In 1900 Benard investigated a fluid, with a free surface, heated from below in a dish, and noticed a rather regular cellular pattern of hexagonal convection cells. Rayleigh explained this in 1916 in terms of a bouyancy driven instability, by doing a linear expansion of the equaions in the fluid velocities. It was later understood that in bouyancy driven convection the expected pattern would be a stripe pattern of convection rolls, rather than the cellular pattern observed by Benard. (This is a non-linear phenomena, that was not accessible by the methods Rayleigh used.) The convection observed by Benard is now understood to be driven by temperature dependent surface tension forces rather than by bouyancy. Nevertheless, the stripe or roll state formed in bouyancy driven convection is today referred to as Rayleigh-Benard Convection. Surface tension induced convection is known as Maringoni Convection.
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