Experimental And Numerical Studies On The Droplet Impact On Micro-pillar Array Textured Surfaces

The droplet impact on micro-pillar array surfaces has huge significance due to their various industrial and commercial applications in different fields such as aerospace,biomedical engineering,mechanical engineering,automobile,agriculture,and chemical engineering.In this study,the micro-pillar array textured surfaces were fabricated on silicon substrates with different micro-pillar spacings.The three surfaces were considered,i.e.a smooth silicon-based surface A,and the silicon-based micro-pillar arrays B and C with micro-pillar spacings of about500 nm and 200 nm,respectively.In this thesis,micro-pillar array textured surfaces with different pitches were fabricated on smooth silicon substrates.The experiment was conducted to compare the dynamic behavior of droplet impact on a smooth silicon surface and two micro-pillar array silicon surfaces.Simultaneously,a 2D numerical simulation was performed to study the droplet impact behavior on micro-pillar arrays using COMSOL Multiphysics.The effects of pillar pitch,pillar width,and pillar height on the spreading factor,contact time,and pinning extremum of droplet impact were numerically investigated.The main conclusions are drawn as follows:(1)When We=1.4-173.1,the droplet impact behavior on the surface of A showed the characteristics of the partial rebound-adhesion process,and it was characterized by the complete rebound-fragmentation process on B and C surfaces.When We=13.9-62.2,the surface of A was partially bounced.When We=33.4-80.2,the droplets on the surfaces of B and C were completely rebounded,the splitting was observed at the top of droplets.(2)The maximum spreading factor of droplets on the B surface was higher than that on the C surface due to the static contact angle difference(?_B?153°,?_C?161°),but the contact time of the droplet on the B surface was less than on the C surface.(3)The droplet impact on the surface of the micro-pillar array with a micro-pillar spacing of20-60?m was simulated,and it was found that the spreading factor and contact time of the droplet could be effectively reduced by increasing the micro-pillar spacing under the same surface wettability condition when We=2.2-72.3.The droplet pinning extreme value is positively correlated with the micro-pillar spacing and the We number.This study helps to generate controlling techniques of the droplet impact dynamics.The project supports the Belt and Road Initiative(BRI)especially the China-Pakistan Economic Corridor(CPEC)in terms of using modern technologies.