Low thermal conductivity substrate accelerates droplet evaporation in transition boiling regime: An abnormal Leidenfrost phenomenon

Abstract

We investigate droplet evaporation on heater surface with different thermal conductivities. The complete droplet evaporation curves are obtained using the phase change lattice Boltzmann model, including four regimes of film evaporation, nucleate boiling, transition and Leidenfrost. Three thermal conductivities of substrate heater (λs) are paid attention. We found that higher λs does not always accelerate droplet evaporation. In the regimes excluding transition regime and Leidenfrost regime, higher λs increases droplet evaporation rate. However, in transition regime, lower λs enhances droplet evaporation, explained by that lower λs triggers second contact of droplet and heater and decreases vapor film thickness underneath droplet. Detailed droplet characteristic features including droplet spreading diameter, projected diameter of suspended drop, and vapor thickness in transition boiling regime are investigated in detail. The droplet oscillation in vertical direction during transition boiling for low thermal conductivity heater is found numerically for the first time. We conclude that low thermal conductivity material is benefit for heat transfer improvement due to the triggering of second contact (TSC) between droplet and solid surface.