Hydrogen-air mixtures

A hydrogen-air mixture is highly explosive and fire hazardous. 

In an obstacle-free channel 30.5 m long x 2.44 m x 1.83 m, hydrogen-air mixtures detonated, both with a completely closed top and with a top opening of 13% (Sherman et al. 1985). 

The effects of turbulence must be taken into account when sizing a relief area. For example, the explosion violence of turbulent methane-air mixture is comparable to that of zero turbulence of hydrogen-air mixtures. From the investigations [54], the nomograms from Figure 7-63 can be applied for turbulent gas mixtures under the following conditions [54] ... 

Ishizuka, S., Koumura, K., and Hasegawa, R., Enhancement of flame speed in vortex rings of rich hydrogen/air mixtures in the air, Proceedings of the Combustion Institute, 28,1949-1956, 2000. 

H. G. Im and J. H. Chen, Structure and propagation of triple flames in partially premixed hydrogen-air mixtures. Combust. Flame 119 436-454, 1999. 

The effect of natural gravity on flammability limits has been known for a long time. The difference between flammability limits for downward and upward flame propagation was first observed by White [26], for hydrogen/air mixtures. Subsequently, similar effects were also found for other mixtures. For propane flames, the lean flammability limit for both downward and upward propagation was observed to be = 0.53. The rich limits were = 1.64 for downward and = 2.62 for upward propagation. Such wide gap between the flammability limits for rich mixtures is explained in... 

The inset of Figure 6.3.7 shows the flame response for rich hydrogen/air mixture of =7.Q. Since the Lewis number of this mixture is sufficiently greater than unity, it is susceptible to diffusional-thermal pulsating instability. Four flames, denoted by Flames 1-lV along the... 

Time variations of maximum flame temperature for Flames I-IV. The inset shows the steady-state flame response for hydrogen/air mixture of 0 = 7.0. Results demonstrate that Flame 1 is dynamically stable. Flame II is monochromatically oscillatory. Flame III exhibits pulsation with period doubling, and Flame IV is extinguished through pulsation. 

Gamezo, V.N., Ogawa, T. and Oran, E.S., Numerical simulations of flame propagation and DDT in obstructed channels filled with hydrogen-air mixture, Proc. Combust. Inst., 31, 2463,2007. 

The value of k is not universal and depends on the nature of the reactive mixture (for example, fhe value of k may be around 26 for mixtures highly diluted with a mono-atomic gas [29], or around 20 for hydrogen/air mixtures [30]), as well as on the diffraction process at the tube... 

The effects of the presence of 44 gaseous or volatile materials upon the upper explosion limits of hydrogen-air mixtures have been tabulated. 

Brandstrom, A., Acta Chem. Scand., 1951, 4, 1608-1610 Air must be excluded dining exothermic interaction of ethanol with sodium finely dispersed in hydrocarbons to avoid the possibility of hydrogen-air mixture explosions. 

Detonation pressure and temperature of hydrogen-air mixtures starting from 101.3 kPa (1 atm) and 298 K (25°C). Chapman-Jouguet calculations using the Gordon-McBride code. (After Gordon, S. and McBride, B.J., Computer Program for Calculation of Complex Chemical Equilibrium Compositions and Applications, NASA Reference Publication, Cleveland, Ohio, 1994.)... 

Other factors that determine the catastrophic effects of an explosion are the initial density of the explosive (which is more than three orders of magnitude higher for TNT than for hydrogen-air mixture) and detonation velocity (which is three to five times higher in TNT). Therefore, the resulting pressure wave from a hydrogen explosion is considerably flatter (longer duration and lower maximum overpressure) than TNT, and destruction effects are mainly caused by impulse rather than overpressure. 

It is reported that the adiabatic flame temperature for H2 at the lower flammability limit (LFL) in air is 700 °C. From this information, estimate the LFL, in % by volume, for the hydrogen-air mixture at 25 °C. Assume water is in its vapor phase within the products. 

It is essential that persons be grounded in hazardous (classified) locations. For most chemical operations, the resistance from skin to round should not exceed 100 MQ. A lower allowable resistance may e specified for locations where the presence of primary explosives, hydrogen-air mixtures, oxygen-enriched mixtures, or certain solid-state devices requires faster charge dissipation. 

Precautions to Prevent Combustion of Hydrogen-Air Mixtures During... 

PL-3.9 PRECAUTIONS TO PREVENT COMBUSTION OF HYDROGEN-AIR MIXTURES DURING CONSTRUCTION OPERATIONS... 

Hydrogen is a stable gas in seclusion, but in air, is very unstable. The flammability properties of such a mixture are well-known at atmospheric pressure, yet little is known about the hydrogen-air mixture at sub-atmospheric pressures. In order to determine the hydrogen reaction limits within a vacuum, a number of experiments were performed and analyzed. The results were used to design a vacuum furnace system and processes with safeguards to protect against a severe hydrogen reaction. 

On what side of stoichiometric would you expect the maximum flame speed of hydrogen-air mixtures Why ... 

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