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

化学、生物学和环境工程中的许多技术和非技术过程中都存在悬浮现象。废水处理和矿石加工只是处理高度多分散、非均匀悬浮液的两个主要领域。在建模和模拟这些过程时，通常假设粒子是球形的。但是粒子很少是完美的球形。根据它们的形状，可以发生不同的效果，这可以极大地影响颗粒系统的沉降行为。纤维悬浮液只是一个例子。在沉降过程中，纤维可以改变它们的取向。与悬浮液中的球体不同，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一种有效的工具，用于研究过程工程中的一些问题。特别是在使用CFD和离散元方法耦合的模拟领域，最近已经开发了用于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形状，如凸多面体，或由球形颗粒组成的颗粒。原则上，后一种方法可用于模拟任意形状的粒子。但是，大量的球体是必要的，以良好的精度模拟复杂的粒子。该项目的目的是研究任意形状颗粒的沉降行为，这些颗粒的几何形状不能用简单的解析表达式来描述，无论是在稀悬浮液中还是在浓悬浮液中。为了实现这一目标，将使用一个专门为模拟任意形状颗粒的运动而开发的数值模型。此外，任意形状颗粒接触的正确建模方法将被扩展并纳入开发的模拟包，以模拟浓悬浮液。µ-CT测量产生任意形状颗粒的几何形状的3D数据，分辨率在微米范围内。使用这些测量的数据，模拟将验证对沉降实验的时间演变的任意形状的颗粒悬浮液。基于广泛的数值实验，进行了与现在可用的模拟平台，将开发新的方法，其中任意形状的颗粒在悬浮液中的沉降行为可以描述。这些方法应仅取决于选定的一组参数。拟议的项目是第一个方法对一个模拟平台，其中的沉降行为的真实的，任意形状的颗粒可以进行调查。

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.