Abstract
Evaporating liquid cascades resulting from gasoline and liquefied natural gas tanks overfilling or rupture of elevated pipes create a source of flammable vapor cloud. Such phenomena were responsible for the formation of the large fuel vapor cloud, the ignition of which resulted in the large scale explosion, in Buncefield [Buncefield Major Incident Investigation Board, Explosion Mechanism Advisory Group Report, 2007] on December 11, 2005 at the Hertfordshire Oil Storage Terminal, an oil storage facility located by Hemel Hempstead in Hertfordshire, England. Despite its significance, there lacks adequate models treating the underlying physics of this phenomenon. The present study numerically analyses fuel cascades which are considered as a droplet-laden system. Consideration is given to vapor production inside the cascade due to droplets evaporation and breakup. The solver used here is a modification of the sprayFoam solver which is present in the open source computational fluid dynamics (CFD) toolbox OpenFOAM (R) [OpenFOAM 2.3.0, Available at http://www.openfoam.com]. The fuel droplets evaporate during their motion and create a cloud of flammable vapor. In order to capture the characteristics of the hazardous phenomena, the CFD model needs to address the underlying physics with adequate submodels. In the present study, the multiphase flow is simulated with a combined Eulerian-Lagrangian approach. The governing equations of the gas phase represent the conservation equations of mass, momentum, and energy including the source terms arising from the interaction with the droplets. The Reynolds Averaged Navier-Stokes simulation approach was used for its computational efficiency. The Large-Eddy Simulation would be more robust in handling the interaction of the droplets with the flow but it would require more computational resource. The particulate phase is simulated through a Lagrangian deterministic or stochastic tracking models to provide particle trajectories and particle concentration. Particular emphasis is given to the effect of impingement of droplets to account for the effect of splashing in the impact region. The study involves developing robust and accurate modeling approaches for the instabilities and aerodynamic breakup in the cascade which contribute to the formation of the cloud, air entrainment, and fuel impingement on deflector plates. Suitable submodels have been implemented in OpenFOAM (R) to facilitate the study. The predictions are compared with the experimental measurements and CFD predictions previously conducted by Atkinson and Coldrick [Research Report 908, 2012] from the Health and Safety Laboratory, an agency of the Health and Safety Executive (HSE). The present predictions are found to better capture the interaction between the droplets and the gas phase. Improved agreement with the experimental measurements in the gasoline fuel cascades has also been achieved. (C) 2015 American Institute of Chemical Engineers