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Thesis Advisor许光文 ; 刘晓星
Degree Grantor中国科学院研究生院
Place of Conferral北京
Degree Discipline化学工程
Keyword密集颗粒物料 移动床 离散元方法 计算流体力学 摩擦粘度模型

工业过程中常涉及到密集颗粒物料的处理,深入认识密集颗粒物料的流动特性对设计、优化和放大相关设备至关重要。本文以移动床和喷动床为研究对象,考察系统中颗粒物料的流动特性,探索现有密集颗粒物料相关本构模型的预测精度和适用性。本论文第二章采用离散单元法模拟研究了移动床中颗粒物料的卸料特性,为第三章连续性模拟结果的合理性提供验证数据。离散模拟结果表明,随着初始堆积高度的增大,颗粒物料的流型逐渐由C类漏斗流过渡到B类半整体流。漏斗流结构下,流动区特征宽度随卸料的进行呈现(增大)—恒定—减小的变化趋势。半整体流结构下,当床层高度降到某一临界值时,流型突变为漏斗流,之后流动区特征宽度呈单调递减的变化趋势。这一结果说明,移动床卸料过程中,流动区宽度与卸料历史密切相关。第三章基于连续介质模拟,考察了目前文献中代表性的颗粒粘度模型(Schaeffer、S-S和μ(I)模型)对模拟结果的影响。模拟结果表明,对于卸料初期为漏斗流的系统,Schaeffer模型和μ(I) 模型都能预测出漏斗流流动结构,但所预测的流动区特征宽度的数值与变化趋势明显偏离离散单元法模拟结果;对于卸料初期为半整体流流型的系统,Schaeffer模型和μ(I)模型能够预测出移动床内物料从B类半整体流向C类漏斗流的转化过程,且流动区特征宽度变化趋势与离散单元法模拟结果定量一致。对于所考察的初始堆积高度,S-S模型的预测结果始终为半整体流,明显偏离了离散单元法数值模拟的结果。 第四章基于气固喷动床,进一步检验了以上三种粘度模型对模拟结果的影响。模拟结果表明,μ(I)模型预测得到的喷泉区高度、平局空隙率以及喷动区轮廓更接近于实验结果;Schaeffer模型得到的床层压降最接近实验测量值。三种粘度模型在喷泉区与喷动区内的预测结果差异不大,但在环隙密相区内μ(I)模型的模拟结果明显优于其他模型。综合考虑,相较于Schaeffer与S-S模型,μ(I)模型在喷动床预测中显示出更大的优越性。 

Other Abstract

Dense granular materials are widely encountered in various industrial processes. Thorough understanding of the complex flow behavior of dense granular materials is thus critical for the design, optimization and scale-up of relevant equipments. Focusing on moving bed and spouted bed systems, in this work the flow characteristics of dense granular are numerically investigated and the suitability and predictive ability of several constitutive laws for granular material are evaluated. In order to provide the basic data for quantitative evaluations of the correctness of continuum simulations, in chapter 2 the discharging behaviors of granular materials from moving bed are simulated using Discrete Element Method (DEM). It is found that, with the increase of initial packing height, the flow structure switches from type C funnel flow pattern to type B semi-mass flow pattern. For funnel flow pattern, there exists a smooth transition of (expansion)-saturation-shrinkage of flowing zone during the whole discharge process. As to semi-mass flow structure, the flow pattern quickly switches into funnel flow pattern when the sample height is smaller than a critical value. After that, the characteristic width of the flowing zone decreases monotonously with the ongoing of discharge. Such results indicate that during silo discharge, the flowing zone width is closely related to the discharging history. In chapter 3, the predictive abilities of three commonly used frictional viscosity models (Schaeffer, S-S, μ(I)) in simulating silo discharge are assessed. It is found that, for systems with initial flow structure being funnel flow, both Schaeffer model and μ(I) model can successfully give the correct flow pattern. However, the predicted variation trend and their quantitative values of the characteristic width of flowing zone clearly deviate from the DEM results. As to systems with initial flow structure being semi-mass flow, Schaeffer model and μ(I) model can correctly predict the flow structure switching from type C to type B. And the obtained characteristic widths of flowing zone are in good agreement with the DEM results. For all the considered initial packing heights, the continuum simulations using S-S model always predict the formation of semi-mass flow, which clearly deviates from the DEM results. To further evaluate the predictive abilities of the considered three frictional viscosity models, in chapter 4 the hydrodynamic characteristics of gas-solid spouted bed are modeled. It is found that the fountain height, voidage and the geometrical shape of spouting region predicted by μ(I) model are very close to the experimental results. The pressure drop given by Schaeffer model is in better agreement with the experimental datum. In fountain region and spouting region, the simulation results predicted by the three model are very close to each other. Nevertheless, in the annulus region the simulation results given by μ(I) model are more close to experimental data. In brief summary, compared with Schaeffer model and S-S model, μ(I) is more suitable for modeling the hydrodynamic behavior of gas-solid spouted bed. 

Document Type学位论文
Recommended Citation
GB/T 7714
田恬. 密集颗粒物料流动特性数值模拟研究[D]. 北京. 中国科学院研究生院,2017.
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