A Unified Model for the Mixing of Non‐Newtonian Fluids in the Laminar,Transition, and Turbulent Region

Summary: Non‐Newtonian fluid behavior has significant influence on quantities in chemical engineering like power input, mixing time, heat transfer etc. In the laminar flow region, the concept of effective viscosity by Metzner and Otto is well established. In the transition region between laminar and turbulent flow, the existing concepts use three and even more empirical parameters to determine the specific power input. Here, a unified and general but simple approach is introduced to calculate the power input for shear thinning fluids over the whole flow region using just one empirical parameter. The Metzner‐Otto relation is obtained as a limiting case for the laminar region. The empirical parameter of the new approach is related to the Metzner‐Otto constant. The concept is validated for eight different stirrer systems. Mixing time and maximum shear rate and heat transfer can also be calculated using this approach. The new concept presented should also be applicable for other apparatuses, e.g., static mixers.

Comparison of experimental data and a curve calculated according to the new method (solid line).     

Flow characteristics of hyperboloid stirrers

The flows in a fully-baffled vessel with a diameter T = 144 mm driven by hyperboloid stirrers of diameters D = 773 and 27/3 have been visualised and characterised by local measurements of velocity and turbulence and by power number. The results were obtained for a range of rotational speeds from 6 to 40 rev/s. The visualisation showed that the larger stirrer gave rise to a radial jet and that the smaller stirrer formed a jet inclined towards the base of the vessel so that there was a tendency for the system of two vortices, one above and one below the jet, to give way to a single vortex as the clearance between the stirrer and the base of the vessel was reduced. The velocity measurements revealed bulk-flow values an order of magnitude less than that of the maximum radial velocity in the jet, that the maximum radial velocity was 24% of the circumferential velocity of the tip of the stirrer, and that the radial velocities were proportional to the rotational speed. The flows generated by the hyperboloid stirrer were less vigorous than those of Rushton impellers of similar radius and were associated with power numbers 28 times less. The power number did not vary with rotational speed or with clearance within the measured range. The contrast with propeller and disc stirrers is less pronounced, but the hyperbolic profile is likely to find application and the present results provide a basis for choice.     

内构件存在时提升管内流动及颗粒混合行为研究

he hydrodynamics and solids mixing behavior in a riser with blunt internals are studied. A uniform radial distribution for solids fraction and particle velocity achieves near the internals. The turbulent velocity of particles near the wall increases with the addition of the internals, with the lateral solids mixing enhanced significantly. Probability density distribution of particle velocity is bimodal in the riser with internals, which is similar to that in the conventional riser, indicating that no significant difference in the micro flow structure exists between the riser with internals and the conventional riser. At the same time, the axial solids mixing behavior changes insignificantly with the addition of internals. These results indicate that the micro flow structure in the riser is very stable, which changes insignificantly with the change of the bed structure.     

水泥库圆形钢筋混凝土筒壁结构施工技术

圆形混凝土护壁结构在水泥生产线中是一种常见形式,如何根据实际施工条件,合理地组织施工,对施工工期、质量、安全、成本都有积极重要影响。对施工中的关键技术和难点问题进行了阐述。     

花菁染料聚乙烯醇延伸膜的三阶非线性光学极化率的各向异性

采用飞秒共振简并四波混频技术,检测了花菁染料的聚乙烯醇延伸膜平行和垂直于延伸方向的三阶非线性光学极化率.结果表明:单向延伸的花菁染料的聚乙烯醇膜具有较高的三阶非线性光学极化率的各向异性.     

氧化铝纳米流体在车用热交换器中的试验研究

研究纳米流体在车用热交换器中的强化传热效果,测试不同纳米粒子体积分数的氧化铝纳米流体在板翅式机油冷却器中的传热和流动特性,并与水、防冻液（乙二醇）及纳米流体基础液体进行对比.试验结果表明,在同一热交换器中,纳米流体的传热系数明显高于其他3种液体.当冷、热侧介质温度为90和120 ℃时,纳米粒子体积分数为5%的纳米流体的传热系数分别比水、乙二醇和基础液体提高6.52%、18.88%和24.62%;当冷、热侧介质温度为120和135 ℃时,体积分数为5%的纳米流体的传热系数比体积分数为1%的纳米流体提高104.72%.在试验条件下,热交换器的换热量随纳米粒子体积分数的增大而增大,但流动阻力并未明显增加,初步证明了纳米流体应用于车用热交换器的可行性.     

涡轮桨变速搅拌槽内湍流混合的实验研究

以NaCl颗粒在水中的溶解为例,对湍流状态下周期性变速旋转的（改变桨叶转向或速度大小,分别称为周期性换向搅拌和周期性依时搅拌）Rushton桨搅拌槽内的混合特性进行了实验研究,并与稳速搅拌进行了对比。实验过程中测量了不同搅拌模式、不同桨叶安装高度时颗粒的溶解时间,结果证明,搅拌槽底部的流型对NaCl的溶解有重要影响;桨叶安装高度对溶解速度的影响不大,周期性依时搅拌时的溶解时间比稳速搅拌时稍短,而周期性换向搅拌则能明显加快溶解速度,提高混合效率。     

超声波钢包精炼冷态模拟

以某钢厂180t钢包为原型,进行超声波改善钢包熔池搅拌效果的冷态模拟实验。通过记录pH计示数变化研究底吹气体搅拌均混时间及超声波搅拌均混时间。实验结果表明,在底吹空气水模实验中,当吹气位置在距离中心为0．33R,流量为0．1m3／h时,底吹气体搅拌所需的均混时间最短为50s;超声波水模实验中,当波源伸入钢包的中心液面下25cm处,输出功率1．8kw,均混时间最短为35s;在超声波和底吹气体联合实验中。当吹气位置在距离中心为0．33R,流量为0．1m^3／h,波源伸入钢包的中心液面下25cm处,输出功率1．8kw时,均混时间最短为48s;可以看出超声波可明显缩短钢包均混时间,改善钢包精炼动力学条件。     

Effects of viscosity ratio and composition on development of morphology in chaotic mixing of polymers

This study investigated the effects of viscosity ratio (p) and composition on morphology development in an immiscible polymer system mixed under chaotic flow conditions. It was seen that morphology of the dispersed phase developed through a widely accepted route involving transitions from lamellas to fibrils and to droplets. It was found in experiments with p≥1 that the dispersed phase converted into droplets very rapidly with narrow droplet size distribution when p∼1. For higher values of p, the speed of morphological transitions slowed down, the droplet size distribution became wider, and much larger droplets were formed. Similar effects were observed at higher concentration of the dispersed phase. No self-similar scaling behavior was observed in the droplet size distribution, which can be attributed to the lack of self-similarity in the breakup of lamellas into fibrils.