【作者】 包佳琨；

【导师】 张金利；

【作者基本信息】 天津大学 ， 化学工程， 2004， 硕士

【摘要】 鼓泡反应器是工业生产中应用较为广泛的一类反应器,但由于其设计与放大困难,因此对其内部气液两相瞬态流动特性的考察日益成为研究的热点。随着计算机技术的发展,计算流体力学(Computational Fluid Dynamics, CFD)的出现与发展为气液两相流领域的研究提供了强有力的手段。特别是近几年发展起来的大涡模拟模型(Large Eddy Simulation, LES),由于可以捕捉到流场内各相很强的瞬态运动信息而倍受关注。本论文在多相流体力学理论的基础上,借鉴前人模拟研究的成功经验,以中心进气式及偏心进气式的气液鼓泡反应器为研究对象,在欧拉-欧拉坐标内选用LES作为湍动模型对气液鼓泡反应器内表征流体力学特性的参数进行考察。以LES作为湍动模型模拟捕捉到了鼓泡塔内任一位置处流体在任一时刻的速度波动,由此获得流体速度高频脉动的细节。中心及偏心进气式鼓泡反应器内的气含率分布及气泡流运动形式与Buwa、Sokolichin和Becker等报道的实验结果吻合较好,说明LES作为湍动模型在研究鼓泡塔内气液瞬态流动方面具有较高的可靠性。速度矢量分布反映了流场内精细的瞬态流动结构,涡结构的演变及涡量的分布说明了流动结构主要受大涡团影响。对中心进气式鼓泡塔反应器内的气液两相流动进行模拟还发现利用时均化的湍动模型进行模拟不能反映流场内气泡流真实的瞬态流动结构;液体的高粘度对旋涡尺度发展具有限制作用;增大进口气速使流场内涡量分布具有更大的不均衡性;而减小气泡尺寸可使能量分布更加均匀,从而提高反应器内传热传质效率。利用LES模型对偏心进气式鼓泡塔内的气液流动进行模拟发现增大气速可使塔内的流体力学特性变量在较短时间内达到较好的分布,流场中的两相达到较好的混合。此外高粘度的液体不利于流场内能量的均匀分布,小高径比的反应器内的涡量分布相对比较集中。更多还原

【Abstract】 Bubble column reactors (BCRs) are widely used in the industrial applications. However, it is very difficult to design and scale up this kind of reactor, in that the present study has focused on the transient characteristics of the inherent gas-liquid flow increasingly. Following the development of the computer technology, Computational Fluid Dynamics (CFD) has become a useful and strong method to study the multiphase flow. Moreover, as a kind of turbulent model, Large Eddy Simulation (LES) can capture the transient flow information of every phase, which has attracted more attention.On the basis of multiphase flow dynamics theory, the paper selected the BCRs as the study objects, which have two kinds of gas distributor, central air aerated and partial air aerated. Using the LES model, the hydrodynamics parameters and the transient flow pattern in the gas-liquid BCRs were investigated in the Euler-Euler coordinate.The simulation results indicated that using LES model could obtain the fluctuation of the velocity at any position and any time, which made us obtain more high frequency pulsing details of the fluid velocity. No matter the central air aerated or the partial air aerated, the gas hold-up distribution and the transient flow pattern were all in agree with the experimental results of Buwa, Sokolichin and Becker. That proved the LES model had high reliability to study the gas-liquid transient flow in BCRs. In addition, the velocity vector distribution reflected the dynamic flow structure. The development of the vortex structure and the vorticity magnitude distribution indicated that the whole flow structure was affected by large eddy.The simulation results of central air aerated BCRs suggested that using time-averaged turbulent model could not reflect the real transient flow structure in BCRs; higher liquid viscosity had limitation to the development of the vortex scale; increasing the gas-in velocity made the vorticity magnitude distribution tend to be more disequilibrium; decreasing the bubble scale made the energy distribution more uniform, which could enhance the efficiency of heat and mass transfer in BCRs.Using LES model to simulate the partial air aerated BCRs also could get the following results: increasing the gas-in velocity made the distribution of the <WP=5>hydrodynamics parameters more uniform in a rather short time; while, higher liquid viscosity were against the energy distribution in the flow field and small aspect ratio would made the vorticity magnitude be more concentrated.更多还原