Study On Chaotic Mixing Performance Of Fluid Intensified By Punched-flexible Combined Impeller

In oil refining, chemical industry and metallurgy industries, such as stirring reactor is an important unit operation. And the effect of fluid mixing determines the economy. The working mechanism includes that stirring shaft transmits mechanical energy to the flow field and form a good flow field structure. So the process strengthens the mass and warm transfer and improves the efficiency of industrial production.As everyone knows, stirred tank is the core part of the blade. The energy is conveyed to flow through it. Designing blade and analyzing the field are two popular directions in fluid dynamics. Combined with the actual needs, researchers have developed many new impellers and applied them in industrial production. Among them, punched-flexible impeller can improve the flow field structure effectively. So it is of great practical value to analyzing mechanism of punched-flexible impeller and mixing behavior.Double impeller was employed in experimental process. In the present research, the signal of pressure fluctuation in flow field and the chaotic characteristic parameters of Kolmogorov entropy, largest Lyapunov exponent and the frequency of macro-instability were collected and calculated by software Labview and Matlab. And the variation of the chaotic characteristic parameters coming after the increased revolving speed in punched-flexible impeller system was also studied. It aimed to provide fluid mixing amplification experiments and practical production application with certain theoretical basis and data support. In this paper, the specific research contents were showed by followings:1.With the help of sampling system, the signal of pressure fluctuation in flow field was collected. Combined with G-P algorithm and least square method, Kolmogorov entropy was calculated. The corresponding results indicated that punched impeller didn't have the effect on the enhancement of chaos under 180 r·min^-1. The Kolmogorov entropy in system of punched-flexible impeller was greater than that in system of traditional impeller. Through the role of flexible parts and the hole, punched-flexible impeller suppressed the oneness and immobility of quasi-ordered structure near the blade. At 180 r·min^-1,in the range of 1 cm 5 cm, Kolmogorov entropy in system of punched-flexible impeller was increased with increasing of length of the flexible material.2. With the help of OpenTSTOOL, the largest Lyapunov exponent was calculated. The influencing factors of the largest Lyapunov exponent has been analyzed, such as sampling point, revolving speed, punched-flexible impeller and the spacing between blade up and down. Besides, the experiment demonstrated that the monitoring point has no effect on the largest Lyapunov exponent in stirred reactor. With the enlargement of revolving speed, the largest Lyapunov exponent increased first, and then decreased rapidly, and the degree of mixing achieved the optimal effect when the revolving speed was 180 r·min^-1. Compared with traditional impeller, the punched-flexible impeller could make chaos state of fluid in an easier way, and the largest Lyapunov exponent increased with the length of flexible part. Under the condition of 180 r·min^-1, the spacing between blade up and down were T and 1.1T, the largest Lyapunov exponent were 0.0136 and 0.0138, respectively, and the best state was under the spacing of 0.3T with the largest Lyapunov exponent of 0.0143.3. The influencing factors of the frequency of macro-instability has been analyzed, such as sampling point, revolving speed, punched-flexible impeller and the spacing between blade up and down. With the increasing of revolving speed, the frequency of macro-instability in stirred reactor increased with a liner relationship of fMI = 0.0018 N. When the revolving speed lower than 180 r·min^-1, the frequency of macro-instability of punched-flexible impeller system was higher than that of traditional impeller system. When the revolving speed was 180 r·min^-1, there was no macro-instability under the spacing of 1.2T, while the frequency of macro-instability was 0.4097 Hz and 0.3356 Hz respectively under the spacing of 1.1T and T.4.The mixing time in stirred reactor was calculated by decolor method. The influencing factors of mixing time the has been analyzed, such as sampling point, revolving speed, punched-flexible impeller and the spacing between blade up and down, and the flow field visualization was analyzed. The mixing time was decreased with the increase of revolving speed. It is found that the mixing time of punched impeller system was lower than that of traditional impeller system, but the phenomenon was little obvious, indicating that the punched impeller system has little effect on reducing mixing time, while the punched-flexible impeller system possessed better effect. Additionally the spacing between blade up and down affected mixing time, the addition of flexible part accelerated the formation of isolation area, which was in favor of fluid mixing.