An Investigation of Geometric Scaling of Mean and Turbulent Flows in Cylindrical Stirred Tank Reactors

Open Access
Author:
Walters, Geoffrey Strohm
Graduate Program:
Civil Engineering
Degree:
Master of Science
Document Type:
Master Thesis
Date of Defense:
April 08, 2008
Committee Members:
  • David N Hill, Thesis Advisor
Keywords:
  • Mean Velocity
  • Nonbaffled
  • Mixing Tank
  • PIV
  • Stirred Tank Reactor
  • Scaling
  • Rushton Turbine
  • RMS Velocity Fluctuations
  • Reynolds Stresses
  • Mean Flows
  • Turbulent Flows
  • CFD
Abstract:
Experiments have been performed in order to study the effects of geometrical scale in stirred tank reactors. Motivation for this study stemmed from the many practical applications of this flow. There is a need to understand how scaling affects mixing tanks in order to accurately scale up laboratory results to large scale prototypes. Previous studies have been conducted on the subject of scaling in mixing tanks, but the present study considered a wider range of physical scales and Reynolds numbers. Four differently sized nonbaffled cylindrical tanks were used and the flow was driven by a six blade radial flow Rushton turbine. The Reynolds number of the flow ranged from 10,000-130,000. Velocity measurements were made on a vertical plane passing through the center of one of the turbine's blade tips. Flow statistics studied included mean velocity, root-mean-square velocity fluctuations, and Reynolds stresses. The research focused specifically on how mean and turbulent flow characteristics near the turbine's blade compared between tanks at specific Reynolds number values. Results of nondimensional mean velocity lacked complete agreement, but demonstrated consistent differences between tank sizes. Nondimensional turbulent flow characteristics showed that as the Reynolds number increased the results between tanks became more alike, but a complete collapse in data, which was expected, was still not observed. Results did, however, show trends which suggest that the magnitude of the nondimensional turbulence parameters are a function of their tank size.