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Offline jdm2008

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Particle Size
« on: October 03, 2011, 09:25:13 AM »
I do not know if this is the appropiate forum for this question but here goes?

I am trying to measure the particle size for a device that creates an aerosol from a liquid(no temperature change).  The way the particle size is measured at the moment is to send it out to a testing house with a cascade impactor.  However the lead time for this test is several weeks sometimes months, and it is very expensive, is there anyway to measure the particle size in house?  I was thinking of measuring the density of the mist, but after thinking about it more closely I am not sure the density of the mist will be correlated to the particle size.
I am expecting the exact particle size per say(though that would great) but I  interested in comparison between devices and trends over time. 

Any other ideas?

Offline fledarmus

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Re: Particle Size
« Reply #1 on: October 03, 2011, 11:09:40 AM »
Are you looking to design a test from scratch, or are you interested in adapting an industry standard test? I can think of a few simple ways to try to test it. One would be to spray it onto a microscope slide etched with a standard grid and measure the droplet size that way. Edmund's scientific used to sell them.

If you are looking for an industry standard method, you might check the ASTM tests. One is here: http://books.google.com/books?id=DiRevS__HUkC&pg=PA157&lpg=PA157&dq=astm+aerosol+size&source=bl&ots=wRLC55EdBl&sig=8iAu3o-_6eJCS8vbSHQogfnSw-U&hl=en&ei=H8-JTu7LI8Hs0gHR7bTMDw&sa=X&oi=book_result&ct=result&resnum=1&ved=0CCcQ6AEwAA#v=onepage&q=astm%20aerosol%20size&f=false

Offline jdm2008

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Re: Particle Size
« Reply #2 on: October 03, 2011, 11:29:33 AM »
Are you looking to design a test from scratch, or are you interested in adapting an industry standard test? I can think of a few simple ways to try to test it. One would be to spray it onto a microscope slide etched with a standard grid and measure the droplet size that way. Edmund's scientific used to sell them.

If you are looking for an industry standard method, you might check the ASTM tests. One is here: http://books.google.com/books?id=DiRevS__HUkC&pg=PA157&lpg=PA157&dq=astm+aerosol+size&source=bl&ots=wRLC55EdBl&sig=8iAu3o-_6eJCS8vbSHQogfnSw-U&hl=en&ei=H8-JTu7LI8Hs0gHR7bTMDw&sa=X&oi=book_result&ct=result&resnum=1&ved=0CCcQ6AEwAA#v=onepage&q=astm%20aerosol%20size&f=false

Thanks for the response fledarmus.  The article you posted is approvimately what we do now.  However that test is expensive with long lead times.  I'm looking for a test more easily done, "quick and dirty" so to speak.  Just to monitor the device and if we see a problem or variation to go ahead with the more accurate test.  The microscope slide seems like it will work for us, however we are looking at particles generally between slightly under 1 micro and all less than 1.5 microns.  I"m not sure we can get the grid this small.  Can we?

Offline fledarmus

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Re: Particle Size
« Reply #3 on: October 03, 2011, 05:35:12 PM »
I'm way outside my field now!  :)  But there are some 2000 mesh grids which have 7.5 micron holes. Not sure exactly how you would set up the test, I would have to actually see one through a microscope to see how it would work.

http://www.proscitech.com.au/cataloguex/online.asp?page=g4

Offline Stepan

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Re: Particle Size
« Reply #4 on: October 03, 2011, 08:19:59 PM »
Particles between 0.5 micron and 10 micron, can be tested directly with Phase Contrast Microscope at magnification 1600. from 0.01 to 2 micron, you will need access to zeta potential instrument. or SEM or TEM. You can also buy or rent direct reading instrument which will read aerosol size distribution in air.

The biggest challenge is that the particle size changes during experiment. Particle size of aerosol is not the same as particle size of precipitated dust.

Work with meshes below 200 is very hard because of static charges on the particles.

Offline fledarmus

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Re: Particle Size
« Reply #5 on: October 04, 2011, 08:22:06 AM »
You can also buy or rent direct reading instrument which will read aerosol size distribution in air.

The biggest challenge is that the particle size changes during experiment. Particle size of aerosol is not the same as particle size of precipitated dust.

Work with meshes below 200 is very hard because of static charges on the particles.

Is this the same when the "particles" are actually droplets of liquid, or does it apply only to solid particles?

My thought was that the aerosol would be sprayed on the glass face of a slide with a mesh grid on the other side, then immediately placed under a microscope and the size of the droplets estimated based on the size of the grid. Thinking more about it though, depth of field is likely to be a serious issue - the grid and aerosol deposit wouldn't be in focus at the same time.

Offline Stepan

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Re: Particle Size
« Reply #6 on: October 04, 2011, 10:24:12 PM »
Direct reading instruments are based on lite scattering technology.  So they will work with any type of particles i.e liquid or solid. They are used to monitor clean rooms , medical facilities, and in Industrial hygiene. If you need to rent one, look for "air sampling", "air monitoring" "air quality" "particle counter" and so on. They are expensive $5000 - $10000. For this application you need multi-channel one with built in particle size classification.

What is your aerosol? What kind of liquid do you use? Are there any dissolved solids? I might have a more affordable solution.

Offline jdm2008

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Re: Particle Size
« Reply #7 on: October 20, 2011, 11:12:08 AM »
Direct reading instruments are based on lite scattering technology.  So they will work with any type of particles i.e liquid or solid. They are used to monitor clean rooms , medical facilities, and in Industrial hygiene. If you need to rent one, look for "air sampling", "air monitoring" "air quality" "particle counter" and so on. They are expensive $5000 - $10000. For this application you need multi-channel one with built in particle size classification.

What is your aerosol? What kind of liquid do you use? Are there any dissolved solids? I might have a more affordable solution.

The aerosol will be alcholol.   No dissolved solids.

Offline Stepan

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Re: Particle Size
« Reply #8 on: October 21, 2011, 12:39:37 AM »
You can use direct reading instrument.... Or try to capture the particles on carbon paper or glass slides coated with ink. The alcohol mist will leave stains size of which is proportional to the particle size.

By the way, be sure that you are using intrinsically safe equipment.   

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