Unstable or Neutral - Crossover Between Momentum and Buoyancy
For cases with stack gas temperature greater than or equal to ambient temperature, it must be determined whether the plume rise is dominated by momentum or buoyancy. The crossover temperature difference, (DT)c, is determined as follows:
for Fb < 55,
(DT)c=0.0297 Ts(vs/ds2)1/3 (9)
and for Fb >= 55,
(DT)c=0.00575 Ts(vs2/ds)1/3 (10)
If DT, exceeds or equals (DT)c, plume rise is assumed to be buoyancy dominated, otherwise plume rise is assumed to be momentum dominated.
Unstable or Neutral - Buoyancy Rise
For situations where DT exceeds (DT)c as determined above, buoyancy is assumed to dominate. The distance to final rise, xf, is assumed to be 3.5x*, where x* is the distance at which atmospheric turbulence begins to dominate entrainment. The value of xf is calculated as follows:
for Fb < 55:
and for Fb >= 55:
The final effective plume height, he (m), is determined as
for Fb < 55:
he=hs+(21.425 Fb3/4/us) (13)
and for Fb = 55:
he=hs+(38.71 Fb3/5/us) (14)
Unstable or Neutral - Momentum Rise
For situations where the stack gas temperature is less than or equal to the ambient air temperature, the assumption is made that the plume rise is dominated by momentum. If DT is less than (DT)c, the assumption is also made that the plume rise is dominated by momentum. The plume height is calculated as:
Briggs suggests that this equation is most applicable when vs/us is greater than 4.
Air pollution map (XY-Plane) produced by continuous discharge in time (three stacks). The red colour represents high pollutant concentrations. Wind: SW (225 degrees).
Pollution map (XY-Plane) produced by continuous discharge in a road region. The fucshia squares represent the road line (position of the different point sources) in a XY-Plane. The red colour represents high pollutant concentrations.