# Analysis of Plasma Ion Distribution and Dust Collection Efficiency of Carbon-Brush Air Purifiers
## 4 Air Purifier Dust Collection Efficiency Simulation  
### Ion Distribution According to the Location and Number of Brushes  
To apply carbon brushes to the air purifier as shown in Figure 6, three brush configuration cases were defined for the back of the air purifier, and the ion concentration distribution according to the number of brushes was simulated. The location of the brushes was 100 mm from the bottom, and a voltage of \(-8.5\) kV was applied. The flow velocity was set to 1.0 m/s, and the ground and an applied voltage of \(-5\) kV were alternately designed for the dust collecting plate in the collector. The length of the air purifier module was set to 400 mm, and two to four brushes were applied depending on the case. The ground was set to the bottom where the dust collecting plate was placed so that ions could be generated in the ground direction. Based on the simulation performed, the charging number for each particle was obtained by applying Equations (3) and (4), which are the charging equations.  
The ion concentration was calculated using the 100 mm line with the highest ion concentration close to the brush location as the dotted line shown in Figure 6. From the charging equations, the charging number for each case was obtained.  
In Case 1, the brushes were installed in the 45\({}^{\circ}\) direction to face each other, and ion distribution simulation was performed. Figure 7 shows the ion concentration contours. It can be seen that the ion concentration distribution developed toward the ground direction.  
The charging number is shown in Figure 8 according to the charging equations by selecting the line with the highest ion concentration. It can be seen that ions were generated from the brush and developed in the ground direction. In addition, the charging number showed a tendency similar to that of the ion concentration.  
In Case 2, a vertical brush was additionally installed in the center compared to Case 1, and ion distribution simulation was performed. Figure 9 shows the ion concentration contours. It can be seen that the ion concentration distribution developed toward the ground direction as in Case 1, and that the ion concentration developed from the brush in the center to both sides. This result indicates that ions are generated at the sharpest part when they are generated from a brush or a metal needle. In the case of brushes, ions are  
Figure 8: Ion concentration and charging number for Case 1.  
Figure 7: Ion concentration distribution for the brushes in Case 1.  
generated at both ends of the fiber bundle, and thus the ion concentration distribution occurs as shown in Figure 9[37; 38; 39].  
The charging number is shown in Figure 10 on the basis of the charging equations by selecting the 100 mm line. It can be seen that two peaks occurred as the concentration of ions generated at both ends of the brush was measured. The same number of ions as in Case 1 was generated in the left and right brushes, but a high ion concentration was observed from the brush in the center because of the overlapping ion flows.  
In Case 3, two brushes in the 45\({}^{\circ}\) direction were additionally installed in the center compared to Case 1, and ion distribution simulation was performed. Figure 11 shows the ion concentration contours. It can be seen that the ion concentration distribution developed toward the ground direction as in Case 1, and the ions generated from the brushes in the center were dispersed because of the same polarity. The charging number is shown in Figure 12 according to the charging equations by selecting the 100 mm line.  
Figure 10: Ion concentration and charging number for Case 2.  
Figure 9: Ion concentration distribution for the brushes in Case 2.