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Impact of Leidenfrost Drops on Spherical Targets.

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Title:Impact of Leidenfrost Drops on Spherical Targets.
Authors:McLean, Mitchel L.
Contributors:Mechanical Engineering (department)
Keywords:Leidenfrost drops
impinging drops
spherical target
experimental fluid dynamics
heat transfer
Date Issued:Aug 2018
Publisher:University of Hawaiʻi at Mānoa
Abstract:Johann Leidenfrost first proposed a physical explanation for the levitation of a water drop on
a metal surface which was at a temperature well above the drop’s boiling point. The drop floats
above the surface and may be propelled vertically by the lateral flow of the vapor layer below.
This phenomenon is known as the Leidenfrost effect. The Leidenfrost effect has been studied
extensively for use in applications as well as its possible detrimental effects on heat transfer
processes. Research advances have been made on impinging drops on superheated planar surfaces
over the past fifteen years. The impingement of drops on spherical targets is less understood and
this has important implications for petroleum processing such as in fluid catalytic cracking.
In this work, an experimental system was designed to heat metallic targets beyond the
Leidenfrost temperature for drop impingement studies. Water drops with Weber numbers ranging
from 10 to 45 were impinged on planar and spherical targets with temperatures from 160 °C to
220 °C. Impinging drops covered a larger surface area on a spherical compared to a planar
surface. In addition, it was observed that the Leidenfrost temperature depended on the ratio of the
drop diameter to the spherical target diameter. For Weber numbers from 10 to 15, drops were
observed to rebound off the target. At Weber numbers from 15 to 30, hole formation was
observed and analyzed. For greater Weber numbers and temperatures, liquid toroids were
observed. The toroidal drop dynamics were measured with high speed photography and these
results were compared with existing models for planar surfaces. The toroids broke up into a
discrete number of smaller drops as a result of a Plateau-Rayleigh instability.
Description:M.S. Thesis. University of Hawaiʻi at Mānoa 2018.
Rights:All UHM dissertations and theses are protected by copyright. They may be viewed from this source for any purpose, but reproduction or distribution in any format is prohibited without written permission from the copyright owner.
Appears in Collections: M.S. - Mechanical Engineering

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