(302e) Influence of Immersed Objects On Liquid Pool Boil-Over

Accidental scenarios involving hydrocarbon pool fires usually involve interaction with objects in the path of the liquid. The interaction depends on object type (steel, concrete), geometry as well as height of the liquid surface. For example an object may be completely immersed or above the liquid surface. In the later case there is also interaction of the flame with the object. In this study, we investigate the influence of nonflammable cylindrical objects in a hydrocarbon (hexane) pool fire. A 10 cm diameter steel pan filled with hexane is used as the base case. As a first part of the investigation, one single cylindrical rod of varying heights with respect to the liquid surface is placed in the pool and the influence on burning rate, flame height and radiative heat flux is explored. Two different materials (glass and aluminum) are chosen because of their low and high thermal diffusivities (5.9×10^-7 m²/s and 731 ×10^-7 m²/s) but similar densities (2200 kg/m³ and 2707 kg/m³). Results show the regression rate is a function of two competing effects. The presence of an obstacle reduces the overall burn area thereby decreasing the mass burning rate of the pool fire. At the same time the flame heats the obstacle and depending on its thermal properties, heat is dissipated into the fuel surface improving the vaporization rate. Occasionally, this causes a recirculating current within the pool eventually resulting in boil-over phenomena.

The second part of study investigates the influence of change in surface area to volume ratio of the obstacle in a pool fire. Several smaller diameter aluminum cylindrical rods are used instead of a single rod (same volume but various total surface area). Cylindrical rods of varying heights with respect to the liquid surface are placed in the pool and the influence on burning rate, flame height and heat fluxes is also explored.

A simple one-dimensional empirical heat transfer model is developed to predict the mass loss rates for various pool sizes, fuel and obstacle sizes. Implications to safety considerations involving cylindrical obstacles in pool fires are explained.