The Impingement of Droplet Train Onto a Flat Hot Surface With High Wall Superheat

Single droplet based investigations have been performed for hundreds of years. However, in many industrial applications, such as printing, spray cooling and coating etc, numerous droplets will be produced. Droplet train, therefore, is a physical model to approach the complex situation. When the wall temperature is higher than the boiling point, the problem becomes even complex. The subcooling of the droplet, the superheat of the wall also influence the hydrodynamic pattern of the droplet impingement. The hydrodynamic behavior of the water droplet train impinging onto a hot surface (up to 220 °C) is investigated. A droplet train generator is employed to produce stable high velocity (around 6.35 to 19.13 m/s) droplet train (with a diameter around 0.1 mm) at the droplet frequency ranges from 27990 Hz to 55560 Hz. The hot surface is made by copper and heated with cartridge heaters. The effect of wall superheat on flow pattern is experimentally examined and reported. The results show that the wall temperature plays an significant role to the impingement. It influences the spreading speed, stable spreading diameter and splashing angle apparently.