Open Access
Experimental study and optimization of thermoelectric-driven autonomous sensors for the chimney of a biomass power plant
(2014) Rodríguez García, Antonio; Astrain Ulibarrena, David; Martínez Echeverri, Álvaro; Aranguren Garacochea, Patricia; Ingeniería Mecánica, Energética y de Materiales; Mekanika, Energetika eta Materialen Ingeniaritza
In the work discussed in this paper a thermoelectric generator was developed to harness waste heat from the exhaust gas of a boiler in a biomass power plant and thus generate electric power to operate a flowmeter installed in the chimney, to make it autonomous. The main objective was to conduct an experimental study to optimize a previous design obtained after computational work based on a simulation model for thermoelectric generators. First, several places inside and outside the chimney were considered as sites for the thermoelectricity-driven autonomous sensor. Second, the thermoelectric generator was built and tested to assess the effect of the cold-side heat exchanger on the electric power, power consumption by the flowmeter, and transmission frequency. These tests provided the best configuration for the heat exchanger, which met the transmission requirements for different working conditions. The final design is able to transmit every second and requires neither batteries nor electric wires. It is a promising application in the field of thermoelectric generation.
Open Access
Net thermoelectric power generation improvement through heat transfer optimization
(Elsevier, 2017) Aranguren Garacochea, Patricia; Astrain Ulibarrena, David; Rodríguez García, Antonio; Martínez Echeverri, Álvaro; Ingeniería Mecánica, Energética y de Materiales; Mekanika, Energetika eta Materialen Ingeniaritza
Thermoelectric generation contributes to obtain a more sustainable energetic system giving its potential to harvest waste heat and convert it into electric power. In the present study a computational optimal net generation of 108.05 MWh/year was produced out of the flue gases of a real tile furnace located in Spain (the equivalent to supply the energy to 31 Spanish dwellings). This maximum generation has been obtained through the optimization of the hot and cold heat exchangers, the number of thermoelectric modules (TEMs) installed and the mass flows of the refrigerants, including the temperature loss of the flue gases and the influence of the heat power to dissipate over the heat dissipators. The results are conclusive, the installation of more TEMs does not always imply higher thermoelectric generation, so the occupancy ratio (δ) has to be optimized. The optimal generation has been achieved covering the 42 % of the surface of the chimney of the tile furnace with TEMs and using heat pipes on the cold side, which present smaller thermal resistances than the finned dissipators for similar consumptions of their fans. Moreover, the high influence of the consumption of the auxiliary equipment shows the importance of considering it to obtain realistic usable electric energy from real applications.
Open Access
Heat pipes thermal performance for a reversible thermoelectric cooler-heat pump for a nZEB
(Elsevier, 2019) Aranguren Garacochea, Patricia; Díaz de Garayo, Sergio; Martínez Echeverri, Álvaro; Araiz Vega, Miguel; Astrain Ulibarrena, David; Ingeniaritza; Institute of Smart Cities - ISC; Ingeniería
The nZEB standards reduce the energy demand of these buildings to a minimum, obtaining this little energy from renewable resources. Taking these aspect into consideration, a thermoelectric cooler-heat pump is proposed to achieve the comfort temperature along the whole year. The same device can provide heat in winter and it can cool down the buildings in summer just by switching the voltage supply polarity. Heat pipes are studied to work on both sides of the thermoelectric modules in order to optimize the heat transfer as these devices present really good thermal resistances and they can work in any position. However, they present pretty different thermal resistances if they work on the cold or on the hot side of the modules. A methodology to thermally characterize these heat exchangers working in both orientations is proposed and a validated computational model is developed to optimize the thermoelectric cooler-heat pump for a nZEB application. The number of thermoelectric modules, the position of the device, the ambient temperature and the air mass flow determine the operation and consequently they need to be studied in order to optimize the application.
Open Access
Study of a complete thermoelectric generator behavior including water-to-ambient heat dissipation on the cold side
(Springer US, 2014) Aranguren Garacochea, Patricia; Astrain Ulibarrena, David; Martínez Echeverri, Álvaro; Ingeniería Mecánica, Energética y de Materiales; Mekanika, Energetika eta Materialen Ingeniaritza
The reduction of the thermal resistances of the heat exchangers of a thermoelectric generation system (TEG), leads to a significant increase in the TEG efficiency. For the cold side of a thermoelectric module (TEM), a wide range of heat exchangers has been studied, form simple finned dissipators to more complex water (water-glycol) heat exchangers. As Nusselt numbers are much higher in water heat exchangers than in conventional air finned dissipators, convective thermal resistances are better. However, to conclude which heat exchanger leads to higher efficiencies, it is necessary to include the whole system involved in the heat dissipation, that is, TEM-to-water heat exchanger, water-to-ambient heat exchanger, as well as the required pumps and fans. This paper presents a dynamic computational model able to simulate the complete behavior of a TEG, including both heat exchangers. The model uses the heat transfer and hydraulic equations to compute TEM-to-water and water-to-ambient thermal resistances, along with the resistance of the hot side heat exchanger at different operating conditions. Likewise, the model includes all the thermoelectric effect with temperature-dependent properties. The model calculates the net power generation at different configurations, providing a methodology to design and optimize the heat exchange in order to maximize the net power generation for a whole variety of TEGs.
Open Access
Thermoelectric self-cooling for power electronics: increasing the cooling power
(Elsevier, 2016) Martínez Echeverri, Álvaro; Astrain Ulibarrena, David; Aranguren Garacochea, Patricia; Ingeniería Mecánica, Energética y de Materiales; Mekanika, Energetika eta Materialen Ingeniaritza
Thermoelectric self-cooling was firstly conceived to increase, without electricity consumption, the cooling power of passive cooling systems. This paper studies the combination of heat pipe exchangers and thermoelectric self-cooling, and demonstrates its applicability to the cooling of power electronics. Experimental tests indicate that source-to-ambient thermal resistance reduces by around 30% when thermoelectric self-cooling system is installed, compared to that of the heat pipe exchanger under natural convection. Neither additional electric power nor cooling fluids are required. This thermal resistance reaches 0.346 K/W for a heat flux of 24.1 kW/m2, being one order of magnitude lower than that obtained in previous designs. In addition, the system adapts to the cooling demand, reducing this thermal resistance for increasing heat. Simulation tests have indicated that simple system modifications allow relevant improvements in the cooling power. Replacement of a thermoelectric module with a thermal bridge leads to 33.54 kW/m2 of top cooling power. Likewise, thermoelectric modules with shorter legs and higher number of pairs lead to a top cooling power of 44.17 kW/m2. These results demonstrate the applicability of thermoelectric self-cooling to power electronics.
Open Access
New opportunities for electricity generation in shallow hot dry rock fields: a study of thermoelectric generators with different heat exchangers
(Elsevier, 2019) Catalán Ros, Leyre; Aranguren Garacochea, Patricia; Araiz Vega, Miguel; Pérez Artieda, Miren Gurutze; Astrain Ulibarrena, David; Institute of Smart Cities - ISC
Despite being one of the largest renewable sources, geothermal energy is not widely utilized for electricity generation. In order to leverage shallow hot dry rock (HDR) fields, the present paper proposes an alternative to enhanced geothermal systems (EGS): thermoelectric generators. Based on the conditions of Timanfaya National Park, a prototype has been built to experimentally analyze the feasibility of the proposed solution. The prototype is composed by a two phase closed thermosyphon (TPCT) as hot side heat exchanger, two thermoelectric modules, and it considers different cold side heat exchangers: fin dissipators assisted by a fan and loop thermosyphons, both with various geometries. Experiments have demonstrated that loop thermosyphons represent the best alternative due to their low thermal resistance and, especially, due to their lack of auxiliary consumption, leading to a maximum net power generation of 3.29 W per module with a temperature difference of 180 °C (200 °C in the hot side and 20 °C as ambient temperature), 54% more than with fin dissipators. Hence, there exists a new opportunity for electricity generation in shallow hot dry rock fields: thermoelectric generators with biphasic thermosyphons as heat exchangers, a patented and robust solution.
Open Access
Auxiliary consumption: a necessary energy that affects thermoelectric generation
(Elsevier, 2018) Aranguren Garacochea, Patricia; Araiz Vega, Miguel; Astrain Ulibarrena, David; Ingeniería Mecánica, Energética y de Materiales; Mekanika, Energetika eta Materialen Ingeniaritza
Waste heat recovery can apply to a wide range of applications, from transportation, or industries to domestic appliances. Thermoelectric generation technology applied to those cases could produce electrical energy and thus improve their efficiency. A validated computational methodology, which simulates the behavior of any thermoelectric generator and calculates the energy consumption of the auxiliary equipment involved, has been used to determine the potential of waste heat harvesting. The usable energy, the net energy, generated has to be maximized, not only the thermoelectric generation has to be maximized, but also the consumption of the auxiliary equipment has to be minimized, or if possible eliminated. Heat exchangers with a liquid as the heat carrier procure high thermoelectric generations, as their thermal resistances are very low, nevertheless when the consumption of their auxiliary consumption is borne in mind, their use is not that promising. The optimal thermoelectric energy obtained from the flue gases of a real industry using these dissipation systems is 119 MWh/year, while the maximum net energy is 73 MWh/year due to the consumption of the auxiliary equipment. The latest scenario does not only represent a 40% reduction from the optimal thermoelectric generation but also a different optimal working point. The complete elimination of the auxiliary equipment using novel biphasic thermosyphons with free convection at the same application produces a net energy of 128 MWh/year. This novel dissipation technology presents an increase on the thermoelectric generation due to its low thermal resistances, but above all due to the elimination of the auxiliary consumption.
Open Access
Experimental investigation of the applicability of a thermoelectric generator to recover waste heat from a combustion chamber
(Elsevier, 2015) Aranguren Garacochea, Patricia; Astrain Ulibarrena, David; Rodríguez García, Antonio; Martínez Echeverri, Álvaro; Ingeniería Mecánica, Energética y de Materiales; Mekanika, Energetika eta Materialen Ingeniaritza
A thermoelectric generator prototype has been built; it produces 21.56 W of net power, the produced thermoelectric power minus the consumption of the auxiliary equipment, using an area of 0.25 m2 (approximately 100 W/m2). The prototype is located at the exhaust of a combustion chamber and it is provided with 48 thermoelectric modules and two different kinds of heat exchangers, finned heat sinks and heat pipes. Globally, the 40 % of the primary energy used is thrown to the ambient as waste heat; one of the many different applications in which thermoelectricity can be applied is to harvest waste heat to produce electrical power. Besides, the influence on the thermoelectric and on the net power generation of key parameters such as the temperature and mass flow of the exhaust gases, the heat dissipation systems in charge of dispatching the heat into the ambient and the consumption of the auxiliary equipment has been studied. In terms of heat dissipation, the heat pipes outperform the finned dissipators, a 43 % more net power is obtained.
Open Access
Development and experimental validation of a thermoelectric test bench for laboratory lessons
(OmniaScience, 2013) Rodríguez García, Antonio; Astrain Ulibarrena, David; Martínez Echeverri, Álvaro; Aranguren Garacochea, Patricia; Pérez Artieda, Miren Gurutze; Ingeniería Mecánica, Energética y de Materiales; Mekanika, Energetika eta Materialen Ingeniaritza
The refrigeration process reduces the temperature of a space or a given volume while the power generation process employs a source of thermal energy to generate electrical power. Because of the importance of these two processes, training of engineers in this area is of great interest. In engineering courses it is normally studied the vapor compression and absorption refrigeration, and power generation systems such as gas turbine and steam turbine. Another type of cooling and generation less studied within the engineering curriculum, having a great interest, it is cooling and thermal generation based on Peltier and Seebeck effects. The theoretical concepts are useful, but students have difculties understanding the physical meaning of their possible applications. Providing students with tools to test and apply the theory in real applications, will lead to a better understanding of the subject. Engineers must have strong theoretical, computational and also experimental skills. A prototype test bench has been built and experimentally validated to perform practical lessons of thermoelectric generation and refrigeration. Using this prototype students learn the most effective way of cooling systems and thermal power generation as well as basic concepts associated with thermoelectricity. It has been proven that students learn the process of data acquisition, and the technology used in thermoelectric devices. These practical lessons are implemented for a 60 people group of students in the development of subject of Thermodynamic including in the Degree in Engineering in Industrial Technologies of Public University of Navarra.
Open Access
Energía sostenible: sin malos humos
(Universidad Pública de Navarra / Nafarroako Unibertsitate Publikoa, 2019) Samanes Pascual, Javier; Pascual Miqueleiz, Julio María; Berrueta Irigoyen, Alberto; Araiz Vega, Miguel; Catalán Ros, Leyre; Aranguren Garacochea, Patricia; Arricibita de Andrés, David; Ingeniería Eléctrica, Electrónica y de Comunicación; Institute of Smart Cities - ISC; Ingeniería; Ingeniaritza Elektrikoa, Elektronikoaren eta Telekomunikazio Ingeniaritzaren; Ingeniaritza
¿Puede España ser sostenible energéticamente? Si alguna vez te has planteado esta pregunta, o quieres saber en qué gastamos la energía y de dónde podría ser obtenida, aquí encontrarás respuestas. Nuestros recursos renovables son inmensos, pero también lo es nuestro consumo. Este libro no solo se centra en analizar la situación actual y las posibilidades que las energías renovables tienen en nuestro país, sino que, presentando de forma clara los datos sobre nuestro gasto energético, permite a cada lector identificar sus mayores consumos, de tal forma que pueda considerar cómo reducirlos. Energía sostenible. Sin malos humos es la adaptación al caso español, actualizando los datos, del libro publicado hace una década por David MacKay en el Reino Unido. La sostenibilidad es hoy en día una preocupación creciente en la sociedad. Pero a menudo este interés se ve contaminado por cifras enormes que resultan muy complicadas de comprender. Además, todos hemos oído hablar en algún momento sobre pequeños gestos al alcance de nuestra mano que podrían permitir un cambio hacia un modelo sostenible. Nada más lejos de la realidad, pequeñas acciones solo permiten pequeños cambios, y el cambio de modelo energético al que nos enfrentamos requiere grandes acciones. Para deshacernos de todo este ruido, en este libro se presentan los números de forma clara y sencilla, utilizando unidades a nuestro alcance y que son comprensibles por todas las personas. Esto permite identificar de una forma mucho más personal los consumos energéticos de nuestro día a día. A lo largo de la primera parte del libro se van construyendo dos columnas: una de color rojo, que representa la agregación de consumos, y otra de color verde, que representa la capacidad de generación. Estas columnas ofrecen una comparación muy visual de la infraestructura renovable que sería necesaria para mantener nuestro ritmo de consumo energético actual. Además, utiliza números «gordos» obtenidos de la experiencia del día a día. Por ejemplo, para calcular la capacidad de generación eólica se parte de una velocidad de viento estimada a partir de la velocidad típica de un ciclista urbano. Toda esta información se encuentra en la primera parte del libro, en los capítulos del 1 al 18. Sin embargo, este libro no se centra únicamente en el análisis de la situación actual, sino que da un paso más y propone alternativas al modelo energético actual con el fin de alcanzar un modelo 100% renovable a medio plazo. Estas medidas incluyen un aumento importante en la potencia renovable instalada, un aumento en la eficiencia energética y algunos ligeros cambios en nuestro estilo de vida que permitan una reducción del consumo. Por supuesto, los tres frentes deben ser atacados al mismo tiempo. Estas propuestas se recogen en la segunda parte del libro, en los capítulos 19 a 32. Por último, este es un libro divulgativo al alcance de todas las personas, que busca transmitir toda la información de forma clara e intuitiva sin perderse en complicados cálculos. Pero si eres de los que les gustan las cuentas, al final del libro encontrarás un apartado en el que se explica de forma rigurosa muchos de los cálculos simples realizados en las primeras partes del libro. Estos apéndices técnicos forman la tercera parte del libro, son los apéndices de la A hasta la H.