John P. Farley

The development and mitigation of backdraft: a real-scale shipboard study

This paper presents the results of a real-scale experimental test series to study the development and mitigation of backdrafts. Experiments consisted of creating backdrafts onboard a US Navy test ship, ex-USS SHADWELL. This study has shown that the key parameter for backdraft development is the fuel mass fraction. The results show that the critical fuel mass fraction, Yf, required for the development of diesel fuel backdraft is 0.16 for fully vitiated conditions. The effects of varying adjacent room boundaries and ventilation conditions are discussed. In general, the intensity of a backdraft is more dependent on the adjacent boundaries than on the ventilation conditions. The injection of water spray into the fire compartment was shown to be an effective mitigating tactic that was able to completely suppress backdrafts primarily by means of diluting the atmosphere and reducing the fuel mass fraction, rather than by a thermal mechanism of cooling.

Mitigation of TNT and Destex explosion effects using water mist

The effects water mist has on the overpressures produced by the detonation of 50 lb equivalent of high explosives (HE) TNT and Destex in a chamber is reported. The overpressures for each charge density were measured with and without mist preemptively sprayed into the space. A droplet analyzer was placed in the chamber prior to the detonation experiments to characterize the water mist used to mitigate the explosion overpressures. The impulse, initial blast wave, and quasi-static overpressure measured in the blast mitigation experiments were reduced by as much as 40%, 36%, 35% for TNT and 43%, 25%, 33% for Destex when water mist was sprayed 60s prior to detonation at a concentration of 70 g/m(3) and droplet Sauter Mean Diameter (SMD) 54 microm. These results suggest that current water mist technology is a potentially promising concept for the mitigation of overpressure effects produced from the detonation of high explosives.

Suppression Dynamics of a Co-flow Diffusion Flame with High Expansion Aqueous Foam

A time-dependent, moving boundary, multiphase Navier—Stokes model is developed to study the effects of aqueous foam with high air-to-water volume ratio (expansion ratio, Ex) on a jet diffusion flame. The flame is formed by combusting a steady flow of propane gas. Both the shape and velocity of the foam surface are affected by evaporation and injection rates, and are obtained by volume of fluid method. The evaporation at the advancing foam front releases water vapor as well as a significant amount of air into the flame. At low foam injection rates, simulations show that the flame spreads along the foam surface and is not extinguished. This is because the injection rate is comparable to the evaporation rate, which causes cooling but prevents the foam from advancing into the flame. However, at high foam injection rates, the simulations show that the flame lifts from the burner lip and the flame is reestablished above the rising foam surface due to the continued supply of the propane gas. Thus, the foam extinguishes the flame locally in its path by increased smothering as it rises towards the top of the burner. Both the smothering and evaporation effects are found to be important.

A Novel Low-Pressure Atomization Method for Burning Emulsified Crude Oil

ABSTRACT A novel, air-assisted atomizer designed for low-pressures and high viscosity fluids was used to produce and burn a spray of emulsified crude oil with different fractions of seawater. For a...