Quality
Waterjet Newsletter – 01/24/2006
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. Beyond High
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