## 3 Results and Discussion
### In-Situ Electro-Chlorination Experiment with CFD Simulation  
In-situ electro-chlorination tests were conducted to obtain the chlorine-forming rate of RuO\({}_{2}\)/Ti electrodes under different current conditions. Figure 5 shows free chlorine concentrations under different current conditions. The concentration of free chlorine linearly increased with chlorination time. The expected chlorine-forming rates under 10, 15, 20, and 25 A were 101, 164, 278, and 381 mg min\({}^{-1}\), respectively. The effective chlorine concentration for biofouling control in power plants is reported to be 0.5-1.5 mg L\({}^{-1}\)[12; 6; 11; 14]. To meet this minimum chlorine concentration, 25 A was chosen for the electro-chlorination experiment and was expected to result in a chlorine concentration of 0.4-0.6 mg L\({}^{-1}\) in the end of the pipe after mixing (point 7). Thus, the artificial concentration was 0.64, 0.54, 0.48, and 0.42 mg L\({}^{-1}\) for the flow rates of 600, 700, 800, and 900 L min\({}^{-1}\), respectively. The in-situ electro-chlorination results are shown in Figure 6. The measured chlorine concentration at each sampling point and the calculated concentration obtained via the CFD simulation were compared under different flow rates. In both cases, model calculated values reasonably followed the measured ones. The chlorine concentrations gradually decreased due to the diffusion while the water passed through the first pipe containing sampling ports 1-5. After that, the concentrations remained relatively stable through the second and third pipes (which correspond to sampling ports 6 to 7) because the chlorine became fully mixed with the seawater when it passed through the pipes bent at 180\({}^{\circ}\) (circled with a red-dotted line in Figure 7). This phenomenon is more marked in the simulated results due to experimental error. The red-dotted line in Figure 6 represents the desirable concentration. As expected, the chlorine concentrations near the wall remained higher than the artificial concentration prior to ports 6 and 7. This chlorine dispersion is clearly shown in the simulation. Figure 7 shows three types of fluid contours, chlorine concentration (Figure 7a,b), velocity magnitude (Figure 7c), and pressure (Figure 7d). As shown in Figure 7a,b, the generated chlorine flowed along the pipe and gradually  
Figure 4: Correlation between model and experimental data in the chlorine kinetics using seawater. diffused through seawater. Thus, chlorine concentrations can vary throughout the length of the pipe, as is further discussed in Section 3.3. The experiment and simulation results, including error, are summarized in Table 2. No significant difference was found in either case both with and without the decay kinetics because the elapsed time was too short for such differences to manifest (3-6 s was required for chlorine from the electrodes to reach sampling port 7). Thus, little chlorine decay was observed while the water passed through the pipe. However, if the pipeline is extended to 100 m, the expected chlorine concentrations with and  
Figure 5: Free chlorine concentrations in West Sea water under different current conditions in an in-situ electro-chlorination system. Figure 6: Free chlorine distribution along the sampling ports under different flow rates. Each dot represents experimental data, and each point on the black line is the expected chlorine concentration obtained from computational fluid dynamics (CFD) simulation with a parallel first-order decay model. The red-dotted line is the desirable concentration at the given flow rate: (**a**) 600 L min\({}^{-1}\) of flow rate, (**b**) 700 L min\({}^{-1}\) of flow rate, (**c**) 800 L min\({}^{-1}\) of flow rate, (**d**) 900 L min\({}^{-1}\) of flow rate. without the decay kinetics are estimated to be 0.22 and 0.45 mg L\({}^{-1}\), respectively. Therefore, the decay kinetics must be considered. Figure 7: Fluid contour images from CFD simulation of the electro-chlorination experiment. Inlet flow rate is 800 L min\({}^{-1}\). Outlet pressure was set to 10.8 kPa.