Controlling secondary atomization during drop impact on hot surfaces by polymer additives

The effect of small amounts of a polymer additive (200 parts per million polyethylene oxide) on the impact dynamics of liquid droplets on heated surfaces is studied experimentally for Weber numbers between 20 and 100, and wall temperatures ranging from 150 to 350 degrees C. The additive is found to oppose the scattering of secondary droplets from the free surface of the liquid, which can be observed if the wall temperature is not sufficiently high to sustain a continuous vapor layer between the impacting drop and the hot surface. Therefore, the critical temperature value for which secondary atomization disappears, also known as dynamic Leidenfrost temperature, is much lower for drops of a dilute polymer solution than for drops of pure solvent. However, the different behaviors of the two fluids suggest that for dilute polymer solutions the expression dynamic Leidenfrost temperature may not be appropriate, because the additive inhibits secondary atomization even if the vapor layer is unstable.(c) 2005 American Institute of Physics.