THE INSTABILITY OF A LIQUID LAYER HEATED FROM THE SIDE WHEN THE UPPERSURFACE IS OPEN TO AIR

When a liquid layer is heated from the side, a monocellular flow devel ops immediately, no matter how small the temperature difference is. If the temperature gradient between the side walls is increased, this fl ow becomes unstable. Laser Doppler velocimetry measurements are report ed here in an attempt to describe the main features of both the basic flow and the instability modes. It is found that before the appearance of traveling waves (the most dangerous mode as predicted by the theor y), stable rolls with their axes perpendicular to the temperature grad ient, span over the whole liquid layer, starting from the hot side, ev en if the aspect ratio (the length of the layer divided by its thickne ss) is very high. This unexpected situation modifies the basic flow. A further increase of the temperature gradient leads to the appearance of a time periodic motion. (C) 1996 American Institute of Physics.