For stable situations, the stability parameter, s, is calculated:
As a default approximation, for stability class E (or 5) dT/dz is taken as 0.020 K/m, and for class F (or 6), dT/dz is taken as 0.035 K/m.
Stable - 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 (DT)c is determined and solving for DT, as follows:
(DT)c=0.019582 Ts vs s1/2 (17)
If the difference between DT exceeds or equals (DT)c, plume rise is assumed to be buoyancy dominated, otherwise plume rise is assumed to be momentum dominated.
Stable - Buoyancy Rise
For situations where DT exceeds (DT)c as determined above, buoyancy is assumed to dominate. The distance xf is determined by
xf=2.0715 us s-1/2 (18)
The plume height, he, is determined by
he=hs+2.6 [Fb/(uss)]1/3 (19)
Stable - Momentum Rise
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. Then,
The equation for unstable-neutral momentum rise is also evaluated. The lower result of these two equations is used as the resulting plume height.
Air pollution map (XY-Plane) produced by continuous discharge in time (three stacks). The red colour represents high pollutant concentrations. Wind: W (270 degrees).
Air pollution map (XY-Plane) produced by continuous discharge in time. The fucshia lines represents a stacks in the XY-Plane. The red colour represents high pollutant concentrations. Winds: NE (45 dregrees) and 145 degrees.