Extraordinary Shifts of the Leidenfrost Temperature from Multiscale Micro/Nanostructured Surfaces

Abstract

In the present work, the effects of surface chemistry and micro/nanostructuring on the Leidenfrost temperature are experimentally investigated. The functional surfaces were fabricated on a 304 stainless steel surface via femtosecond laser surface processing (FLSP). The droplet lifetime experimental method was employed to determine the Leidenfrost temperature for both machine-polished and textured surfaces. A precision dropper was used to control the droplet size to 4.2 μL and surface temperatures were measured by means of an embedded thermocouple. Extraordinary shifts in the Leidenfrost temperatures, as high as 175 °C relative to the polished surface, were observed with the laser-processed surfaces. These extraordinary shifts were attributed to nanoporosity, reduction in contact angle, intermittent liquid/solid contacts, and capillary wicking actions resulting from the presence of self-assembled nanoparticles formed on the surfaces. In addition to the shift in the Leidenfrost temperature, significant enhancement of the heat transfer in the film boiling regime was also observed for the laser-processed surfaces; water droplet evaporation times were reduced by up to 33% for a surface temperature of 500 °C.

Effects of droplet diameter on the Leidenfrost temperature of laser processed multiscale structured surfaces

“…Overall the LFP on the processed surface is higher than that of the polished surface for all droplet sizes investigated. More on the effects of microstructures and contact angle on the LFP can be found on a recently published paper by our group [16]. As for the effects of droplet size, the LFP was shown to shift 45 O C over the range of droplet sizes on the polished sample compared to 85 O C over the same range of droplet sizes on the ASG-Mounds sample.…”

“…A more recent publication by Kruse et al [16], details large shifts in the Leidenfrost temperature on stainless steel via enhanced micro/nanoscale surface roughness. Using Femtosecond Laser Surface Processing (FLSP) techniques to produce superhydrophillic stainless steel surfaces, the LFP was increased from 280 to 455 O C. While others have used coatings, or applied external materials to a surface to change the surface features, our approach does not require the addition of any outside materials.…”

Secondary pool boiling effects

“…Heat flux is measured via embedded thermocouples and surface temperature is calculated. A more in depth description of the FLSP technique and the pool boiling experimental setup is given by Kruse et al 24,26 Five unique surfaces are analyzed in this work, two Inconel, two stainless steel, and one copper. Their surface characteristics have been obtained using a Keyence Laser Confocal Microscope and are tabulated in Table I.…”

Non-wetting droplets on hot superhydrophilic surfaces

“…The reported values of the Leidenfrost temperature on a flat silicon surface ranges from 200 to 390°C 9,[14][15][16][17][18] . Although the majority of the studies on textured surfaces report a relative increase in the Leidenfrost temperature 10,14,[18][19][20][21][22] , a few recent studies reported a significant decrease in the Leidenfrost temperature on microstructured hydrophobic surfaces [23][24][25][26] . For example, del Cerro et al 23 observed suspended droplets on heated surfaces composed of hydrophobic micropillars and microholes at temperatures 70% lower than the Leidenfrost point on a smooth surface.…”