(513c) An Efficient Numerical Approach for Transient Simulation of Multiphase Flow Behavior in Centrifuges

Suspensions are intermediate or finished products in a variety of industrial processes. In order to separate the disperse phase of the liquid phase an attached solid-liquid separation step is required. Centrifuges are widely used for this purpose. Despite the wide range of industrial usage only very simplified analytical approaches like the sigma theory are available for dimensioning centrifuges, allowing only the prediction of a separation grain. Therefore the theoretically calculated separation efficiency differs from the actual separation efficiency in operation. The main reason for the inaccuracy of the simplified dimensioning models is the underlying assumption that the flow conditions within centrifuges are well-known and can be described analytically. As the actual flow conditions within centrifuges are time depending and highly complex. In addition to this, the rising sediment influences the flow conditions. The result is a time-depending separation efficiency. Therefore costly experiments in Terms of raw materials and time are currently required to optimize centrifuges.

A more efficient method compared to experiments is the application of numerical simulations. Standard approaches for multiphase flows are Euler-Lagrange and Euler-Euler simulations. To describe the impact of the sediment on the separation efficiency long-term simulations are necessary. With the current simulation approaches these are not feasible to accomplish. In order to realize long-term simulations a new time-efficient simulation procedure for multiphase flows has to be developed.

An efficient method to simulate the multiphase flow in solid bowl centrifuges taking into consideration the flow behavior of the sediment is being developed at the Institute for Mechanical Process Engineering and Mechanics at the Karlsruhe Institute for Technology. The multiphase is modelled as a mixed phase. To consider the flow behavior, the rheology of suspension and sediment are differently modelled and locally and transient calculated within the centrifuge. The flow behavior of the sediment influences the distribution of the sediment and the homogeneity in the sediment height. The focus of the talk will be on the developed simulation approach and results comparing different process and material parameter.