Condensation particle counter

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The schematic of a condensation particle counter, operated by diffusional thermal cooling. Drawn according to the description at http://www.cas.manchester.ac.uk/restools/instruments/aerosol/cpc/. Notation: 1 – air inlet; 2 – porous material block, which is heated to saturator temperature, 3 – working fluid in reservoir, 4 – condenser, 5 – focusing nozzle, 6 – laser-based counter, 7 – air pump, 8 – air exhaust.
Four small pieces of machinery connected by clear tubes sitting on a table
Equipment used for area sampling of airborne nanomaterials.[1] The instruments shown here include a condensation particle counter, aerosol photometer, and two air sampling pumps for filter-based analysis.

A condensation particle counter or CPC is a

supersaturated gas.[2]

Three techniques have been used to produce nucleation:

The most usually used (also the most efficient) method is cooling by

n-butanol; during last years water is also encountered in this use.[4]

Condensation particle counters are able to detect particles with dimensions from 2

homogeneous nucleation (when liquid molecules collide so often that they form clusters – stable enough to ensure further growth is possible), which will produce false counts. This usually starts at ca. 300% supersaturation.[4]

On the right, a diffusional thermal cooling CPC is shown in operation. In order to ensure a high vapour content, the working liquid is in contact with a hollow block of porous material that is heated. Then the humified air enters the cooler where nucleation occur. Temperature difference between the heater and the cooler determines the supersaturation, which in its turn determines the minimal size of particles that will be detected (the greater the difference, the smaller particles get counted). As proper nucleation conditions occur in the center of the flow, sometimes incoming flow is divided: most of it undergoes filtering and forms the sheath flow, which the rest of flow, still containing particles, is inserted into via a capillary. The more uniform is obtained supersaturation, the sharper is particle minimal size cutoff. During the heterogeneous nucleation process in the nucleation chamber, particles grow up to 10…12 μm large and so are conveniently detected by usual techniques, such as laser nephelometry (measurement of light pulses scattered by the grown-up particles).[4]

References

  1. doi:10.26616/NIOSHPUB2012147
    . Retrieved 2017-03-05.
  2. ^ a b Aerosol Measurement: Principles, Techniques, and Applications, edited by Pramod Kulkarni, Paul A. Baron, Klaus Willeke, p384, [1] retrieved 15 May 2012
  3. ^ Kulkarni, Baronand and Willeke, p381
  4. ^ a b c Condensation Particle Counters (CPC)
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