新型气液分散搅拌桨的设计与性能表征

发布时间：2018-05-23 14:17

本文选题：气液分散 + 搅拌桨设计　；参考：《江南大学》2017年硕士论文

【摘要】：很多涉及氧化反应或氢化反应的过程都需要用到气液分散搅拌桨,如生物发酵过程中需要维持一定量空气以满足微生物对氧的需求。径向流搅拌桨是应用最广泛的气液分散搅拌桨,是通气式机械搅拌罐中的关键装置,也是搅拌系统中的主要耗能部件。随着工业生产规模扩大以及能源逐渐短缺,设计开发一种低功耗、高效率的新型气液分散搅拌桨变得尤为重要。本文通过理论分析、计算流体力学(CFD)模拟和实验测试相结合的手段设计开发一种新型气液分散搅拌桨,并对其进行性能表征。通过CFD模拟分析平直叶桨(RT)、半圆弧桨(CD)和非对称抛物线形桨(BT)三种传统径向流搅拌桨结构和性能特点,发现其演化趋势是功率准数更低、泵送效率更高、轴向覆盖面积更大。同时研究不同桨叶外缘结构和尺寸对搅拌性能的影响,结果表明桨叶外边缘顶点曲率增大可减小功率准数和提高泵送效率,轴向高度减小可使功率准数减小但对泵送效率提升不明显。然后提出新颖的扇环抛物面形桨叶结构设计,发现装配该桨叶的扇环形搅拌桨(FT)表现出最佳操作性能,与传统桨中效果较好的非对称抛物线形桨(BT)相比,其功率准数下降30.8%,泵送效率提高22.6%,轴向投影面积率增加21.5%,具有应用于气液操作时高效传质的潜力。基于3D打印技术加工制作新型FT桨和工业上常用的气液分散搅拌桨RT和BT。实验测试新型FT桨在通气条件下操作性能,并与另外两种搅拌桨对比。结果表明:FT桨功率准数较低,为1.7左右;相对功率需求(RPD)更高,高转速搅拌时接近1.0;临界分散转速比BT略低,明显高于RT;气含率和体积传质系数与BT相近,均高于RT;FT桨氧传质效率明显高于RT和BT,约比RT提升40~70%,比BT提升17~40%。使用粒子成像测速技术(PIV)测试流场速度,并结合其他实验数据验证所建立CFD计算模型可靠性。然后基于CFD手段分析新型FT桨的微观特性,并在相同条件下同RT和BT对比。结果表明:FT桨速度分布规律与BT桨相近,不同于RT桨;在大部分位置上,FT桨的流场速度、剪切力、湍动能和湍动能耗散率的值均小于RT桨,但FT桨特性参数值分布更加均匀,BT桨特性介于RT桨和FT桨之间。通过气液两相流模拟得到,BT桨流场中气泡数量最多,FT桨次之,RT桨最少,但FT桨流场中的小尺寸气泡占比最高。
[Abstract]:Many processes involving oxidation or hydrogenation require the use of gas-liquid dispersed agitators, such as maintaining a certain amount of air during biological fermentation to meet the oxygen requirements of microorganisms. Radial flow impeller is the most widely used gas-liquid dispersed agitator. It is the key device in the aerated mechanical agitator and the main energy consuming part in the mixing system. With the expansion of industrial production and the gradual shortage of energy, it is particularly important to design and develop a new type of gas-liquid dispersed agitator with low power consumption and high efficiency. In this paper, a new type of gas-liquid dispersed agitator is designed and developed by theoretical analysis, computational fluid dynamics (CFD) simulation and experimental test, and its performance is characterized. The structure and performance characteristics of three kinds of traditional radial flow impellers are analyzed by CFD simulation. It is found that the evolution trend is lower power criterion, higher pumping efficiency and larger axial coverage area. At the same time, the influence of the structure and size of the outer edge of the blade on the agitation performance is studied. The results show that the increase of the curvature of the outer edge of the blade can reduce the power standard number and improve the pumping efficiency. The decrease of axial height can reduce the number of power standards, but it can not improve the pumping efficiency obviously. Then a novel structural design of the fan ring paraboloid propeller blade is proposed. It is found that the fan annular impeller (FTF) assembled with the blade exhibits the best operating performance, compared with the asymmetric parabola propeller (BTT), which has a better effect in the traditional propeller. Its power standard number is reduced by 30.8, pumping efficiency is increased by 22.6and axial projection area ratio is increased by 21.5. it has the potential of high efficiency mass transfer in gas-liquid operation. Based on 3D printing technology, a new type of FT propeller and gas liquid dispersed agitator RT and BT are fabricated. The operating performance of the new FT propeller under aeration condition was tested and compared with the other two kinds of impellers. The results show that the power standard number of the rotor is lower (about 1.7), the relative power demand is higher, the critical dispersion speed is slightly lower than BT, and the volume mass transfer coefficient is close to BT, the critical dispersion speed is slightly lower than BT, and the volume mass transfer coefficient is close to BT. The oxygen mass transfer efficiency was significantly higher than that of RT and BTT, about 40 / 70 than RT and 17 / 40 than BT. The particle imaging velocimetry (PIV) is used to measure the velocity of the flow field, and the reliability of the established CFD model is verified by other experimental data. Then the microcosmic characteristics of the new FT propeller are analyzed based on CFD and compared with RT and BT under the same conditions. The results show that the velocity distribution of the rotor is similar to that of BT propeller and is different from that of RT propeller, and the velocity of flow field, shear force, turbulent kinetic energy and turbulent kinetic energy dissipation rate of FT propeller are all smaller than those of RT propeller in most positions. However, the characteristics of FT propeller are more uniform and the characteristics of BT propeller are between RT propeller and FT propeller. Through the simulation of gas-liquid two-phase flow, it is found that the number of bubbles in the flow field of BT propeller is the most, and that of FT propeller is the least, but the fraction of small bubble is the highest in the flow field of FT propeller.
【学位授予单位】：江南大学
【学位级别】：硕士
【学位授予年份】：2017
【分类号】：TQ051.72

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