Re: Isokinetic Flow Standards

[FRAMEP@ORAU.GOV]

It seems that all the key references have been identified that describe
requirements for, and the method of achieving, isokinetic sampling. 

For interest, let me recommend one more easy to obtain reference:
"Single point sampling; evaluation of mixing and probe performance in a
nuclear stack' by Rodgers et al.,  Health Physics 70(1):25-35; 1996.

The idea is that isokinetic sampling might result in a representative sample
entering the probe, but it does not necessarily result in a representative
sample on the filter which is where you want it. In fact, isokinetic
sampling can result in an under representation of large particulates on
the filter because of the losses  in the nozzle and/or the sampling line
(something subisokinetic sampling would help alleviate).

Among other things, the cited paper describes the use of an anisokinetic
shrouded probe that exhibits markedly superior performance to the
standard ANSI/EPA isokinetic probe design. This difference in
performance is evaluated via the "transmission ratio".

The transmission ratio is the ratio of the particulate concentration at the
probe exit plane to the concentration in the free stream (i.e. the probe
inlet plane).  For 10 um particles, the ratio (ideally 1) for the anisokinetic
probe was 1.07 while that for the standard probe was 0.2 

There is a wealth of additional information in this paper. 

Best wishes

Paul Frame
Professional Training Programs
ORISE
framep@orau.gov