粘稠体系下同心双轴搅拌器气液分散和混合特性的研究

发布时间：2018-06-02 11:12

本文选题：同心双轴搅拌器 + 粘稠体系　；参考：《浙江大学》2015年硕士论文

【摘要】：气液搅拌反应器广泛应用于化工、食品、化妆品加工、生物化学、污水处理、聚合等过程工业中。对搅拌器的气液分散和混合性能进行研究,对于深入理解气液分散、混合以及放大机理,进而指导工业生产具有很大的帮助。文献中已有大量关于搅拌器气液分散和混合特性的研究,但仍存在很多不足之处：首先,研究体系大多为水／低粘液体-空气体系,而实际工业生产中体系的物性复杂的多,粘度较大或者为非牛顿流体等；其次,研究对象几乎全为单轴搅拌器,而且粘稠体系下局部参数的实验测量也很是欠缺。因此,对同心双轴搅拌器在粘稠体系下的气液分散和混合特性进行系统研究很有必要。本文创新设计了适用于同心双轴气液搅拌的新型框式外桨和新型进气系统。实验过程中,在比较了同心双轴搅拌器和单轴搅拌器气液分散特性优劣的基础上,系统研究了操作条件(转速、通气量、内外桨的转动模式)、桨型组合(三种桨型组合：框式外桨+Rushton/SBT-6/PBT-6)、不同粘度(最大粘度0.3Pa·s)对同心双轴搅拌器在粘稠体系下气液分散和混合特性的影响。本文还采用计算流体力学(CFD)方法,对三种桨型组合同心双轴搅拌器在粘稠体系下(最大粘度0.8Pa·s)的气液分散和混合特性进行了研究,得到了宏观流场、局部气含率、局部气泡尺寸、剪切速率等信息,并进行分析,很好的验证和补充了实验研究的内容,对深入理解气液分散和混合机理起到了很好的帮助作用。结果发现：a)反向转动模式下的双轴搅拌器相对单轴搅拌器气液分散性能优势明显；b)相同条件下,三种桨型组合中,框式外桨和Rushton桨的组合气液分散和混合特性最好。并且,内外桨反向转动模式优于同向转动；c)一定范围内,粘度增大,整体气含率增大,但粘度的增大对整釜内气液分散的均匀性有不利的影响,导致近壁区局部气含率下降；d)一定条件下,转速越大,气液分散性能越好,整体气含率和局部气含率均越大；e)通气量对整体参数和局部参数的影响相对较复杂。虽然,一定转速下,通气量越大,桨叶背部形成的气穴结构越大,搅拌桨的泵送能力越差,越不利于气泡在釜内的均匀分散。但是,当转速保持在泛点转速之上时,增大通气量,气液分散状态仍较好,整体气含率和局部气含率均有一定程度的提高。模拟得到的结果和实验值对比发现,总体来说,模拟值和实验值吻合良好,并且,模拟结果对解释实验现象和加深对气液分散和混合机理的理解帮助很大。
[Abstract]:Gas-liquid stirrers are widely used in the process of chemical industry, food, cosmetic processing, biochemistry, sewage treatment, polymerization and other process industries. The study of the gas-liquid dispersion and mixing performance of the agitator is very helpful for understanding the gas and liquid dispersion, mixing and amplification mechanism, and then refers to the industrial production. In the study of the gas and liquid dispersion and mixing characteristics of the agitator, there are still a lot of shortcomings. First, most of the research systems are water / low viscosity liquid air system, and in actual industrial production, the system has more complex physical properties, larger viscosity or non Newtonian fluid. Secondly, the research object is almost all the uniaxial agitator, and the viscous body is almost all. Therefore, it is necessary to systematically study the gas-liquid dispersion and mixing characteristics of the concentric biaxial agitator in the viscous system. A new type of frame propeller and a new type of inlet system suitable for the concentric biaxial gas-liquid agitation are innovated and designed in this paper. In the experiment, the concentric double shaft agitation is compared. On the basis of the advantages and disadvantages of the gas-liquid dispersion characteristics of the mixer and the uniaxial agitator, the operating conditions (rotational speed, ventilation volume, and the rotation mode of the inner and outer paddles), the combination of the paddle type (three types of paddle combinations: the frame type outer paddle +Rushton/SBT-6/PBT-6), and the different viscosity (maximum viscosity 0.3Pa s) of the concentric biaxial agitator in the viscous system and the dispersion and mixing of gas and liquid under the viscous system are systematically studied. This paper also uses computational fluid dynamics (CFD) method to study the gas-liquid dispersion and mixing characteristics of three types of propeller type combined concentric biaxial agitators in a viscous system (maximum viscosity 0.8Pa s). The macroscopic flow field, local gas holdup, local bubble size, shear rate and other information are obtained, and the analysis is a good verification. And supplemented the content of the experimental study, it is a good help to understand the mechanism of gas and liquid dispersion and mixing. Results: a) the gas-liquid dispersion performance of the dual axis agitator under the reverse rotation mode is obvious; b) under the same condition, the combined gas-liquid of the frame type and the Rushton paddles in the three type of propeller combinations. The characteristics of dispersion and mixing are best. Moreover, the reverse rotation mode of the inner and outer paddles is superior to the same direction rotation; c) in a certain range, the viscosity increases and the holistic gas holdup increases, but the increase of the viscosity has an adverse effect on the uniformity of the gas and liquid dispersion in the whole kettle, resulting in the decrease of the local gas holdup in the near wall region; under certain conditions, the greater the rotational speed and the dispersion performance of the gas and liquid. The better, the greater the gas holdup and the local gas holdup, the greater the overall gas holdup and the local gas holdup, the more complex the influence of the E) on the overall and local parameters. Although the larger the ventilation volume is, the greater the aeration, the greater the cavitation structure of the blade back, the worse the pumping capacity of the agitator, the more unfavorable to the uniform dispersion of the bubbles in the kettle. When the speed is above the point, the volume of aeration is increased, the dispersion state of the gas and liquid is still better, the overall gas holdup and the local gas holdup are improved to a certain extent. The simulated results are in good agreement with the experimental values compared with the experimental values. The simulation results can explain the experimental phenomena and deepen the dispersion and mixing mechanism of the gas and liquid. Understanding is very helpful.
【学位授予单位】：浙江大学
【学位级别】：硕士
【学位授予年份】：2015
【分类号】：TQ051.72

【参考文献】