Posted by dances_with_barkadas on September 26, 2005, 4:03 am
Let us imagine that Maxwell's Demon has constructed an apparatus for
us.
It comprises two identical vertical pipes capped at the bottom, both
having a gate valve near the bottom which allows the lowest portion to
be sealed off from the upper portion.
We have these empty pipes, and in the first pipe, we spend an amount of
energy to pump water into both portions, then close the gate valve.
In the second pipe, we fill the bottom portion of the pipe with oil,
close the valve, then fill the rest of the pipe with water. Our total
pumping-energy was lower thatn with the first pipe, because oil is
lighter than water, takes less energy to push it around.
I forgot to mention that in both pipes, that upper portion contains a
little paddlewheel which connects ot an electricity generator just
outside the pipe. There's also a certain clever arrangement of baffles
below the paddlewheel.
Three months later, we open both gate valves.
In the first pipe, nothing moves.
In the second pipe, the water in the upper portion flows downward, the
oil in the lower portion floats upward. The baffles are cleverly placed
such that the paddlewheel turns, generating electricity.
Where did this energy come from?!?
By the way, I also want to calculate the speed with which the oil
rises, given its specific gravity. I know the quantity of
gravitational deceleration acting on it, but I don't know how to
calculate the upward force. Ignore all second order effects.
Posted by Robert Morien on September 26, 2005, 5:03 am
dances_with_barkadas@yahoo.com wrote:
> Let us imagine that Maxwell's Demon has constructed an apparatus for
> us.
>
> It comprises two identical vertical pipes capped at the bottom, both
> having a gate valve near the bottom which allows the lowest portion to
> be sealed off from the upper portion.
>
> We have these empty pipes, and in the first pipe, we spend an amount of
> energy to pump water into both portions, then close the gate valve.
>
> In the second pipe, we fill the bottom portion of the pipe with oil,
> close the valve, then fill the rest of the pipe with water. Our total
> pumping-energy was lower thatn with the first pipe, because oil is
> lighter than water, takes less energy to push it around.
>
> I forgot to mention that in both pipes, that upper portion contains a
> little paddlewheel which connects ot an electricity generator just
> outside the pipe. There's also a certain clever arrangement of baffles
> below the paddlewheel.
>
> Three months later, we open both gate valves.
>
> In the first pipe, nothing moves.
>
> In the second pipe, the water in the upper portion flows downward, the
> oil in the lower portion floats upward. The baffles are cleverly placed
> such that the paddlewheel turns, generating electricity.
>
> Where did this energy come from?!?
News will tell you. Just wait
>
> By the way, I also want to calculate the speed with which the oil
> rises, given its specific gravity. I know the quantity of
> gravitational deceleration acting on it, but I don't know how to
> calculate the upward force. Ignore all second order effects.
Posted by tadchem on September 26, 2005, 5:50 am
> Let us imagine that Maxwell's Demon has constructed an apparatus for
> us.
Is he in the Union?
> It comprises two identical vertical pipes capped at the bottom, both
> having a gate valve near the bottom which allows the lowest portion to
> be sealed off from the upper portion.
> We have these empty pipes, and in the first pipe, we spend an amount of
> energy to pump water into both portions, then close the gate valve.
> In the second pipe, we fill the bottom portion of the pipe with oil,
> close the valve, then fill the rest of the pipe with water. Our total
> pumping-energy was lower thatn with the first pipe, because oil is
> lighter than water, takes less energy to push it around.
> I forgot to mention that in both pipes, that upper portion contains a
> little paddlewheel which connects ot an electricity generator just
> outside the pipe. There's also a certain clever arrangement of baffles
> below the paddlewheel.
> Three months later, we open both gate valves.
Why so patient? Are *you* in the Union?
> In the first pipe, nothing moves.
> In the second pipe, the water in the upper portion flows downward, the
> oil in the lower portion floats upward. The baffles are cleverly placed
> such that the paddlewheel turns, generating electricity.
> Where did this energy come from?!?
...Work you did against gravity when you first lifted the water and the oil
into the pipe
> By the way, I also want to calculate the speed with which the oil
> rises, given its specific gravity.
You'll need to know a lot more.
What is the viscosity of the oil and of the water, the temperature of the
system, the surface energy of the oil/water interface, the diameter of the
gate valve, and so on...?
For example, below 0° C the water won't flow unless you have several hundred
feet of it (a glacier), and then only very slowly.
Best set up the experiment and *measure* it.
> I know the quantity of
> gravitational deceleration acting on it, but I don't know how to
> calculate the upward force. Ignore all second order effects.
See Archimedes about that one. He is the Principle authority on buoyancy.
Tom Davidson
Richmond, VA
Posted by donstockbauer on September 26, 2005, 6:00 am
How about a big pipe created going out into space? It removes all the
pollution of the Earth, it pumps it right on out there. What principle
does it use for power?????
The venturi effect.
Thank you. No applause, uh save it for the end.
- Don
Posted by dave.harper on September 29, 2005, 2:54 pm
donstockbauer@hotmail.com wrote:
> How about a big pipe created going out into space? It removes all the
> pollution of the Earth, it pumps it right on out there. What principle
> does it use for power?????
> The venturi effect.
Well, I can't tell if you're kidding, but I'm going to assume you're
not.
The venturi effect requires a fluid velocity to create a pressure
difference. There's not really any real velocity with the situation
you describe. I think you mean just the basic air pressure difference
between the ground and space? If that was the case, why do you need a
tube at all? Why doesn't the air just rush out into space? Answer:
gravity. The air pressure on the earth's surface is due to gravity,
and air can't be sucked out into space because the energy required to
lift it is more than the energy you can get from the pressure
difference.
Dave
XML site map
> us.
>
> It comprises two identical vertical pipes capped at the bottom, both
> having a gate valve near the bottom which allows the lowest portion to
> be sealed off from the upper portion.
>
> We have these empty pipes, and in the first pipe, we spend an amount of
> energy to pump water into both portions, then close the gate valve.
>
> In the second pipe, we fill the bottom portion of the pipe with oil,
> close the valve, then fill the rest of the pipe with water. Our total
> pumping-energy was lower thatn with the first pipe, because oil is
> lighter than water, takes less energy to push it around.
>
> I forgot to mention that in both pipes, that upper portion contains a
> little paddlewheel which connects ot an electricity generator just
> outside the pipe. There's also a certain clever arrangement of baffles
> below the paddlewheel.
>
> Three months later, we open both gate valves.
>
> In the first pipe, nothing moves.
>
> In the second pipe, the water in the upper portion flows downward, the
> oil in the lower portion floats upward. The baffles are cleverly placed
> such that the paddlewheel turns, generating electricity.
>
> Where did this energy come from?!?