Stability of annular liquid film in microgravity

The behavior of liquid partly filled in a horizontally installed closed glass pipe was studied experimentally using a drop shaft facility. Just after the pipe was put in microgravity, the liquid layer at the bottom of the pipe first crept up the inner surface of the pipe to form an annular liquid film. It then broke into a number of groups and finally formed liquid plugs with a nearly equal spacing. To explain this behavior by the instability of liquid-gas interface, a simple linear stability analysis was applied to an annular liquid film formed inside a pipe under 0 G. The drop shaft experiment with an annular falling film flow inside a vertical tube was also performed to validate the analysis. The average pitch of the liquid plugs measured in experiments agreed well with the wavelength of fastest-growing disturbance obtained by the theoretical analysis.