Turbulent flow in stirred vessels agitated by a single, low-clearance hyperboloid impeller

摘要

Detailed angle-resolved measurements of the mean and rms of the three components of the velocity vector were carried out by laser-Doppler anemometry in a stirred vessel mechanically agitated by a ribbed, low power consumption hyperboloid impeller at a Reynolds number of 50,000. Due to the small clearance of the agitator the flow pattern in the vessel was typical of that encountered when using an axial turbine although the flow in the vicinity of the impeller was alike that in a radial device with the mean flow discharge following a X- type pattern. In mbst of the vessel the flow was gentle with mean velocities of the order of 5% of the tip velocity, increasing to about 20% Vimp towards the tip of the impeller because of the ribs. Their small size limited the extent of periodic flow to a region delimited by the bottom and z/R = 0.2 in the vertical direction, and r/R = 0.85—1.4 in the radial direction, plus the volume below the impeller. In these regions the turbulence was not isotropic and reached the highest values so that the maximum turbulence kinetic energy was 65% higher than for the corresponding hyperboloid flow in the absence of shear ribs. ? 2000 Elsevier Science Ltd. All rights reserved.