Blending Time and Velocity Variations During Blending in a Tank Using Dual Opposing Jets

Abstract

Blending times are required for many process industries, and statistical analysis of the measured blending times was used to determine a relationship between CFD (computational fluid dynamics) predictions and experiments. A 95% blending time occurs when tank contents are sufficiently blended to ensure that concentration throughout the tank is within ± 5% of the total change in concentration. To determine 95% blending times, acid and base tracers were added to an eight foot diameter tank, and the pH data were recorded to monitor blending. The data for six pH probes located throughout the tank were normalized to a range of 0 to 1. Then the blending time was established when the pH converged between 0.95 and 1.05 on the normalized graphs. Evaluation of results from 79 different tests concluded that the maximum blending time occurred randomly at any one of the six pH probes. The research then considered the calculated 95% blending times, which had uncertainties up to more than 100% at a 95% confidence level. However, this uncertainty is considered to be an actual variation in blending time, r ather than an experimental error. Not only were there significant variations in the blending times, but there were significant variations in the velocities measured at different points in the blending tank.

Comparison of Experimental Results to CFD Models for Blending in a Tank Using Dual Opposing Jets

“…Also, a brief discussion of the grids used for CFD models used in this research is provided in a companion paper (Leishear, et al [4]). A more detailed discussion of CFD modeling will also be provided in a subsequent Conference publication in this series of papers to describe this research (in process).…”

“…To do so, statistical analyses and engineering evaluations w ere p erformed to evaluate the variability of blending times, which were then used to establish a correction factor to be used with CFD models ( Leishear, e t al. [4]. Statistical analysis was performed for the data shown in Fig.…”

Comparison of Experiments to Computational Fluid Dynamics Models for Mixing Using Dual Opposing Jets in Tanks With and Without Internal Obstructions

“…In short, this paper compares blending times calculated from Computational Fluid Dynamics (CFD) models to experimental results for pilot scale testing in a geometrically scaled, 2.44 meter (8 foot) diameter tank with sub-surface obstructions representing cooling coils, which were both installed and removed from the pilot scale tank during testing. The reader is referred to [1][2][3][4][5][6] for scale-up methods for blending times and other aspects of this blending research, which are specifically related to radioactive liquid waste processing. Developed from [1][2][3][4][5][6], this paper focuses on the blending of two fluids, which is applicable to the more general field of industrial mixing theory.…”

“…The reader is referred to [1][2][3][4][5][6] for scale-up methods for blending times and other aspects of this blending research, which are specifically related to radioactive liquid waste processing. Developed from [1][2][3][4][5][6], this paper focuses on the blending of two fluids, which is applicable to the more general field of industrial mixing theory.…”

“…A series of Conference papers summarize the full extent of this research (Leishear, et al. [1][2][3][4]), and Savannah River National Laboratory (SRNL) reports provide comprehensive experimental data and analysis from the research (Leishear, Lee, et al [5][6][7][8]). In short, this paper compares blending times calculated from Computational Fluid Dynamics (CFD) models to experimental results for pilot scale testing in a geometrically scaled, 2.44 meter (8 foot) diameter tank with sub-surface obstructions representing cooling coils, which were both installed and removed from the pilot scale tank during testing.…”