Effects of Concentration and Surfactant on the Dynamics of SiO<sub>2</sub> Nanodroplets During Evaporation

As a novel functional fluid, silicon dioxide (SiO<sub>2</sub>) nanofluid has attracted growing attention due to the performance limitations of conventional fluids (e.g., water and oil) in thermal conduction, lubrication, and other applications. However, the impact behaviors and underlying mechanisms of SiO<sub>2</sub> nanofluid droplets on high-temperature surfaces remain poorly understood. This study employs experimental approaches to investigate the evaporation characteristics of SiO<sub>2</sub> nanofluid droplets with different concentrations, both in the presence and absence of surfactants. Additionally, the dynamic impact behaviors of these droplets on 7050 aluminum alloy plates at the Leidenfrost temperature are explored. The results demonstrate that higher concentration of SiO<sub>2</sub> nanoparticles accelerates the evaporation kinetics of the solution. The addition of sodium dodecyl sulfate (SDS) surfactant reduces the surface tension of the solution, thereby promoting the evaporation process. Moreover, SiO<sub>2</sub> nanofluid solutions with SDS exhibit a lower Leidenfrost temperature compared to those without SDS. The dynamic processes of SiO<sub>2</sub> nanofluid droplet impact at the Leidenfrost temperature involve the following stages, which are initial deposition, radial spreading, axial retraction, first rebound, secondary contact, sustained bouncing, and eventual stable evaporation. This study is conducive to a deeper understanding of the evaporation characteristics and impact dynamics of SiO<sub>2</sub> nanofluids under specific conditions. And it can provide a theoretical basis for their practical application in related engineering fields such as heat transfer and cooling systems. 二氧化硅（SiO2）纳米流体作为新型功能流体，其研究主要源于传统流体（如水、油）在热传导、润滑等领域的性能局限性。目前SiO2纳米流体液滴撞击高温壁面的规律与机制还不够明确。本文通过试验方法，分析不同浓度下有/无表面活性剂添加时SiO2纳米流体液滴的蒸发规律以及在Leidenfrost温度下撞击7050铝合金板材壁面的动力学行为。结果表明：SiO2纳米流体在一定浓度范围内，较高浓度的SiO2纳米颗粒对溶液的蒸发过程具有促进作用；表面活性剂SDS的添加降低了溶液表面张力，对蒸发过程起到了促进作用；添加SDS的SiO2纳米溶液相对未添加SDS的SiO2纳米溶液的Leidenfrost温度较低；在Leidenfrost温度下SiO2纳米流体液滴的撞击动态过程为：初始下落、径向铺展、轴向回缩、初次反弹、二次接触、持续弹跳以及最终稳定蒸发。本研究有助于深入理解特定条件下SiO2纳米流体的蒸发特性与冲击动力学，为其在传热冷却系统等相关工程领域的实际应用提供理论依据。