BEARINGS FOR ELECTRIC SUBMERSIBLE PUMPS

Anti-rotation bearing assemblies for electric submersible pumps are provided. An electric submersible pump includes a plurality of centrifugal pump stages, each stage including a rotating impeller and a stationary diffuser mounted on a shaft coupled to a motor. In use, the motor rotates the shaft, which rotates the impeller within the stationary diffuser. A bearing assembly can include a bearing sleeve disposed about the shaft and a bushing disposed radially between the bearing sleeve and the diffuser. The bearing sleeve rotates with the shaft in operation, and the bushing remains stationary with the diffuser. The bushing can have an external key that is received in a keyway or groove in the diffuser to act as an anti-rotation feature. In other variations, the bushing can have an eccentric or oblique profile, which can act as an anti-rotation feature.

BACKGROUND

Field

The present disclosure generally relates to systems and methods for artificial lift in oil and gas wells, and more particularly to bearings for use in electric submersible pumps.

Description of the Related Art

Various types of artificial lift equipment and methods are available, for example, electric submersible pumps (ESPs). An ESP includes multiple centrifugal pump stages mounted in series, each stage including a rotating impeller and a stationary diffuser mounted on a shaft, which is coupled to a motor. In use, the motor rotates the shaft, which in turn rotates the impellers within the diffusers. Well fluid flows into the lowest stage and passes through the first impeller, which centrifuges the fluid radially outward such that the fluid gains energy in the form of velocity. Upon exiting the impeller, the fluid flows into the associated diffuser, where fluid velocity is converted to pressure. As the fluid moves through the pump stages, the fluid incrementally gains pressure until the fluid has sufficient energy to travel to the well surface. A bearing assembly can be disposed between the rotating shaft and the stationary diffuser. The bearing assembly may include a bearing sleeve that rotates with the shaft in use, and a bushing that is configured to remain stationary with the diffuser in use. However, in adverse conditions, torque may be applied to the bushing, and the bushing or bearing assembly could fail.

SUMMARY

In some configurations, a bearing assembly for an electric submersible pump (ESP) includes a bearing sleeve configured to be disposed about a shaft of the ESP and a bushing configured to be disposed about the bearing sleeve. An outer surface of the bushing includes a key configured to engage a corresponding keyway in a central bore of a diffuser of the ESP.

The bearing assembly can further include an axial retaining part disposed at, on, or adjacent an upstream end of the bushing. The axial retaining part can be a retaining ring.

The key can be a projection projecting radially outwardly from the outer surface of the bushing, and the keyway can be recessed from the central bore into a wall surrounding the central bore. The key can be an elongated projection extending along at least a portion of an axial length of the bushing, and the keyway can be an elongated groove extending along at least a portion of an axial length of the central bore.

The key can be a groove or recess in the outer surface of the bushing, and the keyway can be a projection projecting radially inwardly into the central bore from a wall surrounding the central bore.

In some configurations, an electric submersible pump (ESP) includes a plurality of stages, each stage comprising an impeller and a diffuser disposed about a shaft, the diffuser having a central bore through which the shaft extends. At least one of the plurality of stages includes a bearing assembly comprising a bearing sleeve disposed about the shaft and configured to rotate with the shaft in use and a bushing disposed radially between the bearing sleeve and a wall surrounding the central bore of the diffuser. The bearing assembly includes an anti-rotation feature configured to prevent or inhibit rotation of the bushing in operation.

The bearing assembly can further include an axial retaining part disposed at, on, or adjacent an upstream end of the bushing. The axial retaining part can be a retaining ring.

The anti-rotation feature can include an external key projecting radially outwardly from an outer surface of the bushing and a recessed keyway in the wall surrounding the central bore, the keyway configured to receive the key. The keyway can be a groove in the wall extending axially along at least a portion of a length of the wall.

The anti-rotation feature can include a recessed key in an outer surface of the bushing and a keyway projecting radially inwardly from the wall into the central bore. The key can be a groove in the outer surface of the bushing extending axially along at least a portion of a length of the bushing.

The anti-rotation feature can include an eccentric profile of the bushing. The anti-rotation feature can include an oblique profile of the bushing.

In some configurations, an electric submersible pump (ESP) includes a plurality of stages, each stage comprising an impeller and a diffuser disposed about a shaft, at least one diffuser comprising a central bore therethrough and a keyway in a wall surrounding the central bore. At least one of the plurality of stages includes a bearing assembly comprising a bearing sleeve disposed about the shaft and configured to rotate with the shaft in use and a bushing disposed radially between the bearing sleeve and the wall surrounding the central bore of the diffuser. An outer surface of the bushing includes a key configured to engage the keyway when the ESP is assembled.

The key can be a projection projecting radially outwardly from the outer surface of the bushing, and the keyway can be recessed radially outward from the central bore into the wall. The key way can be an elongated groove, and the key can be an elongated projection.

The key can be recessed into the outer surface of the bushing, and the keyway can be a projection projecting radially inward from the wall into the central bore. The key can be an elongated groove, and the keyway can be an elongated projection.

DETAILED DESCRIPTION

In the following description, numerous details are set forth to provide an understanding of some embodiments of the present disclosure. It is to be understood that the following disclosure provides many different embodiments, or examples, for implementing different features of various embodiments. Specific examples of components and arrangements are described below to simplify the disclosure. These are, of course, merely examples and are not intended to be limiting. However, it will be understood by those of ordinary skill in the art that the system and/or methodology may be practiced without these details and that numerous variations or modifications from the described embodiments are possible. This description is not to be taken in a limiting sense, but rather made merely for the purpose of describing general principles of the implementations. The scope of the described implementations should be ascertained with reference to the issued claims.

As used herein, the terms “connect”, “connection”, “connected”, “in connection with”, and “connecting” are used to mean “in direct connection with” or “in connection with via one or more elements”; and the term “set” is used to mean “one element” or “more than one element”. Further, the terms “couple”, “coupling”, “coupled”, “coupled together”, and “coupled with” are used to mean “directly coupled together” or “coupled together via one or more elements”. As used herein, the terms “up” and “down”; “upper” and “lower”; “top” and “bottom”; and other like terms indicating relative positions to a given point or element are utilized to more clearly describe some elements. Commonly, these terms relate to a reference point at the surface from which drilling operations are initiated as being the top point and the total depth being the lowest point, wherein the well (e.g., wellbore, borehole) is vertical, horizontal or slanted relative to the surface.

Various types of artificial lift equipment and methods are available, for example, electric submersible pumps (ESP). As shown in the example embodiment ofFIG.1, an ESP110typically includes a motor116, a protector115, a pump112, a pump intake114, and one or more cables111, which can include an electric power cable. The motor116can be powered and controlled by a surface power supply and controller, respectively, via the cables111. In some configurations, the ESP110also includes gas handling features113and/or one or more sensors117(e.g., for temperature, pressure, current leakage, vibration, etc.). As shown, the well may include one or more well sensors120.

The pump112includes multiple centrifugal pump stages mounted in series within a housing230, as shown inFIG.2A. Each stage includes a rotating impeller210and a stationary diffuser220. One or more spacers204can be disposed axially between sequential impellers210. A shaft202extends through the pump112(e.g., through central hubs or bores or the impellers210and diffusers220) and is operatively coupled to the motor116. The shaft202can be coupled to the protector115(e.g., a shaft of the protector), which in turn can be coupled to the motor116(e.g., a shaft of the motor). The impellers210are rotationally coupled, e.g., keyed, to the shaft202. The diffusers220are coupled, e.g., rotationally fixed, to the housing230. In use, the motor116causes rotation of the shaft202(for example, by rotating the protector115shaft, which rotates the pump shaft202), which in turn rotates the impellers210relative to and within the stationary diffusers220.

In use, well fluid flows into the first (lowest) stage of the ESP110and passes through an impeller210, which centrifuges the fluid radially outward such that the fluid gains energy in the form of velocity. Upon exiting the impeller210, the fluid makes a sharp turn to enter a diffuser220, where the fluid's velocity is converted to pressure. The fluid then enters the next impeller210and diffuser220stage to repeat the process. As the fluid passes through the pump stages, the fluid incrementally gains pressure until the fluid has sufficient energy to travel to the well surface.

As shown inFIG.2A, a bearing assembly250can be disposed between, e.g., at least partially radially between, the shaft202and a diffuser220and/or between, e.g., at least partially axially between, an impeller210and its associated diffuser220. A portion of the diffuser220can act as a bearing housing260. In the illustrated embodiment, the bearing assembly250includes a bearing sleeve252disposed about the shaft202and a bushing254disposed about the bearing sleeve252and radially between the bearing sleeve252and a portion of the diffuser220. One or more o-rings258can be disposed about the bushing254, for example, radially between the bushing254and the diffuser220or bearing housing260.

The illustrated bearing assembly250also includes an anti-rotation upthrust ring256disposed about the bearing sleeve252. As shown, the anti-rotation upthrust ring256can be disposed adjacent an upstream end of the bushing254. The bearing sleeve252is keyed or rotationally coupled to the shaft202such that the bearing sleeve252rotates with the shaft in use202. The anti-rotation upthrust ring256prevents or inhibits the bushing254from rotating such that the bushing254is stationary or rotationally fixed relative to the diffuser220. As shown in the view ofFIG.2B, the bushing254can include a notch255extending downstream from the upstream end or edge of the bushing254. The illustrated anti-rotation upthrust ring256includes a stopper or lug257projecting downstream from a downstream end or edge of the anti-rotation upthrust ring256. The lug257is received in the notch255to key the bushing254to the anti-rotation upthrust ring256such that the anti-rotation upthrust ring256can prevent or inhibit the bushing254from rotating. The anti-rotation upthrust ring256can also help prevent or inhibit axial movement of the bushing254and/or the bushing254from dropping out of place from the bearing housing260. In use, the bearing assembly250can help absorb thrust and/or accommodate the rotation of the shaft relative to the diffuser.

FIG.2Cillustrates an alternative bearing assembly250including a retaining ring259instead of the anti-rotation upthrust ring256. The retaining ring259can be at least partially disposed in a groove in the outer diameter or surface of the bushing254and at least partially disposed in a groove in the bearing housing260. The retaining ring259restricts axial movement of the bushing254relative to the bearing housing260. However, the retaining ring259may not prevent or inhibit rotational movement of the bushing254and the bearing254may crack at the retaining ring groove.

Some existing bearing assemblies are abrasion resistant zirconia (ARZ) complaint mount bearings, for example as shown inFIGS.2A-2B. However, the anti-rotation mechanism of such bearing assemblies, e.g., the anti-rotation upthrust ring256, is sometimes inadequate, for example, in unconventional wells and/or wells with extreme sand concentrations. In such cases, a large amount of torque transmitted from the shaft202and bearing sleeve252to the bushing254can cause the bushing254to spin. ARZ complaint bearings can exhibit various failures, for example, the notch255shearing off the lug257, the bushing254cracking, spinning of the upthrust ring256, and/or the upthrust ring256and/or bushing254falling out of the bearing housing260. In some cases, the o-rings258can be damaged, fail, and/or drop out. In such cases, the bushing254may not be held in place properly and/or may be able to spin.

In some configurations, bearing assemblies according to the present disclosure can include a keyed bushing354that acts as an anti-rotation mechanism to advantageously prevent or inhibit the bushing from spinning, while also minimizing stress concentrations. The bushing354is held in place within the bearing housing260. As shown inFIG.3, the bushing354includes an external key or pin355. In the configuration illustrated inFIG.3, the key355is an elongated protrusion extending radially outwardly from an outer diameter or surface of the bushing354and extending axially along at least a portion of an axial length of the bushing354. The key355can have a rounded, squared, or other shape. The key355can be made of a higher strength material (compared to, for example, existing ARZ bearings), for example, stainless steel, Inconel, or Monel. The bearing housing260, for example, a radially inner surface of the bearing housing260, can include a corresponding groove or keyway361as shown. When the bushing354is installed in the bearing housing260, the key355is received in the keyway361to rotationally secure the bushing354to the bearing housing260. The key355can advantageously tolerate higher torque compared to, for example, anti-rotation upthrust ring256.

To assemble the bearing assembly, the bushing354, including the key355, is installed in the bearing housing260. Installing the bushing354in the bearing housing260can include inserting the key355into the keyway361. The bushing354can be installed in the bearing housing260, and/or the key355can be installed in the keyway361, via clearance fit, transition fit, interference fit, and/or any other suitable engineering fit or other means, selected based on, for example, the material of the bushing354and/or key355.

Once the bushing354is installed in the bearing housing260, a retaining part370, for example, an axial retaining part, can be installed in the bearing housing260. As shown in, for example,FIGS.3-4, the retaining part370can be disposed at, on, or adjacent a lower or upstream end of the bushing354. The retaining part370can be at least partially disposed in a recess372formed in the bearing housing360, for example, the radially inner surface of the bearing housing360. The recess372can extend partially or fully around the circumference of the bearing housing260. In the embodiment ofFIG.3, the retaining part370is a retaining ring. The retaining part370can be, for example, a press-fit lock ring, a snap ring, or a threaded ring. In some configurations, the retaining part370is a spiral ring, constant section ring, single turn ring, nested wave spring, or retaining ring having an axial waveform.FIG.4illustrates an embodiment in which the retaining part370is a threaded ring, which can be threaded onto or about an externally threaded portion of the bushing354disposed at, proximate, or adjacent the upstream end of the bushing354. The retaining part370is installed at, adjacent, or proximate the upstream end of the bushing354and/or key355. The retaining part370helps axially retain the bushing354and/or key355and prevent or inhibit the bushing354and/or key355from dropping out of place.

In some configurations, for example as shown inFIGS.5A-5C, the key355is a recess or groove in the outer diameter or surface of the bushing354. The recess or groove can have a rounded profile. The recess or groove can be symmetric or axisymmetric, for example as shown inFIGS.5A-5C. When the bushing354is installed in the bearing housing260, the recess or groove receives a corresponding protrusion extending inwardly (towards the central bore that receives the bushing354) from the bearing housing260. The recess or groove can allow for customization of the wall thickness of the bushing354, which can allow for balancing of cost and required strength.

In some configurations, bearing assemblies according to the present disclosure include a bushing454having an eccentric profile or offset installed in a bearing housing having a bore461with a corresponding eccentric profile (or being designed to accommodate the eccentric bushing454), for example as shown inFIGS.7A-7D. In the illustrated configuration, the bushing454is disposed in a recessed portion of the bearing housing260surrounding the central bore461(for example, a portion of the bearing housing260recessed radially outwardly and into the bearing housing260from the central bore461, such that the central bore461has a greater diameter in the recessed portion of the bearing housing260than the diameter of the central bore461in a portion of the bearing housing260axially separated from the bushing454). The eccentric profile acts as an anti-rotation mechanism to advantageously prevent or inhibit the bushing from spinning. In conventional bearing assemblies, for example as shown inFIGS.6A-6B, the bearing sleeve252and bushing254are concentric (the inner and outer diameters of each are concentric), have uniform radial thicknesses, and their longitudinal axes are aligned. In the illustrated configuration, the bushing254is press-fit into the bearing housing260, and an interference fit prevents or inhibits the bushing254from spinning. However, the interference fit can fail, for example at certain temperatures (e.g., around 300° F.) due to the bushing254and bearing housing260being different materials having different coefficients of thermal expansion.

In the eccentric bearing assembly ofFIG.7A-7D, the central longitudinal axes LA (based on the inner diameters or surfaces) of the bushing454and bearing housing bore461still align with the shaft202axis and axis of rotation, as also shown inFIGS.8A-8B. However, the outer diameter or circumference of the bushing454(and outer diameter or circumference of a portion of the bearing housing260surrounding the bore461and configured to receive the bushing454) is eccentric. In other words, as shown in, for example,FIGS.7B-7D, the thickness (radial thickness) of the bushing454is not equal about the circumference of the bushing454. In the illustrated configuration, the thickness or depth (radial depth) of the recess in the bearing housing260that receives the bushing454is also not equal about the circumference of the bearing housing bore461and corresponds to (e.g., substantially matches) the thickness of the bushing454. In the illustrated configuration, a portion of the bushing454having the greatest thickness t1is diametrically opposed from a portion of the bushing454having the smallest thickness t2. The thickness of the bushing454can increase in both directions around the circumference of the bushing454from the thinnest portion to the thickest portion. In some configurations, the difference between t1and t2can be in the range of about 0.025″ to about 0.100″. A central longitudinal axis of or based on the outer diameter or circumference of the bushing454is therefore offset from the central longitudinal axis of or based on the inner diameter. The eccentric bushing454can be installed in the bearing housing260in an orientation to avoid the bushing454dropping out of the bearing housing260. For example, as shown inFIG.7D, when the bushing454is received in the recessed portion of the bearing housing260, the bushing454can sit on a ledge or lip formed by the bearing housing260, which can prevent or inhibit the bushing454from dropped out. Additionally or alternatively, adhesive can be applied between the bushing454and bearing housing260to secure the bushing454.

The eccentricity of the bushing454, and portion of the bearing housing260that receives the bushing454, restrains the bushing454from spinning. In normal operation, the shaft202and bearing sleeve252rotate or spin freely about their longitudinal axis, and the eccentric bushing454remains stationary or substantially stationary at a 0° rotation, as shown inFIG.9A. If the bearing sleeve252becomes sand jammed (in other words, sand becomes stuck in the running clearance between the bearing sleeve252and the bushing454), torque can be transmitted to the bushing454and start to rotate the bushing454, as shown inFIG.9B, in which the thickest portion t1has rotated about 90°. An anti-rotation frictional force will be generated in the area of the thickest portion t1due to the thicker area of the eccentric bushing454attempting to rotate into a thinner area of the bearing housing260. As the bushing454attempts to continue rotating, toward about 180° as shown inFIG.9C, the anti-rotation frictional force increases. As torque increases and is eventually transmitted to the bearing housing260, the bearing housing260exhibits a restraining reaction torque to prevent or inhibit further rotation of the bushing454and bearing housing260, for example as shown inFIG.9D, in which the shaft202has continued rotation to about 270° but the bushing454has been stopped.

In some configurations, bearing assemblies according to the present disclosure include a bushing554having an oblique profile installed in a bearing housing having a bore561with a corresponding oblique profile (or being designed to accommodate the oblique bushing554), for example as shown inFIGS.10A-10D.

In the oblique bearing assembly ofFIG.10A-10D, the longitudinal axis AH of the bearing housing bore561is oblique relative to (or is non-parallel to and/or intersects) the shaft202axis of rotation AR, as shown inFIG.10A. In other words, the wall surrounding the bore561is angled relative to the shaft202axis and axis of rotation AR. In some configurations, the longitudinal axis AH of the bearing housing bore561extends at an angle in the range of >0° to about 15°, or greater than 15°, relative to the shaft axis of rotation AR. The central longitudinal axis of the bushing554, based on the inner diameter or surface of the bushing554, aligns with the shaft202axis and axis of rotation AR, as shown inFIG.10B. However, the longitudinal axis AB of the bushing554based on the outer diameter or surface of the bushing554is oblique relative to (or is non-parallel to and/or intersects) the shaft202axis of rotation AR. In some configurations, the longitudinal axis AB of the bushing554based on the outer diameter or surface of the bushing554extends at an angle in the range of >0° to about 15°, or greater than 15°, relative to the shaft axis of rotation AR, for example, to correspond to (e.g., match) the angle of the bore561axis AH relative to the shaft axis of rotation AR.

In other words, the thickness (radial thickness) of the bushing554is not equal about the circumference of the bushing554. As shown in the transverse cross-section ofFIG.10D, one side (lateral side) of the bearing assembly has a thinner bushing554radial thickness tn and a thicker (radially thicker or wider) bearing housing bore561compared to the opposite side (lateral side), which has a thicker bushing554radial thickness th and a thinner (radially thinner or narrower) bearing housing bore561. Additionally, when viewing a longitudinal cross-section as shown inFIG.10B, the thickness of each lateral side of the bushing554is not equal or even along the longitudinal length of the bushing554. In other words, the outer surface of the bushing554is tapered and/or angled. Ends (top and bottom ends or edges) of the bushing554can be angled relative to a plane perpendicular to the shaft rotation axis AR as shown inFIGS.10B and10C. In other configurations, the top and/or bottom ends or edges of the bushing554can be trimmed to be perpendicular to the shaft axis, as indicated by the dashed horizontal lines inFIGS.10B and10C.

In the oblique bearing assembly ofFIGS.10A-10C, the center of moment of inertia of the bushing554and bearing housing is located at the intersection of the shaft axis of rotation AR and the oblique axis AB of the bushing554. In a case of, for example, sand jam, if torque is transmitted to the bearing554, the bearing554and/or bushing housing are restrained from spinning due to the oblique profile.

The oblique profile acts as an anti-rotation mechanism to advantageously prevent or inhibit the bushing from spinning. The oblique profile can also prevent or inhibit the bushing554from dislodging and/or dropping out of the bearing housing. The oblique profile bushing554has a concentric axis with the shaft202rotation axis in one plane (e.g., Y-Z, as shown inFIG.11B), but not in another plane (e.g., X-Z, as shown inFIG.11A). When assembled and in use, a gravity force Fg, shown inFIG.11A, may act on the bushing554and could cause the bushing554to drop out. However, a side reaction force Fsr, due to contact between the bearing sleeve252and the bushing554, and a friction force Fos on the oblique surface of the bushing554, due to contact between the outer surface of the bushing554and the inner diameter or surface of the bearing housing bore561, will also act on the bushing554, counteracting the gravity force Fg and causing a wedging effect to prevent or inhibit the bushing554from dropping out of place. In conditions, such as sand jam, in which torque is transferred to the bearing554, the off-set, oblique, or eccentric bearing axis AB relative to the shaft axis of rotation AR will cause an anti-rotation force or torque to be generated as thicker portion(s) of the bushing554attempt to rotate into thinner area(s) of the bearing housing or bearing housing bore561. If the torque is eventually transmitted to the bearing housing, the oblique profile bearing housing bore will cause the bearing housing to exhibit a restraining, or anti-torque force to prevent or inhibit the bearing housing and/or bushing554from spinning. Similar to the eccentric profile bushing454, the oblique profile bushing554can advantageously help prevent or inhibit the bushing454,554from spinning and/or dropping out of the bearing housing, while also only requiring two parts (i.e., the bushing454,554and the bearing housing) instead of a compliant bearing system, which requires a third part in the form of a retaining ring or anti-rotation upthrust ring.

In some existing bearing assemblies, one or more components are made of tungsten carbide, which has a higher hardness compared to, for example, ceramic, to increase wear resistance, for example, to sand. In some configurations according to the present disclosure, the inner diameter or surface of the bearing housing bore is hard coated or includes a hard surface coating262, for example as shown inFIGS.12A-12B. In some configurations, the coating262is or includes tungsten carbide and/or a diamond-like carbon (DLC) coating. The bearing sleeve252and/or bushing (e.g., bushing254,354,454,554) can be made of or include, for example, tungsten carbide or ceramic. In some configurations, a pump including a diffuser220having coating262on the bearing housing bore does not require a bushing, or other components such as a retaining ring or anti-rotation upthrust ring. For example, in the configuration ofFIG.12B, the bearing assembly includes only the bearing sleeve252disposed in the bearing housing bore, which is coated with coating262. The coating262can have a thickness selected to last for the expected run life of the ESP. In some configurations, the coating262is less than about 0.1″ thick. The coating262can have a surface roughness selected to help improve run life.

The coating262can be applied via various technologies or processes, depending on for example, the material type, hardness, and/or property requirements. For example, the coating262can be applied via industrial HVAF, high velocity oxygen fuel (HVOF), plasma spraying, thermal spraying, physical vapor deposition processes such as electron beam physical vapor deposition (EBPVD), ion plating, ion beam assisted deposition (IBAD), magnetron sputtering, pulsed laser deposition, sputter deposition, vacuum deposition, vacuum evaporation, evaporation (deposition), and/or any other suitable process.

Language of degree used herein, such as the terms “approximately,” “about,” “generally,” and “substantially” as used herein represent a value, amount, or characteristic close to the stated value, amount, or characteristic that still performs a desired function or achieves a desired result. For example, the terms “approximately,” “about,” “generally,” and “substantially” may refer to an amount that is within less than 10% of, within less than 5% of, within less than 1% of, within less than 0.1% of, and/or within less than 0.01% of the stated amount. As another example, in certain embodiments, the terms “generally parallel” and “substantially parallel” or “generally perpendicular” and “substantially perpendicular” refer to a value, amount, or characteristic that departs from exactly parallel or perpendicular, respectively, by less than or equal to 15 degrees, 10 degrees, 5 degrees, 3 degrees, 1 degree, or 0.1 degree.

Although a few embodiments of the disclosure have been described in detail above, those of ordinary skill in the art will readily appreciate that many modifications are possible without materially departing from the teachings of this disclosure. Accordingly, such modifications are intended to be included within the scope of this disclosure as defined in the claims. It is also contemplated that various combinations or sub-combinations of the specific features and aspects of the embodiments described may be made and still fall within the scope of the disclosure. It should be understood that various features and aspects of the disclosed embodiments can be combined with, or substituted for, one another in order to form varying modes of the embodiments of the disclosure. Thus, it is intended that the scope of the disclosure herein should not be limited by the particular embodiments described above.