Study on Drag Force Coefficients in Modeling Granular Flows in a Slot-Rectangular Spouted Bed
Drag force coefficient is crucial for modelling gas-solid flows in using Discrete Element Method (DEM). Previous studies seldom concern about the mathematical properties of this coefficient, and just take it as a homogenous function. In this paper, a math
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Abstract Drag force coefficient is crucial for modelling gas-solid flows in using Discrete Element Method (DEM). Previous studies seldom concern about the mathematical properties of this coefficient, and just take it as a homogenous function. In this paper, a mathematical demonstration is carried out to prove that the drag force coefficient is a 2nd order tensor, and indicate it can be reduced to a homogenous function. Then, seven kinds of drag force coefficients adopted by MFIX are listed. Finally, all the listed coefficients are assessed by simulating the granular flows in a slot-rectangular spouted bed. Comparing the simulated velocities of particles with the experimental data in the spouted region, different drag force coefficients are analysed to find which one is the best to model the granular flows in this spouted bed.
1 Introduction The spouted bed is widely used for industry applications such as drying, mixing, coating, granulation, combustion, coal gasification, pyrolysis, reforming, and chemical vapor deposition [1, 2]. Two different regions of flow particles are found out in the spouted beds where granular phase is agitated by the gases through a single nozzle [2, 3]. One is a dilute phase core of upward gas–solid mixtures called the spout, and the other one is a surrounding region of downward quasi-static granular flow called the annulus. Despite the industry need of studying how to design an efficient spouted bed, the understanding of hydrodynamics of gas and solid phase is crucial for knowing the mechanism of gas-solid interactions.
H. Zhang S. Li (&) Department of Thermal Engineering, Tsinghua University, Beijing, China e-mail: [email protected] © Springer Science+Business Media Singapore 2017 X. Li et al. (eds.), Proceedings of the 7th International Conference on Discrete Element Methods, Springer Proceedings in Physics 188, DOI 10.1007/978-981-10-1926-5_72
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The Discrete Element Method (DEM), which is good at resolving particle flow behaviors at an individual particle level, has been developed as a powerful tool for studying gas-solid flows [4–8]. The two key issues of DEM focus on the dynamic interaction model between particles and hydrodynamic model between gas-solid. Two common models for solid-solid interaction are hard-particle and soft-particle approaches [6]. Hard-particle model considers that particle contact instantaneously, and contact forces would not be carried out explicitly. However, soft-particle model simulates the contact process which can determine the solid phase stresses and deformation between particles [9, 10]. Both of these models are most useful in pure granular flows without gas phase. For example, hard-particle method can be used in simulating rapid granular flows, and the soft-sphere method have been extensively used to study various phenomena, such as particle packing, transport properties, heaping/piling process, hopper flow, mixing and granulation [6]. The solid-gas or particle-fluid interaction is crucial for modeling gas-solid two pha
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