Will Fire Truck Water Freeze?
Most recent answer: 09/19/2012
Q:
I am a fire fighter in Alaska and we have recieved a new type of fire truck that sprays water through a turret at a range between 1100psi and 1500psi. What we are wondering is if the water in the tank is at 70 degrees F then what will happen if we spray at outdoor temperatures of -20 to -40. We are worried the water will freeze before reaching its intended target.
- Donald Travers (age 26)
North Pole, AK, USA
- Donald Travers (age 26)
North Pole, AK, USA
A:
There are some key physical properties which we don't know that we'd need to help solve this problem. The most important is to know what the stream of water looks like. Is it made of drops, and if so how big are they? Or is it a thick stream? About how long does it have going from nozzle to fie? maybe a second or two?
The thermal diffusion coefficient in water is about 10-3 cm2/s. So in a second, heat diffuses a distance of a little less than 10-1 cm. Actually, in order to freeze the water time is needed both for it to cool down and for the latent heat of freezing to diffuse away. Under your conditions that should slow things down about a factor of three.
So I bet if you've got either a stream or real droplets, not a fine spray, things should be ok.
Please let us know if experience shows that we're wrong.
In case, somewhere mid-air, some droplets froze, why would that make problems for the fire fighting?
Mike W.
The thermal diffusion coefficient in water is about 10-3 cm2/s. So in a second, heat diffuses a distance of a little less than 10-1 cm. Actually, in order to freeze the water time is needed both for it to cool down and for the latent heat of freezing to diffuse away. Under your conditions that should slow things down about a factor of three.
So I bet if you've got either a stream or real droplets, not a fine spray, things should be ok.
Please let us know if experience shows that we're wrong.
In case, somewhere mid-air, some droplets froze, why would that make problems for the fire fighting?
Mike W.
(published on 09/19/2012)