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ISSN Online: 2377-424X

ISBN Print: 978-1-56700-474-8

ISBN Online: 978-1-56700-473-1

International Heat Transfer Conference 16
August, 10-15, 2018, Beijing, China

EFFECTS OF SURFACE ORIENTATION ON JUMPING-DROPLET CONDENSATION

Get access (open in a dialog) DOI: 10.1615/IHTC16.cod.023745
pages 2455-2468

Résumé

On nanostructured superhydrophobic surfaces, micrometric condensate is able to spontaneously jump ou-tof-plane powered by the surface energy released upon coalescence events. Since the discovery of jumpingdroplet condensation in 2009, myriad studies have characterized the hydrodynamics of the jumping events and found them to be independent of gravity. An aspect rarely considered, however, is the fact that this gravity-independent droplet removal mechanism enables jumping-droplet condensers to operate in any possible surface orientation. This is in sharp contrast to conventional dropwise condensers, where droplet shedding is facilitated by gravity which mandates a vertical surface orientation. Here, we show how the surface orientation (horizontal or inclined) dramatically affects the surface coverage and droplet size distribution of jumping-droplet condensation over an extended period of operation (3 h). In addition to promoting the expected jumping-droplet removal, we observed that gravitational surface orientations benefit from droplet rolling and falling behavior that is facilitated by coalescence-induced oscillations overcoming the surfaces low contact angle hysteresis and work of adhesion. Although it is possible for jumped droplets to come back to an inclined surface, the frequency of such incident is much lower in inclined surface compared to a horizontal surface. For these reasons, the average droplet size can be significantly reduced by employing a gravitational surface orientation.