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, rather 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.