Here's a project that uses some of those dead hard drives you've got lying around.
In the Tesla Turbine, air, steam, oil, or any other fluid is injected at the edge of a series of smooth parallel disks. The fluid spirals inwards and is exhausted through ventilation ports near the center of the disks.
A regular blade turbine operates by transferring kinetic energy from the moving fluid to the turbine fan blades. In the Tesla Turbine, the kinetic energy transfer to the edges of the thin platters is very small. Instead, it uses the boundary layer effect, i.e. adhesion between the moving fluid and the rigid disk. This is the same effect that causes drag on airplanes.
To build a turbine like this, you need some dead hard drives, some stock material (aluminum, acrylic), a milling machine with a rotary table, and a lathe with a 4 jaw chuck.
Wikipedia has a good review article (http://en.wikipedia.org/wiki/Tesla_turbine), as well as articles about
Nikola Tesla http://en.wikipedia.org/wiki/Nikola_Tesla,
the boundary layer effect (http://en.wikipedia.org/wiki/Boundary_layer),
and Reynolds number (http://en.wikipedia.org/wiki/Reynolds_number)
(which determines if the fluid flow is laminar or turbulent).
I run my turbine on compressed air (40 psi), and it easily reaches speeds of 10-15,000 rpm. While the speed is high, the torque is low, and it can be stopped with your bare hand.
I have more details on my webpage (http://staff.washington.edu/sbtroy/turbine/turbine.html).
Step 1: Make Ventilation Holes in the Platters
Step 1 should probably be to disassemble some hard drives but I assume that if you read Make, you've already figured out how to un-Make a hard drive.
The easiest way to make vent holes in the hard drive platters is with a milling machine and a rotary table. Center and clamp a stack of several platters to the rotary table and then you can cut any radially symmetric pattern fairly easily. Just be sure that you use aluminium platters because ceramic platters will shatter when you drill into them.
I made two sets of platters; one with a radial array of holes, and one with radial arcs. The platter with radial arcs in the picture was on the top of the stack and took the most damage. The platters beneath it have very little tear-out and look much better.
Step 2: Make or Reuse Spacers
The ideal spacing between the platters depends on several variables including the fluid viscosity, velocity, and temperature. You could go through the calculations (http://en.wikipedia.org/wiki/Navier-Stokes_equations) and make a set of spacers, or be lazy and just reuse the spacers from the disassembled hard drives.
I was lazy and reused the spacers that were originally in between the platters. The advantage to this is that they'll have the same inside diameter as the platters. They're about .050" thick where the ideal spacing is closer to .012" but the increased distance doesn't make that big a difference in this case.
Step 3: Make the Shaft
This is just a piece of aluminum stock turned on a lathe. The center diameter is about .98" (which is the inside diameter of the platters) and about 1.77" long (so it will fit in a piece of 2" thick acrylic).
The thinner sections on each end are turned to fit the ball bearings I pulled from a box of scrap.
Step 4: Make Collars
The collars are made from more aluminum stock are wider versions of the platter spacers. The inside diameter is also .98" but they're about .3" thick to hold a #10-32 set screw.
Step 5: Rotor Assembly
Center the platters, spacers, and collars on the shaft and tighten the set screws to hold everything together. I used 11 platters, and 10 spacers. Try to line up all of the ventilation ports. If there isn't enough tension between the two collars, the platters can rotate around the shaft instead of with it.
Step 6: Make the Chamber
This is a 4.75" x 4.75" x 2" piece of acrylic that was bored out on a lathe using a 4 jaw chuck. The intake hole is taped for a 1/4" pipe fitting and all of the other holes are 1/4 - 20.
I used acrylic because it's what I had around and because it's going to be used for lecture demonstrations. You can use metal or even wood. However, if you plan to use steam instead of compressed air, wood might expand too much.
Step 7: Make the Side Panels (stators)
The side panels are 4.75" x 4.75" x 0.47" acrylic with untaped .25" holes to screw to the main chamber. The center hole is 0.6" and the counterbore is 0.28" deep.
The two 0.6" holes (one on each side) are the ONLY exhaust ports. The air spirals inwards across the face of the platters, through the ventilation ports, around the air spaces in the bearings (2nd picture), and finally out through these two holes.
However, more exhaust holes in the side panels might improve efficiency.
Step 8: Assemble Everything
Step 9: Complete Turbine and Movie
Please post (or email me) any questions or comments and I'll do my best to answer them.
Thanks for reading,
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