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The "Fire Hose" problem


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#1 Freon

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Posted 25 March 2009 - 03:39 PM

Oh mods, please forgive me for making a work related post...

I am trying to keep some people from making a mistake here at the office. I need an example of what I have always called "the fire hose problem". The basis of the problem is to show the reason that firemen use sectional hoses instead of large hose reels on fire trucks. (You often see a small reel on most fire trucks) We all know the reason why; the friction losses in several hundred feet of reeled-up hose are huge. While sectional hoses can be made-up to length. I don't want to start from scratch on this.

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#2 sschell_PE

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Posted 25 March 2009 - 05:06 PM

I was sure this was a euphemism...

#3 Capt Worley PE

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Posted 25 March 2009 - 07:32 PM

Bigray could help with this one, but you've confused me. You talking about the hose they lay off the back of the truck?

#4 dastuff

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Posted 25 March 2009 - 08:21 PM

This seems the same as a friction loss bernouli's type problem...

Instead of a pipe, you have a fire hose.

#5 Wolverine

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Posted 26 March 2009 - 01:04 PM

In electrical terms, power comes out of a generator at 13.8kV, which is pretty close to the correct voltage needed at the transformer just outside your house. So why don't we just connect the big generator to some cheap little distribution wires on wooden poles and run that to your house? Why do we build giant metal transmission structures on 100 foot right-of-ways that zig-zag all over the state?

It's because the generators are located in East Bumbleflip and you live in Dingleblatt City. The losses in a small wire on the 100 mile journey would leave you with not enough to power a light bulb at the end of the line. So we jack it up by a factor of 10 or 20X, put it in BIG wires, and it sails nicely across the country.

Big power needs a BIG pipe, because you can't hook up a water tower to a garden hose. But that is right back to using water as an analogy, which is a much better way to explain it in the first place.

Maybe you could go to Home Depot and get 100' of 1/4" plastic tubing, then challenge someone to use it as a straw to sip out of a Coke can on the other end of the building?

#6 Freon

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Posted 26 March 2009 - 01:35 PM

I managed to de-fuse the problem. A ten minute discussion using the fire truck example worked. I did a little supporting math and the idea was scraped, as it should have been.

#7 TXengrChickPE

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Posted 26 March 2009 - 02:50 PM

QUOTE (Wolverine @ Mar 26 2009, 08:04 AM) <{POST_SNAPBACK}>
Maybe you could go to Home Depot and get 100' of 1/4" plastic tubing, then challenge someone to use it as a straw to sip out of a Coke can on the other end of the building?

That's awesome! smile.gif

#8 IlPadrino

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Posted 26 March 2009 - 03:04 PM

QUOTE (Wolverine @ Mar 26 2009, 09:04 AM) <{POST_SNAPBACK}>
Maybe you could go to Home Depot and get 100' of 1/4" plastic tubing, then challenge someone to use it as a straw to sip out of a Coke can on the other end of the building?


I'm not sure that would be so hard... at low velocity even with with such a large L/D (4800), friction loss should be reasonable. I could do it! But then again, I'm quite the sucker! Still, maybe I should use the Energy Equation before betting any money on this.

#9 sschell_PE

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Posted 14 April 2009 - 03:09 AM

QUOTE (IlPadrino @ Mar 26 2009, 08:04 AM) <{POST_SNAPBACK}>
I could do it! But then again, I'm quite the sucker!


uhhh... TMI...

#10 IlPadrino

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Posted 14 April 2009 - 12:10 PM

QUOTE (dude @ Apr 13 2009, 11:09 PM) <{POST_SNAPBACK}>
uhhh... TMI...


Yeah... well, better a sucker than a blower!




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