Re: boat propulsion - miniature computer-controlled steam plant?

On 09/03/2024 20:22, Richard Smith wrote:

For what it's worth - I was thinking of
* de Laval turbine

A partial admission turbine is probably a good way, to go. Partial admission means that the incoming fluid only impinges on a few blades at a time rather than over the whole wheel.

* Ljungstrom turbine
With Ljungstrom turbine, wondered if blades could be made on tips of rod
pegs set into the face of the disk.  The centrifugal force isn't in line
to sling the inserts out of their seats. ?

I hadn't thought of that, it's more a bending force isn't it. And you can put rings on the other end of the blades so they are supported at both ends, with the centrifugal and pressure forces going sideways.
Though they would typically have a last ring of axial blades for best efficiency.
And possibly a pre-ring or two of impulse blades if the expansion pressure ratio is higher than about 10 (the two-spool Ljungstrom turbine is necessarily a reaction turbine, though in some ways it behaves like an impulse turbine).
Also good is that the blades are not twisted, makes them much easier to make.

I wondered whether the revs would have been manageable.
Two contra-rotating discs would have been fine - two generators.

Do you have to have two turning spools? [quickly googles Ljungstrom turbine, it's been a while]
Hmmm, looks like one shaft is okay, in  fact there has been a lot of work on that recently (which I haven't read...yet), see eg RAT turbines for ORC.
I would stick to steam though, you don't need huge efficiency.
Peter Fairbrother