The predetermined flow condition might for example be the average tidal flow at an intended installation site, and the desired torsional force may be matched with optimal input torque for the intended output device, which might be a generator or multiple generators. Thus, conventionally rotors are designed with a preferred flow direction.
- Bolto, B. J.: Le corps entre les mains, Hermann Éditeurs
- Torsion spring, 1 special design variants, eg shaped silicon spring (MEMS),
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Thus, rotors as described herein are utilised in preferred embodiments in a two-stage rotor apparatus installed in a rotor housing. In the rotors described herein a solid surface bounding the body of flowing fluid is formed by the front and rear of a pair of rotor blades and the inner and outer rims of the rotor. The terms “inner” and “outer” are used herein to refer to portions of the rotor that are at a smaller or greater radius from the axis of rotation of the rotor. In some embodiments, as in Figures 4A to SB the increasing radius of either conic helix may increase at greater or lesser rates to form a pair of non-parallel conic helixes. The rotor is for extracting kinetic energy from a liquid fluid flow or system of liquid fluid flows by converting the kinetic energy in the liquid fluid flow into a rotational force or torque, hence permitting onward conversion into a more convenient form of energy, such as electrical energy.
However, the radius ri of the inner conic helix 6 increases at a lesser rate than the radius ro of the outer conic helix 5 to thereby form a pair of non-parallel conic helixes that are spaced further apart at the large diameter end of the rotor than at the small diameter end of the rotor. The inner conic helix may increase in radius at a slower rate than the increase in radius of the outer conic helix in order to reduce or restrict the hydrodynamic reaction forces and torsional forces produced by the rotor. The conic helix can be any suitable shape that allows for a three dimensional curve with an increasing radius and decreasing pitch as described above.
Given that the density of seawater is around 1000 kgfm3, the energy density of tidal currents can typically be of the order of 4000 W/m2. However, the potential energy level is much larger in a liquid flow than in a gas flow because the fluid density is generally higher. As the body of fluid flows through the specially shaped rotor and its complicated flow passages it is constantly forced to change direction due to the shape of the blades and the decreasing helical pitch from inlet to outlet which results in an increasing helical frequency, thereby resulting in a continuous rate of change of momentum. Dolor muscular cronico . Naturally occurring fluid flows can be found in tidal currents, coastal or oceanic currents, river flows, thermal currents, air currents and elsewhere. This ensures maximum bidirectionality since an identical fluid flow can enter the two-stage rotor apparatus from either end with the same resulting power take off.
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Internally, the rotor hence has one or more flow passages formed between front and back blade surfaces, the outer rim and the inner surface. Since the outer rim and inner peripheral surface in preferred embodiments has a generally conical surface, multiple generators may be moveably mounted parallel to a conical surface in order to permit variation of the input rotational speed to the generators by movement along the cone surface. The term generally conical is intended to refer to not only perfect right cones but also truncated cones, convex cones and concave cones as discussed above. The invention also encompasses use of the rotor described above for the production of electricity from fluid flows. For higher speed fluid flows the generator connection point can be repositioned at the lower linear velocity end, this being the smaller diameter end of the rotor.
This enables the generators 13 to be moved within the rotors 7, 8 to respond to changes in the rotational speed of the rotors 7, 8. In this way, a relatively constant generator speed within the variable range of the generators 13 can be achieved through a range of fluid flows. Figures 3A and 3B show perspective views of the rotor of Figures 1 and 2 in which further detail of the shape of the blades 2 can be seen. The inner and outer conic helixes may both increase in radius at the same rate, such that the conic surfaces are generally parallel, However, it can be advantageous to adjust the performance of the rotor by having a different rate of increase in diameter for the inner and outer conic helixes. For the reasons discussed above, it is apparent that an underlying spiral possessing a more rapid change in inner and outer radius r with the polar coordinate 0 would induce a more rapid rate of change of momentum necessarily resulting in an increased hydrodynamic reaction force.