10th International Aerosol Conference September 2 - September 7, 2018 America's Center Convention Complex St. Louis, Missouri, USA
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Electro-scavenging of Airborne Particles by Electro Hydrodynamic Atomizer (EHDA) Generated Charged Droplets
Arshad Khan, Sanjay Singh, B.K. Sapra, Y.S. MAYYA, Bhabha Atomic Research Centre, Mumbai
Abstract Number: 1208 Working Group: Control and Mitigation
Abstract Airborne particulates generated during various processes in conventional or nuclear industries are controlled /removed by filtration systems based on their particle size using cyclone, fabric filters and electrostatic precipitator. Cyclone is useful mainly for particles of few micrometers and above. High Efficiency Particulate Air (HEPA) is also suitable and have an efficiency of 99.97 % for particle of 0.3 μm but they are not very cost effective as they need to be replaced frequently due to dust loading. Electrostatic Precipitator (ESP) on the other hand, is used for fine particles of less than 0.3 μm. Though, electrostatic precipitators do not require filter replacement, they produce ozone as a by-product and collection efficiency is low for size 0.1 – 1.0 μm [1].
Alternatively, electro-scavenging of aerosols using charged particles is an upcoming technology in the area of air cleaning. Its advantage is that it does not give rise to ozone in the ambient environment and does not add to the noise level. Herein, we studied the depletion of lab generated aerosols with EHDA generated high charge (~104 elementary charges) droplets and its potential for utilization in air cleaning applications [2].
An EHDA based air cleaning system is designed [3] & fabricated and aerosol scavenging characteristics are studied using smoke and nebulizer generated NaCl aerosols. Both types of aerosols were fully characterised with respect to their number, size and charge distribution. For smoke aerosol, size dependent aerosol collection efficiency showed minima of 20% for particle diameter of 30 nm; increasing to as high as 90% for particle diameter greater than 100 nm. For NaCl aerosols, collection efficiency is almost flat with respect to particle size. The variation is 70% to 90% for the particles more than 200 nm.
The EHDA based cleaning system showed good particle removal efficiency, however a question arises as to whether the removal occurs because of electro-migration of aerosols in the capillary electric field of EHDA or due to scavenging of aerosols by droplets. To confirm this, a comparative aerosol removal study was carried out at applied capillary potentials of 0 V and 4 kV (which is just below the operating voltage of EHDA) and with operating EHDA. The experiment confirms the aerosol removal by interaction of charged droplet with aerosol particles. Results from the current system have been very encouraging for its utilization in air cleaning application.
References: [1] Zhu, J., Zhang, X., Chen, W., Shi, Y., Yan, K., (2010), Electrostatic precipitation of fine particles with a bipolar pre-charger, J. Electrostatics, 68, pp.174 -178. [2] Jaworek, A., Adamiak , K., Balachandran, W., Krupa, A., Castle, P., and MacHowski, W. (2002), Numerical Simulation of Scavenging of Small Particles by Charged Droplets, Aerosol Sci. Technol., 36, pp. 913 – 924. [3] Singh Sanjay, Khan Arshad, Sapra B. K. & Mayya Y. S., (2013), Parameterization of an Electro-Hydrodynamic Atomization Based Aerosol Generator, Particulate Science and Technology: An International Journal, 31:5, pp. 494-500.