Static pressure measurements of enclosure fires

Abstract

Some enclosure-fire s tati c pressure me asurements are presented for both full a nd sca le mode l rooms and are compared with the present hydra uli cs-orifice flow model for fire induced flows into and out of enclosures. Results indicate that the vertical pressu re diffe renti al (enclosure to ambient) follow s the expected hydrostati c distribution qUite well and accura tely reflects the doorway Inflow and outflow gas velocities. .Measure me nt of ceiling a nd floor diffe rential pressure using different numbers of gas burners yields ins ight Int o gross plume e ntrainment and Illus trates how the neutra l p la ne and thermal di scontinuit y vary with upper gas temperature. Corre la ting upper gas tempe ra ture with fire s ize and enclosure he ight ma kes it possible to pred ict at wha t heat release rat e a give n enclosure mi ght become fully involved, i. e., by using the temperature at which the the rma l discontinuity approac hes th e floor.In te rms of present fire plume modeling la rge e ntra inment coeffi cie nt s (0 .3-0.4) are required in order to reproduce the e nc los ure fl ows for both the s ma ll and large scale resu lt s. A noted defi cie ncy in the plume mode l appears In the small sca le results wh e re the data suggest that the e ntrainment s hould exhibit a much stronger dependence on th e fu el injecti on rate tha n that pred icted by the th eory.Key words: Buoyancy pressure; e nclosure fires; entrai nme nt; fire ind uced flow s; models; physica l sca le; plumes.Nomenclature door opening area (m 2 ) orifice discharge coeffic ient gas specifi c heat (J/kg' K) height of thermal discontinuity above floor (m) plume Froude number = uJ/g'Yo gravitational accelerati on (9.8 m/s 2 ) height of enclosure (m) height of door opening (m) entrainmen t coeffi cient gas/air How rate (kg/s) height of ne utral plane above floor (m) pressure (torr, N/m 2 ) pressure difference, enclosure to ambient P-P AMB (torr, also given as N/m 2 ) heat release rate (k W) radial distance from plume axis gas temperature (OC, K) temperature difference eC) gas burner flow velocity (m/s) gas/air velocity (m/s) door opening width (m) entrained flow in plume (kg/s) gas burner flow rate = pf7T1o u f height above floor (m) radius of gas burner (m) distance above or below neutral plane gas densit y (kg/m 3 ) fu el property defined by equation (9) 1 . Introduction Present e nclos ure-fire modeling incorpora tes a hydrauli csorifice approach for calculation of th e How in a nd out of th e opening [1,2,3].1 Due to th e hot gases present in the upper portion of the room a pressure difference with respect to the ambient hydrostati c pressure is developed across the opening which is responsible for driving th e How. The gas in th e room is ass umed stationary and the How ra te is determined using Bernoulli's equation with an appropri a te orifice coefficient. Additionally th e gas Jlow in and ou t of th e e nclos ure is co upled via entra inmen t of th e [ire plume. Figures 1 a nd 2 illustrate th ese ideas sc he mati cally. A s tep functi...

Particle image velocimetry measurements of buoyancy inducted flow through a doorway

“…Ideally this requires a full mapping of the velocity and density fields due to the three dimensional nature of vent flows. Early treatments quantifying fire induced flow through vents relied on Bernoulli's equation and a hydraulics-orifice approach [1,2,3], therefore only a few well placed pressure and temperature measurements were required. Later treatments were improved by adding vertical arrays of pressure and temperature measurements and scanning them across the vents in order to address the three dimensional nature of the flows.…”

A simple correlation for predicting temperature in a room fire

“…(5) and (10) and for enclosure parameters of (1) calcium From eqs. (9) and (16) with m in g/s and t in s. The results of this computation ("estimate") are plotted in figure 8 along with experimental results and results from a more complete model [13].…”

“…Equation (5) combines the initial heating solution of an infinitely thick wall with the steady-state heat conduction result for a wall of thickness 6. By substituting eqs. (3) and (4) [6] and their result will be described.…”

“…Results for example 4: Factory Mutual room test no. 5 ... 30 Table 7. "Flashover" criteria by Thomas [15] AT correlation with floor heat loss taken from Ref.…”

“…Also, combustion products flowing away from the fire will cool due to mixing with colder gases and heat Before proceeding with the details of this simple solution, some background will be presented to explain its development. McCaffrey [2,5] discovered that the gas temperatures measured in the upper part of the room could be correlated in a power law relationship involving the energy release rate of the f ire (Q) , the ventilation factor for the opening (A q i/h^) , and a room geometric scale factor. These data applied to steady gas burner fires and to the peak burning conditions for wood or plastic crib fires.…”