Effects of Droplet Diameter and Fluid Properties on the Leidenfrost Temperature of Polished and Micro/Nanostructured Surfaces

An experimental investigation of the effects of droplet diameters and fluid properties on the Leidenfrost temperature of polished and nano/microstructured surfaces has been carried out. Leidenfrost experiments were conducted on a stainless steel 304 polished surface and a stainless steel surface which was processed by a femtosecond laser to form above surface growth (ASG) nano/microstructures. Surface preparation resulted in a root mean square roughness (R_rms) of 4.8 μm and 0.04 μm on the laser processed and polished surfaces, respectively. To determine the Leidenfrost temperatures, the droplet lifetime method was employed using deionized (DI) water and HFE 7300DL. A precision dropper was used to vary the size of DI water droplets from 1.5 to 4 mm. The Leidenfrost temperature was shown to display increases as high as 100 °C on the processed surface over the range of droplet sizes, as opposed to a 40 °C increase on the polished surface. Average increases of the Leidenfrost temperature between polished and processed samples were as high as 200 °C. The experiment was repeated with HFE 7300DL; however, with no noticeable changes of the Leidenfrost temperatures with droplet size whether on the polished or the processed surface. The difference in the Leidenfrost behavior between DI water and HFE 7300DL and among the various droplet sizes can be attributed to the nature of the force balance and flow hydrodynamics at a temperature slightly below the Leidenfrost point (LFP).