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Lecture-19-(11-23-10)

Lecture-19-(11-23-10) - APPH 4200 Physics of Fluids Fluid...

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APPH 4200 Physics of Fluids Fluid Instabilities (Ch. 12) November 23, 2010 1. Introduction 2. Bénard Thermal Instability 1
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Henri Bénard, (1874-1939) Henri Bénard was a French physicist who performed experiments on fluids for a Collège de France physics course given by Marcel Brillouin at the turn of the century. Bénard was among the first to study the behavior of a thin layer of liquid, about a millimeter in depth, when heated from below, the upper surface being in contact with air at a lower temperature. Experimenting with liquids of different viscosity, he observed in all cases the formation of a striking pattern of hexagonal cells. In his 1900 article, Bénard used a variety of means to visualize the structures he wanted to exhibit. They ranged from material substances he added to the liquid to optical contrivances such as lighting and the design of special photographic setups. His papers were abundantly illustrated with sketches and photographic clichés. In 1916, Lord Rayleigh provided a mathematical explanation for the onset of instability in such a convective system.
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