Dynamical Processes in Slurries
After a brief review of the classical thermodynamics of mixed phase systems, attention is focussed on slurries, i.e. systems of mixed solid and liquid phases in which the solid is in the form of small grains. Slurries of two types are considered: those occurring in single constituent systems (“pure substances”) and those occurring in binary alloys. The reason why mixed phase regions necessarily arise in rapidly chilled systems is explained by means of an example. The effects of surface tension on the nucleation of grains from a supercooled liquid are discussed and it is argued that these effects are small in a “mature” slurry. A way of theoretically modeling moving slurries through mixture theory is developed, and some of the ingredients of such a mixture theory are discussed; a possible difficulty concerning history-dependent behavior is noted. Potentially useful limiting forms of the theory are identified, including both the “dusty gas limit” in which the two phases do not exchange mass, and the “fast melting theory” in which local phase equilibrium is established instantaneously, as compared with the overall timescale of the system.
Fully self-consistent theories are developed for the thermomechanics of both one- and two-constituent slurries. These theories satisfy the conservation laws for mass, momentum, angular momentum and energy, do not permit under any circumstances entropy to decrease, allow the two phases to “interact” (i.e. exchange mass, momentum and energy by melting or freezing), and satisfy the principles of frame indifference (including Galilean invariance). Simplifica -tions of these theories are discussed. The propagation of sound across a one-constituent slurry is studied at high and low frequencies.
KeywordsBinary Alloy Entropy Production Mushy Zone Mixed Phase Pure Substance
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