Cascade impactors consist of 1 or more collection substrates connected in a series of particle collection plates with larger particle ranges captured first, and ever smaller ranges captured on particle collection plates as the airflow travels through the impactor. Impactors are designed for low airflow capacities of 1 LPM to perhaps 5 LPM, or designed for higher airflow capacities of 25 LPM to 50LPM. As the air flow rate decreases a lower concentration particle aerosol can be sampled without over saturating the collection stages. Likewise, as the airflow volume increases, then higher particle aerosol concentrations can be sampled. A filter typically is installed after the last collection substrate, which allows one to sample unwanted particles for chemical analysis, and to filter the output exhaust.
Some drawbacks of poorly designed cascade impactors are the risk of particles bouncing off a collection substrate, then being trapped by the following stage. This causes poor size range separation, which would be cause low resolution of particle collection substrates. One way of reducing the particle bounce issue is to layer the collection substrate with a known sticky substance. This can affect mass measurements of sampled particles ranges. Of course, it is desirable to mechanically resolve the bounce issues with flow control and mechanical dynamics, but the cost of design, which affects the product cost, has to be balanced with the desired goals.
High Aerosol Particle Concentration or Low Aerosol Particle Concentration with Rotate or No Rotate Capabilities
Cascade Impactor with rotate capabilities is able to collect particle data on a substrate with a uniform dispersion of the particle sample across the substrate. Airflow must be highly controlled, along with the method by which each particle size range is separated to one or more collection substrates. The goal is to have high size resolution in the sampling capabilities of each particle size range, such that there is minimal cross over from one particle sample size to the particle sample sizes above and below the size range. Also desired is to minimize the potential of samples particles from bouncing off the collection substrate and re-entering the airflow. The cascade impactor requires critical airflow control and particle control, in order to achieve the desired goals.
Precise size classification of particles in an aerosol stream to support:- air pollution- diesel blow by and engine emission testing- automotive airbag testing- industrial hygiene studies
High particle size separation of each size range with minimal particle bouncing from each collection substrate- 1-50 Liters sampling air flow rates are typical- 1 to 15 particle collection stages are useful- each collection stage is designed around a repeatable, particle collection range, typically from 3nm – 20 microns
Rotate or No Rotate capabilities
A high-performance, cascade impactor provides high sampling
flow rate, low inter-stage wall loss, and highly accurate size ranges deposited on each collection substrate.
Impactors come with single particle collection stages and can be designed with 12 or more collection substrates.
Additional stages add design complexity due to particle size range control