> So anyone come up with a one-piece heat engine yet? =A0Temperature differ=
ence
> in, rotary motion out.

Just to start the ball rolling ...

Angled screw with top/high end and bottom/low end.
Thermosyphon loop with heat introduced at bottom of screw and cooling
at top of screw.
Fluid rises through screw turning it and cooling.
Rotation of screw against a load will cool the fluid fwiw - but this
drop willo be small compared to the delta-T needed for thermosyphon
operation.

Fluid is recirculated - probably though a counterflow heat exchanger
for efficiency.
How unused heat energy is reintroduced to hot end is TBD/exercise for stude=
nt.
May best use a thermal wheel (agh!).
Continuous flow nature of the beast makes a regenerator hard.
Efficiency may not matter if this uses otherwise watse heat.
Upper efficiency ( use Z ) is limited by Carnot considerations so is
low to very low in most waste heat recovery situations.
ie  Z_Carnot =3D (Th-Tc)/Th or Tdelta/Thot.
For eg 10 degree C drop at room temperature (about 300K) that's about
10/300 ~=3D 3%.
Actual efficiency would be far below Carnot. In a well optimised heat
engine (eh high temperature, high pressure Stiling with Hydrogen
working fluid) Zactual/ZCarnot can get over 50% but that takes much
effort.

         Russell McMahon

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