Further Experimental Investigation of Freeze-Lining/Bath Interface at Steady-State Conditions

Abstract

In design of the freeze-lining deposits in high-temperature reaction systems, it has been widely assumed that the interface temperature between the deposit and bath at steady-state conditions, that is, when the deposit interface velocity is zero, is the liquidus of the bulk bath material. Current work provides conclusive evidence that the interface temperature can be lower than that of the bulk liquidus. The observations are consistent with a mechanism involving the nucleation and growth of solids on detached crystals in a subliquidus layer as this fluid material moves toward the stagnant deposit interface and the dissolution of these detached crystals as they are transported away from the interface by turbulent eddies. The temperature and position of the stable deposit/liquid interface are determined by the balance between the extent of crystallization on the detached crystals and mass transfer across the subliquidus layer from the bulk bath. A conceptual framework is developed to analyze the factors influencing the steady-state deposit/interface temperature and deposit thickness in chemical systems operating in a positive temperature gradient. The framework can be used to explain the experimental observations in a diverse range of chemical systems and conditions, including high-temperature melts and aqueous solutions, and to explain why the interface temperature under these conditions can be between T _liquidus and T _solidus.