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1.1.4.1 Stack‑tip Downwash.

     In order to consider stack‑tip downwash, modification of the physical stack height is performed following Briggs (1974, p. 4).  The modified physical stack height h_s´ is found from:

where h_s is physical stack height (m), v_s is stack gas exit velocity (m/s), and d_s is inside stack top diameter (m).  This h_s´ is used throughout the remainder of the plume height computation.  If stack tip downwash is not considered, h_s´ = h_s in the following equations.

 

1.1.4.2 Buoyancy and Momentum Fluxes.

     For most plume rise situations, the value of the Briggs buoyancy flux parameter, F_b (m⁴/s³), is needed.  The following equation is equivalent to Equation (12), (Briggs, 1975, p. 63):

where ΔT = T_s - T_a, T_s is stack gas temperature (K), and T_a is ambient air temperature (K).

     For determining plume rise due to the momentum of the plume, the momentum flux parameter, F_m (m⁴/s²), is calculated based on the following formula:

 

 

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