目的 探讨液滴撞击宏脊曲面时的动态行为,对于防雾防冰等领域提高设备性能具有重要意义。方法 采用3D打印技术制作了三角形结构宏脊曲面,利用高速摄影仪分析了液滴撞击高度、宏脊顶角以及表面浸润性对液滴最大铺展因子、最大铺展时间以及脱离位置的影响。结果 随着撞击韦伯数（We数）逐渐增加,最大铺展因子bmax增大,同时最大铺展时间tc和液膜脱离位置α减小。当We数超过某一临界值后,液滴发生飞溅现象导致最大铺展因子减小。其次,随着宏脊顶角的增大,液滴发生脱离飞溅的临界We数降低,宏脊表面残留液体减少,使得最大铺展因子更大,最大铺展时间tc延长,液膜脱离位置α增大。此外,当液滴撞击超疏水性宏脊曲面时,液滴发生脱离飞溅时的We数更低,铺展速度更快,最大铺展因子显著减小。最后,考虑了表面浸润性和宏脊顶角的影响,获得了液滴的最大铺展因子和最大铺展时间与We数、宏脊顶角和表面浸润性等的关系。结论 宏脊的存在以及表面浸润性的差异显著改变了撞击液滴的最大铺展因子和最大铺展时间。本文考虑宏脊顶角的影响,重新定义了We数,并引入了浸润性修正因子f(f,q)。当液滴撞击宏脊曲面时,液滴的最大铺展因子βmaxµ f(f,q)0.2We0.4,最大铺展时间tc/t0µ f(f,q)We-0.5。
Abstract
It is of great significance to investigate the dynamic behavior of droplets impacting on curved surfaces with macro-ridges for enhancing equipment performance in fields such as anti-fogging and anti-icing. In this work, the curved surfaces with triangular macro-ridges are designed and fabricated by 3D printing technique. The dynamic behavior of droplets impacting these surfaces is captured via a high-speed camera. The effects of impact height, macro-ridge apex angle (30°, 60°, and 100°), and surface wettability on the dynamic behavior are systematically investigated, with a focus on the maximum spreading factor, maximum spreading time (the time to achieve maximum spreading factor), and detachment point. The results indicate that when a droplet impacts on the macro-ridged (MR) surface at a smaller Weber number (We), the droplet undergoes four stages: spreading - splitting at the top - liquid film spreading - liquid film retraction. Initially, under the action of the inertial force, the droplet spreads rapidly along the circumferential direction. Due to the viscous force between the droplet and the surface, the liquid film gradually wraps around the macro-ridge. Then, the liquid film is split into two parts by the macro ridge. Next, the liquid film expands to its maximum extent, the film gets thin, and the front remains in a thick state; After that, the liquid film begins to retract under the action of surface tension, and the maximum spreading length decreases. Thereafter, the liquid film continuously spreads and contracts under the influence of gravity and surface tension, eventually forming a relatively uniform liquid film. As the Weber number (We) increases, the initial kinetic energy of the droplet rises and the inertial force dominates the spreading of droplets on the surface, leading to an increase in the maximum spreading factor, while reducing both the maximum spreading and the detachment point. When the We number exceeds a certain critical value, the droplet splashing occurs, resulting in a reduction of the maximum spreading factor due to reduced droplet volume. Secondly, as the macro-ridge apex angle increases, the critical We number for the detachment of the droplet decreases, resulting in less liquid remaining on the macro-ridge surface. Moreover, a thinner liquid film forms on the surface, so that the maximum spreading factor becomes greater. Meanwhile, the maximum spreading time tc increases and the detachment position α rises. Additionally, when the droplet impacts on the superhydrophobic macro-ridged (SMR) surface, compared with the common macro-ridged surface, the critical We number for the droplet to undergo detachment is lower, the spreading speed is faster due to smaller viscous dissipation, and the maximum spreading factor significantly decreases. Finally, considering the effects of surface wettability and the macro-ridge apex angle, the relationship among the maximum spreading factor and maximum spreading time of the droplet and the We number, the macro-ridge apex angle, and surface wettability is obtained based on the energy conservation method, and compared with the experimental results, the two are in good agreement. The presence of macro-ridges and differences in surface wettability significantly alter the maximum spreading factor and maximum spreading time of impacting droplets. For the macro-rib surface used in this study, the We number is redefined considering the effect of the macro-rib apex angle, and the wettability of the surface is taken into account by introducing a wettability correction factor f(f,q). When a droplet impacts a macroridged surface, the maximum spreading factor of the droplet is βmaxµ f(f,q)0.2We0.4, and the maximum spreading time is tc/t0µ f(f,q)We-0.5.
关键词
液滴 /
撞击 /
宏脊曲面 /
铺展 /
脱离
Key words
droplet /
impact /
curved macro-ridged surface /
spreading /
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基金
国家自然科学基金资助项目（52576166）
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