Re: atmospheric dispersion/dilution.......question

[JOHN.RICH@sargentlundy.com]

Dave,



If i remember correctly (an old man's memory), the atmospheric disperison

is due primarily to the meandering of the plume plus the vertical and

horizontal gaussian dispersion of the plume.  Both of these are based on

the statistics of the local meteorology.  The effect is that the plume

concentration is averaged over the total volume where the plume could be

found during some period of time (e.g., 2 hrs).  Since this volume is much

more than the dilution volume coming out the stack, the effect of stack

dilution can be essentially ignored.  The old meterology and atomic energy

handbook has some good illustrations and a good explanation.  Hope this

helps  - -- jmr







                                                                                                                                            

                      Dave Brown                                                                                                            

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                      owner-radsafe@list.van        Subject:  atmospheric dispersion/dilution.......question                                

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                      04/29/03 06:23 AM                                                                                                     

                      Please respond to Dave                                                                                                

                      Brown                                                                                                                 

                                                                                                                                            

                                                                                                                                            









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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