Aerodynamic particle size measurement has a unique and focused application in several industry sectors.  Pharmaceutical API’s, which utilize an inhalation delivery system and environmental emission control samples are two sample types which can possibly benefit from this specific form of particle size analysis.   In the particle sizing field, a variety of measurement techniques are available and each measure a different physical attribute of a particle.  This measured physical property is converted into an equivalent spherical diameter.   Aerodynamic particle sizing is no different. This technique evaluates how the particle (either solid or droplet) behaves as it settles through air and reports the diameter of a sphere with the same aerodynamic drag properties.

Aerodynamic particle sizing techniques operate by either dispersing a dry powder through an air shearing process or by the generation of droplets from a spray nozzle.  The dispersed dry or liquid particles are then carried to the measurement zone via a moving air stream.  The physical detection mechanism of the instrument will vary depending on the analytical theory of operation (such as time of flight), but all aerodynamic instruments have the following in common:

• They incorporate a form of the Navier-Stokes settling equation to calculate the particle size and thus require a value for the material’s true density in addition to a value for the viscosity of the media in which the particle is settling.  In the case of aerodynamic sizing the media is air.
• They make the assumption the particle is a sphere when using the Navier-Stokes settling equation.  Therefore, actual particle shape will play a significant role in the reported size.  For example, flat flaky particles will behave differently aerodynamically than a sphere.  Liquid droplet size analysis by aerodynamic sizing is well suited for this reason.

Due to the above reasons, not all samples are optimal for aerodynamic particle size analysis.  Aerodynamic sizing instruments typically cover a relatively narrow size range and sample dispersion can be difficult at times.  Fine and cohesive powder samples can be very hard to disperse due to particle-particle attractive forces.  In the case of liquid aerosols, the proper feed rate must be used to prevent over-loading of the nozzle and possible coalescence of droplets as they dry or come in contact upon exiting the nozzle.

It is important to always consider the advantages and limitations of any particle sizing technique.  The actual application of how the sample will be utilized and under what conditions should be considered prior to selection of the most appropriate analytical sizing theory.  PTL’s years of experience in particle size analysis can assist with this decision.  Please contact us to discuss if aerodynamic particle size analysis is the best technique for your material.  Below are the available aerodynamic sizing instruments available at PTL.

 

TSI Aerosizer LD 8050 using Aerodisperser Module   (requires additional True Density analysis of the sample powder unless Density value provided by client)

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ASME Standard Method via BAHCO  (requires additional True Density analysis of the sample powder unless Density value provided by client)

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Analysis with Sample Fraction Collection available

Click here to request a quote or for more information about aerodynamic particle testing.