Liquid-liquid interface stability in accelerating and constant-velocity tube flows

This paper presents new experimental data on interface stability when one l iquid displaces another in a small-diameter tube. Interface stability theor y suggests that the interface is stable when the displacement is directed f rom a dense and viscous liquid to a less dense and less viscous liquid. Thi s theoretical result has important implications in the evaluation of a fast breeder reactor (FBR) core disruptive accident in that it rules out coolan t-boiling-driven compaction of the reactor-core fuel, and has been classifi ed by Fauske (Nucl. Safety, 17 (1976) 550) as one of several general behavi or principles (GBPs) which tray be used to argue against the occurrence of energetic events that could threaten the reactor vessel. The experimental d ata agreed well with the GBP for accelerated liquid/liquid systems with liq uid density ratios and interfacial tensions similar in magnitude to those o f the FBR mixed oxide fuel/sodium coolant pair. The data agreed well with t he GBP when the displacement occurred in the laminar regime at constant spe ed and the viscosity of one of the liquid components was destabilizing. The investigation also uncovered behavior that was not in concert with the GBP , although this behavior appears to be limited to small density-difference, low-interfacial-tension liquid/liquid systems and is probably not relevant to the FBR application. (C) 2001 Elsevier Science B.V. All rights reserved .