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摘要搅拌是化工生产中重要的单元操作之一，搅拌过程中存在着一种大尺度、低频率的流型变化现象，即宏观不稳定现象。研究该现象对缩短混合时间、增强混合效果、提高传热传质效率有着十分重要的意义。本文采用高精度液位变送器与自编基于软件Labview的采样程序与基于软件Matlab的频谱分析程序，研究了双层6-HEDT桨搅拌槽内转速、采样位置、桨间距及离底高度对宏观不稳定性频率的影响，并将部分实验结果与计算机模拟结果对比。实验结果表明，运用压力传感器与Labview程序相结合的方法可以出色的完成对搅拌槽内的信号进行实时监测与采集任务。运用Welch平均交叠法与hanning窗函数对实验数据进行频谱分析，可以获得不同工况时的宏观不稳定性频率。宏观不稳定频率的测量与压力取样位置近似无关。当桨间距为180mm,离底高度为186mm，水为搅拌介质，转速分别为60rpm、100rpm及140rpm时，宏观不稳定性频率的主频分别为0.1563Hz与0.4688Hz、0.3125Hz、0.3906Hz；以聚醚多元醇为搅拌介质，当转速分别为150Hz、180Hz、210Hz时，宏观不稳定性主频分别为0.3516Hz、0.4297Hz及0.5859Hz。说明在不同介质中，搅拌桨转速对宏观不稳定性均有明显的影响，并且转速越低，宏观不稳定频率越低，宏观不稳定现象越明显。转速为140rpm，桨间距为80mm时，两桨间抑制作用强烈，宏观不稳定性主频被噪声掩盖，等效于单桨搅拌。桨间距为300mm时，两桨间抑制作用微弱，观察到0.07813Hz、0.3906Hz两个清晰的主频，等效于两个独立桨叶。此外，离底高度对宏观不稳定性频率也有显著影响。计算机模拟结果与实验结果基本吻合，说明计算机模拟适用于搅拌槽中宏观不稳定现象的研究。19164
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键词 宏观不稳定性；搅拌槽；压力；频谱分析
毕业设计说明书（论文）外文摘要
Title Study on macro-instabilities of fluid in a double-deck stirred tank
Abstract
Stirring is one of the most important unit operations in chemical process industry, there are large-scale and low-frequency phenomena accompanied with stirring processes, these phenomena are referred to as macro-instabilities (MI) and making influences on changes of flow patterns. Studying these phenomena could make great contributions to decreasing mixing time, improving mixing effects, and raising heat and mass transfer efficiencies. In this study, a high-precision pressure sensor, a self-made sampling program (based on Labview) and a self-made spectral analysis program (based on Matlab) were used to study the influences of rotating speeds, sampling locations, propeller pitches and off-bottom clearances on the frequencies of macro-instabilities in a double-deck 6-HEDT stirred tank, part of experimental results were compared with the simulated results. The experimental results showed that the combination of pressure sensor and Labview program was capable of detecting and recording signals in stirred tank in real time. The combination of Welch average overlap method and hanning window was capable of spectral analysis in the experiment. Sampling locations almost had no effects on detecting MI frequencies. When the propeller pitch was set as 180mm, the off-bottom clearance was set as 186mm ，water was used as stirring medium and the rotating speeds reached 60rpm,100rpm,and 140rpm respectively, the dominated frequencies of MI frequency were 0.1563Hz and 0.4688Hz,0.3125Hz,and 0.3906Hz respectively. When polyether polyol was used as stirring medium and the rotating speeds were set as 150Hz, 180Hz, and 210Hz, the dominated frequencies of MI frequency were 0.3516Hz, 0.4297Hz, and 0.5859Hz respectively. It could be known that, in the same stirring medium, the smaller the rotating speeds, the lower the MI frequencies and the less obvious of the MI phenomena. Moreover, when the rotating speed reached 140rpm and propeller pitch was set as 80mm, the inhibiting effects between two impellers were intense and the dominated frequency was overwhelmed by background noises, this situation was equal to single-impeller condition. When propeller pitch was set as 300mm, there were barely no effects between impellers and two obvious dominated frequencies（0.07813Hz and 0.3906Hz） were observed, this situation could be treated as two-separated-impeller condition. What’s more, the MI frequencies were remarkably influenced by the variances of off-bottom clearances. The experimental results matched the simulated results well and it could be known that computer simulation was suited to studying the MI phenomena in stirred tank.