Heat of combustion, explosives

Values for heats of combustion, explosion and formation for some expls of military interest are given in Tables A B compiled from various sources (See opD380 D381) Refs 1) M. Berthelot C. Matignon, CR 113, 246(1891) (Chaleur de combustion)... 

Heats of Combustion, Explosion and Formation For Some Explosives of Militory Interest ... 

The problem of explosion of a vapor cloud is not only that it is potentially very destructive but also that it may occur some distance from the point of vapor release and may thus threaten a considerable area. If the explosion occurs in an unconfined vapor cloud, the energy in the blast wave is generally only a small fraction of the energy theoretically available from the combustion of all the material that constitutes the cloud. The ratio of the actual energy released to that theoretically available from the heat of combustion is referred to as the explosion efficiency. Explosion efficiencies are typically in the range of 1 to 10 percent. A value of 3 percent is often assumed. 

Example 9.1 A process involves the use of benzene as a liquid under pressure. The temperature can be varied over a range. Compare the fire and explosion hazards of operating with a liquid process inventory of 1000 kmol at 100 and 150°C based on the theoretical combustion energy resulting from catastrophic failure of the equipment. The normal boiling point of benzene is 80°C, the latent heat of vaporization is 31,000 kJ kmol the specific heat capacity is 150 kJkmoh °C , and the heat of combustion is 3.2 x 10 kJkmok. ... 

Many finely divided metal powders in suspension in air are potential e] losion hazards, and causes for ignition of such dust clouds are numerous [Hartmann and Greenwald, Min. MetalL, 26, 331 (1945)]. Concentration of the dust in air and its particle size are important fac tors that determine explosibility. Below a lower Umit of concentration, no explosion can result because the heat of combustion is insufficient to propagate it. Above a maximum limiting concentration, an explosion cannot be produced because insufficient oxygen is available. The finer the particles, the more easily is ignition accomplished and the more rapid is the rate of combustion. This is illustrated in Fig. 20-7. 

If the explosion occurs in an unconfined vapor cloud, the energy in the blast wave is only a small fraction of the energy calculated as the product of the cloud mass and the heat of combustion of the cloud material. On this basis, explosion efficiencies are typically in the range of 1-10%. 

In a numerical exercise described in section 4.2.2, it was shown that, for a stoichiometric, hydrocarbon-air detonation, the theoretical maximum efficiency of conversion of heat of combustion into blast is equal to approximately 40%. If the blast energy of TNT is equal to the energy brought into the air as blast by a TNT detonation, a TNT equivalency of approximately 40% would be the theoretical upper limit for a gas explosion process under atmospheric conditions. However, the initial stages in the process of shock propagation in the immediate vicinity of... 

Furthermore, accidental vapor cloud explosions are anything but detonations of the full amount of available fuel. Therefore, practical values for TNT equivalencies of vapor cloud explosions are much lower than the theoretical upper limit. Reported values for TNT equivalency, deduced from the damage observed in many vapor cloud explosion incidents, range from a fraction of one percent up to some tens of percent (Gugan 1978 and Pritchard 1989). For most major vapor cloud explosion incidents, however, TNT equivalencies have been deduced to range from 1% to 10%, based on the heat of combustion of the full quantity of fuel released. Apparently, only a small part of the total available combustion energy is generally involved in actual explosive combustion. 

Explosives and propellants are mixtures of fuel and oxidizer. The intensity of combustion is determined by the heat of combustion per pound of material, the material s density, the gas volume generated per volume of material, and the rate of deflagration or detonation. The latter, the most important variable, is determined by the speed at which fuel and oxidizer molecules combine. 

Heat of Combustion. 102.9kcal/mole (Ref 22) Heat of Explosion. From a differential therm analysis exotherm at 310° the Qe at 227° was calcd to be 557cal/g (Ref 39)... 

Explosion Temperature, Ignited above 240° Heat of Combustion. Q 531,4kcal/mole Impact Sensitivity 11cm with BurMines app with 2kg wt (less sensitive than NG)... 

Ballistic Strength. 100% T NT (BuM ine s) Explosion Temperature. Does not expld or ignite at 360° or below Heat of Combustion. 8l8.1kcal/mole Hygroscopicity. Practically none Impact Sensitivity. Comparable to TNT Power. By Trauzl test, 103% TNT Rifle Bullet Test. No detonations from impact of. 30 cal bullet at 90 ft Thermal Stability. Unsatisfactory, loses 49% of wt in 48 hrs at 75° (International Test) Velocity of Detonation. No information Salts of (m-Nitrophenyll-dinitromethane. Milone and Massa (Ref 2) prepd several metallic salts and found that their expl power decreased with increasing atomic v/t of the metal Following are some of the expl salts K salt—yel crysts ... 

As a general mle, WT boilers are safer from explosion than FT boilers because the dmm is not exposed to the radiant heat of combustion. If tubes rupture, there is only a relatively small volume of water that can instantly flash to steam. 

R = 8.3145 kJ-K 1-kmol 1 and T is the reactor temperature (K). T is also the supply temperature of A whose yet unknown inventory mA is in the form of a superheated liquid. The total amount of B to be produced is 1000 kmol. T and mA are to be selected with the additional consideration of safety. The normal boiling point of A is 70°C, its latent heat of vaporization is 25,000 kJ-kmol-1, the liquid specific heat capacity is 140 kJ-kmol K 1, and its heat of combustion is 2.5 x 106 k.bkrnol. The residence time of the reactor is 1 min, and the safety is measured in terms of fire and explosion hazards on the basis of the theoretical combustion energy resulting form catastrophic failure of the equipment. 

Energy of explosion. The energy of explosion values given in Table 16.2 should be considered as the theoretical maxima, and yield factors of 10% are considered reasonable for fuel-air explosions. For equivalent volume storage, hydrogen has the least theoretical explosive potential of the three fuels considered, albeit it has the highest heat of combustion and explosive potential on a mass basis. 

For many materials the heat of combustion and energy of explosion differ by less than 10%, as shown in appendix B. For most practical purposes the two properties can be used interchangeably. 

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