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Tracer Studies



This is a continuation of the Process Intensifier - Optimization with CFD: Part 1 paper.

Unlike the flow pattern tracer study, this study shows the effect of mixing in a second component (see Figures 17-18). The tracers are neutrally buoyant in this study, but they could easily be made heavier or lighter than the bulk fluid. The injection port of LTR and HGR is directly below the lower radial impeller. 250 particles are injected at this point. The mean residence time of the fluid based on volume and flow rate is 1.35 s (light-blue) at 650 GPM (148 m3/hr) and 0.80 s (blue) at 1100 GPM (250 m3/hr) for LTR and is 1.27 s (light-blue) at 650 GPM (148 m3/hr) and 0.75 s (blue) at 1100 GPM (250 m3/hr) for HGR. The difference is a function of the chamber volume.

The injection port for a Lightnin Line Blender with axial impellers is between 5-10 pipe diameters upstream. We injected it in this study at 4 pipe diameters upstream. Injection was studied at two locations: in the center of the pipe (250 tracer particles) and also split by injecting at the respective heights of the impellers (125 tracer particles each). The mean residence time of the fluid based on volume and flow rate is 2.26 s (green) at 650 GPM (148 m3/hr) and 1.34 s (blue-green) at 1100 GPM (250 m3/hr) .

HGA has a special injection pipe. It can be seen in Figures 5, 8, 9, and 10. It is just upstream of the impellers, right after the flow straighteners. Injection of the tracer was made at the respective impeller heights (125 tracer particles each). The mean residence time of the fluid based on volume and flow rate is 1.27 s (light-blue) at 650 GPM (148 m3/hr) and 0.75 s (blue) at 1100 GPM (250 m3/hr).



650 GPM Radial Process Intensifier Axial Process Intensifier
Lightnin
  LTR injection below lower impeller LTA single injection port
Lightnin  
    LTA two injection ports
Hayward Gordon
  HGR injection below lower impeller HGA two injection ports
Figure 17: Particle tracking to visualize the flow pattern. Dark blue = 0 s, light blue = 1 s, green = 2 s, orange = 3s, red 4 s residence time. Internals other than the impellers and shaft are not shown.

All of these plots (Fig. 17) appear to be doing a good job of mixing in the second component.

It is noticeable that the tracers injected in the Radial Process Intensifiers do not get sucked up straight into the lower impeller, but first swirls toward the back Z-plate wall of the lower chamber. That distance is less for HGR. The colors seem to indicate that LTR is getting a more uniform distribution of the tracer particles. Some are even making it in and out of the T-section. There seems to be a lot of recirculation downstream of the HGR based on the variety of colors seen there.

With a singular injection point, LT1 is able to spread the tracer particles fairly uniform around the pipe cross section. None of the particles are making it into the T-section and they all seem to have a very uniform residence time. To improve on the mixing, 2 injection ports are studied at the respective heights of the impellers. This appears to do a much better job of dispersing the tracer particles. Some particles are getting into the T-section and they are recirculating in there long enough to require more than 4 seconds residence time.

HGA also does a very good job of dispersing the tracer particles about the cross-section of the pipe. It does appear that there is some recirculation going on, though, based on the large number of blue traces among the green at the outlet.

1100 GPM Radial Process Intensifier Axial Process Intensifier
Lightnin
  LTR injection below lower impeller LTA single injection port
Lightnin  
    LTA two injection ports
Hayward Gordon
  HGR injection below lower impeller HGA two injection ports
Figure 18: Particle tracking to visualize the flow pattern. Dark blue = 0 s, light blue = 1 s, green = 2 s, orange = 3s, red 4 s residence time. Internals other than the impellers and shaft are not shown.

The most noticeable difference at 1100 GPM (250 m3/hr) (Fig 18) to the 650 GPM (148 m3/hr) case (Fig 17) is that the LTA appears to be having difficulty staying in control of the flow pattern. With a single injection port, the tracer particles appear to be just passing through the impeller zone. The lower impeller pulls down some particles, and none of the particles are being pushed up into the T-section. Two injection ports do improve the situation. The lower impeller pulls down some particles, and some of the particles are being pushed up into the T-section. There is a noticeable mixture of blue and green tracer tracks in the outlet.

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