Liquid convection effects on the pushing-engulfment transition of insoluble particles by a solidifying interface: Part I
- PDF / 198,180 Bytes
- 9 Pages / 606.24 x 786 pts Page_size
- 7 Downloads / 172 Views
20/1/04
3:07 PM
Page 613
Liquid Convection Effects on the Pushing-Engulfment Transition of Insoluble Particles by a Solidifying Interface: Part I. Analytical Calculation of the Lift Forces SUNDEEP MUKHERJEE and DORU M. STEFANESCU During the solidification of a liquid containing insoluble particles, the particles can be instantaneously engulfed, or continuously pushed, or pushed and subsequently engulfed. A critical velocity for the pushing-engulfment transition is observed experimentally. Most models proposed to date ignore the complications arising from the liquid convection ahead of the solid-liquid interface. They simply solve the balance between the attractive drag force exercised by the liquid on the particle and the repulsive interfacial force. This work is an effort to calculate analytically the lift forces (Saffman and Magnus forces) under certain assumptions regarding the nature of fluid flow ahead of the solid/ liquid interface. This makes possible the quantitative evaluation of the three experimentally observed regimes occurring during particle-interface interaction: (1) at low convection—no effect on the critical velocity for the particle engulfment transition; (2) at intermediate convection—increased critical velocity; (3) at high convection—no particle-interface interaction. The model was applied to evaluate the gravity level required for microgravity experimental work on particle pushing where the effect of liquid convection during solidification is negligible. This is necessary to validate existing theoretical models that do not take into account fluid flow parallel to the solidification interface.
I. BACKGROUND
THE phenomenon of interaction of particles with solidliquid (S/L) interfaces has been studied since the mid-1960s. While the original interest stemmed from geology applications (frost heaving in soil), researchers soon realized that understanding particle behavior at solidifying interfaces might yield practical benefits in other fields, including metallurgy. The issue is the location of particles with respect to grain boundaries at the end of solidification. A considerable amount of experimental and theoretical research was lately focused on applications to metal matrix composites produced by casting or spray forming techniques. Another application of particle-S/L interface interaction is in the growing of Y1Ba2Cu3O7–8 superconductor crystals from an undercooled liquid. The oxide melt contains Y2Ba1Cu1O5 precipitates, which act as flux pinning sites. The distribution of theses precipitates is crucial for the current density carrying ability of ceramic superconductors. Yet another application of particle-S/L interface interaction is in inclusion management in steel. As for most other metallurgical applications, it is desired to avoid inclusion segregation at grain boundaries. The experimental evidence on transparent organic materials,[1] recent in-situ observations on steel,[2] as well as low-gravity experiments on aluminum-zirconia composites[3] demonstrate that there exists a critical
Data Loading...
