Modeling Instabilities in Volatile Liquid Films Flowing over Locally-Heated Substrates using COMSOL

N. Tiwari, and J. M. Davis
Department of Chemical Engineering, University of Massachusetts, Amherst, MA, USA

The dynamics and stability of a liquid film flowing under the influence of gravity over a planar surface with a rectangular heater are modeled using COMSOL. The temperature variation at the liquid-air interface near the heater induces a gradient in surface tension, or Marangoni stress, that distorts the film shape and gives rise to a pronounced ridge.

The shape of the flowing film near the heater is computed for a range of the governing parameters. A linear stability analysis based on the long-wave approximation reveals that the ridge breaks up into parallel rivulets aligned with the flow for sufficiently large heating, which corresponds to a critical value of the Marangoni parameter.

For sufficiently volatile films and large heating, thermocapillary instability can also develop above the heater. Nonlinear simulations of the momentum and energy equations are used to study the evolution of the two qualitatively different instabilities.

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