Evaluation of Blend Time Experiments in Unbaffled Tanks Using 2 Methods

Blend time is defined as the quantity of time required to completely mix two or more solutions in a given tank with a given impeller. Blend time measurements were taken in an 8 inch unbaffled tank using a 3 inch Rushton impeller. For these experiments the impeller speed ranging from 200-600 RPM and liquid levels from 6-13.5 inches. The blend time was determined using the salt tracer method which employs a conductivity probe placed at the top surface of the liquid in the tank. The results of blend time measured using the salt tracer method were found to be well represented by an equation developed by Grenville

5.66 = Np^(⅓)*Re/Fo

Where Np is the power number, Re is the Reynolds number for a stirred tank and Fo is the Fourier number given by F_O=µ𝜽₉₅/(𝜌T²). This data was reanalyzed using the color change method based on the reaction between sodium thiosulfate and iodine in the presence of starch.