Control of minimum film-boiling quench temperature of small spheres with micro-structured surface

The control of minimum film-boiling quench temperature, TMFB is investigated in water quenching experiments with several micro-structured surfaces on small spheres (diameters 10 and 15 mm) under saturation temperature Tsat and 1 atm. The results show increase in TMFB and is related to the temperature drop across the micro-structures, and affected by its effective thermal conductivity 〈k〉, height L, and base diameter D, based on the fin theory. The local temperature drop of surface microstructure depends on the hybrid Biot number,Bih=hL2/(〈k〉D), where h is the heat transfer coefficient. The liquid-solid contact depends on this microstructure-tip temperature, and a model for TMFB with synthetic surface micro-structure is proposed and compared with the experimental results. The theoretical limit of maximum TMFB (under saturated water at 1 atm) for surface micro-structured small sphere is reached when Bih is beyond 102.