發(fā)布時間：2018-01-31 05:19

  本文關鍵詞： 液固流化床 各向異性二階矩模型 顆粒動理學 數值模擬　出處：《東北石油大學》2017年碩士論文　論文類型：學位論文

【摘要】：在石油化工領域里,液固兩相流的流動性質已經成為學者們的重要研究方向,并且液-固流化床中傳熱、傳質和摻混的特性也得到了廣泛的應用。因此利用數值模擬的方法來探究液固流化床內流動本質及機理具有重要的現實意義。目前,對顆粒流動的大部分研究都是基于各向同性假設,但是在實際液固流化床中顆粒脈動會表現出很強的各向異性,所以發(fā)展并完善合理的各向異性顆粒動理學理論對模擬液固兩相流極為重要。本文以稠密液固流化床的顆粒動理學為基礎,建立了顆粒脈動速度各向異性的二階矩輸運方程,封閉顆粒相的本構方程,并結合顆粒與墻面碰撞的切向、法向彈性系數,得出了液固系統(tǒng)下的顆粒相速度及其脈動速度二階矩的壁面邊界條件,構成了完整的各向異性液固兩相流數學模型。分別運用基于各向同性假設的顆粒動理學模型和二階矩模型模擬了液固提升管的流動特性,同時將模擬結果與Razzak實驗的實驗結果進行比較,結果表明各向異性模型更加貼近實際流場中的實驗值。并且二階矩的軸向分量大于徑向分量,顆粒的軸向速度會隨著液相來流速度的增加而增大。顆粒運動過程中脈動能量的耗散主要來自于顆粒之間的相互碰撞和液固相間的曳力作用。顆粒溫度會隨著顆粒濃度的增大出現先增大后減小的現象。為了驗證各向異性液固兩相流數學模型的普適性,模擬了液固下降管的流動特性,模擬結果與實驗結果一致。分析下降管內自由空間,稀相區(qū)和密相區(qū)的模擬結果,都能夠看出顆粒在運動過程中各向異性的特點。由于下降管內液固下行流動過程中各向異性較弱,原各向同性的顆粒動理學模型與各向異性二階矩模型的數值較為接近,但綜合比較結果,二階矩模型能更加吻合原實驗值。
[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.
【學位授予單位】：東北石油大學
【學位級別】：碩士
【學位授予年份】：2017
【分類號】：TQ051.13;TE65

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