Patent Application
20250179919
The present invention relates to dynamic machines typically called turbomachines used to exchange work with fluids, fluids whose pressure and/or speed is modified. Such work exchange is typically performed with volumetric or dynamic machines. More particularly, the invention relates to the type of bladeless turbomachine, also called boundary layer/multiple-disc/Tesla turbomachine. Application examples are turbines/expanders, compressors, pumps/aspirators, operating with a variety of fluids, such as water, air, gas or gas mixtures, non-Newtonian fluids, two-phase fluids.
The “boundary layer disk turbine” also named “Tesla turbine (U.S. Pat. Nos. 1,061,206A and 1,061,142A)”, “multiple disk turbine”, “bladeless turbine”, “Prandtl layer turbine” was invented by Nikola Tesla in the early 19th century. The rotor comprises thin discs with a central hole, mounted parallel on a shaft and spaced by gaps while the stator is positioned at a greater radial distance than the rotor and guides the flow in the desired direction. The periphery of the stator is connected to an external volute. In turbine mode, the fluid at higher pressure enters the volute and then into the stator, which accelerates it tangentially to the rotor and exits the axially central holes of the rotor at lower pressure. In compressor mode, the lower pressure fluid enters the central holes of the discs and exits the rotor with higher pressure from the periphery of the discs. The peripheral fluid at high speed increases its static pressure through the stator and finally using an external volute. Thus, this machine is reversible: by changing the direction of rotation of the rotor, both modes, turbine and compressor, can be achieved using the same single machine with minor or no modifications to the configuration of the machine itself. The relative speed between the fluid and the rotor discs is very low compared to traditional bladed turbines. Due to this low airspeed, the flow inside the rotor is substantially laminar. The laminar flow field within the Tesla turbine rotor is the key to effective energy transfer between fluid and disks. This energy exchange between the fluid layers and the disks is due to the tangential force. The drag force generated on the discs due to these tangential forces lies in the plane of rotation of the discs. Hence, in the case of the Tesla turbine, the viscous shear resistance is favorable and necessary for the generation of mechanical energy unlike an energy loss in the case of a bladed turbine where the viscous resistance dissipates mechanical energy as it is in the opposite direction to the rotation of the rotor. This interesting phenomenon has attracted many researchers to study bladeless turbines.
Tesla claimed to be able to achieve very high rotor efficiency (up to 97%). This has also been demonstrated analytically by researchers. However, experimentally the complete efficiency of the Tesla turbine (including a stator fluid dynamically coupled to the rotor) is typically very low (<35%) (Table 1—the reported efficiencies are of the isentropic adiabatic type). This lower efficiency of the Tesla turbine compared to conventional bladed turbomachinery has been a major reason why the former has not been commercially successful thus far. Table 1 shows the main scientific publications since 1950 with experimental efficiencies obtained by various researchers with different working fluids. It can be noted that the maximum efficiency obtained with air as working fluid is less than 35%. The last row shows the prototypes of a Tesla turbine tested at TPG-DIME, UNIGE (Thermochemical Power Group, Department of Mechanical, Energy, Management and Transport Engineering, University of Genoa, Italy). The efficiency of the Tesla turbine with air as working fluid of about 36% (highest recorded so far) has been demonstrated experimentally.
The table also shows that the Tesla turbine has been tested with different fluids: steam, air, water, organic fluids (refrigerant—mono/two-phase), etc.
The advantages of the Tesla turbine such as resistance to erosion, flow reversibility, simple and economical construction and flexibility in the choice of fluid make it suitable for both energy recovery and small scale power generation applications. Recently, a renewed interest in Tesla machines is clearly emerging. It should be noted that the trend has drastically increased in recent years; this is directly related to the high attention that micro-generation of energy has gained on the energy market, where Tesla turbines have interesting characteristics, mainly due to their high cost-effectiveness and relatively simple manufacture. However, there are still no unique criteria for the design of Tesla machinery and many authors and professionals work on very small prototypes (˜100-1000 Watt scale), where manufacturing tolerances and uncertainties in losses impede the accuracy of the experimentation.
A systematic study oriented towards the development of efficient and well-designed Tesla machines, having powers of the order of at least kW, is therefore necessary to exploit their potential to become one of the players in turbo-machine technologies, where their features are competitive or more promising than other conventional machines.
Consequently, it is necessary to improve this type of devices in order to improve the overall efficiency while maintaining or improving the constructive simplicity and operating costs, for different sizes of turbomachinery.
The authors of this patent specification studied and performed a detailed leakage analysis of a prototype 3 kW Tesla turbomachinery, which achieved the aforementioned record efficiency of approximately 36% for bladeless air expanders. Through a detailed experimental characterization it was possible to identify, for the first time, the main sources of losses, namely:
The present application proposes an innovative solution to both aspects: for the first, which represents an intrinsic loss already present in Tesla's first patent in 1913 and concerning all subsequent designs and worldwide realizations to date, and for the second, which affects many of the prototypes built by researchers.
The present invention relates to specific improvements in bladeless turbomachinery for power generation, energy recovery, compressor/booster, for producing mechanical power to drive mechanical/electrical/magnetic load applications. The working fluid can be single-phase and/or two-phase and/or multi-phase. This turbomachine can be used in a variety of applications, some of which are (but are not limited to) solar energy, hydrogen, natural gas, cryogenics, petrochemicals, power generation, supercritical carbon dioxide cycle, geothermal energy, Rankine cycle Organic, refrigeration, air conditioning and heat pumps, pressure reducing valve replacement for energy recovery, oil and gas applications and hydroelectric power.
From the intimate understanding of the stator-rotor losses phenomenon, the main innovation object of this patent application has arisen, which is able to considerably reduce this significant efficiency loss mechanism.
In fact, one of the reasons why bladeless turbomachinery has not been commercially successful is the low experimental efficiency. This is due to the need for a highly tangential flow at the rotor inlet. The present invention significantly reduces stator-rotor losses by providing less surface area exposed to tangential flow in the stator-rotor region. This invention improves the performance of the bladeless turbine/compressor to the level of conventional bladed machines, making it compete with conventional machines not only on a smaller scale (where bladed machines experience high losses, unlike non-blade machines) but also on a large scale. The innovation described in the present invention identified for the purpose of reducing the stator-rotor interaction losses also allows to define special sealing measures, to also reduce the second main cause of losses, i.e. leakage losses, up to a few percentage points. In addition, additional features have been included, relating to ways to reduce exhaust losses.
The invention achieves the predetermined objects and others by means of a reversible bladeless turbomachine i.e. capable of operating in turbine mode for the transfer of the energy of at least one fluid into mechanical energy or capable of operating in compressor mode for the transfer of mechanical energy in energy of a fluid, said turbomachine comprising:
Since, as mentioned, this machine is able to operate in turbine mode or in compressor mode, where possible reference will be made to the concept of the primary stage in which a fluid with high kinetic energy flows and to the concept of a secondary stage in which low energy fluid flows, where high and low energy are considered in mutually relative terms.
In this situation, a compressor turbomachine will have inlet fluid in the low energy stage and outlet fluid in the high energy stage precisely by virtue of the function of transferring mechanical energy from the shaft to increase the energy of the fluid.
Conversely, turbine operation will have high-energy fluid at the input and low-energy fluid at the output, being designed to transfer part of its energy to the rotating shaft.
As better described below and also in the embodiments of the figures, the invention solves the technical problem of increasing the efficiency of a Tesla type turbine by introducing a rotating distribution chamber interposed between the radial periphery of the rotor and the internal surface of the stator, which rotating chamber favors the distribution of the fluid between stator nozzles and rotor discs.
From the studies carried out by the Applicant it emerged that the configuration with a single stator channel brings benefits in terms of reduction of ventilation losses; however the invention foresees, in its variants, that it is possible to have two or more stator channels also according to the design characteristics of the turbomachine chosen by the person skilled in the art.
In one embodiment, said rotating distribution chamber is arranged coaxially with the discs and rotates at the same angular speed as said discs. In this preferred embodiment, the rotating distribution chamber is at least partially made by means of rotating discs with a specific shape (some embodiments will be described below) which can be made fixed with the shaft and therefore rotate at the same speed as the stator discs, thus defining portions of the surfaces that delimit the distribution chamber.
In one embodiment, said rotary distribution chamber is delimited by at least one chamber wall which radially and at least partially surrounds the rotor, said chamber wall being formed by at least part of the radially inner surface of at least one distribution member which it rotates coaxially with the rotation shaft, preferably at the same angular velocity as the disks.
Conventionally and also according to the present invention, the rotor of the bladeless turbomachine comprises a plurality of thin discs having similar or mutually different external and/or internal diameters with gaps between them (reciprocally spaced by a constant or variable distance between disk and disk) connected to a tree, creating a set of disks.
As regards the reduction of stator-rotor losses, there are two preferred embodiments: one for the traditional radial stator configuration and one for an innovative axial stator configuration.
When operating as a turbine mode, regarding the radial stator, the flow is accelerated through a radial stator and directed to the rotor spaces, where the flow travels and exchanges energy, from the peripheral inlet of the disc to the internal discharge of the disc. Unlike conventional Tesla machines, where the radial passages of the stator placed on the periphery of the rotating disks have an axial dimension close to the set of rotor disks, here the stator has a reduced axial dimension, for example half, and the jets stators are not directed immediately towards the rotating discs, but first enter a rotating “distribution chamber”. In a possible embodiment, this chamber comprises two rotary shaped discs (RSD), symmetrically or asymmetrically mounted on a shaft, which are shaped in such a way as to form a rotating radial passage to guide the fluid from the stator to the rotating discs. In this way there is a significant radial distance, for example 10% of the peripheral radius of the disc, between the stator and the set of rotating discs: consequently the friction between the set of rotating discs and the stator or casing is minimized, reducing friction losses between rotor and stator. A similar principle applies to the distribution chamber formed by the rotating pattern discs (RSD) in compressor mode.
As far as the axial stator is concerned, the stator comprises a radial/axial blade for the transit of the fluid having a high tangential speed, placed in communication with a rotating distribution chamber, which in a possible embodiment comprises one or two shaped rotating discs (RSD), symmetrically or asymmetrically mounted on a shaft, shaped so as to form an axial opening for the passage of fluid from/to the stator, and directing it towards/from the rotating discs. Furthermore, in this way, the friction losses between the rotor and the stator or casing are minimized, reducing the friction losses between the rotor and the stator.
The above configurations, in particular the rotating distribution chamber, are designed in such a way that the same device can operate, with little or no configuration changes, alternatively in turbine mode or in compressor mode depending on the direction of the fluid flow, which can be used to transfer energy to rotating discs (turbine mode) or which can be accelerated by discs which transfer mechanical energy from the shaft into kinetic energy to the fluid (compressor mode).
For various embodiments, in case a high axial length of the rotor (i.e. a large number of disks) is required, to ensure a smooth and well guided inlet flow to the rotating chamber and rotor (with reference to the turbine operating mode), it is possible to insert a flow divider or an intermediate disc/s, one or two or more than two, on the periphery of the rotor, and use it in combination with one or more of the other embodiments. The introduction of these embodiments of the present invention into the bladeless turbomachinery significantly improves the efficiency of the turbine or compressor.
In addition to minimizing stator-to-rotor losses, i.e., at the rotor inlet for turbine operation, this invention also includes ways of reducing losses at the rotor exhaust (turbine mode) or rotor inlet (compressor mode).
In a preferred variant of the invention, with reference to operation as a turbine, the rotor is then connected to an exhaust system to recover at least part of the residual kinetic energy of the outgoing fluid. When operating in compressor mode, the same system can function as a first stage of acceleration for the fluid which will then be accelerated by the main stage of acceleration, i.e. the rotor discs. The turbine exhaust system is preferably provided with a radial diffuser which is further connected to the volute(s) known in the art. The turbine of the present invention may have one axial exhaust or two axial exhausts.
Unlike many inventors who have tried to improve the performance of Tesla turbomachinery by introducing complex features on the discs themselves, increasing the complexity of the original Tesla bladeless design, this invention only adds simple external features to the original turbomachinery. Tesla without shovels. These features are simple to manufacture and simple to implement without introducing further complexities into the original bladeless design.
It is foreseen that, by applying both the conventional sealing devices and the solutions of this invention to the existing prototype, the peak isentropic adiabatic efficiency can be increased from 36% to over 70%, approaching the expected efficiency for the rotor alone, typically in the order of 80%-90% (as noted above, in conventional Tesla machines rotor alone efficiency is greatly affected by stator-to-rotor losses, which can more than half efficiency of the rotor alone).
Nomenclature: to facilitate understanding of the invention, the following terms are defined: Bladeless Turbomachinery—BTM, Bladeless Turbine—BT, Bladeless Compressor—BC.
The present invention discloses an improvement in the BTM—turbine and compressor or the like. However, the various embodiments of the present inventions can be used in combination with any known BTM design.
Some embodiments of the invention are described below according to the accompanying drawings, where:
However, the invention is not limited to the embodiments presented herein and the description is not intended to limit any of the other possible variations of the invention.
The following description relates to the mode of operation of the turbine with reference to the figures in the drawings, i.e., the mode of operation in which the fluid flow expands and produces useful work on the shaft. However, a similar principle of operation applies in case of compressor mode, i.e. when the rotating shaft is driven in the opposite direction of rotation by an external power source and the machine converts the mechanical energy into fluid energy.
Referring to the figures, and more specifically to
The various embodiments of the present invention shown in
In the configuration shown in
The BTM-related embodiments of the present invention shown in
Referring to
The various embodiments of the present invention shown in
For these embodiments as well of the present invention relating to the turbomachinery shown in
In a possible variant of the invention, the turbomachine comprises two rotating distribution chambers 19a and 19b, shown in
As a general overview of operation for the embodiments shown in
As a general overview of operation for embodiments of the present inventions shown in
With reference to
It is noted the presence of a plurality of spiral connection spokes 21 which depart from the hub for connection to the shaft 7 towards the solid body of the rotating shaped disc 11; such spiral connections therefore define a plurality of discharge openings crossed by the fluid on its way from or towards the zone of relatively lower pressure. Advantageously, this shape allows to support the rotation of the disc at high speed (typical of this type of turbine) and further reduce the losses in the transit area of the flow in the axial direction.
In an alternative variant of the invention the multistage turbine comprises several turbomachines of which at least one operates in operating mode and at least one of said turbomachines works in driving mode. This embodiment of the turbo-compressor type preferably provides for the presence of a turbine which converts energy of a fluid into mechanical energy, which mechanical energy is used to accelerate a second fluid to which part of this mechanical energy is transferred. Clearly such an embodiment can find application in the real world only when the efficiencies of the individual machines are such that they can be combined while maintaining a non-negligible part of the work useful at the end of the sequence of turbomachines, or in the case where the output work is negative but is compensated by a net positive external contribution, for example from an electric motor keyed to the same rotating shaft. Advantageously, the present invention allows this application unlike traditional Tesla machines thanks to the significant improvement in performance which is obtained by applying the inventive concepts reported herein.
2D and 3D computational fluid dynamics (CFD) analysis was performed to verify the effectiveness of the embodiments in the present inventions; only the operating mode of the turbine is considered.
Standard CFD approaches are used with ANSYS commercial software. A sensitivity analysis on the grid is performed to ensure that there are no significant changes in the output parameters. The k-w SST and Y+<1 s turbulence model is used for the rotor and walls present in the system. The real gas model is used to accurately predict machine performance.
Below are the details of the rotor used for the simulation:
CFD—Turbine mode without blades—configuration of
In this case, the configuration shown in
The 3D geometry comprises RSDs and discs exactly the same as in the 2D simulation, except the stator is also used here. The 3D simulation is closer to the real working condition of the turbine. A conventional converging nozzle known in the art is used.
The results of the calculations are shown in the following table (the efficiencies are of the adiabatic-isentropic type):
The 2D simulation does not include the stator losses but preserves the stator-rotor interaction losses: for this reason the obtained isentropic efficiency is higher in 2D than in 3D. On the other hand, the 3D stator model (i.e. stator losses are included) predicts 80% of the overall efficiency. The difference in efficiency is due to the losses present inside the stator. Geometric optimization of the nozzle would minimize the difference between 2D and 3D efficiency.
The CFD simulation of the radial diffuser at the exhaust shows a significant improvement in performance, reducing the static pressure at the rotor exhaust by exploiting the residual kinetic energy. One of these analyzes is performed as shown in the attached
The results are very promising and the efficiency values predicted by the CFD analysis are far beyond what can be obtained in the state of the art. The CFD values in the literature have typically been found in the range of 50-60% recovery of kinetic energy under pressure: with the present invention we have already demonstrated values above 80% overall.
From what has been described it is clear that the instrument according to the invention achieves the preset purposes.
The object of the invention is susceptible to modifications and variations, all falling within the inventive concept expressed in the attached claims. All the details can be replaced by other technically equivalent elements, and the materials can be different according to the requirements, without departing from the scope of protection of the present invention.
Although the object has been described with particular reference to the accompanying figures, the reference numbers used in the description and in the claims are used to enhance the understanding of the invention and do not constitute any limitation to the claimed scope of protection.
| Number | Date | Country | Kind |
|---|---|---|---|
| 102022000004460 | Mar 2022 | IT | national |
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/IB2023/051558 | 2/21/2023 | WO |
