Desarrollo Histórico de los Tubos de Calor y sus Aplicaciones

Los tubos de calor son dispositivos que se caracterizan por tener una gran conductancia térmica, lo que los hace muy efectivos para el transporte de calor a grandes distancias con una muy pequeña caída de temperatura. Tienen una excepcional flexibilidad, son de construcción simple, de fácil control, y son de funcionamiento pasivo, no necesitan de potencia externa. La base teórica del funcionamiento de los tubos de calor tiene sus fundamentos en varias disciplinas clásicas como son: la mecánica de fluidos, transferencia de calor y termodinámica. El concepto de tubo de calor data desde 1944. Sin embargo, sus primeros desarrollos se iniciaron sólo el año 1964; impulsados principalmente por requerimientos de los programas espaciales que en esa época se llevaban a cabo. Precisamente, una de las primeras aplicaciones de los tubos de calor fue en satélites, donde se utilizaron como dispositivos para uniformar la distribución de temperaturas en su estructura, es decir, para transferir calor desde la zona expuesta al sol a la no expuesta, con el objeto de minimizar sus tensiones térmicas. Posteriormente, lentamente primero, se empezaron a desarrollar aplicaciones terrestres. En la actualidad, dados las amplias áreas de aplicación que se han descubierto, prácticamente todos los países desarrollados están involucrados en la investigación, desarrollo y comercialización de tubos de calor. Se vislumbra que este interés se mantendrá en el futuro; particularmente impulsado por la miniaturización de los sistemas en el campo de la electrónica, donde los problemas de disipación de calor no pueden ser resueltos utilizando sistemas convencionales

Generación directa de la electricidad a partir de la combustión del metano en medios porosos

La combustión de mezclas pobres metano+aire en medios porosos inertes (MPI) o catalíticos es una tecnología en pleno desarrollo la que encuentra múltiples aplicaciones en la solución de problemas energéticos y medioambientales: permite ahorrar combustibles, reducir al mínimo las emisiones de CO, CO2 y NOx, transformar en forma directa una parte de la energía térmica en la eléctrica y, como resultado, subir la eficiencia de un proceso energético, destruir los compuestos orgánicos volátiles (COVs) en el aire, subir la eficiencia de los ciclos de potencia relacionados con la combustión, producir en forma eficiente el aire o el agua calientes para aplicaciones tanto domésticas como industriales. El objetivo de este trabajo es presentar el desarrollo de esta tecnología en la Universidad de Santiago de Chile en su aplicación a la transformación de la energía térmica de combustión en la energía eléctrica mediante el uso de elementos termoeléctricos sobre la base del efecto físico conocido como el de Seebeck. La presentación del trabajo incluye la descripción breve de a) principales propiedades y principios de funcionamiento de este tipo de combustión, b) metodologías de investigación teóricas y experimentales aplicadas, c) diseños de elementos termoeléctricos y el principio de Seebeck, d) diferentes diseños de acoplamiento de elementos termoeléctricos con medios porosos y e) principales resultados y conclusiones de la investigación realizada

Super-Adiabatic Combustion In Al2O3 And Sic Coated Porous Media For Thermoelectric Power Conversion

The combustion of ultra-lean fuel/air mixtures provides an efficient way to convert the chemical energy of hydrocarbons and low-calorific fuels into useful power. Matrix-stabilized porous medium combustion is an advanced technique in which a solid porous medium within the combustion chamber conducts heat from the hot gaseous products in the upstream direction to preheat incoming reactants. This heat recirculation extends the standard flammability limits, allowing the burning of ultra-lean and low-calorific fuel mixtures and resulting a combustion temperature higher than the thermodynamic equilibrium temperature of the mixture (i.e., super-adiabatic combustion). The heat generated by this combustion process can be converted into electricity with thermoelectric generators, which is the goal of this study.The design of a porous media burner coupled with a thermoelectric generator and its testing are presented. The combustion zone media was a highly-porous alumina matrix interposed between upstream and downstream honeycomb structures with pore sizes smaller than the flame quenching distance, preventing the flame from propagating outside of the central section. Experimental results include temperature distributions inside the combustion chamber and across a thermoelectric generator; along with associated current, voltage and power output values. Measurements were obtained for a catalytically inert Al2O3 medium and a SiC coated medium, which was tested for the ability to catalyze the super-adiabatic combustion. The combustion efficiency was obtained for stoichiometric and ultra-lean (near the lean flammability limit) mixtures of CH4 and air. © 2013 Elsevier Ltd

Electric Power Generation From Combustion In Porous Media

Combustion of lean air/fuel mixtures in an inert porous medium provides an efficient way to convert chemical energy of hydrocarbons into thermal energy. The porous medium effectively redistributes the heat allowing the reacting mixture to be preheated before the combustion front. For a lean propane/air mixture (equivalence ratio Φ∼ 0.6), the combustion front is steady and the combustion temperature is subadiabatic. At lower equivalence ratios the heat wave in the porous media and the combustion front can move synchronously downstream developing superadiabatic temperatures. This superadiabatic effect allows to operate at the range of ultralean mixtures (Φ∼ 0.1). Thermal energy generated by the combustion process can be converted into electricity by thermoelectric modules (TEMs). In this work, a cylindrical porous burner is designed to absorb the heat of combustion of lean propane/air mixtures. The burner is inserted in a rectangular steel block. The surface of the block is covered by a set of operating TEMs. Confining the combustion front is stabilized by using porous media with different pore sizes. Temperatures are recorded in different regions of the burner by using surface and immersion thermocouples. Adjusting the equivalence ratio, the flow rate of the gaseous mixture, the properties of the porous media, and the TEM characteristics, a quasi-static burn rate is achieved with the surrounding surface at the nominal temperatures required by the TEMs. The maximum electrical power of 9.42 W and the overall conversion efficiency of 2.93% are reached with a voltage of 5.93 V and a current of 1.59 A using a setup of four TEMs electrically connected in series

Electric power generation from combustion in porous media

Combustion of lean air/fuel mixtures in an inert porous medium provides an efficient way to convert chemical energy of hydrocarbons into thermal energy. The porous medium effectively redistributes the heat allowing the reacting mixture to be preheated before the combustion front. For a lean propane/air mixture (equivalence ratio F ~ 0.6), the combustion front is steady and the combustion temperature is subadiabatic. At lower equivalence ratios the heat wave in the porous media and the combustion front can move synchronously downstream developing superadiabatic temperatures. This superadiabatic effect allows to operate at the range of ultralean mixtures (F ~ 0.1). Thermal energy generated by the combustion process can be converted into electricity by thermoelectric modules (TEMs). In this work, a cylindrical porous burner is designed to absorb the heat of combustion of lean propane/air mixtures. The burner is inserted in a rectangular steel block. The surface of the block is covered by a set of operating TEMs. Confining the combustion front is stabilized by using porous media with different pore sizes. Temperatures are recorded in different regions of the burner by using surface and immersion thermocouples. Adjusting the equivalence ratio, the flow rate of the gaseous mixture, the properties of the porous media, and the TEM characteristics, a quasi-static burn rate is achieved with the surrounding surface at the nominal temperatures required by the TEMs. The maximum electrical power of 9.42 W and the overall conversion efficiency of 2.93% are reached with a voltage of 5.93 V and a current of 1.59 A using a setup of four TEMs electrically connected in series.Peer ReviewedPreprin

Electric power generation from combustion in porous media

Combustion of lean air/fuel mixtures in an inert porous medium provides an efficient way to convert chemical energy of hydrocarbons into thermal energy. The porous medium effectively redistributes the heat allowing the reacting mixture to be preheated before the combustion front. For a lean propane/air mixture (equivalence ratio F ~ 0.6), the combustion front is steady and the combustion temperature is subadiabatic. At lower equivalence ratios the heat wave in the porous media and the combustion front can move synchronously downstream developing superadiabatic temperatures. This superadiabatic effect allows to operate at the range of ultralean mixtures (F ~ 0.1). Thermal energy generated by the combustion process can be converted into electricity by thermoelectric modules (TEMs). In this work, a cylindrical porous burner is designed to absorb the heat of combustion of lean propane/air mixtures. The burner is inserted in a rectangular steel block. The surface of the block is covered by a set of operating TEMs. Confining the combustion front is stabilized by using porous media with different pore sizes. Temperatures are recorded in different regions of the burner by using surface and immersion thermocouples. Adjusting the equivalence ratio, the flow rate of the gaseous mixture, the properties of the porous media, and the TEM characteristics, a quasi-static burn rate is achieved with the surrounding surface at the nominal temperatures required by the TEMs. The maximum electrical power of 9.42 W and the overall conversion efficiency of 2.93% are reached with a voltage of 5.93 V and a current of 1.59 A using a setup of four TEMs electrically connected in series.Peer Reviewe

Super-adiabatic combustion in Al2O3 and SiC coated porous media for thermoelectric power conversion

The combustion of ultra-lean fuel/air mixtures provides an efficient way to convert the chemical energy of hydrocarbons and low-calorific fuels into useful power. Matrix-stabilized porous medium combustion is an advanced technique in which a solid porous medium within the combustion chamber conducts heat from the hot gaseous products in the upstream direction to preheat incoming reactants. This heat recirculation extends the standard flammability limits, allowing the burning of ultra-lean and low-calorific fuel mixtures and resulting a combustion temperature higher than the thermodynamic equilibrium temperature of the mixture (i.e., super-adiabatic combustion). The heat generated by this combustion process can be converted into electricity with thermoelectric generators, which is the goal of this study.The design of a porous media burner coupled with a thermoelectric generator and its testing are presented. The combustion zone media was a highly-porous alumina matrix interposed between upstream and downstream honeycomb structures with pore sizes smaller than the flame quenching distance, preventing the flame from propagating outside of the central section. Experimental results include temperature distributions inside the combustion chamber and across a thermoelectric generator; along with associated current, voltage and power output values. Measurements were obtained for a catalytically inert Al2O3 medium and a SiC coated medium, which was tested for the ability to catalyze the super-adiabatic combustion. The combustion efficiency was obtained for stoichiometric and ultra-lean (near the lean flammability limit) mixtures of CH4 and air. © 2013 Elsevier Ltd