Investigation of the settling behavior of arbitrarily shaped particles in diluted and concentrated suspensions

• Applicant: Professor Dr.-Ing. Hermann Nirschl
• Subject Area: Mechanical Process Engineering
• Term: from 2015 to 2018
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 278893567

Suspensions occur in many technical and non-technical processes in chemistry, biology and in environmental engineering. Waste water treatment and ore processing are only two fields in which the treatment of highly polydisperse, heterogeneous suspensions plays a major role. When modelling and simulating such processes, particles are usually assumed to be spherical. But particles are seldom perfectly spherical. Depending on their shape, different effects can occur, which can influence the settling behaviour of a system of particles immensely. Suspensions of fibres are just one example. During settling, fibres can change their orientation. Unlike in suspensions of spheres, this results in a concentration dependant increase or decrease of the settling velocity.Numerical simulations have proven to be an effective tool for the investigation of a number of problems in process engineering. Especially in the field of simulations using a coupling of CFD and the discrete-element method, recently new approaches for the treatment of non-spherical particles have been developed. However, these approaches are limited to the simulation of simple convex geometries, such as convex polyhedrons, or particles composed of spherical particles. In principal the latter method can be used to simulate arbitrarily shaped particles. But a high number of spheres is necessary to model complex particles with good accuracy. The aim of the proposed project is the investigation of the settling behaviour of arbitrarily shaped particles, whose geometry cannot be described by simple analytical expressions, in diluted as well as in concentrated suspensions.In order to achieve this, a numerical model will be used, which has specifically been developed for the simulation of the movement of arbitrarily shaped geometries. Furthermore, approaches for the correct modelling of the contact of arbitrarily shaped particles will be extended and included into the developed simulation package, to allow for the simulation of concentrated suspensions. µ-CT measurements yield 3D data of the geometry of arbitrarily shaped particles with a resolution in the range of microns. Using data from such measurements, the simulation will be validated against sedimentation experiments regarding the time evolution of arbitrarily shaped particles in a suspension. Based on extensive numerical experiments, conducted with the now available simulation platform, new approaches will be developed, with which the settling behaviour of arbitrarily shaped particles in suspensions can be described. These approaches shall only depend on a chosen set of parameters. The proposed project is a first approach towards a simulation platform, with which the settling behaviour of real, arbitrarily shaped particles can be investigated.

• DFG Programme: Research Grants
• Co-Investigator: Professor Dr. Willy Dörfler