Impeller helical

FIG. 18-21 Effect of impeller speed on circulation time for a helical impeller in the Reynolds niimher arranged less than 10. 

Figure 5-39. Close-clearance anchor and helical impellers. By permission, Oldshue, J. Y., Fluid Mixing Technology, 1983, Chemical Engineering McGraw-Hill Publications Co., Inc. [29].

Rheologic measurements were performed at 25oC with the cone-and-plate and helical impeller viscometers. Impeller viscometer measurements were performed in a 1000-mL beaker with a diameter of 0.115 m. A liquid height of 0.115 m was used for all tests. 

The value of the shear rate constant, k, was determined for solutions of xanthan gum and guar gum with concentrations of 0.5,1.0, and 1.5%. The shear rate constant k obtained from the cone-and-plate and helical impeller was 10.9. A similar value of ft was obtained for 1.0 and 1.5% of xanthan and guar gum solutions. The same value of k was reported for this type of impeller in earlier investigations (7,9). 

Results for Indirect Yield Stress Determination for Com Stover Suspensions in 1.0-L Beaker (Helical Impeller Method)... 

Finally, the distribution of solid particles across the gap may not be uniform if the fibers separated out of the suspension. Therefore, based on the previous reasoning, it is concluded that the stress method does not offer a reliable and accurate way to measure yield stress in filamentous suspensions. Figure 5 shows the typical torque-time relationship obtained with the helical impeller method for corn stover suspensions. 

The basic assumption of the impeller viscometer approach is that the shear rate constant is independent of the rheologic properties of the fluid. This assumption allows the helical impeller viscometer to be calibrated using Newtonian and non-Newtonian fluids. The calibration results for guar and xanthan gum solutions ranging in concentration from 0.5 to 1.5% produced a single value of k = 10.8, which is sufficient to represent all the data. 

The viscosity of the corn stover suspensions was determined for concentrations up to 30%. The helical impeller method was ineffective above corn stover concentrations of 32%. 

The helical impeller technique is better suited to measure yield stress in a greater variety of fluids, including filamentous suspensions. The helical impeller technique is also less sensitive to initial undesired torque deflections in the measuring spring. The undesired initial torque, introduced at the moment the helical impeller is submerged into the liquid, can easily be... 

Measurement of Rheology of Distiller s Grain Slurries Using a Helical Impeller Viscometer... 

Index Entries Distiller s grain slurries rheologic properties wet grains calibration fluids helical impeller. 

The aim of the present study was to determine rheologic characteristics of wet grain slurries using a helical impeller viscometer. The collected data were analyzed to develop a model describing the rheologic behavior of wet grain slurries. 

The overall Newtonian calibration constant was 151, the same calibration constant obtained by Rieth (3) for the same helical impeller. Previously reported data by Donnelly (4) concluded that c was a function of Re for vane and turbine impeller viscometers. It was concluded by Rieth (3) and confirmed in our study that c is a constant in the laminar region... 

Table 4 lists calculated average shear rate constants and SDs of 10.24 0.55 (0.75% guar gum solution) and 10.36 0.27 (1.0% guar gum solution). The SDs are minimal. The average shear rate constant range calculated by Rieth (3) was 10.45-10.91 for the same helical impeller. The calculated overall average shear rate constant of 10.30 falls below the range reported by Rieth (3). 

Figures 2-4 show that no experimental data were recorded at low impeller shear rates. Experimental data began at y = 8.53 s4 for 21% solids, 5.15 s 1 for 23% solids, and 3.43 s 1 for 25% solids. The reason for the missing data is that the helical impeller viscometer has limitations. Owing to possible viscometer error, data were not recorded until the impeller torque was >10% of the full-scale torque. Therefore, no experimental data were recorded at low impeller rotational speeds. The lack of experimental data at low shear rates made comparison of rheologic models at low shear rates and the prediction of yield stress impossible.

Figure 18-21 gives some data on the circulation time of the helical impeller. It has been observed that it takes about three circulation times to get one blend time being the visual uniformity of a dye added to the material. This is a macro-scale blending definition. 

Figure 6.25(a) shows a novel process for the continuous production of fuels from waste plastics. The proposed process consists primarily of three reactors. A mixture of waste plastics is fed into a pyrolytic reactor with heat-medium-particles stirred by a helical impeller (Figure 6.25(b)), where melted plastics are hydrothermally decomposed with steam and the random scission of C-C bonds. The produced mixture of a heavy oil containing wax and sublimate material is carried by steam stream to the next reactor, which is filled with an FeOOH catalyst (i.e. a catalytic hydrolysis reactor). The gaseous... 

Axial Flow Turbine Compared to Helical Impeller... 

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