Abstract:

The gas-liquid two-phase bubbly flow in a Lightnin static mixer (LSM) with a diameter of 100 mm and an aspect ratio of 1.0 was investigated. The turbulent dispersion and hydrodynamic behavior of bubble groups was focused under the conditions of liquid phase superficial velocity U_L=0.071—0.127 m/s and gas phase superficial velocity U_G=0.007—0.042 m/s. The evolution of bubble populations in different axial windows in the mixer was collected by using a high-speed camera Revealer-2F04M with a resolution of 1920×1080. The results show that the flow pattern in the LSM is in bubbly flow at the superficial velocity of continuous phase U_L no more than 0.085 m/s and U_G=0.025—0.042 m/s. The Sauter mean diameter d₃₂ of bubble groups gradually decreased with the increase of axial mixing length. With the given liquid flow superficial velocity U_L≤0.085 m/s, the Sauter mean diameter d₃₂ firstly decreased and then increased with the increase of gas flow superficial velocity. The local minimum of d₃₂ was obtained at U_G=0.028 m/s and 53% of the d_B/D₀ is in the range of 0.02—0.05. The relationship among Sauter mean diameter, the inner diameter and the non-dimensional residence time satisfies the correlation d₃₂/D₀=0.031τ^-0.14We^-0.41. As the gas superficial velocity increases, the density function of the number of bubbles per unit volume increases significantly. The probability of bubble collided with the surfaces of the element is enhanced which increases the intensity of the vortex secondary flow and leads to a significant decrease in the friction coefficient. By fitting the pressure drop of two-phase flow, the empirical correlation prediction formula C=5.26×10⁵U_{\mathrm{G}}^{-\mathrm{0.91}}/Re^0.74 was obtained.

Key words: static mixer, gas-liquid flow, Sauter mean diameter, gas holdup, pressure drop

摘要：

以Lightnin静态混合器（LSM）内水-空气气液两相体系为研究对象，在连续相水表观速度U_L=0.071~0.127 m/s和离散相空气表观速度U_G=0.007~0.042 m/s的条件下，研究内径100 mm的LSM内气液两相湍流流动阻力与气泡分散水动力学行为。使用分辨率为1920×1080的高速相机Revealer-2F04M采集混合器内不同轴向窗口的气泡群演化过程。结果表明：当U_L<0.085 m/s和U_G=0.025~0.042 m/s时，LSM内的流型为泡状流。随着气泡群流经混合元件数的增加，气泡群的Sauter平均直径d₃₂逐渐减小。当液体表观速度U_L≤0.085 m/s时，Sauter平均直径d₃₂随气体表观速度的增加先减小后增大；U_G =0.028 m/s时d₃₂达到局部最小值，53%的气泡直径d_B/D₀在0.02~0.05范围内。Sauter平均直径、内径与无量纲停留时间τ之间的关系满足d₃₂/D₀=0.031τ^-0.14We^-0.41。平均气含率α的增大显著增加了单位体积内气泡数量密度，加剧气泡与元件表面碰撞频率，增大旋涡二次流强度，导致摩擦系数显著降低；采用Lockhart-Martinelli方法对实验数据回归，得到气液两相流压降预测常数C的关联式：C=5.26×10⁵U_G^-0.91/Re^0.74。

关键词: 静态混合器, 气液两相, Sauter平均直径, 气含率, 压降