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Dave.
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,
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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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