Abstract:
Vane, fin, and hole arrangements establish a predetermined reduced swirl at the inlet of mechanical seals and the inlet of a variable axial orifice gap which act in harmony as an axial thrust equalizing system for use in liquid cryogenic turbines and pumps. In said establishment the stiffness, damping, and inertia in said seal in conjunction with said variable orifice gap is manipulated, including the destabilizing cross-coupled stiffness which is reduced. Said seal is of either labyrinth annular type formed by a plurality of teeth, annular smooth, or a plurality diamond annular surface pattern. Said variable orifice gap is smooth. Liquid for the axial thrust equalizing seal is initially bled from the main to pass through a preset deswirl mechanism. The deswirl mechanism consists of either a plurality of vanes, fins, grooves, or circular holes that guide liquid radial inward before passing through said mechanical seal. After exiting the seal said liquid passes through a second deswirl mechanism consisting of a plurality of vanes, fins, or grooves before entering a variable axial orifice gap. The variable orifice moves in axial position to variably restrict balancing liquid and generate backpressure in the pressure chamber to balance the axial thrust caused by a plurality of impellers on the same single shaft. After passing through the variable orifice the bleed liquid can pass past a sealed lubricated roller bearing for heat exchange to cool said bearing with the cryogenic liquid along grooves in a bearing liner. Alternatively the liquid can also pass directly through an open unsealed bearing for cooling.

Description:
RELATED APPLICATIONS 
       [0001]    This Application is related to U.S. Provisional Patent Application Ser. No. 60/920,618 filed Mar. 29, 2007 entitled DESWIRL MECHANICS AND ROLLER BEARINGS IN AN AXIAL THRUST EQUALIZATION MECHANISM FOR LIQUID CRYOGENIC TURBOMACHINERY, which is incorporated herein by reference in its entirety, and claims any and all benefits to which it is entitled therefrom. 
     
    
     FIELD OF THE INVENTION 
       [0002]    The present invention relates to liquid cryogenic centrifugal pumps and turbines of the submerged motor or generator type. 
       BACKGROUND OF THE INVENTION 
       [0003]    Vertical cryogenic submerged motor pumps and submerged generator turbines operate in the liquefied cryogenic gases industry. They are most prominent in the liquid hydrocarbon industry for liquefied natural gas, liquefied ethane gas, and liquefied propane gas. U.S. Pat. No. 5,659,205 to Weisser, which is hereby incorporated by reference in its entirety herein, teaches that due to the low cryogenic temperatures this style of pump and turbine operates with the axial thrust of the rotating assembly totally equalized to zero. U.S. Pat. No. 6,441,508 to Hylton is also hereby incorporated by reference in its entirety herein. 
         [0004]    To achieve this, a conventional axial thrust equalizing mechanism such as shown in  FIG. 1  is applied that uses pressurized bleed liquid which is passed through a seal restriction at the back of the highest pressure impeller. Afterwards this bleed liquid passes into a pressure chamber whose pressure is controlled by a downstream variable area orifice. This orifice is variable in the axial direction along the pump and turbine shaft and comes from the rotating assembly which is designed to float axially a small distance. In a condition of up axial thrust on the rotating assembly, the variable orifice is pushed smaller. As such, the bleed liquid flow rate is reduced and the pressure drop across the bleed wear ring is reduced. The pressure in the downstream pressure chamber rises which increases the force on the impeller and rotating assembly so that a reaction force is established to push the variable orifice larger and equalize the thrust. Contrarily, in a condition of down axial thrust on the rotating assembly, the variable orifice is pulled larger. As such, the bleed liquid flow rate is increased and the pressure drop across the bleed wear ring is increased. The pressure in the downstream pressure chamber decreases which decreases the force on the impeller and rotating assembly so that a reaction force is established to push the variable orifice smaller and equalize the thrust. So a net zero axial thrust is always established by the thrust equalization mechanism. 
       SUMMARY AND ADVANTAGES OF THE PRESENT INVENTION 
       [0005]    The power rating of liquid cryogenic pumps and turbines in high pressure applications continues to grow as motivated by customer demands. This translates to higher power concentration machinery. So the axial thrust mechanism must balance larger thrust levels. Greater radial thrust levels are also experienced which the seals must react to avoid overly larger shaft deflections and overly large shaft diameters to compensate. Thus, means are sought to increase the stiffness of impeller flow induced reaction forces to stiffen the shaft. Increasing the shaft damping is also beneficial. Benckert, H., et al. teach in “Flow Induced Spring Coefficients of Labyrinth Seals for Application in Rotor Dynamics” published 1980, which is hereby incorporated by reference in its entirety, that means are also sought to reduce the well documented destabilizing cross-coupled stiffness in the mechanical seals. Overall increasing the stiffness and damping while decreasing the cross-coupled stiffness will reduce rotordynamic whirl and vibrations. This can be seen from first principles with the equation of motion applied to a rotating assembly experiencing small displacements δ in the x and y direction written as follows: 
         [0000]    
       
         
           
             
               - 
               
                 [ 
                 
                   
                     
                       
                         
                           F 
                           x 
                         
                          
                         
                           ( 
                           t 
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                           F 
                           y 
                         
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                           ) 
                         
                       
                     
                   
                 
                 ] 
               
             
             = 
             
               
                 
                   [ 
                   
                     
                       
                         
                           
                             k 
                             xx 
                           
                            
                           
                             ( 
                             δ 
                             ) 
                           
                         
                       
                       
                         
                           
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                             ) 
                           
                         
                       
                     
                     
                       
                         
                           
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                            
                           
                             ( 
                             δ 
                             ) 
                           
                         
                       
                       
                         
                           
                             k 
                             yy 
                           
                            
                           
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                             δ 
                             ) 
                           
                         
                       
                     
                   
                   ] 
                 
                 [ 
                 
                     
                 
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                       x 
                     
                   
                   
                     
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                               m 
                               xx 
                             
                              
                             
                               ( 
                               δ 
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                               m 
                               xy 
                             
                              
                             
                               ( 
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                               m 
                               
                                 yx 
                                  
                                 
                                     
                                 
                               
                             
                              
                             
                               ( 
                               δ 
                               ) 
                             
                           
                         
                         
                           
                             
                               m 
                               yy 
                             
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                     ] 
                   
                    
                   
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                             2 
                           
                         
                       
                       
                         
                           
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                             2 
                           
                         
                       
                     
                     ] 
                   
                 
               
             
           
         
       
     
         [0006]    Note: Both the direct coupled and cross coupled terms are represented in the stiffness (k), damping (c), and inertia mass (m) matrix. For small displacements, the coefficients in these equations are taken as linear. Separating the forcing contributions in the absolute reference frame results in the following: 
         [0000]    
       
         
           
             
               [ 
               
                 
                   
                     
                       
                         F 
                         x 
                       
                        
                       
                         ( 
                         t 
                         ) 
                       
                     
                   
                 
                 
                   
                     
                       
                         F 
                         y 
                       
                        
                       
                         ( 
                         t 
                         ) 
                       
                     
                   
                 
               
               ] 
             
             = 
             
               
                 [ 
                 
                   
                     
                       
                         F 
                         xa 
                       
                     
                   
                   
                     
                       
                         F 
                         ya 
                       
                     
                   
                 
                 ] 
               
               + 
               
                 
                   [ 
                   
                     
                       
                         
                           
                             F 
                             x 
                           
                            
                           
                             ( 
                             t 
                             ) 
                           
                         
                       
                     
                     
                       
                         
                           
                             F 
                             y 
                           
                            
                           
                             ( 
                             t 
                             ) 
                           
                         
                       
                     
                   
                   ] 
                 
                 whirl 
               
               + 
               
                 
                   [ 
                   
                     
                       
                         
                           
                             F 
                             x 
                           
                            
                           
                             ( 
                             t 
                             ) 
                           
                         
                       
                     
                     
                       
                         
                           
                             F 
                             y 
                           
                            
                           
                             ( 
                             t 
                             ) 
                           
                         
                       
                     
                   
                   ] 
                 
                 nonwhirl 
               
             
           
         
       
     
         [0007]    The force contributions are dividing into steady and unsteady. The unsteady force contribution is further subdivided into whirl and none whirl portions. The whirl contribution will be taken as a circular orbit that experiences small periodic displacements of δ in x and y so δ=δ o +iy and δ=δ o  exp(iω w t). In this relation, ω w  is the impeller whirl frequency. Now, expanding the previous equation for the whirl terms gives the following: 
         [0000]    
       
         
           
             
               
                 [ 
                 
                   
                     
                       
                         
                           F 
                           x 
                         
                          
                         
                           ( 
                           t 
                           ) 
                         
                       
                     
                   
                   
                     
                       
                         
                           F 
                           y 
                         
                          
                         
                           ( 
                           t 
                           ) 
                         
                       
                     
                   
                 
                 ] 
               
               whirl 
             
             = 
             
                 
               
                 
                   [ 
                   
                     
                       
                         
                           ( 
                           
                             
                               
                                 m 
                                 xx 
                               
                                
                               
                                 ω 
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                                 2 
                               
                             
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                                 c 
                                 xy 
                               
                                
                               
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                  
                 
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                             o 
                           
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         [0008]    It is now more convenient and intuitive to write this equation in dimensionless form as follows: 
         [0000]    
       
         
           
             
               [ 
               
                 
                   
                     
                       
                         F 
                         x 
                         * 
                       
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                         ( 
                         t 
                         ) 
                       
                     
                   
                 
                 
                   
                     
                       
                         F 
                         y 
                         * 
                       
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                         ( 
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             = 
             
                 
               
                 
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                                 * 
                               
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                               yy 
                               * 
                             
                           
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                   ] 
                 
                  
                 
                   [ 
                   
                     
                       
                         
                           
                             δ 
                             o 
                           
                            
                           cos 
                            
                           
                               
                           
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                             ω 
                             w 
                           
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                             t 
                             / 
                             
                               R 
                               2 
                             
                           
                         
                       
                     
                     
                       
                         
                           
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                             o 
                           
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                           sin 
                            
                           
                               
                           
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                             ω 
                             w 
                           
                            
                           
                             t 
                             / 
                             
                               R 
                               2 
                             
                           
                         
                       
                     
                   
                   ] 
                 
               
             
           
         
       
     
         [0009]    The * designates use of the dimensionless quantities with F*=F/πρR 2   3 B 2 ω 2 , x*=x/R2, dx*/dt=(dx/dt)/R 2 ω, and dx 2 */dt=(d 2 x/dt 2 )/R 2 ω 2 . The dimensionless stiffness, damping and added mass coefficients used are k* ij =k ij /πρR 2   2 B 2 ω 2 , c* ij =c ij /πρR 2   2 B 2 ω, m* ij =m ij /πρR 2   2 B 2 . This expression gives the x, y component of the forces but the greater interest for turbomachinery vibrations lies in the tangential and radial forces from the rotating assembly center. So we convert to polar coordinates with F* r +iF* θ =(F* x +iF* y )exp(−iω w t) and get the following equation: 
         [0000]    
       
         
           
             
               
                 [ 
                 
                   
                     
                       
                         F 
                         θ 
                         * 
                       
                     
                   
                   
                     
                       
                         F 
                         r 
                         * 
                       
                     
                   
                 
                 ] 
               
               whirl 
             
             = 
             
               [ 
               
                 
                   
                     
                       
                         - 
                         
                           
                             
                               m 
                               xy 
                               * 
                             
                              
                             
                               ( 
                               
                                 
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                           2 
                         
                       
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                           xx 
                           * 
                         
                          
                         
                           ( 
                           
                             
                               ω 
                               w 
                             
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                           ) 
                         
                       
                       + 
                       
                         k 
                         xy 
                         * 
                       
                       + 
                       
                         
                           
                             m 
                             yz 
                             * 
                           
                            
                           
                             ( 
                             
                               
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                         2 
                       
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                           yy 
                           * 
                         
                          
                         
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                         yx 
                         * 
                       
                     
                   
                 
                 
                   
                     
                       
                         
                           
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                             xx 
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                            
                           
                             ( 
                             
                               
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                         2 
                       
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                           xy 
                           * 
                         
                          
                         
                           ( 
                           
                             
                               ω 
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                           ) 
                         
                       
                       - 
                       
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                         xx 
                         * 
                       
                       + 
                       
                         
                           
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                             yy 
                             * 
                           
                            
                           
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                         2 
                       
                       + 
                       
                         
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                           yx 
                           * 
                         
                          
                         
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                               ω 
                               w 
                             
                             ω 
                           
                           ) 
                         
                       
                       - 
                       
                         k 
                         yy 
                         * 
                       
                     
                   
                 
               
               ] 
             
           
         
       
     
         [0010]    Now the rotation of the coefficients about the x, y axis is taken with isometry, which most whirl related test data supports, meaning the terms with subscript xx equal the yy terms and the subscript xy terms equal the negative yx terms. This then gives the following equation: 
         [0000]    
       
         
           
             
               
                 [ 
                 
                   
                     
                       
                         F 
                         θ 
                         * 
                       
                     
                   
                   
                     
                       
                         F 
                         r 
                         * 
                       
                     
                   
                 
                 ] 
               
               whirl 
             
             = 
             
               2 
                
               
                 [ 
                 
                   
                     
                       
                         
                           - 
                           
                             
                               
                                 m 
                                 xy 
                                 * 
                               
                                
                               
                                 ( 
                                 
                                   
                                     ω 
                                     w 
                                   
                                   ω 
                                 
                                 ) 
                               
                             
                             2 
                           
                         
                         - 
                         
                           
                             c 
                             xx 
                             * 
                           
                            
                           
                             ( 
                             
                               
                                 ω 
                                 w 
                               
                               ω 
                             
                             ) 
                           
                         
                         + 
                         
                           k 
                           xy 
                           * 
                         
                       
                     
                   
                   
                     
                       
                         
                           + 
                           
                             
                               
                                 m 
                                 xx 
                                 * 
                               
                                
                               
                                 ( 
                                 
                                   
                                     ω 
                                     w 
                                   
                                   ω 
                                 
                                 ) 
                               
                             
                             2 
                           
                         
                         - 
                         
                           
                             c 
                             xy 
                             * 
                           
                            
                           
                             ( 
                             
                               
                                 ω 
                                 w 
                               
                               ω 
                             
                             ) 
                           
                         
                         - 
                         
                           k 
                           xx 
                           * 
                         
                       
                     
                   
                 
                 ] 
               
             
           
         
       
     
         [0011]    For the circumferential force if F* θ  is negative, in the reverse direction of the impeller whirl rotation, an impeller whirl stabilizing force is experienced. If F* θ  is positive, in the direction of whirl, this destabilizes the impeller by eliciting greater whirl. The stability boundary is found by taking the value of F* θ =0 and m xy  as negligible in the previous equation to give ω w /ω=k* xy /c* xx  as the whirl ratio limit. Taking m xy  as negligible with respect to the stiffness and damping is reasonable for most but not all rotordynamic problems, although it does illustrate the origins of the whirl ratio limit. In dimensional form, this tangential whirl ratio limit as a stability condition then simplifies to the following: 
         [0000]    
       
         
           
             
               
                 ( 
                 
                   
                     ω 
                     w 
                   
                   ω 
                 
                 ) 
               
               
                 θ 
                  
                 
                     
                 
                  
                 limit 
               
             
             = 
             
               
                 k 
                 xy 
               
               
                 
                   c 
                   xx 
                 
                  
                 ω 
               
             
           
         
       
     
         [0012]    Therefore, the tangential stability whirl ratio limit is a balance between cross coupled stiffness forces k xy  that drive the whirl and damping forces c xx ω that oppose the whirl. For a constant angular frequency with a whirl larger than (ω w /ω) θ limit , the tangential force acts in a stabilizing manner. For a constant angular frequency with a whirl smaller than (ω w /ω) θ limit  the tangential force acts in a destabilizing manner, unless the whirl orbit is backwards in which case this is stabilizing. Hence the desire to decrease the cross-coupled stiffness k xy  (and increase the direct damping) is beneficial for improved whirl stability and reduced rotordynamic vibrations. Applying this finding, several research institutions and patents such as U.S. Pat. No. 5,190,440 to Maier have applied swirl brakes to labyrinth seals in high temperature gas compressors. 
         [0013]    It is this premise applied in conjunction with a thrust equalization mechanism that is unique for liquid cryogenic pumps and turbines. In so doing the benefit of a reduced destabilizing cross-coupled stiffness in the seal and balance mechanism is gained. Further, the direct coupled stiffness k xx  is increased in the seal along with an increase in the direct coupled c xx  damping. The reduced swirl in the variable orifice of the balance mechanism also provides an improved equalization of the axial thrust with unwanted flow separation regions avoided in the orifice gap. So several advancements in thrust balancing devices for liquid cryogenic pumps and turbines are addressed with the claims of this patent. 
         [0014]    Accordingly, there are provided herein several unique improvements to the axial thrust equalizing mechanism which address the deficiencies of preswirl in the prior art of submerged motor liquid cryogenic pumps and turbines. The invention reduces the destabilizing cross-coupled stiffness while concurrently increasing the direct coupled stiffness and direct coupled damping in the mechanical seals. This is achieved within the framework of an improved axial thrust equalization. The seals themselves consist of either labyrinth type, smooth type, or surface pattern type such as diamond surface mesh. Holes are also claimed to locally inject fluid with zero swirl and stop any residual swirling liquid seal flow. 
         [0015]    Another embodiment provides deswirl fins, vanes or grooves upstream of the variable orifice used for the thrust equalization. These ensure the variable orifice receives liquid with adjusted prespecified preswirl which may be zero with the flow directed primarily radially. This avoids fluid instabilities including separation near the orifice which can suddenly collapse or form giving the thrust balance system a rapid change in balance position. The predominately radial flow liquid direction also improves the capacity of balancing higher thrust levels needed for more powerful pumps and turbines. 
         [0016]    A further embodiment provides both a sealed and unsealed roller bearing operating in conjunction with the axial thrust equalizing mechanism and the deswirl devices. Currently unsealed roller bearings are the prior art. Sealed bearings packed with lubricants are not used in cryogenic applications for fear of freezing. Recent advances in synthetic grease now make available unfrozen grease down to temperatures of −60° C. This is applicable to liquid propane and butane pumps and turbines, particularly in situations where the fluid is dirty and can cause reduced bearing life for an unsealed bearing. For situations where the fluid temperature is lower, a bearing heater and sensor are embodied which briefly preheat the frozen grease before start-up. After start-up, the bearing heater may no longer be needed as the bearing itself may generate sufficient heat. 
         [0017]    A last embodiment provides deswirl vanes, fins, or holes on the seals on the plurality of impeller eyes and interstages. These are also useful to reduce the cross-coupled stiffness while concurrently increasing the direct coupled stiffness and direct coupled damping. Surface patterns such as diamond mesh are also utilized with a smooth rotating surface and a inlet deswirl mechanism for the same rotordynamic benefit. 
         [0018]    Numerous other advantages and features of the present invention will become readily apparent from the following detailed description of the invention and the embodiments thereof, from the claims and from the accompanying drawings. 
         [0019]    Benefits and features of the invention are made more apparent with the following detailed description of a presently preferred embodiment thereof in connection with the accompanying drawings, wherein like reference numerals are applied to like elements. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0020]      FIG. 1  is a partial, cross-sectional overall view of a multistage cryogenic pump at the axial thrust equalizing mechanism highest pressure impeller including seal deswirl mechanisms and lubricated sealed roller bearing which are constructed in accordance with the invention. 
           [0021]      FIG. 2  is a partial, cross-sectional view of four embodiments of the vaned or grooved or finned deswirl mechanism upstream of an impeller backside labyrinth seal and the variable axial orifice gap constructed in accordance with the invention. 
           [0022]      FIG. 3  is a partial, cross-sectional view of one embodiment of the deswirl mechanism incorporating holes upstream of an impeller backside labyrinth seal with local injection into the seal constructed in accordance with the invention. 
           [0023]      FIG. 4  is a partial, cross-sectional view of one embodiment of the deswirl mechanism incorporating a diamond surface pattern on the seal stator and smooth surface on the impeller backside constructed in accordance with the invention. 
           [0024]      FIG. 5  is a partial, cross-sectional view of four embodiments of the deswirl mechanism operating in conjunction with the variable axial orifice gap using a cooled lubricated scaled roller bearing constructed in accordance with the invention. 
           [0025]      FIG. 6  is a partial, axial view of two embodiments of the sealed roller bearing liner with a bearing heater and temperature sensor for cold liquid applications constructed in accordance with the invention. 
           [0026]      FIG. 7  is a partial, cross-sectional view of two embodiments of the deswirl mechanism operating in conjunction with the variable axial orifice gap using a cooled dry lubricated unsealed roller bearing constructed in accordance with the invention. 
           [0027]      FIG. 8  is a partial, cross-sectional view of three embodiments with fins or vanes or grooves upstream of the impeller eye seal as a deswirl mechanism constructed in accordance with the invention. 
           [0028]      FIG. 9  is a partial, cross-sectional view of one embodiment with a diamond surface pattern on the stator seal upstream of the impeller eye seal as a deswirl mechanism constructed in accordance with the invention. 
           [0029]      FIG. 10  is a partial, cross-sectional view of three embodiments with fins or vanes or grooves upstream of the impeller interstage seal as a deswirl mechanism constructed in accordance with the invention. 
           [0030]      FIG. 11  is a partial, cross-sectional view of one embodiment with a diamond surface pattern on die seal stator upstream of the impeller interstage seal as a deswirl mechanism constructed in accordance with the invention. 
       
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
       [0031]    The description that follows is presented to enable one skilled in the art to make and use the present invention, and is provided in the context of a particular application and its requirements. Various modifications to the disclosed embodiments will be apparent to those skilled in the art, and the general principals discussed below may be applied to other embodiments and applications without departing from the scope and spirit of the invention. Therefore, the invention is not intended to be limited to the embodiments disclosed, but the invention is to be given the largest possible scope which is consistent with the principals and features described herein. 
         [0032]    It will be understood that while numerous preferred embodiments of the present invention are presented herein, numerous of the individual elements and functional aspects of the embodiments are similar. Therefore, it will be understood that structural elements of the numerous apparatus disclosed herein having similar or identical function may have like reference numerals associated therewith. 
         [0033]    Referring to  FIG. 1  in particular, shown therein is a centrifugal impeller apparatus of a centrifugal pump or turbine used for handling cryogenic liquids. The apparatus incorporates annular labyrinth seal elements that are constructed in accordance with the invention. For clarity, the various components of the centrifugal pump or turbine impeller apparatus, as well as the annular labyrinth seal elements, are shown with sectional views of an upward portion thereof, it being realized that such elements are symmetrically oriented entirely around the rotatable shaft center. 
         [0034]    The case of a centrifugal pump is described realizing the reverse flow equivalent nature of a centrifugal turbine for which the claims also hold. It will be understood that for purposes of the current application, an LNG pump may be used to increase the pressure of the liquid LNG, while a turbine may act to lower the pressure of the liquid LNG. While the terms “pump” and “turbine” may be used interchangeably in certain portions of the current application, in general the primary differences between the two are described as follows: In the case of an LNG pump used to increase the pressure of the liquid LNG, flow of the main stream of liquid LNG will be into the pump at fluid inlet  25 , across impeller portion  2  located toward the radial periphery of the assembly, across return vane  5 , down and up through diffuser housing  3  and out the exhaust  4  at a higher pressure than at the fluid inlet  25 . Flow is from LEFT to RIGHT through the pump. Conversely, in the case of a turbine which lowers the overall pressure of the liquid LNG, flow is from RIGHT to LEFT through the turbine. 
         [0035]    The centrifugal pump comprises a rotatable shaft  1  rotating a plurality of impellers  2  with fluid leaving the impeller to be diffused in the diffuser  3  and then passed to exhaust lines  4  which surround a submerged motor housing  10 . Fluid enters the impeller eye from a return-vane  5  enclosed in a diffuser housing  6  all of which are encompassed in a pump housing  7 . The preceding impeller hub leakage is contained with an annular mechanical hub seal  8  which consists of a labyrinth and a smooth seal arrangement. The impeller eye is sealed with a mechanical shroud seal  9  using a shroud labyrinth or smooth seal arrangement. The impeller is circumferentially locked to the rotatable shaft with a key  14  and axially a locknut  12 . Behind the highest pressure impeller is the axial thrust equalizing mechanism consisting of a high pressure chamber  150  and mechanical seal  100  through which pressurized fluid passes to the low pressure chamber  204  and thrust plate  200 . After passing through this low pressure chamber an axial variable orifice gap  203  is traverse by the thrust equalizing liquid and passes into the thrust plate pocket  16  from where it exits the pocket through motor housing holes  19  or through the roller bearing  17  or through the bearing liner cooling holes  300 . The roller bearing is axially limited in travel with a locknut  15  and washer  22  and spacer  23 . Liquid which passes through the roller bearing or bearing linear then passes through a motor housing bushing  21  before entering the submerged cryogenic motor or generator cavity  20 . 
         [0036]    The destabilizing cross-coupled stiffness is a large influence on the forces that arise in mechanical seals and if too large can lead to excessive synchronous and subsynchronous vibrations in centrifugal pump and turbines. 
         [0037]    The deswirl mechanisms claim in this invention serve two purposes. Firstly they act to deswirl liquid at the inlet of the mechanical seals which make up part of the thrust equalizing mechanism. Secondly the deswirl mechanisms at the inlet of the variable axial orifice gap, also part of the axial thrust equalizing mechanism, removes unwanted circumferential liquid velocity to avoid flow separation pockets which gives a more stable axial thrust equalization than conventional liquid cryogenic systems. Together the mechanical seals and variable axial orifice gap act in harmony to equalize the axial thrust on the rotating shaft. The present invention provides means for achieving the desirable inlet swirl reduction at two key locations in the axial thrust equalizing mechanism of cryogenic pumps and turbines. 
         [0038]    Referring to the drawing and  FIG. 2  in particular, shown therein is a cross section zoom of the region near  100 . High pressure axial thrust equalizing liquid leaves the main core flow and travels inward along the back of the impeller in the annular high pressure chamber. Here substantial swirl is imparted on the liquid. The deswirl mechanisms  101  in the high pressure chamber reduce and preset the circumferential rotation of the liquid before it enters the clearance seal between the stationary wear ring  102  and the rotating labyrinth  103  mounted on the impeller  2 . The deswirl mechanisms are either vanes, fins, or grooves cut into the material of the motor housing  10 . Each of these deswirl mechanisms may be radial or inclined at an angle shown as α. In the case of vanes or fins they are fastened to the motor housing  10  with bolts  104  and are set to give a preswirl in the range 45°&lt;α&lt;135° with α=90° as predominant. Testing and computational fluid dynamics with regard to rotordynamic stability and in particular the stiffness and damping in the seal optimizes the angle setting. After the thrust equalizing liquid leaves the seal and has undergone a substantial pressure drop in enters the low pressure balance chamber  204 . Since at the seal outlet the liquid will again have circumferential swirl a set of deswirl mechanisms  201  are installed on the thrust plate  200 . This deswirl mechanisms can be fins, vanes, grooves or a combination thereof. The deswirl vanes or fins can be pivoted and locked into place with the bolts  202 . The thrust equalizing liquid is then directed radially towards the variable axial orifice gap  203  where due to the lack of swirl it is more stable and avoids separation pockets. This serves for a more stable and improved thrust equalizing mechanism. The impeller  2  is permitted to move axially in the range of 500 μm-3000 μm so that the axial orifice gap  203  is variable. If an axial thrust is not equalized such that the axial orifice gap  203  begins to close the pressure in low pressure balance chamber  204  rises since the flow is restricted and there is less pressure drop across the seal  102  and  103  from the high pressure chamber. This causes an increase in the axial opening force on the back of the impeller which counteracts and equalizes the closing axial thrust imbalance. If the axial thrust is not equalized in the reversed situation such that the axial orifice gap  203  begins to open the pressure in low pressure balance chamber  204  decreases since the flow is less restricted and there is more pressure drop across the seal  102  and  103  from the high pressure chamber. This causes a decrease in the opening force on the back of the impeller which counteracts and equalizes the opening axial thrust imbalance. After the axial thrust equalizing liquid leaves the axial orifice gap  203  it moves to toward the roller bear  17  and the thrust plate pocket  16 . 
         [0039]    Referring to the drawing and  FIG. 3  in particular, shown therein is a cross section zoom of the region near  100 . High pressure axial thrust equalizing liquid leaves the main core flow and travels inward along the back of the impeller in the annular high pressure chamber. Here substantial swirl is imparted on the liquid. A plurality of holes at a larger radius  301  and smaller radius  302  are drilled into the motor housing  10  where liquid by passes the wear ring gap inlet. The plurality of holes are located about the circumference and radially staggered. The holes and bypass liquid enter the clearance gap shortly downstream of the stationary wear ring  102  inlet and before the labyrinth rotating wear ring  103 . The holes are radially oriented so that liquid in the holes is of zero preswirl. After the axial thrust equalizing liquid leaves the seal and has undergone a substantial pressure drop it enters the low pressure balance chamber  204  where it operates in harmony with the variable axial orifice gap  203  as in the previous paragraphs described manner. 
         [0040]    Referring to the drawing and  FIG. 4  in particular, shown therein is a cross section zoom of the region near  100 . High pressure axial thrust equalizing liquid leaves the main core flow and travels inward along the back of the impeller in the annular high pressure chamber. Here substantial swirl is imparted on the liquid. The surface of the rotating wear ring  103  is made smooth as mounted on the impeller  2 . The surface of the stationary wear ring  102  is made up of a plurality of ridges arranged in a diamond like pattern  400 . These ridges  401  can be 1 mm to 5 mm tall. They serve to brake the liquid swirl in the seal gap. The diamond pattern is fixed annular type mounted inside the stationary wear ring  102  which in turn is mounted into the motor housing  10 . After the axial thrust equalizing liquid leaves the seal and has undergone a substantial pressure drop in enters the low pressure balance chamber  204  where it operates in harmony with the variable axial orifice gap  203  as in the previous paragraphs described manner. 
         [0041]    Referring to the drawing and  FIG. 5  in particular, shown therein is a cross section zoom of the region near  300  for the situation after the thrust equalizing liquid leaves the low pressure chamber and variable orifice gap and enters the thrust plate chamber  16  of the thrust plate  200 . The liquid is blocked from entering the roller bearing  17  by a bearing seal  502  that keeps low temperature lubricant  503  encapsulated in the roller bearing. The roller bearing  17  is permitted to move axially approximately 500 μm-3000 μm in total to give the impeller axial travel and vary the axial gap  203  depending on the axial thrust to be equalized. The roller bearing  17  is locked onto the shaft with the locknut  15  washer  22  and spacer  23 . The thrust equalizing liquid passes around the roller bearing either passing though the bearing liner  501  cooling slots  504  or the motor housing holes  19 . If the liquid passes through the bearing liner cooling slots it then travels to the back of the roller bearing where it passes through the motor housing bushing  21  and then to cool the submerged motor or generator. In this manner the roller bearing is completely lubricated with the low temperature lubricant while the cryogenic liquid cools the bearing and lubricant. 
         [0042]    Referring to the drawing and  FIG. 6  in particular, shown therein is a axial section zoom of the bearing liner  501 . A plurality of axial groove cooling slots  504  and lands on the bearing liner  501  are used to pass cooling liquid past the bearing. During start-up the cryogenic liquid may be sufficiently cold to freeze the roller bearing lubricant. A bearing heater  505  is then need at start-up until the lubricant reaches near −60° C. A temperature sensor  506  on the opposite side of the heater is applied to verify the start-up permission. The heater is applied for a few minutes before start-up of the pump or turbine. Afterward the heat from rotation in the roller bearing will keep the bearing lubricant warm and the heater can be shut-off. 
         [0043]    Referring to the drawing and  FIG. 7  in particular, shown therein is a cross section zoom of the region near  300  for the situation after the thrust equalizing liquid leaves the low pressure chamber and variable orifice gap and enters the thrust plate chamber  16  of the thrust plate  200 . The liquid is freely permitted to enter the roller bearing  17  where it cools the bearing along the ball  705 , inner race  704 , and outer race  702  as contact is made during rotation. The bearing cage material  703  is impregnated with a dry lubricant that wipes and partially lubricates the bearing. The entire roller bearing  17  is permitted to move axially approximately 500 μm-3000 μm in the bearing liner  701  to give the impeller axial travel and vary the axial orifice gap  203  depending on the axial thrust to be equalized. The roller bearing  17  is locked onto the shaft with the locknut  15  washer  22  and spacer  23 . The axial thrust equalizing liquid passes either through the roller bearing  17  or through the motor housing holes  19 . If the liquid passes through the roller bearing it then travels to the back of the roller bearing where it passes through the motor housing bushing  21  and then to cool the submerged motor or generator. In this manner the roller bearing is completely cooled by flushing with low temperature thrust equalizing liquid. 
         [0044]    Referring to the drawing and  FIG. 8  in particular, shown therein is a cross section zoom of the impeller  2  and impeller eye seal region  9 . The impeller shroud clearance leakage liquid passes through the mechanical labyrinth seal with a plurality of teeth to the impeller eye. Normally it enters the gap between the stationary smooth wear ring  801  embedded in the diffuser housing  6  and the impeller eye wear ring  802  with substantial circumferential swirl. This swirl increases the destabilizing cross-coupled stiffness. To eliminate this effect the cross-coupled stiffness is reduced using seal inlet deswirl mechanisms  803 . These are fins, vanes, or grooves. This operates to seal the impeller and stabilize the rotordynamics in conjunction with the axial thrust equalizing mechanism. 
         [0045]    Referring to the drawing and  FIG. 9  in particular, shown therein is a cross section zoom of the impeller eye stationary seal wear rings  902  and the smooth impeller eye wear ring  903 , the operation of which is described in the previous paragraph. On the stationary wear ring a diamond like surface pattern  901  like that shown previously in  FIG. 4  deswirls liquid in the clearance gap and reduces the cross-coupled stiffness. This seal operates to seal the impeller and stabilize the rotordynamics in conjunction with the axial thrust equalizing mechanism. 
         [0046]    Referring to the drawing and  FIG. 10  in particular, shown therein is a cross section zoom of the impeller  2  and hub wear ring of region  8 . The impeller hub clearance leakage liquid passes through the mechanical labyrinth seal with a plurality of teeth to the impeller hub. Normally it enters the gap between the stationary smooth wear ring  951  embedded in the return-vane  5  and the impeller hub wear ring  952  with substantial circumferential swirl. This swirl increases in the destabilizing cross-coupled stiffness. To eliminate this the cross-coupled stiffness is reduced using inlet deswirl mechanisms  953 . These are fins, vanes, or grooves. This functions to seal the impeller hub clearance and stabilize the rotordynamics in conjunction with the axial thrust equalizing mechanism. 
         [0047]    Referring to the drawing and  FIG. 11  in particular, shown therein is a cross section zoom of the return-vane stationary seal wear ring  975  and the smooth impeller hub wear ring  977 , the operation of which is described in the previous paragraph. On the stationary wear ring a diamond like surface pattern  976  like that shown previously in  FIG. 4  is made to deswirl liquid in the clearance gap and reduce the cross-coupled stiffness. This seal operates to seal the impeller and stabilize the rotordynamics in conjunction with the axial thrust equalizing mechanism. 
         [0048]    The foregoing description is intended to illustrate the present invention. Those of ordinary skill will be able to envisage certain additions, deletions or modifications to the described embodiments which do not depart from the spirit or scope of the invention as defined by the claims herein. 
         [0049]    Unless defined otherwise, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which the present invention belongs. Although any methods and materials similar or equivalent to those described can be used in the practice or testing of the present invention, the preferred methods and materials are now described. All publications and patent documents referenced in the present invention are incorporated herein by reference. 
         [0050]    While the principles of the invention have been made clear in illustrative embodiments, there will be immediately obvious to those skilled in the art many modifications of structure, arrangement, proportions, the elements, materials, and components used in the practice of the invention, and otherwise, which are particularly adapted to specific environments and operative requirements without departing from those principles. The appended claims are intended to cover and embrace any and all such modifications, with the limits only of the true purview, spirit and scope of the invention.