流场特性对PAC-UF中膜面PAC层不均匀性的影响

Effects of Hydrodynamic Characteristics in PAC-UF System on PAC Layer Nonuniformity

基于数值模拟的方法研究了各工艺条件下粉末活性炭-超滤(PAC-UF)系统的流场特性,评估反应器内流场速度和剪切力对膜面PAC滤饼层不均匀性的影响。模拟结果表明,随着PAC投加量由200 mg/L增至400 mg/L、转速由60 r/min增至150 r/min、膜组件高度由3.25 cm增至8.25 cm,膜组件两端剪切力差值分别增长了9.55%、234.51%、76.19%。反应器内不均匀分布的流场速度造成了膜组件轴向剪切力的明显差异,而该差异对膜面形成下薄上厚的不均匀PAC滤饼层产生重要影响;膜丝轴向剪切力差异性越大,形成的膜面PAC层下薄上厚现象越明显。采用三维电磁测速仪对数值模拟结果进行实验验证,得到反应器内流场速度实验值与模拟值吻合程度良好,印证了数值模拟方法的准确性。

Based on numerical simulation,the hydrodynamic characteristics of PAC-UF system were investigated at different process conditions and the influence of velocity and shear stress on PAC cake layer nonuniformity was evaluated.With the dosage of PAC increasing from 200 mg/L to 400 mg/L,rotate speed increasing from 60 rpm to 150 rpm,membrane module distance increasing from 3.25 cm to 8.25 cm,the difference values of shear stress are increased by 9.55%,234.51%,76.19% respectively. The hydrodynamics in the reactor is affected on the formation of PAC cake layer, causing the phenomenon that thickness of PAC cake layer is thinner on the bottom of membrane and thicker on the top. The larger difference from the shear stress of membrane axial,the more obvious phenomenon it is. Three-dimensional electromagnetic tachymeter is used to measure the flow field of the physical model,and the measured velocity is close to the simulated value,which proves the accuracy of the numerical simulation.