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ISSN Online: 2377-424X

ISBN Print: 978-1-56700-421-2

International Heat Transfer Conference 15
August, 10-15, 2014, Kyoto, Japan

An Experimental Study of the Leidenfrost Transition for Water on Nanostructured Superhydrophilic Surfaces

Get access (open in a dialog) DOI: 10.1615/IHTC15.evp.009581
pages 2431-2445

Sinopsis

This paper summarizes results of experiments that determined the Leidenfrost transition temperature for droplet vaporization on nanostructured superhydrophilic surfaces. The surfaces tested were coated with an array of zinc oxide nanostructures grown on a polished copper surface by hydrothermal synthesis. The randomly-oriented nanostructures are nominally 0.42 ?m in diameter and 2.3 ?m long with a center-to-center spacing of approximately 0.7 ?m. These surfaces were tested along with polished, bare-to-slightly-oxidized copper and aluminum surfaces in an ISO Class 5 clean room enclosure. The copper substrate for the coated surface was temperature controlled and raised to a specific wall superheat prior to depositing distilled and degassed water droplets onto the surface. Droplets ranging from 2 to 4 mm in diameter were deposited on the surface and the droplet evaporation was recorded with a camera at 240 fps. Effective contact angles were determined from the recorded videos for different surface temperatures. The Leidenfrost transition was detected from a recording of the acoustic signal generated from each experiment during the deposition and subsequent evaporation process. It is defined as the first point for which there is no disturbance to the acoustical signal in the form of a popping sound beyond the initial violent popping generated during the droplet deposition. The presence of the nanostructures had a profound effect on the Leidenfrost point, elevating it to values of 317-376 °C compared with approximately 155 °C on bare copper and 231 °C on bare aluminum surfaces.