Explosions thermal limit

There is a third explosion limit indicated in Figure 4.1 at still higher pressures. This limit is a thermal limit. At these pressures the reaction rate becomes so fast that conditions can no longer remain isothermal. At these pressures the energy liberated by the exothermic chain reaction cannot be transferred to the surroundings at a sufficiently fast rate, so the reaction mixture heats up. This increases the rate of the process and the rate at which energy is liberated so one has a snowballing effect until an explosion occurs. 

Andrej Ma ek, "Sensitivity of Explosives , ChemRevs 62, 41-63(1962). "The sensitivity of an explosive can be defined as the minimum amount of energy that must be imparted to the explosive, within limited time and space, to initiate explosive decomposition (p 60). This definition can serve as a basis of quantitative fundamental treatments provided the imparted energy is thermal and provided its initial distribution in time and space is known. If the energy is not supplied directly as heat, but by mechanical means (such as a shock), there is the additional requirement of quantitative assessment of conversion of the stimulus into heat (p60)... 

This is of the same form as Equation 30, but involves the mixed diffusion coefficient, Jci9, instead of the thermal conductivity of the mixture. However, as seen from the kinetic theory of gases, the thermal conductivity is proportional to the diffusion coefficient. Therefore agreement of experimental results with either Equation 30 or 53a is not an adequate criterion for distinguishing between first explosion limits in branching chain reactions and purely thermal limits. It has been reported (52), that, empirically,... 

TNA forms colorless to white to yellowish crystals, which are highly resistant to shock, heat, friction, and percussion. It isa powerful explosive with high thermal stability, and is used in the manufacture of specialty explosives charges for fighting oil wells, forest clearing, line charges, and for missile warheads. Thecostof TNA production is rather high, so its use in explosives is limited. ... 

The theory on light induced thermal explosions is limited. Some theoretical analysis can be found in [27-30]. The photothermal initiation mechanism is complicated because of phase changes, melting, sublimation and vaporation processes, which are not usually taken into account. The same holds for the change of the absorption and reflection coefficient by these processes. 

Given the inertia at the motor shaft, the equations in this section are used to determine whether the torque of the chosen motor is sufficient to accelerate the decanter bowl smoothly to speed, without slippage of the belts. The thermal limits and the torque limit of the number of drive belts used and their cross-sections have to be checked, with the pre-set diameter of the smallest pulley taken into account. Causing the belts to slip will end in their failure, while producing copious amounts of dust in the belt guard, which could be an explosion hazard. 

In the absence of air, TEE disproportionates violently to give carbon and carbon tetrafluoride the same amount of energy is generated as in black powder explosions. This type of decomposition is initiated thermally and equipment hot spots must be avoided. The flammability limits of TEE are 14—43% it bums when mixed with air and forms explosive mixtures with air and oxygen. It can be stored in steel cylinders under controlled conditions inhibited with a suitable stabilizer. The oxygen content of the vapor phase should not exceed 10 ppm. Although TEE is nontoxic, it may be contaminated by highly toxic fluorocarbon compounds. 

Many polymer films, eg, polyethylene and polyacrylonitrile, are permeable to carbon tetrachloride vapor (1). Carbon tetrachloride vapor affects the explosion limits of several gaseous mixtures, eg, air-hydrogen and air-methane. The extinctive effect that carbon tetrachloride has on a flame, mainly because of its cooling action, is derived from its high thermal capacity (2). 

There are situations where thermal oxidation may be preferred over catalytic oxidation for exhaust streams that contain significant amounts of catalyst poisons and/or fouling agents, thermal oxidation may be the only technically feasible control where extremely high VOC destmction efficiencies of difficult to control VOC species are required, thermal oxidation may attain higher performance and for relatively rich VOC waste gas streams, ie, having >20 25% lower explosive limit (LEL), the gas stream s explosive properties and the potential for catalyst overheating may require the addition of dilution air to the waste gas stream (12). 

Design of explosion suppression systems is clearly complex, since the effectiveness of an explosion suppression system is dependent on a large number of parameters. One Hypothesis of suppression system design identifies a limiting combustion wave adiabatic flame temperature, below which combustion reactions are not sustained. Suppression is thus attained, provided that sufficient thermal quenching results in depression of the combustion wave temperature below this critical value. This hypothesis identifies the need to deliver greater than a critical mass of suppressant into the enveloping fireball to effect suppression (see Fig. 26-43). 

Flammability information Flash point Fire point Flammable limits (LEL, UEL) Ignition temperature Spontaneous heating Toxic thermal degradation products Vapour pressure Dielectric constant Electrical resistivity Electrical group Explosion properties of dust in a fire... 

Low flow, low concentration streams are best handled by a catalytic recuperative oxidizer. When the concentration of the stream is between 15% to 20% LEL (Lower Explosion Limit) then both a catalytic recuperative or thermal recuperative is the best technologies. For process streams between 20% to 25% LEL then thermal recuperative is the preferred solution. 

Lower and upper explosive limits (LEL, UEL) must be considered in order TO avoid dangerous operation in the incinerators. Thermal incinerators are normally designed to operate with concentrations below 2.5% of the LEI, lypically, the LEL ranges from 2500 to 10 000 ppmv. ... 

Chemical Reactions. It burns with a luminous flame and is readily expld (Ref 2). It is reduced with Zn dust and Na hydroxide to dimethyl hydrazine (Ref 2). Action of coned HC1 forms methylhydrazine and formaldehyde (Ref 2). Treatment in anhyd eth with Na metal forms a solid adduct which gives dimethylhydrazine on addn of w (Ref 4). For a review of thermal and photochem reactions see Ref 8 Explosive Limits. In mixts with air the crit press at which exp] occurs varies inversely with temp betw 350 and 380° (Ref 6)... 

Silver acetylide decomposition was studied [679] by X-ray diffraction and microscopic measurements and, although the a—time relationship was not established, comparisons of intensities of diffraction lines enabled the value of E to be estimated (170 kj mole 1). The rate-limiting step is believed to involve electron transfer and explosive properties of this compound are attributed to accumulation of solid products which catalyze the decomposition (rather than to thermal deflagration). 

Muller et al. have also examined the enantioselectivity and the stereochemical course of copper-catalyzed intramolecular CH insertions of phenyl-iodonium ylides [34]. The decomposition of diazo compounds in the presence of transition metals leads to typical reactions for metal-carbenoid intermediates, such as cyclopropanations, insertions into X - H bonds, and formation of ylides with heteroatoms that have available lone pairs. Since diazo compounds are potentially explosive, toxic, and carcinogenic, the number of industrial applications is limited. Phenyliodonium ylides are potential substitutes for diazo compounds in metal-carbenoid reactions. Their photochemical, thermal, and transition-metal-catalyzed decompositions exhibit some similarities to those of diazo compounds. 

GP 11] [R 19] Based on an analysis of the thermal and kinetic explosion limits, inherent safety is ascribed to hydrogen/oxygen mixtures in the explosive regime when guided through channels of sub-millimeter dimensions under ambient-pressure conditions [9], This was confirmed by experiments in a quartz micro reactor [9],... 

GP 11] [R 19] The third explosion limit is discussed in detail in [9] as it is important from both practical and mechanistic viewpoints (230-950 °C 10-10 Pa). This limit is normally responsible for the occurrence of explosions imder ambient pressure conditions. In addition, these explosions are known to be kinetically induced by radical formation. The formation of these species is sensitive to size reduction of the processing volume owing to the impact of the wall specific surface area on radical chain termination. It turns out that the wall temperature has a noticeable, but not decisive influence on the position of the third limit The thermal explosion limit lies below the kinetic limit for all conditions specified above (Figure 3.50) [9]. 

Figure 3.50 Extending kinetic explosion (squares) and thermal explosion limits by using a micro reactor with 300 pm channel diameter (filled symbols). Calculated values for (circles) and 7 3 = (triangles). Comparison with 1 m...

The Sudan series of azo dyes, which have also been synthesized in micro reactors, are commonly used as microbial stains. The thermally unstable nature of the diazonium precursors and reported explosions often demand extensive safety procedures when going to an industrial scale, which limits the commercial applicability of the azo reaction. 

By the development of hot spots by friction. This is shown particularly by the effect of added materials of a gritty nature. For initiation to occur, the melting point of the grit must be above a limiting temperature dependent on the explosive. Initiation is favoured by a low thermal conductivity and also by a high hardness value. 

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