How high would a ventilation stack (of optimal dimensions) need to be before the natural up-draft developed would produce enough power through a turbine generator placed within it, to power the average household?
Postpocelipse said:
How high would a ventilation stack (of optimal dimensions) need to be before the natural up-draft developed would produce enough power through a turbine generator placed within it, to power the average household?
There are several conflicting factors here. One is the difference between (wet or dry) adiabatic lapse rate and environmental lapse rate. A second is wall friction. A third is the suction imposed on the top of the vent by the combination of wind speed and the design of the top of the vent. A fourth is the temperature and relative humidity at the bottom of the vent. A fifth is the heating of the vent itself by sunlight and radiation to the night sky.
But you want a simple answer. The simple answer is that the height of the vent has almost no effect on the amount of power generated. The amount of power out cannot exceed the amount of power in, which is given (to first approximation) by the amount of power applied within the house to heat the air at the bottom of the vent.
mollwollfumble said:
Postpocelipse said:
How high would a ventilation stack (of optimal dimensions) need to be before the natural up-draft developed would produce enough power through a turbine generator placed within it, to power the average household?
There are several conflicting factors here. One is the difference between (wet or dry) adiabatic lapse rate and environmental lapse rate. A second is wall friction. A third is the suction imposed on the top of the vent by the combination of wind speed and the design of the top of the vent. A fourth is the temperature and relative humidity at the bottom of the vent. A fifth is the heating of the vent itself by sunlight and radiation to the night sky.
But you want a simple answer. The simple answer is that the height of the vent has almost no effect on the amount of power generated. The amount of power out cannot exceed the amount of power in, which is given (to first approximation) by the amount of power applied within the house to heat the air at the bottom of the vent.
Not speaking in terms of heated ventilation but using air pressure differential…….
Postpocelipse said:
mollwollfumble said:
Postpocelipse said:
How high would a ventilation stack (of optimal dimensions) need to be before the natural up-draft developed would produce enough power through a turbine generator placed within it, to power the average household?
There are several conflicting factors here. One is the difference between (wet or dry) adiabatic lapse rate and environmental lapse rate. A second is wall friction. A third is the suction imposed on the top of the vent by the combination of wind speed and the design of the top of the vent. A fourth is the temperature and relative humidity at the bottom of the vent. A fifth is the heating of the vent itself by sunlight and radiation to the night sky.
But you want a simple answer. The simple answer is that the height of the vent has almost no effect on the amount of power generated. The amount of power out cannot exceed the amount of power in, which is given (to first approximation) by the amount of power applied within the house to heat the air at the bottom of the vent.
Not speaking in terms of heated ventilation but using air pressure differential…….
Then the maximum power you can get out from the turbine is less than the power input from the vent fan, give or take a bit depending on the temperature of the sides of the ventilation tube.
The pressure difference with altitude inside the vent is very similar to the pressure difference with altitude outside the vent.
mollwollfumble said:
Then the maximum power you can get out from the turbine is less than the power input from the vent fan, give or take a bit depending on the temperature of the sides of the ventilation tube.
The pressure difference with altitude inside the vent is very similar to the pressure difference with altitude outside the vent.
A 100mm tube a mile high wouldn’t develop a draft?
Postpocelipse said:
mollwollfumble said:Then the maximum power you can get out from the turbine is less than the power input from the vent fan, give or take a bit depending on the temperature of the sides of the ventilation tube.
The pressure difference with altitude inside the vent is very similar to the pressure difference with altitude outside the vent.
A 100mm tube a mile high wouldn’t develop a draft?
Oooohhhh, flashback. Are we talking a Very Long Cylinder (VLC)?
sibeen said:
Postpocelipse said:
mollwollfumble said:Then the maximum power you can get out from the turbine is less than the power input from the vent fan, give or take a bit depending on the temperature of the sides of the ventilation tube.
The pressure difference with altitude inside the vent is very similar to the pressure difference with altitude outside the vent.
A 100mm tube a mile high wouldn’t develop a draft?
Oooohhhh, flashback. Are we talking a Very Long Cylinder (VLC)?
Never heard of it. I had assumed that a tube long enough to connect two regions of significant temperature and pressure difference there would be equalising interaction.
Postpocelipse said:
sibeen said:
Postpocelipse said:A 100mm tube a mile high wouldn’t develop a draft?
Oooohhhh, flashback. Are we talking a Very Long Cylinder (VLC)?
Never heard of it. I had assumed that a tube long enough to connect two regions of significant temperature and pressure difference there would be equalising interaction.
Say one had a pipe that reached the jet-stream?
If I had a pipe of any diameter connecting (say) sea level with (say) 10000 feet (AMSL) – which seems to be what you’re suggesting – nothing would happen because the air is already connected between those two points, so any movement in the pipe would be matched (and actually exceeded) by the outside air.