Showing papers by "Raymond Viskanta published in 1989"
TL;DR: In this paper, the effect of plate motion on heat transfer in the film boiling regime was investigated and the importance of radiation heat transfer across the vapor layer was shown to be low even at low plate temperatures.
Abstract: The growth in demand for high-quality metallic alloys has placed greater emphasis on the predictability of cooling methods used in manufacturing processes. Several methods involve forced convection film boiling, which can occur on metallic strips or plates cooled by water jet impingement or on strips inside cooling jackets of continuous annealing processes. Since surface temperatures are typically well above the boiling point of water, a substantial portion of the surface area can involve film boiling. The strip or plate speed often exceeds the water velocities and strongly influences boundary layer development in the vapor and liquid. The purpose of this paper is to estimate the effect of plate motion on heat transfer in the film boiling regime. Conservation equations for mass, momentum, and energy have been solved by the integral method for film boiling in forced convection boundary layer flow on a flat isothermal plate in motion parallel to the flow direction. Unlike previous studies, which have shown that heat transfer is chiefly governed by the plate and subcooled liquid temperatures, heat transfer is shown to also depend on the plate velocity. For large velocities, the importance of radiation heat transfer across the vapor layer is reduced. However, when themore » velocities of the plate and liquid are oppositely directed and of nearly equal magnitude, radiation across the vapor layer can become significant, even at low plate temperatures.« less
49 citations
TL;DR: An active thermal insulation system for protecting a structure from intense incident radiation flux is considered in this article, where the system consists of a high-porosity semitransparent material through which a gas is transpired.
Abstract: An active thermal insulation system for protecting a structure from intense incident radiation flux is considered The system consists of a high-porosity semitransparent material through which a gas is transpired A theoretical investigation is performed to study transient heat transfer by combined conduction, convection, and radiation in a layer of a semitransparent porous medium which is subjected to a high-intensity irradiation and injection of gas through the layer Parametric calculations were performed and are reported in the paper In the presence of gas injection through the porous layer, the temperature profile is totally different from that in the absence of injection, and the total heat flux through the layer vanishes within a small thickness Drastic reduction in time to reach steady-state conditions is also achieved by the gas injection The thickness of the porous layer and the radiation properties such as the single scattering albedo greatly affect the temperature distribution and the insulation performance
27 citations