Patent Application
20190055843
The present invention generally relates to turbines. More particularly, the present invention relates to an improved boundary layer turbine having spacers configured to provide a lifting force as fluid passes over the spacers to combine desirable high-efficiency characteristics of a bladed reaction or impulse steam turbine with the relatively low entry temperature, simplicity and durability of a boundary layer turbine.
A boundary layer turbine uses the boundary layer effect and not a fluid impinging upon the blades as in a conventional turbine. Such turbines are sometimes referred to as a Tesla turbine, which is a bladeless centripetal flow turbine, invented by Nikola Tesla in the early 1900s. A boundary layer turbine, or Tesla turbine, consists of a set of smooth discs with nozzles applying a moving fluid to the edge of the disc. The fluid drags on the disc by means of viscosity and the adhesion of the surface layer of the fluid. As the fluid slows and adds energy to the discs, it spirals into the center exhaust. It is well known in the art that boundary layer turbines, also referred to as Tesla turbines, are low-cost, highly durable “bladeless” turbines that can utilize many forms of working fluids under a wide range of working temperatures and pressures.
However, boundary layer turbines have historically been found to have effective operating efficiencies below 50%. Moreover, the high internal temperature, pressure and rotational stresses experienced under long-term use can cause the rotor discs to fracture and otherwise fail.
Conventional bladed steam turbines require Rankine cycle entry point temperatures above 1,049° F., or otherwise they must lower the fluid boiling point by use of Organic Rankine Cycle fluids, which adulterates the pure working fluid, require special materials, and add to design complexity required for successful operation. However, such conventional bladed reaction or impulse steam turbines are relatively highly efficient.
Accordingly, there is a continuing need for improvements in the boundary layer turbine to increase the efficiency of the turbine and resist failure of the rotor discs. The present invention fulfills these needs, and provides other related advantages.
The present invention resides in an improved boundary layer turbine, and related method, which is a high-efficiency working fluid turbine having hybridized traits of various turbine types. More particularly, an airfoil boundary layer turbine of the present invention combines the desirable high-efficiency characteristics of a bladed reaction or impulse steam turbine with the relatively low entry temperature, simplicity and durability of a boundary layer turbine. The present invention optimizes internal airflow, turbulence, adhesion and surface traction efficiency while strengthening the structure and stabilizing destructive blade oscillations which are observed in conventional boundary layer turbines when operating at high revolutions.
The boundary layer turbine of the present invention generally comprises a housing having a fluid inlet and a fluid outlet. A rotatable shaft is at least partially disposed within the housing. Two or more rotor discs are coupled to the shaft in spaced relation to one another. Spacers are attached to the face of at least a plurality of the rotor discs. The spacers have an elongated configuration, wherein a leading portion of the spacer has a greater surface area than a trailing portion of the spacer. The elongated spacers may comprise an airfoil. A lifting force is created as fluid passes over the elongated or airfoil spacers.
The elongated spacers may be spaced from an outer peripheral edge of the rotor disc and arranged end-to-end, such as in a generally circular pattern. A second set of elongated spacers may be arranged end-to-end in a generally circular pattern concentric to the first pattern. The turbine may also include a plurality of spacers having a generally circular configuration. The circular spacers may be disposed intermediate the elongated spacers and the rotor shaft.
The housing may comprise a case ring adjacent to peripheral edges of the rotor discs. An inner surface of the case ring has spaced apart depressions formed thereon. The spaced apart depressions, which may be formed as a pattern, creates a thin layer of turbulence as fluid passes over the inner surface of the case ring.
Other features and advantages of the present invention will become apparent from the following more detailed description, taken in conjunction with the accompanying drawings, which illustrate, by way of example, the principles of the invention.
The accompanying drawings illustrate the invention. In such drawings:
As shown in the accompanying drawings, for purposes of illustration, the present invention resides in an improved boundary layer turbine, generally referred to by the reference number 10. The turbine 10 of the present invention has hybridized traits of different turbine types, including an airfoil boundary layer turbine that combines the desirable high efficiency characteristics of a bladed reaction or impulse steam turbine with the relatively low entry temperature, simplicity and durability of a boundary layer turbine. The turbine 10 of the present invention optimizes internal air flow resistance, turbulence, adhesion, and surface traction efficiency while strengthening the blade structure and stabilizing destructive blade oscillations observed in conventional boundary layer turbines when operating at high revolutions.
With reference now to
With reference now to
The housing 20 may comprise a tubular case ring 30 which is slightly spaced apart from and surrounds the rotatable disc 16. Typically, as illustrated in
In a traditional Tesla or boundary layer turbine design, circular spacers, which may comprise washers, are used between the discs of the rotor assembly. These washers provide exact spacing for the passage of the working fluid between the discs. In addition, they present a curved surface perpendicular to the high velocity working fluid driving the rotor assembly of the turbine. Each time the leading edge curved surface of a circular washer or spacer rotates into the working fluid stream coming from the input nozzle at the perimeter at the turbine, a torque impulse is created. These impulses collectively improve low end startup torque.
When the velocity of the working fluid is greater than the speed of the washers or circular spacers in the rotating rotor, a low pressure zone occurs on the back side of the circular spacers in the direction of rotor rotation. This pressure differential propels the spacer forward. The energy absorbed by the circular washer or spacer adds to the total energy absorbed by the disc assembly. This interaction between working fluid and spacers is most efficient at the outer perimeter of the discs, such that the distance of the spacers to the shaft of the rotor assembly acts as a lever to effectively increase torque.
With reference to
In a particularly preferred embodiment, the elongated spacers 42 have an airfoil configuration, as shown. As such, the airfoil is in the shape (as seen in cross-section) of a wing, blade (propeller, rotor or turbine) or sail or the like. As such, the leading portion or edge 44 is at the point at the front of the airfoil spacer that has a maximum curvature or radius. The trailing portion or edge 46 is defined as the point of minimum curvature or radius at the rear of the airfoil. The width or thickness, in cross-section, of the airfoil spacer 42 varies along the length thereof, and typically includes a curved outer or upper surface 48 and an inwardly directed curve 50 at a lower edge portion thereof.
The airfoil configuration of the elongated spacer 42 creates an aerodynamic feature and the force of two components, namely, lift and drag. The lifting force is generally perpendicular to the direction of motion, whereas the drag force is generally parallel to the direction of motion. As the fluid flows over the elongated spacer 42 having the airfoil configuration, there results a difference in pressure between the upper side or surface 48 and the lower side or surface 50 due to the speed over which the fluid flows due to their respective configurations. More particularly, a low pressure area is created at the upper surface 48 of the elongated airfoil spacer 42 and a positive pressure is created at the lower or bottom edge 50, causing lift forces generally perpendicular to the fluid flow, and directed outwardly of the disc 16. It will be appreciated that various configurations of an airfoil design may be implemented into the present invention so long as the aerodynamic effects of drag and lift, due to a difference in pressure between the upper and lower surfaces 48 and 50 are created.
Replacing the circular washers or spacers in the rotor assembly with properly designed and placed airfoil shaped spacers has been found to significantly improve the transfer of energy from the working fluid and produce greater torque for the same amount of fuel usage. As with the circular spacers, an airfoil of appropriate thickness provides exact spacing for the passage of the working fluid between the discs 16. Also, like the circular spacers, when the high velocity working fluid impacts the leading edge 44 of the airfoil spacer 42, there is a torque impulse created. However, at this point the shape and configuration of the elongated spacer 42 provides a distinct advantage over the circular spacer for the transfer of energy from the working fluid to the rotor 18 and the subsequent gain in torque. There is a much greater pressure differential created between the top and bottom surfaces 48 and 50 of the elongated spacer 42, particularly when having an airfoil configuration, and this exerts a very strong lifting force on the elongated spacer 42 itself. As the elongated spacers 42 are solidly attached between the discs 16, the energy of the lifting force is added to the rotor assembly in the direction of rotation, increasing the efficiency of the turbine 10.
Utilizing the elongated airfoil spacers 42 of the present invention instead of circular spacers combines the most positive attributes of a bladeless boundary layer turbine with the high efficiency of a bladed reaction steam turbine, resulting in a hybridized airfoil bladed boundary layer turbine. The use of the elongated spacers 42, particularly the airfoil configured spacers, has been found to significantly improve the transfer of energy from the working fluid, thus producing greater torque for the same amount of fuel usage. The energy of the lifting force is added to the rotor assembly in the direction of rotation.
Another advantage of utilizing a spacer having an elongated, rounded configuration, and particularly an airfoil configuration, is the increase in surface area along the smooth top and bottom surfaces 48 and 50 of the spacer 42 which provides a much larger area of interaction with the working fluid. The effect of boundary layer drag increases proportionally to the increase in surface area and the transfer of energy from the working fluid to the rotor assembly is thus greatly enhanced. As the elongated spacer 42 moves in the direction of the high velocity working fluid, this allows the working fluid to stay in contact with the spacer 42 and disc 16 for a longer period of time, thereby transferring additional energy to the rotor 18 and further improving efficiency.
In conventional airfoil design lift or speed are maximized and boundary layer drag is kept to a minimum in order to maximize efficiency. However, the design and implementation of an elongated, rounded spacer 42, and particularly a spacer having an airfoil configuration, is unique in that it provides both maximum lift and maximum boundary layer drag to optimize turbine efficiency.
With reference now to
Replacing the circular spacers with the elongated or airfoil configured spacers 42 of the present invention creates a stabilizing effect that is created at the perimeter 52 of the disc 16 and rotor assembly due to the lifting force generated by the airfoil configuration of the spacer 42. This is the same principle as used in aircraft wing design that emphasizes lift and wing stability during flight. The airfoil shape is inherently more stable than the circular shape when operating in a high fluid velocity mass, such as air, steam or liquid.
The elongated or airfoil configured spacer geometry also places more spacer material along the perimeter 52 of the discs, thereby strengthening that region to prevent the problems mentioned above. Moreover, due to the enlarged size and configuration of the elongated, airfoil spacer 42, the spacer 42 may be mounted farther from the disc perimeter 52 in the working fluid stream. This increases the amount of disc material between the perimeter 52 and the spacer mounting holes, which adds to the strength of the material in that region. Aside from the additional spacer material strengthening the region, the configuration of the spacer 42 prevents adverse disc oscillation and subsequent disc failure.
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Although several embodiments have been described in detail for purposes of illustration, various modifications may be made without departing from the scope and spirit of the invention. Accordingly, the invention is not to be limited, except as by the appended claims.
