An Explosive-Driven Jet for Fire-Fighters
An experiment of an explosive-driven waterjet has been reported by Liao et al. * in the proceedings of the 16th International Conference on Water Jetting in 2002. Their experiment will be reviewed here.
Even though conventional waterjets have become popular in the last two decades in various industries, they are not the right tool for some circumstances. A good example is to extinguish sporadic fires in a dangerous environment. To develop a right tool useful for these circumstances, an experimental study of an explosive-driven waterjet was conducted.
This explosive-driven waterjet consists of, mainly, an explosive power source, a dynamic cavity, and a water storage chamber. A gun for shooting nails for civilian use was utilized to provide the power source. When the bullet is fired, the pressure of gas inside the dynamic cavity can reach 300 – 350 Mpa. A spacing block, which separates the water storage chamber and the dynamic cavity, will burst, allowing the water in the storage chamber to be propelled at a speed that can reach 120 m/s. The formation of the jet is affected by several factors, including the size and shape of the dynamic cavity as well as the burst pressure of the spacing block. In their paper, two equations were provided to calculate the proper length of the dynamic cavity and the time for the gas to be kept inside the cavity.
According to their experiment, with 0.2 gram of dynamite (in a single bullet), a waterjet “spindle” (3-litre in volume) will shoot 7 to 12 meters and no water will fall less than 7 meters. By increasing the charge of dynamite, it can shoot as far as 60 meters, with an effective distance (for extinguishing fires) of 40 meters. The maximum volume of water in one shot is 12 liters.
This explosive-driven waterjet produces large drops of water (>200 µm in diameter) that can penetrate into the heart of the fire and quickly extinguish the source of fire. Smaller drops of water, that are also present, vaporize quickly, surrounding the blaze with steam and lowering the temperature. The portability and large shooting range make this kind of waterjet ideal for extinguishing sporadic fires in a dangerous environment. In their experiment using this device, a fire with a 0.4x0.4 meter base was successfully put out with only two shots.
* Liao, Z., Zhang, S., Zhang, J., Tang, C., Zi-Lang, F., and Yang., L., “The experimental study of an explosive jet,” Proceedings of the 16th International Conference on Water Jetting, Aix-en-Provence, France, October 16-18, 2002, pp 119-122.
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