Piv Experimental Study Of Flow Field In A Stirred Tank With Draft Tube

Stirred vessels equipped with draft tube are widely used in both domestic and foreign chemical industry for a variety of mixing processes, such as crystallization, ore dressing, bioengineering and polymerization industry and other fields. In this thesis, mean velocity, turbulent kinetic energy and the nature of flow field in a draft tube stirred tank stirred by a CBY impeller were investigated by using PIV experimental methods. This investigation will help to optimize the mixing equipments designing, and improve the reliability of stirred tank reactor on the field of engineering application.The experiments were carried out in a plexiglass vessel of284mm in diameter. The diameter of draft tube was184mm, and H=450mm. The effects of impeller blade installation, stirred vessel geometries, dual impeller and Reynolds number in a draft tube vessel were systematically investigated. The experiments show that the impeller blade installation of upward can provide a better flow structure in the flow field, but at the bottom area of the vessel it exists an obvious secondary flow phenomenon. When the bottom structure of the stirred tank changed from flat bottom to elliptical bottom, the original dead zone and secondary flow phenomenon at the bottom area disappeared. We can find that an elliptical bottom stirred tank equipped with an upward installation impeller will better improve the mixing efficiency in a draft tube vessel.Under the condition of the guarantee the same clearance of the CBY impeller, we installed a Rushton turbine impeller under the draft tube. In the phase-resolved results, different phases have little effect on the upper CBY impeller. However, there is a significant difference of the lower RT impeller at different phases on the flow field.In this paper, the effects of Renolds number in the draft tube vessel have also been discussed through changing the working medium. The results show that the influence of the Renolds number changed the flow pattern dramatically in the whole tank, especially in the dual impeller mixing system.