Mile High Hg scheme

[matt brown]

Here's a thought experiment from decades ago that used to float around the web.

mile high Hg scheme.png (4.05 KiB) Viewed 1173 times

It's my Mile High Tube scheme where a first tube of liquid mercury descends to a boiler that drives an engine before spent vapor ascends a second tube to a condenser. The only obvious thing is that the massive pressure of 'mile high' mercury at boiler will nix typical feed pump requirement.

Maybe Fool can spot the thing that had many scratching their heads ???

[Fool]

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Cute.

The temperature gradient going a mile high would condense the Hg before turning the top corner.

Effectively the whole 'up' tube would need to be the boiler.

I've been exploring that idea and a 100' tree and water and vacuum. And one tube in the sun. And the other in the shade.

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[Fool]

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Oh of course good luck containing a pressure of 31119.52675392 psi, at least with any real materials.

And a mile high tower. Tallest current record is 2,717 feet.

Of course. I thought that was obvious. LOL

If I could afford 10' of mercury, I'd be tempted to build one myself just to prove the concept. Anyone want to pay me to try? LOL

On the other hand, it would take a minimum of 100' feet of 316 stainless steel 4" tubing, to build one for water. Many other things would be needed too, to make it work. The heater could be a furnace and chimney or solar vertical trough parabolic reflector and shade. Maybe a pivoting mechanism to keep it pointed into the sun. Excellent. I would be happy to build one with sufficient funding. It could provide pure fresh water from salt water. For $10,000.00 or more I could submit a simple proposal, nothing too complete.

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[Fool]

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How do you condense mercury vapor in a vacuum?

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[matt brown]

How do you condense mercury vapor in a vacuum?

Remember this is a thought experiment, so

(1) mercury will be condensed in condenser similar to typical Rankine cycle

(2) shown tubes could be pipes or hoses along hillside

(3) everything is ideal, don't sweat friction, insulation, etc.

I thought you'd spot the magic of this scheme without a phase diagram, but now I'll have to add some more tidbits. The 'mile high' dimension was chosen to game critical point where the latent heat of vaporization disappears. Now reconsider the energy balance for this cycle.

The major snag was addressing the vapor side of cycle which drew a range of comments in past...

[VincentG]

My initial thought was that the weight of a mile of vapor will be the same weight as a mile of liquid. Cycle will only flow if less vapor mass is allowed to rise than liquid mass is falling.

[Fool]

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The vapor weight will definitely be significant. Not the same as liquid, but more than air. Rasing a heavy vapor molecule that high would certainly require plenty of energy. Solar?

I don't think a mile high is necessary. Mercury boils at a lower temperature if in a vacuum. Mercury makes its own perfect vacuum for any column taller than 760 mm.

All that would be needed is two tubes 1 meter long. And a heater and cooler. And a few other things. LOL. Think drinking bird.

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[matt brown]

Mercury has a critical pressure of 1720 atm and a critical temperature of 1750k. The pitch here is to nix the latent heat of vaporization...

[Fool]

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By lifting heavy mercury molecules a mile high? No free lunch.

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[Fool]

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The following web page should give anyone the Heebie-jeebies:

http://www.douglas-self.com/MUSEUM/POWE ... ercury.htm

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[matt brown]

My initial thought was that the weight of a mile of vapor will be the same weight as a mile of liquid. Cycle will only flow if less vapor mass is allowed to rise than liquid mass is falling.

Don't you mean that...the cycle will only flow if rising vapor mass equals falling liquid mass ?

[matt brown]

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The following web page should give anyone the Heebie-jeebies:

http://www.douglas-self.com/MUSEUM/POWE ... ercury.htm

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Awesome link, thanks !!! This mile high scheme was purely a thought experiment where I picked an eye popping example for effect. I come from the steam camp, but not your typical Rankine stuff. Typical Rankine schemes have a latent heat of vaporization akin backwork of single phase gas. Consider water which has such a high latent heat of vaporization that half the total heat energy into water between STP and critical point is this latent heat. Unless you're running supercritical values with steam then at least half your heat energy input will be lost during condensation unless you can utilize this low grade "waste" heat (ancillary process, heating sewers during winter, etc).

The gimmick here is to nix this latent heat via gaming critical values and use the critical pressure on the liquid side vs the critical temperature on the vapor side. In this manner, the input heat supplies the kinetic energy for the gas to flow against gravity similar Minto Wheel, but the liquid side is akin a dam (this scheme) vs a river (Minto Wheel). However, the power output for this scheme remains PV work from "conventional" engine. The major obstacle I see is keeping the vapor T constant until near condenser while adding HeatX scheme between condenser and boiler.

Something like propane would likely be more appropriate and vapor side could include another gas for partial pressure similar Electrolux absorption reefer. Someone should do a study on variables for low end input (geothermal, DIY, etc).

[Fool]

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I get entertainment out of your schemes for attempting to break Carnot, as I do from Tom and VincentG as well. Toms is the easiest to see through, then VincentG. You get a bit more tricky at times.

Let's remove the boiler and condenser. Engine outputs Work=mgh or as you like to say it, 'PV'=mgh.

So replace the up tube side with a conveyer. It moves a little mass at a time so as to not over tax it. M up h high in gravity g or work to run weight up mgh. Now it is obvious that work up equals work down, for no free lunch. Zero zero gain.

Now put the boiler back in. Add the latent heat of vaporization, super heat it to say 1500 K and more. Hot enough to expand against its own weight up one mile, temperature will depend on bittom gas pressure. The amount of heat put into the gas will be equal to mgh, plus the latent heat of vaporization. Law of conservation of energy.

After the gas turns over the top, it must be cooled to return it to liquid. This is tantamount to back-work and rejection of the latent heat of vaporization. Also called heat of compression.

Unless I missed something. Carnot is an optimist.

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[matt brown]

I get entertainment out of your schemes for attempting to break Carnot, as I do from Tom and VincentG as well. Toms is the easiest to see through, then VincentG. You get a bit more tricky at times.

I've have more time and interest to consider energy than most guys.

Let's remove the boiler and condenser. Engine outputs Work=mgh or as you like to say it, 'PV'=mgh.

So replace the up tube side with a conveyer. It moves a little mass at a time so as to not over tax it. M up h high in gravity g or work to run weight up mgh. Now it is obvious that work up equals work down, for no free lunch. Zero zero gain.

Clearly PMD that ain't going anywhere.

Now put the boiler back in. Add the latent heat of vaporization, super heat it to say 1500 K and more. Hot enough to expand against its own weight up one mile, temperature will depend on bittom gas pressure. The amount of heat put into the gas will be equal to mgh, plus the latent heat of vaporization. Law of conservation of energy.

I never looked closely into this scheme, but agree that input will equal mgh due to 1st law. However, this scheme includes nixing latent heat of vaporization via critical pressure. So, in a way, this is similar your common PMD setup, but where boiler acts as a gate at bottom between tubes where this 'gate' also includes an engine. Another way to view this is that each tube has a different density separated by pressure gate at bottom and temperature gate at top. Yes, the engine will have massive back pressure resistance (due to high tube) but this merely means that some (lots) of the thermal energy never converts to PV work...OK as long as the heat is not lost in vapor tube and recovered via heatX prior condenser.

In past, a physicist thought that a 'wholesale' version (megawatts and tons of vapor in vapor tube) would have a massive pressure gradient wherein (at best) a continuous isothermal expansion during vapor tube ascent would continuously suck heat from lower part of vapor tube and 'steal' the energy during this expansion that I was hoping to 'steal' near condenser. Yet, if the vapor density after engine was low enough then this would be like launching tiny spitwads into artificial space (condenser vacuum) similar to a mini (but worthless) hydrological cycle.

Unless I missed something. Carnot is an optimist.

"I never let my schoolin' interfere with my education." - Mark Twain

I don't waste much time trying to beat Carnot, but if the situation arise, why not ??? Someday, someone will, and this isn't as nutty as over-unity.

[VincentG]

My initial thought was that the weight of a mile of vapor will be the same weight as a mile of liquid. Cycle will only flow if less vapor mass is allowed to rise than liquid mass is falling.

Don't you mean that...the cycle will only flow if rising vapor mass equals falling liquid mass ?

I said what I meant wrong as it may be. What would drive the vapor upwards if it had the same mass as falling liquid?