内外单螺带—锚搅拌槽中粘弹性流体的流速分布和混合时间

Velocity Distribution and Mixing Time for the Flow of Highly Viscoelastic Fluids in the Agitafed Vessel with the Inner and Outer Helical Ribbon-Anchor Impeller

本文用照相法测定了内外单螺带锚搅拌槽中高粘牛顿流体和粘弹性流体的流速分布,用示踪粒子法和脱色法分别测定了循环时间和混合时间,结果发现: (1)在低Re~*数下,对于同一转速,粘弹性流体的切向速度大于牛顿流体,而轴向速度则小于牛顿流体。 (2)在槽中的低剪切区,两种流体的剪切率分布相差不大,而高剪切区的剪切率和全槽平均剪切率都是粘弹性流体的大。 (3)粘弹性流体的混合时间NT_M和循环流量N_q与牛顿流体和假塑性流体相比分别增加一倍和降低70％右左。

The velocity distribution was obtained from streak photographs using selective illumination of the vessel and polystyrene pearl as tracer particles for the flow of highly viscoelastic and Newtonian fluids in the agitated vesselwith the inner and outer helical ribbon-anchor impeller, In addition, mxing times were measured using a decoloration technique and circulation times were deferm-ined by the tracer bead method. It was found that( 1 ) In the low Re number regime, the magnitude of the tangential velocity is greater and the axial velocity is smaller for the viscoelastic fluid in co-mparision with Newtonian fluid for the rotational speed of the impeller.( 2 ) The shear rate distribution is similar for two fluids in the low shear rate regime, but the shear rate in the high shear rate regime and average one over the vessel for the vescoelastic fluid are greater;( 3 ) The mixig time NTM for vescoelastic fluid is about two times longer and the cireulation capacity Nqr is 70% lower than those of Newtonian and pseudoplastic fluids respectively.