Dense gas plume rise and touchdown for Jack Rabbit II trial 8 chlorine field experiment

Abstract

The series of nine Jack Rabbit II (JR II) chlorine release field experiments in 2015 and 2016 involved releases of pressurized liquefied chlorine from tanks containing 5–20 tons of liquid. This paper concerns JR II Trial 8, where the release hole (15.2 cm diameter) was oriented upwards at the top of the tank. To our knowledge, this is the only full-scale vertically-directed release of pressurized liquefied chlorine that is available for detailed analysis. Our aim is to improve understanding of the characteristics of the dense jet trajectory (e.g., maximum plume rise, downwind distance where the dense plume first touches the ground, and maximum concentration at touchdown). The chlorine emission rate was measured by instruments in the tank, and the plume rise geometry was estimated from photographs, videos, and lidar scans taken from several angles. During the first 10 s of the release, the videos show that the dense jet rises up to about 40 m, then sinks towards the ground, touching down at a distance of about 60 m. The portion of the plume that sinks to the ground then spreads out about 30–40 m in all directions due to gravity slumping. Due to the decrease with time of the momentum jet mass release rate, the jet gradually becomes less dense and less powerful and the plume remains aloft after about 30–60 s. However, the dense cloud that touched down in the early phases moves downwind as a typical dense cloud. The observed dense jet plume rise and touchdown distance are shown to approximately agree within about a factor of two with integral model predictions by 1) the analytical dense gas plume formulas suggested for vertical jets in 1973 by Hoot, Meroney, and Peterka (HMP), 2) the analytical formula for buoyant (positive or negative) plume trajectory suggested by Briggs in 1969, and 3) the DRIFT dispersion software, which is an integral model. Also, HMP and DRIFT model predictions of concentration at touchdown agree with Trial 8 observations within a factor of about two. It is concluded that the dense jet plume models are able to simulate the Trial 8 plume trajectory and ground level maximum concentration within acceptable ranges (i.e., most of time, within a factor of two).