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

悬浮物存在于化学、生物和环境工程中的许多技术和非技术过程中。废水处理和矿石处理只是高度分散、多相悬浮液处理中的两个主要领域。在对这类过程进行建模和模拟时，通常假定颗粒是球形的。但粒子很少是完美的球形。根据其形状的不同，可能会发生不同的影响，这可能会极大地影响颗粒系统的沉降行为。纤维的悬浮只是一个例子。在沉淀过程中，纤维会改变它们的取向。与球体悬浮液不同，这会导致沉降速度随浓度的增加或减少。数值模拟已被证明是研究过程工程中许多问题的有效工具。特别是在CFD和离散元相结合的数值模拟领域，近年来出现了处理非球形颗粒的新方法。然而，这些方法仅限于模拟简单的凸几何体，如凸多面体或由球形粒子组成的粒子。原则上，后一种方法可以用来模拟任意形状的粒子。但要对复杂粒子进行高精度的建模，需要大量的球体。该项目的目的是研究任意形状颗粒在稀释悬浮液和浓缩悬浮液中的沉降行为，其几何形状不能用简单的解析表达式描述。为了实现这一点，将使用专门为模拟任意形状几何图形的运动而开发的数值模型。此外，将扩展对任意形状颗粒接触的正确建模的方法，并将其包括在开发的模拟程序包中，以允许对浓缩悬浮液进行模拟。µ-CT测量产生了分辨率在微米范围内的任意形状颗粒的几何形状的3D数据。使用这些测量的数据，模拟将通过关于悬浮液中任意形状颗粒的时间演变的沉降实验来验证。基于广泛的数值实验，利用现有的模拟平台，将开发新的方法，用来描述任意形状的颗粒在悬浮液中的沉降行为。这些方法应仅取决于选定的一组参数。该项目是建立模拟平台的第一步，利用该平台可以研究真实的、任意形状的颗粒的沉降行为。

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.