# Detection of Gas-Solid Two-Phase Flow Based on CFD and Capacitance Method
## 4 Experimental Procedure
### ECT Experiments  
The mechanism of ECT technology is that changes in the shape and distribution of multiphase flow or environmental parameters, such as temperature and humanity, contribute to the changes in dielectric constant. Then, the measured capacitance value between each pair of electrodes will follow the variation. Therefore, it is feasible to reconstruct the image of multiphase flow distribution via some reconstruction algorithm according to the capacitance value. Consequently, the solid phase reflects the high grey value of the image, which manifests that the image can reflect the distribution of the medium.  
Based on electrical capacitance tomography technology, the sensor has been arranged on the outer wall of the inner tube to monitor the medium distribution of the annular space. Characteristics in Electrical Capacitance Tomography (ECT) experiments are shown in Table 1. As shown in Figure 13, the sensor consists of detection electrodes, shielding electrodes and covers. The middle of the two electrode pairs for velocity measurement is at the same position with the imaging sensor in the axial direction. Moreover, it is the same position with the point \(M\) in simulation 3 which is at the distance of 400 mm to the solid phase inlet. As shown in Figure 13, twelve detection electrodes are arranged averagely, and the shielding electrodes are arranged between the detection electrodes in the radial direction as well as the upper and lower area in the axial direction. The whole sensor part is surrounded by the shielding cover. The whole shielding part is grounded to prevent inter-signal interference and external interference. \(Ang\_d\) is \(20^{\circ}\), and \(Ang\_s\) is \(8^{\circ}\). \(H\_d\) is 90 mm.  
\begin{table}
\begin{tabular}{c c} \hline \hline
**Experimental Characteristics** & **Description** \\ \hline \(M\) & The point to monitor speed \\ \(Ang\_d\) & The angle of each detection electrode width \\ \(Ang\_s\) & The angle of each radial shielding electrode width \\ \(H\_d\) & The height of detection electrode \\ \hline \hline \end{tabular}
\end{table}
Table 1: Characteristics in Electrical Capacitance Tomography (ECT) experiments.  
Figure 12: Experimental system.  
To verify the feasibility of this structure of the sensor in detecting the annular space, the imaging has been simulated by ANSOFT software. The same solid phase distribution as the cross-section in simulation 3 in CFD is set up, as shown in Figure 14a. The reconstructed image is shown in Figure 14b after the calculation, and the distribution of the solid part in the image is corresponding to the actual situation. The feasibility of this sensor structure to detect annular space is verified. The experimental results are discussed in the following section.  
When a lump of solid passes through the bottom of the channel, the solid distribution can be reconstructed via ECT system. As indicated in Figure 15, the grey value presents relatively high in the position of solid, while the value in the rest is small. The results agree well with the actual condition.  
Figure 14: Simulation: (**a**) True distribution, (**b**) Reconstructed solids distribution.  
Figure 13: Structure of the sensor.