I was just looking back at Yahoo groups “Hot Air Engines”; it has been a very vivid group on this subject, but sadly there is not much anymore than the “bold picture” of the founder sitting at his desk. No new messages in a couple of years…
Founded Oct 17, 2000.
Maximum messages per month:
707 in september 2007.
But now some low level reflections:
I gather, that home build equipment is excluding use of those “laboratory” high performace, high energy carrying gases, mentioned in laboratory reports. (for closed units)
Another exlusion seems to be very high temperatures with heating any gas, as it complicates the handling of inlet valve operation.
But first: Since 1907 the norm has been: A closed system with a displacement of air alternatively from the heater or the cooler side.
This way the enclosed air has been alternatively heated and cooled to get a driving alteration in air pressure to drive a piston in ratio to the surrounding atmosphere.
But now, if we can tolerate some friction losses, we can build a system with re-circulation and constant positive working pressure for a working cylinder (double action) combined with a following re-heter (for feeding the main heater) and then a constant flow cooler.
So, from the cooler the air is taken to a “compressor”, followed by the mentioned
re-heater after the working cylider, and then to the air-heater proper.
This should be the whole circulation loop.
Now, in which “thermal borders” would a home “plant” be able to work,
with air as the driving medium?
If starting with the feeding end: Modest air cooling (without water)
say 50 deg. Celcius = ~122F as the bottom temp in the cycle and
~300 deg. C = ~? F , Sorry, lost my scale. Returning when finding.
~300 deg. C on the top, as to manage inlet valve precaution…
This will result in a (free air) relative volume expansion of:
From abs. zero point: 273 + 50 = 323 as “volume reference”.
And the heated output has: 273 + 300 = 573
The difference is 573 : 323 = 1,77399.
This would be the (atmospheric) volume gain.
So the expansion available, or rather the filling factor
(with no friction or power output) would be:
1 : 1,7740 = 0,5637
Here is some room for a power outtake, or how should it be understood?
I have assumed, that the working cylinder volume is
twice the pumping cylinder volume, to make adjustable expansion possible.