An Approach for Characterizing the Transmission Efficiency of Charged Aerosols through Static Dissipative Tubes Subject to Favorable and Adverse Axial Electric Fields

FARNAZ KHOSRAVI, Francesco Carbone, University of Connecticut

     Abstract Number: 517
     Working Group: Instrumentation and Methods

Abstract
Differential Mobility Analyzer (DMA) classifies charged molecules and nanoparticles based on their electrical mobility but the classified aerosol has to be transported from the high voltage region of the DMA outlet slit to the detection device which is electrically grounded. The aerosol flow is guided by tubes made of Electro Static Dissipative (ESD) materials that can withstand high voltage while minimizing the aerosol electrostatic losses. Measurements or accurate estimates of such losses are necessary to implement quantitative DMA data inversion and, more broadly, are also relevant in understanding the dynamics of aerosols subject to electric fields in enclosed flows. In this study, we introduce an approach to measure the transmission efficiency of charged nanoparticles inside ESD tubes sequentially subject to a favorable and an adverse axial electric field, as a function of the particles' electrical mobility and the electric fields’ intensity. The approach consists of using a Half-Mini High-Resolution DMA to generate monodisperse aerosols at is grounded outlet tube where the size segregated aerosol stream is split equally into two segmented tubes of equal lengths and internal diameters connected to identical Faraday Cup Electrometers (FCE). All parts of the reference tube are made of stainless steel (SS) tube and are grounded so that only easily predictable diffusion losses affect the measured reference signal. The test tube differs from the reference one because two segments are replaced with parts made in the ESD material under investigation. The ESD segments are separated by a short SS connector segment where we apply the test high voltage. The ratio of the test over the reference FCE signals directly measures the transmission efficiency which quantifies the additional losses induced by the aerosol crossing the adverse and favorable electrical fields before reaching the detector, as well by the electrostatic interactions of the aerosol with ESD. The results show that the transmission efficiency is affected by the ESD material properties, the applied voltage, and some geometric parameters (e.g., ESD segments’ length) in a non-trivial manner. A COMSOL model has been implemented to reproduce the results and gain insight into the particle losses mechanisms.