ABSTRACT
Flow instabilities are undesirable in boiling, condensing, and other two-phase flow processes for several reasons. Sustained flow oscillations may cause forced mechanical vibration of components or system control problems. Flow oscillations affect the local heat transfer characteristics and may induce boiling crisis. Flow stability becomes of particular importance in water-cooled and waters moderated nuclear reactors and steam generators. An instability is compound when several elementary mechanisms interact in the process and cannot be studied separately. This chapter describes the physical mechanisms and summarizes the experimentally observed phenomena of flow instabilities. Single dynamic instability involves the propagation of disturbances, which in two phase flow is itself a very complicated phenomenon. Disturbances are transported by two kinds of waves: pressure waves, and void waves. Maulbetsch and Griffith performed a stability analysis of an idealized model of the system in which pressure drop instabilities had been observed.
