Flow and morphological conditions associated with the directional solidification of aqueous ammonium chloride

Technical Report · Fri Jan 01 04:00:00 EST 1993

DOI:https://doi.org/10.2172/6794124· OSTI ID:6794124

Magirl, C S; Incropera, F P

Using 27% aq. NH[sub 4]Cl solutions as transparent analog, shadowgraphy and dye injection were used to observe flow and morphology in unidirectional solidification (UDS) from below. Dendritic crystals that form at the cold surface reject lighter, solute-deficient fluid, and instability is shown by finger-type double-diffusive convection. As the mushy two-phase region grows, perturbations at the liquidus interface cause localized remelting and downward development of channels. Solsutal plumes emanate from the channels, and in time, double-diffusive convection layers also form in the melt. When the solution is chilled at the sides as well as at the bottom, conditions are influenced by detachment and settling of crystals from the sidewall and by plumes from slanted channels. When a slow, oscillatory rocking motion is imposed on UDS, the freckle-type segregates in the final cast is suppressed. Within the melt, plumes and double-diffusive convection are eliminated. Inertially induced convection mixes the melt and produces a dense slurry. Although channels are eliminated from the bottom mushy region, overall heat transfer and macrosegregation in the cavity are unaffected by the slow rocking. Numerical simulations qualitatively predict trends in the field variables and provide insights on interdendritic flows and macrosegregation (freckle-, A-type segregates), although its quantitative predictions are hampered by simplifying assumptions.

• Research Organization: Purdue Univ., Lafayette, IN (United States). Heat Transfer Lab.
• Sponsoring Organization: DOE; USDOE, Washington, DC (United States)
• DOE Contract Number: FG02-87ER13759
• OSTI ID: 6794124
• Report Number(s): DOE/ER/13759-6; ON: DE93008886
• Country of Publication: United States
• Language: English

Related Subjects

36 MATERIALS SCIENCE
360102 -- Metals & Alloys-- Structure & Phase Studies
37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CHEMISTRY
400201* -- Chemical & Physicochemical Properties
ALLOY SYSTEMS
AMMONIUM CHLORIDES
AMMONIUM COMPOUNDS
AMMONIUM HALIDES
AQUEOUS SOLUTIONS
BINARY ALLOY SYSTEMS
BINARY MIXTURES
CHLORIDES
CHLORINE COMPOUNDS
CONVECTION
DISPERSIONS
DOCUMENT TYPES
ENERGY TRANSFER
FLOW VISUALIZATION
HALIDES
HALOGEN COMPOUNDS
HEAT TRANSFER
MASS TRANSFER
MIXTURES
MOTION
NUMERICAL SOLUTION
PHASE TRANSFORMATIONS
PROGRESS REPORT
SEGREGATION
SIMULATION
SOLIDIFICATION
SOLUTIONS