10th International Aerosol Conference September 2 - September 7, 2018 America's Center Convention Complex St. Louis, Missouri, USA
Abstract View
Aerosol Charging with a Piezoelectric Plasma Generator
Mario Anton Schriefl, ALEXANDER BERGMANN, Alexander Melischnig, Markus Puff, Graz University of Technology
Abstract Number: 200 Working Group: Instrumentation
Abstract Recently, a new piezoelectric plasma generator, called CeraPlas™, was developed by EPCOS OHG. CeraPlas™ technology provides a platform consisting of the CeraPlas™ piezo ceramic component and a driving stage which allows to build up specific applications for using cold atmospheric plasma. This device allows for high efficient gas ionization at atmospheric pressure and temperature conditions at safe operating conditions. The dimensions, as well as the low power consumption of the device enable its usage for mobile applications. Depending on operating power, surrounding gas flow rate and position downstream of the device, an ion density of up to 2 x 1013 m-3 for both, positive and negative polarities, can be achieved. Thus, the device can act as an ion source for aerosol charging. However, in order to use the device for that purpose, some issues related with the operation of the CeraPlas™ — like the emission of nanoparticles and generation of ozone — have to be overcome. In this study we characterize the aerosol charging properties of the device.
Bipolar charging of NaCl particles as a test aerosol was performed by turbulent mixing of particles and ions generated by the CeraPlas™. In order to minimize generation of ozone, and to ensure reproducible working conditions, the CeraPlas™ was operated in N2 atmosphere. Contamination of nanoparticles emitted by the CeraPlas™ was suppressed by removing them before mixing with the test aerosol, enabled by a specially designed suction channel. This bipolar charging configuration was used as a neutralizer for a differential mobility analyzer and tested against commercially available bipolar aerosol chargers (x-ray source and radioactive source). First promising results show comparable charge distributions and charging efficiencies.
In order to quantify the charging conditions, a multiphysical simulation of the mixing chamber was performed, including fluid dynamics, transport of the ion species and particle trajectories. Assuming the aforementioned ion densities and an ion recombination coefficient of 1.6 x 1012 m3s-1, we obtained an Nit product about 1012 m-3s for this charging configuration. Enhancement of the charging chamber in order to increase the Nit product is ongoing.
A second charging configuration was used which allows for the shift of the charge distribution by use of an electric field in flow direction of the particles. The goal of this method is the adjustment of the charge distribution up to unipolar charging. Artefact formation due to particle emission by the device itself was suppressed by spatially separating the CeraPlas™ from the test aerosols. This configuration resulted in lower charging efficiencies compared to the former method. Nevertheless, first results proof the capability of shifting the charge distribution in either direction, positive and negative. Next steps focus on the optimization of the charging chamber with respect to charging efficiency.