Dense gas removal from a valley by crosswinds

• Published in: Journal of hazardous materials 1990, Vol.24 (1), p.1-38
• Main Authors: Briggs, Gary A., Thompson, Roger S., Snyder, William H.
• Format: Article
• Language: English
• Subjects: Applied sciences; Atmospheric pollution; Exact sciences and technology; Pollutants physicochemistry study: properties, effects, reactions, transport and distribution; Pollution
• ISSN: 0304-3894; 1873-3336
• DOI: 10.1016/0304-3894(90)80001-K

Wind tunnel experiments were made to determine how rapidly dense gas trapped in a topographic depression could be removed by an entraining crosswind. The two-dimensional outflow volume flux, ν o, was assumed equal to the inflow rate during 92 steady-state experiments with CO 2 continuously supplied into the bottom of two-dimensional, V-shaped valleys. As predicted by theory, at large Reynolds numbers it was found that ν o α U s 3 / g′ i, where U s is the speed just above the dense gas pool and g′ i is gravity times the relative density difference. The width of the pool, w, does not affect ν o when the primary Froude number ⩽ 1, except at low Reynolds numbers; in this case the data suggest ν o α ( U s wK) 1/2 as an asymptote, where K is the molecular diffusivity. A universal relationship is suggested for ν o bridging these two asymptotes Transient experiments were conducted by filling a valley with dense gas, turning it off, then quickly removing a sliding cover; ν o was measured as a function of time with an array of samplers downwind. These experiments essentially confirmed predictions based on the steady-state results, even when SF 6 was substituted for CO 2. Insertion of a flat floor into the valley had only minor effects on ν o( t) until the pool level subsided almost to the floor level. Substantial changes in the removal process were observed for the few tests run at Froude numbers exceeding unity.