Recent Results of Experimental Studies on the Transition of a Deflagration into a Detonation and Some Aspects for the Transposition of these Results to Confined Explosions

Abstract

For the safety of a nuclear power plant it is of substantial interest to know realistic values of the overpressure build-up in a chemical explosion. To obtain a further insight into the complex pattern of events in this field experimental investigations were carried out i n free and partially confined homogenous clouds with hydrogen as a fuel. The results of the experiments in an unconfined hemispherical configuration show a distinct dependence of the flame velocity on the cloud size which does not exceed, however, an upper limiting value. The experiments under partially confined conditions without additional turbulence indicate that the flame velocity and consequently the pressure field is governed by the hemispherical flame front initially formed; i. e. the flame velocity is not affected by a partial confinement. To increase the turbulence effects further experiments were carried out with a fan and with jet ignition. In the case of fan induced turbulence the flame velocity was strongly influenced by the fan speed. At a certain fan capacity the transition of a deflagration into a detonation was observed. With jet ignition produced by venting an explosion chamber into the partially confined cloud the transition occured even with hydrogen concentrations in air as low as 22 Vol%. The results which are discussed on the basis of turbulence models and with respect to their transposition to confined explosions show that high damaging overpressures or the transition from a deflagration into a detonation are only generated by strong turbulences as a consequence of flow and/or obstacles.