Recent postings have sparked my interest in the Tesla Turbine as a robust, easily constructed method of getting pure rotary motion from a hot gas stream, whether the exhaust of an IC engine, or a gas burner fed from a wood- gasifier. A high speed brushless dc generator would allow electrical power to be extracted directly, and a solid state inverter/controller could produce stable dc or 60Hz mains regardless of speed variations in the turbine shaft.

The turbine discs are typically 316 or 416 grade stainless steel and arranged in a stack represent a significant surface area in contact with the hot gas stream. As such they will get red hot, and this could cause problems with warping and overheated bearings as a result of heat conducted through the discs to the shaft.

Here’s an idea which could solve these problems, and also produce some additional power. Remember the old “Hero Turbine” consisting of a sphere with a little water, pivoted on simple bearings and with a couple of steam jets arranged opposite one another. Put this over a burner flame, the water boils and you get a simple reaction turbine.

Now imagine compressing this sphere, so that it becomes a disc. The disc has minimum internal volume compared to the outside surface area, and as such makes a really good flash steam generator. Take a stack of these flash steam discs and build them into a tesla turbine. The edge of each disc would have series of jets drilled such that the steam reacts against the housing and spins the turbine. It then finds its way out through the normal route between the discs.

This not only uses the expansive work of the steam to assist the tesla turbine, but you get the reactive force too. It helps keep the discs down to a reasonable temperature, and f cold water is pumped first around the bearing housings, and up through the hollow shaft, it will keep these cool
as well.

The turbine would start slowly on the hot gas and then you could turn on the water feed pump for maximum boost. The discs could be made simply by sandwiching a spiral “washer” between two thin outer skins and rivetting or spot welding together. Even a small turbine of say 12 runners and 6″ diameter would have a massive surface area. (4.7 sq ft) The hot gas comes into very close coupling with the discs and so the heat up time would be rapid giving a quick response.

Supposing the turbine / alternator spins very fast…too fast for 60 Hz. practicalities. Then could you just have taps on the field windings and with an SCR just “query” the taps at the 60 Hz. sampling rate that you desire? ( Letting the other spikes go to waste so to speak. ) I may be way off base here, but the thought just ran through my head and I admit it sounds like the physics is very weak. Something to ponder.

Generating high frequency ac is not a problem, aircraft have used 400Hz for years. You just need to rectify it to get dc, and then use an inverter toi synthesise whatever frequency you wish just like a modern ac motor speed controller. This technology has come on in leaps & bounds in the last 10 years, so it is all of the shelf. If the Tesla turbine were used i a hybrid electric vehicle, you would need dc for charging the batteries regardless of what type of probulsion drive you had.

My Idea (You’re welcome to it) is to use a common automotive alternator as the “Spindle” holding the Tesla Turbine, this eliminates several problems immediately, the bearings are rated above 15,000 RPM, (Alternators already turn that fast), a “Generator” is built in, (Self regulating, at that) and all that has to be built is the turbine itself.  I also plan to use circular saw blades for my next turbine, the fine toothed ones that are intended to cut plywood would be a source of high strength, steel discs, use them either with, or without the teeth.  Only problem is cutting the exhaust vents in the hard saw blades, maybe you EDM folks can work that out. 

The turbine doesn’t fit inside the alternator, the front end is removed and a new case machined for the “Pulley” end only, (Aluminum) then the Turbine is installed on the alternator’s end shaft as a pulley would be, tech talk, It’s an “Overhung” turbine. (Hangs on the end)  This also lets the alternator  be repaired fairly easily, just remove the three case screws and the entire rear housing, with field windings and brushes slide right off.