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Detonations in capillary tubes with nitrous oxide as an oxidizer


More and more industrial chemical syntheses are run in microstructered process equipment with capillary tubes having a diameter less than 1 mm. The advantage is a better control of the process especially when oxygen, nitrous oxide or nitric oxide is used as oxidizer. Microstructured process equipment is often thought to be intrinsically safe with respect to the propagation of explosions. It could be proven that this is not the case if oxygen is used as an oxidizer. An enhanced experimental setup for investigations of the behavior of detonations in capillary tubes (glass and stainless steel) is described. It allows to characterise detonations of flammable substance/oxidizer mixtures by the detonation limits, the limiting detonation pressure, the detonation velocity, the detonation pressure and the width of the detonation cells at different initial pressures.

The experiments focused on the oxidizers nitrous oxide (N2O) and nitric oxide (NO). For both oxidizers, experiments with Ethane, Propane and n-Butane at different concentrations were operated in different capillary tubes. The smallest diameter of the capillary tubes used was 0.15 mm. The pressure range investigated covered pressures below and above ambient pressure.
The results of the detonation cells width, the detonation velocity and the detonation pressures are given. The possibility to derive a ‘safe capillary diameter’ based on the detonation cell width by the use of the "λ/3-rule" as it is possible with oxygen as oxidizer is discussed and judged.

Diagram Detonations capillary tubes