Abo Bibliothek: Guest

ISSN Online: 2377-424X

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

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

High Speed Observation and Measurement of Surface Temperature and Surface Heat Flux During Impact of a Droplet on Hot Surface

Get access (open in a dialog) DOI: 10.1615/IHTC15.min.008703
pages 4765-4779

Abstrakt

Transient transition boiling phenomena that occur when a single ethanol droplet comes in contact with a hot nickel surface has been studied experimentally. To do so, an extremely fast response chromel-nickel thermocouple was fabricated at 3 ????m beneath the surface. This sensor has a very short response time of 80 ????s enough to measure transient boiling heat transfer. To the best knowledge of the authors, for the first time such fast response thermocouple has been introduced to study the transient transition boiling phenomena. The surface temperature and surface heat flux were evaluated using an inverse heat conduction analysis that was interpreted and discussed in connection to the observed boiling phenomena done by a high speed video camera (22,000 fps). The experiment has been conducted for extensive initial surface temperature range including liquid superheat limit temperature of ethanol with three different liquid subcoolings and three different droplet impact velocities. Our major focus and interest was in stable vapor film generation time which was required to change from initial wetted nucleation boiling to film boiling on the hot surface. The generation time may govern whether a hot surface holds wetting (nucleation boiling) or not (dryout) after liquid-solid contact. Furthermore, we also calculated the total cumulative energy needed to generate a stable vapor film after the droplet impact on the hot surface.