AAAR 31st Annual Conference
October 8-12, 2012
Hyatt Regency Minneapolis
Minneapolis, Minnesota, USA
Abstract View
Advances in Concentrated Particle Collection with the Laminar Flow Growth Tube
GREGORY LEWIS, Steven Spielman, Susanne Hering, Aerosol Dynamics Inc.
Abstract Number: 553 Working Group: Instrumentation and Methods
Abstract Aerosol Dynamics Inc, has developed a series of instruments which collect airborne particle into very concentrated samples. Impaction on a warm dry surface results in a spot size of approximately 0.3mm diameter. Because the particles are coated in water, and dry after impaction, there is no bounce. Impaction is also done into liquid volumes of between 100 and 500 microliters. We have made instruments with maximum flow rates of 1.0, 1.5 and 5 Liter per minute and capable of an approximately 5:1 flow rate range. Collection efficiency above 90% is easily achieved.
The instruments use a water-based laminar flow growth tube technology, which is similar to the basis of TSI's Water-based Condensation Particle Counters (WCPC). The WCPCs use a two stage system--a cold section followed by a hot wet wall section. The fist stage cools and saturates the incoming air. Because water vapor diffuses faster then heat, the flow becomes super saturated in the second stage. In the new instrument we radically shorten the second stage and add a cold third stage. Numerical models and experiment show that the relative humidity profiles and the final particle size are minimally dependent on the third stage temperature, showing no practical disadvantage. However the addition of the third stage, has three advantages. 1) It greatly reduces the water consumption of the instrument. 2) It allows control of the exiting flow dew point, which minimizes excess water when collecting using liquid impaction. 3) The sample collection temperature can be reduced to room temperature or preserving the integrity of biological or volatile components of the particles. 4) The maximum temperature the majority of the flow sees is greatly reduced.