Properties of Water Sprays Injected into Compressed Atmospheres

Abstract

Properties of water sprays injected into compressed atmospheres were studied in order to design an effective fixed spray system for use in a hyperbaric chamber. With the ambient pressure and the vertical distance from the nozzle, a contraction of the spray and an increase of droplet size becomes noticeable because the spray is decelerated more rapidly, commences to drop by the gravity at the higher position, and is transferred more easily toward nozzle axis by the entrained air and consequently the coalescence among spray droplets becomes remarkable. The entrained air velocity becomes a maximum at the spray axis mainly due to the inertia of induced air and so the diffusion of entrained air in the spray is smaller than that of air jet. As ambient pressure increases, the entrained air velocity generally decreases, but is approximately constant in the case of the swirl nozzle. The following spray characteristics are recommended for the extinguishment of fires in hyperbaric chambers :
(1) coarse spray ;
(2) low velocity or the homogeneous distribution of the entrained gas ;
(3) little contraction in the downward stream ;
(4) large flow rate.