A new approach to the detection of Malkus transitions in a horizontal layer of fluid heated from below

The existence of the Malkus transitions in a horizontal layer of fluid heated from below was examined. An optical technique was used which related such transitions to an independently measurable physical parameter of the flow patterns in the heated layer. Using time-lapse photography, pictures of the flow patterns were taken through the transparent upper boundary of the apparatus. In each test, sufficient time was allowed for the fluid layer to reach thermal equilibrium. Only the steady-state results were used in the analysis. The predominant horizontal scale of the flow obtained from the optical apparatus demonstrated the existence of five transitions at Rayleigh numbers between 5000 and 550,000. The results also appeared to support Busse's multi-alpha solutions for the variational problem formulated to derive an upper bound on heat transport by convection in a heated fluid layer.