional critical criterion for liquid droplet breakthrough was established from force analysis of liquid-gas interface in mesh pore in combination with consideration of all influential factors. The critical criterion was matched well to experimental results and would be useful for designing gas-liquid separator with mesh screen membrane. The increase of inclination angle, decrease of droplet diameter, and increase of mesh screen hydrophobicity could increase critical impacting velocity and avoid occurrence of breakthrough condition.

Key words: separation, porous media, interface, mesh screen membrane, droplet impact, water hammer pressure, breakthrough, critical criterion

摘要：

捕沫器等化工气液分离设备中，液滴撞击丝网速度超过临界值，部分液体穿透多孔丝网形成子液滴、发生渗漏，将严重影响下游生产的性能与安全。通过可视化实验测量不同丝网表面液滴临界渗漏速度，讨论倾斜角度、丝网结构参数、液滴直径及表面浸润性等因素对临界渗漏速度的影响。液滴渗漏是法向动压力联合水锤压力克服网孔毛细压力的结果。法向动压力是动压力分量，与丝网倾角相关。液滴撞击丝网极短的瞬间，液体受到压缩，产生的水锤压力与液滴投影下的网孔数存在定量关系。毛细压力与气液界面在网孔间的位置及接触角相关。水锤压力及毛细压力均受丝网结构参数影响。通过网孔间气液界面受力分析，有机地整合渗漏影响因素，得到了渗漏临界量纲1准则。该准则与实验结果高度吻合，可为气液分离器设计提供参考。

关键词: 分离, 多孔介质, 界面, 丝网膜, 液滴撞击, 水锤压力, 渗漏, 临界准则