NIST Time|NIST Home|About NIST|Contact NIST

HomeAll Years:AuthorKeywordTitle2005-2010:AuthorKeywordTitle

Fire-Plume-Generated Ceiling Jet Characteristics and Convective Heat Transfer to Ceiling and Wall Surfaces in a Two-Layer Zone-Type Fire Environment: Uniform Temperature Ceiling and Walls.


pdf icon Fire-Plume-Generated Ceiling Jet Characteristics and Convective Heat Transfer to Ceiling and Wall Surfaces in a Two-Layer Zone-Type Fire Environment: Uniform Temperature Ceiling and Walls. (1285 K)
Cooper, L. Y.

NISTIR 4705; 57 p. November 1991.

Fire Science and Technology, Vol. 13, No. 1/2, 1-17, 1993.

Sponsor:

Nuclear Regulatory Commission, Washington, DC

Available from:

National Technical Information Service
Order number: PB92-123074

Keywords:

ceiling jets; building fires; compartment fires; computer models; fire models; heat transfer; mathematical models; zone models

Abstract:

It has been determined by Sandia National Laboratories and the U. S. Nuclear Regulatory Commission that the use of deterministic, multi-room, zone-type fire modeling technology could enhance the reliability of their recent reactor safety risk studies. These studies are confined to the relatively early detection times of fire development when fire-driven ceiling jets and gas-to-ceiling convective heat transfer are expected to play a particularly important role in room-to-room smoke spread and in the response of near-ceiling mounted detection hardware. A parameter of concern in these risk analyses is the location of the fire within the space of fire origin. One goal of the analyses is to determine the significance to risk of this fire-position parameter. This work presents a model to predict the instantaneous rate of convective heat transfer from fire plume gases to the overhead ceiling surface in a room of fire origin. The room is assumed to be a rectangular parallelopiped and, at times of interest, ceiling temperatures are simulated as being uniform. Also presented is an estimate of the convective heat transfer, due to ceiling-jet-driven wall flows, to both the upper and lower portions of the walls. The effect on the heat transfer of the location of the fire within the room is taken into account. Finally presented is a model of the velocity and temperature distributions in the ceiling jet. The model equations were used to develop an algorithm and associated modular computer subroutine to carry out the indicated heat transfer calculations. The subroutine is written in FORTRAN 77 and called CEILHT. The algorithm and subroutine are suitable for use in two-layer zone-type compartment fire model computer codes. The subroutine was tested for a variety of fire environments involving a 10(7)W fire in a 8m x 8m x 4m high enclosure. While the calculated results were plausible, it is important to point out that CEILHT simulations have not been experimentally validated.