Long wave analysis of interfacial wave stability in vertical countercurrent two-phase flow

Long wave analysis of downward liquid film stability in a countercurrent tw o-phase flow is theoretically studied in terms of a finite-amplitude for a base harmonic and a harmonics of interfacial wave until just before floodin g. We use a method of integral relations of the Navier-Stokes equation in g as and liquid phases to analyze the stability of the interface between the phases. The unstable interfacial wave of the harmonics appears in two diffe rent wave number regions, and both regions are included in the unstable reg ions of the base harmonic. The one region appears in the conditions of a hi gh wave number and a low gas velocity and the other in which the most dange rous 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 an d in the latter region increase of gas velocity induces an unstable interfa cial wave.