is shown that the well-known two-fluid model, despite its success in quite a few steady and transient two-phase flows, is inherently incapable of modeling the evolution of forced periodic trickling flow of relatively high frequency; the latter, which is of practical significance, is dealt with in a recent experimental study by Giakoumakis et al. The above conclusion is based on physical arguments and results of theoretical analysis using computational tools. The alternative approach, emerging in the literature, of using purely phenomenological models to interpret the experimental results is also discussed.