Dispersion Equation – Different Forms General Equation – Plume with Reflection for Stack Height H Ground Level Concentration – Stack at Height H Ground Level Center Line Concentration – Stack at Height H Ground Level Center Line – Ground Point Source Calculation of Effective Stack Height
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General Equation – Plume with Reflection for Stack Height H
Ground Level Concentration – Stack at Height H
Ground Level Center Line Concentration – Stack at Height H
Ground Level Center Line – Ground Point Source
Note that H = hs + h, where h is the stack rise.
Stack rise is dependant on stack characteristics,
Meteorology, and physico-chemical nature of effluent.
* Carson-Moses Equation:
* Holland Formula:
* Concawe Formula:
Accidental Release of Low volatile liquid from a tank on ground:
Accidental Release of Highly Volatile Liquid from Tank on Ground:
Accidental Release of Heavier-than-air gas from a tank on ground:
Concentration / g.m-3
Downwind distance / meters
Reattachment lines on sides and roof
Lateral edge and elevated vortex pair
Mean cavity reattachment line
Separation lines and
Horseshoe vortex system
Length L, Width W, Height H
Note: For long buildings, independent of L/H.
Maximum height of cavity:
1. Correction for stack-induced downwash:
2. Building induced downwash:
- stack induced downwash is first determined, then building effect is appended
Let b be the smaller of H or W
If hs’ > H + 1.5 b, hs” = hs’
If hs’ < H hs” = hs’ – 1.5 b
If H <hs’ hs” = 2hs’ – (H + 1.5 b)
3. Entrained plumes:
If hs” > b, plume remains aloft.
If hs” < b, plume trapped in cavity and treat as ground level
source with area b2.
4. Plume buoyancy effect:
If plume is air (mostly) and Tplume same as Tamb hs’ = hs”
5. Downwind concentration far from the stack:
Use usual formula from dispersion model.
More appropriate (takes bldg. dim. into account):
For trapped plumes consider source as ground level:
For other cases:
Note that both y and z can be obtained from Tables 4-1 and 4-2 of the textbook (Wark,
Warner and Davis: Air Pollution, 3rd edition)