A Cylindrical Thermal Precipitator with a Particle Size-Selective Inlet

We designed a thermal precipitator in a cylindrical configuration with a size-selective inlet, and investigated its performance in experiments using differential mobility analyzer (DMA)-classified particles of sodium chloride (NaCl) and polystyrene latex (PSL). Our investigation was performed in two parts: (1) using the size-selective inlet to determine the best inlet-to-wall distance for optimal impaction of 1 μm particles; (2) using a simple inlet tube to measure particle collection via thermophoresis over a size range from 40 nm to 1000 nm. The results showed that the inlet had a particle cut-off curve, with a 50% particle cut-off Stokes number of 0.238, resulting in removing particles with sizes larger than 1 μm at an aerosol flow rate of 1.5 lpm. The thermophoretic particle collection efficiency in the prototype was measured without the size-selective inlet installed. The size dependence of the collection efficiency was negligible for particles with diameters ≤300 nm and became noticeable for those with diameters >300 nm. An analytical model was further developed to estimate the particle collection efficiency due to thermophoresis of the prototype under various aerosol flow rates and temperature gradients. For particles with diameters less than 400 nm, reasonable agreement was obtained between the measured data and the collection efficiency calculated from the developed analytical model. It was further concluded that the derived formula for the calculation of thermophoretic particle collection efficiency could serve as the backbone for future design of thermal precipitators in any configuration, when combined with the proper formula for the dimensionless thermophoretic particle velocity.

Copyright 2012 American Association for Aerosol Research