Heat Transfer and Fluid Dynamics of Nanofluid Droplets Impacting on a Smooth Heated Surface: Detailing Temporal Scale Effects by Using Time-Resolved Thermography

• Published in: Heat transfer engineering 2021-11, Vol.42 (19-20), p.1720-1731
• Main Authors: Pontes, Pedro, Liang, Qiu J., Matos, Fabrício M., Moita, Ana S., Ribeiro, Ana P. C., Moreira, António L. N.
• Format: Article
• Language: English
• Subjects: Ambient temperature; Distilled water; Droplets; Fluid dynamics; Heat transfer; Impact velocity; Nanofluids; Nanoparticles; Silver; Stainless steels; Thermography; Water drops; Wetting
• ISSN: 0145-7632; 1521-0537
• DOI: 10.1080/01457632.2020.1818418

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.