Department of Mechanical and Aerospace Engineering, Indian Institute of Technology Hyderabad, Kandi, Hyderabad 502284, Telangana, India.
Department of Chemical Engineering, Indian Institute of Technology Hyderabad, Kandi, Hyderabad 502284, Telangana, India.
Langmuir. 2022 Dec 13;38(49):15361-15371. doi: 10.1021/acs.langmuir.2c02590. Epub 2022 Dec 2.
We experimentally investigate the evaporation characteristics of a sessile ethanol droplet containing AlO and Cu nanoparticles of sizes 25 and 75 nm on a heated substrate using shadowgraphy and infrared imaging techniques. Our results demonstrate that the droplet contact line dynamics resulting from the presence of various nanoparticles plays a dominant role in the evaporation process. This is in contrast to the widely held assumption that the enhanced evaporation rate observed in sessile nanofluid droplets is due to the higher thermal conductivity of the added nanoparticles. We observe that even though the thermal conductivity of AlO is an order of magnitude lower than that of Cu, droplets containing 25-nm-sized AlO exhibit pinned contact line dynamics and evaporate much more rapidly than droplets containing Cu nanoparticles of both sizes and 75 nm AlO nanoparticles that exhibit stick-slip behavior. We also found that the droplets with different nanoparticles display distinct thermal patterns due to the difference in contact line behavior, which alters the heat transfer inside the droplets. We establish this counter-intuitive observation by analyzing the temporal variations of the perimeter, free surface area, and deposition patterns on the substrate.
我们使用阴影摄影术和红外成像技术实验研究了含有尺寸为 25nm 和 75nm 的 AlO 和 Cu 纳米粒子的静止乙醇液滴在加热基底上的蒸发特性。我们的结果表明，各种纳米粒子存在导致的液滴接触线动力学在蒸发过程中起主导作用。这与广泛存在的假设相反，即静止纳米流体液滴中观察到的增强蒸发速率是由于添加的纳米粒子具有更高的热导率。我们观察到，尽管 AlO 的热导率比 Cu 低一个数量级，但含有 25nm 尺寸 AlO 的液滴表现出固定的接触线动力学，蒸发速度比含有 Cu 纳米粒子（两种尺寸）和表现出粘滑行为的 75nm AlO 纳米粒子的液滴快得多。我们还发现，由于接触线行为的差异，具有不同纳米粒子的液滴显示出明显不同的热图案，这改变了液滴内部的传热。我们通过分析边界、自由表面积和在基底上的沉积图案的时间变化来验证这一反直觉的观察结果。
