Patent Publication Number: US-11384772-B2

Title: Rotating machine and mating ring included therein

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     The subject application is a continuation-in-part application of U.S. application Ser. No. 16/135,491 filed on Sep. 19, 2018, which is herein incorporated by reference in its entirety. 
    
    
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates generally to a rotating machine and, more specifically, to a mating ring for use in the rotating machine. 
     2. Description of the Related Art 
     Rotating machines, such as turbochargers, electric compressors, and the like, are used in various applications, such as vehicles, heavy equipment, diesel engines, motors, cooling systems, fuel cell assemblies, and the like. Typical rotating machines include a shaft extending along an axis between a first end and a second end, a first impeller wheel coupled to the first end of the shaft, and a second impeller wheel coupled to the second end of the shaft. Typical rotating machines also include one or more bearings for rotatably supporting the shaft. Typical rotating machines also include a first seal assembly adjacent the first impeller wheel, and a second seal assembly adjacent the second impeller wheel. Both the first and second seal assemblies inhibit the flow of lubricant from the one or more bearings in the bearing housing. The first and second seal assemblies typically include a piston ring seal. 
     However, typical sealing assemblies for rotating machines including piston ring seals are often subject to undesired leakage of lubricant and other contaminants through the first seal assembly and the second seal assembly. As such, there remains a need to provide for a rotating machine with an improved first and second seal assembly. 
     Additionally, typical rotating machines may be used in a fuel cell air supply system, which provides airflow to a fuel cell to increase power density of the fuel cell during operation. When a rotating machine is used in a fuel cell air supply system, it is known that fuel cells are extremely sensitive to hydrocarbon poisoning, such as from a lubricant. In view of this, many rotating machines used in fuel cell air supply systems have moved from using lubricant-fed bearings and piston ring seals, which results in hydrocarbon poisoning in the fuel cell, to using rotating machines with air foil bearings or other lubricant free bearings, which are free of any hydrocarbons. However, such air foil bearings and other lubricant free bearings have limited operating ranges, are expensive, result in the rotating machine being less efficient, and have a short life, which requires replacement of such air foil bearings and reduces the longevity of the rotating machine. As such, there remains a need to provide for an improved rotating machine for use in a fuel cell air supply system. 
     SUMMARY OF THE INVENTION AND ADVANTAGES 
     In one embodiment, a rotating machine includes a shaft extending along an axis between a first end and a second end spaced from the first end along the axis, a first impeller wheel coupled to the first end of the shaft, and a second impeller wheel coupled to the second end of the shaft. The rotating machine also includes a first seal assembly including a first carbon ring disposed about the shaft and spaced from the first impeller wheel along the axis, with the first carbon ring having a first carbon surface, and a first mating ring disposed about the shaft and spaced from the first impeller wheel along the axis such that the first carbon ring is disposed between the first impeller wheel and the first mating ring, with the first mating ring having a first mating surface facing and configured to contact the first carbon surface. The rotating machine additionally includes a second seal assembly including a second carbon ring disposed about the shaft and spaced from the second impeller wheel along the axis, with the second carbon ring having a second carbon surface. The second seal assembly also includes a second mating ring disposed about the shaft and spaced from the second impeller wheel along the axis such that the second carbon ring is disposed between the second impeller wheel and the second mating ring, with the second mating ring having a second mating ring surface facing and configured to contact the second carbon surface. 
     Accordingly, the first seal assembly having the first mating ring and first carbon ring, and the second seal assembly having the second mating ring and the second carbon ring reduces leakage of contaminants to the first and second impeller wheels, respectively, which overall increases longevity of the rotating machine. 
     In another embodiment, a rotating machine includes a bearing housing defining a bearing housing interior, a shaft extending along an axis between a first end and a second end spaced from the first end along the axis, with the shaft disposed in the bearing housing interior. The rotating machine also includes an impeller housing coupled to the bearing housing, with the impeller housing defining an impeller housing interior, and an impeller wheel coupled to the shaft at the first end and disposed in the impeller housing interior. The rotating machine additionally includes a seal assembly disposed in the bearing housing interior. The seal assembly includes a carbon ring disposed about the shaft and spaced from the impeller wheel along the axis, with the carbon ring having a carbon surface, and a mating ring disposed about the shaft and spaced from the impeller wheel along the axis such that the carbon ring is disposed between the impeller wheel and the mating ring, with the mating ring having a mating surface facing and configured to contact the carbon surface. The rotating machine further includes a lubricant-fed bearing disposed in the bearing housing interior and rotatably supporting the shaft at the first end, with the seal assembly disposed between the lubricant-fed bearing and the impeller wheel with respect to the axis. The rotating machine also includes an electric machine including a rotor rotatably coupled to the shaft, and a stator disposed about the rotor. The impeller housing interior is adapted to be fluidly coupled to a contaminant free environment, with the carbon ring and the mating ring preventing lubricant from entering the contaminant free environment. 
     Accordingly, the mating ring and the carbon ring prevent lubricant from the lubricant-fed bearing and other contaminants from entering the impeller housing interior and, therefore, from entering the contaminant free environment, which overall increases longevity of the rotating machine, and increases performance of the rotating machine as a result of the lubricant-fed bearing being utilized. 
     In another embodiment, a system includes a rotating machine including a bearing housing defining a bearing housing interior, and a shaft extending along an axis between a first end and a second end spaced from the first end along the axis, with the shaft disposed in the bearing housing interior. The rotating machine also includes a compressor housing coupled to the bearing housing, with the compressor housing defining a compressor housing interior, a compressor wheel coupled to the shaft at the first end and disposed in the compressor housing interior, and a seal assembly disposed in the bearing housing interior. The seal assembly includes a carbon ring disposed about the shaft and spaced from the compressor wheel along the axis, with the carbon ring having a carbon surface, and a mating ring disposed about the shaft and spaced from the compressor wheel along the axis such that the carbon ring is disposed between the compressor wheel and the mating ring, with the mating ring having a mating surface facing and configured to contact the carbon surface. The rotating machine additionally includes a lubricant-fed bearing disposed in the bearing housing interior and rotatably supporting the shaft at the first end, with the seal assembly disposed between the lubricant-fed bearing and the compressor wheel with respect to the axis, and an electric machine including a rotor rotatably coupled to the shaft, and a stator disposed about the rotor, with the electric machine being configured to transmit torque to the shaft to rotate the compressor wheel. The system also includes a fuel cell assembly including a fuel cell housing defining a fuel cell interior, and a fuel cell disposed in the fuel cell interior. The compressor housing is coupled to the fuel cell housing, and the compressor housing interior is fluidly coupled to the fuel cell interior for delivering compressed air to the fuel cell assembly for cooling the fuel cell. 
     Accordingly, the mating ring and the carbon ring prevent lubricant from the lubricant-fed bearing and other contaminants from entering the compressor housing interior and, therefore, from entering the fuel cell interior, which overall increases longevity of the rotating machine, and increases performance of the rotating machine as a result of the lubricant-fed bearing being used. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Other advantages of the present invention will be readily appreciated, as the same becomes better understood by reference to the following detailed description when considered in connection with the accompanying drawings wherein: 
         FIG. 1  is a cross-sectional view of a rotating machine, with the rotating machine including a shaft extending along an axis, a first impeller wheel coupled to the shaft, a second impeller wheel coupled to the shaft, a first seal assembly, and a second seal assembly; 
         FIG. 2  is close-up view of the first seal assembly of  FIG. 1 ; 
         FIG. 3  is a close-up view of the second seal assembly of  FIG. 1 ; 
         FIG. 4  is a perspective cross-sectional view of a seal assembly representative of the first and second seal assemblies, with the seal assembly including a carbon ring and a mating ring; 
         FIG. 5  is a perspective view of the mating ring of the seal assembly defining a plurality of grooved portions; 
         FIG. 6  is a top view of a mating surface of the mating ring, with the mating surface having a land portion and an inner mating diameter adapted to be radially aligned with a carbon ring inner diameter with respect to the axis and an outer mating diameter adapted to be radially aligned with a carbon ring outer diameter with respect to the axis; 
         FIG. 7  is a top view of the mating surface of the mating ring, with the land portion having a land area between the inner and outer mating diameters, and with the land area shaded; 
         FIG. 8  is a top view of the mating surface of the mating ring, with the land portion having an inactive land area that is not between the inner and outer mating diameters, and with the inactive land area shaded; 
         FIG. 9  is a top view of the mating surface of the mating ring, with the plurality of grooved portions having a grooved area between the inner and outer mating diameters, and with the grooved area shaded; 
         FIG. 10  is a top view of the mating surface of the mating ring, with the plurality of grooved portions having an inactive groove area that is not between the inner and outer mating diameters, and with the inactive grooved area shaded; 
         FIG. 11  is a top view of the mating surface of the mating ring, with the land area shown as lightly shaded and the grooved area shown as dark shaded; 
         FIG. 12  is a cross-sectional view of a system including the rotating machine and a fuel cell assembly, with the fuel cell assembly including a fuel cell housing defining a fuel cell interior, and a fuel cell disposed in the fuel cell interior; and 
         FIG. 13  is a cross-sectional view of a system including the rotating machine, with the rotating machine including an impeller housing defining an impeller housing interior, and with the impeller housing interior being fluidly coupled to a contaminant free environment. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     With reference to the Figures, wherein like numerals indicate like parts throughout the several views, a rotating machine  20  is shown in  FIG. 1 . The rotating machine  20  includes a shaft  22  extending along an axis A between a first end  26  and a second end  28  spaced from the first end  26  along the axis A, a first impeller wheel  30  coupled to the first end  26  of the shaft  22 , and a second impeller wheel  32  coupled to the second end  28  of the shaft  22 . The rotating machine  20  also includes a first seal assembly  34  including a first carbon ring  36  disposed about the shaft  22  and spaced from the first impeller wheel  30  along the axis A. The first carbon ring  36  has a first carbon surface  38 , as shown in  FIG. 4 . The first seal assembly  34  also includes a first mating ring  40  disposed about the shaft  22  and spaced from the first impeller wheel  30  along the axis A such that the first carbon ring  36  is disposed between the first impeller wheel  30  and the first mating ring  40 , as shown in  FIG. 1 . With reference to  FIG. 4 , the first mating ring  40  has a first mating surface  42  facing and configured to contact the first carbon surface  38 . 
     With reference to  FIGS. 1, 3, and 4 , the rotating machine  20  additionally includes a second seal assembly  44  including a second carbon ring  46  disposed about the shaft  22  and spaced from the second impeller wheel  32  along the axis A, with the second carbon ring  46  having a second carbon surface  48 . The second seal assembly  44  also includes a second mating ring  50  disposed about the shaft  22  and spaced from the second impeller wheel  32  along the axis A such that the second carbon ring  46  is disposed between the second impeller wheel  32  and the second mating ring  50 , with the second mating ring  50  having a second mating surface  52  facing and configured to contact the second carbon surface  48 . The first and second mating rings  40 ,  50  may have an interior mating surface  53  extending along the axis A between a first mating end  55  and a second mating end  57  spaced from the first mating end  55 , with the interior mating surface  53  defining a bore  59 . The first and second seal assemblies  34 ,  44  are is commonly referred to as a dry-gas seal, a face seal, a lift-off face seal, a non-contacting face seal, a mechanical face seal, a shallow hydropad seal, a groove seal, or a spiral groove seal. 
     The first seal assembly  34  having the first mating ring  40  and first carbon ring  36 , and the second seal assembly  44  having the second mating ring  50  and the second carbon ring  46  reduces leakage of contaminants, such as lubricant and carbon deposits, to the first and second impeller wheels  30 ,  32 , respectively, which overall increases longevity of the rotating machine  20 . Additionally, as described in further detail below, in embodiments where a lubricant-fed bearing is used in the rotating machine  20 , which may be used as a result of the first seal assembly  34  having the first mating ring  40  and first carbon ring  36 , and the second seal assembly  44  having the second mating ring  50  and the second carbon ring  46 , performance of the rotating machine  20  increases. 
     The first mating surface  42  may face the first end  26  of the shaft  22  and the second mating surface  52  may face the second end  28  of the shaft  22  such that the first and second mating surfaces  42 ,  52  are facing opposite directions with respect to the axis A. Having the first and second mating surfaces  42 ,  52  facing in opposite directions with respect to the axis A ensures that the first and second impeller wheels  30 ,  32  are isolated from contaminants, such as lubricant and carbon deposits, due to the first and second seal assemblies  34 ,  44 . 
     The first and second impeller wheels  30 ,  32  may be removably coupled to the shaft  22 . For example, the first and second impeller wheels  30 ,  32  may be removably coupled to the shaft  22  through a nut  54 . In one embodiment, the first and second impeller wheels  30 ,  32  are comprised of aluminum or titanium. In such embodiments, the first and second impeller wheels  30 ,  32  may be referred to as first and second compressor wheels, respectively. In other words, the first and second compressor wheels are configured to deliver compressed air, rather than receive a working fluid, such as exhaust gas. Additionally, in such embodiments, the first and second compressor wheels may be in series (e.g., for higher pressure ratios), or in parallel (e.g., for higher flow rates). When the first and second impeller wheels  30 ,  32  are further defined as first and second compressor wheels, the rotating machine  20  may be referred to as a two-stage compressor. It is to be appreciated that the first and second impeller wheels  30 ,  32  may be axial flow or radial flow impeller wheels (including axial and radial flow compressor wheels). 
     In other embodiments, the first impeller wheel  30  may be further defined as a compressor wheel, and the second impeller wheel  32  may be further defined as a turbine wheel. In other words, when the first impeller wheel  30  is further defined as a compressor wheel, the first impeller wheel  30  is configured to deliver compressed air. When the second impeller wheel  32  is further defined as a turbine wheel, the second impeller wheel is configured to receive a working fluid, such as exhaust gas, to rotate the shaft  22  and, in turn, the first impeller wheel  30  (compressor wheel) to deliver compressed air. The turbine wheel may be integral with (i.e., one piece) the shaft  22 . In embodiments where the first impeller wheel  30  is further defined as a compressor wheel, and the second impeller wheel  32  is further defined as a turbine wheel, the turbine wheel may be part of a fixed geometry turbine (flow area of working fluid remains constant) or a variable geometry turbine (flow area of working fluid may be changed). In embodiments where the turbine wheel is part of a variable geometry turbine, the compressor wheel may be part of a single variable inlet compressor. It is to be appreciated that when the second impeller wheel  32  is further defined as a turbine wheel, the turbine wheel may be an axial flow or radial flow turbine wheel. 
     In other embodiments, the rotating machine  20  may be used in an organic Rankine cycle waste heat recovery system, for example as a turbine expander. In such embodiments, the rotating machine  20  first and second impeller wheels  30 ,  32  may be further defined as first and second turbine wheels for receiving a working fluid. The first and second impeller wheels  30 ,  32 , when further defined as first and second turbine wheels may be in series with one another or in parallel with one another. It is also to be appreciated that when the rotating machine  20  is used in an organic Rankine cycle waste heat recovery system as a turbine expander that the first impeller wheel  30  may be further defined as a turbine wheel for receiving the working fluid, and that the second impeller wheel  32  may be further defined as a pump impeller for pumping the working fluid in the organic Rankine cycle waste heat recovery system. It is to be appreciated that when the first impeller wheel  30  is further defined as a first turbine wheel that the first turbine wheel may be a variable or fixed geometry turbine wheel, and that when the second impeller wheel  32  is further defined a second turbine wheel that the second turbine wheel may be variable or fixed geometry turbine wheel. When the rotating machine  20  is used in an organic Rankine cycle waste heat recovery system, the first and second impeller wheels  30 ,  32  may be comprised of any suitable material, for example aluminum, stainless steel, or nickel alloy, such as Inconel®. 
     The rotating machine  20  may include an electric machine  56 . In such embodiments, the electric machine  56  includes a rotor  58  rotatably coupled to the shaft  22 , and a stator  60  disposed about the rotor  58 . Typically, when the rotating machine  20  includes the electric machine  56 , the first impeller wheel  30  is further defined as a first compressor wheel configured to deliver compressed air, the second impeller wheel  32  is further defined as a second compressor wheel configured to deliver compressed air, and the electric machine  56  is configured to transmit torque to the shaft  22  to rotate the first and second compressor wheels. In such embodiments, the shaft rotates the first and second compressor wheels are rotated as a result of the electric machine  56 , rather than rotating either the first or second impeller wheel  30 ,  32  as a result of one of the first or second impeller wheels  30 ,  32  receiving a working fluid, such as exhaust gas. 
     In one embodiment, the first and second impeller wheels  30 ,  32  may be further defined as a turbine wheel configured to receive a working fluid and a compressor wheel configured to deliver a working fluid, respectively. In such embodiments, the electric machine  56  may be configured as an electric motor for delivering rotational torque to the shaft  22  and/or may be configured as a generator for receiving rotational torque to the shaft  22  to convert mechanical energy into electrical energy. In embodiments where the rotating machine  20  is used in an organic Rankine cycle waste heat recover system as a turbine expander, the first impeller wheel  30  may be further defined as a turbine wheel and the rotating machine  20  may include the electric machine  56  configured as a generator and/or an electric motor. 
     With reference to  FIG. 6 , the first carbon surface  38  may have a first carbon ring inner diameter CID 1  and a first carbon ring inner outer COD 1  spaced from the first carbon ring inner diameter CID 1  radially away from the axis A. The first mating surface  42  may have a first land portion  70  configured to contact the first carbon surface  38  between a first inner mating diameter IMD 1  radially aligned with the first carbon ring inner diameter CID 1  with respect to the axis A and a first outer mating diameter OMD 1  radially aligned with the first carbon ring inner outer COD 1  with respect to the axis A. The first carbon ring  36  is removed in  FIG. 6  such that the first mating ring  40  and first mating surface  42  is shown clearly. The first carbon ring inner diameter CID 1  and first carbon ring inner outer COD 1  are shown with respect to the first mating surface  42  to illustrate where the first carbon surface  38  contacts the first mating surface  42 . 
     With reference to  FIGS. 6 and 7 , the first land portion  70  may have a first land area  76  between the first inner and first outer mating diameters IMD 1 , OMD 1 , with first mating surface  42  defining a first plurality of grooved portions  78  disposed about the axis A. The first plurality of grooved portions  78  may have a first grooved area  80  between the first inner and first outer mating diameters IMD 1 , OMD 1 . A ratio of the first land area  76  to the first grooved area  80  is typically between 1.3 and 2.9. 
     Having the ratio of the first land area  76  to the first grooved area  80  between 1.3 and 2.9 ensures that the first carbon ring  36  lifts off, i.e., becomes disengaged, from the first mating ring  40  at the optimal rotational speed from a fluid pressure, which may be caused by lubricant or air, exiting the first plurality of grooved portions  78  caused by rotation of the first mating ring  40 . For example, having the first carbon ring  36  lift off from the first mating ring  40  reduces mechanical losses of the rotating machine  20  and improves durability of the rotating machine  20 . Specifically, the ratio of the first land area  76  to the first grooved area  80  between 1.3 and 2.9 improves durability of the first carbon ring  36 , and reduces mechanical losses caused by the first carbon ring  36  and the first mating ring  40  remaining in contact for too long. The ratio of the first land area  76  to the first grooved area  80  between 1.3 and 2.9 is optimal for ensuring lift off of the first carbon ring  36  from the first mating ring  40  does not occur at too low or too high of a rotational speed of the first mating ring  40 . 
     The ratio of the first land area  76  to the first grooved area  80  is shown in  FIG. 11 , where the light shaded area is the first land area  76  and the dark shaded area is the first grooved area  80 . Specifically, the first grooved area  80  includes all of the dark shaded area in  FIG. 11 , and the first land area  76  includes all of the light shaded area in  FIG. 11 . As described above, the ratio of the light shaded area, i.e., the first land area  76 , to the dark shaded area, i.e., the first grooved area  80 , may be between 1.3 and 2.9. In one embodiment, the ratio of the first land area  76  to the first grooved area  80  may be between 1.75 and 2.75. In another embodiment, the ratio of the first land area  76  to the first grooved area  80  may be 1.4. In another embodiment, the ratio of the first land area  76  to the first grooved area  80  may be 1.5. In another embodiment, the ratio of the first land area  76  to the first grooved area  80  may be 1.6. In another embodiment, the ratio of the first land area  76  to the first grooved area  80  may be 1.7. In another embodiment, the ratio of the first land area  76  to the first grooved area  80  may be 1.8. In another embodiment, the ratio of the first land area  76  to the first grooved area  80  may be 1.9. In another embodiment, the ratio of the first land area  76  to the first grooved area  80  may be 2.0. In another embodiment, the ratio of the first land area  76  to the first grooved area  80  may be 2.1. In another embodiment, the ratio of the first land area  76  to the first grooved area  80  may be 2.2. In another embodiment, the ratio of the first land area  76  to the first grooved area  80  may be 2.3. In another embodiment, the ratio of the first land area  76  to the first grooved area  80  may be 2.4. In another embodiment, the ratio of the first land area  76  to the first grooved area  80  may be 2.5. In another embodiment, the ratio of the first land area  76  to the first grooved area  80  may be 2.6. In another embodiment, the ratio of the first land area  76  to the first grooved area  80  may be 2.7. In another embodiment, the ratio of the first land area  76  to the first grooved area  80  may be 2.8. In another embodiment, the ratio of the first land area  76  to the first grooved area  80  may be 2.9. 
     Typically, the first plurality of grooved portions  78  are spiraled about the axis A, as shown in  FIGS. 6-11 . With reference to  FIG. 6 , the first plurality of grooved portions  78  may have a first groove inner diameter GID 1 , with a ratio of the first carbon ring inner diameter CID 1  to the first groove inner diameter GID 1  being greater than 1.0. When the ratio of the first carbon ring inner diameter CID 1  to the first groove inner diameter GID 1  is adapted to be greater than 1.0, the first plurality of grooved portions  78  extends beyond the first carbon ring inner diameter CID 1  and inward toward the axis A, as shown in  FIG. 6 . As shown in  FIG. 10 , the first plurality of grooved portions  78  extends beyond the first carbon ring inner diameter CID 1  and inward toward the axis A, which results in the first plurality of grooved portions  78  having a first inactive groove area  86  (or second inactive groove area  106  of a second plurality of grooved portions  102 ), which is shown in  FIG. 10  as the shaded area of the first plurality of grooved portions  78 . Having the first plurality of grooved portions  78  extending beyond the first carbon ring inner diameter CID 1  and inward toward the axis A allows the first plurality of grooved portions  78  to maintain fluid communication to the first carbon surface  38  adjacent the first carbon ring inner diameter CID 1  to promote “lift off” of the first carbon ring  36 . In other words, the first plurality of grooved portions  78  is open at the first groove inner diameter GID 1  such that the first plurality of grooved portions  78  are able to direct fluid toward the first groove outer diameter GOD 1  to generate enough fluid pressure to “lift off” the first carbon ring  36 . Typically, the ratio of the first carbon ring inner diameter CID 1  to the first groove inner diameter GID 1  is less than 1.2. Having the ratio of the first carbon ring inner diameter CID 1  to the first groove inner diameter GID 1  less than 1.2 allows the first carbon ring  36  to be smaller in size, which results in better packaging of the first mating ring  40  and the first carbon ring  36 , which ultimately results in less space occupied in the rotating machine  20 . In one embodiment, the ratio of the first carbon ring inner diameter CID 1  to the first groove inner diameter GID 1  is between 1.02 and 1.10. In one embodiment, the ratio of the first carbon ring inner diameter CID 1  to the first groove inner diameter GID 1  may be adapted to be between 1.03 and 1.09. In another embodiment, the ratio of the first carbon ring inner diameter CID 1  to the first groove inner diameter GID 1  may be adapted to be between 1.04 and 1.08. In another embodiment, the ratio of the first carbon ring inner diameter CID 1  to the first groove inner diameter GID 1  may be adapted to be between 1.05 and 1.07. In another embodiment, the ratio of the first carbon ring inner diameter CID 1  to the first groove inner diameter GID 1  may be adapted to be 1.05. Having the first plurality of grooved portions  78  spiraled about the axis A allows the first mating ring  40  to direct fluid outwardly, which helps with the lift off of the first carbon ring  36  from the first mating ring  40 . Typically, the first plurality of grooved portions  78  are spiraled about the axis A when the rotating machine  20  is a single direction machine, i.e., the shaft  22  spins only in one direction about the axis A. When the rotating machine  20  is not a single direction machine, the first plurality of grooved portions  78  may have a configuration that does not spiral about the axis A, such as T-shaped or rectangular grooves. 
     The first plurality of grooved portions  78  may have a first groove outer diameter GOD 1 , as shown in  FIG. 6 . A ratio of the first carbon ring inner outer COD 1  to the first groove outer diameter GOD 1  may be greater than 1.0. When the ratio of the first carbon ring inner outer COD 1  to the first groove outer diameter GOD 1  is greater than 1.0, the first carbon ring  36  extends beyond the first groove outer diameter GOD 1  radially away from the axis A. As shown in  FIG. 8 , the first mating surface  42  may have a first inactive land area  88 , which is shown in  FIG. 8  as the shaded area on the first mating surface  42 . When present, the first inactive land area  88  is not contacted by the first carbon surface  38 . Having the first carbon ring  36  extending beyond the first groove outer diameter GOD 1  radially away from the axis A allows first plurality of grooved portions  78  at the first groove outer diameter GOD 1  to be sealed against the first carbon surface  38 . Typically, the ratio of the first carbon ring inner outer COD 1  to the first groove outer diameter GOD 1  is less than 1.5. Having the ratio of the first carbon ring inner outer COD 1  to the first groove outer diameter GOD 1  less than 1.5 results in better packaging of the first mating ring  40  and the first carbon ring  36 , which ultimately results in less space occupied in the rotating machine  20 . In one embodiment, the ratio of the first carbon ring inner outer COD 1  to the first groove outer diameter GOD 1  is between 1.05 and 1.25. In one embodiment, the ratio of the first carbon ring inner outer COD 1  to the first groove outer diameter GOD 1  may be adapted to be between 1.10 and 1.20. In another embodiment, the ratio of the first carbon ring inner outer COD 1  to the first groove outer diameter GOD 1  may be adapted to be 1.15. 
     Typically, the first plurality of grooved portions  78  is further defined as having between three and ten grooves. In one embodiment, the first plurality of grooved portions  78  has between four and nine grooves. In another embodiment, the first plurality of grooved portions  78  has between five and eight grooves. In another embodiment, the first plurality of grooved portions  78  has six grooves. In yet another embodiment, the first plurality of grooved portions  78  has seven grooves. Having the first plurality of grooved portions  78  being further defined as having between three and ten grooves, although not required, is helpful to achieve the ratio of the first land area  76  to the first grooved area  80  between 1.3 and 2.9. 
     With reference to  FIG. 6 , the second carbon surface  48  has a second carbon ring inner diameter CID 2  and a second carbon ring outer diameter COD 2  spaced from the second carbon ring inner diameter CID 2  radially away from the axis A. 
     For ease of illustration, the mating ring shown in  FIGS. 4-11  is representative of both the first and second mating rings  40 ,  50 . As such, elements of both the first and second mating rings  40 ,  50  are labeled in  FIGS. 4-11 . 
     As shown in  FIGS. 6 and 7 , the second mating surface  52  may have a second land portion  94  configured to contact the second carbon surface  48  between a second inner mating diameter IMD 2  radially aligned with the second carbon ring inner diameter CID 2  with respect to the axis A and a second outer mating diameter OMD 2  radially aligned with the second carbon ring outer diameter COD 2  with respect to the axis A. The second land portion  94  may have a second land area  100  between the second inner and outer mating diameters IMD 2 , OMD 2 . The second mating surface  52  may define a second plurality of grooved portions  102  disposed about the axis A. The second plurality of grooved portions  102  may have a second grooved area  104  between the second inner and outer mating diameters IMD 2 , OMD 2 , with a ratio of the second land area  100  to the second grooved area  104  being between 1.3 and 2.9. 
     Having the ratio of the second land area  100  to the second grooved area  104  between 1.3 and 2.9 ensures that the second carbon ring  46  lifts off, i.e., becomes disengaged, from the second mating ring  50  at the optimal rotational speed from a fluid pressure, which may be caused by lubricant or air, exiting the second plurality of grooved portions  102  caused by rotation of the second mating ring  50 . For example, having the second carbon ring  46  lift off from the second mating ring  50  reduces mechanical losses of the rotating machine  20  and improves durability of the rotating machine  20 . Specifically, the ratio of the second land area  100  to the second grooved area  104  between 1.3 and 2.9 improves durability of the second carbon ring  46 , and reduces mechanical losses caused by the second carbon ring  46  and the second mating ring  50  remaining in contact for too long. The ratio of the second land area  100  to the second grooved area  104  between 1.3 and 2.9 is optimal for ensuring lift off of the second carbon ring  46  from the second mating ring  50  does not occur at too low or too high of a rotational speed of the second mating ring  50 . 
     The ratio of the second land area  100  to the second grooved area  104  is shown in  FIG. 11 , where the light shaded area is the second land area  100  and the dark shaded area is the second grooved area  104 . Specifically, the second grooved area  104  includes all of the dark shaded area in  FIG. 11 , and the second land area  100  includes all of the light shaded area in  FIG. 11 . As described above, the ratio of the light shaded area, i.e., the second land area  100 , to the dark shaded area, i.e., the second grooved area  104 , may be between 1.3 and 2.9. In one embodiment, the ratio of the second land area  100  to the second grooved area  104  may be between 1.75 and 2.75. In another embodiment, the ratio of the second land area  100  to the second grooved area  104  may be 1.4. In another embodiment, the ratio of the second land area  100  to the second grooved area  104  may be 1.5. In another embodiment, the ratio of the second land area  100  to the second grooved area  104  may be 1.6. In another embodiment, the ratio of the second land area  100  to the second grooved area  104  may be 1.7. In another embodiment, the ratio of the second land area  100  to the second grooved area  104  may be 1.8. In another embodiment, the ratio of the second land area  100  to the second grooved area  104  may be 1.9. In another embodiment, the ratio of the second land area  100  to the second grooved area  104  may be 2.0. In another embodiment, the ratio of the second land area  100  to the second grooved area  104  may be 2.1. In another embodiment, the ratio of the second land area  100  to the second grooved area  104  may be 2.2. In another embodiment, the ratio of the second land area  100  to the second grooved area  104  may be 2.3. In another embodiment, the ratio of the second land area  100  to the second grooved area  104  may be 2.4. In another embodiment, the ratio of the second land area  100  to the second grooved area  104  may be 2.5. In another embodiment, the ratio of the second land area  100  to the second grooved area  104  may be 2.6. In another embodiment, the ratio of the second land area  100  to the second grooved area  104  may be 2.7. In another embodiment, the ratio of the second land area  100  to the second grooved area  104  may be 2.8. In another embodiment, the ratio of the second land area  100  to the second grooved area  104  may be 2.9. 
     In embodiments where the ratio of the first land area  76  to the first grooved area  80  is between 1.3 and 2.9 and where the ratio of the second land area  100  to the second grooved area  104  is between 1.3 and 2.9, the first plurality of grooved portions  78  may be spiraled about the axis A, and the second plurality of grooved portions  102  may be spiraled about the axis A. In such embodiments, as shown in  FIG. 6 , the first plurality of grooved portions  78  may have the first groove inner diameter GID 1 , with a ratio of the first carbon ring inner diameter CID 1  to the first groove inner diameter GID 1  being greater than 1.0, with the second plurality of grooved portions  102  having a second groove inner diameter GID 2 , and with a ratio of the second carbon ring inner diameter GID 2  to the second groove inner diameter GID 2  being greater than 1.0. The ratio of the first carbon ring inner diameter CID 1  to the first groove inner diameter GID 1  may be between 1.02 and 1.10, and the ratio of the second carbon ring inner diameter CID 2  to the second groove inner diameter GID 2  may be between 1.02 and 1.10. 
     In embodiments where the ratio of the first land area  76  to the first grooved area  80  is between 1.3 and 2.9 and where the ratio of the second land area  100  to the second grooved area  104  is between 1.3 and 2.9, the first plurality of grooved portions  78  may have the first groove outer diameter GOD 1 , with the ratio of the first carbon ring inner outer COD 1  to the first groove outer diameter GOD 1  being greater than 1.0, and the second plurality of grooved portions  102  may have a second groove outer diameter GOD 2 , with a ratio of the second carbon ring outer diameter COD 2  to the second groove outer diameter GOD 2  being greater than 1.0. In such embodiments, the ratio of the first carbon ring inner outer COD 1  to the first groove outer diameter GOD 1  may be between 1.05 and 1.25, and the ratio of the second carbon ring outer diameter COD 2  to the second groove outer diameter GOD 2  may be between 1.05 and 1.25. As described above with respect to the first plurality of grooved portions  78 , it is to be appreciated that the second plurality of grooved portions  102  may be further defined as having between three and ten grooves. As shown in  FIG. 8 , the second mating surface  52  may have a second inactive land area  108 , which is shown in  FIG. 8  as the shaded area on the second mating surface  52 . When present, the second inactive land area  108  is not contacted by the second carbon surface  48 . 
     Typically, the first plurality of grooved portions  78  are defined into the first mating surface  42 . It is to be appreciated that the description below of various features of the first plurality of grooved portions  78  may also apply to the second plurality of grooved portions  102 . For example, the second plurality of grooved portions  102  may be defined into the second mating surface  52 . The first plurality of grooved portions  78  may be etched, such as through etching or laser etching, into the first mating surface  42 . The first plurality of grooved portions  78  may be etched or laser etched into the first mating surface  42  at a right angle. It is to be appreciated that the first plurality of grooved portions  78  may have a non-uniform depth, which may result in the first plurality of grooved portions  78  being etched into the first mating surface  42  at a non-right angle. Typically, the first plurality of grooved portions  78  have a depth defined into the first mating surface  42  greater than 0.005 mm. Having the first plurality of grooved portions  78  having a depth defined into the first mating surface  42  greater than 0.005 mm allows the first plurality of grooved portions  78  to still be effective during operation despite carbon deposits in the first plurality of grooved portions  78 . Typically, the first plurality of grooved portions  78  have a depth defined into the first mating surface that is less than 0.040 mm. Having the first plurality of grooved portions  78  having a depth defined into the first mating surface  42  that is less than 0.040 mm reduces time needed to manufacture the first plurality of grooved portions  78 , for example though etching or laser etching. As such, the first plurality of grooved portions  78  typically have a depth defined into the first mating surface  42  between 0.005 mm to 0.040 mm. Having a depth of the first plurality of grooved portions  78  between 0.005 mm and 0.040 mm allows both the first plurality of grooved portions  78  to still be effective during operation despite carbon deposits in the first plurality of grooved portions  50 , and reduces the time needed to manufacture the first plurality of grooved portions  50 , for example though etching or laser etching. In one embodiment, the depth of the first plurality of grooved portions  78  may be between 0.010 mm and 0.035 mm. In another embodiment, the depth of the first plurality of grooved portions  78  may be between 0.015 mm and 0.030 mm. In another embodiment, the depth of the first plurality of grooved portions  78  may be between 0.020 mm and 0.025 mm. 
     With reference to  FIG. 2 , the first mating ring  40  may include a first cylindrical sleeve  110  coupled to and rotatable with the shaft  22 , and a first flange  112  extending radially from the first cylindrical sleeve  110  such that the first mating ring  40  is configured as a flinger, with the first cylindrical sleeve  110  extending from the first flange  112  toward the first impeller wheel  30 . The first flange  112  may have a first flange inner diameter FID 1  and a first flange outer diameter FOD 1  radially spaced from the first flange inner diameter FID 1  with respect to the axis A, as shown in  FIG. 6 . Additionally, when the first mating ring  40  is configured as a flinger, the first mating ring  40  directs fluid outwardly during rotation of the shaft  22  to direct fluid to separate the first carbon ring  36  and the first mating ring  40 . It is to be appreciated that when the first mating ring  40  is configured as a flinger that the first mating ring  40  may also be referred to as a flinger sleeve. It is to be appreciated that a surface facing opposite the first mating surface  42  may be configured as a thrust bearing runner surface. Similarly, as shown in  FIG. 3 , the second mating ring  50  may include a second cylindrical sleeve  118  coupled to and rotatable with the shaft  22 , and a second flange  120  extending radially from the second cylindrical sleeve  118  such that the second mating ring  50  is configured as a flinger, with the second cylindrical sleeve  118  extending from the second flange  120  toward the second impeller wheel  32 . Similarly, the second flange  120  may have a second flange inner diameter FID 2  and a second flange outer diameter FOD 2  radially spaced from the second flange inner diameter FID 2  with respect to the axis A, as shown in  FIG. 6 . 
     With reference to  FIG. 4 , the first seal assembly  34  may include a seal housing  126  defining a seal housing interior  128 . It is to be appreciated that the description of various features of the first seal assembly  34  equally applies to the second seal assembly  44 . For example, the first seal assembly  34  may include the seal housing  126  and the second seal assembly  44  may include a separate seal housing  126 . When the seal housing  126  is present, the first carbon ring  36  is disposed in the seal housing interior  128 . The first seal assembly  34  may also include a biasing member  130  disposed in the seal housing interior  128 . When present, the biasing member  130  is coupled to the seal housing  126  and the first carbon ring  36  such that the biasing member  130  is adapted to bias the first carbon ring  36  toward the first mating ring  40 . Specifically, when present, the biasing member  130  is adapted to bias the first carbon surface  38  toward the first mating surface  42 . In one embodiment, the biasing member  130  is a spring. The first seal assembly  34  may include a secondary seal  132  coupled to the first seal housing  126  and the first carbon ring  36  to prevent leakage of lubricant. In one embodiment, the secondary seal  132  is an O-ring seal. 
     It is to be appreciated that the description of the first carbon ring  36  below may equally apply the second carbon ring  46  and corresponding components. The first carbon ring  36  may be moveable between a first position where the first carbon surface  38  is engaged with the first mating surface  42  (i.e., before startup), and a second position where the first carbon surface  38  is spaced from the first mating surface  42  such that the first carbon surface  38  and the first mating surface  42  are disengaged to allow rotation of the first mating ring  40  (i.e., after startup). Typically, the first carbon surface  38  and the first mating surface  42  define a gap between one another when the first carbon ring  36  is in the second position. The gap may be between 0.5 and 4 microns. The gap defined between the first carbon surface  38  and the first mating surface  42  when the first carbon ring  36  is in the second position results in minimal efficiency loss after “lift-off.” The first carbon surface  38  and the first mating surface  42  may have a gas film formed by rotation of the first mating ring  40  when the first carbon ring  36  is in the second position. As described above, the gap is typically between 0.5 and 4 microns. Having the gap defined between the first carbon surface  38  and the first mating surface  42  allows the rotating machine  20  to be oriented vertically or horizontally, whereas standard piston ring sealing systems require the rotating machine to be horizontally arranged. Additionally, when the first carbon ring  36  is in the second position, the first mating ring  40  directs lubricant radially away from the axis A during rotation of the shaft  22 , which prevents lubricant from leaking to unwanted areas of the rotating machine  20 , such as to the first impeller wheel  30  or other sealing systems, and helps direct lubricant flow toward a lubricant drain. 
     With reference to  FIGS. 1-3 , the rotating machine  20  may include a bearing housing  134  defining a bearing housing interior  136 , a first lubricant-fed bearing  138  disposed in the bearing housing interior  136  and rotatably supporting the shaft  22  at the first end  26  of the shaft, and a second lubricant-fed bearing  140  disposed in the bearing housing interior  136  and rotatably supporting the shaft  22  at the second end  28  of the shaft  22 . The first and/or second lubricant-fed bearings  138 ,  140  may be provided lubricant from a lubricant passage  141 , which may be defined within the bearing housing  134 . When the rotating machine includes the first lubricant-fed bearing  138  and the second lubricant-fed bearing  140 , the first seal assembly  34  having the first mating ring  40  and first carbon ring  36 , and the second seal assembly  44  having the second mating ring  50  and the second carbon ring  46  reduces leakage of lubricant to the first and second impeller wheels  30 ,  32 , respectively, which overall increases longevity of the rotating machine  20 . Additionally, performance of the rotating machine  20  is increased because first and second lubricant-fed bearings  138 ,  140  may be used as a result of the first seal assembly  34  having the first mating ring  40  and first carbon ring  36 , and the second seal assembly  44  having the second mating ring  50  and the second carbon ring  46 . The first and second lubricant-fed bearings  138 ,  140  may be any suitable lubricant-fed bearing, such as a ball bearing. For example, as described in further detail below, utilizing lubricant-fed bearings improves performance and longevity of the rotating machine  20 , and having the first and second seal assemblies  34 ,  44  allows the rotating machine  20  to utilize lubricant-fed bearings as the first and second seal assemblies  34 ,  44  reduce, if not eliminate, any contaminants from the lubricant from reaching the first and second impeller wheels  30 ,  32 . 
     For ease of illustration, it is to be appreciated that the seal assembly, carbon ring, carbon surface, mating ring, lubricant-fed bearing, carbon ring inner diameter, carbon ring outer diameter, land portion, inner mating diameter, outer mating diameter, land area, plurality of grooved portions, and grooved area described below are labeled in  FIGS. 4-12  using element labels of the first seal assembly  34 , first carbon ring  36 , first carbon surface  38 , first mating ring  40 , first lubricant-fed bearing  138 , first carbon ring inner diameter CID 1 , first carbon ring outer diameter COD 1 , first land portion  70 , first inner mating diameter IMD 1 , first outer mating diameter OMD 1 , first land area  76 , first plurality of grooved portions  78 , and first grooved area  80 . 
     In another embodiment, as shown in  FIG. 13 , the rotating machine  20  includes the bearing housing  134  defining the bearing housing interior  136 , the shaft  22  extending along the axis A between the first end  26  and the second end  28  spaced from the first end  26  along the axis A, with the shaft  22  disposed in the bearing housing interior  136 . The rotating machine  20  also includes an impeller housing  150  coupled to the bearing housing  134 . It is to be appreciated that the impeller housing  150  and the bearing housing  134  may be integral with one another (i.e., one-piece), or may be separate components (i.e., two or more pieces). The impeller housing  150  defines an impeller housing interior  152 . The rotating machine  20  further includes an impeller wheel  154  coupled to the shaft  22  at the first end  26  and disposed in the impeller housing interior  152 . The rotating machine  20  additionally includes a seal assembly  34  disposed in the bearing housing interior  136 . The seal assembly  34  includes a carbon ring  36  disposed about the shaft  22  and spaced from the impeller wheel  154  along the axis A, with the carbon ring  36  having a carbon surface  38 , and a mating ring  40  disposed about the shaft  22  and spaced from the impeller wheel  154  along the axis A such that the carbon ring  36  is disposed between the impeller wheel  154  and the mating ring  40 , with the mating ring  40  having a mating surface  42  facing and configured to contact the carbon surface  38 . The rotating machine  20  further includes a lubricant-fed bearing  138  disposed in the bearing housing interior  136  and rotatably supporting the shaft  22  at the first end  26 , with the seal assembly  34  disposed between the lubricant-fed bearing  138  and the impeller wheel  154  with respect to the axis A. The rotating machine  20  also includes the electric machine  56  including the rotor  58  rotatably coupled to the shaft  22 , and the stator  60  disposed about the rotor  58 . The electric machine  56  may be configured as an electric motor for delivering rotational to the shaft  22  to rotate the impeller wheel  154 , and/or may be configured as a generator for receiving rotational torque to the shaft  22  to convert mechanical energy into electrical energy. The impeller housing interior  152  is adapted to be fluidly coupled to a contaminant free environment  156 , with the carbon ring  36  and the mating ring  40  preventing lubricant from entering the contaminant free environment  156 . 
     Having the mating ring  40  and the carbon ring  36  prevent lubricant from and other contaminants from entering the impeller housing interior  152  allows the impeller housing interior  152  to be fluidly coupled to the contaminant free environment  156 . An example of a contaminant free environment is a fuel cell, as described in further detail below. Another example of a contaminant free environment is an organic Rankine cycle waste heat recovery system. 
     When the rotating machine  20  is used in an organic Rankine cycle waste heat recovery system, the impeller wheel  154  may be further defined as a turbine wheel configured to receive a working fluid, and the impeller housing  150  may be further defined as a turbine housing. In such embodiments, the turbine housing defines a turbine housing interior that is fluidly coupled to a contaminant free environment. Further, in such embodiments, the rotating machine  20  may include the electric machine  56 , with the electric machine  56  being configured as a generator. Additionally, in such embodiments, the turbine wheel may be the only impeller wheel rotatably coupled to the shaft  22 . When the impeller housing  150  is further defined as a turbine housing, the turbine housing interior, being fluidly coupled to the contaminant free environment, may also then be considered part of the contaminant free environment. 
     Any contaminant free environment that is sensitive to any form of hydrocarbons and other contaminants, the mating ring  40  and the carbon ring  36  reduce, if not eliminate, hydrocarbons and other contaminants from the lubricant from entering the contaminant free environment. Another example of a contaminant free environment may be in an atmospheric water generator, in which water is recovered from air vapor. 
     In one embodiment, the impeller housing  150  is further defined as a compressor housing, the impeller housing interior  152  is further defined as a compressor housing interior, and the impeller wheel  154  is further defined as a compressor wheel configured to deliver a working fluid, such as air. When the impeller housing  150  is further defined as a compressor housing, the compressor housing interior, being fluidly coupled to the contaminant free environment  156 , may also then be considered part of the contaminant free environment  156 . 
     In such embodiments where the impeller housing interior  152  is adapted to be fluidly coupled to the contaminant free environment  156 , the rotating machine  20  may, as described above, include the second impeller wheel  32 . In such embodiments, the first impeller wheel  30  may be further defined as a compressor wheel configured to deliver a working fluid or may be further defined as a turbine wheel configured to receive a working fluid. Further, in such embodiments, the second impeller wheel  32  may be a further defined as a compressor wheel configured to deliver a working fluid, or as a turbine wheel configured to receive a working fluid. It is to be appreciated that when the second impeller wheel  32  is present, that the rotating machine  20  may optionally include the second seal assembly  44  as described above. As described above, in embodiments where the rotating machine  20  is used in an organic Rankine waste heat recovery system, the second impeller wheel  32  may be further defined as a pump impeller for pumping the working fluid in the organic Rankine cycle waste heat recovery system. In such embodiments, the impeller housing  150  may be further defined as a pump housing defining a pump interior. Further, in such embodiments, the pump housing interior, being fluidly coupled to the contaminant free environment  156 , may also then be considered part of the contaminant free environment  156 . 
     In embodiments where the impeller housing interior  152  is adapted to be fluidly coupled to the contaminant free environment  156 , with the carbon ring  36  and the mating ring  40  preventing lubricant from entering the contaminant free environment, the carbon surface  38  may have a carbon ring inner diameter CID 1  and a carbon ring outer diameter COD 1  spaced from the carbon ring inner diameter CID 1  radially away from the axis A. In such embodiments, the mating surface  42  has a land portion  70  configured to contact the carbon surface  38  between an inner mating diameter IMD 1  radially aligned with the carbon ring inner diameter CID 1  with respect to the axis A and an outer mating diameter OMD 1  radially aligned with the carbon ring outer diameter COD 1  with respect to the axis A. In such embodiments, the land portion  70  has a land area  76  between the inner and outer mating diameters IMD 1 , OMD 1 , the mating surface  42  defines a plurality of grooved portions  78  disposed about the axis A, and the plurality of grooved portions  78  have a grooved area  80  between the inner and outer mating diameters IMD 1 , OMD 1 , and with a ratio of the land area  76  to the grooved area  80  is between 1.3 and 2.9. 
     With reference to  FIG. 12 , a system  142  includes the rotating machine  20  including the bearing housing  134  defining the bearing housing interior  136 , and the shaft  22  extending along the axis A between the first end  26  and the second end  28  spaced from the first end  26  along the axis A, with the shaft  22  disposed in the bearing housing interior  136 . In the system  142 , the rotating machine  20  also includes a compressor housing  158  coupled to the bearing housing  134 , with the compressor housing  158  defining a compressor housing interior  160 , a compressor wheel  162  coupled to the shaft  22  at the first end  26  and disposed in the compressor housing interior  160 , and the seal assembly  34  disposed in the bearing housing interior  136 . The seal assembly  34  includes the carbon ring  36  disposed about the shaft  22  and spaced from the compressor wheel  162  along the axis A, with the carbon ring  36  having the carbon surface  38 , and the mating ring  40  disposed about the shaft  22  and spaced from the compressor wheel  162  along the axis A such that the carbon ring  36  is disposed between the compressor wheel  162  and the mating ring  40 , with the mating ring  40  having the mating surface  42  facing and configured to contact the carbon surface  38 . The rotating machine  20  additionally includes the lubricant-fed bearing  138  disposed in the bearing housing interior  136  and rotatably supporting the shaft  22  at the first end  26 , with the seal assembly  34  disposed between the lubricant-fed bearing  138  and the compressor wheel  162  with respect to the axis A, and the electric machine  56  including the rotor  58  rotatably coupled to the shaft  22 , and stator  60  disposed about the rotor  58 , with the electric machine  56  being configured to transmit torque to the shaft  22  to rotate the compressor wheel  162 . The system  142  also includes a fuel cell assembly  144 , which is shown schematically in  FIG. 12 , including a fuel cell housing  146  defining a fuel cell interior  148 , and a fuel cell  145  disposed in the fuel cell interior  148 . The compressor housing  158  is coupled to the fuel cell housing  146 , and the compressor housing interior  160  is fluidly coupled to the fuel cell interior  148  for delivering compressed air to the fuel cell assembly  144  for cooling the fuel cell  145 . 
     In such environments, it is important to reduce any sort of contaminant from entering into the fuel cell interior  148 . Fuel cells are known to be very sensitive to hydrocarbon poisoning. In view of this, the rotating machine  20  including the first seal assembly  34  having the first mating ring  40  and the first carbon ring  36 , and optionally the second impeller wheel  32  and the second seal assembly  44  having the second mating ring  50  and the second carbon ring  46 , reduces leakage of contaminants to the first impeller wheel  30 , and when present the second impeller wheel  32 , which overall increases performance and longevity of the rotating machine  20 . In particular, the rotating machine  20  including the first seal assembly  34  and optionally the second seal assembly  44  greatly reduces, if not eliminates, hydrocarbons and other contaminants from entering the fuel cell interior  148 . In embodiments where the rotating machine  20  includes the first and second lubricant-fed bearings  138 ,  140 , the first and second seal assemblies  34 ,  44  allow the rotating machine  20  to utilize the cheaper, more efficient, and longer lasting lubricant-fed bearings as the first and second seal assemblies  34 ,  44 , greatly reduce, if not eliminates, any contaminants such as hydrocarbons from entering the fuel cell interior  148 . 
     Having the mating ring  40  and the carbon ring  36  prevent lubricant from the lubricant-fed bearing  138  and other contaminants from entering the compressor housing interior  152  and, therefore, from entering the fuel cell interior  148 , overall increases performance and longevity of the rotating machine  20 . Additionally, as described above, fuel cells are highly sensitive to any form of hydrocarbon contamination, and the mating ring  40  and the carbon ring  36  reduce, if not eliminate, hydrocarbon contaminants from the lubricant from entering into the fuel cell interior  148 . Preventing hydrocarbon contaminants from the lubricant from entering into the fuel cell interior  148  increases efficiency and longevity of the fuel cell  145 , as hydrocarbons and other contaminants are unable to poison the fuel cell  145  and reduce efficiency over time. 
     In some embodiments of the system  142 , the carbon surface  38  has the carbon ring inner diameter CID 1  and the carbon ring outer diameter COD 1  spaced from carbon ring inner diameter CID 1  radially away from the axis A, and the mating surface  42  has the land portion  70  configured to contact the carbon surface  38  the an inner mating diameter IMD 1  radially aligned with the carbon ring inner diameter CID 1  with respect to the axis A and the outer mating diameter OMD 1  radially aligned with the carbon ring outer diameter COD 1  with respect to the axis A. Further, in such embodiments, the land portion  70  has the land area  76  between the inner and outer mating diameters IMD 1 , OMD 1 , the mating surface  42  defines the plurality of grooved portions  78  disposed about the axis A, and the plurality of grooved portions  78  have the grooved area  80  between the inner and outer mating diameters IMD 1 , OMD 1 , with a ratio of the land area  76  to the grooved area is between 1.3 and 2.9. 
     It is to be appreciated that the system  142  includes embodiments where the rotating machine  20  has only one impeller wheel (e.g., first impeller wheel  30 ) and, therefore, only the first seal assembly  34 , and where the rotating machine  20  has two impeller wheels (e.g., the first and second impeller wheels  30 ,  32 ). In such embodiments where the rotating machine  20  of the system  142  includes the first and second impeller wheels  30 ,  32 , it is to be appreciated that the second impeller wheel  32  may be further defined as a compressor wheel configured to deliver compressed air or as a turbine wheel configured to receive a working fluid, such as exhaust gas. In either embodiment, it is to be appreciated that the rotating machine  20  of the system  142  may include the second seal assembly  44  including the second carbon ring  46  and second mating ring  50  as described in detail above. 
     The invention has been described in an illustrative manner, and it is to be understood that the terminology which has been used is intended to be in the nature of words of description rather than of limitation. Many modifications and variations of the present invention are possible in light of the above teachings, and the invention may be practiced otherwise than as specifically described.