An under-appreciated invention was the Tesla turbine, invented by Nikola Tesla and patented in 1913. Taking in air, water, or steam, it rotated without blades and generated electricity from it. Instead, discs with small gaps between them were moved along by the fluid passing by as it spiraled from the outside into the center, and then exhausted from holes on the side.
What makes the design interesting is that in these days of high precision turbine blades, a Tesla Turbine is workable using things like old CD discs (a quick search on Youtube or Instructables will show you many attempts at CD disk turbines). It also handles torque versus speed well: Run at low speeds for higher torque, or low torque/high RPM. In addition, the same design works in reverse as a pump – give the fluid access to the center area (hose, etc), turn the turbine with a motor, and the fluid is pumped out from the outside edge.
The device is sensitive to the gap between the discs because that boundary area is the energy transfer mechanism. Imagine a thick fluid like syrup and you’ll see the discs need to be farther apart, whereas air and steam mean they are closer together (about 0.4mm in some cases). As well, the diameter of the discs is limited only to the materials – obviously high speeds and temperatures mean a more robust material is needed, but even a smaller device can work fine, depending on the use.
With a device like this, it’s simple for an ordinary workshop to make these in different sizes and configurations. Imagine one for microhydro power generation, or another for power generation via solar energy (heat to steam), and you get the idea of how useful this turbine could be.
You can read more about it here on WikiPedia, or search to your heart’s content online. Who knows – maybe the patent’s centennial in 2013 will get people thinking about it more…