Abstract

This study focuses on the experimental characterization of fluid dynamics and heat transfer processes occurring at the interaction between a nanofluid droplet and a heated smooth surface. Time resolved thermography is used to detail the understanding of the role of the particles in wetting modification that affects the heat transfer mechanisms within different characteristic time scales. Gold and silver nanoparticles are dissolved in distilled water in concentrations ranging between 0.1 and 1 wt%. Millimetric droplets with a fixed initial diameter of 3 mm are generated and impact on a smooth stainless steel surface with velocities varying between 0.8 and 2 ms⁻¹. The surface is heated by Joule effect, from ambient temperature up to 120 °C. Results show that the heat transfer is enhanced by the presence of the nanoparticles, for low impact velocities of the order of 0.8 ms⁻¹ and for earlier stages after impact. However, the heat transfer is deteriorated as the impact velocity is increased, as well as for later stages of impact, even though the spreading diameter of the nanofluid droplets is larger than that of the water droplet.

摘要

这项研究的重点是在纳米流体液滴和加热的光滑表面之间相互作用时发生的流体动力学和传热过程的实验表征。时间分辨热成像用于详细了解颗粒在润湿改性中的作用，润湿改性影响不同特征时间尺度内的传热机制。金和银纳米颗粒以 0.1 至 1 重量％的浓度溶解在蒸馏水中。产生固定初始直径为 3 mm 的毫米级液滴并以 0.8 到 2 ms ^{-1 的}速度撞击光滑的不锈钢表面. 表面通过焦耳效应加热，从环境温度到 120 °C。结果表明，对于0.8 ms ^-1数量级的低冲击速度和冲击后的早期阶段，纳米颗粒的存在增强了传热。然而，尽管纳米流体液滴的扩散直径大于水滴的扩散直径，但随着撞击速度的增加以及撞击的后期阶段，传热会恶化。