## 3 Experimental Setup and Observations
### Experimental Facility Setup  
The piezoelectric acceleration sensor and capacitance tomography system are installed in the experimental tube section of the multiphase flow experimental loop to obtain vibration signals of different flow patterns and ECT flow pattern images; see Figure 11 for the experimental equipment setup. The acceleration sensor is a Lance LC0103 with an internal IC piezoelectric accelerometer, which is fixed on the tube wall in order to gather the vibration signal; see Figure 11b. Then the vibration acquisition instrument (Figure 11f) receives the piezoelectric acceleration signal, the signal data are transferred to the host PC via a USB interface, and can be monitored and saved in real-time in the vibration analysis software. These sensors, which combine a piezoelectric acceleration sensor and a charge amplifier, can be linked directly to the recording device, simplifying the test system and enhancing test accuracy and reliability. They also have low noise levels, anti-jamming capabilities, and are appropriate for multi-point measurements. Table 2 displays the acceleration sensor's specifications. The ECT flow pattern images were captured and recorded for various flow conditions through the M3C ECT imaging system designed by Industrial Tomography Systems plc (ITS) in the UK, see Figure 11a. The relevant parameters of the M3C ECT imaging system are shown in Table 3. Before the experimental tests, the ECT signal was calibrated to measure the new scalar quantity, and the parameters for scalar quantity acquisition were \begin{table}
\begin{tabular}{c c c c c} \hline \hline
**Sensitivity** & **Frequency Domain** & **Range** & **Resolution Ratio** & **Sensitive** \\ (**m/g**) & **(Hz)** & **(g)** & **(g)** & **Original** \\ \hline
50 & 0.35–10,000 & \(\pm\)100 & 0.0004 & Ceramics \\ \hline \hline \end{tabular}
\end{table} 
Table 2: Parameters of Lance LC0103 piezoelectric acceleration sensor. Figure 11: Experimental facility setup. set in the control system function unit: 0 for measuring low scalar quantity, 1 for measuring high scalar quantity, and 2 for continuous measurement mode. Firstly, to measure the low scalar quantity, it is necessary to ensure that the sensor is empty inside the tube, close the water valve in the multiphase flow laboratory control system, open the air valve and continuously vent the air, and use the three-phase separator to discharge the remaining water from the tube to the water tank. At the same time, the calibration parameter is set to 0 in the ECT system, and the low calibration graph is presented in Figure 12a. Second, the air valve in the control system must be closed to execute the high scalar quantity measurement. It also requires the material with the highest dielectric constant among the testing materials to be used to fill the sensor, and the water valve must be open for water to flow continually through. Meanwhile, the calibration parameter is set to 1 in the ECT system, and what is presented at this time is the high calibration graph, as in Figure 12b. After setting the standard quantification, flow pattern information can be obtained using the ECT tomography system. It should be noted that after the gas-liquid flow setting at the entrance is completed, it is necessary to wait patiently for the flow pattern in the tube to become stable and formed, taking about 1 min, before data collection can be carried out. In the experimental tube part, as shown in Figure 11c, a clear window with a 220 mm length and an inner diameter matching a plexiglass jumper is placed. A high-speed camera was used as an auxiliary tool to record the flow pattern and flow variations in the tube during the experiment in order to simplify the analysis and validate the experimental data, as shown in Figure 11d. The high-speed camera uses the FASTCAM Mini UX100 from Photron, whose parameters are shown in Table 4.