Flow transition criteria of a liquid jet into a liquid pool

Abstract

To better understand the fundamental interactions between melt jet and coolant during a coredisruptive accident at a sodium-cooled fast reactor, the jet breakup and droplet formation in immiscible liquid-liquid systems were studied experimentally. Experiments using two different pairs of test fluids were carried out at isothermal conditions. The observed jet breakup behavior was classified into characteristic regimes based on the classical Ohnesorge classification in liquid-gas systems. The variation in breakup length obtained in the present liquid-liquid system was similar to that in a liquidgas system. The droplet size distribution in each breakup regime was analyzed using image processing and droplet formation via pinch-off, satellite formation, and entrainment was observed. The measured droplet size was compared with those available from melt jet experiments. Based on the observation and analysis results, the breakup regimes were organized on a dimensionless operating diagram, with the derived correlations representing the criteria for regime boundaries of a liquid-liquid system. Finally, the experimental data were extrapolated to the expected conditions of a sodium-cooled fast reactor. From this, it was implied that most of the hydrodynamic conditions during an accident would be close to the atomization regime, in which entrainment is the dominant process for droplet formation. Nomenclature d droplet diameter Dj0 nozzle diameter

Color-gradient lattice Boltzmann model with nonorthogonal central moments: Hydrodynamic melt-jet breakup simulations

“…The hatched gray region shows the reactor conditions estimated in Ref. [13]; the FT experiment fell within this region. This diagram predicts that the breakup will be in the atomization regime (III).…”

“…Recently, Saito et al [13] used a series of observations to classify the jet breakup regimes in liquid-liquid systems, as shown in Fig. 1(a), extending Ohnesorge's classification scheme for liquid-gas systems [7][8][9].…”

Lattice Boltzmann modeling and simulation of liquid jet breakup

“…A simulation in which the parameters are exactly matched to the target experiment is performed and compared with experimental data. Finally, we assess the reproducibility of the breakup regimes expected by the dimensionless-regime map [22]. Sec.…”

“…(30), the term ∇ · S arises from the perturbation operator given by Eq. (22) and is equivalent to the interfacial force based on the CSF concept [53]; the capillary stress tensor, S, is given by…”

“…The Rayleigh-Taylor instability is a fundamental interfacial instability that is induced when a heavy fluid is placed over a light one subjected to a slightly disturbed interface in a gravitational field [21]. The Rayleigh-Taylor instability has received considerable attention owing to its extensive applications, e.g., in the fundamental process of melt jet breakup [20,22]. To our knowledge, this is the first time a color-fluid model has been applied to the threedimensional Rayleigh-Taylor instability.…”