Enhanced pool boiling critical heat flux with a FeCrAl layer fabricated by DC sputtering

Abstract

During the recent development of Accident Tolerant Fuels (ATFs), FeCrAl has received attention for its excellent high temperature performance and slower reaction kinetics with steam. In this study, we fabricated a FeCrAl layer on top of the metal substrate by DC sputtering. We found that the substrate temperature and sputtering time affected the surface characteristics of the FeCrAl-layered heaters. A substantial increase in surface roughness was realized in the substrate temperature range from 150 to 600 degrees C during DC sputtering. Extensive pool boiling critical heat flux (CHF) experiments were conducted to confirm the effect of the FeCrAl layer on the thermal safety margin of the heaters. Substantial CHF enhancement was achieved for the first time with all types of FeCrAl-layered heaters. The highest CHF enhancement (60%) was observed for the layer sputter deposited for 1 h at a substrate temperature of 150 degrees C. State-of-the-art CHF models incorporating the textured surfaces were employed to elucidate the physical mechanism for the improved CHF. The enhanced CHF was attributed to an increase in the roughness factor at the micrometer scale. This, in turn, could have a desirable effect on shortening the rewetting interval with the FeCrAl-layered heaters. Systematic experiments related to the surface characteristics and high-speed bubble departure images were also obtained. This first-of-a-kind CHF enhancement with FeCrAl-layered heaters is expected to find use for an advanced fuel system.