以離散相模型(DPM)評估立式磨粉機之效能

Abstract

立式磨粉機為一兼俱粉碎塊狀材料、運輸粉料、篩選粉料(和再粉磨)等特性 的機台，由於其優異的工作特性目前廣泛的運用於工業界各大不同領域中，如火 力發電、水泥業、化工業…等。立式磨粉機的改造與升級涉及多種領域之工程問 題, 而本文以立式磨粉機腔內流場的研究為主。本研究以ANSYS-FLUENT 電腦 數值模擬來進行立式磨粉機的參數化設計。利用控制體積法在所有的網格內求解 下列各統御分程式:RNG k-ε Model 求解立式磨粉機腔內部紊流場; Discrete Phase Model(DPM)求解粉磨顆粒的運動形態;求解Multiple Rotating Reference Frame(MRF)或Slidng Mesh Method(SMM)修正下的Navier-Stokes equation以描述立式磨粉機中旋轉機械所造成的流場行為。 本研究主要有兩大目的:一為提高磨腔區細顆粒的傳輸效率，二為以數值模擬 的方式預測選粉機的產品切割粒徑。第一個目的我們透過耦合MRF 描述下的流動 方程與RNG k-ε Model 計算得到流場收斂穩態解後，以DPM 丟入顆粒計算得到顆粒軌跡進而預測顆粒的傳輸效率。並改變立式磨粉機內的結構參數，做出一結構 參數化分析。第二個目的我們則透過耦合SMM 描述下的流動方程與RNG k-ε Model，再加上DPM Model 計算得到的暫態解，成功的以模擬的方式顯現出選粉 機的分級過程。

Vertical roller mill is a machine that combines grinding, transporting and classification of material. Due to its excellent working ability the machine is widely used in various industries such as power plant, cement industry and chemical industry.The alteration and upgrading of vertical roller mill involve multiple physics problem,where in this paper we only focus on the flow field .We conducted a parameter analysis for the vertical roller mill by using a commercial CFD software ANSYS FLUENT. Wepredicted the flow field and particle motion by solving the following governing equations in each cells. Solving the RNG k-ε Model to realize the turbulent flow inside the channel. Solving the Discrete Phase Model (DPM) to visualize the trajectories of particles. Solving a different form of Navier-Stokes equations which are rewritten by the Multiple Rotating Reference Frame (MRF) or by the Sliding Mesh Method (SMM) to predict the flow motion caused by the rotating machine. There are two major purposes in this paper: One is to improve the efficiency in the transportation of fine particles. The other is to predict the cut-off size of particle product that comes from the air classifier. We achieved the first purpose by the following procedure: solving the coupling of flow model that is based on MRF and RNG k-ε Model to obtain a steady state solution of flow field, and then inject the particles into this steady flow to calculate the particle motion by DPM. The information from the DPM calculation would indicate the efficiency of particle transportation. We changed the geometry of the physical model in order to establish a parameter analysis of vertical roller mill, and we achieved the second purpose by solving the coupling of flow model that is based on SMM, RNG k- ε Model, and DPM. Therefore, we are able to successfully model the powder classification process by numerical simulation.