real-time. The operating principle of ELPI is based on particle charging using corona charger, size classification in cascade impactor and electrical charge detection with sensitive electrometers.
The generated aerosols were conditioned using Nafion dryer and passed to the aerosol chamber. Only under steady conditions, charge measurements were carried out. The measurement of size wise charge distribution (net charge per particle) was obtained by keeping ELPI with its internal particle charger ON alternatively for 20 seconds. The particles are charged to a known charge level in a corona charger of ELPI, hence for charge measurement, the charger is put off. Under charger ON condition, ELPI measures number concentration using calibrated penetration function while it measures current over all stages for charger OFF condition.
Results and discussions
Fig. 2, 3, 4 and 5 show number of charges/particle plotted as a function of aerodynamic diameter of each stage of ELPI for aerosols generated from nebulization of NaCl, electrical heating based aerosol generator using nichrome wire (Hot wire generator) and combustion of incense stick.
1. Atomization of NaCl particles
Figure 2: Particle charge and size distribution for particles generated from Nebulization of 10% NaCl solution
Figure 3: Particle charge distribution for particles generated from Nebulization of 10%, 1% and 0.1% NaCl solution
2. Hot wire generator
Figure.4. Particle charge and size distribution for particles generated from HWG
3. Combustion of incense stick
Figure.5. Particle charge and size distribution for particles generated from Combustion of Incense stick
Different concentrations of NaCl viz. 0.1%, 1%, 10% were used to generate aerosols. For each concentration, charge/particle increases with increase in particle size. Charge/particle at mode viz., 120 nm was found to be 0.66. Study of charge obtained at mode is important because this charge is carried by maximum number of particles.
Particles generated in case of combustion of incense stick and hot wire generator were in the lower size ranges. For them as well, charge was considered at mode concentration. The charge/particle at modal size for hot wire generator was 0.036 at 17 nm and for combustion source 0.28 at 72 nm. For both sources, charge/particle increases with size as expected.
Conclusion
Charge size distribution of aerosols generated from nebulization, combustion and hot wire generator were measured. Charge/particle was seen to be increasing with particle size for all the three sources. Charge at modal size was considered important because maximum particles would carry that charge. Charge/particle
at modal size for nebulization, hot wire generator and combustion was measured to be 0.66 at 120 nm, 0.036 at 17 nm and 0.28 at 72 nm respectively.
References
- Bruce Forsyth, Benjamin Y H. Liu, Francisco J. Romay, Aerosol Science and Technology, 1998, 28, 489-501.
- Chuen-Jinn Tsai, Jyh-Shyan Lin, C.G. Deshpande, Li-Chun Liu, Particle and Particle System Characterisation. 2005, 22, 293–298.-1
- M Sahu, J Park, P. Biswas, J Nanopart Res, 2012, 14, 678.-3
- M. V. Rodrigues, W. D. Marra Jr., R. G. Almeida, J. R. Coury, Brazilian journal of chemical engineering, 2006, 23, 125-133.-3
- Dekati Ltd. 2013, ELPI+ User Manual.-3
Mariam , Manish Joshi ,
Arshad Khan , B K Sapra
Radiological Physics and Advisory Division, Health Physics Division, Bhabha Atomic Research Centre, Mumbai – 400085, India
E-Mail: bsapra@barc.gov.in
