Turbulence and ScaleUp in a Deep Tank Water Treatment Reactor.
Abstract
Mixing operations in which agitation is critical, need careful scaleup experiments, often in a number different sizes of equipment before the operations can be attempted on a plant scale with any degree of confidence. The fluctuating velocities of water were measured in geometrically similar, fully baffled stirred tanks. The mixing vessels were 10.9, 100 and 2000 liter cylindrical flat bottom tanks with inlet at the bottom center and outlet at the side. The instantaneous unsteady state velocity was measured as function of position. Flow rates and impeller speed were maintained constant for each experiment. The sensors were calibrated periodically throughout each series of experiments. The need to calibrate the sensors periodically arises due to fouling of the probes while using water as the process fluid. Sensor fouling was included in the velocity calibration equation using both residual and partial residual plots to diagnose the correct functional form in multiple regression analysis. The Eulerian scale of turbulence, the integral microscale, the Kolmogoroff microscale, intensity of turbulence and rate of energy dissipation were calculated from the fluctuating velocity data. The results were consistent with those obtained by other investigators. Correlations have been developed to describe the distribution of integral macroscale, the integral microscale, turbulence intensity, Kolmogoroff microscale and energy dissipation in the 10.9 liter tank. Correlation of turbulence parameters have also been developed to describe the distribution in 10.9, 100 and 2000 liter tank at angular position midway between the baffles. The correlation equations can be used to estimate the turbulence parameters in mixing operations at different radial and height and angular position in the tank. In agitated vessel, the decay of turbulence could be attributed to the transfer of energy from the mean flow to the large eddies and thence to the small eddies where the bulk of the energy dissipation takes place. Scale up based on the rate of energy dissipation in geometrically similar tank is proposed. The scaleup procedure involves the correlation of dimensionless energy dissipation number, varepsilonover {N^3 D_sp {i}{2}}, height above the tank bottom to impeller width ratio Hover d, the impeller speed N, the flow rate Q, radial position to impeller diameter ratio rover D_{i}, and the tank volume V.
 Publication:

Ph.D. Thesis
 Pub Date:
 1989
 Bibcode:
 1989PhDT........97K
 Keywords:

 Engineering: Chemical; Physics: Fluid and Plasma