| Wed February 2nd 2011 16:00 ZH286 | Seminar | 1. Characterization of Leidenfrost droplets by means of laser interferometry 2. Shear thickening and the rheological characterization of liquid gallium Roeland van der Veen, Nikolai Oudalov |
Details:1. Interferometry and high-speed imaging is used to characterize the shape of the bottom surface of a Leidenfrost droplet. Several setups using a laser and LED light, straight and off-axis light rays and different liquids are considered. The predicted gas pocket and a circular neck region are confirmed, and variations in the neck height profile are measured to be of the order of 10 µm for unconstrained liquid nitrogen drops. By using synchronized video of two cameras, the difference between the neck radius and maximum radius is measured to be 0.54 +- 0.03 capillary lengths, in good correspondence to theoretical predictions.2. The creation of suspensions of liquid gallium with various particles was investigated. Some insights were gained in how particles mix with liquid gallium but due to the high surface tension, oxidation issues and wetting problems no suitable suspension could be made. Instead, the oxidation process of the liquid gallium was investigated in the rheometer by varying the concentration of hydrochloric acid that is used to clean off the oxide layer that causes a yield stress when shearing the liquid. Quantitative results show how much of an effect the pH of the acid has on the yield stress from the oxide layer and thus how strong of an acid is required to observe Newtonian behavior, as well as the ability of an Argon atmosphere to prevent the formation of a yield stress. Furthermore, rheological measurements were performed on the liquid gallium with no oxide layer covering it, to verify literature values of the viscosity of liquid gallium that were obtained using a capillary tube method. | ||
