Patent Application
20240145735
The present disclosure relates generally to electrochemical fuel cell systems (FCS) for converting hydrogen-rich fuels into electricity. More specifically, aspects of this disclosure relate to devices for separating hydrogen gas from liquid water in FC Ss.
Current production motor vehicles, such as the modern-day automobile, are originally equipped with a powertrain that operates to propel the vehicle and power the vehicle's onboard electronics. In automotive applications, for example, the vehicle powertrain is generally typified by a prime mover that delivers driving torque through an automatic or manually shifted power transmission to the vehicle's final drive system (e.g., differential, axle shafts, corner modules, road wheels, etc.). Automobiles have historically been powered by a reciprocating-piston type internal combustion engine (ICE) assembly due to its ready availability and relatively inexpensive cost, light weight, and overall efficiency. Such engines include compression-ignited (CI) diesel engines, spark-ignited (SI) gasoline engines, two, four, and six-stroke architectures, and rotary engines, as some non-limiting examples. Hybrid-electric and full-electric vehicles (collectively “electric-drive vehicles”), on the other hand, utilize alternative power sources to propel the vehicle and, thus, minimize or eliminate reliance on a fossil-fuel based engine for tractive power.
Hybrid-electric and full-electric powertrains take on various architectures, some of which utilize a fuel cell system to generate the requisite electricity for powering the vehicle's electric traction motor(s). A fuel cell is an electrochemical device that is generally composed of an anode electrode that receives hydrogen (H2), a cathode electrode that receives oxygen (O2), and an electrolyte barrier interposed between the anode and cathode electrodes. An electrochemical reaction is induced to oxidize hydrogen molecules at the anode side of the FCS—hydrogen gas is catalytically split in an oxidation half-cell reaction—to generate free electrons (−) and free protons (H+). The free hydrogen protons pass through the electrolyte to the cathode, where these protons react with oxygen and electrons in the cathode to form various stack by-products. Free electrons from the anode, however, cannot pass through the electrolyte; these electrons are redirected to a load, such as a vehicle's traction motors and accessories, before being sent to the cathode.
Fuel cell architectures commonly employed in automotive applications contain a semipermeable polymer electrolyte membrane—also referred to as a “proton exchange membrane” or “PEM”—to provide ion transport between the anode and cathode. Proton exchange membrane fuel cells (PEMFC) generally employ a solid polymer electrolyte (SPE) proton-conducting membrane, such as a perfluorosulfonic acid membrane, to separate product gases and provide electrical insulation of electrodes in addition to facilitating the conduction of protons. The anode and cathode typically include finely dispersed catalytic particles (e.g., platinum) that are supported on carbon particles and mixed with an ionomer. For some fuel cell manufacturing processes, this catalytic mixture may be deposited on the sides of the membrane to form the anode and cathode layers. The combination of the anode catalytic layer, cathode catalytic layer, and electrolyte membrane define a membrane electrode assembly (MEA) in which the anode catalyst and cathode catalyst are supported on opposite faces of the ion conductive solid polymer membrane.
To generate the requisite electricity for powering a motor vehicle, numerous fuel cells are typically combined, in series or in parallel, into a fuel cell stack to achieve a higher output voltage and allow for stronger current draw. For example, a typical fuel cell stack for an automobile may have in excess of two hundred stacked cells. These fuel cell stacks receive reactant gas as a cathode input, typically as a metered flow of ambient air or concentrated gaseous oxygen forced through the stack by a compressor. During normal operation, a quantifiable mass of the oxygen is not consumed by the stack; some of the remnant oxygen is output as cathode waste gas that may include water as a stack by-product. The fuel cell stack also receives hydrogen or hydrogen-rich reactant gas as an anode input that flows into the anode side of the stack. The distribution of hydrogen within the anode flow channels is typically held substantially constant for proper fuel cell stack operation. In some operational modes, supplementary hydrogen is fed into the fuel cell stack so that the anode gas is evenly distributed to achieve a calibrated stack output load. Additionally, a fuel cell stack may be operated in a manner that maintains the MEAs in a humidified state in which gases supplied to the fuel cell stack are humidified to prevent drying of the MEAs. Exhaust generated by the fuel cell stack may therefore include water vapor, liquid water, air, low levels of waste hydrogen gas, and other trace elements.
Presented herein are passive separator assemblies for segregating hydrogen and water in fuel cell systems (FCS), methods for making and methods for using such separator assemblies, and FCS-powered vehicles equipped with such separator assemblies. In an example, there are presented integrated H2/H2O separator devices that passively extract entrained gaseous hydrogen from liquid water in fuel cell system exhaust. The separator device, which may be mounted to a humidifier housing of a water vapor transfer (WVT) unit and located fluidly upstream from the FC stack's cathode inlet, receives humidified “moist” air from the WVT unit and hydrogen-entrained water from an anode-side water separator. Exploiting principles of turbulent fluid flow, gravity, and disparities in fluid density (e.g., buoyancy), the separator device separates hydrogen gas (H2) from water (H2O) and transmits the extracted H2 to the stack's cathode inlet and the segregated water to an FCS exhaust manifold for expulsion from the system. The separator device may include a rigid manifold housing that contains an internal exhaust chamber partitioned from an internal hydrogen chamber by a chamber wall. A long and thin connector slot extending through an upper end of the chamber wall fluidly connects the two internal fluid chambers. Within the exhaust chamber, the lighter and less-dense hydrogen lifts away from the heavier and more-dense liquid, enters the hydrogen chamber through the connector slot, and is expelled from the manifold housing, e.g., where it is diluted in the cathode air stream. Segregated water slides, under the force of gravity, down a ramped wall extending along the bottom of the exhaust chamber and drains through a manifold exhaust port, e.g., for routing to the FCS exhaust. To incite turbulent flow, the manifold intake port may include a diametric constriction that increases intake fluid velocity and decreases static pressure.
Attendant benefits for at least some of the disclosed concepts include a lightweight and inexpensive device for passively separating hydrogen from water without the use of moving parts or active electronic controls. Other attendant benefits may include the ability to integrate the passive H2/H2O separator device into an existing manifold; doing so eliminates the need for an independent device with concomitant savings in cost, weight, and packaging space. Removing hydrogen from water minimizes the need to dilute FCS exhaust with extra air from the compressor and enables higher efficiency and lower emissions, which leads to increased driving ranges with reduced range anxiety.
Aspects of this disclosure are directed to passive-type separator assemblies for segregating hydrogen and water in fuel cell systems, including both automotive and non-automotive FCS applications. In an example, there is presented a liquid-gas separator assembly for a fuel cell system that contains a transfer conduit (e.g., transferring hydrogen-entrained water from an anode water separator and/or humidified air from a WVT unit), a hydrogen inlet (e.g., feeding gaseous hydrogen back into an FCS cathode air inlet), and an exhaust manifold (e.g., collecting and evacuating exhaust from the FCS). The separator assembly includes a rigid outer housing that mounts, e.g., to a humidifier housing, and contains a fluid-tight internal compartment. An intake (first) fluid port fluidly connects the housing's internal compartment to the transfer conduit to receive therefrom anode exhaust, whereas an exhaust (second) fluid port fluidly connects the internal compartment to the exhaust manifold to transfer thereto water separated from the anode exhaust. A transfer (third) fluid port fluidly connects the housing's internal compartment to the hydrogen inlet to transfer thereto hydrogen separated from the anode exhaust. A pair of fluid chambers is located inside the outer housing's internal compartment: a liquid (first) chamber that fluidly connects the intake (first) port to the exhaust (second) port and evacuates extracted water from the internal compartment; and a gas (second) chamber that is located above the exhaust chamber, fluidly connects the exhaust chamber to the transfer port, and evacuates extracted hydrogen from the internal compartment and, thus, from the separator assembly.
Additional aspects of this disclosure are directed to electric-drive vehicles with electrified powertrains containing traction motors powered by fuel cell systems employing any of the disclosed H2/H2O separator assemblies. As used herein, the terms “vehicle” and “motor vehicle” may be used interchangeably and synonymously to include any relevant vehicle platform, such as passenger vehicles (ICE, REV, FEV, fully and partially autonomous, etc.), commercial vehicles, industrial vehicles, tracked vehicles, off-road and all-terrain vehicles (ATV), motorcycles, farm equipment, watercraft, aircraft, etc. For non-automotive applications, disclosed concepts may be implemented for all logically relevant uses, including stand-alone power stations, portable power packs, backup generator systems, pumping equipment, residential, commercial and industrial uses, electric vehicle charging stations (EVCS), etc.
In an example, an electric-drive vehicle includes a vehicle body with a passenger compartment, multiple road wheels mounted to the vehicle body (e.g., via corner modules coupled to a unibody or body-on-frame chassis), and other standard original equipment. An electrified powertrain contains one or more vehicle-mounted traction motors that operate alone (e.g., for FEV powertrains) or in conjunction with an internal combustion engine assembly (e.g., for HEV powertrains) to selectively drive one or more of the road wheels and thereby propel the vehicle. A resident FCS, which is mounted to the vehicle, oxidizes a hydrogen-based fuel to thereby generate an FCS voltage to power the electrified powertrain. The FCS includes a stack of fuel cells, a transfer conduit that receives anode exhaust from the fuel cell stack, a cathode air inlet that feeds hydrogen into the fuel cell stack, and an exhaust manifold that evacuates anode exhaust from the FCS.
Continuing with the discussion of the preceding example, the vehicle is also equipped with a liquid-gas separator assembly that passively separates gaseous hydrogen from liquid water in anode exhaust. The separator assembly includes a rigid outer housing that mounts to the FCS and contains a fluid-tight internal compartment. An intake port fluidly connects the housing's internal compartment to the transfer conduit to receive therefrom FCS exhaust, whereas an exhaust port fluidly connects the internal compartment to the exhaust manifold to transfer thereto extracted water separated from the FCS exhaust. Additionally, a transfer port fluidly connects the internal compartment to the cathode air inlet to transfer thereto extracted hydrogen separated from the FCS exhaust. Located inside the housing's internal compartment is an exhaust chamber that fluidly connects the intake and exhaust ports and evacuates extracted water from the internal compartment to the exhaust manifold. Located inside the internal compartment above the exhaust chamber is a hydrogen chamber that fluidly connects the exhaust chamber to the transfer fluid port and evacuates extracted hydrogen from the internal compartment to the cathode air inlet.
Aspects of this disclosure are also directed to manufacturing workflow processes, system control logic, and computer-readable media (CRM) for making and/or using any of the disclosed separator assemblies. In an example, a method is presented for manufacturing a liquid-gas separator assembly for a fuel cell system. This representative method includes, in any order and in any combination with any of the above and below disclosed options and features: receiving an outer housing defining therein a fluid-tight internal compartment; fluidly connecting the internal compartment to a transfer conduit of the FCS via a first fluid port configured to receive from the transfer conduit FCS exhaust containing hydrogen and water; fluidly connecting the internal compartment to an exhaust manifold of the FCS via a second fluid port configured to transfer to the exhaust manifold extracted water separated from the FCS exhaust; and fluidly connecting the internal compartment to a hydrogen inlet of the FCS via a third fluid port configured to transfer to the hydrogen inlet extracted hydrogen separated from the FCS exhaust, wherein a first fluid chamber located inside the internal compartment of the outer housing fluidly connects the first fluid port to the second fluid port and is configured to evacuate the extracted water from the internal compartment through the second fluid port, and wherein a second fluid chamber located inside the internal compartment above the first fluid chamber fluidly connects the first fluid chamber to the third fluid port and is configured to evacuate the extracted hydrogen from the internal compartment through the third fluid port.
For any of the disclosed separator assemblies, methods, and vehicles, a chamber wall may be located inside the housing's internal compartment to separate the two fluid chambers. In this instance, the chamber wall has a connector port that fluidly connects the two fluid chambers. Optionally, the length of the chamber wall, which extends from the intake port to the exhaust port, may be substantially coterminous with the length of the exhaust chamber; the connector port may be an elongated slot with a slot length that extends about 65% or less of the wall's length, e.g., to prevent extracted water from reaching the transfer port and being recirculated back into the fuel cell stack. As yet a further option, the intake port may incorporate a fluid constriction that is interposed between the housing's internal compartment and the transfer conduit. Through Bernoulli's principle, the fluid constriction induces turbulent flow of the FCS exhaust that is entering the exhaust chamber through the intake port from the transfer conduit.
For any of the disclosed separator assemblies, methods, and vehicles, the exhaust chamber may include opposing top and bottom walls that extend between the intake and exhaust ports. In this instance, the bottom wall extends in a downward slope, e.g., at an angle of about 5-15 degrees from a central horizontal plane, from the intake port to the exhaust fluid port such that extracted water flows, under the force of gravity, out of the separator assembly through the exhaust port. As another option, a height of the exhaust chamber, from bottom wall to top wall thereof, may vary (e.g., increases then decreases) when moving along the length of the internal compartment from the intake to the exhaust port. In a similar regard, a width of the exhaust chamber, between opposing sidewalls thereof, may vary (e.g., decreases then increases) when moving along the length of the internal compartment from the intake to the exhaust port. Optionally, a total volume of the exhaust chamber may be markedly less than a total volume of the hydrogen chamber, e.g., to facilitate separation and transfer of hydrogen gas.
For any of the disclosed separator assemblies, methods, and vehicles, the intake port fluidly connects to the internal compartment along a medial (first) horizontal plane, whereas the exhaust port fluidly connects to the internal compartment along a lower (second) horizontal plane below the medial plane, e.g., such that extracted water flows, under the force of gravity, out through the exhaust port. By comparison, the transfer port fluidly connects to the internal compartment along an upper (third) horizontal plane above the medial plane, e.g., such that extracted hydrogen floats up and out through the exhaust port. For some configurations, the intake port has a small (first) diameter, the exhaust port has a medium (second) diameter that is equal to or greater than the intake port's diameter, and the transfer port has a large (third) diameter that is greater than the other two ports' diameters. As another option, the separator assembly's outer housing and three fluid ports may be integrally formed (e.g., from cast or precision-machined metal or injection molded or 3D-printed polymer) as a single-piece structure. In this instance, the exhaust and hydrogen chambers are adjoining segments of the housing's internal compartment, e.g., physically separated and fluidly connected by the internal chamber wall.
The above Summary does not represent every embodiment or every aspect of the present disclosure. Rather, the foregoing summary merely provides a synopsis of some of the novel concepts and features set forth herein. The above features and advantages, and other features and attendant advantages of this disclosure, will be readily apparent from the following Detailed Description of illustrated examples and representative modes for carrying out the disclosure when taken in connection with the accompanying drawings and appended claims. Moreover, this disclosure expressly includes any and all combinations and subcombinations of the elements and features presented above and below.
The present disclosure is amenable to various modifications and alternative forms, and some representative embodiments of the disclosure are shown by way of example in the drawings and will be described in detail herein. It should be understood, however, that the novel aspects of this disclosure are not limited to the particular forms illustrated in the above-enumerated drawings. Rather, this disclosure covers all modifications, equivalents, combinations, permutations, groupings, and alternatives falling within the scope of this disclosure as encompassed, for example, by the appended claims.
This disclosure is susceptible of embodiment in many different forms. Representative embodiments of the disclosure are shown in the drawings and will herein be described in detail with the understanding that these embodiments are provided as an exemplification of the disclosed principles, not limitations of the broad aspects of the disclosure. To that extent, elements and limitations that are described, for example, in the Abstract, Introduction, Summary, and Detailed Description sections, but not explicitly set forth in the claims, should not be incorporated into the claims, singly or collectively, by implication, inference or otherwise.
For purposes of the present detailed description, unless specifically disclaimed: the singular includes the plural and vice versa; the words “and” and “or” shall be both conjunctive and disjunctive; the words “any” and “all” shall both mean “any and all”; and the words “including,” “containing,” “comprising,” “having,” and the like, shall each mean “including without limitation.” Moreover, words of approximation, such as “about,” “almost,” “substantially,” “generally,” “approximately,” and the like, may each be used herein in the sense of “at, near, or nearly at,” or “within 0-5% of,” or “within acceptable manufacturing tolerances,” or any logical combination thereof, for example. Lastly, directional adjectives and adverbs, such as fore, aft, inboard, outboard, starboard, port, vertical, horizontal, upward, downward, front, back, left, right, etc., may be with respect to a motor vehicle, such as a forward driving direction of a motor vehicle when the vehicle is operatively oriented on a horizontal driving surface.
Discussed below are integrated passive-type separator devices for segregating gaseous hydrogen and liquid water in fuel cell systems. In an example, an H2/H2O separator assembly separates entrained hydrogen from liquid water in FCS exhaust without using mechanical parts, fluid pumps, or electronic control. Doing so allows the separator assembly to be integrated into existing hardware of a fuel cell system without the added cost, mass, packaging space, or complexity of active separator devices. The separator assembly uses principles of turbulent fluid flow, gravity, and buoyancy to separate hydrogen gas from streaming water, recirculate the extracted hydrogen back into the fuel cell stack, and concomitantly drain the extracted water from the FCS. Rather than using a dedicated pump, the separator assembly may use an existing cathode air stream to draw the hydrogen away from the water and out of the separator assembly to reintroduce the extracted hydrogen back into the fuel cell stack. To facilitate separation, the separator assembly's intake port may incorporate a diametric constriction that increases intake fluid velocity and decreases static pressure to incite turbulent flow. Segregated water slides, under the force of gravity, down a ramped wall of the separator's internal exhaust chamber and drains out of the assembly through a liquid exhaust port.
Referring now to the drawings, wherein like reference numbers refer to like features throughout the several views, there is shown in
Packaged within the vehicle body 12 of automobile 10 is a representative fuel cell system 14 for powering a prime mover, such as electric motor generator unit (MGU) 16, that is operable for driving any one or more of the vehicle's road wheels 18. Proton exchange membrane fuel cell system 14 of
The diffusion media layers 30 and 34 are porous constructions that provide for fluid inlet transport to and fluid exhaust transport from the MEA 38. An anode flow field plate (or “first plate”) 40 is provided on the anode side 24 in abutting relation to the anode diffusion media layer 30. In the same vein, a cathode flow field plate (or “second plate”) 42 is provided on the cathode side 26 in abutting relation to the cathode diffusion media layer 34. Coolant flow channels 44 traverse each of the plates 40 and 42 to allow cooling fluid to flow through the fuel cell 22. Fluid inlet ports and headers direct a hydrogen-rich fuel and an oxidizing agent to respective passages in the anode and cathode flow field plates 40, 42. A central active region of the anode's plate 40 that faces the proton-conductive membrane 28 may be fabricated with an anode flow field composed of serpentine flow channels for distributing hydrogen over an opposing face of the membrane 28. The MEA 38 and plates 40, 42 may be stacked together between stainless steel clamping plates and monopolar end plates (not shown). These clamping plates may be electrically insulated from the end plates by a gasket or dielectric coating. The fuel cell system 14 may also employ anode recirculation where an anode recirculation gas is fed from an exhaust manifold or headers through an anode recirculation line for recycling hydrogen back to the anode side 24 input so as to conserve hydrogen gas in the stack 20.
Hydrogen (H2) inlet flow—be it gaseous, concentrated, entrained, or otherwise—is transmitted from a hydrogen source, such as fuel storage tank 46, to the anode side 24 of the fuel cell stack 20 via a fluid injector 47 coupled to a (first) fluid intake conduit or hose 48. Anode exhaust exits the stack 20 via a (first) fluid exhaust conduit or hose 50. Although shown on the inlet side of the stack, a compressor or pump 52 provides a cathode inlet flow, such as ambient air and/or concentrated gaseous oxygen (O2), via a (second) fluid intake line or manifold 54 to the cathode side 26 of the stack 20. Cathode exhaust is output from the stack 20 via a (second) fluid exhaust conduit or manifold 56. Flow control valves, flow restrictions, filters, and other available devices for regulating fluid flow can be implemented by the PEMFC system 14 of
Fuel cell system 14 of
Programmable electronic control unit (ECU) 72 helps to control operation of the fuel cell system 14. As an example, ECU 72 receives temperature signals T1 from temperature sensors 66, 68 that indicate the temperature of the fuel cell stack 20; ECU 72 may be programmed to responsively issue command signals C1 to modulate operation of the stack 20. ECU 72 of
With continuing reference to
Turning next to
Once separated, extracted hydrogen and, in some instances, a restricted volume of moist air may be passively transferred from the separator assembly 100 back into the cathode side of the stack 120 and directed into the cathode diffusion media and flow channels of the individual fuel cells (FC). At the same time, the separator assembly 100 passively collects and drains segregated water to a fuel cell system exhaust (FCSE) 108, which may be equipped with a bleed line and a dump valve (not shown) that selectively exhaust water and nitrogen from the FCS or recycle metered amounts of the waste water as desired. It should be appreciated that the separator assembly 100 may be packaged at other locations within or external to the FCS and may be fluidly interconnected to greater, fewer, or alternative FCS components than what are shown.
Separator assembly 100 of
To shut and seal the separator assembly 100, the interior opening 115 is closed off by the WVT's humidifier housing 104 upon mounting of the manifold housing 104 to the WVT unit 102, e.g., via bolts 116 received through bolt holes 117 in the flange 111. A complementary gasket or silicone adhesive may be applied to seal the inboard face of the separator assembly 100 to the humidifier housing 104. The exterior closing 119 is closed off by an optional face plate 112 that is mounted over the gasket seat 113, e.g., via a set of bolts 116. An optional polymeric ring gasket 114 fits into a complementary channel in the gasket seat 113 and compresses between the face plate 112 and the housing 110 to thereby seal closed the outboard face. When the interior and exterior faces of the manifold housing 110 are closed off, the separator assembly 110 creates a fluid-tight internal compartment 118 (
In order to collect anode and cathode exhaust from the FCS, an intake (first) port 122 fluidly connects the internal compartment 118 within the separator assembly's outer housing 110 to an FCS exhaust transfer conduit 101; in so doing, the intake port 122 receives hydrogen-and-water filled FCS exhaust from the transfer conduit 101. Although shown as receiving humidified air from the WVT unit 102 via the exhaust transfer conduit 101 and intake port 122, the separator assembly 100 may function as an “endcone” of the WVT unit 102 with the exhaust chamber 130 fluidly connected to the WVT's fluid stream via a dedicated slot. To evacuate collected water from the outer housing 110, an exhaust (second) port 124 fluidly connects the internal compartment 118 to an exhaust manifold in the FCS exhaust 108 and transfers thereto water extracted from FCS exhaust by the separator assembly 100. In order to recycle gaseous hydrogen back into the FCS, a transfer (third) port 126 fluidly connects the internal compartment 118 to a hydrogen inlet of the fuel cell stack 120 and transmits thereto hydrogen extracted from the FCS exhaust by the separator assembly 100. While it is envisioned that the fluid porting may be individually manufactured and subsequently coupled to the separator housing, it may be desirable that the outer housing 110 and three fluid ports 122, 124, 126 be integrally formed (e.g., from cast or precision-machined metal or injection molded or 3D-printed polymer) as a one-piece, unitary structure.
Fluid porting of the separator assembly housing 110 may be designed to optimize exhaust intake, H2/H2O segregation, water drainage, and hydrogen recirculation. In accord with the example illustrated in
Collection, separation, and transfer of hydrogen and water is performed within two collaborating fluid chambers located inside the internal compartment 118 of the outer housing 110: an exhaust chamber (or “first fluid chamber”) 130 that extends lengthwise along a lower extent of the compartment 110, and a hydrogen chamber (or “second fluid chamber”) 132 extending lengthwise along an upper extent of the compartment 110. As shown, the two neighboring fluid chambers 130, 132 are adjoining segments of the internal compartment 118 that are physically separated by an internal chamber wall 128. The exhaust chamber 130 fluidly connects the intake port 122 to the exhaust port 124 and passively evacuates therethrough extracted water from the internal compartment 118. At least a portion of the hydrogen chamber 132 is located on top of the exhaust chamber 130 and fluidly connects the exhaust chamber 130 to the transfer port 126; with this arrangement, the chamber 132 passively evacuates therethrough extracted hydrogen from the internal compartment 118. The sectional view of
It may be desirable that a vertical (first) height H1 of the exhaust chamber 130 varies when traversing along the length of the internal compartment 118 between the intake and exhaust ports 122, 124 (e.g., progressively increases then decreases when moving left to right in
Located inside the separator assembly's internal compartment 118 is a chamber wall 128 that partitions the two chambers 130, 132 and, at the same time, governs the flow of fluid between these chambers 130, 132. In accord with the illustrated example, the internal chamber wall 128 may have a curvilinear plan-view geometry (e.g., longitudinal section of
To facilitate separation of gaseous hydrogen from the incoming flow of FCS exhaust, the intake port 122 may incorporate a fluid constriction 121 (
Aspects of the present disclosure have been described in detail with reference to the illustrated embodiments; those skilled in the art will recognize, however, that many modifications may be made thereto without departing from the scope of the present disclosure. The present disclosure is not limited to the precise construction and compositions disclosed herein; any and all modifications, changes, and variations apparent from the foregoing descriptions are within the scope of the disclosure as defined by the appended claims. Moreover, the present concepts expressly include any and all combinations and subcombinations of the preceding elements and features.
