The effect of air bubbles on the diffusion-controlled solidification of water and aqueous solutions of ammonium chloride

Gas pores appear during solidification when the gas concentration in the li quid is higher than the gas solubility at a certain location. Since the the rmal conductivity of the gas can be orders of magnitude lower than that of the solid phases, the effective thermal conductivity of the porous solid ma y be lower when gas bubbles are present. In this study, experiments have be en carried out to determine the effect of air bubbles on the process of sol idification and solid formation. Water and ammonium chloride solutions have been solidified under diffusion controlled conditions and the temperature distributions as well as the interface positions have been measured during the experiments. The amount of dissolved air in the liquid was determined b y controlling the pressure of the test cell. which was placed under a bell jar. The results of the experiments show that nucleation of air bubbles at the interface does not significantly affect the effective thermal conductiv ity of the solid. The results art: supported using microscopic experimental observations of the bubble nucleation and growth. (C) 1998 Elsevier Scienc e Ltd. All rights reserved.