【作者】 赵兵涛；

【导师】 沈恒根；

【作者基本信息】 东华大学 ， 环境工程， 2005， 博士

【摘要】 旋转流气固分离器(旋风器)作为重要的多用途气固两相分离设备,已广泛应用于气固分离、物料回收、颗粒分级和污染控制等领域,并已显示了独特的不可替代的作用。针对高温高压分离技术的要求、流态化技术的发展、能源有效利用矛盾的突出以及环境保护问题(微型化分离技术)的需要等问题,本文提出一种新型具有轴对称蜗向进口通道的旋风器,并通过试验研究、理论解析和数值计算方法对其分离机理和过程等性能特性进行较为深入系统的研究。 首先,在总结与回顾不同旋风器进口结构型式研究现状的基础上,本文提出了新型具有轴对称蜗向进口型式的Stairmand HE型旋风器。采用质量分析法和压差法等试验研究的方法测定了包括直接式和渐缩通道式新型进口结构在内的四种旋风器的分离特性和阻力特性,分析对比了不同进口结构型式、不同流量条件下旋风器性能的变化规律。在此基础上应用灰色综合评价模型评价了各旋风器的性能,指出轴对称蜗向进口通道结构型式的旋风器具有较优的性能。 其次,为对旋风器的性能评估和设计方法提供理论依据,本文采用理论解析的方法对具有轴对称蜗向进口通道旋风器的分离特性和阻力特性进行了研究,提出其理论计算模型并与试验值进行了比较。其中,在柱坐标系下详细分析了气固两相流场中固相颗粒的受力情况,突破了基于旋风器内径向截面上固相颗粒浓度分布均一的假设并认为径向浓度梯度对于分离效率的影响不可忽视,同时发展了空间定点分离的概念与理论,首次提出采用临界粒径分离理论、边界层分离理论和固相颗粒粒径分布规律相结合的新型理论与方法来推导旋风器的分离理论模型并将模型的计算结果与试验结果进行比较和分析,结果表明理论与试验结果符合较好;同时结合旋风器内部流场特性,详细分析旋风器内部阻力的产生机理与构成因素,将旋风起内部的阻力构成分为进口阻力、摩擦阻力、涡流阻力和出口阻力,首次从新的角度给出新型旋风器阻力的分步计算模型,并将计算结果与不同结构的旋风器阻力的试验结果进行比较,结果表明理论值与试验值取得较好一致。从而进一步验证了分离模型和阻力模型的准确性与有效性。 再次,为深入详细的探讨新型进口结构旋风器内部气固两相的分离机理,本文应用计算流体动力学(Computational Fluid Dynamics,CFD)技术对新型旋风器内部的气固两相流动规律进行数值模拟。在建立新型旋风器的物理模型并对其进行网格划分的基础上,应用Euler-Lagrange气固两相流理论,以雷诺应力模型(Reynolds Stress Model,RSM)模拟气相、颗粒追踪技术(Particle Tracking Method,PTM)模拟颗粒相,同时采用有限体积法和SIMPLE压力速度耦合算法分析讨论了新型旋风器内部的气相流场的压力分布、三维速度分布和固相颗粒轨迹,并在此基础上提出旋风器分离效率和阻力的数值计算方法。数值模拟结果与试验结果取得较好的一致,同时表明CFD作为一种更为基础的理论和方法,可更为有效的模拟旋风器内部的气固两相三维强旋湍流流动。更多还原

【Abstract】 Cyclone separators, as important gas-solid phase separation equipments, have been widely used in the field of gas-particle separation, product recovery, particulate size classifiers and pollution control. At present, cyclone separators have also demonstrated the irreplaceable use value. In order to adapt well to the extremely harsh operating conditions and special requirements including the high temperature and high pressure, fluidization, energy utilization and environmental protection, a novel cyclone separator with symmetrical spiral inlet channel (SSIC) is conceived and designed for engineering and processing application. The performance characteristics including collection efficiency and pressure drop for this cyclone separator is investigated by using the experimental, theoretical and numerical methods in this work.Firstly, on basis of the overview of current status on cyclone separator geometries, a new cyclone separator with symmetrical spiral inlet is presented in terms of the Stairmand high efficiency cyclone configuration. The separation characteristics and pressure drop characteristics for four kinds of cyclone separators with different inlet type are measured by using mass analysis method and differential pressure method, and are compared as functions of inlet type and flow rate. Moreover, the performances of cyclone separators are evaluated according to the grey correlation evaluation model. The results show the cyclone separator with symmetrical spiral inlet channel provides the optimized performance.Secondly, theoretical investigation on both the collection efficiency characteristics and pressure drop characteristics are carried out for symmetrical spiral inlet channel cyclone respectively. A new theoretical method for evaluating cyclone efficiency is developed based on the investigation of flow pattern, the critical particle size separation theory and the boundary layer separation theory. The radial particle concentration gradient, instead of the usually assumed uniform radial particle concentration within the cyclone, is considered in this mathematical model. The local particle concentration and the cyclone grade efficiency can be calculated on the base of a time-of-flight model in terms of the particle size distribution of the feed. The availability of the method is verified by comparison of the calculated grade efficiency with experimental data and theoretical counterparts in the literature. On the other hand, a new theoretical model was developed for prediction of pressure drop across cyclone separators. This model includes the effect of the geometrical dimensions and flow parameters, and assumes that total pressure drop consists of five main partial pressure drops due to gas expansion at the separator entrance, wall friction within the separator, swirling motion of gas, gas flow through the outlet pipe. The availability of themethod is verified by comparison of calculated value with experimental data as well as with the other models for different dimensions of cyclones. The both theoretical results indicate a good agreement with the experimental data.Thirdly, to analyze the separation mechanisms of symmetrical spiral inlet channel cyclone, A Computation Fluid Dynamics (CFD) simulation is performed for prediction of gas flow pattern and particle collection efficiency in this new type cyclone separator. The governing gas flow equations, along with the three-dimensional Reynolds Stress Model (RSM), are solved using the finite volume method and the SIMPLE pressure-velocity coupling algorithm in a body-fitted coordinate system. A particle tracking method (PTM) is employed to calculate the particle grade efficiency. The numerical flow simulations confirm the main characteristics of vortex structure and particle separation inside the main body of the cyclone. On this basis, a numerical method for calculating the collection efficiency and pressure drop is proposed. The comparisons between numerical and experimental results have to be regarded as a reasonable agreement, and also demonstrate CFD is a liab更多还原