Effects of liquid subcooling on droplet-wall collision heat transfer in film boiling

Abstract

The effects of subcooling on single droplet-wall collision heat transfer characteristics during film boiling were experimentally investigated. Water droplet subcooling was varied from 0 to 60 K under atmospheric conditions, while the collision velocity and substrate temperature remained constant at 0.7 m/s and 500 °C. The instantaneous and localized heat transfer properties associated with dynamic collision of a water droplet were measured by integrated high-speed shadowgraph and infrared thermometry. Liquid subcooling greatly affected heat transfer. The residence time, effective heat transfer area, and local heat flux were measured. Only the local heat flux correlated strongly with liquid subcooling. When heat flux partitioning at the liquid–vapor interface was considered, i.e., conduction heat transfer into the subcooled droplet and the heat required for evaporation, heat transfer effectiveness was accurately predicted under various subcooling conditions.