Expe r iments have been conducted to determine cr I tical Froude numbers associated with required inflow of air to a fire space through wall and ceil ing apertures to prevent escape of smoke.The exper iments were conducted mostly on reduced, model scale, with verification in a 2.4 m high test room.Critical Froude numbers, as formulated, were insensitive to aperture geometry.Those for wall apertures varied slowly and predictably with the vertical temperature distribution in the room, consistent with a discharge coefficient of 0.64 for the inflow. Those for ceiling apertures exhibited a dependence on an aperture Grashof number, with both a highGrashof number asymptote and an apparent low-Grashof number asymptote. While discharge coefficients for wall apertures can be considered constant near 0.64 for aperture Froude numbers larger than cr itical, the discharge coefficient for ceiling apertures increased from 0.19 near the critical Froude number, toward the familiar isothermal value for sharp-edged orifices of 0.61 near a Froude number seven times larger than the critical.
A series of fire tests was conducted under a smooth ceiling to investigate the ceiling gas flow as affected by ceiling slope, convective heat release rate of the fire and clearance between the fuel top surface and the ceiling.Besides a horizontal ceiling reference, three ceiling slopes were investigated: 10°, 20°and 30°. Pool fires were used as fire sources. Two pool diameters, two different fuels (heptane and methanol) and three ceiling clearances were used.In each test, measurements were made of ceiling gas temperatures, ceiling gas velocities, and fuel mass loss. Empirical correlations for the near-maximum gas velocity and excess temperature of the ceiling flow along the steepest run were established in terms of ceiling slope, radius from the point of intersection of the ceiling with the pool centerline, and characteristics of the undeflected plume at the ceiling level. The ceiling slope had a more pronounced effect on velocity variation along the steepest run than on temperature variation.In the upward direction, the rate of velocity decr-ease with radius was reduced significantly as the ceiling slope increased.In the downward direction, at a certain distance from the pool cent.e r-I ine, the flow separated from the ce il ing and turned upward. The larger the ce i I ing slope, the sooner' the turning occurred. Fur thermor-e , the rate at which gas temperature approached ambient in the downward direction increased wi th ceil ing slope, while the temperature decrease in the upward direction was not much affected by change of ceiling slope.
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