Yeah, interesting how words can be so fuzzy.
For the cycle to maintain, the same mass must ascend as descend (same kg up and down per time constant). The liquid has only downward force due to gravity while the vapor can use its kinetic energy against gravity. In OP, the liquid slowly sinks while the vapor tries to "get out of Dodge" at the speed of sound. This thought experiment is right about the limit of most average guys, since it introduces too many obscure issues. My premise of nixing the latent heat of vaporization was sweet, but such schemes must be carefully considered.
In past, this scheme drew many odd comments until a physicist sank it with a hipshot. Yep, the devil was in the details, not my latent heat premise.
Mile High Hg scheme
Re: Mile High Hg scheme
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VincentG, The vapor is driven up by its own pressure. Gasses expand to fill the container. If hot enough, the pressure will be high enough to push all the way to the top.
Matt, breaking the second law allows overunity. Just as nutty, but more obfuscated.
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VincentG, The vapor is driven up by its own pressure. Gasses expand to fill the container. If hot enough, the pressure will be high enough to push all the way to the top.
Matt, breaking the second law allows overunity. Just as nutty, but more obfuscated.
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matt brown
- Posts: 749
- Joined: Thu Feb 10, 2022 11:25 pm
Re: Mile High Hg scheme
For anyone who wanders by in future, here's a better graphic of this scheme:
The vapor tube values are totally bogus and merely pulled out of the air, but they'll suffice.
The basic idea is to avoid the latent heat of vaporization during 'boiling' via using the critical pressure of the working fluid (ie no latent heat at/above critical pressure). Despite crazy values shown, everything is hunky-dory on fluid side, but the rest of this scheme has issues:
(1) the boiler heats the mercury and converts it from HP fluid to HP gas
(2) then HP gas does PV work in engine
(3) water expands about 1700x from liquid to gas, so I used bogus 1700 bar to 100 bar as round numbers which is 17x expansion with bogus 2000k to 1000k values
(4) these bogus tube values merely indicate that PV work was done by engine while exhaust T will have to be high to maintain exhaust P that drives vapor column (needs that kinetic energy to drive gas mass)
(5) note high heat input from 300k to 2000k, despite no latent heat input due to critical pressure 'advantage'
(6) assuming bogus 1000k exhaust value, this heat must recovered prior 300k condenser or "the crow comes home"
The problem with this pie in the sky scheme is that the vapor column has its own agenda and the variable pressure (my bogus 100 bar >>> 1 bar) means that this vapor is expanding during its ascent, thus cooling during its ascent. No one needs a calculator to consider what happens to any 1000k gas if it expands 100x (my bogus vapor column P values). So, any wouldbe heat recovery disappears and likely equates to conventional latent heat of vaporization. Kinda funny how this energy balance stuff always jacks a slick scheme LOL.
Very interesting how Fool analyzed this from the get-go, ignoring critical value premise. This makes me think that he's considered something similar...
- Hg mile high tube.png (6.89 KiB) Viewed 680 times
The basic idea is to avoid the latent heat of vaporization during 'boiling' via using the critical pressure of the working fluid (ie no latent heat at/above critical pressure). Despite crazy values shown, everything is hunky-dory on fluid side, but the rest of this scheme has issues:
(1) the boiler heats the mercury and converts it from HP fluid to HP gas
(2) then HP gas does PV work in engine
(3) water expands about 1700x from liquid to gas, so I used bogus 1700 bar to 100 bar as round numbers which is 17x expansion with bogus 2000k to 1000k values
(4) these bogus tube values merely indicate that PV work was done by engine while exhaust T will have to be high to maintain exhaust P that drives vapor column (needs that kinetic energy to drive gas mass)
(5) note high heat input from 300k to 2000k, despite no latent heat input due to critical pressure 'advantage'
(6) assuming bogus 1000k exhaust value, this heat must recovered prior 300k condenser or "the crow comes home"
The problem with this pie in the sky scheme is that the vapor column has its own agenda and the variable pressure (my bogus 100 bar >>> 1 bar) means that this vapor is expanding during its ascent, thus cooling during its ascent. No one needs a calculator to consider what happens to any 1000k gas if it expands 100x (my bogus vapor column P values). So, any wouldbe heat recovery disappears and likely equates to conventional latent heat of vaporization. Kinda funny how this energy balance stuff always jacks a slick scheme LOL.
Very interesting how Fool analyzed this from the get-go, ignoring critical value premise. This makes me think that he's considered something similar...
Re: Mile High Hg scheme
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Yes, but my heater, solar, goes to the top. Then a nozzle through an engine turbine at the top, in the gaseous phase, cooling, condensing, liquefying, and pulling a vacuum on the way down. Enough vacuum on the way down to make the water on the hot side boil on the way up, at 100F or so.
I'd have to think more to see if trying to, "avoid the latent heat of vaporization", would be any benefit. It kind of sounds like you've already ruled it out.
My problem is vacuum boiling means very low density through the turbine. I.E., low power per size and weight. And of course, low efficiency from the Carnot rule, but the fuel is cheap. The apparatus, maybe not so much. Hopefully enough power to keep the vacuum going.
Of course using a height difference on the cold side through a water turbine might help. It still would be low T.
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Yes, but my heater, solar, goes to the top. Then a nozzle through an engine turbine at the top, in the gaseous phase, cooling, condensing, liquefying, and pulling a vacuum on the way down. Enough vacuum on the way down to make the water on the hot side boil on the way up, at 100F or so.
I'd have to think more to see if trying to, "avoid the latent heat of vaporization", would be any benefit. It kind of sounds like you've already ruled it out.
My problem is vacuum boiling means very low density through the turbine. I.E., low power per size and weight. And of course, low efficiency from the Carnot rule, but the fuel is cheap. The apparatus, maybe not so much. Hopefully enough power to keep the vacuum going.
Of course using a height difference on the cold side through a water turbine might help. It still would be low T.
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Re: Mile High Hg scheme
Interesting.
Why not have valve a mile high before condenser? Close valve and let vapor column build in pressure until pressure at valve is high enough, then open valve enough to let vapor expand enough into condenser that it again picks up some heat from mile high solar tank. That will feed next power cycle as valve is closed again.
I always thought just boiling water with conventional fuel at high elevation power plant might do the trick? Rain water collection or natural lake would be ideal, but either way not practical.
Why not have valve a mile high before condenser? Close valve and let vapor column build in pressure until pressure at valve is high enough, then open valve enough to let vapor expand enough into condenser that it again picks up some heat from mile high solar tank. That will feed next power cycle as valve is closed again.
I always thought just boiling water with conventional fuel at high elevation power plant might do the trick? Rain water collection or natural lake would be ideal, but either way not practical.
Re: Mile High Hg scheme
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Expanding gas cools but it expands not condenses.
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Expanding gas cools but it expands not condenses.
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Re: Mile High Hg scheme
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Expanding gas through a condenser to pick up heat. Nice fantasy. Care to elaborate on how that would work? Temperatures and pressures please. And maybe densities?
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Expanding gas through a condenser to pick up heat. Nice fantasy. Care to elaborate on how that would work? Temperatures and pressures please. And maybe densities?
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Re: Mile High Hg scheme
I was asking not preaching.
If the expansion of the vapor can be delayed until it's in the condenser, could a solar heater or even ambient heat at 1mile put enough heat back to make the cycle viable? Matt said the cooling from expansion is what kills the cycle as the vapor is ascending in the tube.
This would obviously require a modified two chamber "condenser" where the first stage acts more like an evaporator and the second stage is the actual condenser.
If the expansion of the vapor can be delayed until it's in the condenser, could a solar heater or even ambient heat at 1mile put enough heat back to make the cycle viable? Matt said the cooling from expansion is what kills the cycle as the vapor is ascending in the tube.
This would obviously require a modified two chamber "condenser" where the first stage acts more like an evaporator and the second stage is the actual condenser.
Re: Mile High Hg scheme
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I can't see what you think any beneficial mechanism would be.
The expansion during a mile elevation of any vapour column would come from the weight reduction as it nears the top. By allowing the pressure at the top to build, the pressure at the bottom will build. The pressure at the bottom is what's pushing the vapor to the top. Expansive cooling is not the worst of the problems in the case of mercury. Mercury requires several hundred degrees above ambient to vaporize, even at very low pressures. Sure the pipe could be double walled insulated thermos like pipe. But when at the top it would still take a temperature much higher than ambient to 'boil'. I don't know the Q heat loss per foot length of thermos bottle.
Now you want to increase the pressure, which would increase the boiling point, to then release the pressure to absorb heat while condensing.
Condensing is just the opposite. Increase pressure, boiling point above ambient, let heat out, T higher than ambient, dropping until at ambient, now condensing the vapour.
That is why I suggested that the entire mile high going up section be heated, as the pressure drops, boiling point drops, providing vapor all the way to the top. It only works if there is free solar heat, and cheap pipes all the way to the top. Think parabolic trough reflector.
With some fluids boiling point can be adjusted some with a vacuum. For mercury, not so much.
For Matt's idea, the pressure is the same for the vapor and liquid sides. The density of the hot vapor is lower than for the cold vapor. That has the liquid vapor transition altitude higher on the cold side than the hot side. So there will be a driving pressure head to push the liquid through the turbine and into the boiler.
For Vincent's idea, pressure is built up before the condenser, and release through it, the pressure from weight must build up to above the ambient temperature now at a lower pressure than the hot vapor, for it to condense on the way down. The liquid gas transition altitude will be lower on the cold side. The cold side will need to be much longer.
There goes the pressure difference to drive the liquid into the hot side. Extra outside work energy will be needed to pump liquid into the boiler. It won't gravity feed, as Matt was hoping.
It becomes a regular steam engine with no benefit from gravity. As expected. Weight up weight down. Like a waterwheel that can't dump out the water.
What does work, is the Minto Wheel.
https://en.m.wikipedia.org/wiki/Minto_wheel
The pressure change from bottom to top is minimal, it uses an easily vaporized low density fluid, like propane, butane, or freon. So the boiling point at the bottom is below the temperature at the bottom, and the boiling point at the top is still above ambient.
It is a solar Th heated, and a Ambien Tc cooled, engine.
The drawback is efficiency and cost per dollar of construction.
The mass of the fluid and metal bulb, must be heated and cooled. They both really are wasted heat each cycle, and contributes nothing to the work output. It is in addition to the Carnot necessary heat rejection losses.
Now my thought is to use several displacer chambers to power a Minto like cold wheel such that just the displacer gas is heated and cooled and piped to the wheel, efficiency would improve. Or just have a well designed Stirling Engine.
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I can't see what you think any beneficial mechanism would be.
The expansion during a mile elevation of any vapour column would come from the weight reduction as it nears the top. By allowing the pressure at the top to build, the pressure at the bottom will build. The pressure at the bottom is what's pushing the vapor to the top. Expansive cooling is not the worst of the problems in the case of mercury. Mercury requires several hundred degrees above ambient to vaporize, even at very low pressures. Sure the pipe could be double walled insulated thermos like pipe. But when at the top it would still take a temperature much higher than ambient to 'boil'. I don't know the Q heat loss per foot length of thermos bottle.
Now you want to increase the pressure, which would increase the boiling point, to then release the pressure to absorb heat while condensing.
Condensing is just the opposite. Increase pressure, boiling point above ambient, let heat out, T higher than ambient, dropping until at ambient, now condensing the vapour.
That is why I suggested that the entire mile high going up section be heated, as the pressure drops, boiling point drops, providing vapor all the way to the top. It only works if there is free solar heat, and cheap pipes all the way to the top. Think parabolic trough reflector.
With some fluids boiling point can be adjusted some with a vacuum. For mercury, not so much.
For Matt's idea, the pressure is the same for the vapor and liquid sides. The density of the hot vapor is lower than for the cold vapor. That has the liquid vapor transition altitude higher on the cold side than the hot side. So there will be a driving pressure head to push the liquid through the turbine and into the boiler.
For Vincent's idea, pressure is built up before the condenser, and release through it, the pressure from weight must build up to above the ambient temperature now at a lower pressure than the hot vapor, for it to condense on the way down. The liquid gas transition altitude will be lower on the cold side. The cold side will need to be much longer.
There goes the pressure difference to drive the liquid into the hot side. Extra outside work energy will be needed to pump liquid into the boiler. It won't gravity feed, as Matt was hoping.
It becomes a regular steam engine with no benefit from gravity. As expected. Weight up weight down. Like a waterwheel that can't dump out the water.
What does work, is the Minto Wheel.
https://en.m.wikipedia.org/wiki/Minto_wheel
The pressure change from bottom to top is minimal, it uses an easily vaporized low density fluid, like propane, butane, or freon. So the boiling point at the bottom is below the temperature at the bottom, and the boiling point at the top is still above ambient.
It is a solar Th heated, and a Ambien Tc cooled, engine.
The drawback is efficiency and cost per dollar of construction.
The mass of the fluid and metal bulb, must be heated and cooled. They both really are wasted heat each cycle, and contributes nothing to the work output. It is in addition to the Carnot necessary heat rejection losses.
Now my thought is to use several displacer chambers to power a Minto like cold wheel such that just the displacer gas is heated and cooled and piped to the wheel, efficiency would improve. Or just have a well designed Stirling Engine.
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Re: Mile High Hg scheme
The point was to use a slightly higher exhaust pressure from the engine, combined with a valve at the top, and together maybe they can reduce the expansion ratio while traveling up the tube enough to make the cycle viable.
I don't know the real numbers associated with mercury but a 100 bar engine exhaust from a 1700bar boiler pressure seems like a huge drop. What would change if the exhaust pressure was 200, 300, or 400 bar? The gravity fed pressure is still higher than that, no?
I don't know the real numbers associated with mercury but a 100 bar engine exhaust from a 1700bar boiler pressure seems like a huge drop. What would change if the exhaust pressure was 200, 300, or 400 bar? The gravity fed pressure is still higher than that, no?
Re: Mile High Hg scheme
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Well, any engineer knows, the devil is in the numbers.
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Well, any engineer knows, the devil is in the numbers.
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Re: Mile High Hg scheme
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I think Matt's idea would work for a much lighter fluid, and with a shorter elevation. But it won't beat Carnot. Sill solar powered it would be way more efficient than a Minto Wheel or Drinking Bird. It could scale more easily too. If run from a parabolic trough, it's efficiency could be quite high.
The pressure hot and cold top sides needs to be equal. Increasing pressure at the top hot seems to shut it down, more than helpful. Increasing pressure on the lower cold side, through a turbine, would be beneficial.
Thanks to Matt.
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I think Matt's idea would work for a much lighter fluid, and with a shorter elevation. But it won't beat Carnot. Sill solar powered it would be way more efficient than a Minto Wheel or Drinking Bird. It could scale more easily too. If run from a parabolic trough, it's efficiency could be quite high.
The pressure hot and cold top sides needs to be equal. Increasing pressure at the top hot seems to shut it down, more than helpful. Increasing pressure on the lower cold side, through a turbine, would be beneficial.
Thanks to Matt.
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matt brown
- Posts: 749
- Joined: Thu Feb 10, 2022 11:25 pm
Re: Mile High Hg scheme
I'll return to this thread in near future, but until then, enjoy this video
https://www.youtube.com/watch?v=0syJ8L0fRp8
This reminds me of Elon's favorite interview question:
If you row out into a lake and dump a bunch of weight overboard, what happens to the level of the lake ?
As a guy who's spent too much time designing and building sailboats, I knew this in a heartbeat. Nevertheless, a great question for the cocky KIA guys...
clue: I ran this past my boss last week who didn't agree with my sketchy answer until I reached in my pocket and pulled out 2 coins...
- the question everyone gets wrong.png (128.97 KiB) Viewed 399 times
https://www.youtube.com/watch?v=0syJ8L0fRp8
This reminds me of Elon's favorite interview question:
If you row out into a lake and dump a bunch of weight overboard, what happens to the level of the lake ?
As a guy who's spent too much time designing and building sailboats, I knew this in a heartbeat. Nevertheless, a great question for the cocky KIA guys...
clue: I ran this past my boss last week who didn't agree with my sketchy answer until I reached in my pocket and pulled out 2 coins...