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Characterization of the Confined Ceiling Jet in the Presence of an Upper Layer in Transient and Steady-State Conditions. Final Report. August 1990-July 1991.


pdf icon Characterization of the Confined Ceiling Jet in the Presence of an Upper Layer in Transient and Steady-State Conditions. Final Report. August 1990-July 1991. (2895 K)
Motevalli, V.; Ricciuti, C.

NIST GCR 92-613; 151 p. August 1992.

Sponsor:

National Institute of Standards and Technology, Gaithersburg, MD

Available from:

National Technical Information Service
Order number: PB92-238690

Keywords:

ceiling jets; ceilings; fire plumes; heat transfer; temperature; walls

Abstract:

Although both confined and unconfined smooth ceiling jets have been previously studied, the data from small-scale experiments evaluated in this report provided a unique opportunity to characterize the transience of a ceiling jet in the presence of a developing upper layer. The development of an upper layer in an enclosure fire has notable effects on the ceiling jet. The presence of this hot gas layer increases the temperature in the ceiling jet and the heat transfer to the ceiling. Accurate prediction of the characteristics of the confined ceiling jet is important in calculating the response time of detection and suppression devices. This report examines data from a study of small-scale fire induced ceiling jet in a confined situation for a smooth horizontal ceiling. These results were obtained from experiments conducted at the National Institute of Standards and Technology, Center for Fire Research using 2.0 and 0.75 kW fires at r/H locations of 0.26 and 0.75. The data gathered from these experiments represents a collection of transient and steady-state temperature and velocity measurements of a confined ceiling jet and upper layer. The results from this data were compared to similar experimental data collected in a previous study for unconfined ceiling jet using the same apparatus. Comparison of the confined and unconfined ceiling jet data, quantification of the developing upper layer and analysis of heat transfer to the ceiling, are presented in this report. Despite the limited data, it is concluded that the unconfined ceiling jet correlations may only be valid at the very early time, prior to development of the upper layer and that steady-state unconfined correlations are certainly invalid for confined conditions. The velocity of the confined ceiling jet within the upper layer is 20-25 % less than the unconfined case affecting the heat transfer coefficient. The heat transfer analysis showed that values of 4-5 W/m2 deg C can be expected.