ISSN Online: 2688-7231
ISBN Online: 978-1-56700-524-0
Proceedings of the 26thNational and 4th International ISHMT-ASTFE Heat and Mass Transfer Conference December 17-20, 2021, IIT Madras, Chennai-600036, Tamil Nadu, India
Effect of surface roughness on water droplet's disintegration mechanism in different heat transfer regimes
Water spray cooling is a dominant method of cooling adopted in metals industry where high amount of heat is extracted with low coolant inventory. During spray cooling millions of tiny droplets of water interact with the heated surface and extract heat from the surface through different mechanisms. Depending upon surface temperature, surface roughness and impact conditions, droplets exhibit different hydrodynamic behaviour during spray colling. This behaviour forces the droplets to either evaporate completely on the surface or disintegrate into secondary droplets and separate from the main droplet. The contrasting hydrodynamic behaviour leads to variation in the cooling efficiency of the spray. This work presents an experimental investigation of the hydrodynamic behaviour of water droplets impacting rough and heated surface in different heat transfer regimes.
The droplets undergo different hydrodynamic behaviour such as deposition and evaporation in the film evaporation regime; foaming into pagoda shaped bubbles and evaporation in the nucleate boiling regime; thermal atomisation in the lower transition regime; magic carpet breakup in the upper transition regime, and the dry rebound and tip toe in the film boiling or Leidenfrost regime.
The effect of impact conditions, droplet size and surface roughness on each of these hydrodynamic behaviours was assessed. It was found that surface roughness has the most profound influence in the transition regimes. The intensity of thermal atomization and magic carpet breakup is significantly influenced by the surface roughness. In all other regimes, the impact of surface roughness is rather subdued.