Freezing on Subcooled surfaces, Phenomena, Modeling and Applications
The earliest scientific study of the layer growth of ice on subcooled surfaces generated the famous Neumann problem of partial differential equation in the middle of the 19th century, which greatly contributed to the establishment of modern heat and mass transfer theory. In the classical Neumann problem, the growth direction of ice layer is perpendicular to the cooling surface, i.e. ice appears on the cooling surface as a uniform thin film and then grows thicker. However, microscopic observation of the onset of ice formation in this study showed that ice patches appeared in separate of spots on the subcooled surface. They spread out along the cooling surface to form ice films, during this time the ice thickness was almost unchanged until the cooling surface was fully covered. Heat flux across the cooling surface in this time was subjected to a steep increase. After this initial period, the ice film then grew into a thicker layer fouling the cooling surface. This paper presents the real-time microscopic observation on the phenomena of freezing on subcooled surfaces; the new mathematical problem of heat transfer for the onset time of freezing; the heat transfer driven growth-kinetics of ice film. Understanding of water freezing on subcooled surface benefits a number of engineering fields, such as freeze concentration (or desalination); cold storage and transportation in air conditioning system, etc.