Heat transfer correlation for film boiling during quenching of micro-structured surfaces

This work investigates the separate effects of liquid subcooling, substrate material, and surface micro-structure on the film boiling characteristics. A quenching facility was constructed to conduct vertical quenching experiments using rods with various substrate materials and surface morphologies. The surface morphology is characterized using field emission scanning electron microscopy (FESEM). Stainless steel, zirconium, and Inconel-600 rods are used with a diameter of 9.5 mm that simulates the size of fuel rods in commercial nuclear reactors. Other Inconel-600 rods with different porosity percentages are used to study the effect of fouling on the quenching behavior. The surface temperature and wall heat flux at the surface are deducted from the temperatures measured by the thermocouples embedded inside the rods using an inverse heat conduction code, from which the heat transfer coefficient and Nusselt number are calculated. The data are used to develop a generalized heat transfer correlations that includes the effects of liquid subcooling and substrate materials. It predicted the data within ±40% error band. The results also suggest that the heat transfer coefficient increases gradually as the sample cools down and in higher subcooled pools. Moreover, the variation in the substrate material shows a significant effect on the heat transfer characteristics. However, the surface micro-structure impact on the film boiling regime is negligible.