Mixing motions produced by pipe elbows

Mixers are critical links in the chain of events and operations that make up a continuous processing system.Mixing can be done using various techniquesstirred tanks, fluid injections schemes, or via a range of elements placed inside pipelines to produce mixedness through the generation of secondary flows and turbulence levels at the expense of fluid pipeline pressure.However, conventional pipeline elements -elbow configurations, reducers, valves, etc. produce pipeflow effects similar to those generated by in-line pipeline mixers.For this reason and for the reason that these elements which, generally, are already in the process piping system -thus adding no additional pressure loss -these elements are examined for their potential as effective pipeline mixers.Experimental measurements have been made, using laser Doppler velocimetry (LDV) of the pipeflows produced by a range of pipe-elbow configurations.The 1 secondary flow characteristics of these pipeflows are described qualitatively and quantitatively together with their decay rates in the downstream piping.The potential these flows have as mixing environments is described on the basis of the profiles of the mean and turbulent velocity components, the change of these with downstream distance, and the pressure losses.Parameters characterizing these flow fields are defined from the measured velocity profiles in a single fluid-water.Conclusions drawn from our results include comparisons of our defined mixing parameters for several elbow combinations.It is concluded that our results should be applicable to pipeflows of miscible fluids having parameters matching those in our study.It is shown that double elbow "out-of -plane" combinations where minimal pipelengths separate the elbows can produce very energetic, long-lasting, swirling flows that can serve as effective mixers.Such effectiveness suggests that process designers might consider adding an additional elbow (and the slight increase in pressure loss) to pipe turns so as to take advantage of the enhanced mixedness that can be achieved via close-coupled elbows-out-of- plane .