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REMOVAL OF SLIGHTLY HEAVY GASES FROM A VALLEY BY CROSSWINDS
Citation:
Castro, I., A. Kumar, W. Snyder, AND S. Arya. REMOVAL OF SLIGHTLY HEAVY GASES FROM A VALLEY BY CROSSWINDS. U.S. Environmental Protection Agency, Washington, D.C., EPA/600/J-94/102 (NTIS PB94146446).
Description:
Wind-tunnel experiments made to determine how rapidly dense gas is removed from a topographical depression by a crosswind are reported. he density and flow rate of the gas (input at the bottom of a V-shaped valley in otherwise homogeneous, flat terrain)were together sufficiently low to prevent pooling of the gas on the valley floor. n terms of the earlier and complementary work of Briggs et al [1], who considered only pooling cases, the present work concentrates on cases for which the relevant Richardson numbers (Rio = gHp/(pU2o) are relatively low. imple theory is described, based on assumptions about the way in which the (slightly) heavy gas is removed by turbulent entrainment from the separated flow in the valley. or the steady-state case, the simple theoretical result Co/C3 = Vo(1 + aRi ino) is shown to fit the data quite well, where Co/C is the ratio ot the average valley concentration to the source-gas concentration, V is the dimensionless source flow rate, and , a, and n are constants. or the transient experiments, in which the source was suddenly removed and the ecay of valley concentration was measured, the data are shown to be reasonably consist6nt with the theory for both neutral and heavy-gas releases: -In C' + aRi ino(1 - C'n)/n = t'/T, where C, = C(t)/C. and -r is a decay time constant. lthough Reynolds number effects are shown to be significant in certain cases, the results provide a framework for estimating how long a heavy gas spill will take to disperse from depressions which are sufficiently steep-sided to embody regions f separation in windy onditions aloft.