EFFECT OF BOUNDARY CONDITIONS AND INITIAL CONCENTARTIONS ON THE SOLIDFICATION OF BINARY MIXTURE IN TRAPEZOIDAL CAVITY

摘要

The solidification of binary mixture (NFL_4Cl-H_2O) inside a trapezoidal cavity is investigated experimentally in this study. The experiments are carried out in a trapezoidal cavity measuring 65 mm x 130 mm x 150 mm with inclined angle of 69°. Solidification of ammonium chloride occurs on the left inclined copper wall held under constant heat rate condition while the other walls are maintained at adiabatic conditions. Particle image velocimetry was used in this study for visualization of the dynamic field during the solidification process. The temperatures of the solution inside the cavity and the boundary walls were measured by 32 thermocouples during the solidification process. Convective flow field, temperature distribution and frozen layer thickness were obtained for different initial concentrations of ammonium chloride varying from 0 to 19.8 % (sub-eutectic and near-eutectic growth) and various boundary conditions (T_(cold) = -30 ℃ to 0 ℃). The results obtained in the course of study reveal that (1) the solidification rate is higher during initial stages of the solidification process, (2) the process of solidification is slower with increase in the initial concentration levels of the ammonium chloride and (3) the initial concentration play a significant role in the evolution of convection flow patterns.