EXPERIMENTAL AND NUMERICAL INVESTIGATION OF TRANSIENT SOOT BUILDUP ON A CYLINDRICAL CONTAINER IMMERSED IN A JET FUEL POOL FIRE

Abstract

Soot buildup and its effects on heat transfer have been investigated as part of an effort to understand the thermal response of containers of high-energy materials immersed in fires. Soot deposition rates were measured for cooled and uncooled cylindrical containers immersed in a jet fuel pool fire. The soot buildup was measured at different time intervals with a wet film gage with an uncertainty of 20%. These rates were compared with those calculated by solving the boundary layer equations along the cylinder surface including the thermophoretic transport of soot particles. Thermophoresis was the dominant soot transport mechanism controlling the deposition of soot on the container wall and gave deposition rates in good agreement with the measured values. The soot buildup was found to have an important insulating effect on the heat transfer to the container. A soot deposit thickness of 1.2 mm resulted in as much as a 35% reduction in heat flux.

Keywords:

• deposition
• pool fires
• soot buildup
• thermal conductivity
• thermophoresis

Acknowledgments

This work was sponsored by the Center for the Simulation of Accidental Fires and Explosions at the University of Utah, which was funded by the U.S. Department of Energy under Contract No. LLL B341493, with matching funds provided by the University of Utah Research Fund.

Notes

¹The thermocouples placed at the inlet and outlet sections of the calorimeter, as well as the top of the calorimeter, were heavily insulated and therefore it is assumed that the area exposed to the fire environment is only the bottom half of the pipe.

²Soot absorption coefficient is usually measured at a wavelength in the visible region of the spectrum. The effective absorption coefficient must account for the dominant contributions in the infrared region. The wavelength λ_0.5 below which half of the blackbody radiation lies is given by λ_0.5*T = 4107nmK.ForT = 1200K, λ_0.5 ≅ 3400nm. If the absorption coefficient was measured at 633 nm, then the effective absorption coefficient can be calculated as