EXPERIMENTS ON DOUBLE-DIFFUSION IN A COMPOSITE SYSTEM COMPRISED OF A PACKED LAYER OF SPHERES AND AN UNDERLYING FLUID LAYER

In this paper an experimental study is reported on the problem of doub le-diffusion in a composite system comprised of a liquid-saturated pac ked layer of spheres and an underlying clear (of solid matrix) fluid l ayer. The liquid is a mixture of water and ammonium chloride. The init ial species concentration of the porous layer is linear and stable and of the clear liquid layer uniform. The system is initially isothermal and it is suddenly cooled from above. The study investigates the evol ving temperature and flow fields in the system by utilizing direct tem perature measurements as well as holographic interferometry visualizat ion of the density field. The effect of the thermal Rayleigh number, t he species Rayleigh number, the thermal conductivity of the beads cons tituting the porous matrix, and the height of the porous matrix on the evolving temperature and flow fields are determined. Comparisons of t he experimental results to the predictions of an existing theoretical model define the limitations of this model and the time domain in whic h the model performs acceptably well. The findings of this study are r elevant to double-diffusion phenomena occuring in the mixed phase and liquid regions of solidifying binary mixtures.