INVENTOR: John Clark Hanna
Provisional Patent: 62/708,462
Closed Loop Mono-Radial Turbine
The device is an Impulse-type mono-radial air turbine PTO (power take-off) for wave energy conversion. The turbine can be driven by two separate systems: (1) Oscillating Water Column (OWC) or (2) pressure differential. Both will convert the rise and fall of oceanic waves into bi-directional air flows. In the case of the first system, this air/water interchange can be developed by the oscillating free surface of water inside the capture chamber of a shore-based OWC installation or inside the acceleration tube of a floating power buoy. In the second system, bi-directional air flows are harvested by placing the turbine between pressure differential compartments within a tethered subsurface buoy or inside a floating data acquisition buoy. In the first instance, the turbine can operate in a typical open-ended OWC-type system. In the second instance, it can operate within a hermetically sealed, closed-loop system. The U.S. Department of Energy has funded a top-tier numerical and computational study to evaluate both the open-ended and closed-loop versions of the Mono-radial turbine. The research is presently underway and the results of the study will be available in September, 2021.
The turbine’s rotor (runner) resembles that of a Pelton Wheel with air collecting impulse vanes (buckets) distributed about the rotor’s periphery. The light weight rotor with its spoon-shaped impulse vanes acts as a flywheel. In the center of the rotor is a drive shaft that spins a generator. In the closed loop system, two opposing nozzles force high velocity air into the rotor’s impulse vanes. While one nozzle pushes air into the turbine the other nozzle is simultaneously sucking out air at an equal volume and force. The nozzles alternate back and forth with the rise and fall of waves. Despite these reciprocating air flows; the rotor will always turn in one direction only. This is because the turbine employs a simple mechanism that assures its one-way motion: it uses two hinged, V-shaped air guides to redirect the bi-directional flows to create a one-way driving force.
In-house bench tests on a 7-inch diameter prototype have been successful using bi-directional air flows. To simulate the up and down action of ocean waves, reciprocating air flows were developed by a 24-cylinder air pump. The pump forced air through the turbine to test two different system configurations: the open-ended OWC type configuration and a fully sealed, closed loop configuration. To view a short video of the air pump and testing of the closed loop configuration, go to: https://youtu.be/E1TWdQkGeU4.
The closed loop configuration showed excellent response to the bi-directional flows. It is hypothesized that this configuration offers less internal damping and frictional resistance to the flows because there is a simultaneous “pushing and pulling” of air through the turbine. The bi-directional flows are equal in force and volume as the air passes through the turbine.
In comparison, conventional open-ended OWC-type configurations have unequal bi-directional flows. Flows in conventional OWC systems have to push air out into the atmosphere from the ocean side and then, suck air back into the turbine from the atmosphere. The air flows coming from ocean side half cycle are actually weaker than those being sucked back through the turbine from the atmospheric half cycle. Compressed flows coming from the capture chamber are less robust and have a reduced volume of usable air because the compressed flows are damped by the turbine itself. The turbine obstruction prevents the capture chamber to fill completely with water, thus there is less wave energy to be captured. There are two solutions to this imbalanced flow: The first solution has been utilized by the Australian developer Wave Swell Energy. They allow the oceanic half-cycle to vent freely into the atmosphere, bypassing the turbine entirely. Then, when the wave height lowers in the capture chamber, ambient air is sucked through the turbine during the reverse flow atmospheric half cycle. In this scenario, the turbine extracts air flow energy in one direction only. Nevertheless, this arrangement is more efficient than conventional OWC systems that normally push air through the turbine from the capture chamber. Dr. Tom Denniss of Wave Swell Energy, says "Comprehensive testing has shown that there's 15% more energy on average in the system...". The second alternative solution to the imbalanced OWC flows, is to utilize the Hanna closed loop system. This allows the turbine to extract air flow energy in both directions, where the energy cycles have an equal force and volume both ways.
Generally, OWC or OAC systems use a self-rectifying turbine. Commonly, these systems push air into the turbine as a wave crests in the capture chamber. Then, the used air continues to be pushed out into the atmosphere. When the wave’s height falls off, air is drawn back through the turbine from the atmosphere. In this case, an OWC is considered to be an open system. This is because it has an atmospheric component. Pushing air out of the system, through the turbine and then into the atmosphere, has a damping effect that reduces energy capture. Drawing air back in from the atmosphere is less dynamic (forceful) than the air that is pushed out from the ocean side. Thus, there are two inherent pressure losses at the turbine when air is either pushed out from the ocean side or when air reenters from the atmospheric side. The system is imbalanced.
The present invention is balanced. It has no atmospheric component. It is a closed loop system. The total movement of air is fully utilized within the rotor Casement (1). There are no pressure losses like those experienced in common OWC systems which have the atmospheric component in every half cycle. For the present invention, the pressure and volume of air in both half cycles is virtually identical. Because of the closed loop configuration, there is a simultaneous push and pull of air. While one Nozzle (3) pushes air into the rotary drive, the opposing Nozzle (3) is sucking out air at the very same time.
The simultaneous push and pull alternates with each wave cycle. This arrangement produces less damping (resistance) and a more efficient power capture than seen with conventional OWC systems. The present invention uses two lightweight “Hinged Flappers” (4a and 4b) to redirect the alternating air flows within the sealed rotary drive. To produce angular momentum, one Flapper (4a) will direct air from a Nozzle (3a) onto the Rotor’s radial Collector Fins (2). Simultaneously, the other Flapper (4b) directs air to be sucked out at a second Nozzle (3b) which is placed on the opposite side of the rotary Casement (1). The position of either Flapper will simultaneously reverse at every half cycle of passing incident waves. The result is a Power Take-Off (PTO) that is mechanically rectified and maintains a continuous one way rotary force to efficiently spin a Generator (5).
DESCRIPTION of the INVENTION:
The PTO is a sealed, circular, pancake-shaped hollow Casement (1). The Casement contains a single light weight Rotor (2) with numerous slanted Collector Fins (2) placed around the Rotor’s periphery. The rotor’s spinning mass acts as a flywheel. There are two openings at opposite sides of the Casement. The openings serve as Nozzles (3a and 3b) to convey alternating streams of air. For instance, one Nozzle (3a) pushes air in while the opposite Nozzle (3b) is simultaneously sucking air out. Depending on which Nozzle has the incoming air, the relative position of either of the two Hinged Flappers (4a or 4b) will direct the incoming air flow to maintain a continuous one way movement of the Rotor (2). At the same instant, the outgoing air flow is being sucked out through the opposite Nozzle (3b). Then, when the air flow reverses direction, the V-shaped Hinged Flappers will instantaneously alternate their respective positions so the Rotor is able to spin continuously in the same direction.
The alternating air flows can be produced by three different types of OWC systems: (1) by open-ended shore based installations; or (2) by closed loop floating point absorbers that use a prime mover such as a stacked set of air bellows. Submerged buoys that use the closed loop turbine will use alternating air flows created by (3) pressure differentials. The air held inside the subsurface buoy, will move back and forth through the turbine by the fluctuating pressures of passing waves. See a description of a submerged buoy using a mechanical PTO by clicking HERE. The closed loop turbine PTO can easily replace the mechanical PTO in the submerged buoy. See a description of the floating surveillance buoy by clicking HERE.
BACKGROUND OF THE INVENTION:
The current invention is similar to the familiar water wheel which turns a shaft to do useful work, i.e. milling grain or corn. Another similar device is the Pelton Wheel, commonly used in hydropower plants to spin generators. Pelton wheels have peripheral buckets that fill with water, rotating the wheel and shaft. For wave energy conversion, there exists OWC-type, self-rectifying turbines of the Impulse or Reaction variety. As discussed in the previous Operating Principle section, these OWC-type turbines are open to the atmosphere and have uneven reciprocating flows caused by the less robust oceanic half-cycle component.
An example of a patented PTO is a bi-radial turbine invented by Antonio Falcão and Luis Gato of Portugal (US 9,371,815 B2). This device has two radial rotors and is energized by an open OWC air flow. It is not a closed loop design.
Additional examples of prior art are: M3 Wave’s subsurface device that uses closed loop differential pressures and dual flexible air bladders to drive a turbine, WO 2013/019214 A1; a subsurface closed loop buoy that uses a turbine by S.K. Song, US 9,518,556 B2 (now expired); a submerged device by 40South Energy, CA 2,670,311 C, and an invention by W.W. Hirsch, US 7,199,481 B2.
The present invention is an improved PTO. Since it is a closed loop system, the inefficient losses seen in open systems are eliminated. These inefficiencies are caused by damped air flows being pushed out from the ocean side and reduced flows being drawn back in from the atmosphere. The present design is not a turbine. It is more accurately a simple air wheel that is rotated by alternating air flows within a closed loop system. The closed loop design spins a generator with greater efficiency than prior art designs which use an open-ended OWC system. Reciprocating air flows coming in and exiting the sealed Casement are always equal. The simultaneous “push and pull” of the air streams reduce drag and resistance so more energy is conserved to spin the rotor. The new design is simple to manufacture with only one moving part. No components come in contact with water. The use of two Hinged Flappers is a novel, uncomplicated means of mechanically rectifying the bi-directional air flows to continuously spin the rotor in one direction only. The device will not contaminate the ocean. The primary driving force is clean pneumatic energy.
NOMENCLATURE of the TWO FIGURES:
1: Sealed Casement 4: Hinged Flappers (a) and (b)
2: Rotor with Collector Fins 5: Generator Housing
3: Inlet and Outlet Nozzles (a) and (b)
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