## 5 Results  
In case of no electric field applied to the agglomerator, Figure 3a shows numerical calculation results for the front and top views of flow streamlines inside the agglomerator when the inlet air speed was 0.1 m/s. The front view shows that the flow upstream of the agglomerator is in a straight line with an average velocity of 0.1 m/s (light blue). However, the flow curves when it passes through the region of the vortex generator. At the same time, the flow is accelerated to speeds ranging from 0.2 to 0.4 m/s (light green to yellow). Furthermore, the flow becomes more complicated near the exit region, compared to its relatively straight behavior at the entrance region. As shown in the magnified image of the top view, where upward and downward movements of the flow are clearly visible, the presence of vortices is confirmed. Figure 3b shows the contours of the turbulent energy dissipation rate in the agglomerator when the inlet air speed was 0.1 m/s. The turbulent energy dissipation rate was calculated using the standard k-\(\epsilon\) turbulence model. The left-side contour shows a case of no vortex generator installed in the agglomerator, while the right-side contour represents a case of the vortex generator installed in the agglomerator. In the left-side contour, the turbulent energy dissipation rate is as low as 0.01 m\({}^{2}\)/s\({}^{3}\), depicted in blue. However, in the right-side contour, the turbulent energy dissipation rate increases up to 1.5 m\({}^{2}\)/s\({}^{3}\) inside the vortex generator region, depicted in various colors such as green, yellow, and red. This increase can be attributed to the increased agglomeration efficacy, as explained in Equation (6). Figure 3: (a) Flow fields in the vortex generator in the absence of an electric field, (b) surface contours of turbulent energy dissipation rate, (c) six iso-surfaces of turbulent energy dissipation rate. The turbulent energy dissipation rate values shown in the right-side contour of Figure 3b are separated into six different values: 0.01, 0.1, 0.25, 0.5, 1, and 1.5 m\({}^{2}\)/s\({}^{3}\). Each value is represented in a contour in Figure 3c. The values of 0.01 and 0.1 m\({}^{2}\)/s\({}^{3}\) are represented in blue at the inlet and outlet regions of the vortex generator. The values from 0.25 m\({}^{2}\)/s\({}^{3}\) to a maximum of 1.5 m\({}^{2}\)/s\({}^{3}\) are distinctly observable inside the regions near the vortex generator. Figure 4 presents the current/voltage characteristics of the corona chargers used in our study. The corona currents were measured at various applied voltages, showing that the current gradually increased once the corona onset voltage was exceeded. It was observed that the current for negative voltage was higher than for positive voltage of the same magnitude, which was a phenomenon also noted by [PERSON] [24]. Since corona current is proportional to air ion concentration, the negative discharge produced more air ions compared to the positive discharge. At applied voltages of (+) 6 kV and (-) 6 kV, the measured currents were (+) 1.32 uA and (-) 3.51 uA, respectively. Particle size distributions were measured both upstream and downstream of the agglomerator in which the vortex generator was placed. The electric field was not applied to the agglomerator (see Figure 5a). For the measurement, NaCl (count mean diameter, CMD; 100 nm) and Arizona test dust (count mean diameter, CMD; 1 um) were generated, as explained in Section 4, and delivered to the agglomerator. The results for submicron particles are shown in Figure 5b. The solid orange line represents the upstream distribution of submicron particles (NaCI) generated through experiments, while the solid black line indicates the downstream distribution measured after passing through the vortex generator.