射流循环DTB结晶器内的CFD模拟

CFD simulation of circulation flow caused by jet in DTB crystallizer

采用RNG k-ε湍流模型对实验室级射流循环DTB蒸发结晶器内的单相流流场进行了数值模拟并优化结晶器结构,用欧拉多相流模型对优化的结晶器进行多相流模拟分析。结果表明,导流筒内射流满足线性扩展,其轴向速度分布基本满足高斯分布。刚进入导流筒内的射流段,轴线速度倒数与流程呈良好的线性关系,随射流的发展,轴线速度加速衰减。在入口直径恒定时,循环速率比随导流筒挡板间环隙面积与导流筒横截面积比的增加呈先增大再减小的趋势,存在最优值。优化的实验级DTB结晶器中导流筒内颗粒浓度分布沿径向方向减小,但基本可实现颗粒浓度较为均匀的分布,其循环速率与单相流模拟结果相比较低。

The circulation jet flow field in a DTB evaporating crystallizer was simulated and analyzed using RNG k-ε turbulent model. Based on the Eulerian multiphase flow model, the structure of the crystallizer and the flow field in the crystallizer were simulated and optimized. The simulation results showed that the jet could satisfy linear expansion in the draft tube and the axial velocity distribution basically met the Gaussian distribution. For the jet flow at entrance region of the draft tube, the reciprocal of axis velocity and flow distance showed a good linearity. However, axial velocity decayed faster with the development of the jet flow. The area ratio （β） of the annulus between draft tube and the baffle to the cross-section of the draft tube significantly influenced the circulation flow ratio （γ）. With the increase of β, γ increased at first, and then decreased, accordingly an optimal γ exists. Although the particle concentration of the crystal slurry decreased along the radial direction in the draft tube, it still had a more even distribution within the optimized structure crystallizer.