Heat transfer to bouncing droplets on superhydrophobic surfaces. (July 2019)

• Record Type: Journal Article
• Authors: Guo, Chunfang; Maynes, Daniel; Crockett, Julie; Zhao, Danyang
• Is Part Of: International journal of heat and mass transfer. Volume 137(2019)
• Page Start: 857
• Page End: 867
• Publication Date: 2019-07
• Subjects: Heat transfer -- Superhydrophobic surfaces -- Droplet impact -- Contact time; Heat -- Transmission -- Periodicals; Mass transfer -- Periodicals; Chaleur -- Transmission -- Périodiques; Transfert de masse -- Périodiques; Electronic journals; 621.4022
• DOI: 10.1016/j.ijheatmasstransfer.2019.03.103
• Languages: English
• ISSNs: 0017-9310

Abstract

Highlights: The heat transfer to impinging drops on superhydrophobic surfaces is explored. Experiments are conducted using high speed visual and IR imaging. The influence superhdryophobic surfaces exert on heat transfer is also presented theoretically. Results from the model and theory show good agreement. Increasing the surface cavity fraction leads to a significant decrease in the heat transfer. Abstract: This study experimentally and theoretically investigates the dynamics and heat transfer to impinging water droplets on superhydrophobic surfaces heated below the boiling temperature. Different from impingement on hydrophilic substrates, the droplets rebound from the surface after the spreading and retraction stages. Experiments are performed using simultaneous high speed video and infrared (IR) imaging to capture droplet dynamics and temperature variation during the transient event. Thermal images allow estimation of bulk droplet temperature change during contact such that the cooling effectiveness for an individual droplet can be estimated. A similarity solution is utilized to yield a model for the transient heat flux at the droplet-wall interface, where convection inside the droplet is accounted for. The experimental and theoretical results for the cooling effectiveness show good agreement. It is revealed that the cooling effectiveness increases with Weber number but decreases with droplet diameter and surface cavity fraction (the ratio of cavity area to total surface area).