## 4 Electrical Tomography Applications
### Applications of ET in the Pulp Suspensions Domain
A 10% (wt/wt) softwood pulp suspension mixture, flowing at a mean velocity of ~2.1 m/s, was again quantified based on the mixing index (quotient between the standard deviation of the conductivity distribution and the mean value of the distribution of an image data set). When a tracer was used (air, steam or cold water) and added to the mixture, and by the use of ERT, the observed mixing quality decreases; however, when the mixer was on, the mixing quality was enhanced, and the observed results were quite similar to those obtained from temperature profiling. Nevertheless, having performed some trials, the results were not totally conclusive. Based on Electrical Impedance Tomography (EIT), [PERSON] et al. [125] described a low-cost system to measure the consistency profile in pulp flow. A 16-electrode sensor was used to acquire the cross-sectional data. Data acquisition was controlled by a single-chip computer, which received commands from a host computer, initialised hardware, acquired data and sent them to the host computer via a serial port. All the measurement parameters such as the amplitude and frequency of the injected current could be set by software in host computer. The consistency profile images were reconstructed by the modified Newton-Raphson algorithm. EIT system was used to measure pulp suspensions in a shallow flow. Experiments were conducted on a laboratory-scale flow rig that was constructed to simulate the spreading of pulp from a headbox. EIT measurements were acquired from a set of linear array electrodes flush-mounted to the base of the slice opening located at the bottom of the headbox. The EIT measurements were derived from a'sliding' measurement protocol that involved selectively scanning subsets of the electrode array while using the standard adjacent measurement protocol. The results of the experiments showed that EIT could resolve pulp consistency down to 0.1% (wt/wt) with a spatial resolution that was less than 1 cm. [PERSON] et al. [55] studied the ability to create uniform liquor flow in the counter-current zones of a lab-scale continuous digester using a 40 L model digester equipped with an eight-plane electrical resistance tomography (ERT) sensor array. Conductively tagged fluid flows were visualised moving through a stationary bed of uncooked wood chips for a range of process flow conditions. Tests were conducted for a range of flow conditions (\(Q_{A}\)/\(Q_{R}\) = 0.5 to 2.0, with \(Q_{A}\) being the axial up flow and \(Q_{R}\) being the radial or screen-circulation flow) and liquor fluxes (\(Q_{A}\) and \(Q_{R}\) to a maximum of 250 mL/s). To create distinct concentration zones within a chip column with liquid flows configured as in a continuous digester the ratio between the axial up flowing liquor and the radial down corner-screen liquor circulation should be less than or equal to one. As the intensity of the down corner screen flow, \(Q_{R}\), increased, the zones became more distinct as more of the rising liquor was diluted and withdrawn prior to exiting the screens. While the intensity of the circulation flow does not significantly alter the uniformity of the zones when \(Q_{A}\leq Q_{R}\), it may be significant in determining the radial uniformity of temperature and liquor concentration in an operating digester. The flow conditions modelled for two industrial digesters showed formation of distinct and uniform zones above and below the screen region, indicating that they were operating with potential good uniformity. [PERSON] et al.