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
Thermoelectric generators for waste heat harvesting: a computational and experimental approach
(Elsevier, 2017) Aranguren Garacochea, Patricia; Araiz Vega, Miguel; Astrain Ulibarrena, David; Martínez Echeverri, Álvaro; Ingeniería Mecánica, Energética y de Materiales; Mekanika, Energetika eta Materialen Ingeniaritza
Waste heat generation has a widespread presence into daily applications, however, due to the low-temperature grade which presents, its exploitation with the most common technologies is complicated. Thermoelectricity presents the possibility of harvesting any temperature grade heat; besides it also includes many other advantages which make thermoelectric generators perfect for generating electric power from waste heat. A prototype divided into two levels along the chimney which uses the waste heat of a combustion has been built. The experimentation has been used to determine the parameters that influence the generation and to validate a generic computational model able to predict the thermoelectric generation of any application, but specially applications where waste heat is harvested. The temperature and mass flow of the flue gases and the load resistance determine the generation, and consequently, these parameters have been included into the model, among many others. This computational model incorporates all the elements included into the generators (heat exchangers, ceramics, unions) and all the thermoelectric phenomena and moreover, it takes into account the temperature loss of the flue gases while circulating along the thermoelectric generator. The built prototype presents a 65 % reduction in the generation of the two levels of the thermoelectric generator due to the temperature loss of the flue gases. The general computational model predicts the thermoelectric generation with an accuracy of the ±12 %.
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
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
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
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
Prototype of an air to air thermoelectric heat pump integrated with a double flux mechanical ventilation system for passive houses
(Elsevier, 2021) Díaz de Garayo, Sergio; Martínez Echeverri, Álvaro; Aranguren Garacochea, Patricia; Astrain Ulibarrena, David; Ingeniería; Ingeniaritza; Institute of Smart Cities - ISC
This paper describes the design of an air-to-air thermoelectric heat pump for its integration with a double flux mechanical ventilation system for domestic use in Passive House standard. The prototype has been built and thermally characterized in a test bench reproducing winter and summer conditions, with different gaps between indoor and outdoor temperatures. In addition, two different integration possibilities have been analyzed and tested: a stand-alone installation and the combination with a heat recovery unit. This prototype is composed of 10 thermoelectric modules and finned heat pipes to transfer the heat between the modules and the incoming and outgoing ventilation flows. The maximum heating capacity with 12 V supply was proven to be 1,250 W for heating and 375 W for cooling, with COPs ranging 1.5–4 and 0.5–2.5 respectively. Results show the variations in the performance of the thermoelectric heat pump depending on the voltage supply (3–12 V), the air flows (55–130 m3/h) and the temperature gaps between them. This paper demonstrates the convenience of combining passive and active heat recovery technologies (thermoelectric pump coupled to a heat recovery unit), bringing improvements on the thermal power higher than 25% for heating and 10% for cooling, with respect to the thermoelectric heat pump working directly between the incoming and outgoing air flows. The COP is also increased, especially for low energy demands, when the voltage is 3–6 V. In these cases, the COP might be improved by 50% for heating and 30% for cooling.
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
Experimental and computational study on thermoelectric generators using thermosyphons with phase change as heat exchangers
(Elsevier, 2017) Araiz Vega, Miguel; Martínez Echeverri, Álvaro; Astrain Ulibarrena, David; Aranguren Garacochea, Patricia; Mekanika, Energetika eta Materialen Ingeniaritza; Institute for Advanced Materials and Mathematics - INAMAT2; Ingeniería Mecánica, Energética y de Materiales
An important issue in thermoelectric generators is the thermal design of the heat exchangers since it can improve their performance by increasing the heat absorbed or dissipated by the thermoelectric modules. Due to its several advantages, compared to conventional dissipation systems, a thermosyphon heat exchanger with phase change is proposed to be placed on the cold side of thermoelectric generators. Some of these advantages are: high heat-transfer rates; absence of moving parts and lack of auxiliary con- sumption (because fans or pumps are not required); and the fact that these systems are wickless. A com- putational model is developed to design and predict the behaviour of this heat exchangers. Furthermore, a prototype has been built and tested in order to demonstrate its performance and validate the compu- tational model. The model predicts the thermal resistance of the heat exchanger with a relative error in the interval [?8.09;7.83] in the 95% of the cases. Finally, the use of thermosyphons with phase change in thermoelectric generators has been studied in a waste-heat recovery application, stating that including them on the cold side of the generators improves the net thermoelectric production by 36% compared to that obtained with finned dissipators under forced convection.
Open Access
Development and experimental validation of a two-stage thermoelectric heat pump computational model for heating applications
(Elsevier, 2024) Erro Iturralde, Irantzu; Aranguren Garacochea, Patricia; Martínez Echeverri, Álvaro; Astrain Ulibarrena, David; Ingeniería; Ingeniaritza; Institute of Smart Cities - ISC; Universidad Pública de Navarra - Nafarroako Unibertsitate Publikoa
The utilisation of thermoelectric technology as a heat pump in heating applications necessitates comprehensive investigation. The scalable nature of thermoelectric technology enables its operation at elevated temperatures without the requirement of refrigerants. In this work, an accurate computational model that can simulate one- and two-stage thermoelectric heat pumps is developed. This model uses the electric-thermal analogy and the finite difference method, including the thermoelectric effects, temperature dependent properties, thermal contact resistances and all heat exchangers, even the intermediate heat exchanger in the case of a two-stage configuration. Moreover, the model has been experimentally validated by built and tested prototypes, being the first time that a two-stage thermoelectric heat pump model is experimentally validated. The discrepancy between the simulated and experimental results is below the ± 10 % for , ± 8 % for generated heat and temperature lift in the airflow, and less than the ± 6 % for consumed power. Additonally, the model simulates real tendencies under different operating conditions, proving the reliability of the developed thermoelectric heat pump model. Finally, the model is used to optimise a thermoelectric system combining one- and two-stage thermoelectric heat pumps, and hybridising them with electric resistances. An airflow of 16.5 m3/h is heated from 25 °C to 160 °C, achieving a maximum of 1.21. Lastly, the importance of considering the thermal resistances of the heat exchangers is computationally modelled and demonstrated. Not taking them into account would overestimate the performance of the TEHP system by more than the 7 %.