Stability of annular liquid film in microgravity

Behavior of gas and liquid was observed during the experiments, where a horizontally oriented closed glass pipe filled with air and well-wetting liquid was suddenly set in microgravity using a drop shaft facility. Just after it was set in microgravity, the liquid first crept up the inner surface of the pipe to form a liquid film and then broke into a number of groups to form liquid plugs with a nearly equal spacing. The mechanism of this interesting behavior was explained by the linear stability analysis of an annular liquid film, where the average pitch of these liquid plugs agreed well with the most-dangerous wavelength of disturbance obtained by the analysis. The theory was also checked by the microgravity experiment for an annular downward film flow as a initial condition in normal gravity.