Multiscale experimental investigations of flow pattern and slag interaction in a bubble stirred water basin during unsteady operation

This work presents experimental investigations of unsteady multi-phase flow phenomena in a rectangular air stirred water vessel which is intended to model metallurgical ladles with bottom stirring. The investigations focuses on the influence of the alternating frequency of two spatially separated aeration plugs on (I) the global flow field,(II) the turbulence pattern,(III) the efficiency of homogenisation,and (IV) the potential of wall erosion. Multiphase flow data are obtained by an multi-scale in-plane PIV and advanced image processing techniques for efficient phase discrimination. In this multi-scale concept,a smaller sub-region is monitored by a second simultaneous operating PIV system with higher temporal and spatial resolution. In order to asses turbulent flow characteristics,mixing parameters,and the erosive potential,a numerical toolbox has been developed. As the experiments are intended to be used as validation basis for CFD models this toolbox is designed to analyse arbitrary flow fields stemming from either experiments or simulations. To evaluate the vessels mixture characteristic a new mixture potential is introduced and validated which is solely based on the velocity flow-field information. In a second step the differences of these parameters with respect to the presence or absence of an overlaying third phase (oil) at various input-parameter combinations are investigated. The scaling of the oil which substitutes the slag is performed via Laplace similarity. In a final stage further implications of this slag layer (like open-eye formation or slag entrainment phenomena) and their sensitivity to the alternation frequency and gas rate are explored. Therefore,the spatial distribution of the entrained oil droplets are analysed based on optical methods and image processing techniques. The characteristics of the formation and closing of an open-eye with respect to the input parameters are studied and procedures for an eye reduction of up to 62% are presented.