- Author
-
Koslowski, C. C.
- Title
- Effects of Beams and Ceiling Obstructions on Steady State Ceiling Jet Flow.
- Coporate
- Worcester Polytechnic Inst., MA
- Report
-
Thesis,
December 1991,
202 p.
- Keywords
-
beams
|
ceilings
|
ceiling jets
|
steady state
|
temperature
|
heat detectors
|
cross correlation
- Abstract
- Ensuring heat detector actuation before a fire reaches a maximum allowable fire size is important for proper design of heat detection systems. Ceiling obstructions, such as beams, delay heat detector response by redirecting ceiling jet flow. Without a detailed understanding of the affect of ceiling obstructions on the ceiling jet, prediction of heat detector response is not possible. The lack of data for the obstructed ceiling jet velocity and temperature, limits heat detector response calculations to smooth ceiling cases. This report examines the steady state, turbulent ceiling jet under a ceiling with rectangular obstructions such as beams. Correlations have been developed for predicting ceiling jet velocity and temperature for a beamed ceiling, in the primary and secondary bays, based on smooth ceiling correlations. To facilitate heat detector calculations, both the temperature and velocity of the ceiling jet under a beamed ceiling have been expressed as a function of ceiling configuration. In this study, measurements of the ceiling jet velocity and temperature were obtained at three locations relative to the fire source. Assuming a fire occurs centered between two ceiling obstructions, the ceiling jet flow is examined within the primary bay, under the obstruction, and within the secondary channel. The latter two cases have been studied along a line of action from the fire source perpendicular to the beam span. The ceiling jet flow in the primary bay was studied as a function of distance from the fire source. Experimental data has been collected from 28 tests which were conducted at the Fire Science Laboratory of Worcester Polytechnic Institute. Data for both the temperature and velocity of the obstructed ceiling jet produced by a steady fire source has been collected at the three described positions. The ceiling jet velocity was measured using the Cross Correlation Velocimetry technique. The current study focuses on the steady state ceiling jet, however, transient data is available for further analysis. All of the tests were conducted with no framing girder present. Within the primary bay, the ceiling jet flow is thought to be subcritical (Froude number less than one) with transition to critical flow as described by Delichatsios. This study confirms the limited entrainment rate in the primary channel. The temperature reduction of the ceiling jet occurs as a result of heat transfer to the ceiling. The heat transfer coefficient and ceiling configuration factor have been determined for the primary channel so that the ceiling jet temperature may be determined as a function of fire size, ceiling configuration, and distance from the fire source. For the remaining locations, under the beam and in the secondary channel, the temperature and velocity of the ceiling jet are expressed in nondimensional form. This nondimensional form relates the obstructed ceiling jet temperature and velocity to the smooth unconfined ceiling conditions. The results are presented as a function of the ratio of beam depth to ceiling height. Therefore, both the temperature and velocity of the ceiling jet may be predicted as a function of ceiling configuration.