Lavel Turbine vs Pelton Wheel Efficiencies

The best efficiency of a 100% impulse turbine using a liquid as the
driving fluid is 95% while the gas equivalent is only 80%.
The nozzle efficiency for a liquid isn't much below 95% so the buckets
on the pelton wheel must be pretty close to 100% efficient at
converting the linear kinetic energy of the fluid stream to rotational
shaft work.
A reasonable efficiency for a gas nozzle is about 93% so 13% of energy
is lost spinning the lavel turbine.
I'm guessing windage is one to three orders of magnitude more important
in the gas turbine than the liquid turbine, partly because the speed
and U^2 term causing drag is much higher and partly because of the
differences in densities of the working fluids with the surrounding
fluid which is a gas. You couldn't get 95% efficiency from a pelton
wheel submerged in water.
Most photos and drawings show only have one or two nozzles for the
pelton wheel while the lavel turbine has "high admittance" -- the full
circle of nozzles in all gast turbines.
I've seen patents for stationary power plants where waste industrial
gas under pressure displaces water out of a vessel to drive a water
turbine. Two vessels are used in tandem for continuous operation.
Floating ceramic balls insulate the liquid from hot gases.
Most industrial gas turbines are aeroderivatives which don't use the
lavel turbine.
Bret Cahill
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Bret Cahill
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