COMPETITION BETWEEN CAPILLARY AND GRAVITY FORCES IN A VISCOUS-LIQUID FILM HEATED BY A GAUSSIAN LASER-BEAM

THE FREE-SURFACE OF A LIQUID SAMPLE (HEAVY OIL) IS LOCALLY HEATED BY IRRADIATION WITH A GAUSSIAN LASER BEAM. PHOTOGRAPHIC RECORDS OF THE SURFACE PROFILE AND FLOW PATTERN ARE PRESENTED. THE FREE-SURFACE PASSES BY AN EARLIER DILATATION STAGE, FOLLOWED BY THE FORMATION OF A PIT IN THE TOP OF THE EXPANDED REGION. A THEORETICAL ANALYSIS BASED ON THE STATIONARY SOLUTION OF NAVIER-STOKES EQUATION WITH TEMPERATURE-DEPENDENTDENSITY AND SURFACE-TENSION IS MADE. IT IS SHOWN THAT THE SIGN OF THE SURFACE-HEIGHT VARIATIONS IN THE HOT REGION DEPENDS CRITICALLY ON THE VALUES OF THE DIMENSIONLESS QUANTITIES CHARACTERIZING THE EXPERIMENT. THE SURFACE PROFILE AND THE VELOCITY DISTRIBUTION ARE CALCULATED AND COMPARED WITH THE EXPERIMENTAL RESULTS. IT IS CONCLUDED THAT THE PHENOMENA OBSERVED ARE DUE TO COMPETITION BETWEEN THE DENSITY- AND SURFACE-TENSION GRADIENTS.