The performance of an electrical ionizer as a bipolar aerosol charger for charging ultrafine particles

Figures & data

Figure 1. (a, b) The structures of SMAC and the MHM charger. (c, d) The schematic diagrams of SMAC and the MHM charger.

Figure 2. The pulse width modulated voltage signal of MHM + and MHM–.

Figure 3. The experimental setups for measuring (a) ion concentration and (b) ion mobility.

Figure 4. The experimental setups for evaluating (a) new particle formation by the chargers, (b) the charged particle penetration ratio of the chargers, (c) the neutral particle penetration of the MHM charger, (d) the charging probability, and (e) the electrical mobility distribution.

Table 1. Summary of the measured parameters, experimental condition, and calculation used for evaluating the MHM charger.

Setup	The measured parameters	Experimental conditions	Calculation	Equation
Figure 4a	New particle generation	SMAC/MHM charger: ON	Ng
Figure 4b	Charged-particle penetration ratio (rc)	SMAC/MHM charger: ON and OFF	$r_c=\frac{N_1^{\mathrm{ON}}}{N_1^{\mathrm{OFF}}}$	(3)
Figure 4c	Neutral-particle penetration when the MHM charger was in the OFF condition (ηn^OFF)	SMAC: ON Condenser 1: ON MHM charger: OFF	${\eta }_n^{\mathrm{OFF}}=\frac{N_2^{\mathrm{OFF}}}{N_0^n}$	(4)
Figure 4c	Neutral-particle penetration when the MHM charger was in the ON condition (ηn^ON)	SMAC: ON Condenser 1: ON MHM charger: ON	${\eta }_n^{\mathrm{ON}}=\frac{N_2^{\mathrm{ON}}}{N_0^n}$	(5)
Figure 4d	The total neutral-particle penetration of the MHM charger and Condenser 2 when both of them were in the OFF condition (ξn^OFF)	SMAC: ON Condenser 1: ON MHM charger: OFF Condenser 2: OFF	${\xi }_n^{\mathit{OFF}}=\frac{N_4^{\mathrm{OFF}}}{N_0^n}$	(6)
Figure 4d	The total charged-particle penetration of the MHM charger and Condenser 2 when both of them were in the OFF condition (ξc^OFF)	SMAC: OFF Condenser 1: OFF MHM charger: OFF Condenser 2: OFF	${\xi }_c^{\mathit{OFF}}=\frac{N_4^{\mathrm{OFF}}}{N_0^c}$	(7)
Figure 4d	Neutral fraction (f0)	SMAC: ON Condenser 1: ON MHM charger: ON Condenser 2: ON and OFF	$f_0=\frac{N_4^{\mathrm{ON}}}{N_4^{\mathrm{OFF}}}$	(8)
Figure 4d	Intrinsic charging efficiency (ηintr)	SMAC: ON Condenser 1: ON MHM charger: ON Condenser 2: ON	${\eta }_{\mathit{intr}}=\frac{{\eta }_n^{\mathrm{OFF}}{N}_0^n-N_4^{\mathrm{ON}}}{N_0^n}$	(9)
Figure 4d	Extrinsic charging efficiency (ηextr)	SMAC: ON Condenser 1: ON MHM charger: ON Condenser 2: ON and OFF	${\eta }_{\mathit{extr}}=\frac{N_4^{\mathrm{OFF}}-N_4^{\mathrm{ON}}}{N_0^n}$	(10)

Figure 5. The ratio of ion concentration in various duty-cycle configurations. The model was calculated using Equations (12)(12) $$\frac{d{n}_{g\pm }\left(t\right)}{dt}=q\left(t\right)-\alpha n_{g+}\left(t\right)n_{g-}\left(t\right)-\omega \prime n_{g\pm }\left(t\right),$$(12) and (13)(13) $$\frac{d{n}_{i\pm }\left(t^{\prime }\right)}{dt\prime }=-\alpha n_{i+}\left(t^{\prime }\right)n_{i-}\left(t^{\prime }\right),$$(13) .

Figure 6. The effect of flow rate on the ion concentration produced by the MHM charger. The model was calculated using Equations (12)(12) $$\frac{d{n}_{g\pm }\left(t\right)}{dt}=q\left(t\right)-\alpha n_{g+}\left(t\right)n_{g-}\left(t\right)-\omega \prime n_{g\pm }\left(t\right),$$(12) and (13)(13) $$\frac{d{n}_{i\pm }\left(t^{\prime }\right)}{dt\prime }=-\alpha n_{i+}\left(t^{\prime }\right)n_{i-}\left(t^{\prime }\right),$$(13) .

Table 2. The air ion mobility produced by SMAC and the MHM charger with P50N50 configuration.

Ion properties	Ion source	Ion polarity
		(+)		(–)
		Mean	Median	Mean	Median
Peak 1 (cm^2 V^-1 s^-1)	SMAC	0.880	0.872	1.432	1.399
	MHM	0.931	0.919	1.348	1.311
Peak 2 (cm^2 V^-1 s^-1)	SMAC	1.297	1.280	2.121	2.108
	MHM	1.384	1.373	2.056	2.045
Mean mobility (cm^2 V^-1 s^-1)	SMAC	1.140		1.910
	MHM	1.090		1.670
Ion concentration (cm^-3)	SMAC	2.15 × 10^6		2.27 × 10^6
	MHM	2.45 × 10^6		2.47 × 10^6
Diffusion coefficient (m^2 s^-1)	SMAC	2.96 × 10^-6		4.95 × 10^-6
	MHM	2.83 × 10^-6		4.33 × 10^-6.

Figure 7. The distribution of positive and negative air ions induced by SMAC and the MHM charger with peak analysis data obtained through the lognormal distribution function.

Figure 8. The charged particle penetration ratios of SMAC and the MHM charger (measured using the experimental setup in Figure 4b and calculated using Equation (3)(1) $$D_{\pm }=\frac{T_{\mathrm{ON}\pm }}{T_s}\times 100\%,$$(1) ) compared with the previous study of SMAC by Kwon et al. (2006).

Figure 9. The neutral particle penetration of the MHM charger calculated in Equations (4)(2) $$n_{\pm }=\frac{|I-I_o|}{e{Q}_{ae}},$$(2) and (5)(11) $$f_0^{\prime }=\frac{N_4^{\mathrm{ON}}}{\frac{{\xi }_n^{\mathrm{OFF}}}{{\xi }_c^{\mathrm{OFF}}{r}_c}{N}_4^{\mathrm{OFF}}+\left(1-\frac{{\xi }_n^{\mathrm{OFF}}}{{\xi }_c^{\mathrm{OFF}}}\right)N_4^{\mathrm{ON}}}.$$(11) and measured using the experimental setup in Figure 4c.

Figure 10. The total penetration of neutral and charged particles of the MHM-Condenser 2 calculated in Equations (6)(12) $$\frac{d{n}_{g\pm }\left(t\right)}{dt}=q\left(t\right)-\alpha n_{g+}\left(t\right)n_{g-}\left(t\right)-\omega \prime n_{g\pm }\left(t\right),$$(12) and (7)(13) $$\frac{d{n}_{i\pm }\left(t^{\prime }\right)}{dt\prime }=-\alpha n_{i+}\left(t^{\prime }\right)n_{i-}\left(t^{\prime }\right),$$(13) and measured using the experimental setup in Figure 4d. The third-order polynomial fit was applied to the total penetration of charged particles.

Figure 11. The corrected fraction of neutral particles obtained by the MHM charger compared with the uncorrected value and the calculation model proposed by Gunn (1955), with an ion concentration ratio and ion mobility ratio of 0.992 and 0.653, respectively.

Figure 12. The intrinsic and extrinsic charging efficiencies of the MHM charger calculated in Equations (9)(14) $$D_{\mathit{ion}\pm }=\frac{kT{Z}_{i\pm }}{e},$$(14) and (10)(14) $$D_{\mathit{ion}\pm }=\frac{kT{Z}_{i\pm }}{e},$$(14) and measured using the experimental setup in Figure 4d.

Figure 13. The particle mobility distributions of negatively charged particles obtained by SMAC and the MHM charger using the experimental setup in Figure 4c.

Kwon, S. B., H. Sakurai, T. Seto, and Y. J. Kim. 2006. Charge neutralization of submicron aerosols using surface-discharge microplasma. J. Aerosol Sci. 37 (4):483–99. doi:10.1016/j.jaerosci.2005.05.007.

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