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Energy generation

 
 
Dave12
 
Reply Thu 19 Mar, 2009 03:21 pm
If a hollow tube were to be lowered to a sufficient depth in the ocean,would the greater pressure at that depth force the water up the tube if valves in the bottom were then opened, thus driving electricity generating turbines within the tube,would this be a self sustaining system. ??.
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Type: Question • Score: 6 • Views: 2,335 • Replies: 7
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rosborne979
 
  2  
Reply Thu 19 Mar, 2009 04:18 pm
@Dave12,
Unfortunately, it would not be self-sustaining.

Once the valves in the tube were opened the pressure along the entire tube would equalize and the system would stop.

When the initial rush of water filled the pipe you would recover a little bit of the energy that you used to push the pipe down into the water in the first place, but after that everything would stop.

Dave12
 
  1  
Reply Thu 19 Mar, 2009 04:31 pm
@rosborne979,
How would the pressure equalise ?,the pressure from the bottom would be consistently higher than at any any other point above it,I'm not saying that you are wrong in that it would probably not be self sustaining,just trying to figure out why it wouldn't.
rosborne979
 
  1  
Reply Thu 19 Mar, 2009 04:37 pm
@Dave12,
Hi Dave,

If both ends of the tube are open, then the water will fill the tube and the water inside the tube will be the same pressure as the water outside the tube.

Just imagine if the tube were a much larger diameter than a pipe, say it was 100yards in diameter and you sunk it down into the water with both ends open. Then whether you were inside the tube or outside the tube the pressure would be the same. The same thing applies to a 2" pipe.
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dadpad
 
  1  
Reply Thu 19 Mar, 2009 05:30 pm
I know this is gonna be a dumb post but here goes.

one end of a 1000 meter pipe is sealed. Lower the pipe vertically into the water until all but 1 meter is submerged. The air pressure at the top is 14 psi, the water pressure at the bottom is ? greater. now open the bottom of the tube water pressure forces the tube to fill.

How is this pressure lost as the water rises up the tube?
Cycloptichorn
 
  1  
Reply Thu 19 Mar, 2009 05:36 pm
@dadpad,
dadpad wrote:

I know this is gonna be a dumb post but here goes.

one end of a 1000 meter pipe is sealed. Lower the pipe vertically into the water until all but 1 meter is submerged. The air pressure at the top is 14 psi, the water pressure at the bottom is ? greater. now open the bottom of the tube water pressure forces the tube to fill.

How is this pressure lost as the water rises up the tube?


Um. The pressure differential goes away after the tube fills with water. Essentially once it's full of water it's just like any other piece of ocean.

Cycloptichorn
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Thomas
 
  1  
Reply Thu 19 Mar, 2009 06:23 pm
@rosborne979,
rosborne979 wrote:
When the initial rush of water filled the pipe you would recover a little bit of the energy that you used to push the pipe down into the water in the first place, but after that everything would stop.

Minor quibble: I would have said the initial rush of water gives you back exactly the amount of energy you used to push the pipe down into the water in the first place. In both cases, the energy equals the work of displacing the same volume of water against the same pressure. (With opposite signs, of course.)
rosborne979
 
  1  
Reply Fri 20 Mar, 2009 11:14 am
@Thomas,
Thomas wrote:
Minor quibble: I would have said the initial rush of water gives you back exactly the amount of energy you used to push the pipe down into the water in the first place. In both cases, the energy equals the work of displacing the same volume of water against the same pressure. (With opposite signs, of course.)

Ok, here's my quibble quibble Smile On the way down you get help from gravity to push the enclosed pipe down. Also, the waves and temperature and salinity of the ocean vary, so by the time the pipe is uncorked conditions will have changed (ever so slightly) from when the pipe was originally submerged, thus resulting an "approximate" return of energy from the system.

It's funny that I originally chose to say "similar" return of energy rather than "exact" because I was afraid someone would quibble with me about it being an "exact" return. And then the opposite quibble happened. Life is funny Wink
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