Patent Publication Number: US-10316667-B2

Title: Apparats for decreasing thrust of radial inflow turbine

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     A claim for priority under 35 U.S.C. § 119 is made to Korean Patent Application No. 10-2015-0107044 filed Jul. 29, 2015, in the Korean Intellectual Property Office, the entire contents of which are hereby incorporated by reference. 
     BACKGROUND 
     The inventive concept relates to an apparatus for decreasing a thrust of a radial flow turbine. More particularly, it relates to an apparatus for decreasing a thrust of a radial flow turbine, which decreases a pressure that influences a shaft seal. 
     A radial flow turbine is a turbine in which rotor blades are rotated with a working fluid such as vapor or gas flows radially on a plane perpendicular to a rotary shaft. The radial flow turbines may be classified into radial outflow turbines and radial inflow turbines. In the radial outflow turbine, vapor or gas is introduced into the center of the turbine to flow radially outwards, whereas in the radial inflow turbine, vapor or gas flows radially from the outer circumference to the inside of the turbine to drive rotor blades of the turbine. 
     Korean Patent Application Publication No. 10-2004-0081075 relates to a conduit apparatus for a radial flow turbine, and describes a technology of a conduit apparatus for a radial flow turbine of a type that significantly avoids disturbances of functions when blades (rotor blades) are adjusted. 
     Meanwhile, a high pressure ratio has recently been required for turbines to increase a pure output of a vapor power cycle and an organic Rankine cycle, due to the problem of lack of energy. Accordingly, recently, radial flow turbines have required a durability against a high thrust. 
     In general, a thrust bearing is installed to eliminate a thrust applied to a radial flow turbine. However, the thrust bearing decreases the efficiency of the radial flow turbine by generating work due to a non-conservative force. If a thrust bearing is excluded from a radial flow turbine that requires an excessive thrust force or the size of the thrust bearing is reduced, the development costs and the size of the radial flow turbine may be reduced and the efficiency of the radial flow turbine may be improved. 
     SUMMARY 
     Embodiments of the inventive concept describe an apparatus for decreasing a thrust of a radial flow turbine, and in more detail, provide a technology of an apparatus for decreasing a thrust of a radial flow turbine, which decreases a pressure that influences a shaft seal. 
     The embodiments provide an apparatus for decreasing a thrust of a radial flow turbine, which decreases a thrust by forming at least one ring on a back face (rotor back face) of a rotor of a radial flow turbine exposed to a relatively high pressure and forming a blind-hole in a rotary shaft of the radial flow turbine such that a pressure on the rotor back face decreases as the pressure goes from an inlet of the rotor towards a rotary shaft. 
     The embodiments also provides an apparatus for decreasing a thrust of a radial flow turbine, which satisfies a required performance of a shaft seal and reduce costs, by decreasing a pressure that influences the shaft seal by a ring formed on a back face of to rotor and a blind-hole formed in a rotary shaft. 
     In an aspect of the inventive concept, there is provided an apparatus for decreasing a thrust of a radial flow turbine, the apparatus including a rotary shaft having an axial blind-hole in the interior thereof, a rotor assembled in the rotary shaft and having a rotor hub and rotor blades formed on an outer peripheral surface thereof, a casing configured to isolate the rotary shaft and the rotor from the outside, and a shaft seal configured to maintain a seal between the rotary shaft and the casing. 
     According to an aspect, at least one protrusion is formed on a back face of the rotor hub, and at least one groove, by which the at least one protrusion is guided, is formed on an inner face of the casing, which faces the back face of the rotor hub. 
     According to another aspect, the at least one groove may be at least one ring-shaped groove, by which the at least one protrusion is guided. 
     According to another aspect, the at least one protrusion may be at least one protruding ring formed about the rotary shaft, and the at least one ring may be guided by the at least one groove. 
     According to another aspect, the at least one ring may include a plurality of rings having different diameters and the at least one groove may include a plurality of grooves guiding the plurality of rings to form a multi-ring structure. 
     According to another aspect, a first protruding ring and a second protruding ring having a diameter greater than that of the first ring may be formed on the back face of the rotor hub, and a first ring-shaped groove configured to guide the first ring and a second ring-shaped groove having a diameter greater than that of the first groove and configured to guide the second ring are formed on an inner face of the casing, which faces the back face of the rotor hub to form a dual ring structure. 
     According to another aspect, at least one protrusion may be formed on a back face of the rotor hub, a disk facing the back face of the rotor hub may be formed on an inner face of the casing, and at least one groove, by which the at least one protrusion is guided, may be formed on a front face of the disk. 
     According to another aspect, the blind-hole may be formed in the interior of the rotary shaft, in which the rotor is disposed, and is hollowed to a front end of a diffuser. 
     According to another aspect, the at least one ring may be integrally formed with the rotor hub. 
     In accordance with another aspect of the inventive concept, there is provided an apparatus for decreasing a thrust of a radial flow turbine, the apparatus including a rotary shaft, a rotor formed on an outer peripheral surface of the rotary shaft and rotated by a working fluid, a casing configured to isolate the rotary shaft and the rotor from the outside, and a shaft seal configured to maintain a seal between the rotary shaft and the casing, wherein a plurality of protruding rings having different diameters are formed on a back face of the rotor, and a plurality of ring-shaped grooves, by which the plurality of rings are guided, are formed on an inner face of the casing, which faces a back face of the rotor. 
     According to an aspect, the rotary shaft may have a blind-hole axially extending to a front end of a diffuser in the interior thereof. 
     According to another aspect, the plurality of rings may be integrally formed with the rotor. 
    
    
     
       BRIEF DESCRIPTION OF THE FIGURES 
       The above and other objects and features will become apparent from the following description with reference to the following figures, wherein like reference numerals refer to like parts throughout the various figures unless otherwise specified, and wherein: 
         FIG. 1  is a view illustrating a fluid flow direction of a radial flow turbine according to an embodiment; 
         FIG. 2  is a perspective view illustrating an apparatus for decreasing a thrust of a radial flow turbine according to an embodiment; 
         FIG. 3  is a front view illustrating an apparatus for decreasing a thrust of a radial flow turbine according to an embodiment; 
         FIG. 4  is a rear view illustrating an apparatus for decreasing a thrust of a radial flow turbine according to an embodiment; 
         FIG. 5  is a side view illustrating an apparatus for decreasing a thrust of a radial flow turbine according to an embodiment; 
         FIG. 6  is a sectional view taken along line A-A′ in  FIG. 5 ; and 
         FIG. 7  is an exploded view illustrating an apparatus for decreasing a thrust of a radial flow turbine according to an embodiment. 
     
    
    
     DETAILED DESCRIPTION 
     Hereinafter, embodiments of the inventive concept will be described with reference to the accompanying drawings. However, the embodiments may be modified into other various forms, and the scope of the inventive concept is not limited by the embodiments. Further, the embodiments are provided to describe the inventive concept to those skilled in the art more completely. In the drawings, the shapes and sizes of the elements may be exaggerated for clearer description. 
     The following embodiments relate to a technology for decreasing a thrust of a radial flow turbine, and more particularly to an apparatus for decreasing a thrust of a radial flow turbine, which decreases a pressure that influences a shaft seal. 
     A thrust bearing may be made unnecessary or the size of a thrust bearing may be reduced by decreasing a thrust of the radial flow turbine, making it possible to reduce the size of the radial flow turbine or decrease development costs, and a performance index required for a shaft seal may be attenuated by decreasing a pressure that influences a shaft seal. 
       FIG. 1  is a view illustrating a fluid flow direction of a radial flow turbine according to an embodiment. 
     Referring to  FIG. 1 , a working fluid of the radial flow turbine is introduced radially and discharged axially. Hereinafter, a fluid flow direction of a radial inflow turbine, as a representative of radial flow turbines, will be described. 
     In the radial flow turbine, a working fluid may be introduced radially from a volute  11  through a nozzle  12 , may be introduced into a rotor  14  through an interface  13 , and may be discharged axially towards a diffuser  15 . 
     In more detail, the working fluid of a high temperature and a high pressure, which is heated by an evaporator, is guided to the nozzle  12  via a volute  11 , and is accelerated in the nozzle  12  such that the flow of the working fluid is rectified while the working fluid passes through the interface  13 . Thereafter, the rotor  14  retrieves energy of the working fluid, and the pressure of the working fluid may be recovered through the diffuser  15  such that the working fluid is smoothly condensed by a condenser. That is, the energy of the working fluid may be converted into rotational energy by rotor blades arranged on a rotor hub  16 , and the rotor blades may discharge a gas that has consumed energy in the direction of a rotary shaft. 
     The working fluid in the volute  11  or the nozzle  12 , a pressure of which is relatively high, is applied to a back face  18  of the rotor  14  in the radial flow turbine to generate an axial thrust. Because the magnitude of the thrust is proportional to a difference between the area of the back face  18  of the rotor and the projection area of an exit of the rotor  14 , and a difference between the pressures of an inlet and an exit of the rotor  14 , the thrust increases when the radius of the inlet of the rotor  14  is large or a pressure ratio (Pinlet/Pexit) required by the radial flow turbine is large. 
     Meanwhile, a high pressure ratio has recently been required for turbines to increase a pure output of a vapor power cycle and an organic Rankine cycle, due to the problem of lack of energy. Accordingly, recently, radial flow turbines have required a durability against a high thrust. In general, a thrust bearing is installed to eliminate a thrust applied to a radial flow turbine. However, because the thrust bearing decreases the efficiency of the radial flow turbine by generating work due to a non-conservative force, it is preferable to exclude a thrust bearing or decrease the size of a thrust bearing. 
     An apparatus for decreasing a thrust of a radial flow turbine according to an embodiment will be described with reference to  FIGS. 2 to 4 . 
       FIG. 2  is a perspective view illustrating an apparatus for decreasing a thrust of a radial flow turbine according to an embodiment.  FIG. 3  is a front view illustrating an apparatus for decreasing a thrust of a radial flow turbine according to an embodiment.  FIG. 4  is a rear view illustrating an apparatus for decreasing a thrust of a radial flow turbine according to an embodiment. 
     Referring to  FIGS. 2 to 4 , the apparatus  100  for decreasing a thrust of a radial flow turbine may include a rotary shaft  110 , a rotor  120 , a casing  130 , and a shaft seal  140 . Further, although not illustrated, the casing  130  may extend to block the rotary shaft  110  and the rotor  120  from the outside. 
     The rotary shaft  110  is formed in the interiors of the rotor  120  and the casing  130 , and may be rotated together with rotor blades  123  and a rotor hub  121  by a working fluid. An axial blind-hole  111  is formed in the interior of the rotary shaft  110  to decrease an axial thrust and a pressure that influences the shaft seal  140 . For example, the blind-hole  111  may be formed in the interior of the rotary shaft  110 , in which the rotor  120  is disposed, and may be hollowed to a front end of a diffuser. 
     The rotor  120  may include a rotor hub  121  and rotor blades  123 . 
     The rotor  120  may be assembled on one side of the rotary shaft  110 , and may include the rotor hub  121  and the rotor blades  123  formed on an outer peripheral surface of the rotor hub  121  to be rotated about the rotary shaft  110 . 
     For example, a dual ring or a multi-ring having a protruding shape may be formed on a back face of the rotor hub  121 . The dual ring or multi-ring may be coupled to a ring-shaped groove formed in the casing  130 . 
     The rotor blades  123  may be arranged around the rotor hub  121 , and in more detail, may be formed radially on an outer peripheral surface of the rotor hub  121 . The rotor blades  123  may be rotated by a working fluid, and may be attached or coupled to the rotor hub  121  to be rotated. 
     The rotor  120  applies a rotational force to the rotor blades  123  to convert energy of the working fluid into mechanical work as the rotor blades  123  is rotated about the rotary shaft  110 . 
     The casing  130  may isolate the rotary shaft  110  and the rotor  120  from the outside. The casing  130  is formed outside the rotary shaft  110  and the rotor  120 , and at least an interior portion of the casing  130  faces the back face of the rotor  120  rotated by the working fluid while being spaced apart from the back face of the rotor  120  by a predetermined distance. For example, a ring-shaped groove may be formed on an inner face of the casing  130 , and the ring-shaped groove may be coupled the protruding dual ring or multi-ring formed in the rotor hub  121 , correspondingly. 
     The shaft seal  140  may be formed between the rotary shaft  110  and the casing  130  to maintain a seal. 
     In this way, because the apparatus  100  for decreasing a thrust of a radial flow turbine according to an embodiment is configured such that a blind-hole  111  is formed in the interiors of the dual ring or multi-ring structure and the rotary shaft  110 , a pressure formed on the back face of the rotor hub  121  may gradually decrease from inlets of the rotor blades  123  towards the rotary shaft  110  to decrease an axial thrust. 
     When a radial thrust is generated, the rotor  120  may be pushed towards one side so that power consumption increases as the casing  130  and the rotor  120  make contact with each other and the materials of the elements are worn out. 
     Accordingly, the apparatus  100  for decreasing a thrust of a radial flow turbine according to an embodiment may decrease a thrust of the radial flow turbine, or may exclude a thrust bearing or reduce the size of a thrust bearing, thereby decreasing the size of the radial flow turbine or development costs. Further, a high performance may be obtained by reducing power consumption and wearing of the materials. 
     Hereinafter, the apparatus for decreasing a thrust of a radial flow turbine according to the embodiment will be described in more detail with reference to  FIGS. 5 and 6 . 
       FIG. 5  is a side view illustrating an apparatus for decreasing a thrust of a radial flow turbine according to an embodiment.  FIG. 6  is a sectional view taken along line A-A′ in  FIG. 5 . 
     Referring to  FIGS. 5 to 6 , the apparatus  100  for decreasing a thrust of a radial flow turbine may include a rotary shaft  110 , a rotor  120 , a casing  130 , and a shaft seal  140 . Here, the rotor  120  may include a rotor hub  121  and rotor blades  123 . 
     The rotary shaft  110  is formed in the interiors of the rotor  120  and the casing  130 , and the rotor blades  123  and the rotor hub  121  may be rotated about the rotary shaft  110  by a working fluid. 
     An axial blind-hole  111  may be formed in the interior of the rotary shaft  110 , and in particular, the interior of the rotary shaft  110 , in which the rotor  120  is disposed, may be hollowed. The blind-hole  111  may extend axially and may be hollowed to a front end of a diffuser, which is the lowest pressure part of a passage of the radial flow turbine. 
     The rotor  120  may include a rotor hub  121  and rotor blades  123 . 
     The rotor hub  121  is assembled on one side of the rotary shaft  110 , and the rotor blades  123  may be formed on an outer peripheral surface of the rotor hub  121 . At least one protrusion  122  may be formed on a back face of the rotor hub  121  to decrease a pressure generated on the back face of the rotor. 
     Then, the at least one protrusion  122  may be integrally formed with the rotor hub  121 , but the inventive concept is not limited thereto. 
     Further, the at least one protrusion  122  may be at least one protruding ring  122  formed about the rotary shaft  110 . The at least one ring  122  may be integrally formed with the rotor hub  121  through machining to maintain a predetermined strength during rotation. 
     The rotor blades  123  may be radially formed on an outer peripheral surface of the rotor hub  121  to be rotated about the rotary shaft  110  by a working fluid together with the rotor hub  121 . 
     Meanwhile, the rotor hub  121  may be formed integrally with the rotor blades  123  or formed separately from the rotor blades  123  to be attached and coupled to the rotor blades  123 . 
     The casing  130  may isolate the rotary shaft  110  and the rotor  120  from the outside. 
     The casing  130  is formed outside the rotary shaft  110  and the rotor  120 , and at least an interior portion of the casing  130  faces the back face of the rotor  120  rotated by the working fluid. 
     At least one groove  132 , by which the at least one protrusion  122  is guided, may be formed on an inner face of the casing  130  through machining. 
     The at least one groove  132  may be at least one ring-shaped groove, by which the at least one protrusion  122  or the at least one ring  122  is guided. Accordingly, at least a portion of the protruding ring formed on the back face of the rotor hub  121  may be inserted into or coupled to the ring-shaped groove formed in the casing  130 , and may be guided during rotation of the rotor. 
     Further, a disk  131  facing the back face of the rotor hub  121  may be formed integrally with or separately from the inner face of the casing  130 . The disk  131  may be a circular plate, and may be formed integrally with the casing  130  or formed separately from the casing  130  to be coupled to the casing  130 . The front face of the disk  131  may be formed to face the back face of the rotor hub  121 , and at least one groove  132 , by which the at least one protrusion  122  is guided, may be formed on the front face of the disk  131 . 
     That is, the at least one protrusion  122  may be formed on the back face of the rotor hub  121 , the disk  131  facing the back face of the rotor hub  121  may be formed on the inner face of the casing  130 , and the at least one groove  132 , by which the at least one protrusion  122  is guided, may be formed on the front face of the disk  131 . Accordingly, the at least one protrusion  122  may be fitted with the at least one groove  132 , and the protrusion  122  may be moved along the groove  132  as the rotor hub  121  is rotated. 
     Here, the at least one groove  132  may have a ring shape, and may be coupled to and guided by the at least one ring  122  formed on the back face of the rotor hub  121 . 
     As described above, the apparatus  100  for decreasing a thrust of a radial flow turbine includes a rotary shaft  110 , a rotor  120  including a rotor hub  121  and rotor blades  123 , a casing  130 , and a shaft seal  140 , and at least one protrusion  122  is formed in the rotor hub  121  and at least one groove  132  is formed in the casing  130  such that rotation of the protrusion  122  may be guided by the groove  132 . 
     As an example, the at least one protrusion  122  may be formed on the back face of the rotor hub  121 , and the at least one groove  132 , by which the at least one protrusion  122  is guided, may be formed on the inner face of the casing  130 , which faces the back face of the rotor hub  121 . Accordingly, as the rotor hub  121  is rotated, at least a portion of the protrusion  122  may be inserted into the groove  132  and may be guided by and moved along the groove  132 . 
     As another example, the at least one groove  132  may be at least one ring-shaped groove, by which the at least one protrusion  122  is guided. That is, the at least one protrusion  122  may be formed on the back face of the rotor hub  121 , and the at least one ring-shaped groove  132 , by which the at least one protrusion  122  is guided, may be formed on the inner face of the casing  130 , which faces the back face of the rotor hub  121 . 
     As another example, the at least one protrusion  122  may be at least one protruding ring  122  formed about the rotary shaft  110 , and the at least one ring  122  may be guided by the at least one ring-shaped groove  132 . 
     Then, the at least one ring  122  may include a plurality of rings having different diameters. Further, the at least one groove  132  may include a plurality of grooves  132  guiding the plurality of rings  122 , and a multi-ring structure in which the plurality of rings  122  may be inserted into the plurality of grooves  132 , respectively, to be guided during rotation may be formed. 
     Hereinafter, a dual ring structure of the apparatus for decreasing a thrust of a radial flow turbine may be described as an example with reference to  FIG. 6 . 
     As illustrated in  FIG. 6 , a first protruding ring  122   a  and a second protruding ring  122   b  having a diameter greater than that of the first ring  122   a  may be formed on a back face of the rotor hub  121 . Correspondingly, a first groove  132   a , by which the first ring  122   a  is guided, may be formed on an inner face of the casing  130 , which faces the back face of the rotor hub  121 , and a second groove  132   b  having a diameter greater than that of the first groove  132   a , by which the second ring  122   b  is guided, may be formed. That is, at least a portion of the first ring  122   a  may be inserted into the first groove  132   a  to be guided as the first ring  122   a  is rotated, and at least a portion of the second ring  122   b  may be inserted into the second groove  132   b  to be guided as the second ring  122   b  is rotated, in order to form a dual ring structure. 
     At least one protrusion  122  may be formed on the back face of the rotor hub  121 , a disk  131  facing the back face of the rotor hub  121  may be formed on the inner face of the casing  130 , and at least one groove  132 , by which the at least one protrusion  122  is guided, may be formed on the front face of the disk  131 . 
     Meanwhile, as the rotor blades  123  rotated by a working fluid, the rotor hub  121  coupled to the rotor blades  123 , and the rotor shaft  110  are rotated, the rotary shaft  110  in the casing  130  also may be rotated. 
     While a pressure of a volute or a nozzle is applied to the entire back face of a rotor relatively constantly in an existing radial flow turbine, the apparatus for decreasing a thrust of a radial flow turbine according to the embodiment may gradually decreases a pressure on the back face of the rotor  120  or the rotor hub  121  as the pressure goes from an inlet of the rotor towards the rotary shaft  110  due to the multiple rings  122  and the blind-hole  111  and thus may decrease a thrust. 
     Moreover, because the multiple rings  122  and the blind-hole  111  decreases a pressure that influences the shaft seal  140 , the apparatus may satisfy the required performance of the shaft seal  140  and may reduce costs. 
     The shaft seal  140  is an apparatus for maintaining a seal or preventing a leakage, and may be used for the purpose of preventing a fluid of a high pressure from being leaked to the outside at a portion of the shaft seal, which passes through the casing or air from being introduced from the outside to a lower pressure side. It is necessary to minimize the pressure that influences the shaft seal  140  in order to prevent leakage of the shaft seal  140 . 
       FIG. 7  is an exploded view illustrating an apparatus for decreasing a thrust of a radial flow turbine according to an embodiment. 
     Referring to  FIG. 7 , the apparatus  100  for decreasing a thrust of a radial flow turbine may include a rotary shaft  110 , a rotor  120 , a casing  130 , and a shaft seal  140 . Further, although not illustrated, the casing  130  may extend to block the rotary shaft  110  and the rotor  120  from the outside. 
     Here, the at least one protrusion  122  may be formed on the back face of the rotor hub  121 , and the at least one groove  132 , by which the at least one protrusion  122  is guided, may be formed on the inner face of the casing  130 , which faces the back face of the rotor hub  121 . 
     For example, a first protruding ring  122   a  and a second protruding ring  122   b  may be formed on a back face of the rotor hub  121 . Here, the second ring  122   b  may be a second protruding ring  122   b  having a diameter greater than that of the first ring  122   a.    
     Further, a first groove  132   a  and a second groove  132   b  may be formed on an inner face of the casing  130 , which faces the back face of the rotor hub  121 , to correspond to the first ring  122   a  and the second ring  122   b.    
     That is, a first groove  132   a , by which the first ring  122   a  is guided, may be formed on an inner face of the casing  130  and a second groove  132   b  having a diameter greater than that of the first groove  132   a , by which the second ring  122   b  is guided, may be formed. That is, the first ring  122   a  is coupled to the first groove  132   a , and the second ring  122   b  may be coupled to the second groove  132   b  in order to a dual ring structure. 
     As another example, the at least one protrusion  122  may be formed on the back face of the rotor hub  121 , the disk  131  facing the back face of the rotor hub  121  may be formed on the inner face of the casing  130 , and the at least one groove  132 , by which the at least one protrusion  122  is guided, may be formed on the front face of the disk  131 . 
     That is, a first protruding ring  122   a  and a second protruding ring  122   b  may be formed on a back face of the rotor hub  121 . Here, the second ring  122   b  may be a second protruding ring  122   b  having a diameter greater than that of the first ring  122   a.    
     Further, because a first ring-shaped groove  132   a , by which the first ring  122   a  is guided, and a second ring-shaped groove  132   b  having a diameter greater than the first groove  132   a , by which the second ring  122   b  is guided, are formed on a front face of the disk  131 , which faces the back face of the rotor hub  121 , to correspond to the first ring  122   a  and the second ring  122   b , the first ring  122   a  is coupled to the first groove  132   a  and the second ring  122   b  is coupled to the second groove  132   b  in order to form a dual ring structure. 
     Although the dual ring structure has been described as an example, a single ring structure and a multi-ring structure may be formed instead of the dual ring structure. 
     Hereinafter, the apparatus for decreasing a thrust of a radial flow turbine according to another embodiment will be described. 
     The apparatus  100  for decreasing a thrust of a radial flow turbine according to the embodiment may include a rotary shaft  110 , a rotor  120 , a casing  130 , and a shaft seal  140 . These elements may be described in detail by using the apparatus  100  for decreasing a thrust of a radial flow turbine according to the embodiments of  FIGS. 2 to 7 . 
     The rotor  120  may be formed on an outer peripheral surface of the rotary shaft  110  to be rotated by a working fluid. The rotor  120  may have radial rotor blades  123 . 
     Here, an axial blind-hole  111  may be formed in the interior of the rotary shaft  110 , in which the rotor  120  is disposed. The blind-hole  111  may extend axially to a front end of a diffuser. 
     A plurality of protruding rings  122  having different diameters may be formed on a back face of the rotor  120  through machining. The plurality of rings  122  may be integrally formed with the rotor  120 , but the inventive concept is not limited thereto. 
     The casing  130  may be formed outside the rotary shaft  110  to isolate the rotary shaft  110  and the rotor  120  from the outside. 
     A plurality of ring-shaped grooves  132 , by which the plurality of rings  122  are guided, respectively, may be formed on an inner face of the casing  130  through machining. 
     That is, because a plurality of protruding rings  122  having different diameters are formed on a back face of the rotor  120  and a plurality of ring-shaped grooves  132 , by which the plurality of rings are guided, are formed on an inner face of the casing  130 , which faces the back face of the rotor  120 , the plurality of rings  122  may be inserted into and coupled to the plurality of grooves  132 . 
     For example, a dual ring  122  integrally machined with the rotor  120  may be formed on the back face of the rotor of the radial flow turbine, which is exposed to a relatively high pressure. Here, it is not necessary to radially form several rings  122  according to occasions to form a multi-ring, and the rings  122  may not be integral with the rotor  120 . 
     The shaft seal  140  may be formed between the rotary shaft  110  and the casing  130  to maintain a seal. 
     According to the embodiments, the rotary shaft  110  of the radial flow turbine may have a blind-hole  111  hollowed to a front end of the diffuser, which is the lowest pressure part of the turbine passage. While a pressure of a volute or a nozzle is applied relatively constantly to the entire back face of the rotor in the structure of an existing radial flow turbine, a pressure on the back face of the rotor gradually decreases as the pressure goes from the inlet of the rotor towards the rotary shaft  110  due to the multiple rings and the blind-hole in the radial flow turbine according to the embodiments. Accordingly, the axial thrust may be reduced. 
     Moreover, because the multiple rings  122  and the blind-hole  111  decreases a pressure that influences the shaft seal  140 , the apparatus may satisfy the required performance of the shaft seal  140  and may reduce costs. 
     According to the embodiments, an apparatus  100  for decreasing a thrust of a radial flow turbine, which decreases a thrust by forming at least one ring  122  on a back face of a rotor  120  of a radial flow turbine exposed to a relatively high pressure and forming a blind-hole  111  in a rotary shaft  110  of the radial flow turbine such that a pressure on the rotor  120  back face decreases as the pressure goes from an inlet of the rotor  120  towards a rotary shaft  110  may be provided. 
     Further, according to the embodiments, an apparatus  100  for decreasing a thrust of a radial flow turbine, which maximizes a performance of a shaft seal  140  and reduce costs, by decreasing a pressure that influences the shaft seal  140  by a ring  122  formed on a back face of the rotor  120  and a blind-hole  111  formed in a rotary shaft  110  may be provided. 
     Although the embodiments of the inventive concept have been described with reference to the limited embodiments and the drawings, the inventive concept may be variously corrected and modified from the above description by those skilled in the art to which the inventive concept pertains. For example, the above-described technologies can achieve a suitable result even though they are performed in different sequences from those of the above-mentioned method and/or coupled or combined in different forms from the method in which the constituent elements such as the system, the architecture, the device, or the circuit are described, or replaced or substituted by other constituent elements or equivalents. 
     Therefore, the other implementations, other embodiments, and the equivalents of the claims pertain to the scope of the claims.