Abstract:
A radial flow turbine has a rotor with an internal cavity that includes a vaporization section and a condensation section. The condensation section is disposed radially inward toward the shaft and the vaporization section extends radially outward adjacent to the surface of the rotor blade. The vaporization section includes a series of pockets for dispersing the cooling fluid within each blade, and a cascaded series of capture protrusions to distribute the liquid coolant to the successive radially-arrayed pockets. A working system includes a centrifugal compressor which feeds a compressed air fuel mixture to an annular combustion chamber that, in turn, feeds the combustion gases along a radial direction to impinge on the surface of the cooled radial flow rotor. Optionally, the system is a regenerative system including a heat exchange sub-assembly which couples heat from the exhaust stream to a position between the compressor and combustion chamber.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     Not Applicable. 
     STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH 
     Not Applicable. 
     FIELD OF THE INVENTION 
     This invention relates generally to the field of turbines and power systems. Fuel fired internal combustion engines such as gas turbine engines utilize a working fluid, namely an air/fuel mixture, which changes composition during combustion to drive the turbine with hot expanded gases. A conventional gas turbine engine includes a compressor, a combustion chamber and a turbine made up of an arrangement of stators and rotors. Each of the rotors includes blades and a supporting disk. Ideally, for the optimum extraction of energy, the combustion process should occur at about 4000° Fahrenheit. However, as a practical matter due to metallurgical concerns, the components of a turbine must operate at considerably lower temperatures. Cooling of the stationary housing and stators in combustion chamber walls is relatively straightforward by any of a number of means; however the rotors, due to their high rotational speed, present many problems for conventional cooling. 
     Various approaches have been proposed for utilizing internal fluid cooling to more effectively cool engine parts such as combustion chamber walls, turbine rotors and stators. In the case of rotor blades, some approaches have involved the internal use of a vaporizable cooling fluid that travels from the root of the rotor out through the tip of the rotor blade. Another approach has been to utilize a closed cycle cooling system in which a cooling fluid occupies only a portion of an internal cavity in the blade and circulates as a heat exchange medium. The physical properties of the cooling fluid are such that it is vaporized in certain regions of the cavity by virtue of the operating temperature prevailing in those regions during normal operation of the engine. Applicant has previously obtained a patent, U.S. Pat. No. 5,299,418, which describes one particularly advantageous structure for closed circulation of a vaporizable liquid phase coolant within the cavity of a turbine blade. The improvement claimed in that patent involves a geometry for distributing coolant fairly uniformly over the inner surface of a blade in an axial-flow gas turbine so as to achieve a distributed cooling effect for the entire blade. 
     While that patent illustrates an axial flow turbine with its characteristic blade shape, other forms of turbine have a configuration entirely different and pose different challenges to implementing effective coolant circulation. Thus, for example, in a relatively common turbine architecture utilizing a centrifugal compressor with an annular combustion chamber to feed a radial flow turbine, the foregoing construction would find no application. Similarly, in the case of smaller turbines where a regenerative loop architecture is used to enhance heat efficiency of a radial flow turbine, the aforesaid patented construction would not apply. 
     Accordingly, it would be desirable to provide a system and construction for cooling the blades of a radial flow turbine so that the combustion process may be operated at higher temperatures without impairing the structural integrity of the turbine itself. 
     In general, it is an object of the invention to provide an internal combustion engine wherein higher combustion temperatures can be achieved while maintaining material temperatures at levels at least as low as those associated with known turbine engines. 
     Another object of the invention is to provide a radial flow gas turbine engine utilizing closed cycled evaporative cooling for the moving parts of the engine. 
     Still another object is to provide a rotor or rotor blade for use in a turbine of such an engine. 
     SUMMARY OF THE INVENTION 
     One or more of the above desirable objects are achieved in accordance with the present invention by a system including a radial flow turbine having an arrangement of one or more stators and rotors in which each of the rotors defines an internal cavity that includes a vaporization section and a condensation section. The condensation section is disposed radially inward toward the shaft and the vaporization section extends over the rotor in thermal proximity to the blades. The vaporization section includes a series of pockets or passages for dispersing the cooling fluid proximate to heated surfaces of each blade, and a cascaded series of catchment channels or protruding shelves to distribute coolant to the pockets. A working system includes a centrifugal compressor which feeds a compressed air/fuel mixture to an annular combustion chamber that, in turn, provides hot gases along a radial direction to impinge on the surface of a radial flow rotor. Optionally, the system is a regenerative system including a heat exchange sub-assembly which couples heat from the exhaust stream to a position between the compressor and combustion chamber. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     These and other features of the invention will be understood from the description below taken in conjunction with the accompanying drawings, wherein: 
     FIG. 1 is a schematic diagram of an axial flow gas turbine of the prior art; 
     FIG. 2 is a schematic diagram of a prior art evaporatively cooled blade for the turbine of FIG. 1; 
     FIG. 3 illustrates a radial flow turbine and centrifugal compressor suitable for the practice of the present invention; 
     FIG. 4 illustrates a regenerative radial flow gas turbine suitable for the practice of the present invention; 
     FIG. 5 shows a cross-section through a disk and radial flow turbine blade of the present invention for use in the systems of FIGS. 3 and 4; and 
     FIG. 5A shows a front plan view of the rotor of FIG. 5, illustrating blade placement and coolant channel alignment. 
    
    
     DETAILED DESCRIPTION 
     In the prior art there have been many proposals to cool turbine blades by providing a vaporizable liquid in a hollow chamber formed in each blade. For example, U.S. Pat. Nos. 2,812,157 and 2,952,441 each show such an arrangement. More recently, applicant has proposed in U.S. Patent 5,299,418 an arrangement whereby such a phase change coolant evaporates and condenses within the blade of an axial flow turbine. In the device of that patent, coolant circulation is controlled and uniformized to some extent by a plurality of transverse ridges or capture shelves which cause the cooling fluid to cascade outwardly in the centrifugal field and be distributed at successive radial levels extending along the inner surface of the blade. 
     FIGS. 1 and 2 illustrate an axial flow turbine system and the cooled blades of that patent, which is hereby incorporated herein in its entirety. As shown therein, an engine  10  includes a compressor  12 , a combustion chamber  13 , and a turbine  14 . The turbine  14  comprises an arrangement of stators  16  and rotors  18 , with the rotors being connected to drive shafts  20  that are supported in bearings  22 . Through rapid combustion, working fluid exiting the combustion chamber  13  performs work on the rotors  18  and causes them to drive the shafts  20 . As best seen in FIG. 2, each of the rotors  18  of that prior art system includes an internal cooling system carried out by phase transition and circulation in a closed cycle of a cooling fluid within the blade. The liquid phase of the cooling fluid occupies a portion only of an internal cavity provided in the rotor. 
     This internal cavity is more clearly shown in FIG. 2, which is a cross-section of a representative rotor  18 . The rotor  18  is formed with a wall  32  that encloses an internal cavity  34 . The internal cavity  34  is divided into a condensing section  36  located along a radially inward section at the rotor disk  28 , and a vaporization section  38  located more outwardly to effect heat transfer at the rotor blade  26 . Typically multiple rotor blades  26  are supported by the rotor disk  28 . 
     Cooling fluid F is contained within the internal cavity  34  and receives heat from the wall  32  at the vaporization section  38  which resides in the flow of combustion gases of the engine working fluid. The physical properties of the cooling fluid are such that it vaporizes at the temperatures experienced in the vaporization section  38  during normal operation of the rotor  18 . Various liquid metals such as sodium, potassium or a mixture of these are suitable for use as the cooling fluid F. Other appropriate cooling fluids will be apparent to those skilled in the art. 
     The geometry and operation of the axial flow turbine of FIGS. 1 and 2 results in a flow of the cooling fluid F in liquid phase in the direction of the arrows  40  to the vaporization section  38 , and the flowing cooling fluid is distributed over the internal surface of the wall  32  by the array of protruding ridges or lips  46  which are arranged so that the cooling fluid cascades from one ridge radially outward to the next ridge while some fluid is evaporated at each ridge and thereby removes heat from the area of the wall  32  locally in that region. The vaporized fluid filling the section  38  experiences a radially inward flow as vapor in the direction of arrows  42  to the condensing section  36 , where it re-liquefies to again circulate outward and effect further cooling. Return of the vapor is effected by a pumping action generated by the difference in vapor pressures in the vaporization and condensing sections of the rotor  18 . Thus, the overall operation involves a cooling liquid washing radially outward over a ridge plate. 
     The present invention is directed to implementation of a cooling structure for a different form of turbine, in which the blades take a different geometry, namely that of a radial flow turbine. 
     FIG. 3 illustrates a basic radial flow turbine system  50 , in which illustratively a centrifugal compressor  55  provides a flow of working fluid to a combustion chamber  60  disposed circumferentially about the radially outer periphery of a turbine  70 , and wherein the turbine  70  has blades disposed for movement in a radially-directed flow of the hot combustion gases. As shown, the heated gas may then be provided to a second stage power turbine  75 , that may be driven by either radial or axial flow. 
     FIG. 4 illustrates another system  100  also employing a radial flow turbine  70 . System  100  differs from the system  50  of FIG. 3 in having a heat exchange unit  80  shown as a rotating heat storage unit, at a position to preheat the working fluid or air exiting from the compressor with energy from the turbine output stream before the working fluid enters the combustion chamber  60 . Such an architecture is common in smaller turbines where it is desired to increase the overall thermal efficiency. In both the system  50  of FIG.  3  and the system  100  of FIG. 4, the combustion gases pass in a radial direction to drive the turbine  70 , impinging on the rotor and blade assembly  71 . 
     In accordance with the present invention, the assembly  71  is configured such that the rotor assembly includes an internal chamber containing a vaporizable fluid and arranged for vaporization and condensation of the fluid to effectively cool the blades carried by the rotor and residing in the hot combustion gases. FIG. 5 illustrates the evaporatively cooled radial flow turbine blade element of the present invention. 
     As shown in FIG. 5, the radial flow rotor assembly  71  comprises a generally central body portion including a shaft  80  and hub  82 , with a disk  84  extending radially outward that carries the blades  86 . As shown in FIG. 5A, a plan view facing directly along the axis of rotation, the disk  84  carries a plurality of blades  86  which extend from the center outwardly toward the periphery and are arrayed in a regular arrangement configured for catching the hot gas stream and driving the rotor. The direction of gas flow is indicated by the arrow GF, which as shown extends along a generally radial direction. FIG. 5 shows a plane section extending through the rotor  71  in a plane containing the axis and passing centrally through a pair of the blades  86 . As shown therein, the rotor is constructed with an internal chamber  90  which is partially filled with a vaporizable heat exchange cooling material such as a metal of moderate vapor point as described above. The chamber  90  includes a vaporization section  90   a  and a condensation section  90   b . The vaporization section  90   a  extends radially outward along the body of the disk in the region spanned by the blades  86 . The condensation section  90   b  lies radially inward of the vaporization section  90   a , and close to the shaft  80 . The outer wall of the condensation section  90   b  may include condensor fins  91  which may, for example, ride in a stream of cooling air supplied to that region of the backside of the disk. Other forms of cooling for the shaft or central hub region may also be used to remove heat from the condensor housing, such as the provision of a circulating coolant through internal passages in the shaft or contiguous bearing or housing structures, with appropriate seals. 
     As further shown in FIG. 5, circulation of the heat exchange fluid within the chamber  90  proceeds by passage of liquid from the condensation chamber  90   b  through a liquid transfer viaduct such as a trough, or a drilling, passage or small aperture  101  which may be angled slightly as shown to direct the condensed fluid into the chamber  90   a  where it is driven centrifugally outward and captured by an overhanging capture lip  110   a . The lip, while illustrated in cross-section, will be understood to preferably extend substantially uniformly at a radially constant distance circumferentially around the entire front wall of the chamber  90   a . It thus forms a circumferential surface channel or trough, so that as the rotor  71  rotates, the cooling fluid is urged against the slightly dished shelf at constant radial distance and distributed uniformly along the length of the first capture lip  110   a.    
     Extending from the shelf and at the same radial distance, is a recess  112   a  which extends forwardly into the body of the turbine blade  86 , so as to distribute the liquid from the shelf  110   a  along a penetrating passage into the blade  86  and extending close to its side and front surfaces  86   a  which are heated by the gas flow. As further shown in FIG. 5, a plurality of similar capture lips  110   b ,  110   c ,  110   d  . . . are positioned at successively greater radial distances from the center or axis of rotation. These successive lips each lie along an incline cone angle indicated by dashed line C, and are positioned such that each extends slightly past the previous one, so that excess fluid driven against the shelf  110   a  overflows radially outward and is captured by the next shelf  110   b , and then successively cascades so that liquid is captured by each of the successive shelves and is distributed to the interior of the blade along a corresponding successive set of recesses or drillings  112   b ,  112   c ,  112   d  . . . . The radially outer edge of each of these distribution apertures  112  extends at the level of the surface of the corresponding shelf  110  to receive liquid coolant therefrom. A similar set of drillings  112   a ,  112   b  . . . is formed in each blade of the rotor. 
     FIG. 5A illustrates the general configuration of the penetrating coolant distribution recesses  112 . These may be formed by drilling in from the front face of the blade, i.e., from the right as shown in FIG. 5, to the depth of the shelf  110 , then plugging and welding closed the surface of each hole so made in the face of the blade. In a typical manufacturing process, the front, blade-carrying portion of the rotor may be machined as one piece, and the internal chamber structure may then be completed by assembling that piece to a second disk structure consisting of the back wall  95  and central condenser elements  91 ,  96 ,  101 . Such assembly is illustrated in FIG. 5 by the perimeter welds W 1  and W 2  closing the two-piece assembly into a structure with an internal chamber arranged for the vaporization, return, condensation and distribution of material in an ordered and highly uniform manner. 
     In operation, the liquid entering each recess  112  cools the corresponding local region of the rotor blade  86 , and is heated so that it vaporizes and fills the vaporization chamber  90   a . This results in a flow of the less dense vapor centrifugally inward along a direction of vapor flow indicated by arrow VF. The returning vapor enters the cooler condensing chamber  90   b , where it condenses and is again driven by centrifugal force outwardly to the cascaded radial sequence of capture lips  110  for depth dispersion from the shelves into the penetrating pockets  112  to enhance cooling of the blade surfaces. The flow of vapor along the return direction VF is driven in part by the vapor pressure gradient directed toward the cooler region of the condensation chamber  90   b.    
     Thus, the sequence of arcuate capture shelves and penetrating pockets results in a centrifugal distribution of the coolant liquid to remove heat from the angled blade surfaces of the radial flow turbine rotor, while providing a self-sustaining circulation of condensing vapor away from the blades that efficiently cools the entire rotor. 
     The invention being thus disclosed and a representative embodiment described, further variations and modifications will occur to those skilled in the art, and all such variations and modifications are considered to be within the scope of the invention, as defined by the claims appended hereto and equivalents thereof.