[en] A combined experimental and analytical program undertaken to evaluate an interfield momentum coupling model used in the computer code SIMMER is described. The behavior of a slugging, vapor-particle flow system was observed and recorded using gamma densitometry, differential pressure measurement, and motion pictures. The primary parameter observed was slug period. When the system was modeled using SIMMER, the calculated behavior of the flow was qualitatively similar to that observed experimentally, but both the period and maximum slug height were underestimated, indicating too weak coupling between the vapor and particle fields. The SIMMER drag correlation was modified, resulting in much better agreement. Final discrepancies between experiment and analysis are discussed