Study On The Numerical Simulation And Experiment Of The Three-Dimensional Flow Field In Straight-Gradient Impeller Stirred Tank

Stirred equipment are widely used in chemical engineering, biomedical engineering, pharmaceutical engineering, material processing and food processing. When the media in stirred tank is shear-stress-sensitive, mixing is often required in a laminar flow state with low Reynoles number. How to deal with the attendant phenomena such as the mixing efficiency falling and the by-products increasing, have been becoming the urgent problem in laminar stirred tank study.In the paper, the studies of theory analysis,numerical simulation and experiment were done to reveal the form mechanism,flow characteristic,influence factor and application in engineering of mixing in double straight-gradient impeller stirred tank.(1)Introduce the flow characteristic in stirred tank, bring forward an idea of dissymmetrical three-dimensional mixing, and use the variety of impeller configuration and the dissymmetrical disposal in stirred tank to enhance the agitation of laminar fluid in stirred tank and improve the mixing efficiency.(2)Using CFD software FLUENT6.1, adopting MRF and Laminar-model to simulate separately the agitation flow field of non-Newtonian fluid (a mixture of glycerin and water) in aΦ200mm plexiglass stirred tank with different organizational impellers. Study the flow characteristic of double straight impeller,double gradient impeller and double straight-gradient impeller centered mixing,eccentric mixing and reverse eccentric to axis mixing, compare and analyse the simulation result. The results show that the factors such as shape of the blades,organizational structure have a great influence on the form of fluid field.(3)Using the durative laser sheet and the tracer particles to describe qualitatively the macro fluid field in the stirred tank with two organizational impellers in three different layouts. The flow field is basically consistent with the numerical simulation result, that is to say the CFD method can have a good simulation of the true situation. The gradient blade make the synthesis speed at the junction of the two circles which above and below it is not level. Take the pressure impeller for example, it can make the synthesis speed at the junction declined and the above circle stronger than the below one. And the more gradient blades it has, the more obvious this phenomenon is.