|
|
|
This is a continuation of the Process Intensifier - Optimization with CFD: Part 1 paper. Mixing Xanthan GumUntil now, the continuous medium in this report has been water. The CFD program handles many different types of rheologies. For Xanthan Gum, a power-law correlation works well. The ACUSOLVE code represents this as:
In this case, the operative constants were mu0 = 2.5 kg/m s, a shear-thinning exponent of 0.7, and the time constant was set to 1.0. According to our estimates, the apparent viscosity around the impeller tip region is in the ballpark of 200 cPs, the material bulk is about 2500 cPs. We used 1000 kg/m3 for the density. Xanthan Gum is used as an emulsifier, lubricant, suspending agent, and/or a thickener. We ran our Xanthan Gum, at 1500 RPM and with a flow rate of 750 GPM in our 10" Schedule 40 pipe. We used the HGR.
Both pictures from Figure 25 are under the same conditions. It is interesting to see that the Eddy Viscosity surface is not symmetrical. This has to do with the rotational direction of the impeller and the flow. On the right hand side, the volume is larger. This is the side where the impeller blades are moving against the current. On the left hand side, the blades are moving with the current. The lower impeller is slightly visible. This means that it is not completely engulfed in this high-energy zone. Table 1 also shows that the lower impeller has a lower power number. The particles are added below the lower impeller. The picture on the right shows that the tracers are swept toward the back Z-plate wall before being forced up. Then it appears that every tracer particle goes into this high-energy zone. It does not appear that this high viscosity will have a problem mixing in a Process intensifier. Figure 26 compares this non-Newtonian case with water. The residence time distributions look fairly similar. The fastest and longest times are about the same. Some particles in the Xanthan Gum only take one second longer to leave the device. The statistics are given in Table 6. The Eddy Viscosity volume for the water case is much larger than the Xanthan Gum (Fig 26). Obviously the shear drops quicker away from the impellers than does water. The power numbers are essentially the same (see Table 7). The pressure drop was essentially the same, too. The Xanthan Gum is essentially behaving like water inside the Process Intensifier.
Continue with the Conclusions or Go back to Results or Go back to the Title Page | ||||||||||||||||||||||||||||||||||||
|
Send mail to webmaster@postmixing.com with questions or comments about this web site. |
