5 ms·

Why not both? And why can't you state your analysis without calling other analyses offered in good faith bullshit?

mikeash 9y ago
This site is pretty much on the same level as sites advertising perpetual motion machines. I don't need every little detail to observe that it's bullshit. Unless you confine a parcel of air in all directions, it will match the pressure of the surrounding air. Consider an arbitrary cubic meter of air at 15°C at sea level at the base of the tube. Now raise it 1,000m inside the tube. That air now occupies roughly 1.12 cubic meters and is at a temperature of roughly 5°C, the same as if it had risen 1,000m outside the tube. The tube will work sometimes, but only when the atmosphere is unstable. Since the chimney is 5km tall, that means thunderstorm conditions. You can only extract energy from a tube like this if there's some energy potential between the two ends. The atmosphere is constantly erasing differences in energy potential, so large-scale differences are ephemeral.
- elago 9y ago
  >You can only extract energy from a tube like this if there's some energy potential between the two ends. The difference in temperature between the air at the bottom of the tube and the top of the tube is that potential.
  - mikeash 9y ago
    It's not, because it's canceled out by the pressure difference. The net energy change of raising a parcel of air in the atmosphere is roughly zero. (Depending on the exact temperature profile of the atmosphere at any given moment, of course.)
    - deleted 9y ago
      [deleted]
    - elago 9y ago
      Consider either a thermoelectric generator[1] or sterling engine[2]. Either of these can produce power given a hot and cold reservoir. Of course neither device is appropriate for this specific application (the temperature differential between 'surface' air and air in the high atmosphere), but they demonstrate the concept that any temperature gradient represents a form of potential energy. Whether or not this specific design is an effective way to capture usable energy, I am not sure about. But, having something hot on one end, and cold on the other is a form of potential. [1]https://en.wikipedia.org/wiki/Thermoelectric_generator https://en.wikipedia.org/wiki/Thermoelectric_generator [2]https://en.wikipedia.org/wiki/Stirling_engine#Theory https://en.wikipedia.org/wiki/Stirling_engine#Theory
      - wahern 9y ago
        Both of those involve effectively closed systems where heat transfer can only occur at a point where you can extract work. But what makes ambient air at the ground preferentially rise through the chimney? Real solar chimneys, as posted elsethread, have a greenhouse at the bottom. Air at the bottom of the chimney, heated by the sun, preferentially rises up the chimney because it's constrained within the greenhouse. If it were possible to "bootstrap" the system with an initial kick so that it became self-perpetuating with solar energy alone, notwithstanding changes in weather patterns, then I would think we'd also see standing hurricanes and tornados. But we don't because, I assume, these phenomena develop precisely because they're highly efficient at dissipating energy; and they dissipate it faster than a stable system can setup which preserves the initial constraints which developed (e.g. large scale climatic pressure differentials, boundary layers, etc).
      - mikeash 9y ago
        Sure, you can potentially exploit the differential with other sorts of devices. But you can't do it using the same fluid that already contains the temperature difference, and attempting to use that temperature difference to drive motion in the fluid. A generator that runs on heat differentials works by transferring heat from hot to cold and arranging it so that transfer does something useful. In a stable atmosphere, air rising through an open tube doesn't transfer heat, because it cools as it rises at the same rate that the surrounding atmosphere cools.
- Cheapshotx 9y ago
  Thunderf00t has debunked similar concepts its late now i'd go into more detail but people can look up thunderf00t waterseer
  - gus_massa 9y ago
    Waterseer is a different impossible idea: They ignore that they need to remove a lot of heat to transform water vapor into liquid vapor. And that there is not so much water in the air anyway. [Clouds are huge.] SuperTallChemney: They ignore that in equilibrium the column of air is has different pressures and temperatures that are related by the adiabatic process laws. Anyway, it's interesting that both project try to be people friendly and offer a lot of water for the desert. In the SuperTallChimney it's not very clear if the plan is to put it in the middle of a dessert [1] or nearby a wet place that usually has no so big temperature variations. [1] As another user commented, desserts are very hot during the day and very cold at night. What is the plan to keep the chimney working at night?

This site is pretty much on the same level as sites advertising perpetual motion machines. I don't need every little detail to observe that it's bullshit. Unless you confine a parcel of air in all directions, it will match the pressure of the surrounding air. Consider an arbitrary cubic meter of air at 15°C at sea level at the base of the tube. Now raise it 1,000m inside the tube. That air now occupies roughly 1.12 cubic meters and is at a temperature of roughly 5°C, the same as if it had risen 1,000m outside the tube. The tube will work sometimes, but only when the atmosphere is unstable. Since the chimney is 5km tall, that means thunderstorm conditions. You can only extract energy from a tube like this if there's some energy potential between the two ends. The atmosphere is constantly erasing differences in energy potential, so large-scale differences are ephemeral.

elago 9y ago
>You can only extract energy from a tube like this if there's some energy potential between the two ends. The difference in temperature between the air at the bottom of the tube and the top of the tube is that potential.
- mikeash 9y ago
  It's not, because it's canceled out by the pressure difference. The net energy change of raising a parcel of air in the atmosphere is roughly zero. (Depending on the exact temperature profile of the atmosphere at any given moment, of course.)
  - deleted 9y ago
    [deleted]
  - elago 9y ago
    Consider either a thermoelectric generator[1] or sterling engine[2]. Either of these can produce power given a hot and cold reservoir. Of course neither device is appropriate for this specific application (the temperature differential between 'surface' air and air in the high atmosphere), but they demonstrate the concept that any temperature gradient represents a form of potential energy. Whether or not this specific design is an effective way to capture usable energy, I am not sure about. But, having something hot on one end, and cold on the other is a form of potential. [1]https://en.wikipedia.org/wiki/Thermoelectric_generator https://en.wikipedia.org/wiki/Thermoelectric_generator [2]https://en.wikipedia.org/wiki/Stirling_engine#Theory https://en.wikipedia.org/wiki/Stirling_engine#Theory
    - wahern 9y ago
      Both of those involve effectively closed systems where heat transfer can only occur at a point where you can extract work. But what makes ambient air at the ground preferentially rise through the chimney? Real solar chimneys, as posted elsethread, have a greenhouse at the bottom. Air at the bottom of the chimney, heated by the sun, preferentially rises up the chimney because it's constrained within the greenhouse. If it were possible to "bootstrap" the system with an initial kick so that it became self-perpetuating with solar energy alone, notwithstanding changes in weather patterns, then I would think we'd also see standing hurricanes and tornados. But we don't because, I assume, these phenomena develop precisely because they're highly efficient at dissipating energy; and they dissipate it faster than a stable system can setup which preserves the initial constraints which developed (e.g. large scale climatic pressure differentials, boundary layers, etc).
    - mikeash 9y ago
      Sure, you can potentially exploit the differential with other sorts of devices. But you can't do it using the same fluid that already contains the temperature difference, and attempting to use that temperature difference to drive motion in the fluid. A generator that runs on heat differentials works by transferring heat from hot to cold and arranging it so that transfer does something useful. In a stable atmosphere, air rising through an open tube doesn't transfer heat, because it cools as it rises at the same rate that the surrounding atmosphere cools.
Cheapshotx 9y ago
Thunderf00t has debunked similar concepts its late now i'd go into more detail but people can look up thunderf00t waterseer
- gus_massa 9y ago
  Waterseer is a different impossible idea: They ignore that they need to remove a lot of heat to transform water vapor into liquid vapor. And that there is not so much water in the air anyway. [Clouds are huge.] SuperTallChemney: They ignore that in equilibrium the column of air is has different pressures and temperatures that are related by the adiabatic process laws. Anyway, it's interesting that both project try to be people friendly and offer a lot of water for the desert. In the SuperTallChimney it's not very clear if the plan is to put it in the middle of a dessert [1] or nearby a wet place that usually has no so big temperature variations. [1] As another user commented, desserts are very hot during the day and very cold at night. What is the plan to keep the chimney working at night?