基于各向异性二阶矩模型的液固流化床流动特性的研究

发布时间：2018-01-31 05:19

本文关键词： 液固流化床各向异性二阶矩模型颗粒动理学数值模拟　出处：《东北石油大学》2017年硕士论文　论文类型：学位论文

【摘要】：在石油化工领域里,液固两相流的流动性质已经成为学者们的重要研究方向,并且液-固流化床中传热、传质和掺混的特性也得到了广泛的应用。因此利用数值模拟的方法来探究液固流化床内流动本质及机理具有重要的现实意义。目前,对颗粒流动的大部分研究都是基于各向同性假设,但是在实际液固流化床中颗粒脉动会表现出很强的各向异性,所以发展并完善合理的各向异性颗粒动理学理论对模拟液固两相流极为重要。本文以稠密液固流化床的颗粒动理学为基础,建立了颗粒脉动速度各向异性的二阶矩输运方程,封闭颗粒相的本构方程,并结合颗粒与墙面碰撞的切向、法向弹性系数,得出了液固系统下的颗粒相速度及其脉动速度二阶矩的壁面边界条件,构成了完整的各向异性液固两相流数学模型。分别运用基于各向同性假设的颗粒动理学模型和二阶矩模型模拟了液固提升管的流动特性,同时将模拟结果与Razzak实验的实验结果进行比较,结果表明各向异性模型更加贴近实际流场中的实验值。并且二阶矩的轴向分量大于径向分量,颗粒的轴向速度会随着液相来流速度的增加而增大。颗粒运动过程中脉动能量的耗散主要来自于颗粒之间的相互碰撞和液固相间的曳力作用。颗粒温度会随着颗粒浓度的增大出现先增大后减小的现象。为了验证各向异性液固两相流数学模型的普适性,模拟了液固下降管的流动特性,模拟结果与实验结果一致。分析下降管内自由空间,稀相区和密相区的模拟结果,都能够看出颗粒在运动过程中各向异性的特点。由于下降管内液固下行流动过程中各向异性较弱,原各向同性的颗粒动理学模型与各向异性二阶矩模型的数值较为接近,但综合比较结果,二阶矩模型能更加吻合原实验值。
[Abstract]:In the field of petrochemical industry, fluidity of liquid-solid two-phase flow has become an important research direction of scholars, and heat transfer in liquid-solid fluidized bed. The characteristics of mass transfer and mixing have also been widely used. Therefore, it is of great practical significance to study the nature and mechanism of fluid flow in liquid-solid fluidized bed by numerical simulation. Most of the studies on particle flow are based on the isotropic hypothesis, but the particle pulsation will show strong anisotropy in the actual liquid-solid fluidized bed. Therefore, it is very important to develop and perfect the theory of anisotropic particle dynamics for the simulation of liquid-solid two-phase flow. This paper is based on the particle dynamics of dense liquid-solid fluidized bed. The second moment transport equation of particle pulsating velocity anisotropy and the constitutive equation of closed particle phase are established. The normal elastic coefficient is obtained by combining the tangential direction of particle collision with wall surface. The wall boundary conditions of particle phase velocity and its pulsation velocity are obtained. A complete mathematical model of anisotropic liquid-solid two-phase flow is constructed, and the flow characteristics of liquid-solid riser are simulated by using the particle kinetic model based on isotropic hypothesis and the second-order moment model, respectively. At the same time, the simulation results are compared with the experimental results of Razzak experiment. The results show that the anisotropic model is closer to the experimental value in the actual flow field, and the axial component of the second moment is larger than the radial component. The axial velocity of particles increases with the increase of liquid flow velocity. The dissipation of pulsating energy in particle motion mainly comes from the interaction between particles and the drag between liquid and solid phases. The particle temperature increases with the particle. In order to verify the universality of the mathematical model of anisotropic liquid-solid two-phase flow, the particle concentration increases first and then decreases. The flow characteristics of liquid-solid descent tube are simulated, and the simulation results are consistent with the experimental results. The simulation results of free space, rare-phase region and dense phase region are analyzed. It can be seen that the anisotropy of particles in the moving process is weak because of the weak anisotropy in the downflow of liquid and solid in the descending pipe. The original isotropic particle kinetic model is close to the anisotropic second-moment model, but the results show that the second-order moment model is more consistent with the original experimental value.
【学位授予单位】：东北石油大学
【学位级别】：硕士
【学位授予年份】：2017
【分类号】：TQ051.13;TE65

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