Controlling the leidenfrost temperature through laserassisted surface micro/nano texturing

In the present work, the effect of surface features and wettability on the Leidenfrost temperature are experimentally investigated. The surface features were fabricated on a 304 stainless steel surface using a femtosecond laser. This technique allows for a wide variety of surface microstructures (spikes, mounds, holes, and pyramids) to be created, ranging in size, shape, and spacing. Changing the fluence and shots of the laser produce different micro/nano textured surfaces. A smooth surface sample was fabricated as a reference surface with a measured Leidenfrost temperature as a benchmark. The droplet lifetime experimental method was employed to determine the Leidenfrost temperature for both the smooth and the textured surfaces. A precision dropper was used to control the droplet size to 4.2 microliters (diameter of 2.0mm) while surface temperatures were measured by means of an embedded thermocouple. In comparison to the smooth stainless steel surface, a shift in the Leidenfrost temperature, as high as 55 °C, was observed with the textured surface. The textured surface hasa high emissivity, compared to the smooth surface. As a result, in addition to the shift in the Leidenfrost temperature, significant enhancement of the film boiling heat transfer coefficients were also observed.