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Title:  Stability of planefront and dendritic solidification of binary liquids: The effects of rotation 
Author(s):  Oztekin, Alparslan 
Doctoral Committee Chair(s):  Pearlstein, Arne J. 
Department / Program:  Mechanical Science and Engineering 
Discipline:  Mechanical Science and Engineering 
Degree Granting Institution:  University of Illinois at UrbanaChampaign 
Degree:  Ph.D. 
Genre:  Dissertation 
Subject(s):  Engineering, Mechanical 
Abstract:  Convective and morphological instabilities in horizontally unbounded binary liquids solidified by cooling from below are studied by linear stability analysis. Use of uniform rotation about the vertical to suppress onset of buoyancydriven convection is considered for planefront solidification (PFS) and dendritic solidification (DeS). For dilute PbSn alloys, onset is suppressed significantly at modest rotation rates. PFS is stable at higher Sn concentrations in a rotating configuration than in a nonrotating one. Predicted inhibitory effects of rotation are discussed relative to previous studies of rotating singlecomponent fluids heated from below and thermally and solutally stratified binary fluids. For Hg$\sb{\rm 1x}$Cd$\sb{\rm x}$Te, the liquid density depends nonmonotonically on temperature for small CdTe bulk mole fractions (x$\sb\infty).$ For certain operating parameters (solidification rate, liquidside temperature gradient, x$\sb\infty)$ there exists a critical x$\sb\infty$ below which PFS is unstable at all dimensionless solidification rates $\gamma$, whereas in the normal case in which density depends monotonically on temperature (e.g., PbSn) PFS is stable at any x$\sb\infty$ for sufficiently small $\gamma$. When density varies nonmonotonically with temperature, there exists a critical $\gamma\sb{\rm c}$ such that for $\gamma > \gamma\sb{\rm c}$ PFS is unstable for all x$\sb\infty$ and for $\gamma < \gamma\sb{\rm c}$ PFS is stable for a finite range of x$\sb\infty$. This differs from the normal case, for which at all $\gamma$, PFS is stable for x$\sb\infty$ sufficiently small. These results are discussed in terms of a thermally destabilizing sublayer adjacent to the interface. For Hg$\sb{\rm 1x}$Cd$\sb{\rm x}$Te, modest rotation rates significantly suppress onset of convection. For DeS, the mushy zone, consisting of liquid and solid phases, is modeled as a porous medium with anisotropic permeability. Local porosity and locations of boundaries separating solid, mushy zone, and liquid are treated as dynamical variables. The basic state, computed using a thermodynamically selfconsistent nonlinear solidification model, exists for only some operating parameters. The dendritic solution also exists when PFS is linearly stable. This is discussed in light of previous nonlinear morphological stability analyses. Division of the parameter space according to existence and stability of PFS and DeS is discussed for PbSn. Uniform rotation is shown to be less stabilizing for DeS than for PFS. 
Issue Date:  1992 
Type:  Text 
Language:  English 
URI:  http://hdl.handle.net/2142/23082 
Rights Information:  Copyright 1992 Oztekin, Alparslan 
Date Available in IDEALS:  20110507 
Identifier in Online Catalog:  AAI9236560 
OCLC Identifier:  (UMI)AAI9236560 
This item appears in the following Collection(s)

Dissertations and Theses  Mechanical Science and Engineering

Graduate Dissertations and Theses at Illinois
Graduate Theses and Dissertations at Illinois