稠密气体多分散颗粒相间作用与混合粗糙颗粒动理学研究

Hydrodynamics of gas and polydisperse particles are investigated from theoretical and experimental approaches. The distributions of velocities for two species is measured by means of quick frozen method. The profiles of velocities and volume fractions of two species are calculated, which are used to valid models and simulations. Based on kinetic theory of non-uniform gases, the kinetic theory of polydisperse rough particles is developed by means of kinetic theory of collision. The exchange and dissipation of translational kinetic energy and rotational kinetic energy are predicted to investigate collisional interaction of species. The energy dissipation caused by interactions between species is analyzed in gas-polydisperse particles flow. The momentum exchange of heterogeneous flow structure is studied as a function of independent variables. The flow stability criterion of heterogeneous flow structure is proposed to judge of the formation of heterogeneous flow structure. The momentum exchange is established to give an interaction between gas phase and heterogeneous flow structure. The effect of rotations of rough spheres on kinetic energy exchange and dissipations is investigated. The large eddy simulation model for gas phase is proposed to consider the fluctuation of solids volume fraction. The effect of gas turbulence on motion of polydosperse particles is analyzed. The gas-solid multi-fluid model is established to combine the kinetic theory of polydisperse rough spheres and large eddy simulations. The hydrodynamics of gas and solids phases are simulated, and reconstitute flow structure of particles in gas-solid fluidized beds. Present project will promote to understand flow mechanism of dense gas-solid turbulent flow, and provide a foundation for investigate flow, heat and mass transfer and chemical reactions in dense gas-solid flow systems.

本项目将以气体多分散粗糙颗粒两相流动为研究对象，采用快速切断气源测量技术测量气体双颗粒组分流化床内两种组分颗粒质量分数分布。以稠密气体分子运动论为基础，采用碰撞间隔理论，建立混合粗糙颗粒动理学，研究粗糙颗粒碰撞和摩擦对多分散颗粒的颗粒组分与颗粒组分之间动量和能量的传递和耗散规律，揭示粗糙颗粒组分之间的相间作用机理。构建气体多分散颗粒流动的非均匀流动结构的相间作用模型，研究多分散颗粒非均匀流动结构对气固相间作用的影响。建立考虑高浓度颗粒脉动流动影响的气相大涡模拟方法，研究气相湍流对多分散颗粒脉动特性的影响。结合混合粗糙颗粒动理学和气相大涡模拟，建立气体多分散颗粒的多流体模型，研究气体多分散颗粒两相流体动力特性，重构多分散粗糙颗粒流化行为。为正确预测高浓度气固两相流动、传热传质和化学反应特性和工程应用等奠定理论基础。

燃煤流化床锅炉和生物质流化床锅炉等的共性特征是：流化颗粒由不同密度或者直径的多分散颗粒所组成。多分散颗粒不仅存在同一颗粒组分内颗粒之间的相互作用，同时存在不同颗粒组分之间的相互作用。本项目将以气体多分散颗粒两相流动为研究对象，构建多分散流化床实验平台。基于气体分子动力学建立混合颗粒动理学，研究不同颗粒组分之间相互作用规律。主要结论如下：. 基于分子动理论和颗粒碰撞动力学，建立了多分散颗粒的固相本构方程和固相压力和粘度等输运参数模型，形成了完整、封闭固相流动模型，阐明了多分散颗粒流动的动量和能量传递规律，揭示了多分散颗粒内的颗粒个体运动特性与固相宏观输运规律内在关系。. 构建了多分散气固流化床实验平台，实验玻璃球、河砂、煤和生物质二元颗粒和多分散颗粒的流化特性，提出了多分散颗粒混合物料临界流化速度的经验模型，发现多分散颗粒混合物料的流化平均平均粒径分布服从以自然常数为底的指数函数分布，统计回归得到函数的经验系数，预测流化床压降与实测相互吻合。. 基于沿流化床床高的颗粒浓度分布，提出了偏析协同角的方法表征床内颗粒分布均匀性。当偏析协同角为零度，表明床内小颗粒和大颗粒完全混合均匀；当偏析协同角为180度，表明床内小颗粒和大颗粒完全分离。偏析协同角越小，反映流化床内颗粒混合越均匀。. 数值模拟常压流化床内多分散颗粒流化特性，模拟结果与实测不同颗粒质量分数分布吻合。数值模拟单床和双床循环流化床锅炉燃烧室内气体和颗粒的流化特性，获得了单床和双床循环流化床内煤和床料多分散化颗粒流动特性分布，揭示了多分散颗粒沿燃烧室轴向的浓度和速度分布特性。. 数值模拟超临界水和二氧化碳流化床内由均匀散式流态到聚式流态的特征和过渡流化特征。发现超临界流化床反应器内过渡流化是以床底部为浓度波流动为特征，形成两区流化。随着压力和温度的提高，两区流化逐渐消失，多分散颗粒分布趋于均匀，有助于抑制床内颗粒分布的不均匀性。