283019 Parametric Sensitivity Study of Interaction Properties for Simulation of Realistic Packed Bed Structures

Thursday, November 1, 2012: 2:10 PM
305 (Convention Center )
Vaibhav Khane, Chemical Engineering, Missouri University of Science & Technology, Rolla, MO, Gary E. Mueller, Nuclear Engineering Department, Missouri University of Science & Technology, Rolla, MO and Al-Dahhan Muthanna, Chemical & Biological Engineering, Missouri University of Science and Technology, Rolla, MO

Experts in Discrete Element Modeling (EDEMTM) is a discrete element method (DEM) based modeling software program, capable of providing information about granular solids flows occurring in many industrial applications. Packing of particles inside the container is the first and main step in EDEMTM based analysis. Packing algorithms available with commercial codes such as EDEMTM are used as a ‘Black-Box’ and are without any detailed validation exercise. In most cases, average porosity results are compared to benchmark the numerical packing results with available experimental results, which is not sufficient. The packing algorithm used in EDEM demands accurate input interaction properties which are not readily available in the literature for materials of interest. Hence, the objective of the current study is to perform parametric sensitivity study of interaction properties from reliable numerical analysis point of view. This sensitivity study will also highlight important interaction properties which need to be provided as an input to EDEMTM contact force model.  The obtained results will provide a new and better understanding about the packing algorithm used in EDEMTM as well as recommendations to simulate realistic packed bed structures using EDEMTM. The cylindrical packed bed has been chosen as a model for this parametric sensitivity study. Also, the slow and dense granular flow encountered in a Pebble Bed Reactor (PBR) can be approximated by static packed beds. The ongoing experimental work at Missouri S&T involves the implementation of a radioactive particle tracking (RPT) technique and a gamma ray densitometry (GRD) technique around a cold flow continuous pebble recirculation experimental set-up, which mimics operation of PBR, for the evaluation of solids dynamics and associated hold-up distribution. In addition, computed tomography experiments are being done on static packed beds to evaluate cross-sectional averaged solids and voids distribution. Experimental benchmark data obtained using above mentioned techniques can be used to validate EDEMTM based simulation results by mimicking same diameter aspect ratio (which is defined as the ratio of the diameter of container to the diameter of the particles) as that of experimental geometry. Hence, diameter aspect ratio of 23.9 (derived from experimental geometry dimensions) has been chosen for EDEMTM based analysis. EDEMTM based analysis requires the accurate input of coefficient of static and rolling friction and coefficient of restitution (COR). Various cases are designed and simulated in EDEMTM  to test the effects of one particular parameter, while keeping other parameters constant at a value determined through the development of simple experimental set-ups. It is found that static friction for particle-wall and particle-particle interaction plays an important role in EDEMTM based simulations of packed beds. Interaction parameters such as the coefficient of rolling friction and COR are found to have minor or no influence on packed beds' structural properties. Results of this study also indicate that existing empirical correlations for mean porosity values should include static friction characteristics in addition to the diameter aspect ratio.

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