Patent Publication Number: US-2016240585-A1

Title: High efficiency thermoelectric generation

Description:
RELATED APPLICATIONS 
     This application is a continuation of U.S. patent application Ser. No. 13/954,786, filed on Jul. 30, 2013 and which claims the benefit of U.S. Provisional Appl. No. 61/678,511, filed Aug. 1, 2012 and U.S. Provisional Appl. No. 61/678,975, filed Aug. 2, 2012. The entire contents of each of the applications identified above are incorporated by reference herein and made a part of this specification. 
    
    
     BACKGROUND 
     1. Field 
     The present application relates generally to thermoelectric cooling, heating, and power generation systems. 
     2. Description of Related Art 
     Thermoelectric (TE) devices and systems can be operated in either heating/cooling or power generation modes. In the former, electric current is passed through a TE device to pump the heat from the cold side to the hot side. In the latter, a heat flux driven by a temperature gradient across a TE device is converted into electricity. In both modalities, the performance of the TE device is largely determined by the figure of merit of the TE material and by the parasitic (dissipative) losses throughout the system. Working elements in the TE device are typically p-type and n-type semiconducting materials. 
     SUMMARY 
     In certain embodiments, a thermoelectric power generating system is provided comprising at least one thermoelectric assembly. The at least one thermoelectric assembly comprises at least one first heat exchanger in thermal communication with at least a first portion of a first working fluid. The first portion of the first working fluid flows through the at least one thermoelectric assembly. The at least one thermoelectric assembly further comprises a plurality of thermoelectric elements in thermal communication with the at least one first heat exchanger. The at least one thermoelectric assembly further comprises at least one second heat exchanger in thermal communication with the plurality of thermoelectric elements and with a second working fluid flowing through the at least one thermoelectric assembly. The second working fluid is cooler than the first working fluid. The thermoelectric power generating system further comprises at least one heat exchanger portion configured to have at least some of the first portion of the first working fluid flow through the at least one heat exchanger portion after having flowed through the at least one thermoelectric assembly. The at least one heat exchanger portion is configured to recover heat from the at least some of the first portion of the first working fluid. 
     In some embodiments, the at least one heat exchanger portion can comprise a first conduit through which the at least some of the first portion of the first working fluid flows. The at least one heat exchanger portion can further comprise a second conduit through which at least a portion of the second working fluid flows. The second conduit is in thermal communication with the first conduit such that the portion of the second working fluid receives heat from the at least some of the first portion of the first working fluid. 
     In some embodiments, the at least one thermoelectric assembly is configured to convert high-temperature heat of the first working fluid to electricity such that low-temperature heat of the first working fluid is received by the at least one heat exchanger portion. 
     In some embodiments, the thermoelectric power generating system can comprise at least one bypass conduit. The thermoelectric power generating system further comprises at least one valve configured to selectively allow at least the first portion of the first working fluid to flow through the at least one first heat exchanger and to selectively allow at least a second portion of the first working fluid to flow through the bypass conduit. 
     In some embodiments, the at least one heat exchanger portion is configured to receive at least some of the second portion of the first working fluid after having flowed through the at least one bypass conduit and to recover heat from the at least some of the second portion of the first working fluid. 
     In some embodiments, the at least one valve can comprise a proportional valve. 
     In some embodiments, the at least one valve can comprise at least one component that is sensitive to high temperatures, and the at least one component is in thermal communication with the second working fluid. 
     In some embodiments, the first working fluid can comprise exhaust gas from an engine. The at least one heat exchanger portion is further configured to use the recovered heat to warm at least one of an engine block of the engine and a catalytic converter of the engine. 
     In some embodiments, the thermoelectric power generating system can further comprise at least one second heat exchanger portion configured to have at least the first portion of the first working fluid flow through the at least one second heat exchanger portion prior to flowing through the at least one thermoelectric assembly. The at least one second heat exchanger portion is configured to reduce a temperature of the first portion of the first working fluid. 
     In some embodiments, the first working fluid can comprise exhaust gas from an engine. The at least one thermoelectric assembly is integrated into at least one muffler of the engine. 
     In certain embodiments, a method of generating electricity is provided comprising receiving at least a first portion of a first working fluid. The method further comprises flowing the first portion of the first working fluid through at least one thermoelectric assembly and converting at least some heat from the first portion of the first working fluid to electricity. The method further comprises receiving at least some of the first portion of the first working fluid after having flowed through the at least one thermoelectric assembly. The method further comprises recovering at least some heat from the at least some of the first portion of the first working fluid. 
     In some embodiments, converting at least some heat from the first portion of the first working fluid to electricity can comprise converting high-temperature heat from the first working fluid to electricity. Recovering at least some heat from the at least some of the first portion of the first working fluid can comprise recovering low-temperature heat of the first working fluid. 
     In some embodiments, the method can further comprise selectively allowing at least the first portion of the first working fluid to flow through the at least one thermoelectric assembly and selectively allowing at least a second portion of the first working fluid to not flow through the at least one thermoelectric assembly. 
     In some embodiments, the first working fluid can comprise an exhaust gas from an engine. The method further comprises using the recovered heat to warm at least one of an engine block of the engine and a catalytic converter of the engine. 
     In some embodiments, the method can further comprise reducing a temperature of the first portion of the first working fluid prior to flowing through the at least one thermoelectric assembly. 
     In certain embodiments, a thermoelectric power generation system is provided comprising at least one thermoelectric assembly and a first flow path with a first flow resistance. The first flow path through the at least one thermoelectric assembly. The system further comprises a second flow path with a second flow resistance lower than the first flow resistance. The second flow path bypasses the at least one thermoelectric assembly. The system further comprises at least one valve configured to vary a first amount of a working fluid flowing along the first flow path and a second amount of the working fluid flowing along the second flow path. 
     In some embodiments, the system can further comprise at least one conduit comprising at least one wall portion having a plurality of perforations. The first flow path extends through the plurality of perforations. 
     In some embodiments, the at least one conduit can further comprises an inlet and an outlet. The at least one valve is between the inlet and the outlet. 
     In some embodiments, the at least one wall portion can further comprise a first wall portion with a first plurality of perforations and a second wall portion with a second plurality of perforations. The at least one valve between the first wall portion and the second wall portion. The first flow path extends through the first plurality of perforations outwardly from the at least one conduit and through the second plurality of perforations inwardly to the at least one conduit. The second flow path does not extend through the first plurality of perforations and not through the second plurality of perforations. 
     In some embodiments, the at least one valve can comprise a proportional valve. In some embodiments, the at least one valve can comprise a flap valve. 
     In some embodiments, the at least one thermoelectric assembly is integrated in a muffler of an engine exhaust system. 
     In certain embodiments, a method of generating electricity is provided comprising receiving a working fluid and selectively flowing at least a portion of the working fluid either along a first flow path having a first flow resistance or along a second flow path having a second flow resistance lower than the first flow resistance. The first flow path extends through at least one thermoelectric assembly. The second flow path does not extend through the at least one thermoelectric assembly. 
     In some embodiments, the first flow path extends through a plurality of perforations of at least one wall portion of at least one conduit. 
     In some embodiments, the at least one wall portion can further comprise a first wall portion with a first plurality of perforations and a second wall portion with a second plurality of perforations. The first flow path extends through the first plurality of perforations outwardly from the at least one conduit and through the second plurality of perforations inwardly to the at least one conduit. 
     The paragraphs above recite various features and configurations of one or more of a thermoelectric assembly, a thermoelectric module, or a thermoelectric system, that have been contemplated by the inventors. It is to be understood that the inventors have also contemplated thermoelectric assemblies, thermoelectric modules, and thermoelectric systems which comprise combinations of these features and configurations from the above paragraphs, as well as thermoelectric assemblies, thermoelectric modules, and thermoelectric systems which comprise combinations of these features and configurations from the above paragraphs with other features and configurations disclosed in the following paragraphs. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Various embodiments are depicted in the accompanying drawings for illustrative purposes, and should in no way be interpreted as limiting the scope of the thermoelectric assemblies or systems described herein. In addition, various features of different disclosed embodiments can be combined with one another to form additional embodiments, which are part of this disclosure. Any feature or structure can be removed, altered, or omitted. Throughout the drawings, reference numbers may be reused to indicate correspondence between reference elements. 
         FIG. 1A  schematically illustrates an example thermoelectric power generating system. 
         FIG. 1B  schematically illustrates an example thermoelectric power generating system with a heat exchanger portion engaged to a bypass conduit. 
         FIG. 2  schematically illustrates an example thermoelectric power generating system with a pre-heat exchanger portion. 
         FIG. 3  schematically illustrates a cross-sectional view of an example heat exchanger portion. 
         FIG. 4  schematically illustrates a cross-sectional view of an example heat exchanger portion. 
         FIGS. 5A-5B  schematically illustrate two example thermoelectric power generating systems. 
         FIG. 6  schematically illustrates an example thermoelectric power generating system having at least one TEG device integrated into a muffler. 
         FIG. 7  schematically illustrates another example thermoelectric power generating system having at least one TEG device integrated into a muffler. 
         FIG. 8  schematically illustrates another example thermoelectric power generating system having at least one TEG device integrated into a muffler. 
         FIG. 9A  schematically illustrates an example thermoelectric power generating system having a multiple-shell muffler. 
         FIG. 9B  schematically illustrates an example thermoelectric power generating system having a coolant routing integrated into a multiple-shell muffler. 
         FIG. 9C  schematically illustrates a cross-sectional view of the thermoelectric power generating system of  FIG. 9A . 
         FIG. 10  schematically illustrates an example thermoelectric power generating system having at least one Helmholtz resonator. 
         FIG. 11  schematically illustrates an example thermoelectric power generating system having at least one TEG device integrated into a muffler. 
         FIG. 12  is a flow diagram of an example method of generating electricity. 
         FIG. 13  is a flow diagram of another example method of generating electricity. 
         FIG. 14  schematically illustrates some external features an example thermoelectric power generating system. 
         FIGS. 15A-15B  schematically illustrate some internal features an example thermoelectric power generating system. 
         FIG. 16A-16C  schematically illustrate an example thermoelectric power generating system having a valve in three different positions. 
     
    
    
     DETAILED DESCRIPTION 
     Although certain embodiments and examples are disclosed herein, the subject matter extends beyond the examples in the specifically disclosed embodiments to other alternative embodiments and/or uses, and to modifications and equivalents thereof. Thus, the scope of the claims appended hereto is not limited by any of the particular embodiments described below. For example, in any method or process disclosed herein, the acts or operations of the method or process may be performed in any suitable sequence and are not necessarily limited to any particular disclosed sequence. Various operations may be described as multiple discrete operations in turn, in a manner that may be helpful in understanding certain embodiments; however, the order of description should not be construed to imply that these operations are order dependent. Additionally, the structures, systems, and/or devices described herein may be embodied as integrated components or as separate components. For purposes of comparing various embodiments, certain aspects and advantages of these embodiments are described. Not necessarily all such aspects or advantages are achieved by any particular embodiment. Thus, for example, various embodiments may be carried out in a manner that achieves or optimizes one advantage or group of advantages as taught herein without necessarily achieving other aspects or advantages as may also be taught or suggested herein. 
     A thermoelectric system as described herein comprise a thermoelectric generator (TEG) which uses the temperature difference between two fluids, two solids (e.g., rods), or a solid and a fluid to produce electrical power via thermoelectric materials. Alternatively, a thermoelectric system as described herein can comprise a heater, cooler, or both which serves as a solid state heat pump used to move heat from one surface to another, thereby creating a temperature difference between the two surfaces via the thermoelectric materials. Each of the surfaces can be in thermal communication with or comprise a solid, a liquid, a gas, or a combination of two or more of a solid, a liquid, and a gas, and the two surfaces can both be in thermal communication with a solid, both be in thermal communication with a liquid, both be in thermal communication with a gas, or one can be in thermal communication with a material selected from a solid, a liquid, and a gas, and the other can be in thermal communication with a material selected from the other two of a solid, a liquid, and a gas. 
     The thermoelectric system can include a single thermoelectric assembly (e.g., a single TE cartridge) or a group of thermoelectric assemblies (e.g., a group of TE cartridges), depending on usage, power output, heating/cooling capacity, coefficient of performance (COP) or voltage. Although the examples described herein may be described in connection with either a power generator or a heating/cooling system, the described features can be utilized with either a power generator or a heating/cooling system. Examples of TE cartridges compatible with certain embodiments described herein are provided by U.S. Pat. Appl. Publ. No. 2013/0104953, filed Jun. 5, 2012 and U.S. patent application Ser. No. 13/794,453, filed Mar. 11, 2013, each of which is incorporated in its entirety by reference herein. 
     The term “thermal communication” is used herein in its broad and ordinary sense, describing two or more components that are configured to allow heat transfer from one component to another. For example, such thermal communication can be achieved, without loss of generality, by snug contact between surfaces at an interface; one or more heat transfer materials or devices between surfaces; a connection between solid surfaces using a thermally conductive material system, wherein such a system can include pads, thermal grease, paste, one or more working fluids, or other structures with high thermal conductivity between the surfaces (e.g., heat exchangers); other suitable structures; or combinations of structures. Substantial thermal communication can take place between surfaces that are directly connected (e.g., contact each other) or indirectly connected via one or more interface materials. 
     As used herein, the terms “shunt” and “heat exchanger” have their broadest reasonable interpretation, including but not limited to a component (e.g., a thermally conductive device or material) that allows heat to flow from one portion of the component to another portion of the component. Shunts can be in thermal communication with one or more thermoelectric materials (e.g., one or more thermoelectric elements) and in thermal communication with one or more heat exchangers of the thermoelectric assembly or system. Shunts described herein can also be electrically conductive and in electrical communication with the one or more thermoelectric materials so as to also allow electrical current to flow from one portion of the shunt to another portion of the shunt (e.g., thereby providing electrical communication between multiple thermoelectric materials or elements). Heat exchangers (e.g., tubes and/or conduits) can be in thermal communication with the one or more shunts and one or more working fluids of the thermoelectric assembly or system. Various configurations of one or more shunts and one or more heat exchangers can be used (e.g., one or more shunts and one or more heat exchangers can be portions of the same unitary element, one or more shunts can be in electrical communication with one or more heat exchangers, one or more shunts can be electrically isolated from one or more heat exchangers, one or more shunts can be in direct thermal communication with the thermoelectric elements, one or more shunts can be in direct thermal communication with the one or more heat exchangers, an intervening material can be positioned between the one or more shunts and the one or more heat exchangers). Furthermore, as used herein, the words “cold,” “hot,” “cooler,” “hotter” and the like are relative terms, and do not signify a particular temperature or temperature range. 
     Certain embodiments described herein provide a thermoelectric power generating (TEG) system comprising at least one thermoelectric subsystem and at least one heat exchanger (or portion thereof) in thermal communication with the at least one thermoelectric subsystem. 
     For example, the at least one thermoelectric subsystem can comprise at least one “cartridge-based thermoelectric system” or “cartridge” with at least one thermoelectric assembly  10  or at least one thermoelectric system as disclosed in U.S. Pat. Appl. Publ. No. 2013/0104953, which is incorporated in its entirety by reference herein. The cartridge is configured to apply a temperature differential across an array of thermoelectric elements  30 ,  40  of the cartridge in accordance with certain embodiments described herein. FIG. 6B of U.S. Pat. Appl. Publ. No. 2013/0104953 illustrates a perspective cross-sectional view of an example cartridge compatible with certain embodiments described herein. The cartridge of this figure includes an anodized aluminum “cold side” tube or conduit which is in thermal communication with a plurality of thermoelectric elements and a plurality of “hot side” heat transfer assemblies in thermal communication with the plurality of thermoelectric elements, such that a temperature differential is applied across the thermoelectric elements. As described in U.S. Pat. Appl. Publ. No. 2013/0104953 regarding certain configurations, the “hot side” heat transfer assemblies can have a first working fluid (e.g., gas or vapor) flowing across the “hot side” heat transfer assemblies and the “cold side” tube can have a second working fluid (e.g., water) flowing through it. 
     In certain embodiments, the at least one heat exchanger comprises at least one heat pipe or at least one thermosyphon. For example, the at least one heat pipe or at least one thermosyphon can replace the “cold side” tube of the cartridge of FIG. 6B of U.S. Pat. Appl. Publ. No. 2013/0104953. As used herein, the term “heat pipe” has its broadest reasonable interpretation, including but not limited to a device that contains a material in a first phase (e.g., a liquid) that is configured (i) to absorb heat at a first position within the device and to change (e.g., evaporate) into a second phase (e.g., gas or vapor) and (ii) to move while in the second phase from the first position to a second position within the device, (iii) to emit heat at the second position and to change back (e.g., condense) into the first phase, and (iv) to return while in the first phase to the first position. As used herein, the term “thermosyphon” has its broadest reasonable interpretation, including but not limited to a device that contains a material (e.g., water) that is configured (i) to absorb heat at a first position within the device, (ii) to move from the first position to a second position within the device, (iii) to emit heat at the second position. For example, the material within the thermosyphon can circulate between the first position and the second position passively (e.g., without being pumped by a mechanical liquid pump) to provide convective heat transfer from the first position to the second position. In certain embodiments, the at least one heat exchanger can utilize gravity or can otherwise be orientation-dependent. In certain embodiments, the at least one heat exchanger does not comprise any moving parts (except the material moving between the first and second positions), and can be characterized as providing passive energy transfer or heat exchange. 
     TEG Portion and HEX Portion 
       FIGS. 1A and 1B  schematically illustrate example TEG systems in accordance with certain embodiments described herein. The TEG system  100  comprises a thermoelectric subsystem (e.g., a TEG portion  13  such as one or more TE cartridges) and a heat exchanger (HEX) portion  15  (e.g., in fluidic communication with the TEG portion  13 , in thermal communication with the TEG portion  13 , or both). In some embodiments, the example TEG systems  100  of  FIGS. 1A and 1B  also comprise at least one valve  17  that can allow flow of at least a portion of the first working fluid (e.g., gas as indicated by arrow  19 ) through the TEG portion  13 , with any remaining portion of the first working fluid (as indicated by arrow  21 ) flowing through a bypass  23  as discussed in accordance with certain embodiments herein. 
     In some embodiments, a TEG system  100  is provided that comprises at least one thermoelectric assembly  10  (e.g., at least one TEG portion  13  such as one or more TE cartridges as disclosed in U.S. Pat. Appl. Publ. No. 2013/0104953). The at least one thermoelectric assembly  10  comprises at least one first heat exchanger  50  in thermal communication with at least a first portion of a first working fluid (e.g., hot-side fluid, gas, vapor as indicated by arrow  19 ). The first portion of the first working fluid flows through the at least one thermoelectric assembly  10 . The at least one thermoelectric assembly  10  further comprises a plurality of thermoelectric elements  30 ,  40  (e.g., n-type and/or p-type) in thermal communication with the at least one first heat exchanger  50 . The at least one thermoelectric assembly  10  further comprises at least one second heat exchanger (e.g., thermally conductive conduit or tube  102  and/or shunts  110 ) in thermal communication with the plurality of thermoelectric elements  30 ,  40  and with a second working fluid (e.g., cold-side fluid, gas, vapor, water) flowing through the at least one thermoelectric assembly  10 . The second working fluid is cooler than the first working fluid. The TEG system  100  further comprises at least one heat exchanger portion  15  configured to have at least some of the first portion of the first working fluid flow through the at least one heat exchanger portion  15  after having flowed through the at least one thermoelectric assembly  10 . The at least one heat exchanger portion  15  is configured to recover heat from the at least some of the first portion of the first working fluid as discussed below. 
     In some embodiments, the at least one thermoelectric assembly  10  (e.g., the at least one TEG portion  13 ) can be located in a region having a high temperature differential between the first working fluid and the environment of the at least one thermoelectric assembly  10 , thereby providing a high thermoelectric efficiency. The at least one heat exchanger portion  15  can be in fluidic communication with the TEG portion  13  (e.g., downstream of the TEG portion  13 ) and dedicated to a particular use of the heat of the first working fluid that is not converted into electricity by the TEG portion  13 . 
     For example, as schematically illustrated by  FIG. 1A , the at least one thermoelectric assembly  10  may not convert all of the heat of the first working fluid (e.g., exhaust gas, hot fluid, first working fluid as indicated by arrow  19 ) into electricity, so the at least some of the first working fluid flowing out of the at least one thermoelectric assembly  10  and through the at least one heat exchanger portion  15  can be used by the at least one heat exchanger portion  15  for a particular purpose. The at least one thermoelectric assembly  10  may only be able to effectively convert “high quality” or “high temperature” heat of the first working fluid into electricity, so the “low quality” or “low temperature” heat that is not converted can be utilized for a particular purpose by the at least one heat exchanger portion  15 , resulting in an overall increase of efficiency. In some embodiments, the at least one thermoelectric assembly  10  is configured to convert high-temperature heat of the first working fluid to electricity such that low-temperature heat of the first working fluid is received by the at least one heat exchanger portion  15 . For example, the heat extracted from the first working fluid by the at least one thermoelectric assembly  10  can be less than or equal to a predetermined percentage (e.g., 40%, 50%, 60%, 70%) of the total amount of extractable or usable heat carried by the first working fluid to the at least one thermoelectric assembly  10 , and the at least one heat exchanger portion  15  can be configured (e.g., optimized) to utilize (e.g., extract) some or all of the remaining portion (e.g., 60%, 50%, 40%, 30%) of the total amount of extractable or usable heat carried by the first working fluid to the at least one thermoelectric assembly  10 ). 
     As another example, as schematically illustrated by  FIG. 1B , under certain conditions (e.g., having a first working fluid comprising a relatively low temperature exhaust gas, such as at start-up of an engine), at least a portion of the first working fluid (as indicated by arrow  21 ) can be diverted from flowing through the at least one thermoelectric assembly  10  (which may not be efficient at these conditions) but can be directed to the at least one heat exchanger portion  15  (e.g., via a bypass conduit  23 ) which receives and uses the first working fluid for a particular purpose. 
     Thus, the TEG system  100  can be configured to provide electrical power generation with high efficiency, and/or to provide recuperation (e.g., recovery) of the residual (e.g., low quality or low temperature) heat with high efficiency. In certain embodiments, the particular purpose for which the at least one heat exchanger portion  15  can use the low quality or low temperature heat can comprise recovering heat and applying it to other portions of the engine. In some embodiments, the first working fluid of the TEG system  100  comprises exhaust gas from an engine, and the at least one heat exchanger portion  15  is further configured to use recovered heat to warm at least one of an engine block of the engine, a catalytic converter of the engine, or a passenger compartment (e.g., cabin) of a vehicle. For example, at least a portion of the recovered heat can be put into the cooling system of an engine to achieve faster heating of the engine block at start-up (e.g., to warm up the oil lubrication system sooner) and/or at least a portion of the recovered heat can be put into the emission system to achieve faster heating or engagement of the catalytic converter to reach the “light-off” temperature sooner after start-up, thereby reducing overall emissions and/or at least a portion of the recovered heat can be used to improve the thermal comfort of the cabin to the driver and passengers of a vehicle. In certain such embodiments, the at least one heat exchanger portion  15  can comprise a first conduit through which the at least some of the first portion of the first working fluid flows and a second conduit through which at least a portion of the second working fluid flows. The second conduit can be in thermal communication with the first conduit such that the portion of the second working fluid receives heat from the at least some of the first portion of the first working fluid. In certain embodiments, the at least one thermoelectric assembly  10  and the at least one heat exchanger  15  can both utilize the same second working fluid. 
     As illustrated and disclosed with respect to  FIGS. 1A and 1B , in some embodiments, the TEG system  100  further comprises at least one bypass conduit  23  and at least one valve  17 . The at least one valve  17  is configured to selectively allow at least the first portion of the first working fluid (as indicated by arrow  19 ) to flow through the at least one first heat exchanger  50  and to selectively allow at least a second portion of the first working fluid (as indicated by arrow  21 ) to flow through the bypass conduit  23 . In some embodiments, as illustrated in  FIG. 1B , the at least one heat exchanger portion  15  is configured to receive at least some of the second portion of the first working fluid after having flowed through the at least one bypass conduit  23  and to recover heat from the at least some of the second portion of the first working fluid. For example, in some embodiments, a portion of at least one heat exchanger portion  15  can be in fluidic and/or thermal communication with the bypass conduit  23 . 
     While the example TEG systems  100  of  FIGS. 1A and 1B  have the at least one valve  17  positioned upstream of the at least one thermoelectric assembly  10  and the at least one heat exchanger portion  15 , other embodiments can have the at least one valve  17  positioned downstream of the at least one thermoelectric assembly  10  and the at least one heat exchanger portion  15  or between the at least one heat exchanger portion  15  and the at least one thermoelectric assembly  10 . The at least one valve  17  can comprise one or more valves selected from the group consisting of a multi-port valve and a proportional valve. The at least one valve  17  can determine whether the at least one thermoelectric assembly  10  only is engaged (e.g., the first working fluid flows through the at least one thermoelectric assembly  10  but not through the at least one heat exchanger portion  15 ), the at least one heat exchanger portion  15  only is engaged (e.g., the first working fluid flows through the at least one heat exchanger portion  15  but not through the at least one thermoelectric assembly  10 ), or both the at least one thermoelectric assembly  10  and the at least one heat exchanger portion  15  are engaged (e.g., the first working fluid flows through both the at least one thermoelectric assembly  10  and the at least one heat exchanger portion  15 ). The at least one heat exchanger portion  15  can be engaged with the at least one bypass conduit  23 , in addition to being engaged to the primary gas flow (as indicated by arrow  19 ), as schematically illustrated by  FIG. 1B . 
       FIG. 2  schematically illustrates another example TEG system  100  in accordance with certain embodiments described herein. In some embodiments, the TEG system  100  comprises at least one second heat exchanger portion  25  (e.g., located upstream of the at least one thermoelectric assembly  10 ) configured to have at least the first portion of the first working fluid (as indicated by arrow  19 ) flow through the at least one second heat exchanger portion  25  prior to flowing through the at least one thermoelectric assembly  10 . The at least one second heat exchanger portion  25  can be configured to reduce a temperature of the first portion of the first working fluid. 
     For example, as illustrated in  FIG. 2 , the at least one second heat exchanger portion  25  is located upstream of the at least one thermoelectric assembly  10  in order to decrease the temperature of the flowing first working fluid as indicated by arrow  19  prior to flowing through the at least one thermoelectric assembly  10  (e.g., for applications in which the temperature of the first working fluid would be too high for the TE materials of the at least one thermoelectric assembly  10 ). Possible advantages of such an example TEG system  100  include, but are not limited to, protection of the TE material or elements from overheating (e.g., excessive temperatures), electrical power generation with high efficiency, and/or recuperation of the residual heat with high efficiency. 
     A method  300  for generating electricity according to certain embodiments described herein is illustrated in the flow diagram of  FIG. 12 . While the method  300  is described below by referencing the structures described above, the method  300  may also be practiced using other structures. In an operational block  310 , the method  300  comprises receiving at least a portion of a first working fluid. In an operational block  320 , the method  300  further comprises flowing the first portion of the first working fluid through at least one thermoelectric assembly  10  and converting at least some heat from the first portion of the first working fluid to electricity. In an operational block  330 , the method  300  further comprises receiving at least some of the first portion of the first working fluid after having flowed through the at least one thermoelectric assembly  10 . In an operational block  340 , the method  300  further comprises recovering at least some heat from the at least some of the first portion of the first working fluid (e.g., using the at least one heat exchanger portion  15 ). 
     In some embodiments, converting at least some heat from the first portion of the first working fluid to electricity comprises converting high-temperature heat from the first working fluid to electricity. Further, recovering at least some heat from the at least some of the first portion of the first working fluid comprises recovering low-temperature heat of the first working fluid. 
     In some embodiments, the method  300  of generating electricity further comprises selectively allowing at least the first portion of the first working fluid to flow through the at least one thermoelectric assembly  10  and selectively allowing at least a second portion of the first working fluid to not flow through the at least one thermoelectric assembly  10  (e.g., through at least one bypass conduit  23 ). 
     In some embodiments, the first working fluid comprises an exhaust gas from an engine and the method further comprises using the recovered heat to warm at least one of an engine block of the engine and a catalytic converter of the engine. 
     In some embodiments, the method  300  of generating electricity further comprises reducing a temperature of the first portion of the first working fluid prior to flowing through the at least one thermoelectric assembly  10  (e.g., using at least one second heat exchanger portion  25 ). 
     Temperature-Activated Heat Exchanger 
     Regarding the overheating protection, in TEG operation, there is often a limit to the temperatures that the TE material can withstand. Unfortunately, in extreme situations, the exhaust gas temperatures can be excessive and can cause the TE surface temperature to exceed its limit unless it is regulated. To prevent the TE material from overheating, some or all of the exhaust flow can be bypassed (e.g., be directed away) from the TE material. However, such an embodiment may bypass more potentially valuable heat than is necessary or desirable. For example, all of the heat may be bypassed when the flow is bypassed, as opposed to just the high quality or high temperature heat. 
     In certain embodiments described herein, the TE surface temperature can be controlled by dissipating the excessive heat prior to entering the at least one thermoelectric assembly  10 . The remainder of the heat in the exhaust flow could then continue into the at least one thermoelectric assembly  10 , thereby preventing the unnecessary bypass of valuable heat. 
     Certain embodiments described herein advantageously only dissipate heat when there is an excess amount of heat.  FIGS. 3 and 4  schematically illustrate cross-sectional view of example heat exchanger portions  26  in accordance with certain embodiments described herein. The heat exchanger portion  26  can be located upstream from the at least one thermoelectric assembly  10  and in series with at least one thermoelectric assembly  10  (e.g., the first working fluid flows through the heat exchanger portion  26  prior to flowing through the at least one thermoelectric assembly  10 ). For example, the at least one heat exchanger portion  25  described above can comprise the heat exchanger portion  26 . In certain embodiments, the heat exchanger portion  26  can dissipate relatively little heat at low temperatures, can use heat pipe technology to be activated at higher temperatures to dissipate excess heat without bypassing valuable flow, and can be a passive way to provide TEG overtemperature or overheating protection.  FIGS. 3 and 4  schematically illustrate some example embodiments and do not represent all of the related embodiments that could be employed in accordance with certain embodiments described herein. Furthermore, the heat exchanger portion  26  can be used in a TEG system that also includes the structures described above with regard to  FIGS. 1A, 1B, and 2 . 
     As schematically illustrated in  FIG. 3 , the heat exchanger portion  26  can comprise a central region  19  (e.g., conduit) and at least one heat pipe  27  (e.g., a first annular region concentric with the central region  19 ). The central region  19  can be configured to allow the exhaust gas to flow through (e.g., in a direction generally perpendicular to the plane of the cross-sectional view in  FIG. 3 ). The at least one heat pipe  27  can be configured to contain a high-temperature fluid  31 . An inner wall  33  of the heat pipe  27  can be in thermal communication with the exhaust gas and an outer wall  35  of the heat pipe  27  can be in thermal communication with an outer region  21  (e.g., a second concentric annular region bounded by a second conduit, as schematically illustrated in  FIG. 3 ). The high-temperature fluid  31  can be configured to undergo evaporation at the inner wall  33  (e.g., in thermal communication with the exhaust gas at a first temperature) and can be configured to undergo condensation at the outer wall  35  (e.g., in thermal communication with the outer region  21  at a second temperature less than the first temperature). 
     For example, the outer region  21  (e.g., the second concentric annular region bounded by the second conduit) can be configured to allow a coolant (e.g., gas or liquid) to flow through (e.g., in a direction generally perpendicular to the plane of the cross-sectional view in  FIG. 3 ). While  FIG. 3  shows the central region  19 , the heat pipe  27 , and outer region  21  being generally circular and generally concentric with one another, other shapes and configurations (e.g., non-concentric) are also compatible with certain embodiments described herein. In other embodiments, the outer region  21  can comprise a heat sink (e.g., a device that dissipates at least a portion of the heat from the high-temperature fluid). 
     In certain embodiments, the heat pipe  27  can be used to provide a temperature-activated heat exchanger. The evaporator portion of the heat pipe or thermal plane could work above a certain temperature (e.g., 700 C), for example, using one or more high-temperature heat pipe fluids  31 , such as Li, Na, K, and Cs, which are known in the art. In certain embodiments, at low temperatures (e.g., before the high temperature condition is reached), the heat transfer is poor, based on natural convection of the high-temperature fluid. Once activated, the heat exchanger portion  26  of certain embodiments can use the high heat transfer capability of boiling and condensing to transfer heat. For example, heat transfer coefficients can go up by a factor of 100 from the low temperature regime to the high temperature regime. 
       FIG. 4  schematically illustrates a cross-sectional view of another example heat exchanger portion  26  in accordance with certain embodiments described herein. The at least one heat pipe  27  can extend from the central region  19  containing the exhaust gas to the outer region  21  containing the coolant or heat sink. For example, a first portion  37  of the at least one heat pipe  27  can be in thermal communication with the exhaust gas and a second portion  39  of the at least one heat pipe  27  can be in thermal communication with the coolant or heat sink. A region  41  between the central region  19  and the outer region  21  can be substantially thermally insulating (e.g., can contain gas or air), or can contain another material. In certain embodiments, the at least one heat pipe  27  can comprise one or more generally cylindrical heat pipes (e.g., a series of cylindrical heat pipes), while in certain other embodiments, the at least one heat pipe can comprise one or more generally planar heat pipes extending along the axis of the heat exchanger portion  26  (e.g., along a direction generally perpendicular to the cross-sectional view of  FIG. 4 ). 
     Protecting Temperature-Sensitive Components 
       FIGS. 5A and 5B  schematically illustrate two example TEG systems  100  comprising temperature-sensitive components in accordance with certain embodiments described herein. In some embodiments, the TEG system  100  can comprise at least one valve  17  that comprises at least one component that is sensitive to high temperatures, and the at least one component is in thermal communication with the second working fluid (e.g., flowing through a coolant circuit  51  of the TEG system  100 ). In certain embodiments, the TEG system  100  takes advantage of available colder surfaces (e.g., due to the presence of a coolant circuit  51  configured to have the second working fluid flow therethrough) in order to protect temperature-sensitive components (e.g., temperature-sensitive valve sub-components, such as the actuator  53  and the electronics  55 ). The temperature-sensitive components can be used to move, control or actuate the at least one valve  17  or a drive shaft or flexible wire  57  connected to the valve  17 . For example, the TEG system  100  can keep such temperature-sensitive components below a predetermined temperature (e.g., below 150 C). In certain embodiments, the TEG system  100  can comprise a phase-change material located between the coolant circuit  51  and the temperature-sensitive components (e.g., electronics  55 ) to further protect against temperature spikes. Having the at least one valve  17  in thermal communication with the coolant circuit  51  can be used in a TEG system  100  that also includes one or more of the structures described above with regard to  FIGS. 1-4 . 
     Thermoelectric Assemblies Integrated into a Muffler 
     In certain embodiments, the TEG system  100  can integrate at least one thermoelectric assembly  10  with acoustic dampening components (e.g., mufflers).  FIG. 6  schematically illustrates an example TEG system  100  comprising at least one thermoelectric assembly  10  (e.g., one or more cartridges) integrated into a muffler  59 , in accordance with certain embodiments described herein. In some embodiments, the first working fluid of such a TEG system  100  comprises exhaust gas  75  from an engine as discussed above. The at least one thermoelectric assembly  10  is integrated into at least one muffler  59  of the engine exhaust system. For example, the at least one thermoelectric assembly  10  can be positioned between two muffler baffles  61 ,  63 , and additional muffler chambers can be used to achieve the desired acoustic performance. In certain embodiments, the at least one thermoelectric assembly  10  can be positioned in a first chamber (e.g., inlet chamber  65 ) to reduce temperature loss before the at least one thermoelectric assembly  10 . The gas can stream into the first chamber through a perforation field  67  (see, e.g.,  FIG. 6 ) or directly into the first chamber. An additional deflecting plate could be used to get a homogeneous flow distribution to the at least one thermoelectric assembly  10 . The gas can stream out of the muffler  59  through a second chamber (e.g., outlet chamber  66 ). 
       FIG. 7  schematically illustrates another example TEG system  100  comprising at least one thermoelectric assembly  10  (e.g., one or more cartridges) integrated into a muffler  59 , in accordance with certain embodiments described herein. The TEG system  100  comprises at least one spring-forced valve  69  (e.g., having mechanical control) between the chambers (e.g., at the inner baffle  63  of the muffler) which is configured to open at a predetermined condition (e.g., the maximum mass flow/temperature conditions) to allow the exhaust gas to bypass the at least one thermoelectric assembly  10  and to avoid overheating of the at least one thermoelectric assembly  10 . The at least one valve  69  can be tuned appropriately be selection of the spring force and the cross-sectional area through which exhaust gas can flow. For example, these parameters can be selected based on system-level constraints or requirements such as the maximum engine back-pressure and the exhaust gas flow rate at which the maximum engine back-pressure is to occur. 
       FIG. 8  schematically illustrates another example TEG system  100  comprising at least one thermoelectric assembly  10  (e.g., one or more cartridges) integrated into a muffler  59 , in accordance with certain embodiments described herein. The TEG system  100  can be configured to protect various components, such as the electrical cables  71  and coolant (e.g., water) pipes  73 , against environment conditions and to have them covered to avoid damage caused by any other objects. In certain embodiments, the cabling and tubing are not visible from outside the muffler  59 . In certain embodiments, the TEG system  100  can comprise acoustic material downstream of the at least one thermoelectric assembly  10 . Other benefits can include, but are not limited to, lower temperatures of the acoustic material, lower flow velocities, and the potential to use lower cost and weight canning/shell (e.g., plastic versus metal) due to the lower temperatures. Integration of the at least one thermoelectric assembly  10  with a muffler as described above can be used in a TEG system  100  that also includes one or more of the structures described above with regard to  FIGS. 1-5 . 
     Multiple-Shell Muffler 
       FIG. 9A  schematically illustrates an example TEG system  100  comprising a multiple-shell muffler  77  in which an inner shell  79  contains at least one thermoelectric assembly  10  (e.g., one or more cartridges) and an outer shell  81  contains components (e.g., electrical cables, coolant pipes, tubes, or conduits), portions of which are outside the inner shell  79  and that are to be protected, in accordance with certain embodiments described herein.  FIG. 9C  schematically illustrates a cross-sectional view of the example TEG system  100  of  FIG. 9A  in the plane indicated by arrows. Certain embodiments advantageously integrate multiple functions into the shells of the muffler  77 . One or all of the muffler shells can be a stamped part so that the geometry can be design flexible. 
     In certain embodiments, the inner shell  79  contains or carries the at least one thermoelectric assembly  10  and the outer shell  81  (e.g., cover shell) contains, supports, and protects the electrical cables and coolant (e.g., water) pipes. For a controlled routing of the pipes and their fixation, the shell design can be formed accordingly. Various configurations are also compatible with certain embodiments described herein. For example, the TEG system  100  can comprise an inner shell  79  for the at least one thermoelectric assembly  10  and inner baffles that can provide the desired acoustic reduction. A catalytic converter can be integrated into the inner shell  79  (e.g., upstream of the at least one thermoelectric assembly). The TEG system  100  can comprise a first (e.g., inner) shell  79  for the TE cartridges, a second shell containing a thermal insulation material  83 , and a third (e.g., outer) shell  81  containing the electrical cabling and coolant (e.g., water) routing. 
     Coolant channels can be formed into the half-shell design without separate coolant tubing.  FIG. 9B  schematically illustrates an example TEG system  100  in which coolant (e.g., water) routing is integrated into the multiple-shell muffler  77 , in accordance with certain embodiments described herein. The TEG system  100  can comprise an inner shell  79 , a middle shell  83 , and an outer shell  81 . In certain embodiments, the coolant (e.g., water) routing is in the outer shell  81  (e.g., between the middle shell  83  and the outer shell  81 ), and the electrical cables  89  are routed in the middle shell  83  (e.g., between the middle shell  83  and the inner shell  79 ) or on the surface of the middle shell  83 . In some embodiments, the coolant enters through one or more inlets  85  and exits through one or more outlets  87  in the outer shell  81 . Certain embodiments further comprise an insulation mat  91  between the cartridge support shell (e.g., inner shell  79 ) and the middle shell  83 . The insulation mat  91  can provide one or more of the following functions: (i) heat protection of the cables  89  and the coolant conduit (e.g., manifold  93 ); (ii) noise reduction of the muffler to the environment; (iii) reduction of the outer surface temperature; and (iv) reduction of thermal losses. The multiple-shell muffler can be used in a TEG system  100  that also includes one or more of the structures described above with regard to  FIGS. 1-8 . 
     Integration of Bypass and Helmholtz Resonator 
       FIG. 10  schematically illustrates an example TEG system  100  comprising a bypass  103 , at least one thermoelectric assembly  10 , and at least one Helmholtz resonator  105 . Helmholtz resonators are often used in of exhaust systems, in order to dampen low frequency engine noises, or to mitigate noise peaks at specific frequencies. The bypass  103  can be designed in order to act as a Helmholtz resonator when the valve  107  is closed (e.g., by adding an expansion chamber). The large volume of air in the chamber can serve as the spring and the air in the neck can serve as the oscillating mass. The working fluid  75  (e.g., exhaust, air) can enter through an inlet  78  and exit through an outlet  80  as indicated by the arrows. The at least one Hemholtz resonator  105  can be used in a TEG system  100  that also includes one or more of the structures described above with regard to  FIGS. 1-9 . 
     Valve to Control Mass Flow 
       FIG. 11  schematically illustrates an example TEG system  200  in accordance with certain embodiments described herein. In some embodiments, the TEG system  200  comprises at least one thermoelectric assembly  10  (e.g., TEG device, cartridge). The TEG system  200  further comprises a first flow path (indicated by arrows  203 ) with a first flow resistance. The first flow path  203  is through the at least one thermoelectric assembly  10 . The TEG system  200  further comprises a second flow path (indicated by arrows  205 ) with a second flow resistance lower than the first flow resistance. The second flow path bypasses the at least one thermoelectric assembly  10 . The TEG system  200  further comprises at least one valve  201  (e.g., flap valve, proportional valve, three-way valve) configured to vary a first amount of a working fluid (e.g., exhaust) flowing along the first flow path and a second amount of the working fluid flowing along the second flow path. 
     For example, the at least one valve  201  can be controlled to vary the first amount (e.g., fraction) of the working fluid to be any value between zero and 100% of the total amount of working fluid flowing through the TEG system  200  (e.g., 0%, 5%, 10%, 15%, 20%, 25%, 30%, 40%, 50%, 60%, 70%, 75%, 80%, 85%, 90%, 95%, 100%). The at least one valve  201  can be controlled to vary the second amount (e.g., fraction) of the working fluid to be any value between zero and 100% of the total amount of working fluid flowing through the TEG system  200  (e.g., 0%, 5%, 10%, 15%, 20%, 25%, 30%, 40%, 50%, 60%, 70%, 75%, 80%, 85%, 90%, 95%, 100%). 
     In some embodiments, the at least one thermoelectric assembly  10  is integrated into a muffler of an engine exhaust system, in accordance with certain embodiments described herein. In certain embodiments, the TEG system  200  can be designed in order to ensure 100% mass flow through the bypass (e.g., second flow path) when the valve  201  is open. 
     In some embodiments, the TEG system  200  further comprises at least one conduit  207  comprising at least one wall portion  209  having a plurality of perforations  211 . The first flow path extends through the plurality of perforations  211 . In some embodiments, the at least one conduit  207  further comprises an inlet  213  and an outlet  215 , and the at least one valve  201  is between the inlet  213  and the outlet  215   
     In some embodiments, the at least one wall portion  209  comprises a first wall portion  209 A with a first plurality of perforations  211 A and a second wall portion  209 B with a second plurality of perforations  211 B. The at least one valve  201  is positioned between the first wall portion  209 A and the second wall portion  209 B. The first flow path extends through the first plurality of perforations  211 A outwardly from the at least one conduit  207  and through the second plurality of perforations  211 B inwardly to the at least one conduit  207 . The second flow path does not extend through the first plurality of perforations  211 A and does not extend through the second plurality of perforations  211 B. 
     For example, a flow path can be designed for the TEG branch in which the back-pressure field is higher than the pressure field in the bypass when the at least one valve  201  is open. While  FIG. 11  schematically illustrates the first plurality of perforations  211 A and the second plurality of perforations  211 B, other structures (e.g., by introducing flow bends) may be used instead to cause the flow resistance in the TEG branch (e.g., first flow path) to be higher than the flow resistance in the bypass (e.g., the second flow path). The flow path can also be designed to use the flow momentum to increase the flow passage in the bypass pipe (e.g., by using a straight pipe) when the valve is closed. Certain embodiments advantageously provide and utilize a simpler and cost-effective flap valve, instead of a three-way valve. Certain embodiments described herein can use one or more passive (e.g., spring-actuated) valves or valves actuated by thermal wax actuators connected to the coolant circuit. The at least one valve  201  can be used in a TEG system  100  that also includes one or more of the structures described above with regard to  FIGS. 1-10 . 
     A method  400  for generating electricity according to certain embodiments described herein is illustrated in the flow diagram of  FIG. 13 . While the method  400  is described below by referencing the structures described above, the method  400  may also be practiced using other structures. In an operational block  410 , the method  400  comprises receiving a working fluid. In an operational block  420 , the method  400  further comprises selectively flowing at least a portion of the working fluid either along a first flow path having a first flow resistance or along a second flow path having a second flow resistance lower than the first flow resistance. The first flow path extends through at least one thermoelectric assembly  10  and the second flow path does not extending through the at least one thermoelectric assembly  10 . 
     In some embodiments, the first flow path extends through a plurality of perforations  211  of at least one wall portion  209  of at least one conduit  207 . 
     In some embodiments, the at least one wall portion  209  comprises a first wall portion  209 A with a first plurality of perforations  211 A and a second wall portion  209 B with a second plurality of perforations  211 B. The first flow path extends through the first plurality of perforations  211 A outwardly from the at least one conduit  207  and through the second plurality of perforations  211 B inwardly to the at least one conduit  207 . 
     Integrated Proportional Bypass Valve 
     Certain embodiments described herein provide a thermoelectric power generating (TEG) system  500  comprising at least one thermoelectric subsystem  509  (e.g., at least one thermoelectric assembly  10 ) and at least one bypass conduit  511 . The TEG system  500  further comprises at least one proportional valve  513  and is configured to receive a first working fluid (e.g., hot gas such as exhaust gas) from a source (e.g., an engine). The at least one proportional valve  513  is configured to controllably allow a first fraction of the first working fluid to flow in thermal communication with the at least one thermoelectric subsystem  509  and to controllably allow a second fraction of the first working fluid to flow through the at least one bypass conduit  511  such that the second fraction is not in thermal communication with the at least one thermoelectric subsystem  509 . For example, the at least one proportional valve  513  can be integrated into the TEG system  500 , the at least one bypass conduit  511  can be integrated into a main shell  515  of the TEG system  500 , and the TEG system  500  can have double-wall thermal insulation  517  (e.g., top and bottom walls) that provide thermal insulation of the at least one thermoelectric subsystem  509  from the environment. 
       FIG. 14  schematically illustrates at least some external features of an example TEG system  500  in accordance with certain embodiments described herein. The TEG system  500  can comprise a TEG main shell  515 , one or more inlets  503  configured to receive the first working fluid (e.g., exhaust gas), and one or more outlets  505  configured to output the first working fluid. The TEG system  500  can further comprise a cooling subsystem  507  (e.g., coolant circuit) configured to receive a second working fluid (e.g., coolant, water) that flows in thermal communication with the at least one thermoelectric subsystem  509 . For example, the cooling subsystem  507  can comprise one or more coolant conduits  519  configured to receive and output the second working fluid and one or more coolant manifolds  521  (e.g., one on each side of the TEG system  500 ) configured to distribute the second working fluid to and from the at least one thermoelectric subsystem  509 . The TEG system  500  can further comprise at least one valve actuator  523  in mechanical communication with the at least one proportional valve  513  and configured to control the at least one proportional valve  513 . In certain embodiments, the TEG system  500  can include some or all of the structures described above with regard to  FIGS. 1-11 . 
       FIGS. 15A and 15B  schematically illustrate at least some internal features of an example TEG system  500  in accordance with certain embodiments described herein. The TEG system  500  can comprise a double wall thermal insulation structure  517  that is configured to at least partially thermally isolate the at least thermoelectric subsystem  509  (e.g., at least one thermoelectric assembly  10 ) from the surrounding environment, from the at least one bypass conduit  511 , or both. The region between the two walls of the double-wall thermal insulation structure can contain a generally thermally insulative material. 
       FIGS. 16A-16C  schematically illustrate the at least one proportional valve  513  in three different positions in accordance with certain embodiments described herein. The at least one proportional valve  513  can comprise one or more movable structures (e.g., flap or flaps) configured to vary the entrance area of the at least one bypass conduit  511  through which the first working fluid can flow and to vary the entrance area of the thermoelectric subsystem  509  through which the first working fluid can flow. For example, the at least one proportional valve  513  can be controlled to vary the first fraction of the working fluid to be any value between zero and 100% of the received working fluid (e.g., 0%, 5%, 10%, 15%, 20%, 25%, 30%, 40%, 50%, 60%, 70%, 75%, 80%, 85%, 90%, 95%, 100%). The at least one proportional valve  513  can be controlled to vary the second fraction of the working fluid to be any value between zero and 100% of the received working fluid (e.g., 0%, 5%, 10%, 15%, 20%, 25%, 30%, 40%, 50%, 60%, 70%, 75%, 80%, 85%, 90%, 95%, 100%). In certain embodiments having a single bypass conduit  511  and a plurality of thermoelectric subsystems  509  (e.g., as shown in  FIGS. 14, 15A, and 15B ), the at least one proportional valve  513  (e.g., a single proportional valve) can be configured to direct a first portion of the first working fluid through the bypass conduit  511  and the remaining portion of the first working fluid through the thermoelectric subsystems  509 .  FIG. 16A  illustrates the at least one proportional valve  513  in a position that controls the flow such that 100% of the flow (indicated by arrows  525 ) is through the thermoelectric subsystem  509 .  FIG. 16B  illustrates the at least one proportional valve  513  in a position that controls the flow such that a fraction of the flow is through the thermoelectric subsystem  509  and the remaining fraction is through the bypass conduit  511 .  FIG. 16C  illustrates the at least one proportional valve  513  in a position that controls the flow such that 100% of the flow is through the bypass conduit  511 . 
     As discussed in accordance with other embodiments above, the at least one thermoelectric subsystem  509  can comprise at least one “cartridge-based thermoelectric system” or “cartridge” with at least one thermoelectric assembly or at least one thermoelectric system as disclosed in U.S. Pat. Appl. Publ. No. 2013/0104953 which is incorporated in its entirety by reference herein. The thermoelectric subsystem  509  can be configured to apply a temperature differential across an array of thermoelectric elements of the thermoelectric subsystem  509  in accordance with certain embodiments described herein. For example, FIG. 6B of U.S. Pat. Appl. Publ. No. 2013/0104953 illustrates a perspective cross-sectional view of an example cartridge of the thermoelectric subsystem  509  compatible with certain embodiments described herein. The cartridge of this figure can include an anodized aluminum “cold side” tube which is in thermal communication with a plurality of thermoelectric elements, and a plurality of “hot side” heat transfer assemblies in thermal communication with the plurality of thermoelectric elements, such that a temperature differential is applied across the thermoelectric elements. As described in U.S. Pat. Appl. Publ. No. 2013/0104953 regarding certain configurations, the “cold side” tube can have a first working fluid (e.g., water) flowing through it, and the “hot side” heat transfer assemblies can have a second working fluid (e.g., gas or vapor) flowing across the “hot side” heat transfer assemblies. The at least one proportional valve  513  can be used in a TEG system  100  that also includes one or more of the structures described above with regard to  FIGS. 1-11 . 
     Discussion of the various embodiments herein has generally followed the embodiments schematically illustrated in the figures. However, it is contemplated that the particular features, structures, or characteristics of any embodiments discussed herein may be combined in any suitable manner in one or more separate embodiments not expressly illustrated or described. In many cases, structures that are described or illustrated as unitary or contiguous can be separated while still performing the function(s) of the unitary structure. In many instances, structures that are described or illustrated as separate can be joined or combined while still performing the function(s) of the separated structures. 
     Various embodiments have been described above. Although the inventions have been described with reference to these specific embodiments, the descriptions are intended to be illustrative and are not intended to be limiting. Various modifications and applications may occur to those skilled in the art without departing from the spirit and scope of the inventions as defined in the appended claims.