Abstract:
A direct thermoelectric converter includes a condensing surface. The condensing surface conducts heat to a silicon matrix to cool the condensing surface to a temperature to precipitate a gas fraction from a flow of gas. The matrix includes a first layer of low recombination material fused to a first layer of high recombination material at a first n-type junction, the first layer high recombination material fused to a second layer of low recombination material at a p-type junction, the second layer of low recombination material fused to a second layer of high recombination material at a second n-type junction. Each of a positive and a negative terminal are affixed conductively to the silicon matrix thereby to supply a current of electrons at a supply voltage. A controller senses the current of electrons and selectively connects the direct thermoelectric converter to a load in response to the supply of electrons.

Description:
PRIORITY CLAIM 
       [0001]    This application claims the benefit of and priority to U.S. provisional application entitled “Gas Fraction Extractor Utilizing Direct Thermoelectric Converters”, having application Ser. No. 61/568,645, filed Dec. 8, 2011 and which is incorporated herein by reference in its entirety. 
     
    
     BACKGROUND OF THE INVENTION 
       [0002]    Extraction of selected portions from gas mixtures becomes cost-effective if cost of extraction can be reduced sufficiently. A prime example is water in the atmosphere, particularly valuable in regions where it is not readily available in liquid form. Direct Thermoelectric Converters (DTEC) can implement cost-effective extraction. The theory and construction of DTEC is described in provisional application entitled “Useful Electrical Power from Thermally Generated Carrier Pairs”, having application Ser. No. 61/381,984, filed Sep. 11, 2010, as well as the subsequent utility application claiming priority therefrom and having Ser. No. 13/397,404 and a filing date of Feb. 15, 2012, the pair of which are incorporated herein by reference in their entireties. 
         [0003]    Conventional means of gas fraction extraction rely upon cooling a surface for condensation through apparatus and methods such as heat pumps and generally described as ‘Refrigeration’. Refrigeration relies upon a working fluid as a circulating refrigerant such as Freon enters a compressor as a vapor. The vapor is compressed at constant entropy and exits the compressor superheated. The superheated vapor travels through the condenser which first cools and removes the superheat and then condenses the vapor into a liquid by removing additional heat at constant pressure and temperature. The liquid refrigerant goes through the expansion valve (also called a throttle valve) where its pressure abruptly decreases, causing flash evaporation and auto-refrigeration of, typically, less than half of the liquid. 
         [0004]    The flash evaporation upon expansion results in a mixture of liquid and vapor at a lower temperature and pressure. It is at this point that the resulting cold liquid-vapor mixture then travels through the evaporator coil or tubes, embedded in the condensing surface and heat removed from the ambient causes the liquid refrigerant to be completely vaporized by cooling the warm ambient air (from the space being refrigerated). As the ambient is directed, often by a fan across the condensing surface enveloping the evaporator coil or tubes, a condensate forms for collection as the ambient air is cooled below the phase change temperature, precipitating the gas fraction as liquid condensate. 
         [0005]    The resulting refrigerant vapor, on the other hand, returns to the compressor inlet to complete the thermodynamic cycle. Compression requires the provision of energy, often kinetic energy from a rotating shaft. Motors or internal combustion engines are frequently used to provide that rotary motion. As is clear, the refrigeration cycle, thus, relies upon some source of energy to drive the compressor. 
         [0006]    Often times, however, the requirement for this provision of energy is too cumbersome for the situation. Provision of water for persons in a harsh environment, such as provision for persons on a lifeboat, is one such situation where condensation by conventional means is too burdensome. Neither internal combustion engines nor electric power to drive motors may be available to drive the compressor. Yet, the condensation of water from the ambient air is necessary as it could provide humans, on board, with potable water. What the conventional art lacks is a self-contained device for removing gas fractions without requiring a refrigeration cycle to cool a condensing surface. Conventional art relies upon the energy to drive a compressor to condense water from the ambient air. 
       SUMMARY OF THE INVENTION 
       [0007]    Systems and methods for extracting gases by extraction of thermal energy from heat in ambient air are disclosed. As indicated above, the inventor has also invented and described the direct thermoelectric converter in an earlier application. 
         [0008]    By way of overview, the DTEC relies upon heat in the ambient environment to excite electrons into a flow of current. By relying upon the heat to drive a current, the DTEC uses known properties of semiconductor materials and the behavior of electrons and holes within these materials, along with a layered structure that creates channels for electrons. Heat pushes electrons through these channels, consuming the heat in the proximity of the semiconductors and yields a current of electrons available to drive any device such as a motor or a resistive heater. 
         [0009]    Extraction occurs at the semiconductors in one or more DTECs to create a chilled condensing region. A fan, compressor, chimney effect, or equivalent process, drives a gas mixture that is moved through the chilled region, to remove one or more gases, such as water vapor, by condensing it out of the gas mixture. The remaining gases may be exhausted or captured. Excess energy may be dumped into the exhaust stream as heat or used for other purposes such as evaporation or electrical power. In one preferred embodiment, the energy is used, in whole or in part, to turn the fan that drives the gas mixture through the chilled region. 
         [0010]    Invention is powered by heat within its source gas stream. Because the cooling of the gas mixture at the DTEC provides not only condensed gases but a current of electrons or electricity, without resorting to outside energy, the DTEC can also drive a processor which can manage one or more DTECs to perform operations to run the DTEC including the management of energy flow and conditions within the device. Exploitation of a processor is advantageous as failure to properly manage energy flow can quickly fill the device with solidified condensate (such as ice), impeding its operation. As it progresses, this condition can render the device inoperable without selective operation to remove the condensate (as detailed below). 
         [0011]    In one preferred embodiment, a processor repeatedly drives the DTEC in a control loop, sensing the presences and rate of formation of condensate. Exploiting the fact that when operated at lower condensing temperatures, more available gas such as water vapor will be extracted, the processor drives the DTEC to function at or near the boundary. In such a control loop, where the temperature or volume of condensate fall outside of optimal conditions, the processor shuts down the DTEC until the temperature rises or the volume is reestablished. Thus, in the preferred embodiment operation straddles an optimum condition which occurs when the DTEC operates close to failure while avoiding it, allow for cycles of failure and recovery, or defer that choice until time of use (as described below). 
         [0012]    The drawings depict a single non-limiting exemplary embodiment wherein the exemplary DTECs comprise materials that are unstable, for example at room temperature. In particular, Mercury Cadmium Telluride (HgCdTe) is sufficiently unstable to adversely affect device operating lifetimes. More broadly, peak performance for DTEC occurs when there is enough thermal energy to knock a substantial fraction of electrons free from their lattices, which tends to occur when the thermal energy is approaching breaking the lattices themselves. To protect against the effects of instability, the design of the example embodiment maintains the DTECs at a cryogenic temperature, even when the system is in storage. In other embodiments, alternative DTEC materials may be used that are more stable at the operating temperatures of the system. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0013]    Preferred and alternative examples of the present invention are described in detail below with reference to the following drawings: 
           [0014]      FIG. 1  depicts a mechanical overview of an exemplary gas fraction extractor; 
           [0015]      FIG. 2  shows an exemplary embodiment of an electrical system for an embodiment of a gas fraction extractor; 
           [0016]      FIG. 3  shows an electrical system for two units operating in parallel with allowances for freezing and thawing condensate; 
           [0017]      FIG. 4  illustrates the behavior of an electron in the presence of a Hole; 
           [0018]      FIG. 5  shows the operation of the DETC device as it turns heat into electricity; 
           [0019]      FIG. 6  illustrates more doped semiconductor materials; and 
           [0020]      FIG. 7  represents a common and easily recognizable package, commonly known as a “C” cell battery. 
       
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
       [0021]    An exemplary embodiment of a Gas Fraction Extractor is depicted in block diagram as including the elements shown in  FIG. 1 . In operation, the Gas Fraction Extractor relies upon heat and gas fractions, an input air stream supplies. The Input stream should be filtered ( 101 ) to prevent accumulation of debris and dust which would tend to insulate the condensation surfaces. For this reason, while optional, the presence of a filter is presently preferred. 
         [0022]    A fan or compressor  102  drives the gas flow into a condensing chamber. Within the condensing chamber  103 , the fan or compressor drives gas flow across condensing surfaces cooling the gas flow or, more accurately, leaving some of the thermal energy within the gas flow or within the condensing surface, generally by convection. 
         [0023]    While the gas flow heats one side of the condensing surfaces, the DTEC  105  removes the heat from the condensing surface from the opposite side. By extraction of thermal energy from the condensing surfaces  104 , the DTEC  105  continually cools the condensing surfaces while exciting a current of electrons. 
         [0024]    Advantageously, electrical power is produced by the DTEC  105  as heat is extracted by the DTEC  105 , and, once the energy of the extracted heat excites the electrons within the semiconductors, those electrons form the current motivated by the heat, and cooling of the condensing surfaces  104 . Temperature of DTEC  105  can be determined by monitoring power output or, alternatively, by direct measurement. Temperature of condensing surface may be monitored by temperature sensors such as thermocouples (not shown,  201 ). 
         [0025]    In one preferred embodiment, heat flow from condensing surface  104  to DTEC  105  may be controlled by operation of an optional thermal control  106 . Peltier devices are advantageously solid state and can be used bidirectionally, i.e. to either heat or cool the condensing surface. The Peltier effect creates a heat flux between the junction of two different types of materials in response to a current of electrons, i.e. electricity. A Peltier cooler, heater, or thermoelectric heat pump is a solid-state active heat pump which transfers heat from one side of the device to the other, with consumption of electrical energy, depending on the direction of the current. Such an instrument is also called a Peltier device, Peltier heat pump, solid state refrigerator, or thermoelectric cooler (TEC). They can be used either for heating or for cooling (refrigeration), although in practice the main application is cooling. It can also be used as a temperature controller that either heats or cools as that process is described here. 
         [0026]    Gas flow continues through and then exiting the condensing chamber  103 . Remembering that the gas flow as it exits is cooler than the ambient, in one embodiment, that gas flow is used to cool associated electronics  107 . 
         [0027]    In some further embodiments, to make the flow of electrons more consistent, excess energy must be dissipated. Such a purpose may be achieved by using a load resistor as a heat dump. Joule heating, also known as ohmic heating and resistive heating, is the process by which the passage of an electric current through a conductor releases heat. Selectively exposing a load resistor within a circuit allows the resistor to serve as a heat dump  108  dissipating excess energy. The cooled gas flow may advantageously flow across a heat dump  108  or load resistor to cool it as it exhausts any excess energy. There may be other load that can be advantageously included in the circuit to use the generated electricity. 
         [0028]    Condenser drain  109  captures the liquefied gas mixture fraction or fractions. Not show are any collection reservoirs as they are not necessary for operation. Nonetheless, in operation, presumably the captured liquids are either collected or conducted away for use. 
         [0029]    Gas Fraction Extractors may be put in series at successively lower operating temperatures to capture successively more fractions. 
         [0030]      FIG. 2  shows a simple exemplary electrical system to control the operation of a Gas Fraction Extractor. As discussed above, neither of the temperature sensor  201  nor the heat dump  108  are necessary, they are provided in this exemplary embodiment to describe an optimized single DTEC condenser. That preferred embodiment is a DTEC driven by controller  205  and including the following elements: 
         [0031]    A) The DTEC  105 , which feeds voltage (Sense 1 ) and current (measured by Rsense  206  and Sense 2 ) to Vsystem. 
         [0032]    B) Temperature sensor  201 , a thermocouple or other temperature sensor, mounted to the condensing surface of the thermal control  106  and used to monitor the surface temperature. 
         [0033]    C) Heat dump  108 , a resistor for dumping excess energy into the exhaust as heat. 
         [0034]    D) Rsense  206 , a current sensing resistor for monitoring the output current from the DTEC  105 . 
         [0035]    In operation, Vsystem voltage will vary with variations in ambient temperature and load as it is the current output of the DTEC  105  in operation. While the DTEC  105  in operation can provide an operating voltage, variations in power are not suitable for providing an operating voltage Vsystem, so it is passed through a regulator  203  to supply Vlogic, a constant voltage to power the controller  205 . At the controller, therefore, a constant voltage is provided and current flows through the regulator  203  in accord with current draw in operation of the controller  205 . 
         [0036]    At the controller  205 , voltages on opposite sides of a current sensing resistor, Rsense  206 , (voltages shown here as Sense 1  and Sense 2 ) are measured at the controller  205  to sense temperature. As stated by Ohm&#39;s Law, there is a voltage drop across any resistance when current is flowing. A current sensing resistor is designed for low resistance so as to minimize power consumption. As a result, the calibrated resistance senses the current flowing through it in the form of a voltage drop, which is detected and monitored by the control circuitry. In summary, current sensing resistors translate current into a voltage that is monitored by the controlled circuitry. Because the DTEC operates to directly convert thermal energy into a current of electrons, the current optional embodiment exploits the relation between temperature of the semiconductive material and the resulting flow of electrons to determine the actual temperature of the DTEC as the current passes through the current sensing resistor  206 . 
         [0037]    The controller  205 , typically a micro-controller, monitors Vswitched to determine the operating mode (storage or running). Based on these values, it sends control signals to the output control  204  to maintain DTEC  105  temperature and optimize performance. Controller  205  may also have means of indicating unit status to the user (not shown). 
         [0038]    An output control  204 , a transistor, relay, or other control device which is used to control the load portion, selectively exposes either or both of the heat dump  108  and the fan or compressor  102  in the manner to optimally exploit the flow of current in order to suitably control the temperature of the condensing surfaces and the output of the system. 
         [0039]    Switch  202  turns the entire system on and off. 
         [0040]      FIG. 3  shows an electrical system for two units operating side by side in a single enclosure, with separated gas streams. To configure two units for operation in this side-by-side mode allows for cycles of freezing and thawing condensate in a manner to achieve optimal condensate flow. In this exemplary embodiment, for illustrative purposes, the two units are designated as units ‘A’ and ‘B’. Drawing elements having reference numbers ending in either ‘a’ or ‘b’ are elements in use in the respective streams for units A and B. Sensing elements other than temperature are omitted for clarity. Descriptions of new elements are as follows: 
         [0041]    DTECs  105   a  and  105   b , which extract heat from their respective streams, providing power to respective power busses. In designed operation, peaks in current flow from Unit A will likely fall into troughs in current flow from Unit B and vice versa as each is operating in a controlled loop mode and intentionally offset from each other to exploit the presence of each. 
         [0042]    Naturally, there is an issue as to scale. In this exemplary embodiment, the DTEC units are selected to be adequate to power, and to drive the regulator  203  and controller  205 , i.e. the size and mode of each of the regulator  203  and controller  205  are selected, relative to DTEC units A and B, to consume negligible power relative to the capacity of DTEC  105   a , so its impact on operation is not significant. 
         [0043]    Heater A  303   a  is used in place of thermal control  106  in stream A. Heater B  303   b  is located in place of thermal control  106  in stream B. Each heater is a resister configured to cover as great a proportion of the condenser surface in the condenser chamber  103  as possible, much as an electrical rear window defroster is a number of fixed resistance wires also configured to span the rear window of an automobile. Directing a current through either heater  303   a  or  303   b  will warm the surface of its respective condensing chamber  103 . 
         [0044]    Controller  205  has separate channels to control heat dump  108   a /b, fan  102   a /b and heater A/B  303   a /b. In loop control operation, the controller will run one DTEC, in this instance Unit A  105   a  until such time as the unit will have a thin layer of frozen condensate across the condensing surface and the insulating effect of that layer is noted in operation of DTEC Unit A  105   a . At such a point, continued operation of DTEC Unit A  105   a  is less than optimal and the controller advantageously activates DTEC unit B  105   b  to begin to cool a flow of air, while DTEC Unit A  105   a  stops working in order to regain temperature from a combination of the ambient, and heater A  303   a . The controller  205  can selectively activate both of the DTEC units and the heater units, and in practice will alternate between them to keep the flow of both condensate and power relatively stable. 
         [0045]    In an exemplary embodiment, during thawing, blowing more of the warm ambient air through the condenser chamber  103  will cause more rapid thawing of the frozen condensate on the condenser surface. Where the ambient air temperature is closer to to the temperature of frozen condensate, a running fan might actually dissipate the warming effect the heaters impart and slowing or stopping the fan might be most advantageous to operation. Algorithms may be constructed to optimally use both the heater units  303   a ,  303   b  and a flow of ambient air to thaw the frozen condensate. Thus, in a preferred embodiment, a fan control  302  will allow for variable speed operation selecting which loads, fan  102  or heater  303  and in what proportions will optimally thaw the frozen condensate. 
         [0046]    Thaw control  304  turns the respective thawing heaters on or off (see below). This generally does not require finer control than on/off, however, these too may be configured as variable if experience determines variable heating to be advantageous. 
         [0047]    As described above, in this arrangement, power from one stream may be used to thaw the other. If stream A is to be thawed, then the following sequence would be followed: 
         [0048]    A) Remove all loads from DTEC  105   a . This will allow the DTEC to return to a warmer temperature. 
         [0049]    B) Apply power to heater A  303   a.    
         [0050]    C) If necessary, disable heat dump  108   b  to conserve available power. 
         [0051]    D) If necessary, slow fan  102   b  to minimize exhaust temperature. 
         [0052]    E) Maintain heating until temperature sensor  201   a  indicates thaw temperature reached. 
         [0053]    As shown in  FIG. 3 , the controller as shown, can activate and deactivate DTECs  105 , heaters  303 , fans  102  in any of multiple methods based upon the controller&#39;s  205  ability to determining operating conditions. For example, Rsense  206  may be used to calculate the temperature approximate of the DTEC  105 , as power output is a function of temperature. This calculation will be specific to the specific configuration of the DTEC  105  used in any given embodiment, but can be sensed once the relationship between that DTEC  105  and its characteristic output is known. By extension, the level of ice formation in the condensing chamber  103  may be estimated from the DTEC  105  temperature, and comparing against implementation-specific experimental data. As the condensing chamber  103  fills with ice, the insulating effect of the ice will result in a lower DTEC  105  temperature. 
         [0054]    As an alternative to the single cabinet solution shown in  FIG. 3 , a similar arrangement can be achieved by connecting single channel units in the field. Where a single controller module can be connected to each of a plurality of units, those units may be optimally configured to “kick in’ and “kick out” as appropriate. Still greater geometries can be imagined by exploiting the same principles that allow the combined pair to operate as a two-channel unit as required by field conditions (i.e., dew-point near or below freezing). In this configuration, only control data and power for thawing (before or after thaw control  304 ) would cross between units. The power busses themselves may function without being interconnected, should the current configuration be used as interconnection will prevent selective removing of the load from DTEC  105 . Alternatives, however, can readily be configured and in the presence of a more complex controller  205 , numerous field connections can be implemented using sensing technologies and controller options such as look up tables to drive dynamic configuration. 
         [0055]    For further understanding of the cooling process by use of a DTEC, further nonlimiting information is useful. Current in a DTEC is derived by receiving ambient heat at a semiconductor. This phenomenon is based upon:
       Defining the relevant behaviors of electrons   Describing the relevant behaviors of semiconductor materials   Showing how electrons move without channel restrictions   Showing the effect of channel restrictions   Showing the resulting channeled flow of electrons.       
 
         [0061]    The following definitions assist the reader in understanding the operation of DTEC operation. 
         [0062]    Atoms: All matter is made up of atoms, which consist of a central nucleus of neutrons and positively charged protons with negatively charged electrons in orbit around them. 
         [0063]    Bound Electrons: Electrons in their normal state are in orbit around a specific atom, and are bound to that atom by the electromagnetic pull of its nucleus. These are also known as valence electrons. 
         [0064]    Free Electrons: These are electrons that have disengaged from their place around an atom and are traveling on their own. The electricity moving through electrical wires or coming out of flashlight batteries, for example, is carried as Free Electrons. 
         [0065]    In metals, each atom almost always releases one or more electrons. In semiconductors, however, electrons disengage from atoms randomly, but at predictable rates based on the materials and their temperature. 
         [0066]    Holes: These are places in atoms that are left behind when Free Electrons break out of their places. A Hole A 1 , A 2 , A 3  ( FIG. 4 ) can be treated as if it, too, is a thing in movement across a matrix. Atoms “trade” Holes as they trade Bound Electrons. As an electron moves from one site in the matrix to a Hole, the former site becomes a Hole and where, in the matrix the electron then resides is filled and disappears as a Hole. If there is a Hole in atom ‘A 1 ’, a Bound Electron can move into it from atom ‘A 2 ’, leaving a Hole in atom ‘A 2 ’ that in turn can accept a Bound Electron from atom ‘A 3 ’ to fill its Hole. In effect, Holes also move around at the same time as Bound Electrons do. For example,  FIG. 4  illustrates the behavior of an electron in the presence of a Hole. 
         [0067]    Semiconductor: A semiconductor is a material, such as silicon, with electrical conductivity between an insulator (such as glass) and a conductor (such copper wire). Semiconductors are basic components of various electronic devices such as cell phones and computers. Electrons in semiconductors are normally bound to atoms. Sometimes electrons are knocked loose by heat, light or radiation producing Free Electrons. This “knocking loose” leaves behind a Hole where an atom is missing an electron. Free Electrons and Holes, thus created in pairs, separate and can each recombine later into other atoms in a continual process. 
         [0068]    Generation: In Semiconductor materials, as an electron is knocked loose, it and its matching Hole separate and wander around. The frequency of this Generation process depends upon the material and typically increases with temperature. 
         [0069]    Recombination: Free Electrons and Holes interact with each other to recombine. The rate at which Recombination takes place varies by material. In some materials it is a simple process and therefore faster while in others it is more complex and slower. For example, recombination is much faster in Gallium-Arsenide than in Silicon This difference in Recombination rates is a critical feature of the DTEC that we exploit to create different concentrations of Free Electrons and Holes. 
         [0070]    Junctions: A DTEC comprises layers of differently doped semiconductor materials. The region where layers having distinct semiconductor makeup meet forms a Junction, also referred to as a Heterojunction. Adjacent layers have different properties, including different or unequal Recombination rates. Free Electrons and Holes tend to move across a Junction from one material to the other and recombine at a predictable rate. Electrons and Holes generated in the Lower Recombination rate material also tend to move across the Junction to the Higher Recombination rate material before recombining. 
         [0071]    Electrons and Holes behave in this described manner simply because there are more opportunities to recombine in the Higher Recombination rate material. 
         [0072]    Doping: The Doping of Semiconductors adds an impurity to the material to change its electrical properties. It is used to either restrict or increase the movement of Free Electrons or Holes through a layer of material, effectively creating channels for Holes and Free Electrons. For example, Negative Doping (n-type) changes the material to add extra Free Electrons. This allows electrons to migrate from a Low Recombination material to a High Recombination material while blocking the flow of Holes. The effect is a net flow of electrons in that direction. Positive Doping (p-type) changes the material to have extra Holes and therefore it has the reverse effect on the movement. 
         [0073]    In  FIG. 5 , the operation of the DETC device is shown as it turns heat into electricity. Purposefully doping semiconductors to provide a predictable rate of Generation, movement and Recombination across junctions between the materials enables the effect to occur. The DTEC employs layers of Doped Semiconductor material arranged as shown in  FIG. 5 . With Positive (p-type) and Negative (n-type) Doped layers between the Low Recombination and High Recombination layers as shown, the circular flows confined to the layers are broken. What remains are:
       Free Electrons flowing from left to right (still from the Low to High Recombination layers); and   Holes flowing from right to left (still from Low to High Recombination layers).       
 
         [0076]    The net effect is a flow of Free Electrons from left to right and a flow of Holes from right to left that keeps the layers in balance, which is the electric current that can be drawn from the device. 
         [0077]    As shown in  FIG. 5 , Free Electrons and Holes are forced by relatively higher concentrations to migrate across a Junction. For example, both Free Electrons and Holes migrate from higher concentration in the Low Recombination layer to lower concentrations in the High Recombination layer. However, once they migrate across that Junction, they are under the influence of the Higher Recombination rate there, so they tend to recombine. The effect of the different Recombination rates is a circular flow of Free and Bound Electrons. 
         [0078]    In  FIG. 6 , the illustrated configuration, the more doped semiconductor materials used, the greater the flow of electrons in one direction. In the DTEC, the electron and hole pairs are generated in a lower recombination material and recombine in the higher recombination material (see picture below), channeled in a useful direction much like a funnel. As higher temperature is applied, the process generally becomes faster, thus increasing the electrical output. 
         [0079]    On exemplary configuration of the device is shown in  FIG. 7 , The DTEC layers are assembled into a convenient package for particular applications.  FIG. 7  represents a common and easily recognizable package, commonly known as a “C” cell battery, such as that we might use in a flashlight. As shown, the conventional positive and negative terminals are embodied in a knob and a face respectively. By virtue of alignment of semiconductive material in layers throughout the cell (only three shown for clarity), electrons pass through the junctions  503  from low recombination material  403  to high recombination mater  404 . Doping in the junctions  503  is alternatively n-type to prevent passage of bound electrons and p-type to prevent passage of free electrons  701  in such a manner, the cell is configured to “ratchet” a flow of electrons to create current. 
         [0080]    While the preferred embodiment of the invention has been illustrated and described, as noted above, many changes can be made without departing from the spirit and scope of the invention. For example, to facilitate further convection exchange, DTECS can be configured in a fin-like manner on a cooling surface. Accordingly, the scope of the invention is not limited by the disclosure of the preferred embodiment. Instead, the invention should be determined entirely by reference to the claims that follow.