Effect of bubble generation on hot zone formation in tank fires

Abstract

Boilover is a phenomenon that both stakeholders and fire-fighters in the petrochemical industry try to avoid. This phenomenon results in an explosion of liquid hydrocarbon materials (e.g., crude oil) due to prolonged oil tank fires. The elevated temperature provides energy to vaporize the water sub-layer, which commonly resides at bottom of storage tanks, leading to tremendous fire enlargement as fuel tends to spill over around the tank. Boilover follows the formation of an isothermal layer called ‘hot zone’, and is typically accompanied by continuing bubble appearance in the hot zone. Previous studies have suggested that bubble generation could be a driving force for boilover, as it accelerates heat mixing. However, the effect of bubble generation on the mechanism of hot zone formation has not yet been systematically studied. This work investigates the effect of bubble formation on hot zone formation by installing a metal mesh in a burning fuel container. The size of the mesh grid and the position of the mesh are varied to generate bubbles with different volumes from different depths from the fuel surface. Experimental results demonstrate that the metal mesh definitely increases the volume of bubbles, and significantly reduces the time to form a hot zone. The mesh with small grids generates more bubbles than that with large grids. Additionally, bubbles start to generate earlier when the mesh is fixed nearer the fuel surface. Experimental results provide direct evidence of the bubble effect on hot zone formation.