Eccentric Jet Strengthen Fluid Chaotic Mixing

Stirred tank was widely used in many industries, such as chemical engineering,petrochemical, light industry, medicine, metallurgy, water treatment and so on. It wasinput to mechanical energy by the rotation of agitator, which make fluid obtain anappropriate flow field, the process of the heat transfer and mass transfer were intensifiedand the production efficiency and ability were improved. The Research showed thatnearly70%the energy of agitator concentrated dissipative in blades tips. Therefore thefluid turbulent area was formed in the tip area of impeller. The transmission of turbulentarea concentration energy relied on fluid motion around agitator. Therefore the flowfield structure of fluid in the stirred tank was regulated and controlled and fluid motionaround agitator was intensified, which were being attention by researchers.With the development of nonlinear and chaos theory, the chaos phenomenonstarted to be used to control the flow structure in order to strengthen the mixedperformance of the fluid. The flow field structure contains the chaotic mixing zone andseparation mixed zone. The fluid trajectories in the chaotic mixing region are morecomplex, which is stretched by the law of Lyapunov exponents, leading a high degree ofmixing. While the fluid trajectories rules in the separation zone only stretched by thelinear law, leading that the degree of coupling and the mixing degree is not high.Therefore, changing the structure of the flow field (to increase chaotic mixing zone, toreduce the mixing zone of separation), to achieve the chaotic mixing is an effective wayto improve the mixing efficiency.Focus on the characteristics of the eccentric jet, the jet mixing and mechanicalmixing will form a different flow field,and the coupling of these two flow fieldinevitably induce chaotic mixing.While the eccentric mixing and jet mixing to improvethe asymmetric structure of the flow field,prompting the chaotic region in the flow fieldincreases. Thus, this paper presents the eccentric jet mixing method.the experimentacquired the pressure fluctuation signal of the stirred tank reactor with LabViewsoftware, and made the anaysis of the signals by Matlab software.This work willprovide a theoretical guidance for the amplification experiment and industrialization bycombining the chaotic mixing characteristics of the chaotic parameters and simulationof flow field in stirred tank. This paper mainly studied the following respects:①The LABVIEW virtual instrument software was used to acquit the pressure fluctuation signal of the stirred tank, and after the processing by wavelet analysis, themacro-instability frequency of the fluid could be acquested. In the single liquid phase,macro-instability dimensionless frequency peak followed by0.02548,0.01500,0.00148,0.00146at100,130,165,195rpm stirring speed respectively.Result showed thatthe peak decreases,which meaned the macro-instability weakened. Macro-instabilitydimensionless frequency (f/N) and stirring speed is linearly proportional, ie, f=10-4N,while with the joinment of the jet the macro-instability frequency disappeared andbands phenomenon appeared.The multi-scale structural character of the coherentstructures in flow field is more pronounced, leading to chaotic fluid mixingcharacteristics enhanced.②The experimental studied the fractal dimension variation of the flow structure indouble-layer tank with eccentric jetting by the image processing software.Theexperimental results showed that the the fractal dimension of the flow field wasinfluenced by the stirring speed and air flow. At the speed of350rpm, the fractaldimension of the fluid in the stirred tank fluid is1.1552,1.2189,0.9875,1.2157,1.1974,1.2484,1.2870by the flow of40,50,60,70,80,90,100L/min;③The variation of the largest Lyapunov exponent in stirred tank was calculatedwith the collection of pressure fluctuation signal in the wall by pressure sensortransmission and programming analysis of the collected singles in the Matlabplatform.The results showed that: the Lyapunov exponent value approaching equal tozero when the stirring speed up to130rpm by the single stirring,while with the join ofthe jetting,the fluid in tank will enter a chaotic state when the stirring speed up to20rpm.Which means that,with the join of jetting,at a low-speed mechanical stirringspeed the fluid in the stirred tank could enter a chaotic state easily;④The computational fluid dynamics software fluent was employed to simulate thefluid structure of the gas-liquid jet mixing system by the multiple reference frame(MRF)method. The simulation results verified that the jetting induce chaotic mixing.