At 12:27 18-02-02 +1000, you wrote:
>I've just been reading the latest Electrical World and have come across an
>article (the third I have seen in various publications over the past year)
>which describes an electrical generation plant using hot air as the motive
>force. The power plant consists of a 5km diameter area of glass supported
>above the ground by some small distance, with 1km high chimney tower at
>the centre. The glass area heats the air underneath, and the hot air exits
>through the chimney. The article says that the turbines will generate
>200MW. How much residual power will be left after the electricity has been
>extracted?
>
>I wonder if the glider pilots near the proposed site (Mildura) have heard
>of it? I wonder how effective it would be as a manmade thermal? I wonder
>if the authorities will ban soaring over it?
>
>Phill Glasson
Perhaps one of the engineers could do a few simple calculations relating to
matters like:
maximum volume of air carried aloft
inwards velocity of air (mean) at the circumference of the 5 km thermal and
approaching the centre
ideal shape of the junction ("chimney root?) for minimum turbulent losses
as the flow transitions from horizontal to vertical
Total energy available (is it 21 watts / sq m from incoming soar radiation
- I forget)
Efficiency if the thing produces 200 megawatt
Optimum chimney height to prevent friction losses in the tower exceeding
extractable benefit from turbines
Best shape (Bernoulli) for tower to encourage maximum energy at level of
turbines
Likely radius of affected sinking air to supply inflow and disperse
uplifted air.
Some other thoughts:
Will it work in reverse at night due to katabatic flow down the chimney?
How will they prevent the inflow and giant thermal creating a ginormous
dust devil?
Will the silica in the dust devil cause erosion of the turbine?
Would a fluted inflow shape (like the noise-reducing and energy-dissipating
exhaust design of early jet engine effluxes) be more efficient or
environmentally friendly?
Would a bypass ratio sucking in some air from closer than the circumference
be helpful?
Would something so totally dependent on a diurnal cycle really help, given
that coal-fired power stations work most efficiently at a constant output
rate so it will be difficult to turn them off during the day and then on
again in the evening to feed power back into the area supplied by it?
Will it be capable of connection to the National Grid?
Maybe they could build up Lake Victoria and Lake Cullulleraine so they
could pump the waters of the Murray backwards to absorb the excess power,
then run hydro turbines with a low head like a tidal power station to
release the power at night. Would this require extensive earthworks to
avoid flooding Renmark? Would the rainfall from the resident cu-nim that
someone else has already mentioned supply enough water to add to the river
flow and the irrigation potential of Sunraysia? Would it add to soil erosion?
Would CASA raise an objection to a tower of this magnitude in the middle of
an area with a LSALT of about 1700 ft (raising them all to around 4700 ft
if the tower goes to 300 ft ground elevation plus 3300 ft for the tower
plus a bit for the lightning rod they would have to build on top of it?
How would the structure stand up to the horizontal wind shears through its
height? Area 22 this morning was quoting 080/15 at 2000' and 340/20 at 5000'!
Finally, I predict that the vorticity from a thermal of this size would
have about a 65% chance of rotating clockwise in accordance with Buys
Ballot's law and a 35% chance of rotating counter-clockwise due to Sod's
Law. [But once it started it would, like thermals often seem to, rotate the
same way all day!]
Wombat (with tongue in cheek like all the rest of you, I suspect)
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