4.5"
Experimenter's Tesla Turbine
Construction Details - Part
II
November 2005
Continuing on from last month's description of our 4.5-inch new Tesla
turbine builds, we see in Photo 1 a completed engine ready to spool up
with 100-150 psi of compressed air or steam.
As mentioned in previous articles, this turbine was designed for
experimenters with less than industrial level resources. Because of its
small rotor (both in diameter and disk number), anyone with very modest
shop resources can power up this engine and obtain good experimental
data.
| In Photo 2 we are looking directly into the
exhaust port of the engine. If you look closely, you can see the
exhaust slots laser-cut into the rotor assembly. The triangular
hole pattern allows the experimenter to bolt an exhaust flange
onto the end plate for steam recovery.
|
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| Photo 3 shows the bearing retainer plate held on
with six cap screws. |
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| In Photo 4 we see a number of brass fittings,
installed in the bearing block. The two hose barbs protruding
from the side of the case are air seal inlets. Over the years we
have tried using nitrile rubber shaft seals only to find that
they exerted too much drag on the shaft for proper spool
up.
The air seals we designed use an array of channel cut into
the shaft/spacer to aerodynamically trap gas around the shaft
and resist the movement of air, oil or dirt along the shaft. A
small air pressure (5-10 psi) charges the seal with positive
pressure to create a more positive barrier.
Keep in mind that this feature is in itself experimental and
will require some minimal experimentation to find an ideal air
pressure. |
 |
| Going on to Photo 5 we see three brass hose barbs
on the other side of the engine. One is obviously the gas inlet
for the hot rotor. The other two are oil inlet and outlet.
The top fitting is also the oil jet.
There are two small holes drilled in the bottom of the
fitting pointed towards the bearings. Oil is ideally pulsed
through these holes intermittently to lightly spray the
bearings. |
 |
The 6005 ball bearing normally has an upper rpm limit of about 18,000
in an oil bath. By adopting a "dry sump" system we can
increase the upper rpm limit by a factor of 3-4. Dry sumps drain off the
oil immediately to an auxiliary oil holding tank so the bearings are
never immersed in oil. To oil the bearings, a pulsed jet or mist of oil
is injected into the side cage of the bearing at a small flow rate.
Since this is also an experimental area in terms of pressure and
pulse rate, we can begin with a much simplified system of a continuous
jet flow. - In future experiments we will study pulsed injection flow.
| The last photo is a shot from above. Notice the
two set screws near the oil inlet. These set screws are used to
exert a very slight pressure on the outer bearing races to
eliminate bearing/case play. |
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Well, that concludes our first look at a relatively low-cost,
industrial quality Tesla turbine.
Ken Rieli
