A THEORETICAL SPONGY SPRAY ICING MODEL WITH SURFICIAL STRUCTURE

In an attempt to improve the predictive capability of atmospheric icin g models, we have developed a theoretical model of spongy ice formatio n, including the surficial morphology under a falling supercooled liqu id film. A steady-state model of freshwater spongy spray icing for a s tationary vertical cylinder is presented. A falling film submodel acco unts for the flow of excess liquid on the icing surface. Traditional h eat and mass balance equations at the outer surface of the falling fil m are formulated, along with heat and mass balances for the falling fi lm and for the dendritic freezing zone. The rate of advance of the ici ng interface is calculated by analogy with the rate of advance of free ly-growing ice crystals in bulk supercooled liquid. This allows, for t he first time, the prediction of ice accretion flux and accretion spon giness, for a specific icing configuration and environmental condition s. An analysis of the model's sensitivity to spray temperature reveals that spray supercooling enhances both the rate of accretion and its s ponginess. A comparison of the model's performance with experiments sh ows rather good agreement, and suggests that further research into the nature of the icing surface and its effect on the accreted ice is war ranted. (C) 1998 Elsevier Science B.V. All rights reserved.