Onset of Convection in a Layer of Fluid Cooled from Above

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Abstract
Experiments were performed in which a layer of water was cooled by evaporation from its top surface. The top surface temperature was measured using an infrared radiometer. The onset of manifest convective behavior was determined by visual observation of the motion of a thin layer of ink at the bottom of the water layer. Within the accuracy of the observations, the experiments show that at large Rayleigh numbers the time needed for the fluid to manifest convective behavior and the horizontal wavenumber of the disturbances amplified most at manifestation of convection are independent of the depth of the fluid layer.