Speaker
Oliver Leys
(Institute for Applied Materials)
Description
Advanced tritium breeder pebbles, composed of lithium orthosilicate with additions of lithium metatitanate as a secondary strengthening phase, are produced using a melt-based process. Synthesis powders are heated to high temperatures in a platinum alloy crucible, forming a melt, which is then ejected through a nozzle to form a laminar jet. Longitudinal surface instabilities cause the disintegration of the jet into droplets as described by the Plateau-Rayleigh instability theory. The droplets are subsequently solidified using liquid nitrogen to form the pebbles. A high-speed camera is used to record the droplet formation dynamics at 3500 FPS (frames per second) and offline analysis is performed to determine various jet characteristics including the droplet generation frequency and the jet velocity, from which the instability wavelength can then be derived.
Due to various problems when determining rheological properties of melts at high temperatures, optimum process parameters are usually determined empirically. However, according to Rayleigh, the wavelength on the surface of the jet can also be used to characterise the jet stability and determine the optimum droplet formation parameters. As the operating pressure is the only adjustable parameter during the production ‘jetting stage’ which affects the jet dynamics, it was varied during the production of pebbles at standard temperatures and subsequently the relationship between the operating pressure and wavelength was determined. Additionally, samples were manually extracted at each operating pressure to test the practicality of the study, as well as the relevance of the optimum wavelength as described by Rayleigh’s theory. The results were used to optimise the jet dynamics and subsequently to improve the yield and the pebble size distribution by establishing an optimum operating pressure.
Co-authors
Jorg Matthes
(Institute for Applied Computer Science , Karlsruhe Institute of Technology, Eggenstein-Leopoldshafen, Germany)
Oliver Leys
(Institute for Applied Materials, Karlsruhe Institute of Technology, Eggenstein-Leopoldshafen, Germany)
Patrick Waibel
(Institute for Applied Computer Science , Karlsruhe Institute of Technology, Eggenstein-Leopoldshafen, Germany)
Regina Knitter
(Institute for Applied Materials, Karlsruhe Institute of Technology, Eggenstein-Leopoldshafen, Germany)
