PIV Experimental Reseach And Numerical Simulation Study On Flow Field Of The Mechanical Agitation Tank

Mechanical stirring device could be used in many engineering fields and it is anecessary device in the chemical industry, water treatment,etc.The fluid mixing couldpromote heat transfer and mass transfer and could do many other things then itsfunction is very important. Mechanical agitation tank also could be widely used in ourcountry’s main biological technology such as biological pharmacy and foodfermentation industry，it is an essential equipment to promote good solid-liquidmixing.For mixing，convection, pulsation and molecular diffusion are the internaldriving factors for promoting mixing or why mixing can occur，so the research oncharacteristics of flow field in stirred tank has the great significance.In this paper，PIV measurement technique has been carried on the mechanicalagitation tank flow field experimental study，at the same time the commercial softwareFluent has been used for the flow field experimental study，specifically multiplereference frame method has been used based on RNGk-ε model and Large eddysimulation model on the numerical calculation research，and in this paper the foldpaddle of45°blade has been adopted. In the PIV experimental research，important flowfield influencing factors such as rotational speed，the distance between the two layers ofblade，the distance between the lower blade and the bottom have been analyzed throughthe flow field distribution， the vorticity distribution， the pulse distribution ofinstantaneous velocity with time and the turbulent kinetic energy distribution.In addition，the interaction mechanism of the flow field between two layers of blade has beenanalyzed.The analysis results show that the increase of rotational speed does not changethe flow pattern of flow field but it would increase the average velocity，fluctuationvelocity and turbulent kinetic energy;and expand the distance between the blades of twolayers could not only help to expand the scope of the subject big circulation but alsohelps to expand the scope of turbulence; what’s more,the change of the distance betweenthe lower blade and the bottom could change the relative positionof the main body bigcirculation in the flow field and could lead to the anticlockwise circulation under liquidsurface and near the stirring shaft compression or expansion.The lower blade area underthe convection and pulsating seems so weak，so properly reduce the height from thebottom of the lower blade is quite necessary；In terms of the influence of the flow field， two layers of blade is equal to the upward displacement of the two blade series.Throughnumerical simulation and the results contrast analysis between experimental andnumerical simulation，it was found that RNGk-ε model and Large eddy simulationalmost has the same effect on the flow field distribution and basically can match withthe experimental results.But by comparing the area under the lower blade and flow fieldmain body big circulation around the center position and flow pattern，Large eddysimulation results is more close to experimental value. Through the comparisons ofvelocity distribution images we could find that generally the value of the large eddysimulation conforms to the the experimental value better compared with RNGmodel，but dose not deny that the phenomenon of local differences also exist in someplaces.