The separation efficiency of a pilot‐scale zigzag apparatus is investigated numerically using computational fluid dynamics simulations and discrete particle modeling in a coupled manner. The effects of various process variables, like particle size and air flow velocity, and of turbulence models were analyzed. The resulting changes concerning the process performance expressed by separation function and sharpness are discussed. Moreover, the residence time distribution was found to differ for fine and coarse particle discharges. Small particles are easily carried away by the fluid and respond immediately to almost every change in flow velocity. Therefore, they are affected by vortices, which increase their residence times compared to bigger particles.
Die Trennung von Partikelkollektiven erfolgt meist anhand der stationären Sinkgeschwindigkeit als Trennmerkmal. Die Bewegungszustände der Partikel werden bisher sehr aufwendig durch die numerische Lösung des Kräftegleichgewichts ermittelt. In dieser Arbeit werden algebraische Gleichungen hergeleitet, die die zeitlichen Ä nderungen von Sinkgeschwindigkeit und -weg bei laminarer und turbulenter Partikelumströmung beschreiben und lediglich von der Partikelgröße, -dichte und -form abhängen. Unabhängig von der Anfangsgeschwindigkeit lassen sich charakteristische Werte ermitteln, mit denen der Zeitpunkt abgeschätzt werden kann, ab dem eine ausreichende Annäherung an die stationäre Sinkgeschwindigkeit erreicht ist.
Unsteady Settling of Solid Particles in Laminar and Turbulent FlowSeparation of particles is often designed based on the terminal settling velocity as separation parameter. Until now, the particle state of motion is described by solving the force balance equation numerically, which is highly complex. In this work, algebraic equations are presented, which describe the temporal changes of the setting velocity and the displacement at sinking in laminar and turbulent flows around the particle. These equations solely depend upon particle size, density and shape and are independent of the initial velocity. Using the characteristic values, the time period where a sufficient convergence to the terminal sinking velocity is reached, can be clearly identified.
Numerical and Analytical Description of Mechanical Properties of Quasi Tetrahedral AgglomeratesQuasi tetrahedral agglomerates consist of four primary particles, from which three primary particles generally form a base area on which the fourth primary particle is arranged centrally; in the regular case the primary particles having equal radii. The coordinates of the centers of the primary particles are derived for agglomerates exhibiting equal primary particles (regular tetrahedron) and primary particles of different radii (inclined tetrahedron). Moreover, an analytical model for elastic contact deformation is derived on the basis of the Hertz model. Subsequently, tetrahedral agglomerates are modeled using the discrete element method and the compression test between two rigid plates is simulated and compared with experimental results.
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