SUMMARY

Turbulent mixers are widely used today in many different industries from chemical mixing to paper production. In paper manufacturing, local basis weight distribution is one of the most important properties that must be controlled. Basis weight is defined as the ratio of the mass of the sheet of paper to its area. Paper thickness is difficult to measure and therefore basis weight is used to implicitly describe it. The basis weight of the final paper product is directly related to the flow rate of the pulp mixture running through the paper machine. Because of the importance of the basis weight, the flow rate is strictly controlled. One of the methods for controlling flow rate is by locally diluting the pulp mixture with water. In the flow distribution section of a paper machine, known as the head box, water is injected into the fiber suspension (stock) flow through a tee-mixer for more uniform production. This dilution process has two important requirements that must be fulfilled: (1) sufficient mixing so that the dilution flow spreads across the suspension flow and (2) that the injection flow rate not be so large to significantly alter the local head box flow rate. The objective of this research was to find a combination of velocity ratio and tee mixer geometry that lead to the injection flow being well mixed into the stock flow, but at the same time, the injection should not cause the total flow rate to change by more than 1%. Various injection flow rates were examined for four different cases of tee mixer geometries using the CFD software Fluent. Two of the cases had added contractions located near the injection point, while the other two cases had a more standard geometry with no added complexities. Mixing was qualitatively measured by simulating the injection of a passive tracer into the dilution flow. The mixing was further quantified by measuring the variance in the concentration of the tracer across the diameter of the tee-mixer.