On Mon, 26 Sep 2005, Byron A Jeff wrote:

>> Only if it works. Anyway it would cost less than half to build, compared
>> to what a 500 Watt Stirling costs (5000 EUR).
>>
>> I have been thinking some more about it. I think that a normal
>> automotive exhaust manifold could be used as the hot part heat exchanger
>> somehow. It would mate perfectly with the turbine inlet. That could take
>> care of the high temp. seal which is a problem anyway.
>
> The only problem I see is that an exhaust manifold isn't designed to heat gas
> though hot gas goes through it. For this project to work there would need to
> be an efficient "air burner" that's the target for the solar collector. A high
> temp evaporated tube passing air through it is something along the right lines.
> Or using a flat steel plate (18in x 18in x 1in) with tubes drilled through it.

I made a drawing and you can see it here (thanks to James for putting it 
up - I have yet to learn how to use the piclist system):

http://www.piclist.com/techref/member/plp-actcom-f00/sun-turbo-1.htm

The manifold is optimised in many ways and perfectly mates with the 
turbo inlet. I would suggest most of its branches to be capped off with 
lids, glass wool insulation of 1-2 inches wrapped around it, and an 
inset tube welded to a holed flange put in. The inset tube would be the 
blackbody of the sun target, through a hole in the flange that bolts it 
on the manifold. The air from the compressor would enter through another 
of the flanges and run between the inside tube and the wall of the 
manifold to heat up, with several circuits until it would exit towards 
the turbine. It will pass something like 0.08 m^3/second on the cold 
side and 2-3 times as much on the hot side.

> Any idea of the temp and pressure that the turbine inlet is expecting?

> Also I gotta ask again: are you sure that steam is out of reach? The conversion from
> water to steam will give a huge expansion giving a lot of pressure to drive the
> turbine.

Conversion of water to steam gives not 'a lot' of expansion but exactly 
as predicted by steam tables. To get out power you have to use high 
temperature. The characteristics of steam are such that at the same 
700-800K where the automotive turbo will work with 2-3bar, steam needs 
210+ bar. This means that the boiler, the turbine, and the feed pump 
must take 210bars continuous. Nobody I know has the technology to work 
with 210bar steam in the garage, even if not at 700K. Even 40 bars is 
too much for most 'home use' equipent. If you feel courageous obtain a 
scuba tank and use it to power your turbine or generator (very 
dangerous - you cannot blame me if you get hurt).

Steam is good to use for a certain range of combustion temperatures 
where the pressure does not become excessive and where it can do a good 
job (at low efficiency).

Power stations that use steam at high temperature have complicated and 
dangerous installations constantly purifying the water in the circuit, 
adding chemicals like Hydrazine (poison!) to remove oxygen. Any oxygen 
in the circuit will instantly convert the innards of the equipment into 
high quality rust, when combined with steam at 700+K.

Peter
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