Re: 1974 Saab Steam Car
Posted by:
Peter Brow (IP Logged)
Date: April 25, 2002 07:05AM
<HTML>Hi Jim,
On that rotary valve, the material might take it, but I wouldn't trust the sealing surfaces to take all the mechanical loads. I'm not sure exactly how the valve is designed, as the drawing I have doesn't show many details. Rotary steam valves don't have a good track record, to put it mildly.
40-120 tiny paths is too many to deal with. I wouldn't even consider more than a dozen, except maybe with a circulating pump as envisioned for Jerry People's SPAT steam generator. For a once-through multipath, I think the end of the generating zone, and the superheater, would have to be kept in a final radiant monotube section, at least 2-3 coils, downline from a plenum. The multiple paths (like finned tubing) should only be in the convective zone, no radiant heat, and should have horizontal radial symmetry, all exactly the same length & shape, plenums (plena?) and gas flow passages too.
1 mm tube bore is just too small, and the resulting ultralight tube stack would be a bear to control under varying loads -- strictly microprocessor territory, a serious programming project, and maybe a terabyte hard drive. :) A Stanley boiler isn't necessary, but I think good performance requires at least _some_ stored energy under the hood. Another plus for the Lamont.
The Saab condenser design looks doable for a production vehicle, but probably more work than it's worth for a one-off or prototype (buy junkyard radiators instead). In production, some of the header work could be injection-molded hi-temp plastics, as used in today's aluminum radiators. I repaired a crack/leak in one of those plastic radiator headers with epoxy resin and fiberglass cloth, and it ran fine for a couple years of hard use until the owner moved to Arizona in the summer. I never did find out if it failed at the repair, or elsewhere. But maybe the headers in a Saab-type condenser could be made of epoxy/fiberglass composite, if the fiber/cloth layup & molding could be worked out?
Nothing beats "take it apart and study it" work. My shop is full of compressors, engines, and other mechanisms which I took apart to study. One interesting item was an A.I.R. pump from a '74 VW bus smog system. This was a vane-type compressor with the inner ends of the vanes supported by roller bearings on an eccentric shaft (that was nearly 20 years ago, & I don't remember all the details).
I think the vane tips operated with slight clearance in the housing, and at the time I wondered about the possibility of building an all-metal version with seal strips along the pressurized edges of the vanes. Centrifugal force would only load the seal strips, while the large vanes would allow more displacement volume for a given unit volume (and surface area).
Some vane-type rotary engines try to do the same friction/wear-reduction thing with very small one-piece vanes, but these units end up much larger for a given displacement.
Speaking of which, did you ever look into the Hinckley-Beloit rotary steam engine? I just came across an article in Vol. 14, #1 (1972) of The Steam Automobile (pp. 4-5) about this. Developer (John Hinckley) claimed lower surface-to-volume ratio than either Wankels or piston engines (an amazing claim, IMO). I wonder if he ever patented it. Of course, Wankels have already had billions in R&D put into the seals, which are the hard (& crucial) part of any rotary design. At the time of this article, Hinckley was only beginning tests for hi-temp steam seals.
Peter</HTML>