Abstract View
The Addition of a Downstream DC Bias to an Atmospheric-pressure, Flow-through RF Plasma for Enhanced Charging of Aerosol Nanoparticles
SUKRANT DHAWAN, Abhay Vidwans, Girish Sharma, Nabiel Abuyazid, R. Mohan Sankaran, Pratim Biswas, Washington University in St Louis
Abstract Number: 291
Working Group: Dusty Plasma
Abstract
Electrostatic precipitators (ESPs) are widely employed in industry and indoor environments for the removal of aerosol particles. ESPs typically use a corona discharge to charge the particles and allow them to be removed by a DC electric field. However, corona discharges are weakly ionized plasmas with plasma densities of the order of 1014-1016 #/m3. In comparison, other types of atmospheric-pressure plasmas including radio frequency (RF) microplasmas are characterized by orders of magnitude higher plasma densities ~1020 #/m3. We have recently shown that high charging efficiencies (>90%) can be achieved by these plasmas for particles larger than 100 nm, while the charging efficiency of particles smaller than 100 nm was low. A two-stage charging mechanism based on a characteristic time scale analysis suggested that while particles were predominantly charged negatively in the plasma volume, the relatively faster rate of loss of the electrons in the spatial afterglow resulted in neutralization by positive ions.
Here, we present a new design concept for aerosol particle charging in atmospheric-pressure plasmas: a DC field downstream of the plasma volume in the spatial afterglow to potentially remove the positive ions and prevent neutralization of the particles. The overall charge fraction and polarity were measured as a function of particle diameter at different downstream DC voltages of a flow-through, RF atmospheric-pressure plasma. We find that when the magnitude of the applied DC voltage was higher than a critical value, the charge fraction of particles increased, and the charge polarity shifted from bipolar to unipolarly negative. The results were supported by analyzing the characteristic timescales for neutralization by and loss to the walls of positive ions in the spatial afterglow at different downstream DC voltages.
Reference:
[1] Sharma, G. et al (2020). J Phys D. 53(24), 245204.