Transient measurement of heat transfer in metal quenching with atomized sprays

Abstract

In atomized spray quenching water is atomized with the help of compressed air. The drop flow produced is sprayed onto a hot surface. The drops partially evaporate there and are carried away by air flow afterwards. An irregular collapse of steam film at corners, edges and surface roughness, as known from water spray quenching, does not occur. The influence of water impingement density, distribution of drop diameter, distribution of drop velocity, surface temperature and air flow superposed are investigated with the help of a transient measurement procedure. The measurement procedure is a combination of contact-free measurement of surface temperature achieved through an infrared technique and the measurement of spray characteristics with a 2D-phase Doppler anemometer and a patternator. The atomized spray quenching heat transfer coefficient at temperatures higher than Leidenfrost temperature is nearly independent of surface temperature. The highest influence is exerted by the water impingement density. The heat transfer coefficient increases with increasing nozzle air pressure. Heat transfer coefficients up to 3000 W/(m 2 K) have been measured. Atomized spray quenching results in quality enhancement in metal quenching.