The Integral Dense-Gas Dispersion Model (IDDM) and Comparisons with the Jack Rabbit II Experiments

The Jack Rabbit (JR) II experiments on large-scale chlorine releases were conducted at the Dugway Proving Ground, Utah to improve our knowledge of their atmospheric transport and dispersion. This paper presents a new integral model IDDM for the transport and growth of the dense-gas cloud and a comparisons with observations from the JR II experiment. The model includes growth due to source momentum along with density-driven gravitational spreading and puff-top entrainment. The modeled puff radius initially varies with time to the 1/2 power (momentum driven), later with time to the 3/4 power (buoyancy driven), and even later with time to the 1/2 power; these regimes are supported by laboratory experiments. In addition, the model includes a radial pressure gradient term in the momentum equation, which provides for a seamless transition of puff properties from the momentum phase to the buoyancy regime. Furthermore, both horizontally circular and non-circular clouds are considered and for one trial in a mock urban array, an internal boundary layer (IBL) model is adopted to account for the altered wind profile and enhanced turbulence.

Comparison of the IDDM results on maximum surface concentrations with observations shows good agreement and demonstrates the appropriate concentration decrease with distance.