Reserarch On The Flow Field In A Stirred Tank Under Low Reynolds Number

Fluid of low Reynolds number plays an important role in chemical, pulp, polymer, and other process industries while Existing researches are mainly concentrated on high Reynolds number (fully turbulent) conditions. Therefore, this project focused on low Reynolds number experimental research of stirred tank flow field characteristics to strive to provide basic data for numerical simulation of stirred tank/reactor, and for guidance of plant design.In this paper, stereoscopic particle image velocimetry(SPIV) technique is introduced to study flow field of6-blade Rushton turbine in a stirred tank under low Reynolds number(Re) conditions. We choose Re as main parameters, and by means of adjusting the viscosity and speed, we succeeded in controlling Reynolds number(50to3000,and1000) for flow field analysis and comparison.It is revealed in this study that turbulent kinetic energy improved significantly as Reynolds number increases when Re was less than1000; while in range of1000<Re<3000, the impact of Re on turbulent kinetic energy was very small. It was also shown that when compared to radial and axial velocity, tangential velocity was less affected by Re. Comparison indicated that the flow field of10°phase angle had the maximum average value of tangential velocity back of the blade and the distribution gradually moved towards the tank wall following the radial jet as the phase angle increases. Trailing vortex structure disappeared at40°when Re number was larger than1400. The value of tangential velocity field didn’t decrease as it was thought when Re fell down, while turbulent kinetic energy distribution was affected by the Re obviously in phase average flow fields. The results also showed that in the conditions of low Re numbers using a Rushton turbine impeller, the Turbulent Kinetic Energy (TKE) estimated by2D method was lower than the value computed by3D method in the range of r/R from0.75to1.25. But this situation changed when r/R<0.75and r/R>1.25. In these coordinate intervals, TKE attained by two methods were in good agreement which illustrated the real flow field around the impeller was anisotropic.In addition, it is clear that flow field of low Reynolds number is very different from flow field of high Reynolds number. Comparison of results of two-dimensional PIV and three-dimensional PIV shows that the latter is closer to real flow field.