一种新型下行管入口结构流体力学性能的数值模拟

提出了一种新型下行管入口结构，并采用计算流体力学对这种下行管入口结构的流体动力学进行数值模拟。对气固两相流采用双流体模型，其中采用颗粒动理学模型描述固相粘度和固相压力。模拟结果表明新型下行管入口区相对周围其它区域为负压区，气固初始接触区的流体被抽吸进入下行管。下行管入口段颗粒浓度在径向上的分布呈中心高、边壁低的分布，随着轴向位置的增加，颗粒逐渐向边壁方向扩散，使得颗粒浓度在径向上分布趋向均匀。气固初始接触区颗粒浓度相对较高。颗粒在下行管中运动历程可分为三个阶段：加速段、减速段和恒速段，这与气固并流接触入口结构的颗粒运动历程不同。

Numerical simulation of hydrodynamics in a new type of downer entrance

A new type of downer entrance( also names gas-solids distributor) was proposed, in which gas contacts solids by countercurrent. The distributor is positioned concentrically to the downer. The solids arrive at the gas-solids contact area via the gap between the downer and the distributor, and contact primary gas from top gas distributor, then, the gas-solids mixture redirects and enters the downer pipe. Numerical simulation of hydrodynamics in a new type of downer entrance was carried out. Result of simulation can match well with experiment data. Simulation result data show that pressure of downer entrance region is negative, and the mixture in gas/solids contact area is pumped into downer pipe. In the inlet section of the downer pipe, the solids concentration radial profile is parabolic. Solids concentration at initial gas/solids contact area is much higher than that in downer, which may improve gas/solids contact efficiency. The simulation results of axial mean pressure and average particle velocity show that the particle movement in the downer reactor is three-section axial flow structure: velocity increasing section, velocity decreasing section and constant velocity section, which is different from the downer reactor with gas-solids contacting by co-current down-flow.