Thermocapillary structure formation in a falling film: Experiment and calculations

The present experimental and numerical study is focused on regular structure formation in a film falling down a vertical plate with a built-in rectangular heater. The data on critical Marangoni number and on the wavelength of the most unstable spanwise mode depending on Reynolds and Weber numbers are obtained. The influence of heating intensity on structure geometry is also investigated. The critical Marangoni number is shown to increase nonlinearly with the increase of Reynolds number. The wavelength of the most unstable spanwise mode appears to depend weakly on Reynolds number and much stronger on Weber number. We obtained that the height of the critical two-dimensional bump is not invariant, but depends almost inversely on Reynolds number. The appearance of a reverse flow in the bump is not a criterium for instability onset. For the different fixed Reynolds number values, the structure width significantly grows with the increase of Marangoni number. Numerical results and experimental data are compared and show good enough agreement. (C) 2006 American Institute of Physics.