A Low Pressure Drop Preseparator for Elimination of Particles Larger than 450 nm

C Asbach,H Shin,H Fissan,D.Y.H Pui,H.G Horn,T Hase,H Kaminski,T.A.J Kuhlbusch

doi:10.4209/aaqr.2011.05.0057

Abstract

Measurement techniques which allow the detection of airborne nanoparticles are of great interest for e.g. exposure monitoring and quality control during nanoparticle production. An increasing number of commercial devices use a unipolar diffusion charger to charge the particles and determine the nanoparticle concentration and sometimes size. The analysis however may be biased by the presence of large particles. We therefore developed a preseparator that removes particles larger than 450 nm, i. e the minimum in the range of particle lung deposition curves, but only causes a low pressure drop. The preseparator uses a total flow rate of 2.5 L/min and consists of two stages. The first stage is a virtual impactor that removes particles larger than approximately 1 μm with a minor flow of 1 L/min. Particles above 450 nm are removed from the remaining 1.5 L/min in the cyclone of the second stage. The combination of a cyclone with a virtual impactor was shown to reduce the pressure drop of the preseparator from 8.1 to 5.6 kPa compared with a cyclone alone and improve the sharpness of the separation curve for cut-off diameters around 450 nm. Furthermore the virtual impactor extends the cleaning intervals of the preseparator, because large particles are no longer deposited in the cyclone. Eventually the preseparator was tested with an opposed flow diffusion charger and it was shown that particle charging is not affected by the pressure drop.

Highlights

Nanoparticles, here synonymously used for nanoplates and nanofibres, can be considered as important building blocks for nanostructured materials
It was shown for the Nanoparticle Surface Area Monitor (NSAM, TSI model 3550) that the device only delivers accurate estimates of the lung deposited surface area in a size range of approximately 20–400 nm (Asbach et al, 2009), because the lung deposition curves show a minimum around 300–500 nm
This paper describes the development and evaluation of a preseparator with a 450 nm cut-off and low pressure drop for this modular system, which operates at a total flow rate of 2.5 L/min

Summary

INTRODUCTION

Nanoparticles, here synonymously used for nanoplates and nanofibres, can be considered as important building blocks for nanostructured materials. There is concern that these engineered nanoparticles can be released into the environmental media air, water and soil, during their entire lifecycle, i.e. during synthesis, handling, downstream use or recycling (Mueller and Nowack, 2008; Som et al, 2010) This may lead to exposure of human beings and the ecosystem with corresponding possible risks (Borm et al, 2006; Warheit et al, 2008). This paper describes the development and evaluation of a preseparator with a 450 nm cut-off and low pressure drop for this modular system, which operates at a total flow rate of 2.5 L/min It is designed such that it can be used for other diffusion charger based instruments, NSAM (TSI, model 3550) or the largely identical TSI Aerotrak 9000. The preseparator is kept as small as possible so that it can be used in portable or personal instruments

DESIGN OF PRESEPARATOR

SUMMARY