Re: Membrane filter collection efficiency

["Otto G. Raabe" <ograabe@UCDAVIS.EDU>]

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March 20, 2001

Davis, CA



Dear Tim:



Although the exact collection efficiency depends on particle size and on

the filter type and face velocity (face velocity depends on flow rate and

cross-sectional area of the filter), in general you can expect that the

collection efficiencies of membrane-type filters for respirable particles

(~.3 micron) will be greater than 99% even for filters with a "pore size"

rating of 5 microns. This is because these membrane filters are not sieves

and efficiently collect small particles by diffusional deposition in

addition to inertial deposition. 



The membrane filter vendor or manufacturer should be able to provide you

with efficiency curves as a function of membrane type and face velocity for

0.3 micrometer particles.



Otto



**********************************************

Prof. Otto G. Raabe, Ph.D., CHP

Institute of Toxicology & Environmental Health

(Street Address: Bldg. 3792, Old Davis Road) 

University of California, Davis, CA 95616

E-Mail: ograabe@ucdavis.edu

Phone: (530) 752-7754   FAX: (530) 758-6140

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