Patent Publication Number: US-2022220922-A1

Title: A Tubular Reactor Serving as a Combustor and Heat Exchanger

Description:
FIELD 
     The present disclosure relates to a tubular reactor that can be used in a heat pump, heat engine, or other thermodynamic apparatus. 
     BACKGROUND 
     One example of a thermodynamic apparatus, a compression-expansion heat pump  200 , is shown in  FIG. 1 . Heat pump  200  has a hot heat exchanger  202 , a cylinder  204  in which a hot displacer  206  reciprocates and a cylinder  208  in which a cold displacer  210  reciprocates. Mechatronics actuators, in mechatronics section  220 , are coupled to hot and cold displacers  206  and  210  and drive the displacers between ends of travel. A low molecular weight gas, such as helium, is contained within cylinders  204  and  208  and inside tubes of hot heat exchanger  202 . There is a hot chamber  276  delimited by dome  278 , cylinder walls  280 , and a top surface of displacer  206 . There is also a warm-hot chamber, which is not visible in  FIG. 1  since displacer  206  is shown in its lower position in  FIG. 1 . The warm-hot chamber is located between mechatronics section and displacer  206 . A cold chamber  280  below cold displacer  210  is visible in  FIG. 1 ; although a cold-warm chamber is not visible due to displacer  210  being shown in its upper position. When displacers  206  and  210  are caused to reciprocate, the working gas moves among cold chamber  280 , hot chamber  276 , the warm-hot chamber, and the warm-cold chamber. The working gas accesses the various chambers by traveling through regenerators and/or heat exchangers located in an annular space located outside of cylinders  204  and  208 . When hot displacer  206  moves upward toward hot heat exchanger  202 , the working gas flows: from tubes of hot heat exchanger  202  into a regenerator  230 ; from regenerator  230  flow into a warm-hot heat exchanger  240 ; and from the warm-hot heat exchanger into the warm-hot chamber. When hot displacer  206  moves the other direction, flow is reversed compared to that described above. 
     In regard to movement of cold displacer  210 , working fluid moves between the volume within cylinder  208  below cold displacer  210  (away from mechatronics section  220 ) and a cold heat exchanger  260 ; between cold heat exchanger  260  and a cold regenerator  270 ; between cold regenerator  270  and a warm-cold heat exchanger  250 ; and between cold warm-cold heat exchanger  250  and the warm-cold chamber. 
     One of the fluids passing through heat exchangers  240 ,  250 , and  260  is the working fluid. The other fluid in the present example is a liquid coolant. In regard to warm-hot heat exchanger  240 , coolant accesses passageways of warm-hot heat exchanger  240  through inlet  242  and exits through outlet  244 . Similarly, passages of warm-cold heat exchanger  250  are coupled to an inlet  252  and an outlet  254 ; and passages of cold heat exchanger  260  are coupled to an inlet  262  and an outlet  264 . 
     Air and fuel are provided to heat pump  200  via a blower  270 . Premixed air and fuel are routed through a heat exchanger for preheating by exhaust gases leaving heat pump  200 . It is a rather convoluted path that is not described here. However, the air and fuel are provided to a wire-mesh diffuser/combustor  272  through an inlet  274 . Wire-mesh diffuser/combustor  272  has opening on the outer surface that prevent blow back of combustion into the interior of combustor  272 . Diffuser/combustor  272  acts as a combustion holder with fuel oxidizing near an outer surface of diffuser/combustor  272 . Diffuser/combustor  272  gets very hot and radiates to tubes of hot heat exchanger  202 . The tubes are U-shaped with one side of the one of the legs of the U nearer diffuser/combustor  272 , with a better shape factor for radiation. Surface area of the tubes is ill used to effect heat transfer to the helium flowing therethrough because the one surface of the inner leg of the tubes face diffuser/combustor  272  sets a limit to how much air and fuel can be combusted due to its melting or softening temperature. And, the other tube surfaces to which there is limited radiation are insufficiently hot to promote effective heat transfer to the helium. 
     It is desirable to have a combustion system that uses the surface area of the tubes more uniformly for heat transfer than the combustion system of  FIG. 1 . 
     SUMMARY 
     To overcome at least one problem in the prior art a tubular reactor is disclosed that has: a diffuser having an inlet for a fuel-and-air mixture and a plurality of holes defined in its surface through which the fuel-and-air mixture exits the diffuser; and a plurality of tubes. A first portion along the length of each tube is linear. A centerline of the first portion of each of the tubes is displaced from an outer surface of the diffuser by a first predetermined displacement. The centerline of the first portion of each tube is spaced from the centerline of the first portion of each adjacent tube by a predetermined gap. A second portion along the length of each tube is U shaped. The U-shaped portion can be curved through the length that is U shaped or, alternatively, can have two curved portions with a straight portion therebetween. 
     The first portion of each of the tubes is mutually parallel with all other first portions of the tubes. A third portion along the length of each tube is linear and a center line of the third portion is displaced from the outer surface of the diffuser by a second predetermined displacement. The first and third portions of each tube are fluidly coupled via the second portion of the tube. The first portion of the tube is fluidly coupled with a first chamber. The third portion of the tube is fluidly coupled with a second chamber. In some embodiments the first chamber is a hot chamber in a heat pump and the second chamber has a regenerator disposed therein. 
     The plurality of tubes is a first plurality of tubes. The tubular reactor further includes a second plurality of tubes with a first linear portion of the length of each of the second plurality of tubes mutually parallel. A centerline of the first portion of each of the tubes of the second plurality of tubes is displaced from an outer surface of the diffuser by a second predetermined displacement. The second predetermined displacement is greater than the first predetermined displacement. 
     In some embodiments, the predetermined gap is based on a quench distance. 
     The tubular reactor includes a reflective cylinder with a majority of the first and second portions of the tubes disposed inside the reflective cylinder. 
     The tubular reactor also has an ignitor disposed between the first and third portions of the tubes. 
     In some embodiments, the tubular reactor also includes a mesh of a material having a melting temperature greater than a predetermined threshold adhered to the first portion of the tubes. In other embodiments, a porous media is adhered to the first portion of the tubes wherein the porous media has a melting temperature greater than a predetermined threshold. The predetermined gap is based at least on number of tubes in the plurality of tubes, a cross-sectional area of the tubes, a desired flowrate through the tubes, and an allowable pressure drop through the tubes. 
     A tubular reactor is disclosed that has a substantially cylindrical diffuser. The diffuser has: an inlet for fuel and air; a plurality of exit holes defined in its cylindrical surface; and a diffuser centerline. The tubular reactor also has: a first plurality of tubes and a second plurality of tubes. A centerline of a first linear portion of each tube of the first plurality of tubes intersects a first circle of a first diameter. The centerlines of the first linear portion of each tube of the first plurality of tubes is evenly arranged on the first circle. A centerline of a first linear portion of each tube of the second plurality of tubes intersects a second circle of a second diameter. The centerlines of the second linear portion of each tube of the second plurality of tubes is evenly arranged on the second circle. A centerline of a second linear portion of each tube of the first and second pluralities of tubes intersects a third circle of a third diameter. The second linear portions are evenly arranged on the third circle. The diffuser centerline, a centerline of the first circle, a centerline of the second circle, and a third centerline are coaxial. Each tube has a U-shaped portion that couples the first linear portion to the second linear portion. 
     The first linear portion of each tube of the first plurality of tubes is offset from adjacent first linear portions of tubes of the first plurality of tubes by a first predetermined gap. 
     In some embodiment, a catalytic material is provided on an outer surface of the first portion of the tubes of the first plurality of tubes. 
     The tubular reactor, in some embodiments, a reflective cylinder with a reflective surface on an inside surface of the cylinder. The reflective cylinder has a diameter greater than a diameter of the third circle. A centerline of the reflective cylinder being coaxial with the diffuser. 
     The tubular reactor has an ignitor disposed between the centerlines of the first and second linear portions of the first plurality of tubes. 
     The first linear portion of the first and second pluralities of tubes are fluidly coupled to a first chamber via a first transition portion of each of the first and second pluralities of tubes; and the second linear portion of the first and second pluralities of tubes are fluidly coupled to a second chamber via a second transition portion of each of the first and second pluralities of tubes. 
     In some embodiments, a mesh or a porous media is adhered to the first linear portion of the first plurality of tubes. 
     Also disclosed is a thermodynamic device that has: a cylinder; a displacer disposed in the cylinder; an actuator that causes the displacer to reciprocate; and a hot chamber delimited by the cylinder, the displacer, and a dome with orifices defined therein. The device has a diffuser having an inlet for a fuel-and-air mixture and a plurality of holes defined in its surface through for the fuel-and-air mixture to exit the diffuser; a regenerator chamber; an ignitor; and a plurality of tubes. A first linear portion along the length of each tube has a centerline which is displaced from an outer surface of the diffuser by a predetermined displacement. The centerline of the linear portion of each tube is displaced from the centerline of the linear portion of each adjacent tube by a predetermined distance. The ignitor is displaced from the diffuser farther than the linear portions of the plurality of tubes. The tubes are fluidly coupled to the hot chamber on a first end and fluidly coupled to the regenerator chamber on a second end. Gas within the tubes moves from the hot chamber into the tubes and from the tubes into the regenerator chamber when the displacer moves toward the dome; and gas within the tubes moves from the regenerator chamber into the tubes and from the tubes into the hot chamber when the displacer moves away from the dome. 
     An outer surface of the first linear portion of the tubes has one of a porous media and a mesh adhered thereto, in some applications. 
     The first linear portions of the plurality of tubes are mutually parallel and a distance between adjacent first linear portions of the plurality of tubes is a predetermined gap, in other applications. 
     In some applications, there is concern that the tubes deform or otherwise move slightly and the gaps between the tubes would become deflected. It is possible that the tubes could move enough that the desired gap is exceeded and flashback onto the diffuser occurs. To retain the tubes as desired, the tubular reactor also includes a cap having a covering portion that rests on the second portion of the plurality of tubes and a cylindrical portion that has a smooth inner surface and a notched outer surface. The annular portion of the cap has an inner edge having an inner diameter and an outer edge having an outer diameter. The cylindrical portion of the cap couples to the annular portion at the inner edge of the annular portion. A number of notches on the notched outer surface equals a number of the plurality of tubes. Each of the first portions of the plurality of tubes engages with a notch on the notched outer surface. 
     The covering portion of the cap has a cut out defined therein to thereby accommodate installation of an ignitor. 
     In some embodiments to further control adjustments of the tubes, a ring slid over the third portions of the second plurality of tubes with the ring abutting a surface of the third portions of the second plurality of tubes that is farthest away from the diffuser. 
     In some embodiments, the tubular reactor includes a fourth portion along the length of the plurality of tubes that is fluidly coupled to the first portion. In cases where that fourth portion is angled or bent in a particular direction to accommodate other aspects of the application, the gap may be greater than the predetermined gap. In such embodiments, a refractory material is stuffed into gaps between adjacent fourth portions of the plurality of the tubes. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is cross section of a compression-expansion heat pump having a combined fuel diffuser and combustor; 
         FIG. 2  is a cross section of a compression-expansion heat pump having separated fuel diffusing and combusting elements; 
         FIG. 3  is a cross-section of a combustion and heat exchanger system according to an embodiment of the disclosure; 
         FIG. 4  is an illustration of a single tube of a combustion/heat exchanger system; 
         FIG. 5  is an illustration of a cross-section of a combustion and heat exchanger system having a porous media surrounding some of the heat exchanger tubes; 
         FIGS. 6 and 7  are illustrations of portions of a combustion and heat exchanger system having a mesh next to some of the heat exchanger tubes; and 
         FIG. 8  is an illustration of a cap that is placed over a U-shaped portion of the tubes; 
         FIG. 9  is a cross-sectional illustration of the cap of  FIG. 8  placed over the U-shaped portion of the tubes; 
         FIG. 10  shows an embodiment of the assembly of a tubular reactor; 
         FIG. 11  shows an alternative cap for the tubular reactor; and 
         FIG. 12  is a view from within the tubular reactor showing insulation material packed into gaps between adjacent tubes in one section along the length of the tubes. 
     
    
    
     DETAILED DESCRIPTION 
     As those of ordinary skill in the art will understand, various features of the embodiments illustrated and described with reference to any one of the Figures may be combined with features illustrated in one or more other Figures to produce alternative embodiments that are not explicitly illustrated or described. The combinations of features illustrated provide representative embodiments for typical applications. However, various combinations and modifications of the features consistent with the teachings of the present disclosure may be desired for particular applications or implementations. Those of ordinary skill in the art may recognize similar applications or implementations whether or not explicitly described or illustrated. 
     In  FIG. 2 , an alternative combustion and heat exchange system is shown. An upper portion of a heat pump  140  has a displacer  90  disposed within a cylinder  88 . Displacer  90  is coupled to a mechatronics system (not illustrated in  FIG. 2 ), analogous to the system described in  FIG. 1 , that commands displacer  90  to reciprocate within cylinder  88 . The volume of working gas, such as helium or hydrogen, in a hot chamber  84  changes as a result of the movement of displacer  90 . When the working gas is pushed out of hot chamber  84 , the working gas is pushed into orifices  94  that pass through a dome  96 . Orifices  94  are coupled to tubes, each having a first connector section  142  coupled to a first linear portion  150  coupled to a U-shaped portion  158  coupled to a second linear portion  154  coupled to a second connector section  144 . Second connector section  144  fluidly couples to a regenerator  92  that is located between a housing  86  and cylinder  88 . The space between housing  86  and cylinder  88  is an annulus. Regenerator  92  is annular. 
     At the center of the tubes is a diffuser  68  to which premixed fuel and air are provided. Diffuser  68  is a cylinder with a plurality of small holes on the outer surface. The diffuser causes the fuel and air to be distributed uniformly to the first linear portion of the tubes  150 . 
     A cross-section of  FIG. 2 , as indicated by 3-3, is shown in  FIG. 3 . The cross-section in  FIG. 3  is through the entire heat pump  140  (of  FIG. 2 ), not just the cross section of  FIG. 2 . Diffuser  68  is in the center (center of combustor at  49 ). At a displacement  60 , from the surface of diffuser  68 , is a first linear portion of a first plurality of tubes  50 . First linear portions  50  are mutually parallel and are displaced from each other centerline to centerline by a distance  58 . A gap  59  is the edge to edge distance. Gap  59  is less than or equal to a predetermined gap to avoid flashback. Air and fuel from diffuser  68  travels toward first linear portions  50 . It is preferred that there is no combustion occurring between diffuser  68  and first linear portions  50 ; instead, it is desired for oxidation of the fuel with the air to occur near first linear portions  50 . Thus, gap  59 is less than the predetermined gap so that the combustion of oxidation of the fuel and air does not propagate from the side of linear portions  50  that is remote from diffuser  68  toward diffuser  68 . 
     First linear portions of a second plurality of tubes  52  is show in  FIG. 3 . Referringto  FIG. 2 , first linear portion  152  of the second plurality of tubes are coupled via a U-shaped portion  158  to second linear portion  154  of the second plurality of tubes. The second plurality of tubes is displaced farther from diffuser  68  than first plurality of tubes (including portions  150 ,  154 , and  158 ). Now referring to  FIG. 3 , first linear portions of the second plurality of tubes  52  are viewed in cross section. First linear portions of the second plurality of tubes  54  are mutually parallel. Centerlines of the second plurality of tubes and are displaced from an outer surface of diffuser  68  by a displacement  62 . Second linear portions of the first plurality of tubes  54  and second linear portions of the second plurality of tubes  56  are interspersed at the same distance from diffuser  68 . Also shown in  FIG. 3  is an ignitor  70 . A tip of ignitor  70  is positioned between first linear portions of the second plurality of tubes  52  and the second linear portions of the first and second plurality of tubes  54 ,  56 . Such position of ignitor  70  is one non-limiting example. 
     In some embodiments, a ring  72  is provided that is reflecting on the inner surface. The reflective surface causes radiant energy from tubes  50 ,  52 ,  54 , and  56  to be reflected onto those same tubes to reduce heat losses from the system. 
     Referring to  FIG. 2 , some of the tubes have a lower U-shaped portion  168  than the rest of the tubes that have a U-shaped portion  158 . In the embodiment in  FIG. 2 , the ignitor (not shown) is inserted from the top and extends below the level of U-shaped portions  158 . Oxidation of the fuel occurs in the volume between first linear portions  150  and second linear portions  154 , more of it occurs next to first linear portions  150  and  152 , which causes heat transfer from the oxidizing gases at elevated temperature to the linear portions and the U-shaped portions of the tubes to be more effective than oxidation at other locations. That is, oxidation occurring proximate the tube portions is more effective than oxidation, for example, at a centrally-located burner. 
     A single tube of the first plurality of tubes is shown in  FIG. 4 . First connector portion  142  is fluidly coupled to first linear portion  150 , which is fluidly coupled to U-shaped portion  158 , which is fluidly coupled to second linear portion  154 , which is coupled to second connector portion  144 . 
     Combustion is quenched when heat transfer from the combustion zone, e.g., into a solid surface is such that the flame fails to propagate. The quench distance can be determined, for example, by determining the maximum distance that two plates can be displaced from each other which does not allow a flame to propagate therethrough. In the present example, tubes have a gap therebetween which prevents flame propagation. The quench distance depends on the fuel type and the mixture concentration with air. (If the oxidizer is not air, quench distance also depends on the oxidizer composition.) In some embodiments where a range of mixture concentrations and/or fuel types is contemplated, the gap between adjacent tubes is selected for the most demanding condition anticipated in practice. 
     Depending on the performance goals in designing a heat pump system of other device into which the tubular reactor is employed, the flow of helium, or other low-molecular weight gas, through the tubes is determined. Based on the fluid flow rate, the maximum gap, and the additional considerations that the pressure drop through the tubes shouldn&#39;t be excessive and the typical wall thickness of tubes, the number of tubes can be determined. In the embodiment in  FIG. 3 , two rows of tubes are used to provide sufficient flow cross-sectional area for flowing the helium. In other examples, it is possible that one ring of tubes is sufficient. And in even other examples, more than two rings of tubes are used. 
     For each tube in  FIG. 3 , two orifices are formed in dome  96  to accommodate first and second connector sections  142  and  144 . A high concentration of orifices in dome  96  weakens the dome. In  FIG. 3 , first and second connector sections  142  and  144  are bent so that the orifices in dome  96  are less weakening than if arranged close together. 
     An alternative embodiment is shown in  FIG. 5 . Diffuser  68  has a ring of tubes  290  arranged at a displacement  284  from the outer surface of diffuser  68 . A porous media  280  is arranged on the outer surface of tubes  290 . Because of porous media  280 , a gap  286  between adjacent tubes  290  can be much greater than gap  58  ( FIG. 3 ) for tubes  50  that has no such porous media. Flame propagation toward diffuser  68  is prevented by porous media  280 , i.e., the gaps in the porous media are much smaller than that needed to quench the flame. Instead, gap  286  is determined based on providing sufficient flow through tubes  290  with low pressure drop and preserving strength in the dome through which tubes  290  pass. (Tubes  290  pass through a dome  96  analogously to what is shown in  FIG. 4 .) 
     Because arresting the flame (quench), in  FIG. 5 , is provided by porous media  280 , tubes  290  are substantially larger in diameter than tubes  50  of  FIG. 3  in which tubes  50  are used for quenching and thus must be spaced close together. 
     Of course, tubes  290  is an illustration of a cross section of first linear portions of the full tubes. First linear portions  290  are mutually parallel. First linear portions  290  are fluidly coupled to second linear portions  292  via a U-shaped portion, the latter of which is not illustrated in the cross-section in  FIG. 5 . 
     A similar embodiment to that in  FIG. 5 , is shown in  FIG. 6 , in which gap  286  is not based on a quench distance. Instead, a mesh  282  is adhered to first linear portions  290  of a plurality of tubes that are displaced from the outer surface of diffuser  68 . The mesh size of mesh  282  is selected to prevent combustion from propagating toward diffuser  68 . 
     To support alternative fuels and mixture concentrations in practice, one embodiment in  FIG. 5  shows a portion of the combustion with tubes  50 ,  52 ,  54  and  56 . A porous media  280  is provided surrounding tubes  50 . Porous media  280  has randomly sized openings that allow fuel and air to pass from the inside of the ring of tubes  50  to the outside for combustion. However, the pore size of porous media  280  is significantly smaller than the gap between adjacent tubes  50 . 
     In an alternative in  FIG. 6 , a mesh  282  is applied to tubes  50 . Mesh  282  is shown on the outer edge of tubes  50 . Alternatively, the mesh could be applied on the inner edge of tubes  50 . In  FIG. 7 , a portion of three tubes  50  is shown with the mesh on the surface of tubes  50 . The mesh openings are smaller than the gap between adjacent tubes  50 . The embodiments in  FIGS. 5-7  are more robust to variabilities in the fuel/oxidizer conditions. 
     As described above, to prevent flashback from the space beyond tubes  150  of  FIG. 2  toward diffuser  68 . A consistent gap  59 , as seen in  FIG. 3 , prevents such flashback. In some applications, temperature variations due to warmup, cooldown, and operational range of output can cause the tubes to deflect slightly. To avoid the deflection to becoming more than can be tolerated to prevent flashback, a fixture is applied to maintain the proper gap between adjacent tubes. Such a cap  300  is shown in  FIG. 8 . Cap  300  has a covering portion  302  that sits atop the U-shaped portion of the tubes. Covering portion  302  is an annulus with an outer edge  310  and an inner edge  312 . Inner edge  312  couples to a cylindrical portion  304 . Cylindrical portion  304  has an inner surface that is substantially smooth. An outer surface  306  of cylindrical portion  304  has a plurality of notches formed therein. First linear portions  150  of the first plurality of tubes snap into the notches, in one embodiment, with a slight interference fit. A notch is provided for each of first linear portions  150 . Also shown in  FIG. 8  is a cut out  314  of covering portion  302  to accommodate insertion of an ignitor (not shown). 
     A portion of a tubular reactor is shown in cross section in  FIG. 9  where notches of cap  302  are engaged with first linear portions  320  of the first plurality of tubes. The first plurality of tubes includes linear portion  320 , linear portion  320 ″ and U-shaped portion  320 ′ that fluidly couples  320  with  320 ″. Only a portion of notch  308  is visible in  FIG. 9  because first portion  320  is engaged with notch  308  over most of the length of notch  308 . Shorter tubes are shown on the left-hand side of  FIG. 9 . A tube has a first linear portion  330 , a second linear portion  330 ″, and a U-shaped portion  330 ′ that couples linear portions  330  and  330 ″ together. Another tube that is displaced from the centerline  336  further than the tube including  330 ,  330 ′, and  330 ″ has a first linear portion  332  fluidly coupled to a U-shaped portion  332 ′. A second linear portion that fluidly couples to U-shaped portion  332 ′ is barely visible as it is behind second linear portion  330 ″. The cutout for the ignitor is not visible in cap  300  in the view in  FIG. 9 . However, it is located above U-shaped portions  330 ′ and  332 ′. 
     Referring now to  FIG. 10 , a view of tubes with cap  300  over the top of the tubes. An ignitor  326  is placed near cut out  314 . An additional feature is shown in  FIG. 10  that helps to retain the tubes in their desired positions in the form of a band  328 . 
     In some applications, cap  300  allows for the placement of ignitor  326  as shown, i.e., near the shorter tubes. Also, cap  300  covers gaps in the U-shaped portions of the pluralities of tubes that in some applications exceeds the desired gap. In such situations, cap  300  can prevent flashback. 
     Referring not to  FIG. 11 , an alternative cap  400  is shown. Covering  402  has an outside end  404  and an inside edge  406 . A cylindrical portion  410  of the cap has a notched portion. The notches are arranged to engage with tubes of the tubular reactor. Covering  402  is curved to wrap around the tubes more closely than cap  300  of  FIG. 8 . Covering  402  also includes a cut out  408  for an ignitor (not shown). 
     In the embodiments in  FIG. 2  and, more particularly, in  FIG. 4 , portions  142  and  144  are bent to account for other features of the apparatus into which the tubular reactor is installed. In some situations, the gaps between adjacent tubes, due to the bends is greater than the desired gap to avoid flashback. To prevent such flashback, insulation  350  is placed against portions  142  and  144  of the tubes and insultation is also at the bottom of the tubes. The insulation is refractory material such as fiberglass, ceramic fiber, or any suitable material. A ring  354  is put in place to hold insulation  350  and  352  in place. 
     While the best mode has been described in detail with respect to particular embodiments, those familiar with the art will recognize various alternative designs and embodiments within the scope of the following claims. While various embodiments may have been described as providing advantages or being preferred over other embodiments with respect to one or more desired characteristics, as one skilled in the art is aware, one or more characteristics may be compromised to achieve desired system attributes, which depend on the specific application and implementation. These attributes include, but are not limited to: cost, strength, durability, life cycle cost, marketability, appearance, packaging, size, serviceability, weight, manufacturability, ease of assembly, etc. The embodiments described herein that are characterized as less desirable than other embodiments or prior art implementations with respect to one or more characteristics are not outside the scope of the disclosure and may be desirable for particular applications.