## 3 Results and Discussion  
### Optimization of the Flow Path  
CFD simulations of the three models in Section 2.2 were carried out to optimize the flow path of the ten-layer DBD reactor. The initial gas flow rate of the boundary conditions was set to 1000 L/min and the flow velocity per flow channel at the measurement points was computed, as shown in the upper-right panel in Figure 3a. The maximum velocity of each flow channel was used to determine the velocity uniformity. As shown in Figure 3(b1), at an initial gas flow rate of 1000 L/min at the inlet surface, a concentrated airflow was initiated and extended to the flow channels. As a result, a localized high-velocity field was  
Figure 2: Schematic of the experimental setup used for the electrical and spectroscopic characterizations. formed in the central flow channels, resulting in a maximum velocity difference of 0.93 m/s between the max- and mini-velocity flow channels, with the standard deviation of the 10 layers being 0.35 m/s, 3.39% of the average velocity (10.20 m/s). However, the nonuniformity of the flow velocity among the flow channels was significantly reduced by the introduction of an airflow diffuser plate, which decentralized the  
Figure 3: (**a**) Measurement points in CFD (**upper right**) and for practical velocity measurements (**lower right**); the flow vector profiles at the fifth layer (**middle left**) and flow velocity per channel (**middle right**) of the three simulation models of the ten-layer DBD reactor: (**b**) None, (**c**) airflow diffuser, and (**d**) airflow diffuser + perforated metal. concentrated airflow, as shown in Figure 3(c1). Accordingly, the uniformity of the velocity field of each flow channel was improved to a significantly reduced velocity difference of 0.24 m/s between the max- and mini-velocity flow channels, with a standard deviation of 0.08 m/s, 0.79% of the average velocity (10.34 m/s). In addition, the combination of the airflow diffuser and the perforated metal plates further refined the uniformity, bringing the velocity difference down to 0.13 m/s, with a standard deviation of 0.04 m/s, 0.41% of the average velocity (10.40 m/s), as observed in Figure 3(d2). This finding suggests that introducing an airflow diffuser and perforated metal plates is a practical and effective tactic for improving nonuniformity without major modifications to the DBD reactor configuration. According to the results derived from the CFD simulations, the ten-layer DBD reactor was successfully fabricated. Subsequently, practical measurements of the flow velocity per channel were implemented. Benefitting from the modular design, the flow velocities of three patterns (none, airflow diffuser, and airflow diffuser + perforated metal) corresponding to the three models analyzed in the CFD simulations were measured using a hot-wire anemometer at the measurement points, as shown in the lower right of Figure 3a, where the gas flow rate induced by the vortex blower was adjusted and fixed at 1000 L/min with the third pattern (airflow diffuser + perforated metal). The three patterns exhibited trends similar to those of the CFD-computed results with excellent agreement. Obviously, the pattern airflow diffuser + perforated metal outperformed the other patterns (none: average velocity of 14.91 m/s, velocity difference of 3.9 m/s, standard deviation of 1.38 m/s; airflow diffuser: average velocity of 12.52 m/s, velocity difference of 0.87 m/s, standard deviation of 0.71 m/s), with the minimum velocity difference of 0.37 m/s between the max- and min-velocity flow channels, and the standard deviation of the 10 layers being 0.13 m/s, 1.47% of the average velocity (9.12 m/s), as shown in Figure 4a. This result was also evidenced by the retention time per channel of the three patterns, where the third pattern presented the lowest standard deviation with a retention time of 0.32 ms compared to the other two patterns (none: 1.26 ms, airflow diffuser: 0.77 ms), as rendered in Figure 4b.