Hydrophobic coatings for film boiling based drag reduction on a torpedo model

Previous research has shown that porous, hydrophobic surfaces exhibit a dramatic reduction in critical heat flux (CHF), the amount of heat over a surface area required to initiate film boiling. Film boiling is characterized by the presence of a vapor layer which remains as long as the surface temperature stays above the Leidenfrost point. This vapor layer has poor heat transfer characteristics but has the potential to reduce drag by acting as a buffer between the solid surface and the liquid. The goals of this research were to quantify the drag reduction due to film boiling, examine the durability of the coating and explore the feasibility of this concept for application to a torpedo. A torpedo was chosen due to its high speed and reduced emphasis on durability, since it is only used operationally once. A hydrophobic coating was created in the laboratory using a layer-by-layer (LBL) process and its performance was compared to that of a commercial hydrophobic coating. Drop tests of uncoated and hydrophobic aluminum torpedo models were conducted in a custom-built apparatus housing a water column and a furnace, and recorded with a high-speed video camera in order to measure position versus time. Terminal velocity was extrapolated from the data and used to calculate drag coefficients. The data from this set of experiments showed that film boiling increased average terminal velocity by 23%, which corresponded to a 32% reduction in the drag coefficient.

Department dc:contributor.department

Massachusetts Institute of Technology. Department of Mechanical Engineering.

Grantor dc:publisher

Massachusetts Institute of Technology

Year dc:date.issued

2015

Author dc:creator

• Campbell, Ian J. (Ian James Kenneth)

Advisor dc:contributor.advisor

• Jacopo Buongiorno and Thomas McKrell.

• Mechanical Engineering.

Statement dc:rights

• M.I.T. 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. See provided URL for inquiries about permission.

Licence dc:rights.uri

• http://dspace.mit.edu/handle/1721.1/7582

Language dc:language.iso

eng

Handle dc:identifier.uri

http://hdl.handle.net/1721.1/100104

OAI identifier oai:identifier

oai:dspace.mit.edu:1721.1/100104