同心双轴搅拌器固相悬浮特性研究

发布时间：2018-03-28 13:28

本文选题：同心双轴搅拌器　切入点：粘性体系　出处：《浙江大学》2017年硕士论文

【摘要】：同心双轴搅拌器是一种新型宽适应性搅拌器,具有灵活可调和高效低耗的优点,在工业界得到了广泛的认可。目前国内外对同心双轴搅拌器的研究较少,且主要集中在对单相体系的研究上。本文对同心双轴搅拌器在固液粘性体系中的临界离底悬浮转速、功耗特性进行了实验研究。首先提出了一种新的基于压力测量的临界离底悬浮状态判定方法,实验证明该方法能较好的应用于固液、气液固体系临界离底悬浮状态的判定。基于新提出的临界离底悬浮状态判定方法,实验对比了三组同心双轴搅拌器(锚式外桨+六直叶圆盘涡轮/上扬式六斜叶开式涡轮/上扬式推进桨)以及三种单轴桨(六直叶圆盘涡轮/上扬式六斜叶开式涡轮/上扬式推进桨;D=0.35T/D=0.53T)在粘性固液体系中的临界离底悬浮转速和功耗。结果表明,同心双轴搅拌器较单轴搅拌器具有更高的功率效率,特别是当外桨转速较大时,同心双轴搅拌器的优势更加突出,而三种桨型组合中,锚式外桨加推进式桨组合的功耗效率最高。实验研究还对比了同心双轴搅拌器在不同的转动模式(内外桨同向转动、外桨静止不动、内外桨反向转动)条件下的固相悬浮能力,结果表明固相悬浮性能同向模式好于单轴模式好于反向模式。此外,考虑了液相粘度、固相粒径、固含率、固液相密度差等因柰对临界离底悬浮转速和功耗的影响,提出了一个适用于同心双轴搅拌器的临界离底悬浮转速预测公式。为了更加直观地描述同心双轴搅拌器固相悬浮特性,采用CFD方法研究了同心双轴搅拌器的固相悬浮特性。为了建立合理的数学模型,首先将常用的Gidaspow曳力模型和修正Brucato曳力模型的模拟结果与前人的实验结果进行了对比,发现修正的Brucato曳力模型对固液两相搅拌体系流动参数的预测更加准确。监测距釜底1mm平面上平均固含率随转速的变化发现,平均固含率随转速增加先缓慢降低,后急剧下降,最后趋于平稳。根据距釜底1mm平面上平均固含率-转速曲线对临界离底悬浮转速进行了模拟预测,和实验结果吻合良好。模拟还直观地展示了三种桨型组合条件下的固相流型,展示了不同转动模式和外桨转速条件下的固含率分布和流型分布,以及研究了液相粘度、固含率对固相分布的影响。
[Abstract]:Concentric biaxial stirrer is a new type of wide adaptive agitator, which has the advantages of flexible, adjustable, high efficiency and low consumption, and has been widely recognized in industry. At present, there are few researches on concentric biaxial stirrer at home and abroad. In this paper, the critical off-bottom suspension speed of concentric biaxial agitator in solid-liquid viscous system is studied. Firstly, a new critical off-bottom suspension state determination method based on pressure measurement is proposed, and the experimental results show that this method can be applied to solid-liquid system. Determination of critical off-bottom suspension state of gas-liquid solid system. Three sets of concentric biaxial agitators (anchor outer propeller six-straight disk turbine / upturned six-blade open turbine / hoist propeller) and three kinds of single-axis propellers (six-straight blade disk turbine / hoisting hexagonal blade open impeller) were experimentally compared with that of three groups of concentric biaxial agitators. The critical off-bottom suspension speed and power consumption of turbine / propeller D _ (0.35) T / D _ (0.53T) in viscous solid-liquid system are obtained. The concentric biaxial stirrer has higher power efficiency than the single-axis agitator, especially when the rotating speed of the outer propeller is larger, the advantages of the concentric biaxial stirrer are more prominent, and among the three kinds of propeller combinations, The power efficiency of the combination of anchor propeller and propulsive propeller is the highest. The solid suspension capability of concentric biaxial stirrer under different rotating modes (internal and external propeller stationary, external propeller stationary, internal and external propeller reverse rotation) is also compared. The results show that the performance of solid phase suspension is better in the same direction mode than in the reverse mode. In addition, the effects of liquid viscosity, solid particle size, solid holdup and solid liquid density difference on the critical bottom suspension speed and power consumption are considered. A prediction formula of critical off-bottom suspension speed for concentric biaxial stirrer is presented. In order to describe the solid suspension characteristics of concentric biaxial agitator more intuitively, The solid suspension characteristics of a concentric biaxial stirrer are studied by CFD method. In order to establish a reasonable mathematical model, the simulation results of the commonly used Gidaspow drag model and the modified Brucato drag model are compared with the previous experimental results. It is found that the modified Brucato drag model is more accurate in predicting the flow parameters of solid-liquid two-phase stirring system, and the average solid holdup of the 1mm plane from the bottom of the kettle changes with the rotational speed. It is found that the average solid holdup decreases slowly at first and then decreases sharply with the increase of the rotational speed. Finally, it tends to be stable. According to the curve of average solid holdup and rotational speed on the plane of 1mm from the bottom of the kettle, the critical off-bottom suspension speed is simulated and predicted, which is in good agreement with the experimental results. The simulation also shows the solid state flow patterns directly under three kinds of propeller combination conditions. The distribution of solid holdup and flow pattern under different rotation modes and rotational speeds of the outer propeller are shown, and the effects of liquid viscosity and solid holdup on the distribution of solid phase are also studied.
【学位授予单位】：浙江大学
【学位级别】：硕士
【学位授予年份】：2017
【分类号】：TQ051.72

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