Overview

In 1900 Henri Bénard heated whale oil in a pan and noted a system of hexagonal convection cells. Lord Rayleigh in 1916 analyzed this in terms of the instability of a fluid heated from below. Since that time Rayleigh–Bénard convection has been taken as the classic example of thermal convection, and the hexagonal planform has been considered to be typical of convective patterns at the onset of thermal convection. Fifty years went by before it was realized that Bénard's patterns were actually driven from above, by surface tension, not from below by an unstable thermal boundary layer. Experiments showed the same style of convection when the fluid was heated from above, cooled from below or when performed in the absence of gravity. This confirmed the top-down surface-driven nature of the convection which is now called Marangoni or Bénard–Marangoni convection.