The use of photoactivatable fluorophores in the study of turbulent pipe mixing: effects of inlet geometry

The effects of inlet conditions on downstream mixing in turbulent pipe flow have been studied with the use of photoactivatable fluorophores and standard laser-induced fluorescence techniques. The different inlet conditions included both geometry changes and changes in the manner in which the constituents were introduced into the flow. Results indicate that small changes in inlet geometry can greatly affect the downstream mixing rate. Changes in the geometry of the inlet had a greater influence on downstream mixing than did the manner in which constituents were introduced into the flow. Further experiments included a static mixer that was used in conjunction with two different inlet conditions. It was found that the inlet condition greatly affects the effectiveness of the static mixer. The static mixer is most effective when placed downstream of an inlet that produces scalar length scales that are similar in size to the elements in the mixer (i.e., the pipe diameter). Overall, the results of these experiments demonstrate that the method used to introduce two constituents to be mixed in pipe flow can profoundly affect the downstream mixing rate.