## 4 Electrical Tomography Applications
### Examples of Applications of Electrical Tomography to Chemical Engineering Processes
#### 4.1.2 Type of Media Conditioning  
Diverse media have been studied, independent of the pipe or container characteristics to which the electrical tomography is applied. Aqueous phase-non-conductive particles, aqueous phase-air, and aqueous phase-oil mixtures, among others, are some of the case studies that can be found in the literature. As already mentioned, a high contrast between the phases present in the media is desirable, once electrical tomography measurements use the conductivity differences to distinguish them.  
For instance, if ET is used in a medium consisting of non-conductive particles suspended in a conductive liquid phase, which is a highly common situation in industry, it would be expected to provide valuable information about that media flowing behaviour. Many liquid phases have been used in conducted studies: however, in the majority of them, the chosen medium has been some type of brine or water. In particular, water has been used on a large scale as an aqueous phase medium [56]. However, because water itself has low conductivity, it may not be the most suitable liquid phase in some situations; increasing its conductivity by the adding a salt (e.g., NaCl, KCl) can provide better measurement accuracy [96; 102; 103; 74; 104]. With respect to the non-conductive phase, several types of particles have been used in the works reported in the literature: among these are studies using glass, nylon or plastic beads [102; 105], lava rock [106], quartzite particles [102], sand [107], and silica [108].  
Another widely addressed, two-phase system using electrical tomography, and which is common in many processes, is liquid-air medium. In the conducted works, water has generally been used as liquid phase, while air bubbles, distributed through it, act as non-conductive particles [109; 110]. However, understanding the aptitude of electrical tomography for detecting the air bubbles and understanding the relation between the size and location of sensing electrodes and the minimum detectable bubble size are still important areas of study, even if there have already been several reports in the literature about these issues.  
Two-phase systems in which both phases are liquids with different conductivities also comprise an important research area, particularly when one of them is an oil. In the literature, there are mentions of the use of linseed oil [111], shell sol D70 [97], sunflower oil [108], and paraffin oil [112; 113], among others. In the food industry domain, the dairy industry also presents great potential for the application of electrical tomography. Successful application of ET measurements to yogurt using either water or a salted plug of yogurt to obtain the conductivity difference [114; 115] has been achieved. In another situation, electrical tomography measurements on whole and skim milk solutions of various concentrations were performed by [PERSON] et al. [116]; as the second phase, and to assure the requiredconductivity difference, they used either another milk solution with a different concentration, cream, or water.