Flame pressure effect

Explosion venting is always accompanied by flame propagation plus pressure consequences in the surrounding areas. Tne flame length will be larger with a lesser static activation pressure and smaller vent area. Depending on the volume of the protected equipment, it can reach up to 50 m. The pressure effect in the vicinity of the vent area is... 

It would appear that measurement of the integrated absorption coefficient should furnish an ideal method of quantitative analysis. In practice, however, the absolute measurement of the absorption coefficients of atomic spectral lines is extremely difficult. The natural line width of an atomic spectral line is about 10 5 nm, but owing to the influence of Doppler and pressure effects, the line is broadened to about 0.002 nm at flame temperatures of2000-3000 K. To measure the absorption coefficient of a line thus broadened would require a spectrometer with a resolving power of 500000. This difficulty was overcome by Walsh,41 who used a source of sharp emission lines with a much smaller half width than the absorption line, and the radiation frequency of which is centred on the absorption frequency. In this way, the absorption coefficient at the centre of the line, Kmax, may be measured. If the profile of the absorption line is assumed to be due only to Doppler broadening, then there is a relationship between Kmax and N0. Thus the only requirement of the spectrometer is that it shall be capable of isolating the required resonance line from all other lines emitted by the source. 

Because the flame thickness in this equation is the same parameter discussed and analyzed by Summerfield (S7), Penner (P3), and Nachbar (Nl), this equation suggests that the pressure effect on burning rate should approximate... 

The whole set-up for partial oxidation comprises a micro mixer for safe handling of explosive mixtures downstream (flame-arrestor effect), a micro heat exchanger for pre-heating reactant gases, the pressure vessel with the monolith reactor, a double-pipe heat exchanger for product gas cooling and a pneumatic pressure control valve to allow operation at elevated pressure [3]. 

If the mixture (or a dust cloud) is confined, even if only by surface irregularities or local partial obstructions, significant pressure effects can occur. Fuel-air mixtures near to stoicheiometric composition and closely confined will develop pressures of several bar within milliseconds, and material damage will be severe. Unconfined vapour explosions of large dimensions may involve higher flame velocities and significant pressure effects, as shown in the Flixborough disaster. 

Froude number W1 /( bQ is nearly the same for the near and far field plumes, 1.60 0.1. The entrainment coefficients are much larger, which probably includes pressure effects near the base for the axisymmetric fires and tornado-flame filament effects for the line fire, which are actually three dimensional. It should be realized that the data corresponding to these correlations contain results for finite fires D > 0, not idealized sources. The correlations in Tables 10.1 and 10.2 are one set of formulas others exist with equal validity. 

These theories fostered a great deal of experimental research to determine the effect of temperature and pressure on the flame velocity and thus to verify which of the theories were correct. In the thermal theory, the higher the ambient temperature, the higher is the final temperature and therefore the faster is the reaction rate and flame velocity. Similarly, in the diffusion theory, the higher the temperature, the greater is the dissociation, the greater is the concentration of radicals to diffuse back, and therefore the faster is the velocity. Consequently, data obtained from temperature and pressure effects did not give conclusive results. 

Aluminium hydroxide has a Moh hardness of about 3 and a specific gravity of 2.4. It decomposes endothermically with the release of water at about 200 °C and this makes it a very useful flame retardant filler, this being the principal reason for its use in polymers. The decomposition temperature is in fact too low for many thermoplastics applications, but it is widely used in low smoke P VC applications and finds some use in polyolefins. For these applications low aspect ratio particles with a size of about 1 micron and a specific surface area of 4-10 m g are preferred. The decomposition pathway can be diverted through the mono-hydrate by the application of pressure, and this may reduce the flame retardant effect [97]. This effect can be observed with the larger sized particles. Although it is chemically the hydroxide, it has for many years been known as alumina trihydrate and by the acronym ATH. 

Some of the gas dissolves in the aqueous solution, and the gas pressure developed within the apparatus forces the mixture out through the nozzle, which is directed onto the flame. If some heavy molasses or similar gluelike material is added to the sodium carbonate solution and some aluminum sulfate is added to the sulfuric acid, the solution discharges from the nozzle in the form of a foam in which the carbon dioxide gas is trapped. This heavy blanket of foam containing carbon dioxide settles over and around the burning object. The aluminum sulfate hydrolyzes to form aluminum hydroxide, which, at the temperature of the flame, dehydrates to produce a crust of aluminum oxide over the flame. Both effects serve to extinguish the flame. The common Foamite fire extinguisher is an example of this type. 

Since many factors such as nature of flame propagation, effect of radiant energy, effect of temperature and pressure, influence of turbulence, composition of fuel, etc., are operative, it is not surprising that no single, simple theory has been evolved which satisfactorily explains all the attending phenomena. Recent trends in the research on knock prevention have been concerned largely with the actual oxidation mechanism of single, pure hydrocarbons both in the presence of and without materials known to inhibit knock. 

Burning is not well defined it is a relatively low rate combustion reaction that looks like burning . (There is flame production but no pressure effects.)... 

Vapor cloud explosions are due to rapid combustion of flammable gas, mist, or small particles that generate pressure effects due to confinement they can occur inside process equipment or pipes, buildings, and other contained areas. A vapor cloud explosion can be either a deflagration or a detonation (the distinction between deflagrations and detonations is important when deciding on whether or not to use a flame arrestor in pressure relief systems). 

The pressure effect and the small sample size do limit the type of detector used for medium-high-pressure g.l.c. The commonly used type is the flame-ionization detector which at high pressures must be linked with a stream splitter. 

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