搅拌槽内部流场及固液悬浮特性的数值模拟分析

发布时间：2018-11-08 13:05

【摘要】：搅拌设备因具有操作灵活、混合效果好、相接触面积大和适用性强的优点而广泛用在机械、化工等过程工业中,是应用最广泛的化工单元操作之一。其中,搅拌槽内部流场和固液悬浮特性的研究,对工业生产有重要意义,因此是国内外学者研究的热点内容之一。近几年来,搅拌反应器的规模逐渐变大,相与相之间混合不均匀的问题也越来越明显,并且当前机械过程逐渐转向“绿色”、节能方向,越来越看重产品回收率和产品质量,因此合理设计和选择搅拌设备就显得特别重要。但如今对搅拌设备的选择和设计仍然是主要依赖于小规模实验结果以及半理论和半经验的方法,由于技术和条件的限制在设计中并不能清晰的了解搅拌槽内部流场的详细分布情况,而且对搅拌反应器放大规律缺乏较深入的认识,实验模拟周期长、偏差和花费大。新的交叉学科计算流体力学技术为解决上述问题提供了新思路和新方法,其技术优势使得搅拌槽内部流场及固液悬浮特性的数值模拟成为搅拌领域的研究热点之一,但是搅拌槽内部流场及固液悬浮特性的数值模拟还没有形成较为完善的理论。本文以计算流体力学技术为主要研究手段,采用多重参考系法和标准κ—ε湍流模型对搅拌槽内部流场及固液悬浮特性进行了数值模拟,研究分析了搅拌转速、桨离底间隙、固体颗粒浓度等因素对流场分布、固体颗粒浓度分布、临界悬浮转速和功率消耗的影响。研究结果表明,桨叶离底间隙对搅拌槽内流场及固液悬浮状态影响很大,低离底间隙有利于槽内固体颗粒的悬浮,但是当离底间隙过低时,功率消耗比较大,且桨叶离底间隙越低越容易出现清液层；增加搅拌转速能够改善搅拌效果,但是考虑到搅拌功率、耐久度等因素的影响,并不是搅拌转速越大越好,需要综合考虑来确定合适的搅拌转速；桨离底间隙、固体颗粒直径和固体体积浓度对搅拌功率均有影响,在相同条件下,功率消耗随桨离底间隙的不同而不同,在C=T／4、T／5和T／6三种工况下,C=T／4时功率消耗最小；在相同条件下,功率消耗随固体颗粒直径的增大而增加；在同一搅拌转速下,功率消耗随固体体积浓度的减小而增加。
[Abstract]:Because of its advantages of flexible operation, good mixing effect, large contact area and strong applicability, mixing equipment is widely used in mechanical, chemical and other process industries, and is one of the most widely used chemical unit operations. Among them, the study of flow field and solid-liquid suspension characteristics in stirred tank is of great significance to industrial production, so it is one of the hot topics of domestic and foreign scholars. In recent years, the scale of stirred reactor has gradually become larger and the problem of uneven mixing between phases has become more and more obvious, and the current mechanical process is gradually turning to "green", energy-saving direction, and more emphasis on product recovery and product quality. Therefore, reasonable design and selection of mixing equipment is particularly important. But today, the selection and design of mixing equipment is still mainly dependent on small-scale experimental results and semi-theoretical and semi-empirical methods. Due to the limitation of technology and conditions, the detailed distribution of the flow field in the stirred tank can not be clearly understood in the design, and the detailed distribution of the flow field in the stirred tank is not well understood, and the experimental simulation period is long, the deviation and the cost are large. The new cross-disciplinary computational fluid dynamics (CFD) technology provides a new way of thinking and a new method to solve the above problems. Its technical advantages make the numerical simulation of the flow field and solid-liquid suspension characteristics in the stirred tank become one of the hot spots in the agitation field. However, the numerical simulation of the flow field and solid-liquid suspension characteristics in the stirred tank has not yet formed a more perfect theory. Based on computational fluid dynamics (CFD) technique, the flow field and solid liquid suspension characteristics in stirred tank are numerically simulated by means of multiple reference system method and standard 魏-蔚 turbulence model. The stirring speed and the bottom clearance of the impeller are studied and analyzed. The influence of factors such as solid particle concentration on flow field distribution, concentration distribution of solid particles, critical suspension speed and power consumption. The results show that the clearance of blade bottom has a great influence on the flow field and the solid liquid suspension state in the stirred tank. The low bottom gap is favorable to the suspension of solid particles in the tank, but when the gap is too low, the power consumption is relatively large. The lower the clearance from the bottom of the blade is, the easier it is to appear the liquid-clearing layer. Increasing the stirring speed can improve the stirring effect, but considering the influence of the stirring power and durability, it is not better to increase the stirring speed, so it is necessary to determine the appropriate stirring speed synthetically. The impeller bottom clearance, solid particle diameter and solid volume concentration have effects on the stirring power. Under the same conditions, the power consumption varies with the bottom clearance of the propeller. Under the three conditions of C / T / 4 / T / 5 and T / 6, The power consumption is minimum at C=T/ 4; Under the same conditions, the power consumption increases with the increase of solid particle diameter, and increases with the decrease of solid volume concentration at the same stirring speed.
【学位授予单位】：安徽理工大学
【学位级别】：硕士
【学位授予年份】：2015
【分类号】：TQ051.72

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