Long-wavelength instability in surface-tension-driven Benard convection

Surface-tension-driven Benard convection in liquid layers heated from below can exhibit a long-wavelength primary instability that differs from the more familiar instability to hexagonal convection cells studied by Benard (1900). This long-wavelength instability is predicted to be significant in microgravity and for thin viscous liquid layers. Although the instability was predicted over 30 years ago, it has never been observed in any previous experiments. We report the first experimental observations of this long-wavelength instability; the instability is studied in terrestrial gravity for silicone oil layers 0.007- to 0.027-cm-thick on a conducting plate. For shallow liquid depths (...