Gas-liquid two-phase flow in minichannels and microchannels display a unique flow pattern called ring film flow, in which stable waves of relatively large amplitudes appear at seemingly regular intervals and propagate in the flow direction. In this work, the behavior of ring films has been investigated experimentally in a 150 μm diameter silica tube experimentally to elucidate their generation mechanism and propagation behavior. High speed video images were taken at 6,000 frames per second and the formation of ring films and the relationship between the wave amplitude and velocity were determined. The results indicate an interfacial instability leading to the formation and growth of ring waves with both low and high wave amplitudes. The wave velocity is correlated to the wave amplitude with the large amplitude waves moving much faster than the low amplitude waves. As a result, coalescence of large and low amplitude waves has been observed.

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