|Budget Amount *help
¥1,900,000 (Direct Cost : ¥1,900,000)
Fiscal Year 1991 : ¥600,000 (Direct Cost : ¥600,000)
Fiscal Year 1990 : ¥1,300,000 (Direct Cost : ¥1,300,000)
Experiments for solidification have been conducted using aqueous ammonium chloride (NH_4Cl-H_2O) as a binary mixture. Effects of the initial concentration and the initial superheat of the solution, the orientation and the temperature of a cold surface, and attached brass plates to the cold surface on the solidification process have been systematically examined from observations of timewise variation of the solidification morphology and from measurement of temperature distributions. Numerical calculations have also been performed for various conditions. Obtained conclusions are summarized as follows :
(1) Since solute-rich fluid is released from the solid/liquid two-phase region when the initial concentration, C_o, is set at a value which is smaller than the eutectic one, C_e, solutal convection largely affect the two phase region when the cold surface is located at the side and at the bottom of the cell, and various solidification morphologies are observed.
(2) When the initial concentration is smaller than the eutectic one, the effect of the initial superheat is larger for a larger initial concentration. A large initial superheat causes dense dendrites and the retardation of the development of the two-phase region.
(3) When C_o is larger than C_e and the cold surface is located at the bottom, several projections and channels are observed on the liquid/two-phase interface and in the two-phase region, respectively.
(4) From the melting experiments, it is shown that for small initial concentrations the phenomenon is similar that for C_o=O (the pure water), but for C_o=C_e the thermal convection is coupled with the solutal one, a complicated interface is observed, and the melting rate becomes larger.
(5) Results obtained by the developed numerical method show good agreements with experimental ones, and detailed information (e. g. concentration distribution), which is difficult to measure, is obtained.