Key Laboratory for Thermal Science and Power Engineering of Ministry of Education, Beijing Key Laboratory for CO(2) Utilization and Reduction Technology, Department of Energy and Power Engineering, Tsinghua University, Beijing 100084, China.
School of Energy and Environmental Engineering, University of Science and Technology Beijing, Beijing 100083, China.
J Colloid Interface Sci. 2021 Oct;599:130-139. doi: 10.1016/j.jcis.2021.04.078. Epub 2021 Apr 19.
Due to the complex hydrodynamics of droplet impact on ridged superhydrophobic surfaces, quantitative droplet spreading characteristics are unrevealed, limiting the practical applications of ridged superhydrophobic surfaces. During droplet impacting, the size ratio (the ratio of the ridge diameter to the droplet diameter) is an important factor that affects droplet spreading dynamics.
We fabricated ridged superhydrophobic surfaces with size ratios ranging from zero to one, and conduct water droplet impact experiments on these surfaces at varied Weber numbers. Aided by the numerical simulations and theoretical analysis, we illustrate the droplet spreading dynamics and reveal the law on the maximum axial spreading coefficient.
The results show that the droplet spreading and retraction dynamics on ridged superhydrophobic surfaces are significantly asymmetric in the axial and spanwise directions. Focusing on the maximum axial spreading coefficient, we find it decreases first and then increases with increasing size ratios, indicating the existence of the critical size ratio. The maximum axial spreading coefficient can be reduced by 25-40% at the critical size ratio compared with that on flat surfaces. To predict the maximum axial spreading coefficient, two theoretical models are proposed respectively for size ratios smaller and larger than the critical size ratio.
由于液滴冲击脊状超疏水表面的复杂流体动力学，定量的液滴扩展特性尚不清楚，这限制了脊状超疏水表面的实际应用。在液滴冲击过程中，大小比（脊直径与液滴直径的比值）是影响液滴扩展动力学的重要因素。
我们制造了大小比从零到一的脊状超疏水表面，并在不同韦伯数下对这些表面进行了水滴冲击实验。借助数值模拟和理论分析，我们说明了液滴扩展动力学，并揭示了最大轴向扩展系数的规律。
结果表明，脊状超疏水表面上液滴的扩展和收缩动力学在轴向和横向方向上具有显著的不对称性。关注最大轴向扩展系数，我们发现它随大小比的增加先减小后增大，表明存在临界大小比。与在平面上相比，在临界大小比下，最大轴向扩展系数可降低 25-40%。为了预测最大轴向扩展系数，分别针对大小比小于和大于临界大小比提出了两个理论模型。
