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.
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.
Motevalli, V.; Ricciuti, C.
NIST GCR 92-613; 151 p. August 1992.
Sponsor:National Institute of Standards and Technology,
Available from: National Technical Information Service
Order number: PB92-238690
ceiling jets; ceilings; fire plumes; heat transfer;
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.