Open Access
Experimental evaluation of a transcritical CO2 refrigeration facility working with an internal heat exchanger and a thermoelectric subcooler: performance assessment and comparative
(Elsevier, 2022) Casi Satrústegui, Álvaro; Aranguren Garacochea, Patricia; Araiz Vega, Miguel; Sánchez, Daniel; Cabello, Ramón; Astrain Ulibarrena, David; Ingeniería; Ingeniaritza; Gobierno de Navarra / Nafarroako Gobernua; Universidad Pública de Navarra / Nafarroako Unibertsitate Publikoa
The use of carbon dioxide in transcritical state has become one of the most used solutions to comply with the F-Gas directive and reduce greenhouse gases emissions from refrigeration systems at high ambient temperatures. For low-medium power units, the commonly used solutions to improve the efficiency such as the ejector, multiple compressor arrangements, mechanical subcooler, etc., add complexity and increase the cost of the refrigeration facility, which is not ideal for small units. In this low-medium power range, two technologies stand out to increase the performance of a carbon dioxide transcritical cycle: the internal heat exchanger and the thermoelectric subcooler. This study brings a complete research in which both solutions have been tested in the same experimental transcritical carbon dioxide refrigeration facility under the same working conditions. It focuses on the real performance of both systems and discusses the strengths and weaknesses of using an internal heat exchanger or a thermoelectric subcooler. The results show that the thermoelectric subcooler outperforms the internal heat exchanger in both the coefficient of performance and the cooling capacity while also being a more controllable and flexible solution.
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
Thermoelectric heat recovery in a real industry: from laboratory optimization to reality
(Elsevier, 2021) Casi Satrústegui, Álvaro; Araiz Vega, Miguel; Catalán Ros, Leyre; Astrain Ulibarrena, David; Ingeniaritza; Institute of Smart Cities - ISC; Ingeniería; Gobierno de Navarra / Nafarroako Gobernua, 0011-1365-2018-000101
Thermoelectricity, in the form of thermoelectric generators, holds a great potential in waste heat recovery, this potential has been studied and proved in several laboratory and theoretical works. By the means of a thermoelectric generator, part of the energy that normally is wasted in a manufacturing process, can be transformed into electricity, however, implementing this technology in real industries still remains a challenge and on-site tests need to be performed in order to prove the real capabilities of this technology. In this work, a computational model to simulate the behaviour of a thermoelectric generator that harvest waste heat from hot fumes is developed. Using the computational model an optimal configuration for a thermoelectric generator is obtained, also an experimental study of the performance of different heat pipes working as cold side heat exchangers is carried out in order to optimize the performance of the whole thermoelectric generator, thermal resistances of under 0,25 K/W are obtained. The optimized configuration of the thermoelectric generator has been built, installed and tested under real conditions at a rockwool manufacturing plant and experimental data has been obtained during the 30 days field test period. Results show that 4.6 W of average electrical power are produced during the testing period with an efficiency of 2.38%. Moreover, the computational model is validated using this experimental data. Furthermore, the full harvesting potential of an optimized designed that takes advantage of the whole pipe is calculated using the validated computational model, resulting in 30.8 MWh of energy harvested during a sample year which could meet the demand of 8.34 Spanish average households.
Open Access
Prospects of autonomous volcanic monitoring stations: experimental investigation on thermoelectric generation from fumaroles
(MDPI, 2020) Catalán Ros, Leyre; Araiz Vega, Miguel; Padilla, Germán D.; Hernández, Pedro A.; Pérez, Nemesio M.; García de la Noceda, Celestino; Albert, José F.; Astrain Ulibarrena, David; Ingeniaritza; Institute of Smart Cities - ISC; Ingeniería
Fumaroles represent evidence of volcanic activity, emitting steam and volcanic gases at temperatures between 70 and 100 °C. Due to the well-known advantages of thermoelectricity, such as reliability, reduced maintenance and scalability, the present paper studies the possibilities of thermoelectric generators, devices based on solid-state physics, to directly convert fumaroles heat into electricity due to the Seebeck effect. For this purpose, a thermoelectric generator composed of two bismuth-telluride thermoelectric modules and heat pipes as heat exchangers was installed, for the first time, at Teide volcano (Canary Islands, Spain), where fumaroles arise in the surface at 82 °C. The installed thermoelectric generator has demonstrated the feasibility of the proposed solution, leading to a compact generator with no moving parts that produces a net generation between 0.32 and 0.33 W per module given a temperature difference between the heat reservoirs encompassed in the 69–86 °C range. These results become interesting due to the possibilities of supplying power to the volcanic monitoring stations that measure the precursors of volcanic eruptions, making them completely autonomous. Nonetheless, in order to achieve this objective, corrosion prevention measures must be taken because the hydrogen sulfide contained in the fumaroles reacts with steam, forming sulfuric acid.
Open Access
Zero-power-consumption thermoelectric system to prevent overheating in solar collectors
(Elsevier, 2014) Martínez Echeverri, Álvaro; Astrain Ulibarrena, David; Rodríguez García, Antonio; Ingeniería Mecánica, Energética y de Materiales; Mekanika, Energetika eta Materialen Ingeniaritza
Highly promoted by the European Union Climate and Energy Package for 2020, solar collectors stand out as the most promising alternative to meet water heating demands. One of the most limiting problems in these systems involves the overheating of the working fluid, resulting in rapid fluid degradation, scaling and premature component failure. This paper presents the computational design of a zero-power-consumption system that combines thermoelectric-self-cooling technology and thermosyphon effect to dissipate the excess heat from a real solar-collector installation. Thermoelectric self-cooling is a novel thermoelectric application proven to enhance the heat dissipation of any hot spot without electricity consumption. The simplest design outperforms currently-used static and dynamic dissipaters for overheating protection in solar collectors, since it increases the global heat transfer coefficient of a static dissipater by 75 % and requires no electricity. Likewise, the final design presents a global heat transfer coefficient of 15.23 W/(m2K), 155 % higher than that provided by static dissipaters, forming a reliable, robust and autonomous system that stands out as a promising alternative to prevent the overheating of solar collectors.
Open Access
Influence of temperature and aging on the thermal contact resistance in thermoelectric devices
(Springer, 2020) Rodríguez García, Antonio; Pérez Artieda, Miren Gurutze; Beisti Antoñanzas, Irene; Astrain Ulibarrena, David; Martínez Echeverri, Álvaro; Ingeniaritza; Institute of Smart Cities - ISC; Ingeniería
During thermal design in the first phases development, thermoelectric systems, such as thermoelectric generators, the most important parameter affecting the performance is thermal resistance of the components. This paper focusses on the thermal contact resistance (TCR), analyzing the influence of aging and temperature on different thermal interface materials (TIMs), i.e., thermal paste, graphite and indium. In previous papers, TCR has been studied depending on parameters such as surface roughness, bonding pressure, thermal conductivity and surface hardness. However, in thermoelectric applications, a relevant aspect to consider when choosing a TIM is aging due to thermal stress. The exposure of this type of material to high temperatures for long periods of time leads to deterioration, which causes an increase in the TCR impairing the conduction of the heat flow. Therefore, there is a need to study the behavior of TIMs exposed to temperatures typical in thermoelectric generators to make a correct selection of the TIM. It has been observed that exposure to temperatures of around 180°C induces a significant increase in the thermal impedance of the three TIMs under study, although this effect is much more relevant for thermal paste. The contact, comprising steel, thermal paste and ceramic, presents a 300% increase in the thermal impedance after 70 days of aging, whereas that exceeds 185% for the contact of aluminum, thermal paste and ceramic. In the tests with exposure temperature of 60°C, there is no observed decrease in the thermal impedance.
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 computational model in order to simulate ice cube production in a thermoelectric ice maker
(Elsevier, 2009) Rodríguez García, Antonio; González Vian, José; Astrain Ulibarrena, David; Ingeniería Mecánica, Energética y de Materiales; Mekanika, Energetika eta Materialen Ingeniaritza
We have developed a computational model which allows the simulation of a thermoelectric device to make ice cubes in a vapor compression domestic fridge. This model solves both the thermoelectric and heat transfer equations, including the phase change equations in the ice cube production. The inputs of the model are: the thermoelectric parameters as a function of the temperature; dimensions; material properties (thermal resistances and capacities) and the boundary conditions (room temperature and voltage supplied to the Peltier module). The outputs are the values of the temperature for all the elements of the thermoelectric ice-maker and the ice production. In the experimental phase a prototype of a thermoelectric ice maker incorporated in a vapour compression domestic fridge was constructed in order to adjust and validate the computational model, and to optimize the experimental application. This ice-maker has two Peltier modules, some aluminum cylinders, called fingers, where the ice is made, and a component that acts as heat extender and dissipater which connects the hot side of Peltier module with the freezer compartment. The ice formation on the fingers is obtained by the cooling on the Peltier modules. When the ice cubes are formed, the voltage polarity of the thermoelectric modules is switched so the fingers warm up until the ice around the fingers melts. Then the ice cubes are dropped by gravity. This paper studies the production of ice cubes using the computational model and the experiment results and analyzes the most important parameters for the optimisation of the ice-maker (voltage supplied to the Peltier module, thermal resistance of the hot side dissipater and initial water temperature).
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
Optimal combination of an air-to-air thermoelectric heat pump with a heat recovery system to HVAC a passive house dwelling
(Elsevier, 2022) Díaz de Garayo, Sergio; Martínez Echeverri, Álvaro; Astrain Ulibarrena, David; Ingeniería; Ingeniaritza; Institute of Smart Cities - ISC
The main objective of this research is to propose a HVAC system for an 80–100 m2 passive house dwelling based on a thermoelectric air-to-air heat pump combined with a heat recovery unit. The computational parametric investigation demonstrates that the integration of the heat recovery unit significantly improves the coefficient of performance of the heat pump: 2–3 times for partial load operation and 12.5 % for maximum load. Moreover, the number of required modules to reach the maximum performance is at least 5 times lower. A second analysis assesses its seasonal heating performance in three climates as stated by the energy labeling Directive 2010/30/EU. The optimum number of thermoelectric modules in all cases is close to 15, regardless of the climate. This 15-modules thermoelectric heat pump provides a maximum heating capacity of 2500 W and 405 W for cooling, which compensates the typical internal heat gains and the transmission heat flux through the building envelope and the ventilation in the passive house dwelling. Finally, the analysis reveals that, in order to increase this cooling capacity, it is more convenient the improvement of the heat exchangers between the thermoelectric modules and the cooling air stream, rather than increasing the number of modules.