Scale analysis for water jet impingement over a horizontal flat plate under film boiling configuration

Abstract

A scale analysis has been performed to investigate the film boiling heat transfer associated with cooling of a horizontal flat plate through water jet impinging. The forced convection film boiling of water is treated by classifying a wide spectrum of subcooling regime by two extreme situations of low and high subcooling dominated by mass evaporation and sensible heating respectively. A simple expression of heat ratio is derived for executing the classification. The ratio is derived by considering the heat and mass transport phenomena and vaporization effect. The radiation heat effect is considered, while obtaining the scale of wall Nusselt number for convective and total heat transfer under both low and high subcooling cases. The comparison of the developed correlations, based on scaling, are made for the wall superheat between 290 and 1100 °C and jet velocity of water between 0.4–3.2 m/s along with the variation of water subcooling between 5 and 45 °C. The proper coefficient of the scaling is developed by making overall comparison of the data from the analysis with experimental data to predict the heat transfer. The effect of liquid to vapor viscosity ratio indicates a substantially higher Nusselt number for the jet impingement of plate under film boiling condition. The density ratio influences the heat transfer only at low subcooling condition. A lower Jakob superheat number, higher Jakob liquid subcooling number, and higher jet Reynolds number increases Nusselt number.