Patent Application
20180058295
The application of a thermopile module generator device to generate electrical energy from waste heat energy carried by exhaust gases from an external combustion Stirling-Electric Hybrid Automobile (ibid) is novel. Additionally, previous designs of automotive thermoelectric generators, did not take advantage of both active and passive systems of heat energy transfer. Previous designs did not employ a plurality of heat sink(s) pin(s) which have superior heat transfer characteristics to those of heat transfer fins, due to a more favorable surface area to mass ratio typically found in the heat sink(s) pin(s) design. Additionally, heat sink(s) pin(s) do not inhibit heat transfer by boundary layer effects as is typical with the laminar fluid flow with the employment of heat transfer fins. Previous automotive applications could not take advantage of more efficient heat sink materials such as Aluminum, which would melt at the higher temperatures of operation typically found in the exhaust manifold of an internal combustion engine. Additionally, the geometric configuration of the heat sink(s) pin(s), improves heat energy transfer rates from the exhaust gases to the thermopile(s) array(s) by creating turbulent fluid flow within the exhaust module conduit which increases residence time of the exhaust gas molecules, allowing for a more complete heat energy transfer to the thermopile(s) array(s), while minimizing back pressure within the exhaust system.
Exhaust gas temperatures from an external combustion automotive Stirling Cycle engine typically range from 150° C. to 250° C. when measured at the exhaust manifold. The current state of the art of thermopile power generation requires at least a 50° C. temperature difference (ΔT) to generate power at optimum efficiencies. The current invention utilizes lower exhaust gas temperature ranges found in the external combustion automotive Stirling Cycle engine which allows for the employment of materials with more efficient and higher coefficients of thermal conductivity than can be currently employed with higher temperatures found in the exhaust gases produced by an internal combustion engine. The external combustion exhaust gas temperatures are significantly lower than those of conventional internal combustion engines, this lower temperature range presents an opportunity for an improvement on the art since high temperature range thermopiles are not as efficient as lower temperature range thermopiles due, in part, because at lower temperatures, it is less difficult to maintain more favorable temperature differences, from the hot side of the thermopile to the cold side of the thermopile. This improvement is due, in part, to the increase in thermal conductivity at lower temperatures of heat sink materials. Heat sink materials are more efficient at lower temperature ranges due to the inverse relationship between the coefficient of thermal conductivity and temperature. The coefficients of thermal conductivity for materials at high temperatures are lower than the thermal conductivity of the same material at a lower temperature which means as temperatures drop the coefficient of thermal conductivity increases. The lower temperatures of the Stirling Cycle engine exhaust gases provide for an improved rate of heat energy transfer to heat sink materials resulting in a more favorable ΔT from the hot side of the thermopile to the cold side when the more efficient heat sinks materials are employed.
The technical problems that the present invention resolves are not limited to those mentioned above, and those that are not mentioned shall be clearly understood by a person skilled in the art by examining the specifications of the present invention disclosed herein.
Thermopile technology is based upon the thermoelectric effect, or Seebeck effect. By applying a temperature difference to a pair of dissimilar metallic junctions in an electrical circuit, an electrical voltage is generated.
The practice of using thermopiles to generate electrical power, by means of applying heat energy from a variety of heat sources, including radioisotopes, has been employed by both the U.S. Department of Energy and the National Aeronautics and Space Administration (NASA). These applications include Radioisotope Thermoelectric Generators (i.e. RTGs) for remote power supplies for equipment deployed in Antarctica, and spacecraft power supplies (i.e. Pioneer 10 Spacecraft). Thermopiles are more efficient as ΔT increases.
Previous automotive applications of thermopiles have had limited success in part because the temperatures of exhaust gases from internal combustion engines can reach 800° C. when measured at the exhaust manifold. Conventional heat sink materials, stable at these high temperatures, are not as thermally conductive as they are at lower temperatures resulting in less favorable ΔT across the thermopile for the generation of electrical voltage. These higher exhaust gas temperatures limit the types of materials that can be employed to maintain favorable rates of efficient heat energy transfer. Additionally, previous designs have not employed both active, and passive, heat energy transfer techniques, and more effective heat energy transfer methodologies as disclosed herein the present invention, such as heat sink(s) pin(s), rather than less efficient heat transfer fins. None of the previous designs were specific to a series hybrid electric automotive application employing an external combustion Stirling Cycle engine. The operation of an automotive Stirling Cycle engine produces exhaust gases at significantly lower temperatures than exhaust gas temperatures produced by current internal combustion engines. These lower temperatures provide for more efficient application of thermopile technology since a broader range of more effective heat sink materials are stable at these lower temperature ranges. It is a general characteristic that heat sink materials have a greater coefficient of thermal conductivity at lower temperatures. There is roughly a 50% loss in thermal conductivity of a heat sink composed of Iron at 800° C. when compared to the thermal conductivity of the same material at 200° C. An example of a heat sink material available for use with the external combustion Stirling Cycle engine is Aluminum. Aluminum, when employed as a heat sink material, has superior coefficient of thermal conductivity to that of Iron. Aluminum cannot be used at the higher exhaust gas temperatures produced by internal combustion engines, since exhaust gas temperatures are well above the melting point of 660° C. These physical properties of Aluminum make it unsuitable as a heat sink material at the higher temperatures found in the exhaust gases of the internal combustion engine, but make it one of many ideal materials to be employed when recovering heat energy from the exhaust gases produced by an external combustion Stirling Cycle engine.
Information disclosed in this Background of the Invention section, is only for enhanced and detailed understanding of the general background of the invention, and should not be taken as an acknowledgement, nor any form of suggestion, that this information forms the prior art already known to a person skilled in the art.
The various aspects of the present invention are directed to provide a thermoelectric module generator device to convert waste heat energy from exhaust gases, produced by an automotive external combustion Stirling Cycle engine, into electrical energy by employing the Seebeck effect.
In the aspect of the present invention, a thermoelectric generator module device of a Stirling-Electric Hybrid Automobile (ibid), may include an inlet conduit to transfer the flow of exhaust gases from the exhaust system, be it an exhaust manifold or exhaust pipe, into the module generator device where interior heat sink(s) pin(s)s, which may be of varying lengths, may be arranged in a plurality of alternating offset, overlapping rows, to facilitate turbulent flow of the exhaust gases, such that there is no direct line of sight path as the exhaust gases flow from the inlet to the outlet. The overall geometric shape of the device may be such that the surface area of the top surface and the bottom surface of the device exceeds the surface area of the lateral surface(s) of the device by a factor of two or higher. The rows of heat sink(s) pin(s) may be affixed to the top and bottom interior surface(s) of the device to absorb heat energy from the exhaust gases and thermally conduct the heat energy to the top and bottom interior surface(s) of the module conduit. The volumetric dimensions of the module conduit may be fabricated to accommodate twice the volumetric capacity of the exhaust pipe or manifold, to minimize exhaust system backpressure. A plurality of the interior heat sink(s) pin(s) may be arranged geometrically, to provide for a fluid dynamic porosity and permeability of 50% or higher.
On the lateral side(s) of the module conduit, in close proximity to the outlet on the outer surface(s) edge, an aerodynamically contoured air foil may be affixed at an angle to direct air flow toward the area where the outlet is vented to the atmosphere. The air foil may take advantage of air movement under the frame of the automobile as the automobile moves along the roadway directing air past the air toil, to create a Venturi effect to assist in evacuating the exhaust gases out of the module conduit to further minimize exhaust system back pressure.
The outer surface(s) of the top and bottom of the module conduit may have a plurality of layers of thermopile(s) in an array(s) affixed to the surface(s) via a thermally conductive adhesive and/or fixture(s). The plurality of the thermopile(s) array(s) may be wired in series and/or parallel in wiring harnesses, which may be shielded in a wiring conduit, to satisfy the specifications of the electrical system of the Stirling-Electric Hybrid Automobile (ibid). The heat energy absorbed by the heat sink(s) pin(s) on the interior surface(s) of the module conduit may be conducted through the inner surface(s) of the module conduit to the outer surface(s) of the module conduit to the hot side of the thermopile(s) in the thermopile(s) array(s) by thermal conduction.
A cooling plate(s), which may be composed of a material with a high coefficient of thermal conductivity, which may include, but not limited to, a material composition of ceramic, ceramic composite(s), metallic alloy and/or metallic alloy composite(s), incorporating into the matrix of the material Cubic-Boron Nitride and/or other substance(s) to provide for improved thermal conductivity. The cooling plate(s) may be affixed to the cold side of the plurality of the thermopiles in the thermopile(s) array(s) via a thermally conductive adhesive and/or fixture. A cooling fluid may circulate through a plurality of tubular channel(s) in a pattern to include, but not limited to, a serpentine pattern, to circulate the cooling fluid to and from a radiator device(s) to expel excess waste heat energy.
The radiator device(s) may be composed of material with a high coefficient of thermal conductivity to include but not limited to, ceramic, ceramic composite(s), metallic alloy and/or metallic alloy composite(s), incorporating into the matrix of the material Cubic-Boron Nitride and/or other substance(s) to provide for improved thermal conductivity. The radiator device(s) may be affixed with a fan(s), which is driven either by electricity or mechanically, to provide motive power to the fan, for the purpose of directing ambient air over, and/or through, the radiator device(s) to expel excess waste heat energy thermally conducted to the surface(s) of the radiator device(s) from the cooling fluid. This radiator device(s) may be part of the overall cooling radiator(s) system of the Stirling-Electric Hybrid Automobile (ibid) or separate from the overall radiator(s) cooling system.
The outer surface(s) of the cooling plate(s) may be affixed with a plurality of heat sink(s) pin(s) by a thermally conductive adhesive and/or fixture(s) such that passive transfer of heat energy from the surface(s) of the cooling plate(s) to the heat sink(s) pin(s) is accomplished. The heat sink(s) pin(s) may expel excess waste heat energy passively via air movement under the frame of the automobile as the automobile moves along the roadway, directing air over and/or through the arrangement of heat sink(s) pin(s).
A plurality of thermopile(s) array(s) (4) may be affixed, via thermally conductive adhesive and/or fixture(s), to the outer surface(s) of the module generator device to absorb heat energy from the outer surface(s) of the module generator device. The geometric arrangement of the plurality of the thermopile(s) are arrayed such that they may be in a plurality of layers, wired in series and/or parallel and connected to the electrical system of the Stirling-Electric Hybrid Automobile (ibid) via a conduit (6) or other shielding device.
A cooling plate(s) (2) may be affixed via thermally conductive adhesive and/or fixture(s) to the outer most surface(s) of the thermopile(s) array(s) (4) in such a manner as to absorb heat energy from the surface(s) of the thermopile(s) (4) arrayed on the surface(s) of the module conduit. The cooling plate(s) (2) may have a plurality of tubular channels through which cooling fluid may flow from one tubular channel to the adjacent tubular channel via external return loops (3) in a pattern similar to, but not limited to, a serpentine pattern such that the cooling fluid circulates through the majority of the mass, and/or area, of the cooling plate(s) (2).
A plurality of exterior heat sink(s) pin(s) (1) of varying length may be affixed to the outer surface(s) of the cooling plate(s) (2) and geometrically arranged in offset overlapping rows, to take advantage of air movement under the frame of the Stirling-Electric hybrid Automobile (ibid) as the automobile moves along the roadway; the air movement will help to expel heat energy derived from the module generator device to the ambient air.
Affixed to the lateral side of the module conduit by means of a bracket (8) or other fixture, is an air foil (7) to direct air flow past the outlet of the module generator device.
The wiring may be bundled into a conduit to carry the electrical power to the electrical system of the Stirling-Electric Hybrid Automobile (ibid). The plurality of thermopile(s) array(s) may be arranged in a plurality of layers.
This embodiment of the invention is a Stirling-Electric Hybrid automotive exhaust module generator device for converting waste heat energy into electrical energy by employing the Thermoelectric Effect, also known as the Seebeck Effect. The disclosure herein describes how the invention converts heat energy, from hot exhaust gases, from the operation of an automotive external combustion engine (e. g. Stirling Cycle engine), into electrical energy which is fed back into the electrical system of the Stirling-Electric Hybrid Automobile (U.S. Pat. No. 7,726,130 B2) minimizing losses due to the second law of thermodynamics. The improvements on the art in this disclosure focus on taking advantage of the first law of thermodynamics by increasing residence time of the hot exhaust gases through the module conduit by employing heat sink(s), in the form of a plurality of pins, on the interior surface(s) of the module conduit. Additional improvements on the art may be implemented by fabricating the module conduit with materials having higher coefficients of thermal conductivity such as ceramic, ceramic composite(s), metallic alloys and/or metallic alloy composite(s) which may include Cubic Boron Nitride and/or other materials high coefficients of thermal conductivity, within the material matrix of the module conduit.
The fabrication of the module generator device may consist of components to include the module conduit, interior heat sink(s) pin(s), thermopile(s) array(s), electrical wiring conduit, cooling plate(s), external heat sink(s) pin(s) and an air foil. These components are configured to draw a maximum amount of heat energy out of the module generator device and convert it into electrical energy by maintain a favorable ΔT.
As exhaust gases move from the module conduit inlet of the module generator device, to the outlet, the plurality of interior pin(s) of the heat sink(s) create turbulent flow such that micro-vortices move the exhaust gas molecules over more heat transfer surface(s) area(s) of the module conduit with a resultant of significant improvement in heat energy transfer rates than can be currently attained with heat transfer fins due to the boundary layer effect typical in laminar fluid flow. Additionally, this configuration of the plurality of the interior heat sink(s) pin(s) will resolve the problem of creating back-pressure in the exhaust system that is inherent in heat transfer fin designs due to laminar fluid flow boundary layer effects. The plurality of the interior heat sink(s) pin(s) transfers the heat energy to the outer surface(s) of the module conduit where, on the outer surface of the module conduit, a plurality of thermopile(s) absorb the heat energy conducted through to the outer surface of the module conduit. The plurality of thermopile(s), on the outer surface of the module conduit, are wired in both series and/or parallel bundles, to meet the voltage specifications of the electrical system. The wiring bundles may be connected to the electrical system via wiring conduit or other shielding device. The plurality of the thermopile(s) on the outer surface of the module conduit composes an array(s), which may be affixed to the hot outer surface(s) on the module conduit via thermally conductive adhesive and/or fixture such that the thermopile(s) are in direct contact with the outer surface(s) of the module conduit, to provide for heat energy transfer via thermal conduction. The thermopile(s) array(s), on the outer surface(s) of the module conduit, may be in a plurality of layers, each layer in direct contact with the adjacent layer to transfer heat energy, one from the other, by thermal conduction. Cooling plate(s) may be affixed in direct contact to the outer most surface(s) of the thermopile(s) array(s) with a thermally conductive adhesive and or fixture(s) to provide for heat energy transfer via thermal conduction. The cooling plate(s) may be composed of a material with a high coefficient of thermal conductivity to include, but not limited to ceramic, ceramic composite(s), metallic alloy and/or metallic alloy composite(s) which may include Cubic-Boron Nitride of other substance(s) to improve thermal conductivity. The cooling plate(s) is to provide for a significant ΔT between the two major surface(s) of the thermopile(s) array(s), which are in direct contact with both the outer surface(s) of the module conduit and the inner surface(s) of the cooling plate(s) such that an electrical voltage is generated when a minimum threshold of ΔT is achieved. The cooling plate(s) may transfer heat energy from the thermopile(s) array(s) to the ambient air, both actively and passively. The active cooling may be provided by the employment of a serpentine arrangement of tubular channels in the cooling plate(s) through which cooling fluid circulates to and from the cooling plate(s) via a radiator(s) to expel heat energy from the circulating fluid to the ambient air. The cooling fluid circulation may flow though the plurality of tubular channels in the cooling plate(s) from the cooling fluid inlet(s) into the plurality of tubular channels successively via a plurality of external tubular return loops such that cooling fluid is transferred from one tubular channel successively to the adjacent channel(s) and then to the cooling fluid outlet(s). The outlet(s) of the cooling plate(s) may circulate cooling fluid to the radiator(s), which may be separate from the main radiator system, via a circulating pump which may be driven electrically of mechanically. The passive cooling may be accomplished by affixing a plurality of external heat sink(s) pin(s) to the outer surface(s) of the cooling plate(s) to take advantage of the air movement under the automobile frame, to expel heat energy to the ambient air, as the automobile moves along the roadway.
