Simple Tunnel ram Question

[Kevin Johnson]

...
I am open to being convinced, but your analogies with differing densities don't fit the actual scenario.
Could you please edit one of the images in paint to make your point?
When you do, please include the difference in the atmospheric pressure at the different openings; I think your previous explanation ignored that.

BTW, I just did a quick estimate of the acceleration of air in an engine and got 2,000 G's
If that number is correct, and in the best scenario, gravity added 1 G to that, it is 0.0005 significant.

Hi Jon,

I just picked a number at random for h1 : 5 inches (0.000127km).

I am assuming that the base of h1 is at sea level and that the gravitational constant at sea level is 9.8ms^-2 (a gift considering our misshapen planet).

So, 9.799999611062511ms^-2 is the gravitational constant at 5” above sea level.

Assume 29 in/Hg pressure at sea level to make your calculations easier (another gift).

Now, with this information YOU can calculate the difference in atmospheric pressure at the different openings for YOUR diagram.

With this information I would like you to then calculate how many moles of atoms are present in a reasonable manifold vacuum of 14.5 in/Hg.

Please diagram, using Paint if you prefer, the individual atoms and then assign random velocity vectors. There's more to come.

~~~~~~~~~~~~~~~~~~

So basically the technique is to divert your opponent and get him or her to waste prodigious amounts of time and then demand yet another task. I never would have guessed this in a million years.

[digger]

Given that there are no local density differences in the original scenario, I think it is fair to say that my argument is correct.

no the PE you stated was plain wrong. i.e the change in height going from point A to point B on the original picture was incorrect irresepective of whether or not this results in additional KE

I am open to being convinced, but your analogies with differing densities don't fit the actual scenario.
Could you please edit one of the images in paint to make your point?
When you do, please include the difference in the atmospheric pressure at the different openings; I think your previous explanation ignored that.

BTW, I just did a quick estimate of the acceleration of air in an engine and got 2,000 G's
If that number is correct, and in the best scenario, gravity added 1 G to that, it is 0.0005 significant.

It's just the difference in height of the openings.
Yes like I said in earlier posts the change in height is a negligible compared to the other terms (pressure differences ) the argument was whether it was actually truly zero

[SchmidtMotorWorks]

no the PE you stated was plain wrong. i.e the change in height going from point A to point B on the original picture was incorrect irresepective of whether or not this results in additional KE

I am open to being convinced, but your analogies with differing densities don't fit the actual scenario.
Could you please edit one of the images in paint to make your point?
When you do, please include the difference in the atmospheric pressure at the different openings; I think your previous explanation ignored that.

BTW, I just did a quick estimate of the acceleration of air in an engine and got 2,000 G's
If that number is correct, and in the best scenario, gravity added 1 G to that, it is 0.0005 significant.

It's just the difference in height of the openings.
Yes like I said in earlier posts the change in height is a negligible compared to the other terms (pressure differences ) the argument was whether it was actually truly zero

I think it might be incorrect to use the openings as the reference point.
I am not at a computer at the moment so I can't easily make a diagram. So imagine that you added a larger diameter duct on top of the existing duct.
If the larger extended duct is a benefit, then imagine the duct is one mile wide.
Now imagine it is one mile tall.
Then to the height of the atmosphere.

It seems to me that the reference point should not be the tops of the ducts. Instead it should be the mass of all atmosphere above the destination.

One reason I think that is the correct way to look at it is that we are not considering a fluid in a vacuum, it is effected by the atmosphere above it. And when the fluid in the ducts moves, the atmosphere accelerates to fill the space. Given that it seems wrong to consider them in isolation.

[SchmidtMotorWorks]

no the PE you stated was plain wrong. i.e the change in height going from point A to point B on the original picture was incorrect irresepective of whether or not this results in additional KE

I am open to being convinced, but your analogies with differing densities don't fit the actual scenario.
Could you please edit one of the images in paint to make your point?
When you do, please include the difference in the atmospheric pressure at the different openings; I think your previous explanation ignored that.

BTW, I just did a quick estimate of the acceleration of air in an engine and got 2,000 G's
If that number is correct, and in the best scenario, gravity added 1 G to that, it is 0.0005 significant.

It's just the difference in height of the openings.
Yes like I said in earlier posts the change in height is a negligible compared to the other terms (pressure differences ) the argument was whether it was actually truly zero

I think it might be incorrect to use the openings as the reference point.
I am not at a computer at the moment so I can't easily make a diagram. So imagine that you added a larger diameter duct on top of the existing duct.
If the larger extended duct is a benefit, then imagine the duct is one mile wide.
Now imagine it is one mile tall.
Then to the height of the atmosphere.

It seems to me that the reference point should not be the tops of the ducts. Instead it should be the mass of all atmosphere above the destination.

One reason I think that is the correct way to look at it is that we are not considering a fluid in a vacuum, it is effected by the atmosphere above it. And when the fluid in the ducts moves, the atmosphere accelerates to fill the space. Given that, it seems wrong to consider them in isolation.

[Kevin Johnson]

Oh my gosh, you will have some wicked calculations to do given that the normal hydrostatic formulae do not account for the variance of G with altitude. Be sure to budget for the additional CPU hours and for heavens sake keep track of the lunar cycles and local weather conditions in the planetary boundary layer as this could really throw everything to pot.

Waiting for the diagram.

[digger]

The common reference is not the opening but the vessel. The difference between A and B is where the air starts to move and the kinetic energy starts (I.e the openings)

The hydrostatic reference is different

[Kevin Johnson]

The common reference is not the opening but the vessel. The difference between A and B is where the air starts to move and the kinetic energy starts (I.e the openings)

The hydrostatic reference is different

Sorry for the prolepsis. All in good time.

[SchmidtMotorWorks]

The common reference is not the opening but the vessel. The difference between A and B is where the air starts to move and the kinetic energy starts (I.e the openings)

The hydrostatic reference is different

It doesn't seem correct to say that the air motion starts at the openings. The atmosphere above it also moves.

If the material in the ducts were solid and the environment were a vacuum it would seem right to say it begins at the top of the ducts, but that is not the case.

[SchmidtMotorWorks]

In the case of a dam,,,

If the full side of the dam has a drain pipe that protrudes up from the floor of the dam some short distance (to avoid taking in debris) the energy of water flowing through the drain pipe/time would be increased as the water level increased and decline as the water level declined regardless of the length of the protruding end of the pipe (so long as the opening was below the dams water level.)
The head in the pipe is determined by the water level, not the length of the pipe.

This seems to support the argument that PE is determined by the full column of atmosphere not the opening of the duct.

[digger]

The common reference is not the opening but the vessel. The difference between A and B is where the air starts to move and the kinetic energy starts (I.e the openings)

The hydrostatic reference is different

It doesn't seem correct to say that the air motion starts at the openings. The atmosphere above it also moves.

If the material in the ducts were solid and the environment were a vacuum it would seem right to say it begins at the top of the ducts, but that is not the case.

Kinetic energy is v^2 so slow moving air is not significant from energy perspective only once in the pipe or probably just inside 0.5-1" does any significant velocity occur.