Two-Phase Description of Hydrodynamic Fragmentation Processes Within Thermal Detonation Waves

Abstract

Large-scale vapor explosions are described by thermal detonation waves, proceeding through a fuel-coolant mixture. A two-phase flow model is used for modeling the processes inside a wave. One phase is formed by the drops of melt and the other by the coolant and the fragments. For the interfacial transfer relations between the phases new descriptions are presented, which extend earlier thermal detonation models. The fragmentation behavior can be calculated from two different models, one based on deformation breakup and Taylor instability and another describing fragmentation by stripping of capillary waves induced by shear flow instabilities. In addition to the time development of the fragmented mass, the models give also the actual sizes of the fragments. Results of the fragmentation models are compared with the experiments on hydrodynamic fragmentation of single drops of gallium in water flows. For vapor explosion experiments with tin-water and salt-water systems the detonation cases are determined using the wave stripping model.

Fragmentation of a molten metal droplet in an ambient water flow

“…This mechanism of instabilities developing and being stripped at the equator is similar in concept to the model proposed in [13] in which wave rings around the axis of the droplet in the flow direction, are stripped as they travel towards the equator of the drop. The main difference between the model and the experimental observations is the type of instability that is dominant.…”

“…In a propagating meltcoolant interaction, the fine fragmentation of the melt governs the rapid increase of interfluid surface area and heat transfer. Previous studies of propagating vapour explosions [12,13] have shown that the fragmentation mechanisms of single melt drops can be classified into two main groups: thermally-induced mechanisms, driven by vapour film collapse and subsequent bubble dynamics, or hydrodynamic fragmentation mechanisms due to the relative velocity between the melt and coolant. Although much is known about each class of fragmentation mechanism, the transition from thermal to hydrodynamic fragmentation as the ambient flow velocity is increased, which is relevant to the developing phase of a steam explosion, is poorly understood.…”

Simultaneous high speed digital cinematographic and X-ray radiographic imaging of a intense multi-fluid interaction with rapid phase changes

“…A number of phenomenological models have been proposed to depict the fine fragmentation of the high temperature liquid [1], which are commonly categorized into two groups: thermal [2,3] and hydrodynamic [4,5]. The thermal fragmentation models are based on the formation of micro coolant jets that penetrate the surface of the hot melt or the generation of local high-pressure regions which stretch and break up the melt.…”

A hydrodynamic fragmentation model based on boundary layer stripping

“…DS-15 and 18 of Kim's experiment (Kim, 1985) on gallium droplets, prediction model based on gas-liquid system (Pilch and Erdman, 1987), capillary wave model and Taylor wave model (Burger, 1984) are introduced to validate the calculations of Eq. (27).…”

“…Ranger and Nicholls (1969) built a boundary layer stripping model based on droplet-stripping process in aerodynamic experiments. Burger (1984) gave an introduction to Rayleigh-Taylor instability model and capillary wave stripping model.…”