Characterization of velocity and shear rate distribution in a continuous mixer

Computer simulations have been increasingly used to model mixing for uses in many industries. These simulations have given much insight into the mixing that takes place in different types of mixers. However, most computer simulations are unvalidated. Experiments have not been performed on the same systems to compare the results therefore the accuracy of a simulation is not precisely known. Validation is most important in complex systems or when working with fluids of a non-Newtonian nature. Understanding the mixing that takes place within the mixer allows for changes to be made to the mixer for different materials and aids in mixer design. In order to quantify the mixing taking place in a Readco two inch continuous processor, laser Doppler anemometry was used to measure fluid velocity. This velocity was compared to computer simulation results and was used to calculate the shear rate, length stretch, area stretch and mixing efficiency at different points within the mixer. With this information, the accuracy of the computer simulations was determined. Differences among the mixing of three fluids with different rheology were found. The mixing taking place in different areas of the mixer was assessed. Shear thinning fluids were found to be better mixed with the paddle configuration used. The fluids were mixed best in the intermeshing region and between the tip of the paddle and the barrel wall.