Falling liquid films in confined channels
Résumé
Thin liquid films flowing in strongly-confined channels are common in several engineering equipments, such as heat exchangers and distillation columns. In these equipments, the liquid film is driven by gravity and eventually interacts with a counter-current gas flow. This work aims at studying how the stability of the falling film and the non-linear surface waves are affected by
the gas phase in the case of very strong confinement. Using linear stability calculations and experiments, we find that strong confinement stabilizes the liquid film up to the point of fully suppressing the Kapitza instability. In particular, we identify the critical confinement at which this suppression occurs with both aerostatic gas, i.e. when the driving pressure difference balances the weight of the gas column, and counter-current laminar gas flow. Non-linear saturated waves which develop at the gas-liquid interface are then investigated by means of our Direct Numerical Simulation. We characterize how and under what flow conditions these waves are modified by strongly confining the gas, and identify the confinement threshold at which their amplitude is either reduced or increased by the gas flow.