Analysis of the behavior of a freely burning fire in a quiescent atmosphere

Abstract

INTRODUCTIONNo horizontal pressure variation exists between the flame and the surrounding air.4.The distributions of the velocity, temperature, and concentration in the transverse direction can be represented by the shape of a "top-hat" profile. 5.The transverse momentum flux due to the entrainmcnt of ambient air is pro-portional to the local upv/ard mom.entum flux of the rising flame gas.6.Ambient air is of uniform density and temperature.7.The gaseous fuel, combustion products and aml'^ient air are perfect gases with identical values of temperature-independent specific heat. The molecular v/eight of the combustion products in the buoyant plume zone and the ambient air are equal.8.In the combustion zone, the combustible volatiles mix with the entrained oxygen and burn instantaneously. 9.Radiative heat transfer can be neglected. The off-center maximum tends to shift to the flame axis as the unburned fuel reacts and the turbulent flame develops.It can be expected that velocity and concentration profiles within the flame plume will be similar to the temperature distribution. Therefore a "top-hat" profile for the mean vertical temperature, velocity, and concentration distributions although over-simplified is a reasonable assumption.The assumption that the entrainment constant for a turbulent buoyant jet with a density differing from the ambient air is proportional to the square root of the ratio of ambient 6 density to the average density inside the jet has been supported experimentally [21] and derived theoretically [22].Most fires in the open are not sufficiently large enough to cause significant variation of the temperature and density of the ambient atmosphere. However, these non-uniformity effects can be included in a manner similar to that used for natural convection column above fires [23][24][25].The assumption that the gas mixture inside the flame plume the plume is a black body emitter [11] , the plume gas is considered as an optically transparent medium [24], that the radiation can be divided into lateral and vertical components [26 , 27], and the radiating gas is a gray medium and the radiative interchange within the flame can be neglected [10]

Static pressure measurements of enclosure fires

“…The problem reduces to finding a relation involving the amount of e ntrainme nt and the he igh t of the thermal discontinuity for a given fi re such tha t its locus will intersect the enclosure flow at the appropriate flow and height, i. e., the points on figure 13 . Several fire plume models exist; the one chosen here from reference [1] is an adaptation of work by Fang [9] and Stewart [10]. The total flow in the plume , Wp , is given as a fun ction of the fu el inj ection rate , WI; a fuel property, w; density ratio , ambient to fu el , PO /PI ; plume entrainment coeffi cient , ke, and finall y, th e height above the burner , D.…”

“…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.…”

Perspectives of big experimental database and artificial intelligence in tunnel fire research

“…Thomas et al (1961) did several wood crib experiments taking into account the density of fuel and volume flow. Steward (1970) established a theory based on conservation equations, which was further simplified by Fang (1973). McCaffrey (1979) proposed to calculate the flame length by separating the whole flame into a continuous flame region and an intermittent flame region.…”

Small Scale Application of a Horizontal Ceiling/Floor Vent Algorithm

“…The division of the visible flame into an upper zone and a lower zone is adopted from the work of Delichatsios (1988), Fang (1973), Heskestad (1984), McCaffrey (1979and 1983), and Steward (1970. There is fairly good agreement between the various correlations with respect to flame height and temperature.…”