Ceiling Jet Research Articles

A computer model for estimating the response of sprinkler links to compartment fires with draft curtains and fusible link-actuated ceiling vents

A computer program, LAVENT, is now available which computes the heating of fusible links due to the presence of a ceiling jet imbedded in an upper layer. An important new feature in this program is that the two-dimensional structure of the ceiling jet is taken into account such that the location of the link beneath the ceiling plays a role in the response of the link. The links can be used to activate ceiling vents such that the effect of venting the upper layer on the ceiling jet may be studied. Additional applications would include the study of upper layer containment through the use of a combination of draft curtains and ceiling vents. The geometry modeled by the program is that of a large compartment enclosed by a combination of walls and draft curtains.

On the Reverse Flow Ceiling Jet in Pool Fire-Ventilation Crossflow Interactions in a Simulated Aircraft Cabin Interior

The behavior of the reverse flow ceiling jet against the ventilation flow from 0.58 to 0.87 m/s was investigated in a 1/3 scale model of a wide body aircraft interior. For all tests, strong reverse flow ceiling jets of hot gases were detected well upstream of the fire. The penetration lengths of the reverse flow ceiling jet for the tests agree fairly well with the relation, lr/H = 0.6 [F−5] where F is the fire-crossflow parameter, F = 2gHQ˙/ρcTsAua3. Both the thicknesses of the reverse flow ceiling jet and the smoke layer increased with the fire-crossflow parameter. The thickness of the smoke layer where the smoke flows along the main flow below the reverse flow ceiling jet was almost twice that of the reverse flow ceiling jet. Detailed spatial and time-varying temperatures of the gas in the test section were measured and velocity profiles were also measured using a temperature-compensated hot film.

Characterizing The Unconfined Ceiling Jet Under Steady-state Conditions: A Reassessment

Detailed velocity and temperature measurements using cross-correlation velocimetry were obtained for unconfined ceiling jets under ceiling transient and steady-state conditions. Small fires of 0.5 to 2.0 kW were produced with a premixed methane-air burner. These measurements represent one of the most detailed studies of unconfined ceiling jets to date and seem to be in general agreement with large-scale data. Empirical correlations for the steady-state ceiling jet temperature and velocity profi1es are described herein. The correlations compare we1 1 with, and have improved, results from previous works. The maximum temperature may not be scaled as a function of fire-to-ceiling heights for large radial distances. Furthermore, the Gaussian and boundary 1ayer thermal and momentum thicknesses of the ceiling jet are not equal, contrary to the assumptions made in other works.

The Ceiling Jet In Fires

The steady fire-produced ceiling jet in an open ended corridor is examined with a simplified "top hat" theory. At a corridor open end, the hot fluid accelerates upward producing a Richardson Number equal to 1 for tranquil flow as the flow control. Friction satisfies this condition by upstream waves with a hydraulic jump, if necessary. Entrainment has qualitatively the same result, but with quantitative differences. Heat transfer at low friction causes the Richardson Number and depth to rise. The manner of adjustment to Ri = 1 at an open end needs further study.

Solid-wall Boundary Effect on a Building Fire Field Model

Abstract The solid-wall boundary effect on a building fire field model is discussed. In this model, the k - e model is used to predict the fire-induced flow (in primitive variables) and temperature field. The low Reynolds number model is proposed to substitute the traditional wall-function approach for describing solid-wall boundary effects. This is better because both the velocity and temperature distribution can be predicted within the buffer layer. Numerical experiments are performed on a physical model studying compartmental fire and an experiment on unconfined ceiling jet, both performed at the National Bureau of standards, U.S.A. For these simulations, better results arc achieved using this modified solid-wall boundary approach.

Transient ceiling jet development in large scale fires

This study considers a buoyant plume of hot gas which impinges on an unconfined ceiling and spreads radially outward to form a boundary layer growth. The boundary layer thickness and radial velocity for the ceiling jet are obtained by a numerical solution of the derived governing equations. The results are presented for steady state and transient cases for both laminar and turbulent flows. For steady state and transient conditions, the boundary layer thickness increases due to the wall shear and radiation effects, while the radial velocity decreases for the same effects for both laminar and turbulent flows. The buoyancy effect had negligible influence on the boundary layer thickness and radial velocity. A transient “wave-like” behavior is observed for laminar and turbulent flows for a wide range of Reynolds and Rayleigh numbers.

A Numerical Study Of Ceiling Jets Based On "t" Pattern Flames

This paper describes the nnmerical analysis of ceiling jets relevant to the T pattern flame which accelerates the fire growth due to a flame burning upward along a corner, using a three-dimensional field model. It vas found in calculations that ceiling jets split into two directions along ceiling-wall intersections when a heat source is located at a marked distance from a corner. Isotherms, velocity vectors and isobaric contours of the split ceiling jet showed the configulation similar to the T pattern in the experiments of Williamson et al. The T-shaped flow was investigated using open and closed type fire rooms. Further , it was found that the distance between the corner and heat source plays an important role in forming the T pattern and that the temperatures and pressures at the ceiling corner oscillate regularly.

Thermal Response of Unconfined Ceilings Above Growing Fires and the Importance of Convective Heat Transfer

A procedure is developed to calculate the thermal response of unconfined nonburning ceilings above growing fires. The procedure uses an algorithm for conduction into the ceiling material. It takes account of heat transfer due to radiation from the combustion zone to the ceiling surface, and due to reradiation from the ceiling to the floor and furnishings. Finally, the procedure uses a previously developed algorithm for convective heat transfer to the ceiling from the fire-plume-driven ceiling jet. The procedure is used to predict radial-dependent surface temperature histories of typical ceiling materials under a variety of different realistic levels of hazardous fire energy generation rates and combustion zone-ceiling separation distances. The results give an indication of the influence of convective heat transfer on peak ceiling thermal response, losses from fire plume gases, and radial variations and peak values of ceiling-to-floor irradiation during enclosure fires.

Ceiling Jet-Driven Wall Flows in Compartment Fires

Abstract Analytic estimates are developed for depth of penetration and lateral entrainment of negatively buoyant, ceiling jet-driven wall flows during early times of compartment fire scenarios. When walls are not too far from the fire source of the order of the fire-to-ceiling distance, it is found that the penetration of these downward wall flows is a large fraction of the fire-to-ceiling distance, and that this Traction is relatively independent of the details of fire size and fire-to-wall spacing. Also, net rate of entrainment into the wall flow as it is buoyed back upward to the ceiling elevation is found to be several times larger than the Row rate of the driving ceiling jet flow immediately upstream of wall impingement. Data from five studies reported in the literature are reviewed relative to the analytic results obtained. One of these involved a field model simulation of the flow generated by a buoyant source in an enclosure. Two experimental laboratory studies involved fires in enclosures with ch...

Calculating the performance of sprinkler pipe exposed to fire conditions

A computer model for predicting the onset of yielding in pressurized plastic pipe exposed to fire conditions has been developed. The model couples the aspects of solid mechanics and heat transfer to simulate the pipe performance. The von Mises yield criterion from solid mechanics is applied to predict yielding resulting from the plane stress induced in the pipe wall from the internal water pressure. The heat transfer analysis is performed via a finite difference approach to estimate the temperature profile in the pipe wall resulting from exposure to a heated ceiling jet. Results are reported of estimates for the time to yielding for 1 and 1 1/4 in. (25 and 32 mm) SDR-11 polybutylene pipe at three selected locations relative to the fire considering a range of internal pressures and water flow rates inside the pipe.

The flow of fire gases under a beamed ceiling

A simple model is presented of the ceiling flow induced by fire centrally located at the floor between two long unobstructed ceiling beams of such depth that no fire gases are able to leak to adjacent beam channels. According to the model, the radial ceiling jet (a supercritical gravity flow) induced by the fire transforms to a subcritical gravity flow (by means of a density jump) due to interaction with the beams until, finally, critical gravity flow conditions are established when the flow of gases is channeled between the beams. Theoretical predictions of the flow properties (temperature, velocity) agree very well with existing experimental results. Analytic expressions for the gas temperature rise variation along the fire channel are also developed. The model can be applied to other practical situations of similar geometry, as, for example, the flow of warm effluent discharges in water.

Intermittent air injection into rooms—the isothermal ceiling jet

The transient velocity field of a plane ‘wall jet’ formed on the ceiling of a test room has been studied. This ‘simple’, isothermal flow provided an insight into the mechanisms underlying the more complex jet/room geometries which are employed in intermittent warm-air heating systems for the domestic environment. Data are presented which may be used to predict the development of these intermittent wall jets, in either a starting or stopping mode, within typical room geometries. The time taken for the starting and stopping jets to attain their steady-state values, the so-called ‘growth’ and ‘decrement’ times respectively, were relatively short (less than 60 s). The duration of the supply fan off period required to maintain thermal comfort will therefore largely depend on the strength of local, natural draughts and not on the jet decrement time.