h a l f b a k e r yWhy not imagine it in a way that works?
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When conventional firefighing aircraft dumps it's water on a fire, most of it evaporates before it even hits the ground. What we need is refrigerated aircraft filled with ice cubes, that can dump it's load on a fire without it being boiled off.
Dry Ice Forest Fire Retardant
http://www.halfbake..._20Fire_20Retardant
Since dry ice has been mentioned... (shameless self-promotion) [st3f, Oct 04 2004, last modified Oct 05 2004]
(?) Eductor
http://www.foxvalve.com/main.html
also called venturis, usually by older folks. [swamilad, Oct 04 2004, last modified Oct 21 2004]
[link]
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Or even powdered dry ice - that would still do its work after evaporating. |
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I think that most of the benefit of these aircraft is not that the water wets the flames, but that it smothers them. Ice would not do this. |
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How long do you think it would remain ice?? |
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You need 3 things to create a fire (called the Fire Triangle) : Fuel, Heat and Oxygen. Firefighting involves taking away at least one of the sides of this triangle. |
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Ice would work in a sense that it's able to remove more heat from a fire prior to it's evaporation. |
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DryIce works because it's cold and removes heat but it also removes oxygen from the fire. [Angel] is right in saying that water both smothers and cools. Ice could not smother a fire as easily. |
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//How long do you think it would remain ice//
Not long, but I also think that it would tend to land either still frozen or in concentrated patches, rather than spreading out well before it hits the flames. Try it. Drop a bucket's worth of ice cubes on a bonfire from an upper floor window, then try with a bucket of water. I may be wrong, but I don't think the ice would work. |
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[jon] water would not smother or cool if it has turned to steam, which was the problem I was addressing in the first place. |
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[simon] Water does smother fires, albeit just for a the few moments it takes to heat it to steam. Ice is very unlikely ever to smother a fire... unless crushed? |
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I'm not disagreeing with you about the fact that ice to steam takes more energy than water to steam, thus helping to cool a fire. |
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Ice shavings would work better than cubes or balls as they would spread out better and the increased surface area would speed up heat transfer form the fire to the ice. |
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was going to post as a separate idea, but surely saltwater is best for this job? |
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It can be cooled to -5 without freezing so if the fireengine was refridgerated, it could apply supercooled water to a fire, thus taking away the heat. |
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Better still, saltwater has a higher Specific Heat Capacity, meaning it takes more energy to raise it's temperature, which in turn means that it'll be able to take even more energy(heat) away from the fire as it raises it's own. |
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The problem with using salt water form a fire engine is that the corrosion within the pump would become a major factor in the longevity of the appliance. |
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Dumping a lot of salt onto a forest (where fire-fighting aircraft tend to be used) would also not be good. |
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Usually aircraft are only used on massive forest fires. The aircraft will scoop water from the sea or nearby lake to dump on the fire, bucket-brigade style, around one tonne per journey. |
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There are thirty-eight thousand million million tons of water on land and one thousand three hundred million million tons of water in the sea. |
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Don't fire-fgthing aircraft take off empty and fill up from the most convenient water source? I know that some of them dump water with added fire retardant (probably a better solution than ice) |
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oneoffdave, an eductor can be used to move the saltwater without corroding a pump. See link for description of eductor and a few samples. The Slurry eductor would do the trick, but might be better to use a liquid eductor in an airplane. |
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Oops forgot: angel, I do think you're probably right, but I like talking about eductors. |
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The most detrimental aspect of using ice over water would be the expansion of water as it turns into ice. You just couldn't carry the same payload.
Perhaps someone out there with math skills could figure whether the cooling effect of ice would off-set the reduction in volume of water.. |
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