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Production of Test Aerosols

• Ideal aerosol generator: a constant and reproducible output of (monodisperse), stable, uncharged, (solid), spherical aerosol particles whose size and concentration can be easily controlled.

Q: In our daily life, do we generate aerosols?Q: What are the criteria for producing aerosols for testing?

Reading: Chap 21

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Atomization of Liquids

3/1Fdd ds

Q: Do the solution’s properties change after a while?

Mass conc. of 5-50 g/m3

MMDs of 1-10 mm g of 1.5-2.2

LiquidSolutionSuspension

Q: Do we generate mono- or poly-disperse droplets by atomization?

Q: Can we produce high conc. aerosol by atomization?Q: What type of aerosols do we generate?

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Ultrasonic Nebulizer

Compressed Air Nebulizer

Q: How does the particle size change wrt air velocity, viscosity and surface tension?

Q: If dry particles are produced from nebulizing liquid, how does the g compare to that of the liquid?

3/1

2

fCMD

L

Metered Dose

Inhaler (MDI)

http://aerosol.ees.ufl.edu/Healthaerosol/section03-2.html

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3/16

fQd L

p

Vibrating Orifice Aerosol Generator (VOAG)

Q: How can we control droplet size?

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Spinning Disc Aerosol Generator

http://www.bgiusa.com/img/stag2.jpg

Rd

Ld

47.0

Q: How can we control droplet size?

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Electrospray

http://www.newobjective.com/electrospray/

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Atomization of Liquid SuspensionLiquid suspension containing monodisperse solid particles of known size.

Q: More than 1 particle present in a droplet?

3

where exp!

)(

p

dn

ddFxx

nxnP

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2.1 GSD and 0.9for

)exp(ln5.01ln5.4exp)1(

23

23

R

GSDMMDGSDdR

F p

(R: ratio of singlets to droplets containing particles)

Considering the size distribution of droplets …..

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Dispersion of Powders

Requirement:¨a means to continuously metering a powder into the generator at a constant rate¨a means to dispersing the powder

Common methods:¨High velocity air stream¨Scraper¨Fluidized bed generator

Wright Dust Feeder

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Dispersibility depends on:¨Powder material¨Particle size¨Shape¨Moisture content

Dry Powder Inhaler (DPI)

http://aerosol.ees.ufl.edu/Healthaerosol/section04-2.html

Fluidized Bed Aerosol Generator

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3/16

NCdL

md

Condensation Methods

Q: How do we control the particle size?

Basic principle to generate monodisperse aerosol: allow condensation to occur under slow and controlled condition

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Reflections