Liquid Jet Impingement Cooling of Strip Metals

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A major objective of the proposed investigation is to address fundamental issues related to the cooling of high temperature, high heat flux surfaces by liquid jet impingement. Such issues concern the delineation of regions associated with single phase forced convections, forced convection nucleate boiling, and film boiling on a heated plate exposed to a single jet or an array of jets. Transitions from one region to another are strongly influenced by jet hydrodynamic condition (turbulence intensity and velocity profile), by the transition from a laminar to turbulent boundary layer for flow on the plate, and by the interactions of such flows for an array of jets. Photography will be used to identify nucleate, transition and film boiling, while local heat transfer measurements will be used to determine convection coefficients in single and two-phase flow regimes. Parameters to be studied include hydrodynamic and geometrical features of the jet and jet arrays, plate speed and surface conditions, and the presence of noncondensibles in the liquid. Where possible transition and convection heat transfer coefficient data will be correlated. In an attempt to predict heat transfer data for the single phase forced convection and film boiling regions, finite-difference and integral solutions of the conservation equations will be developed. To assess the applicability of basic results inferred from laboratory studies, flow visualization experiments will also be performed at Inland Steel Corporation's hot rolling mill, and scaling considerations will be addressed by contrasting results obtained in the laboratory and the mill. A model which uses laboratory generated data to predict the thermal response of strip steel under mill conditions will be developed, and predictions will be compared with available data. In recent years, cooling by means of low turbulence, liquid jets has become widely used in the processing of primary metals such as steel and aluminum. However, currently the knowledge base required to support the establishment of optimal design and operating conditions is limited, and recourse must be made to trial-and-error procedures. In a single application, cooling of hot metals simultaneously involve regions of single phase forced convection, forced convection nucleate boiling, and film boiling, and the attendant temperature history of the metal strongly influences its final mechnical and metallurical properties. To develop tools for establishing optimal design and operating conditions, it is essential that flow and heat transfer processes associated with jet impingement be well understood. This research program should provide such a knowledge base.