Jerry and Radsafers,
The classic Gaussian Plume dispersion
equation is for a tall stack where the emission point is effectively a point
source. If you have a BIG dilution fan instead of a smallish stack opening, you
have the equivalent of many Gaussian plumes starting from different places in a
horizontal plane. So, in effect, you have added spatial dispersion at the
source in addition to dispersion you get from the usual atmospheric dilution.
Best regards,
Wes
-----Original Message-----
From:
owner-radsafe@list.vanderbilt.edu [mailto:owner-radsafe@list.vanderbilt.edu] On Behalf Of Jerry Cohen
Sent: Tuesday, April 29, 2003
11:46 AM
To: Dave Brown;
radsafe@list.vanderbilt.edu
Subject: Re: atmospheric
dispersion/dilution.......question
You are correct in assuming the
"dilution fan" will have little,if any, effect on distant downwind
predicted dose. It might however reduce "close in" doses and
therefore cause a lower predicted maximum offsite dose.
----- Original Message -----
Sent: Tuesday, April 29,
2003 4:23 AM
Subject: atmospheric
dispersion/dilution.......question
I have a question related to an observation of some calculations I've
done recently regarding atmospheric diffusion of effluent releases.
Consider a case where there is a fixed release rate, Ci/sec, at a fixed stack
flow rate, cfm. There is also the option of a large dilution fan that
uses outside air to dilute the effluent concentration going out the stack by
say a factor of 500. In this case, although the effluent concentration
has significantly decreased, the effective Q or Ci/sec remains the same.
My observation is that the only thing this dilution fan accomplishes in the
calculations is to increase the effective stack height thus changing the
vertical dispersion coefficient and the effective wind speed. This does not
have a proportionally significant affect on the resulting downwind
concentrations. It would seem that this dilution fan should have more impact on
the downwind dilution....but it doesn't. Anyone have a good
explanation/justification for this...? My initial thoughts are that in the
scope of atmospheric dilution , the dilution fan is small in comparison. This
is just an observation though, I'm looking for a more technical explanation
Regards,
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
Dave Brown, CHP
National Institute of Standards and Technology
100 Bureau Drive, Stop 3543
Bldg 235 Rm B104
Gaithersburg, MD 20899-3543
301-975-5810 - office
301-921-9847 - fax
david.brown@nist.gov
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