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Processes of flame spread

This result can conveniently be expressed in terms of the laminar flame speed Vq by employing equation (5-2) the result is [Pg.509]

A characteristic transverse dimension d of the flame holder can be measured more easily than the length / of the recirculation zone. The ratio l/d experimentally has a practically constant value between 5 and 10, independent of flow conditions for hot turbulent wakes. Hence, I d in equation (65), so that d. Of greater interest than the dependence [Pg.509]

The dependences of the blowoff velocity on size, d, pressure, p, and flame speed, Vq, given by equation (66) generally agree with experiment and provide reasonable correlations of empirical data [2], [69]. Although this reasoning is very rough, the complexity of the flow field about a bluff body necessitates the use of imprecise concepts such as this at the present time if simple correlation formulas are to be derived.  [Pg.509]

Imprecise concepts are also helpful for describing the spread of flames in the gas phase, through condensed-phase fuels. A general approach, applicable in complex configurations, is first to identify a surface of fuel involvement that encloses the fuel. This surface, which flames approach at some [Pg.509]

Let q denote an energy per unit area per unit time transferred across the surface. As a first approximation, let us assume that a critical enthalpy increase Ah per unit mass of fuel is needed for ignition to occur. If p is the fuel density and L is a spread velocity, then, according to an energy balance, [Pg.510]


In the final two sections, mechanisms of flame stabilization and processes of flame spread will be considered. In the first of these sections, we shall see that the onset of combustion can cause the boundary-layer approximation to fail. Physical aspects of various types of flame stabilization will be reviewed. The discussion of flame spread also will focus on the many different types of physical processes that may be involved. The presentation should serve to emphasize approximate unifying concepts as well as various currently outstanding unknowns. [Pg.486]

Sanchez Tarifa, C., Perez del Notario, P. and Munoz Torralbo, A. On the process of flame spreading over the surface of plastic fuels in an oxidizing atmosphere. In llth Int. Symp. on Combustion, The Combustion Institute, London 1969, p. 229... [Pg.92]

This type of model works well at high applied heat flux levels, where the pyrolysis front is thin. Simplicity is its advantage it is not necessary to specify any parameters related to the decomposition kinetics. A large body of flame spread modeling work has applied this type of model, but there is a tendency to focus with great detail on gas-phase phenomena (i.e., full Navier-Stokes, detailed radiation models, multistep combustion reactions) and treat the condensed-phase fuel generation process in an approximate manner. [Pg.566]

The theory advanced by De Ris belongs to the first group. In his model of flame spread along a horizontal surface it is assumed that the diffusion flame contacts the surface at the point where the polymer vaporization (gasification) begins. Reactant diffusion to the narrow zone of chemical reaction controls the heat generation process. If heat is transferred from the laminar diffusion flame to the surface by conduction, then the flame spread rate follows the Equations a) for thermally thin materials... [Pg.189]

AB STRACT The characteristics of horizontal flame spread over two kinds of typical insulation foams under external radiation were experimentally investigated. Laboratory-scale experiments of flame spread were conducted at two altitudes for comparisons. The height and length of flame under different external radiations were measured. The rates of flame spread over the two different materials in the plain are larger than those on the plateau under the same external radiant flux. At both altitudes, the flame spread rate of PUR and EPS foams both increase with the increasing external radiation intensity in general. The expression of flame spread rate of the insulation materials under external applied radiation was deduced. The mechanism of heat transfer during the flame spread process was analyzed in detail. [Pg.157]

Many studies have been conducted to explore the characteristics of flame spread with external radiations because the flame spread process in real fire scenarios is usually accompanied with external radiant flux. In the 1970s, Williams, Femandez-Pello, Hirano, Takashi, and Kashiwagi have conducted a large number of experimental studies on the flame spread over solid surface under the influence of external radiation. It has been indicated that the influence of external radiation on flame spread is mainly embodied by initial surface temperature rising. Fernandez-Pello considered that the rate of flame spread of thick PMMA slabs has an exponential relationship with the difference between the temperature of ignition and solid phase. [Pg.157]

This work has described the influences of external applied radiation on the horizontal flame spread rates and heat transfer mechanisms of two typical insulation materials (rigid polyurethane and molded polystyrene foams) in bench-scale both in Hefei plain and on Tibetan plateau. The different flame spread rates of two kinds of insulation foams with increasing radiant flux were analyzed qualitatively. The mechanisms of heat transfer in flame spread process of PUR and EPS foams were discussed and an expression of flame spread rate under external radiations was obtained. The results are summarized as follows ... [Pg.161]

Finishes Thermal insulations require an external covering (finish) to provide protection against entry of water or process fluids, mechanical damage, and ultraviolet degradation of foamed materials. In some cases the finish can reduce the flame-spread rating and/or provide fire protection. [Pg.1098]

The flame spread process in adiabatic. There is no heat transfer to the tube wall and the temperature of the burned products, Tb, and the unburned mixture, 7i are therefore... [Pg.111]


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