**7. Slurry tank applications**

CSIRO has a long history of mixing tank research as shown in [38] and has recently started to apply ERT to this area of slurry flow dynamics. ERT allows for a deeper exploration of concentration inhomogeneities as a function of the agitation type. These inhomogeneities have been observed in unbaffled tanks under certain agitation conditions and have recently started to be investigated by ERT by [39] using a 1-m diameter tank at CSIRO and water/sand slurry.

A time series of ERT images from a single plane of the 1-m diameter tank are shown in **Figure 15**, and stills from a video are shown in **Figure 16**. A low concentration region is evident, traveling around the tank near the slurry surface. These concentration transients can then be correlated with other aspects of tank performance such as impeller torque and particle suspension. This research activity is continuing at CSIRO at the time of writing.

Further recent ERT work has commenced at CSIRO in a smaller (390 mm diameter) tank which is unbaffled. A photograph of the tank with the impeller turned off and particles settled is shown in **Figure 17**. This tank is used for fundamental research into impeller suspension performance before scaling up to the larger 1-m diameter tanks.

The object of the initial work with the tank was to investigate the performance of the various options for ERT processing using the ITS Reconstruction Tool Suite [21]

*Electrical Resistance Tomography Applied to Slurry Flows DOI: http://dx.doi.org/10.5772/intechopen.107889*

**Figure 15.**

*Time-dependent concentration in unbaffled tank. Electrode plane near the top of the tank.*

#### **Figure 16.**

*Stills from video taken at the same time as Figure 15.*

for tank applications, especially when settled solids were present. **Figure 18** shows a comparison between the LBP and the Laplace option where it is seen that the Laplace option performs significantly better in capturing the settled solids without the artifacts in the center of the images from the LBP. Work is ongoing at the time of writing to further optimize the imaging of the suspension in the tank as well as obtain data on the effect of different impellers, etc.

### **8. Conclusions**

ERT has been a part of CSIRO's research into slurry pipe flows for nearly 20 years and is now being extended to mixing tanks.

The insight that ERT offers into the state of suspension of the flow is difficult to obtain by other means, especially given the opaque nature of industrial slurries.

#### **Figure 17.**

*Photograph of tank with settled solids. Plane 7 is the lower-most electrode ring, with plane 1 at approximately the impeller height.*

A variety of image processing options are available for ERT, both commercial and open source, and both approaches are useful in a slurry flow research environment. At CSIRO the preferred approaches are currently:


There are continuing developments in reconstruction algorithms both in the literature and commercially available which are aimed at improving the quantitative accuracy of ERT for slurry applications.

*Electrical Resistance Tomography Applied to Slurry Flows DOI: http://dx.doi.org/10.5772/intechopen.107889*

#### **Figure 18.**

*Images from seven planes of the 390-mm tank with settled solids lower image set processed with the ITS reconstruction tool suite, Laplace algorithm. 50-mA injection current, 9600 Hz. Threshold set to 1.5–5.0 ms/cm. Liquid conductivity of 4.99 ms/cm. Photograph and ERT images courtesy of Michael Hurley, CSIRO mineral resources.*

The significance of ERT (and previously MRI) for CSIRO was that the data demonstrated the regimes of flow in cases where visual observation or other diagnostic instruments were not usable. These results were then used to feed back into development of slurry pipe flow prediction models which were based on correct flow mechanisms rather than purely empirical methods. The demonstration of stratification of high yield stress carrier fluid-based slurries in laminar pipe flow was of particular significance in gaining acceptance of stratified flow models for that flow regime.

### **Acknowledgements**

The author is grateful for the collaborations and support of Dr. Jie Wu, Dr. Lionel Pullum, Bon Nguyen, Kosta Simic, Dr. Andrew Chryss, Dr. Enzu Zheng, Jeremy Kieruj, Michael Hurley, Greg Short, Prof. Murray Rudman, and Dean Harris. The support of previous AMIRA research projects as well as industrial clients for the slurry research activities is also acknowledged.

*Advances in Slurry Technology*
