ARTICLE:

• EXPERIMENTAL AND NUMERICAL STUDY ON COUPLED MICRO-MACRO HEAT AND MASS TRANSFER WITH THE SOLIDIFICATION OF AN NH₄CL-H₂O SOLUTION  download article

Y. Feng
Department of Energy Engineering, University of Science & Technology Beijing, Beijing, China, 100083

H. Nie
University of Science and Technology Beijing, Beijing, China

X. Zhang
Dept. of Thermal Engineering, University of Science and Technology Beijing, Beijing 1000083, CHINA

D. Xia
University of Science and Technology Beijing, Beijing, China

ABSTRACT

In this article, an experiment of unidirectional solidification is performed to study and visualize the solidification characteristics of a binary aqueous ammonium chloride solution system. The growth rate of phase interfaces, the mushy zone depth, solidification time and the temperature distribution along the height of the cell are obtained from experiment. Experimental data are further employed to validate the micro and macro numerical results as well as the coupling method of the micro-macro numerical solidification model presented in the paper. The concentration and temperature profiles in a one-dimensional plate-like control volume at the scale of secondary dendrite arm spacing are calculated by developing and numerically solving the micro heat and mass transfer model considering finite solid and liquid solute diffusion. The microsegregation results are compared with classical analytical models such as Lever rule and Scheil equation. The micro analysis also gives the temperature variation at the micro solid/liquid interface. In addition, macro program, which is developed to couple with micro heat and mass transfer for the solidification, is one-dimensional continuum model for heat and species transport in a binary solid-liquid phase change system. The new phase growth and change of the concentration distribution with the time are numerically analyzed for NH₄Cl-H₂O solution. The coupled micro-macro numerical results are in agreement with experimental data of phase interface movement for NH₄Cl-H₂O solution, which proves the reliability of the micro-macro coupling method.

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