抑尘液滴对煤表面动态润湿特征模拟评估方法

Simulation and evaluation method of dynamic wetting characteristics of dust suppression droplets on coal surface

在煤体表面喷洒抑尘液是涉煤工业企业常用抑尘手段,而抑尘液滴撞击煤表面的润湿过程对抑尘效果具有重要意义。为研究抑尘液滴在煤表面动态润湿过程以及进一步评估液滴润湿性能,提出了液滴撞击煤表面过程中动态润湿指标,基于CLSVOF数值模拟法研究了液滴在煤表面动态润湿过程;利用无量纲润湿长度和无量纲润湿面积评价该过程中体现的润湿性能,并得出最大无量纲润湿长度与最大无量纲润湿面积相关理论表达,同时与表面张力的润湿性评估能力进行了比较。结果表明:CLSVOF方法能够较好地模拟液滴在煤表面的撞击以及动态润湿过程,可用来评估液滴对煤的动态润湿能力。液滴滴落在煤表面上,首先展铺为圆盘状,达到最大展铺时,圆盘边缘与中心存在速度差。当速度差较小时,液滴回缩汇聚成为一个液滴;当速度差较大时,液滴出现断裂行为,形成许多微小液滴。液滴粒径越大,断裂行为越早出现、现象越明显。一旦液滴在煤表面发生破裂,无量纲润湿长度与无量纲润湿面积并不是保持着一致性变化趋势,无量纲润湿面积评估能力更佳。液滴粒径相同时,撞击煤表面的韦伯数越大,润湿能力越好;相同速度下增加粒径对液滴润湿能力影响较小。与表面张力相比,无量纲润湿长度和无量纲润湿面积具有更好的液滴润湿性评估能力,体现出在润湿剂评价、优选中的潜在应用价值。

Spraying dust suppression liquid on the coal surface is a common dust suppression method for coal-related in-dustrial enterprises,and the wetting process of dust suppression droplets impacting the coal surface is of great significance to the dust suppression effect.In order to study the dynamic wetting process of dust suppression droplets on the coal sur-face and further evaluate the wetting performance of droplets,the index of dynamic wettability during droplets impacting on the coal surface is proposed.The dynamic wetting process of droplets on the coal surface is investigated based on CLS-VOF numerical simulation method.The wetting performance in the process is evaluated by using the dimensionless wet-ting length and the dimensionless wetting area,and the theoretical expressions of the maximum dimensionless wetting length and the maximum dimensionless wetting area are derived.At the same time,they are compared with the wettability evaluation ability of surface tension.The results show that the CLSVOF method can better simulate the impact and dy-namic wetting process of droplets on the coal surface,and can be used to evaluate the dynamic wetting ability of different droplets on the coal surface under different conditions.The droplet drops on the coal surface,and first spreads as a disk.When the maximum spreading is reached,there is a velocity difference between the edge and the center of the disk droplet.When the velocity difference is small,the droplet retracts and coalesces into a sphere.When the velocity difference is large,the droplet breaks and forms many tiny droplets.And the larger the droplet size is,the earlier the breakage behavior appears and the more obvious the phenomenon is.Once the droplet breaks on the coal surface,the dimensionless wetting length and the dimensionless wetting area do not maintain the consistent trend,and the evaluation ability of the dimension-less wetting area is better.When the droplet size is the same,the larger the We number of droplet impacting the coal sur-face,the better the wetting ability.Increasing the droplet size at the same velocity has less effect on its wetting ability.Compared with surface tension,the dimensionless wetting length and dimensionless wetting area have better ability to evaluate wettability of droplets,which reflects the potential application value in the evaluation and optimization wetting agents.