BUOYANCY EFFECTS OF A GROWING ISOLATED DENDRITE

An axisymmetric dendrite of pure material solidies downward into an undercooled melt Surface energy and kinetic undercooling are negligible The Ivantsov parabolic dendrite is modied by buoyant convection We construct an approximate solution to the growthconvection problem in powers of a buoyancy parameter G The solution depends on Prandtl number P and Stefan number S undercooling When P andor S are large enough buoyancy enhances growth and distorts the dendrite by sharpening the tip and widening the base These results compare well with the experiments on succinonitrile P of Huang and Glicksman and the local theory of Ananth and Gill up to G but overpredict convective eects for larger G When P and S are small enough buoyancy slows growth and attens the tip Physical explanations are given for the dierences in buoyant eects at dierent P The results suggest that neartip eects of buoyancy should be dierent in metallics than in organics Solidication processes are important in a variety of contexts and are of particular i