High-Efficiency Unipolar Charger for Sub-10 nm Aerosol Particles Using Surface-Discharge Microplasma with a Voltage of Sinc Function

Figures & data

TABLE 1 Comparison of the SMAC by Kwon et al. (2007), the SMAC by Osone et al. (2012), and the present charger

	SMAC by Kwon	SMAC by Osone
	et al. (2007)	et al. (2012)	Present charger
Dimensions of the charging zone	SUS cylindrical tube	SUS cylindrical tube	SUS semi-cylindrical tube
	36-mm-inner diameter	22-mm-inner diameter	15.6-mm-inner diameter
	140-mm long	275-mm long	300-mm long
Disposition of the ionizer chip	Outside of the charging zone (ions supplied via a slit)	Inside the charging zone (set into the charging zone)	Inside the charging zone (set into the charging zone)
Applied voltage	DC-biased pulse	DC-biased pulse	DC-biased sin x/x wave
	(2 kV: peak-peak)	(2 ∼ 3 kV: peak-peak)	(3 ∼ 4.5 kV: peak-peak)
Length of the ionizer chip	22 mm	275 mm	300 mm
Volume of the charging zone	142.4 cm^3	104.5 cm^3	28.7 cm^3
Effective charging volume	39.0 cm^3	104.5 cm^3	28.7 cm^3
Effective charging time (t) at 1.5 LPM	1.56 s	4.2 s	1.2 s
(residence time)	(5.7 s)	(4.2 s)	(1.2 s)
Measured ion concentration (N)	2.5 × 10 ^12 per m^3	N/A	3.1 × 10 ^14 per m^3
Effective ion concentration (N)*	5.0 × 10 ^12 per m^3(*1)	0.7 × 10 ^13 per m^3(*1)	2.9 × 10 ^13 per m^3(*2)
Nt-product*	3.5 × 10 ^12 s/m^3(*1)	3.0 × 10 ^13 s/m^3(*1)	2.0 × 10 ^13 s/m^3(*2)
Intrinsic charging efficiency at 10 nm	N/A	0.90 at 1.5 LPM	0.79 at 2.5 LPM
Extrinsic charging efficiency at 10 nm	0.22 at 1.5 LPM (10.5 nm)	N/A	0.61 at 2.5 LPM
*Estimated values from experimental charging efficiencies at 1.5 LPM^(*1) and 2.5 LPM^(*2).

FIG. 1 Schematic of (a) the microplasma-based unipolar charger and (b) a cross-section of the charging chamber.

FIG. 2 Upper view of the ionizer chip and the disposition of electrodes.

FIG. 3 Schematic diagram of the experimental setup for the evaluation of the charging performance.

FIG. 4 Typical negative sin /x voltage waveform and discharge current waveform when f = 1500 Hz, V _o = −3.05 kV, and V _bias = +850 V.

TABLE 2 Extrinsic charging efficiencies of 10 nm-particles obtained experimentally by various voltage waveforms at Q = 3.5 L/min. DC pulses are those used by Kwon et al. (2007), and the corresponding extrinsic efficiency is for 10.5-nm particles

					Extrinsic
				Bias	charging
		Amplitude	Frequency	voltage	efficiency
Waveforms		[kV]	[kHz]	[kV]	[%]
ramp (−)		−2.64	9.1	−520	5.9
Triangle		2.28	4.8	1040	5.9
Square		2.48	3.6	760	7.4
Sine		3.36	2	620	16.9
ramp (+)		2.32	10.5	700	18.4
DC pulses^1		±2.00	1	500	25
sin x/x (−)		−3.05	1.5	850	66.7
^1Kwon et al. (2007).

FIG. 5 Effect of amplitude voltage on the charging efficiencies at constant V _bias = 0 V, f = 1500 Hz for (a) 5-nm and (b) 10-nm particles and at constant V _bias = +800 V, f = 1500 Hz for (c) 5-nm and (d) 10-nm particles.

FIG. 6 Effect of bias voltage (offset voltage), V _bias, on the charging efficiencies of 10-nm particles at f = 1500 Hz, V ₀ = −3.05 kV, and Q = 3.5 L/min.

FIG. 7 Effect of frequency, f, on the charging efficiencies of 10-nm particles at V ₀ = −3.2 kV, V _bias = 800 V, and Q = 3.5 L/min.

FIG. 8 Experimental result of the (a) intrinsic charging efficiency and (b) extrinsic charging efficiency against the particle diameter at various aerosol flow rates: Q = 2.5 L/min, Q = 3.5 L/min, Q = 4.5 L/min, V ₀ = −3.05 kV, V _bias = +850 V, and f = 1500 Hz. The lines are the theoretical values of the intrinsic charging efficiency (η _intr) and extrinsic charging efficiency (η _extr).

Kwon , S. B. , Sakurai , H. and Seto , T. 2007 . Unipolar Charging of Nanoparticles by the Surface-Discharge Microplasma Aerosol Charge (SMAC) . J. Nanopart. Res. , 9 : 621 – 630 .

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Osone , S. , Manirakiza , E. , Seto , T. , Otani , Y. and Fujimoto , T. 2012 . Potential of Surface-Discharge Microplasma Device as Ion Source for High Efficiency Electrical Charging of Nanoparticles . J. Chem. Eng. Japan , 45 ( 1 ) : 21 – 27 .

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