Critical Conditions for Explosion Transmission between Two Chambers

A number of previous studies have indicated that the quenching of flames, as they propagate in a combustible gas mixture from one chamber to another through an orifice, depends not only on orifice diameter but also on flow velocity [1-2]. The problem may be divided into three regimes with increasing flow velocity at the orifice: 1) a “thermal diffusion” quenching regime associated with laminar burning velocity and loss of heat and free radicals to the orifice wall, 2) a “turbulent mixing” regime where the rate of turbulence entrainment of cold unburned mixtures into burned mixtures dominates the overall quenching and 3) a “sonic choking” regime where a temperature decrease in an underexpanded jet structure downstream of the orifice contributes to the flame quenching. Motivated by the importance of quenching or transmission of the explosion from a condensed explosive in chambers, the present paper investigates critical conditions for explosion transmission from a donor chamber (where detonation of an explosive charge occurs) to a receptor chamber (initially filled with air only). The experimental facility consisted of two steel chambers connected with an orifice plate between them (Fig. 1). The donor chamber, 26 m in volume and 3 m in diameter, was designed to sustain a 1500 psi hydrostatic pressure and can be vacuum-sealed using a blind flange, while the receptor chamber was 23 m in volume and has the same internal diameter. The venting orifice plate was interchangeable for various hole diameters up to 1.22 m corresponding to a venting area of 1.169 m. The donor chamber was equipped with 12 gauge holes 33 cm in interval along the two sides and the front end, and 7 circular windows 10 cm in diameter, three pairs on the two sides facing each other and one on the front end. The receptor chamber was equipped with 25 gauge mounts, three 45 cm x 15 cm windows on the side and a window 15 cm in diameter looking through the end wall downstream and opposite the orifice. The diagnostics included pressure transducers, a pyrometer and high-speed digital video cameras. The experiments were conducted using IPN/Mg and IPN/RDX/Al heterogeneous mixtures and baseline C-4 charges in three masses: 1.1 kg, 4 kg and 7.7 kg. The mixtures were contained in a thin-walled polyethylene cylindrical casing whose length/diameter ratio has been maintained at L/D ≈ 1. The charge was suspended and detonated in the center of the donor chamber. Figure 1. Two chambers with orifice plates P2 C3