Gel Beads to Investigate Sedimentation

Separation of liquid-liquid dispersions with multiple phases involves different interactions between the different dispersed species present in the system, which makes it difficult to predict e.g. the separation behaviour. Nevertheless such systems are relevant in chemical engineering e.g. for systems involving gas bubbles and simultaneously solid particles like in a fermentation broth. Models for describing the sedimentation behaviour as a basis for settler design are available in principle but have not been systematically validated for variation in size-distribution and e.g. density differences between the various species in the system. Thus, to design technical separation equipment, the separation process has to be better understood, which requires the study of the sedimentation as a first step.
This project is focused on the interactions which may occur between each species during the sedimentation e.g. the effect on sedimentation of descending particles when they meet ascending drops. However, a proper study of the sedimentation with fluid phases is difficult due to other phenomena occurring simultaneously, e.g. coalescence. To overcome this issue, the use of gel beads is proposed, which due to their solid interface cannot coalesce. In addition, it is easy to define their parameters which are the density, the hardness and the size distribution. Besides, they can also be preserved during an extended period of time, experiments can thus be reproduced many times with identical beads.
During the project, gel beads are designed with different particle size distributions and with different densities. Different batches of the produced gel beads will be mixed to simulate systems with different dispersed phases discriminated via density and different size distributions. With these multiple dispersed phases Experiments will be performed in a settling cell in order to evaluate the overall sedimentation velocity at certain hold up. Simultaneously a new method for measurement of local hold-up profile in the dispersion is tested, which allows hold-up measurement even in opaque systems. Finally sedimentation models found in the literature are compared and adapted to experimental results for predict the sedimentation of systems which involve different dispersed phases.
In the presentation the new hold-up measurement will be presented together with an error analysis, experiments on the sedimentation of multiple dispersed phases and the model evaluation will be presented.