上喷式喷射器内气液两相流的流体力学特征

Hydrodynamic characteristics of gas-liquid flow in an up-flow ejector

喷射器作为气液混合装置,比传统接触混合器具有更高的混合强度和传质系数。计算流体力学(computational fluid dy- namics,CFD)模拟作为研究气液混合流的方法,有助于理解喷射器的流体力学和混合特征。它能提供详细的信息来量化操作条件对喷射器性能的影响。本文利用CFD模拟了上喷式喷射器内的气液两相流的流体力学特征。结果表明在较高的混合段长径比下,混合段入口处的压力较低。但是存在一个最大的压力降,此时混合段长径比约为4.0。在相同的喷嘴速度下,混合段入口处压力降最低,气体卷吸量最大。模拟中混合管与喷嘴面积比范围为1～16。无论是保持喷嘴直径不变还是混合管直径不变,混合段入口处的压力都随着D_M^2/D_N^2的增加而增加。但是对应的最大气体卷吸率发生在面积比为4.0。当喷射器的结构参数不变,混合段入口处的压力降和气体卷吸率随着喷嘴速度的增加而增大。

Ejectors as gas-liquid mixing devices have been reported to give higher mixing intensity and mass transfer coefficient than other conventional contactors. Computational fluid dynamics （CFD） simulation as a research method to study the gas-liquid mixing flow has been potent to help understand the hydrodynamic and mixing characteristics of ejectors. CFD simulation can also provide detailed information for quantifying the effects of operating conditions on ejector performance. In this paper, the hydrodynamic characteristics of gas-liquid flow in an up-flow ejector were studied using CFD modeling. The results show that the higher of mixing tube length to diameter ratio, the lower of the pressure at the cross-section of mixing tube inlet is. There is a largest pressure drop at about LM/DM = 4. O. At the same nozzle velocity, the entrained air at the lowest pressure drop is largest. The area ratios （ ratio of mixing tube area to nozzle 2 2 area, DM/DN） used in the simulation are 1 - 16. Under the conditions of either the nozzle diameter or the mixing tube is constant, the 2 2 pressure at the inlet of mixing tube increases with the increases of the D^2M/D^2N ratio. However, the air entrainment rate is largest at the value of D^2M/D^2N =4. 0. When the ejector geometry is changeless, the pressure drop at the mixing tube inlet and the air entrainment rate increases with the nozzle velocity increases.