Heat Transfer Enhancement and Applications of Femtosecond Laser Processed Metallic Surfaces

In the present work, functionalized 304 stainless steel metallic surfaces were created with the use of a Femtosecond Laser Surface Processing (FLSP) technique. The laser processing technique produces self-organized micro/nanostructures on the surface. The heat transfer performance of various FLSP functionalized surfaces were characterized through pool boiling and Leidenfrost experiments. Enhancement in both the nucleate and film boiling heat transfer were observed through an increase of the critical heat flux and heat transfer coefficient as well as shifts in the Leidenfrost temperature respectively. For both experiments, a polished reference sample was used as a baseline line to compare against the functionalized metallic surfaces. Using deionized water as the working fluid, a maximum critical heat flux of 142 W/cm 2 and a maximum heat transfer coefficient of 67,400 W/m 2-K were found for the processed samples compared to 91 W/cm 2 and 23,000 Wm 2-K for the polished sample. The Leidenfrost temperatures on the FLSP and polished surfaces were experimentally determined using the droplet lifetime technique. Extraordinary shifts in the Leidenfrost temperatures as high as 175 °C were recorded for a laser processed surface relative to a polished reference sample. Enhancement of the film boiling heat transfer was also observed as water droplets were found to evaporate up to 33% faster on processed surfaces compared to polished surfaces. Enhancement of both the film boiling and iii nucleate boiling heat transfer is attributed to increased wettability and capillary wicking of the FLSP surfaces. Besides excellent two-phase thermal transport properties, self-propelled liquid droplets on heated angled FLSP surface microstructures were also achieved. Experiments are carried out to characterize the dynamics and mechanisms of self-propelled liquid droplets on angled FLSP surface microstructures. It was found that the droplet motion direction on angled FLSP surfaces is opposite of that for a surface with conventional ratchet microstructures reported in the literature. A new mechanism for a self-propelled droplet on asymmetric three dimensional self-assembled microstructured surfaces is proposed. iv ACKNOWLEDGEMENTS I'd like to first thank both of my advisers Dr. Sidy Ndao and Dr. George Gogos. You were both extremely helpful in guiding me through my research as well as helping me prepare my work for publications. I would also like to thank all of those in the Center for Electro-Optics and Functionalized Surfaces for providing functionalized surfaces for my work as well as assisting me in the writing process. Fig. 1.1 Standard boiling curve for a …