Posted by *mn_mn* on May 11, 2009, 5:30 am

*> Suppose the cross-sectional area of the chimney is 0.25 square*

*> metres and the air in it moves upward at 4 metres per second.*

*> Those figures are in the right ball-park for a residential chimney.*

*> So, every second, 1 m^3 of air is accelerated upward to 4 m/s.*

*> The density of air is about 1.5 kg/m^3. So the power that the fire*

*> puts into moving the air up the chimney is 0.5 x 1.5 x 4^2 watts*

*> (0.5mv^2), which comes to 12 watts. A turbine in the airflow could*

*> recover only part of that, let's guess 5 watts. That could be enough*

*> for some simple applications, but not for anything large.*

Thanks for the information. That explains why people had to go

through steam to get any useful energy from heat

How about a "Hot Air Ballon Line" running up a km high line attached

to side of tower or building with attached small hot air balloons

pulling line up until at top they are collapsed to return to bottom to

be refilled, , , , or not.

Posted by *williamsdavid65* on May 11, 2009, 11:41 pm

*> How about a "Hot Air Ballon Line" running up a km high line attached*

*> to side of tower or building with attached small hot air balloons*

*> pulling line up until at top they are collapsed to return to bottom to*

*> be refilled, , , , or not.*

Suppose one of the balloons holds 1 m^3 of air at a temperature

of 400 K, and the surrounding air is at 300 K. The air would have a

mass of about 1 kg, in very round numbers, so heating it from 300

to 400 K will have taken about 4e5 joules of heat. (The specific

heat of air is about 4e3 J/kg./deg.) The buoyancy force on the

balloon will be about 0.3 kg wt, or 3 newtons, so if it rises 1 km

it will produce 3000 joules of mechanical energy. That's less

than one percent of the energy that was needed to heat the air

in the first place. Not a very efficient machine!

dow

Posted by *mn_mn* on May 14, 2009, 1:45 am

On May 11, 6:41pm, williamsdavi...@gmail.com wrote:

*> > How about a "Hot Air Ballon Line" running up a km high line attached*

*> > to side of tower or building with attached small hot air balloons*

*> > pulling line up until at top they are collapsed to return to bottom to*

*> > be refilled, , , , or not.*

*> Suppose one of the balloons holds 1 m^3 of air at a temperature*

*> of 400 K, and the surrounding air is at 300 K. The air would have a*

*> mass of about 1 kg, in very round numbers, so heating it from 300*

*> to 400 K will have taken about 4e5 joules of heat. (The specific*

*> heat of air is about 4e3 J/kg./deg.) The buoyancy force on the*

*> balloon will be about 0.3 kg wt, or 3 newtons, so if it rises 1 km*

*> it will produce 3000 joules of mechanical energy. That's less*

*> than one percent of the energy that was needed to heat the air*

*> in the first place. Not a very efficient machine!*

*> dow*

Balloon powered machines or generators might be inefficient but, and

this is big, it is a simple machine so 1) it cannot break down, 2) can

use low temp heat like campfire or hot springs, 3) is easily built and

maintained (without lathe, high pressure boiler, anything). Ancient

greeks could have built these ,, , , , ,and one at home could build

this if stuck in woods.

I wonder if balloon could lift water up watertower where it is dumped,

then when needed one would draw down water using water-motors or

electricity generators or whatever, ,, , or just gear down the lifting

power and lift a 10 ton weight, ,,

Posted by *williamsdavid65* on May 14, 2009, 7:45 pm

*> Balloon powered machines or generators might be inefficient but, and*

*> this is big, it is a simple machine so 1) it cannot break down, 2) can*

*> use low temp heat like campfire or hot springs, 3) is easily built and*

*> maintained (without lathe, high pressure boiler, anything). Ancient*

*> greeks could have built these ,, , , , ,and one at home could build*

*> this if stuck in woods.*

What would ancient Greeks have have made balloons out of?

Ditto for a modern person stuck in the woods.

*> I wonder if balloon could lift water up watertower where it is dumped,*

*> then when needed one would draw down water using water-motors or*

*> electricity generators or whatever, ,, , or just gear down the lifting*

*> power and lift a 10 ton weight, *

I can imagine problems with balloons being blown around by wind,

and so on. Maybe they could be solved, but the machine would no

longer be cheap and simple.

dow

> Suppose the cross-sectional area of the chimney is 0.25 square> metres and the air in it moves upward at 4 metres per second.> Those figures are in the right ball-park for a residential chimney.> So, every second, 1 m^3 of air is accelerated upward to 4 m/s.> The density of air is about 1.5 kg/m^3. So the power that the fire> puts into moving the air up the chimney is 0.5 x 1.5 x 4^2 watts> (0.5mv^2), which comes to 12 watts. A turbine in the airflow could> recover only part of that, let's guess 5 watts. That could be enough> for some simple applications, but not for anything large.