Abstract
Long wave analysis of downward liquid film stability in a countercurrent two-phase flow is theoretically studied in terms of a finite-amplitude for a base harmonic and a harmonics of interfacial wave until just befor flooding. We use a method of integral relations of the Navier-Stokes equation in gas and liquid phases to analyze the stability of the interface between the phases. The unstable interfacial wave of the harmonics appears in two different wave number regions, and both regions are included in the unstable regions of the base harmonic. The one region appears in the conditions of a high wave number and a low gas velocity and the other in which the most dangerous wave is indicated appears in a low wave number and high gas velocity. In the former region increase of gas velocity gives a stable liquid film and in the latter region increase of gas velocity induces an unstable interfacial wave.
