ENERGY CONVERSION SYSTEM FOR USE IN BIDIRECTIONAL FLOWS AND

ITS METHOD OF OPERATION

Field of the invention

The present invention relates to a pneumatic energy conversion system for use in alternated bidirectional flows. As such, it operates between two spaces with an associated relative pressure difference that alternately changes sign.

To efficiently extract energy, the system comprises a set of rotors designed for unidirectional flow and an integrated rectifying system.

While keeping the same rotor rotational speed direction, the system efficiently operates between the two spaces, designated as first space (A) and second space {B5 , with pressures p _A and p ₈ ,, respectively. The sign of the pressure difference P _A -P _B alternately changes.

One possible application domain for Che present invention are oscillating water column systems for wave energy conversion and any other case where there is energy associated with a pressure difference that changes sign with time.

Field of the invention

There is a wide variety of wave energy converter systems. One class of such systems is named the Oscillating Water Column (OWC) . These devices comprise a hollow structure with an opening submerged in the water in such a way that there is an air chamber inside said structure, above the water level. Through wave action, the water level moves and oscillates in relation to the structure. The movement alternately compresses and decompresses the air in the chamber. As a consequence, pressure inside the air chamber is alternately superior or inferior to the atmospheric pressure. The pressure difference is used to drive an air turbine placed in a duct connecting the air chamber to the atmosphere. The turbine is used to drive an electrical generator or another piece of equipment depending on the application. Since the water level moves periodically according to the wave cycle, the air flow through the turbine is bidirectional. The turbine should therefore be self- rectifying or have an airflow rectifying system.

OWC systems were invented by Yoshio Masuda, as described in Patent US3200255. These converters use one unidirectional conventional turbine and an external rectifying system with non-return valves to produce the unidirectional flow. These turbines were applied only to small scale converters in navigation buoys. For large scale devices, the complexity of the rectifying system and its related energy losses have restrained a broader application. Self-rectifying turbines keep the same rotational speed direction independently of the flow direction. From the several turbines, one should highlight the Wells turbine, described in Patent G3159570G. It is possibly the most studied and used turbine for bidirectional flows. However, it operates efficiently only over a relatively narrow range of flow rates. In practice, the mean efficiency is low compared with conventional unidirectional turbines.

The axial impulse turbine described in Patent US3922739 is the most frequent alternative to the Weils turbine. It is sometimes used in OWC converters. In this turbine, the flow is accelerated and deflected by two sets of guide vane systems, before crossing the rotor. The two guide vane systems may be regarded as the mirror image of each other with respect to a plane perpendicular to the rotational, axis. Due to this symmetry, the air flow leaving the rotor is not aligned with the second guide vane system and has a large incidence angle that leads to flow separation and significant, energy losses. There are several approaches to mitigate these aerodynamic losses. One solution is to use a control mechanism that changes the second guide vane system angle to reduce incidence. Another solution is to increase the radial distance between the guide vane systems and the rotor and in this way decrease flow kinetic energy and consequently the losses at the entrance to che second guide vane system. This solution is described in Patent US8596955B2. The bi-radial turbine is another type of self-rectifying turbine that is described in Patent WO2011102746. This turbine has a radial entry and a radial exit, in which the flow is centripetal at the rotor entry and centrifugal at. the exit. Outside the rotor, the flow is essentially radial in direction. The guide vane system comprises two rows of guide vanes circumferentially positioned around the rotor; its wails are tendencially flat disks which are perpendicular to the rotational axis. A comparison between the bi-radial turbine, the Wells turbine, and the axial-flow impulse turbine shows that the first one is more compact in the axial direction and has superior aerodynamic efficiency. In the fixed guide vane version, the bi-radial turbine also has significant losses in the second guide vane system.

Another two-rotor air turbine for OWC wave energy converters is described in Patent WO2014185806. This turbine has two rotors and its respective guide vane systems assembled on the same axis. The two blade row systems are axially offset from each other and resemble two coaxial conventional turbines. The air flows unidirectional iy from the OWC chamber to the atmosphere through one of the .rotors, and flows unidirectional ly from the atmosphere to the OWC chamber through the other rotor. One rotor converts the flow from the OWC chamber to the atmosphere and the other rotor converts the flow from the atmosphere to the chamber. This flow configuration is only possible due to a double set of duces and a valve system for flow rectification.

Another configuration was published in the scientific paper «A twin unidirectional impulse turbine topology for OWC based wave energy plants* published in the journal Renewable Energy, Vol. 34, pp. 692-698, 2009. This configuration, called twin-rotor, uses two identical unidirectional turbines coupled with an electric generator and with a pneumatic chamber. For one flow direction, one turbine is driven efficiently (direct drive) while the other turbine is driven with heavy aerodynamic losses (inverse drive) . The inverse drive turbine partially blocks the fluid flow, causing the majority of the flow to pass through the direct drive turbine. The operation roles are inverted each time the pressure difference between the OWC chamber and the atmosphere changes sign. While a turbine operating in direct drive may be highly efficient, when operating in inverse drive its efficiency is negative: the rotors produce a resistive torque which reduces the system global efficiency. This configuration operates without any type of valves. Detailed description of the invention

The present invention relates to a twin-rotor pneumatic energy conversion system that has an integrated flow rectification system designed to efficiently extract energy in alternated bidirectional flows.

The proposed new twin-rotor and rectification system configuration allows the device to attain the performance of conventional turbines with a rectification capability that is affordable to build and maintain.

One possible version of the present invention is schematically shown in Figure 1, representing a section by a plane containing the rotational axis of the rotors. Figure 2 shows an exterior view of the same implementation. The overall system operates between, the first space (A) and the second space {B} . These spaces are pressure reservoirs and can be, for example, the pneumatic chamber of an OWC device and the atmosphere. The system is divided into the first sector (100) and the second sector (200), the places where conversion of pneumatic energy into mechanical energy occurs. In the center, there is one or more devices that use mechanical energy (300), such as electrical generators, pumps or compressors.

The system configuration has the following key characteristics: (i) inside the first sector (100) there is a route through which the working fluid flows, unidirecticnaily, from the second space {B5 to the first, space (A); (ii) in the route of the first sector (100) there is, at least, one rotor that converts pneumatic energy into mechanical energy; (iii) inside the second sector (200) there is a route through the working fluid flows, unidirecti.onal.ly, from the first space (A) to the second space (B) ; (iv) in the route of the second sector (200) there is, at least, one rotor that, converts pneumatic energy into mechanical energy; (v) the route of the first sector (100) does not intersect the route of the second sector (200); (vi) the selection of the sectors through which the working fluid flows is done by the first mean of flow restriction (1705 and by the second mean of flow restriction (270) .

The means of flow restriction have one or more movable components, such as cylindrical or plug obturators, which depending on the position, block or allow fluid flow in the sector routes.

Considering the case where the pressure in the second space (B) is greater than the pressure in the first space (A), p» > pa, as in the representation of Figure l-(i), the second mean of flow restriction (270) is in the "closed" state and the first mean of flow restriction (170) is in the "open" state. Therefore, the working fluid flows from the second space (B) to the first space (A) . It. flows in the route of the first sector (100) and energy conversion occurs in the first rotor (110) .

When P _A > pa, as represented in Figure l-(ii), the first mean of flow restriction (170) is in the "closed" state and the second mean of flow restriction (270) is in the "open" state. Therefore, the working fluid flows from the first space (A) to the second space (B) , passing by the route of the second sector (200), with energy conversion on the second rotor (210).

The first mean of flow restriction (170) and the second mean of flow restriction (270) can actuate simultaneously, blocking both routes between the first space (A) and the second space (B) . This action is essential for phase control of a wave energy converter and allows a significant increase in energy extraction. Simultaneous blockage also protects the system from the exterior in case of too energetic sea states associated with extreme weather conditions. Partial blockage of the routes is a possible action to control the flow rate through the rotors. The actuation mechanism can be electrical, hydraulic:, pneumatic or of another type.

The connection between any of the spaces, first space (A) or second space (B) , can be achieved with a set of manifolds. These can be classified according to their function: intake manifolds or exhaust manifolds. The application of intake and exhaust manifolds depend on the nature of the first space (A) and the second space (B) . These may be confined spaces, such as a pneumatic chamber of an OWC wave energy converter, or non-confined spaces, such as the atmosphere . In Figures 1 and 2, the confined space is the second space (B5. In this case, the connection between the second space (B) and the first sector (100) is made by the first intake manifold (140), that collects working fluid for conversion in the first sector {100} (Figures 1 and 2-{i}). The connection between the second sector {200} and the second space (8) is made by the first exhaust manifold (240) that emits the working fluid after conversion in the second rotor {210} (H'igures 1 and 2{iij).

Considering a non-confined space, such as the atmosphere, represented by the first space (A) in the Figures 1 and 2, this space, by definition, surrounds the components of both the first sector (100) and the second sector {200}, As such, the first exit duct (130) and the second entry duct (260) are in direct connection with the first space (A) , making the use of manitoIds opt iona1. The manifolds can be similar to plenum chambers or to spiral casings. For both types, the connection to the sector routes is preferably made in a direction that is perpendicular to the rotational axis of the rotors, as shown in Figures 2, 9 and 10.

Depending on the type of intake manifolds, Che system may incorporate the first guide vane system (120) and/or the second guide vane system {220} that contain one or more sets of blades that guide the flow, as shown in Figures 3 and 6.

Considering the first intake manifold (140) to be a plenum chamber as represented in Figure 1, this manifold supplies a uniform radial flow to the first entry duct (160) . To efficiently extract energy from this flow in the first rotor (110), it is necessary to use the first guide vane system (120) to deflect the flow and add a tangential speed component. A projection cf the rotor and the guide vane system in a perpendicular plane to the rotational axis in shown in Figure

In the implementation represented in Figure 9, use of a spiral casing as a first intake manifold (140) is made. The working fluid enters the first entry duct (not visible) with tangential speed, therefore the use of the first, guide vane system is optional .

The system described in the present invention has the capability to use rotors like the ones used in conventional gas turbines. The rotors and guide vane systems can be radial (Figure 3), axial (Figure 6) or mixed-flow types. Since the flow is unidirectional, the blades can be slightly asymmetric and with a reaction degree different from aero (reaction turbine), splitting the pressure drop between the rotor and the guide vane system. Other configurations may also be considered: multiple sets of rotors arranged in series and/or guide vane systems with adjustable stagger angles.

The rotors are physically connected to means of mechanical transmission that, in the simplest implementation, are shafts fixed to the rotors' hubs. Independently of their complexity, the means of mechanical transmission transfer mechanical energy from the rotors to other devices. Depending on the application, it may be necessary to use mechanical transmission to increase or reduce the rotational speed, rod-cranks or rack and pinion systems .

To reduce kinetic energy losses at rotor exit, the present invention comprises the first exit duct (1305 and the second exit duct (230! . These ducts convert part of the flow kinetic energy into static pressure, increasing the device's tota.L-t.o-- static efficiency. Duct geometry can be defined by the rotation of two generatrixes with respect to the rotational axis of the rotors of each sector (first sector (100) or second sector (200) ) .

The components of the first sector (100) can be arranged to form a mirrored image of the components of the second sector (200) with respect to a symmetry plane perpendicular to the rotational axis of the rotor of each sector, considering these axes to be collinear. However, sector asymmetry may be used in some cases to better adapt the preset invention to specific operating conditions.

The present energy conversion system combines, in the same device, the high efficiency of conventional gas turbines and the capability to extract energy in biridectionai flows, without using complex mechanisms. Apart from the rotors, the only moving parts are the means of flow restriction, which have. a small displacement and, when open, do not induce pressure losses on the flow. The present invention also allows maintenance access to the generator and the actuators of the means of flow restriction from the exterior of the system. The means of flow restriction can be used for phase control, safety shutdown and flow control.

Description of the figures

Figure 1. Schematic representation of a cross-section of the energy conversion system by a symmetry plane that contains the rotational axis of its rotors. The first space (A) (non- confined space) and the second space (8) {confined space) are the two air volumes with an alternating pressure difference between them and from which the system converts energy. The first sector (100) and the second sector (200) are the two zones where the system converts pneumatic energy into mechanical energy. Conversion is made in the first rotor (110; and the second rotor (210) . Energy is supplied to one or more devices that use mechanical energy (300) by the first mean of mechanical transmission !150) and by the second mean of mechanical transmission (250) . For the represented configuration, the first entry duct (160) and the second entry duct (260) are inlet nozzles. The first exit duct. (130) and the second exit duct (230) are outlet diffusers. The gemometries of the first rotor (110), the second rotor (210), the first guide vane system (120) and the second guide vane system (220) are like the ones in conventional radial gas turbines. Working fluid flow intake from the second space (B) to the first sector (100) passes through the first intake manifold (140! . Working fluid flow exhaust from the first sector {100} to the first space (A) is made directly by the first exit duct (130) . Working fluid flow intake from, the first space (A) to the second sector (200) is made directly by the second entry duct (260) . Working fluid flow exhaust from the second sector {200} to the second space (B) is made by the first exhaust manifold (240) . Both the first intake manifold (140) and the first exhaust manifold (240) are plenum chambers. Both the first mean of flow restriction (170) and the second mean of flow restriction (270) have a plug obturator. In Figure l-(i) the first mean of flow restriction {170} is in the «open» state and the second mean of flow restriction (270) is in the «closed» state; energy conversion and transmission occur in the first sector (100). In Figure l-(ii), the first mean of flow restriction (170) is in the «closed» state and the second mean of flow restriction (270) is in the «open» state; energy conversion and transmission occur in the second sector (200) .

Figure 2. Exterior perspective of the energy conversion system in the same configuration as the representation of Figure i. The first space (A) (non-confined space) and the second space (B) {confined space) are the two air volumes with an alternating pressure difference between them and from which the system converts energy. The first sector (100) and the second sector (200) are the two zones where the system converts pneumatic energy into mechanical energy. Energy is supplied to one or more devices that use mechanical energy (300). Working fluid flow intake from the second space (B) to the first sector (100) passes through the first intake manifold (140). Working fluid flow exhaust from the first sector (100) to the first space (A) is made directly by the first exit duct (130) . Working fluid flow intake from the first, space (A) to the second sector (200) is made directly by the second entry duct (260) . Working fluid flow exhaust from the second sector (200) to the second space (B) is made by the first exhaust manifold (240) . Both the first intake manifold (140) and the first exhaust manifold (240) are plenum chambers. In Figure 2-(i) _/ the first mean of flow restriction (170) is in the «open» state and the second mean of flow restriction (270) is in the «closed» state; energy conversion and transmission occur in the first sector (100) . In Figure 2-{ii), the first mean of flow restriction (170) is in the «closed» state and the second mean of flow restriction is in the «open» state; energy conversion and transmission occur in the second sector (200) .

Figure 3. Schematic representation of the first rotor (110), the second rotor (210), the first guide vane system (120) and the second guide vane system (220) that equip the configuration of the invention in Figures 1 and 2. The drawing plane is perpendicular to the rotational axis of the rotor. The blades of the first guide vane system (120) and of the second guide vane system (220) can have an airfoil shape. The curvature of the mean line of the guide vane blades deflects the inlet centripetal flow by adding a circumferential speed component. At the entry of both the first rotor (110) and of the second rotor (210), the flow is mainly centripetal and at the exit its direction is mainly axial.

Figure 4. Schematic representation of a cross-section of the energy conversion system by a symmetry plane that contains the rotational axis of its rotors. The first space (A) (non- confined space) and the second space (B) (confined space) are the two air volumes with an alternating pressure difference between them and from which the system converts energy. The first sector (100) and the second sector (200) are the two zones where the system converts pneumatic energy into mechanical energy. Conversion is made in the first rotor (liO) and in the second rotor (210) . Energy is supplied to one or more devices that use mechanical energy (300) by the first mean of mechanical transmission (150) and by the second mean of mechanical transmission (250) . For the represented configuration, the first entry duct (160) and the second entry duct (260) are inlet nozzles. The first exit duct (130) and the second exit duct (230) are outlet diffusers. The geometries of the first rotor (110), the second rotor (210), the first guide vane system (120) and the second guide vane system (220) are like the ones in the conventional "Kaplan" hydraulic turbines. Working fluid flow intake from the second space (B) to the first sector (100) passes through the first intake manifold (140) . Working fluid flow exhaust from the first sector (100) to the first space (A) is made directly by the first exit duct (130) . Working fluid flow intake from the first space (A) to the second sector (200) is made directly by the second entry duct (260) . Working fluid flow exhaust from the second sector (200) to the second space (Β· is made by the first exhaust manifold (240) . Both the first mean of flow restriction (170) and the second mean of flow restriction (270) have a cylindrical obturator. In this representation, the first mean of flow restriction (170) is in the «open» state and the second mean of flow restriction (270) is in the «closed» state; energy conversion and transmission occur in the first sector (100) .

Figure 5. Schematic representation of a cross-section of the energy conversion system by a symmetry plane that contains the rotational axis of its rotors. The first space (A) (non- confined space) and the second space (B) {confined space) are the two air volumes with an alternating pressure difference between them and from which the system converts energy. The first sector (100) and the second sector (200} are the two zones where the system converts pneumatic energy into mechanical energy. Conversion is made in the first rotor {110} and in the second rotor (210) . Energy is supplied to one or more devices that use mechanical energy (300) by the first mean of mechanical transmission (150) and by the second mean of mechanical transmission (250) . For the represented configuration, the first entry duct (160) and the second entry duct (260) are inlet nozzles. The first exit duct (130) and the second exit duct (230) are outlet diffusers. The geometries of the first rotor (110), the second rotor (210), the first guide vane system (120) and the second guide vane system (220) are like the ones in conventional axial gas turbines. Working fluid flow intake from the second space (B) to the first sector (100) passes through the first intake manifold (140) . Working fluid flow exhaust from the first sector (100) to the first space (A) is made directly by the first exit duct (130) , Working fluid flow intake from the first space (A) to the second sector (200) is made directly by the second entry duct (260) . Working fluid flow exhaust from the second sector (200) to the second space (B; is made by the first exhaust manifold (240) . Both the first intake manifold (140) and the first exhaust manifold (240) are plenum chambers. Both the first mean of flow restriction (170) and the second mean of flow restriction (270) have a cylindrical obturator. In this representation, the first mean of flow restriction (170) is in the «open» state and the second mean of flow restriction (270) is in the «ciosed» state; energy conversion and transmission occur in the first sector (100). Figure 6. Schematic representation of the first rotor sliOj, the second rotor (210), the first guide vane system (120) and the second guide vane system (220) that equip the configuration of Figure 5. The drawing plane is parallel to the rotational axis of the rotor. The blades of the first guide vane system (120), the second guide vane system (220), the first rotor (110) and the second rotor (210) can have an airfoil shape. The curvature of the mean line of the guide vane blades deflects the inlet axial flow by adding a circumferential speed component. At the entry of both the first rotor (110) and of the second rotor (210), the flow is mainly axial. Fluid flow across the blades of both the first rotor (110) and the second rotor (210) produces torque on the axes of the rotors.

Figure 7. Schematic representation of a cross-section of the energy conversion system by a symmetry plane that contains the rotational axis of its rotors. The first space (A) {non- confined space) and the second space (B) {confined space) are the two air volumes with an alternating pressure difference between them and from which the system converts energy. The first sector (100) and the second sector (200) are the two zones where the system converts pneumatic energy into mechanical energy. Conversion is made in the first rotor {110) and in the second rotor (210) . Energy is supplied to one or more devices that use mechanical energy (300) by the first mean of mechanical transmission (150) and by the second mean of mechanical transmission (250) . For the represented configuration, the first entry duct (160) and the second entry duct (260) are inlet nozzles. The first exit duct (130) and the second exit duct (230) are outlet diffusers. The geometries of the first rotor (110), the second rotor (210), the first guide vane system (120) and the second guide vane system (220) are like the ones in the conventional "Kaplan" hydraulic turbines. Working fluid flow intake from the second space (B) to the first entry duct (160) and collection of working fluid flow that passes through the second exit duct (230) are made directly by the central manifold (400) . The first space (A) is directly connected to the first exit duct (130) and to the second entry duct (260) . The central manifold (400) is a plenum chamber. Both the first mean of flow restriction (170) and the second mean of flow restriction {270} have a cylindrical obturator. In this configuration, the first mean of flow restriction (170) is in the «cpen» state and the second mean of flow restriction (270) is in the «closed» state; energy conversion and transmission occur in the first sector (100) .

Figure 8. Schematic representation of a cross-section of the energy conversion system by a symmetry plane that contains the rotational axis of its rotors. The first space (A) ⁽ non- confined space) and the second space (3) (confined space) are the two air volumes with an alternating pressure difference between them and from which the system converts energy. The first sector (100) and the second sector (200) are the two zones where the system converts pneumatic energy into mechanical energy. Conversion is made in the first, rotor (110) and in the second rotor (210) . Energy is supplied to one or more devices that use mechanical energy ⁽ 300) by the first mean of mechanical transmission (150) and by the second mean of mechanical transmission (250) . For the represented configuration, the first entry duct (160) and the second entry duct (260) are inlet nozzles. The first exit duct (130) and the second exit duct (230) are outlet diffusers. The geometries of the first rotor (110), the second rotor (210), the first guide vane system (120) and the second guide vane system (220) are like the ones in conventional radial gas turbines. Working fluid flow intake from the second space (B; to the first entry duct (1605 is made through the first intake manifold (140). Collection of working fluid flow between the first exit duct (130) and the first exit duct (130) and the first space (A) is made through the second exhaust manifold (180) . Working fluid flow intake from the first space (A) to the second entry duct (260) is made through the second intake manifold (280) . Collection of working fluid flow between the second exit duct (230) and the second space (B) is made through the first exhaust manifold (240). The first intake manifold (140), the first exhaust manifold (240), the second exhaust manifold (180) and the second intake manifold (280) are plenum chambers. Both the first mean of flow restriction (170) and the second mean of flow restriction (270) have a plug obturator. In this configuration, the first mean of flow restriction (170) is in the «open» state and the second mean of flow restriction {2705 is in the «closed» state; energy conversion and transmission occur in the first sector (100) .

Figure 9. Exterior perspective of the energy conversion system. The first space (A) (non-confined space) and the second space (B) (confined space) are the two air volumes with an alternating pressure difference between them and from which the system converts energy. The first sector (100) and the second sector (200) are the two zones where the system converts pneumatic energy into mechanical energy. Energy is supplied to one or more devices that use mechanical energy (300). Working fluid flow intake from the second space (B) to the first sector (100) passes through the first intake manifold (140). Working fluid flow exhaust from the first sector (100) to the first space (A) is made directly by the first exit duct (130) . Working fluid flow intake from the first space (A) to the second sector (200) is made directly by the second entry duct (260). Working fluid flow exhaust from the second sector (200) is collected by the first exhaust manifold (240) and discharged to the second space (B) . 3oth the first intake manifold (140) and the first exhaust manifold (240) are spiral casings.

Figure 10. Exterior perspective of the energy conversion system. The first space (A) (non-confined space) and the second space (B) (confined space) are the two air volumes with an alternating pressure difference between them and from which the system converts energy. The first sector (100) and the second sector (200) are the two zones where the system converts pneumatic energy into mechanical, energy. Energy is supplied to one or more devices that use mechanical energy (3005. Working fluid flow intake from, the second space (B) to the first sector (100} passes through the first intake manifold (140). Working fluid flow exhaust from the first sector (100) is directly discharged by the first exit duct (1305 to the first space (A) . Working fluid flow intake from the first space (A) to the second sector (200) passes through the second intake manifold (280) . Working fluid flow exhaust from the second sector (2005 is collected by the first exhaust manifold (240) and discharged to the second space (B) . Both the first, intake manifold (140) and the second intake manifold (280) are spiral casings. The first exhaust manifold (240) is a plenum chamber.

Figure 11. Schematic representation of a cross-section of the energy conversion system by a symmetry plane that contains the rotational axis of its rotors. The first space (A) (non- confined space) and the second space (B) (confined space) are the two air volumes with an alternating pressure difference between them and from which the system converts energy. The first sector (100) and the second sector (200} are the two zones where the system converts pneumatic energy into mechanical energy. Conversion is made in the first set of rotors (115) and in the second set of rotors (215) . Energy is supplied to one or more devices that use mechanical energy (300) by the first mean of mechanical transmission (150) and by the second mean of mechanical transmission (250) .

For the represented configuration, the first entry duct. (160) and the second entry duct (260) are inlet nozzles. The first exit duct (1305 and the second exit duct (230) are outlet diffusers .

The geometries of the first set of rotors (115), the second set of rotors (215), the first guide vane system (1205 and the second guide vane system (220), of the first set of guide vanes (125) and the second set of guide vanes (225) are like the ones in conventional radial gas turbines. Working fluid flow intake from the second space (B) to the first sector (100) passes through the first intake manifold (140). Working fluid flow exhaust from the first sector (100) to the first, space (A) is made directly by the first exit duct (130} . Working fluid flow intake from the first space (A) to the second sector (200) is made directly by the second entry duct (260) . Working fluid flow exhaust from the second sector (200) to the second space (3) is made by the first exhaust manifold (240) . Both the first intake manifold (140) and the first exhaust manifold (240) are plenum chambers. Both the first mean of flow restriction (170) and the second mean of flow restriction (270) have a plug obturator. The first mean of flow restriction (170) is in the «open» state and the second mean of flow restriction (270) is in the «closeci» state; energy conversion and transmission occur in the first sector (100).

Figure 12. Schematic representation of a cross-section of the energy conversion system by a symmetry plane that contains the rotational axis of its rotors. The first space (A) (non- confined space) and the second space (B) (confined space) are the two air volumes with an alternating pressure difference between them and from which the system converts energy. The first sector (100) and the second sector (200) are the two zones where the system converts pneumatic energy into mechanical energy. Conversion is made in the first rotor (110) and in the second rotor (210) . Energy is supplied to one or more devices that use mechanical energy (300) by the first mean of mechanical transmission (150) and by the second mean of mechanical transmission (250) . The geometries of the first rotor (110) and the second rotor (210} are like the ones in conventional radial gas turbines. The first mean of flow restriction (.170) is in the «open» state and the second mean of flow restriction (270} is in the «ciosed» state; energy conversion and transmission occurs in the first sector (100) .

Lisbon, September 22 ^rd , 2017.