螺带型搅拌槽内异物性液体的混合性能

针对高固含量木质纤维素同步糖化与发酵生产燃料乙醇过程，研究了螺带型搅拌槽内层流流动条件下少量低粘低密度液体(a)加入大量高粘高密度主体液体(b)中的混合性能，考察了转速、两种液体体积比(Va/Vb)、粘度比(mb/ma)、密度差等影响因素. 结果表明，当Va/Vb>1%时，异物性物系混合时间远高于相同物性液体混合时间，可延长2~5倍；Va/Vb对混合时间影响最显著，Va/Vb=0.2%~3.7%范围内，无量纲混合时间Ntm随体积比增大先降低后升高存在一最小值；当Va/Vb≥2%，单位主体液体密度之差Dr/rb>0.2时，Ntm随着Va/Vb, Dr/rb增加线性增大；Ntm随着mb/ma增大而减小；加入相加在主体液体内所得混合时间比加在液体表面时短；Va/Vb>2%时，混合工况可分为Re数控制区(桨叶控制)及Ri数控制区(重力控制).

Mixing of Liquids with Different Viscosities and Densities in a Helical Ribbon Impeller Stirred Tank

The mixing of liquid addition in a stirred tank installed with a helical ribbon impeller under laminar flow regimes during inoculation in the simultaneous saccharification and fermentation of lignocellulosic biomass at high solids loading was studied. The effects of impeller rotational speed, volume ratio of added liquid a to bulk liquid b, Va/Vb, and their viscosity and density on mixing time, tm, were examined. The results show that it takes longer time for the liquids with different viscosities and densities to get homogenization than that of similar property liquids when Va/Vb is above 1%. tm of the liquids with different properties is 2~5 times longer than that of similar property liquids at identical conditions. Va/Vb is the most important operating parameter, dimensionless mixing time, Ntm, first decreases and then increases with Va/Vb, there is a minimum value. When Va/Vb≥2% and Dr/rb>0.2, Ntm increases linearly with them. Liquid addition in the bulk has shorter mixing time than that of addition on the surface. The mixing regime in the tank can be classified into Re controlled (stirrer controlled) regime and Ri controlled (gravity controlled) regime at high Va/Vb (>2%).